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Upward flame spread

2026-11-02T21:35:45Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Upward flame spread''' is the advance of burning along a combustible surface in an upward direction, assisted by the rising flow generated by the fire. On a vertical wall, the flow carries flame and hot gases towards material above the burning region. Quintiere classifies this as wind-aided spread: the relevant flow can be generated by buoyancy, without an external wind.<ref name="Q-250-251">Quintiere (2002), pp. 2-250–2-251.</ref>

The visible flame and the surface region supplying combustible gases have different boundaries. Flames can extend above the actively pyrolysing material and heat the unburned surface ahead. The surface spread rate describes the movement of the pyrolysis front, rather than simply the movement of the visible flame tip.<ref name="Q-246">Quintiere (2002), p. 2-246.</ref><ref name="Q-251-252">Quintiere (2002), pp. 2-251–2-252.</ref>

Upward spread can accelerate because the growing burning region increases heat release and extends the region heated by the flame. This feedback competes with burnout of material already involved. The outcome therefore depends on the material, exposure, geometry and flow. Upward orientation creates the potential for rapid growth, but does not establish one universal spread speed or growth law.<ref name="Q-252-253">Quintiere (2002), pp. 2-252–2-253.</ref>

== Heat feedback and the direction of flow ==

[[Flame spread|Surface flame spread]] requires heat to pass from the existing fire to material that has not yet become involved. For a solid, this heating produces combustible gases through thermal decomposition. Those gases burn near the surface and contribute further heat. The moving pyrolysis boundary is the material-side expression of that continuing process.<ref name="Q-246" />

In upward spread, buoyancy aligns the hot flow with the direction of advance. The flame and combustion products can heat a substantial length of surface above the pyrolysis front. In [[Opposed-flow flame spread|opposed-flow flame spread]], the flow is directed against the advance, and the region supplying forward heating is much shorter. Quintiere identifies this difference in heating extent as central to the different behaviour.<ref name="Q-247">Quintiere (2002), p. 2-247.</ref><ref name="Q-251">Quintiere (2002), p. 2-251.</ref>
[[File:fse-upward-flame-spread-v1.svg|thumb|upright=1.5|alt=Vertical surface diagram distinguishes burnout, pyrolysis front and flame extent, with heat transferred to unignited material above.|The flame can heat material above the advancing pyrolysis front. Based on Quintiere (2002), pp. 2-251–2-252.]]

Wind-aided spread is the broader category. Quintiere includes spread driven by external flow and spread beneath a ceiling within that category, as well as upward wall spread. The classification describes the relationship between the flow and the advancing front. It does not mean that all these geometries have the same flame attachment, heat transfer or spread correlation.<ref name="Q-250-251" /><ref name="Q-253" />

The relevant [[Heat flux|heat flux]] is distributed over that forward region. A high value at one location does not by itself determine the spread rate. The length exposed, duration of heating and material response also matter. Quintiere's simplified comparison explicitly includes both the flux and the distance over which it heats unburned material.<ref name="Q-251-252" />

This explains why comparing only peak heat fluxes can be misleading. Quintiere reports an orientation study in which downward spread had a higher local maximum than upward spread. The upward configuration nevertheless exposes a longer region ahead of the front. A point measurement and an extended preheating process describe different aspects of the heat feedback.<ref name="Q-254">Quintiere (2002), p. 2-254.</ref>

Ignition position can therefore change the subsequent development even when the material and pilot flame are similar. Iqbal and Salley use a curtain as an example. Ignition near its lower end permits rapid upward spread; ignition near its upper end leads to slower downward spread. The example illustrates the role of orientation and available fuel above the ignition location.<ref name="N-6-3">Iqbal and Salley (2004), p. 6-3.</ref>

== Acceleration, flame extent and burnout ==

A growing pyrolysis region can supply more fuel vapour and increase heat release. A longer flame can then heat more material ahead of the front, allowing the burning region to grow further. Quintiere relates the flame extent to heat release per unit width and uses this connection in models of upward spread. The feedback links material burning behaviour with flame geometry.<ref name="Q-252">Quintiere (2002), p. 2-252.</ref>

[[Flame height|Flame height]] therefore helps describe the region capable of heating the surface, but it must be distinguished from pyrolysis height. The flame may extend beyond the point at which the solid is producing combustible gases. Treating the flame tip as the boundary of already burning material would overstate the pyrolysing area and alter the inferred heat release.<ref name="Q-246" /><ref name="Q-252" />

Burnout introduces a second moving boundary behind the advancing front. Material that has exhausted its available fuel no longer contributes in the same way to the burning region. Quintiere represents the active region between the burnout position and the pyrolysis front. Its length can grow, approach a limit or decline, depending on the relative progress of these boundaries.<ref name="Q-252-253" />
[[File:fse-upward-flame-spread-v2.svg|thumb|upright=1.5|alt=A feedback loop for upward growth has a competing burnout branch that reduces the active burning region.|Growth depends on forward spread and the loss of active fuel through burnout. Based on Quintiere (2002), pp. 2-246 and 2-252–2-253.]]

The competition between spread time and burning duration is consequently important. If new material ignites rapidly while previously ignited material continues burning, the active region can expand. If the material burns out before sufficient new area becomes involved, growth can slow or stop. The upward direction alone does not remove this competition.<ref name="Q-246" /><ref name="Q-252-253" />

Some simplified limiting cases give exponential growth, but that result depends on particular relationships and negligible burnout. Quintiere discusses other observed and modelled behaviours, including an active region approaching a steady limit. An exponential fit should therefore be tied to its assumptions and conditions. It is not an inherent law applying to every vertical combustible surface.<ref name="Q-252-253" />

The feedback also depends on configuration. A relation between heat release and flame extent established for one arrangement is not automatically valid for another. Quintiere requires configuration-specific descriptions of flame heat flux and length when developing a spread solution. This requirement becomes important when moving from a flat wall to a corner, ceiling or constrained channel.<ref name="Q-252" /><ref name="Q-254" />

Different parts of the active surface can also be at different stages of their burning history. Quintiere combines the contributions of previously ignited regions when formulating the heat release that drives flame extent. A single peak heat release rate multiplied by the entire involved area does not preserve that timing. The history of ignition and subsequent burning is part of the feedback calculation.<ref name="Q-252" />

== A simplified relation and worked example ==

Quintiere expresses the spread speed through the distance between the pyrolysis front and the flame extent, divided by an associated ignition time. The relation connects the extent of forward heating with the time required for the heated material to become involved. It is a simplified representation, including an assumption of uniform flame heat flux over that region.<ref name="Q-252-e21">Quintiere (2002), p. 2-252, Equation 21.</ref>

<div class="fse-equation">V = dx<sub>p</sub>/dt = (x<sub>f</sub> − x<sub>p</sub>) / τ</div>

{| class="wikitable"
! Symbol !! Meaning !! Unit
|-
| V || Upward movement rate of the pyrolysis front || m/s
|-
| x<sub>p</sub> || Pyrolysis-front position measured from the chosen origin || m
|-
| x<sub>f</sub> || Flame extent measured from the same origin || m
|-
| t || Time || s
|-
| τ || Ignition time associated with the represented flame heat flux || s
|}

For a vertical surface, the positions can be expressed as heights above a common origin. The quantity in the numerator then represents the forward heating length in the simplified model. The associated ignition time must correspond to the heating conditions being represented. An ignition time measured under an unrelated exposure cannot be substituted merely because it is available.<ref name="Q-252" />

Consider hypothetical positions of 0.60 m for the pyrolysis front and 1.20 m for the flame extent. With an associated ignition time of 60 s, the heating length is 0.60 m. The calculated instantaneous spread speed is 0.010 m/s, or 10 mm/s. These values are selected to illustrate the relation, rather than taken from a particular material test.<ref name="Q-252-e21" />
[[File:fse-upward-flame-spread-v3.svg|thumb|upright=1.5|alt=Three bars show instantaneous calculated speeds of 10, 15 and 20 millimetres per second for hypothetical input combinations.|The simplified relation separates the effects of heating length and associated ignition time. Based on Quintiere (2002), p. 2-252, with hypothetical inputs.]]

If the flame extent becomes 1.50 m while the other example inputs remain unchanged, the heating length becomes 0.90 m. The calculated speed increases to 15 mm/s. Alternatively, retaining the original heating length but reducing the associated ignition time to 30 s gives 20 mm/s. The examples separate the influence of heating extent from that of material ignition response.<ref name="Q-252-e21" />

{| class="wikitable"
! Hypothetical comparison !! Forward heating length (m) !! Associated ignition time (s) !! Calculated speed (mm/s)
|-
| Base illustration || 0.60 || 60 || 10
|-
| Longer heated region || 0.90 || 60 || 15
|-
| Shorter ignition time || 0.60 || 30 || 20
|}

These calculations are conditional snapshots. They do not predict how flame extent, pyrolysis height or ignition response will change during a real fire. A time-dependent model requires additional relationships for heat release, heat transfer and burnout. Holding the example inputs constant throughout an assumed growth period would add a further assumption that has not been demonstrated here.<ref name="Q-252-253" />

The relation also presumes a flame extending ahead of the pyrolysis front and a positive associated ignition time. If those conditions no longer represent the fire, the simplified expression is outside its intended interpretation. A zero or negative numerator should not automatically be treated as a validated prediction of extinction or reverse spread.<ref name="Q-251-252" />

== Material response and the imposed exposure ==

Material properties enter through the heating needed to produce combustible gases and through the subsequent burning history. Quintiere distinguishes thermally thin and thermally thick behaviour in simplified spread analyses. A thin specimen can approach a uniform temperature through its thickness; a thick specimen develops a temperature gradient. The heat required to advance the front consequently depends on the relevant thermal response.<ref name="Q-248-251">Quintiere (2002), pp. 2-248–2-251.</ref>

Thickness alone is not a universal classification independent of time and exposure. Quintiere discusses the effects of thermal penetration and the adjacent substrate, particularly for intermediate thicknesses. A surface layer tested on one backing can therefore have a different heating response from the same layer in another construction. The represented material arrangement needs to accompany the material name.<ref name="Q-249">Quintiere (2002), p. 2-249.</ref>

Preheating changes the energy needed to reach the ignition condition. Van Rossum explains that upward orientation transfers heat to material above the burning region and can accelerate subsequent involvement. Additional heating in an enclosure can also raise the temperature of fuel ahead of the front. The initial surface condition is therefore part of the spread problem.<ref name="V-4-3">Van Rossum (2027), §4.3.</ref><ref name="Q-247" />

There is no single flame heat flux appropriate to every upward fire. Quintiere reports approximately 25 kW/m² ahead of the pyrolysis zone for moderate turbulent wall fires with flame extents below about 1.4 m. The same discussion shows that larger and laminar fires can exceed this value. The numerical approximation belongs to the described exposure regime.<ref name="Q-253">Quintiere (2002), p. 2-253.</ref>

Babrauskas describes a broader cluster of wall-flame measurements between approximately 25 and 45 kW/m², suggesting 35 kW/m² as representative in that context. He also notes the additional heating possible within a hot gas layer. These accounts illustrate why exposure selection needs its experimental basis and scenario conditions, rather than an unexplained universal flux assumption.<ref name="B-6-7">Babrauskas (2002), pp. 3-6–3-7.</ref>

The heat release history used in a spread calculation must correspond to that exposure. Quintiere identifies cone calorimeter data as a possible source of material burning information, while warning that the relevant flame-spread flux need not equal the selected test irradiance. The transfer from a material test to a spread model therefore requires a reasoned exposure match.<ref name="Q-252" />

== Geometry, confinement and external walls ==

A wall affects the surrounding flow as well as providing a possible combustible surface. Iqbal and Salley explain that a fuel package near a wall has less surrounding cool-air entrainment than one burning freely. This can produce higher flames and temperatures. Surface orientation and proximity to boundaries therefore influence the exposure that drives further spread.<ref name="N-6-3" />

Corners and channels can introduce additional geometric effects. Quintiere describes how escalator sidewalls in the King's Cross fire caused flames to remain close to the steps. This is the [[Trench effect|trench effect]] context cited in his discussion of orientation. It demonstrates that inclined, constrained spread can differ from the behaviour represented by an isolated vertical flat-wall model.<ref name="Q-254" />

In a [[Facade fire|facade fire]], vertical travel of flames does not necessarily mean that the cladding itself is sustaining upward surface spread. The New Zealand commentary distinguishes spread over facade materials from fire plumes projecting through openings and exposing openings above. Identifying which mechanism is active is necessary before selecting a surface-spread model.<ref name="NZ-134">Ministry of Business, Innovation and Employment (2013), p. 134.</ref>

The external-wall assembly can also behave differently from a small isolated material specimen. The commentary identifies connections and jointing details as reasons why small-scale testing may be unsuitable. A large-scale facade fire test can address the behaviour of an arrangement whose relevant details are not represented by the material specimen alone. The cited commentary supports this distinction without defining one universal facade test procedure.<ref name="NZ-135-136">Ministry of Business, Innovation and Employment (2013), pp. 135–136.</ref>

== Interpreting tests and model results ==

A useful assessment identifies the measured or predicted front. Visible flame extent, pyrolysis height, burnout position and heat release describe different features of the event. Quintiere's model separates these quantities because their relationships drive the growth. Reporting only a maximum flame height can leave the actual surface involvement and its rate of advance unresolved.<ref name="Q-246" /><ref name="Q-252-253" />

A test rating is likewise not automatically a spread velocity. Quintiere describes the historical Steiner tunnel test as a complex wind-aided configuration and notes that it does not measure the pyrolysis or burnout positions. Its output cannot simply replace those variables in a physical spread equation. The test arrangement and reported quantity need to match the intended use of the data.<ref name="Q-253" />

The material, orientation, dimensions, substrate, ignition source and external heating should therefore remain explicit when interpreting a result. Quintiere concludes that spread depends on the fuel's configuration and ambient conditions as well as its properties. Applying an experimental or modelled result beyond those conditions requires evidence that the controlling heat-transfer and burning processes remain represented.<ref name="Q-256">Quintiere (2002), p. 2-256.</ref>

== Notes ==
<references />

== References ==
* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-1). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code Clauses C1–C6 and Verification Method C/VM2''.
* Quintiere, J. G. (2002). Surface flame spread. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 2-12, pp. 2-246–2-257). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Ignition & Flame Spread]]

Warehouse fire

2026-11-02T21:35:42Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''warehouse fire''' is a fire in a building used to store goods, often in large undivided spaces with goods stacked on pallets or in racks to heights of several metres. The combination of a large floor area, a high fire load and tall vertical fuel surfaces makes such fires grow quickly and burn intensely.<ref name="MBIE13-55">Ministry of Business, Innovation and Employment (2013), p. 55.</ref><ref name="MBIE13-73">Ministry of Business, Innovation and Employment (2013), p. 73.</ref> Warehouse fires are relatively rare, but in an analysis of fire investigations in Greater London from 1996 to 2000, warehouses had the largest mean fire damage area of all occupancies studied.<ref name="MBIE13-73" /><ref name="Hol-B2-7">Holborn et al. (2004), as cited in Australian Building Codes Board (2020a), Data Sheet B2, p. 7.</ref>

Design guidance for warehouses therefore deals with the growth of the fire in the stored goods, the heat it can release, and its control by sprinklers, smoke venting and the fire service. In New Zealand, Verification Method C/VM2 (second edition, 2025) uses an ultra-fast design fire with a peak of 50 MW for storage 3.0 to 5.0 m high. Higher racks get an even faster growth.<ref name="MBIE25-20">Ministry of Business, Innovation and Employment (2025b), p. 20.</ref> In the United States, sprinkler criteria for storage are based on full-scale tests and were merged into NFPA 13 from its 1999 edition.<ref name="Fle-73">Fleming (2002), p. 4-73.</ref>

== Characteristics of warehouse fires ==
A small room of about 200 m² behaves roughly as one well-mixed fire zone. In a warehouse of more than about 1,000 m², the fire is more complex and its burning rate is not uniform. It is expected to travel around the space and to burn with varying intensity. The intensity depends on the distribution of fuel, the geometry, the combustibility of the goods and the ventilation through roof vents, make-up air and, eventually, a failed roof.<ref name="MBIE13-73" />

In most warehouse designs the roof has no fire rating and is expected to fail early. Before it fails, heat and smoke are held in and the walls are exposed more intensely; after it fails, the hot gases escape and flame radiation dominates.<ref name="MBIE13-73" /> The fire behaviour of metal-faced [[sandwich panel]]s cannot be predicted from small-scale cone calorimeter tests, so the usual correlation with the full-scale room test does not apply to them.<ref name="MBIE13-141">Ministry of Business, Innovation and Employment (2013), p. 141.</ref>

Large-scale data are scarce. Fire experiments at warehouse scale are uncommon, and taking such a building to burnout in a test is almost unheard of.<ref name="MBIE13-73" /> The International Fire Engineering Guidelines note that the usual relations for compartment temperatures come from rooms of about 10 m², sometimes up to 50 m². If simultaneous burning is assumed in a large enclosure, the predicted temperatures are unrealistically high. As a first approximation, the floor can be divided into grids of 10 to 50 m², whose heat release rates are added with time delays for the spread from grid to grid.<ref name="IFEG-2.6-12">National Research Council of Canada et al. (2005), p. 2.6-12.</ref>

Stored goods present large vertical surfaces, which favour fire growth far faster than the ''fast'' design fire used for most buildings.<ref name="MBIE13-55" /> Standard t-squared growth curves assume horizontal spread in all directions and do not suit fires that also spread upwards, as in high racks.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> The point of ignition matters too. In one comparison, igniting a rack at its front face delayed the fire events by about 470 s compared with ignition in the centre of the flue spaces, the gaps between the stored loads.<ref name="Bab-18">Babrauskas (2002b), p. 3-18.</ref><ref name="Bab-19">Babrauskas (2002b), p. 3-19.</ref> Wooden pallets become a fire hazard mainly when idle pallets are stacked many units high.<ref name="Bab-22">Babrauskas (2002b), p. 3-22.</ref>

In a high distribution centre, the hot smoke layer can ignite goods stored high in the racks. Most materials ignite at about 200 to 500 °C, so a smoke layer above 200 °C with goods in it gives a chance of such secondary fires.<ref name="VR-9.3">Van Rossum (2027), §9.3 (Results from zone models).</ref> In the London fire investigation data, a fire damage area of 100 m² was used as the criterion for flashover in large spaces. Of 20 warehouse fires, 20.8 % exceeded this area, and the mean damage area was 170 m².<ref name="Hol-B2-7" /><ref name="Hol-B2-8">Holborn et al. (2004), as cited in Australian Building Codes Board (2020a), Data Sheet B2, p. 8.</ref>

== Fire load ==
The [[fire load density]] of storage depends on the height of the goods. In the International Fire Engineering Guidelines, the storage values from Swiss surveys of 1967 to 1969 are given per metre of storage height and must be multiplied by that height.<ref name="Eng-3.4-2">England et al. (2000), as cited in National Research Council of Canada et al. (2005), p. 3.4-2.</ref> Examples are 600 MJ/m² per metre for storage at a box manufacturer, 1,700 at a carpet manufacturer and 4,200 at a cardboard manufacturer.<ref name="Eng-3.4-3">England et al. (2000), as cited in National Research Council of Canada et al. (2005), p. 3.4-3.</ref> For occupancies with very different goods, such as industrial buildings, the coefficient of variation is 50 to 80 % of the average, and isolated peaks can reach 2.5 times the average.<ref name="IFEG-3.4-2">National Research Council of Canada et al. (2005), p. 3.4-2.</ref>

New Zealand's C/VM2 (second edition, 2025) prescribes a design fire load of 1,200 MJ/m² for storage up to 3.0 m high, other than foamed plastics. For storage of combustible materials above 3.0 m, it prescribes 800 MJ/m² per metre of height, with a minimum of 2,400 MJ/m².<ref name="MBIE25-22">Ministry of Business, Innovation and Employment (2025b), p. 22.</ref> A store of 6 m high goods therefore has a design fire load of 4,800 MJ/m². In Australia, the 2020 data sheets for the Fire Safety Verification Method assign a ''very high'' fire load distribution to storage buildings, with a mean of 1,000 MJ/m², but explicitly exclude high-rack storage from it.<ref name="ABCB-B2-9">Australian Building Codes Board (2020a), Data Sheet B2, p. 9.</ref>

The total energy in a store varies greatly with what is stored. The C/VM2 commentary compares 1,000 m³ of different goods: low-density polyurethane foam contains about 1.3 TJ, MDF board 11.5 TJ and rolled polyethylene about 20 TJ.<ref name="MBIE13-25">Ministry of Business, Innovation and Employment (2013), p. 25.</ref><ref name="MBIE13-27">Ministry of Business, Innovation and Employment (2013), p. 27.</ref> The book ''Introduction to Fire Safety Engineering'' gives the example of a shed with 3,500 m³ of stored goods with a heat of combustion of 23 MJ/kg and a density of 135 kg/m³. This contains 10,867,500 MJ, equivalent to about 572,000 kg of wood.<ref name="VR-4.4">Van Rossum (2027), §4.4.</ref>

== Fire growth and heat release ==
Design fires for warehouses usually describe the growth of the fire with a t-squared curve, in which the heat release rate increases with the square of the time since ignition. The growth coefficient expresses how quickly the fire grows; for a ''fast'' fire, for example, it is 0.047 kW/s²:<ref name="ABCB-B2-3">Australian Building Codes Board (2020a), Data Sheet B2, p. 3.</ref>

<math display="block">\dot{Q} = \alpha \, t^2</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot{Q}</math> || heat release rate || kW
|-
| <math>\alpha</math> || fire growth coefficient || kW/s²
|-
| <math>t</math> || time from effective ignition || s
|}

For an ''ultra-fast'' fire, α is 0.188 kW/s², which means the fire reaches 1,055 kW after 75 s.<ref name="ABCB-B2-3" /> C/VM2 uses this value for buildings that can store goods to a height of 3.0 to 5.0 m, with a peak of 50 MW. The growth stops at that peak, at flashover, at the limit set by the available ventilation or, for some calculations, at sprinkler activation. For goods stored above 5.0 m, C/VM2 uses a cubic growth that also increases with the storage height, so the t-squared curve is not valid for high racks.<ref name="MBIE25-20" /><ref name="MBIE25-21">Ministry of Business, Innovation and Employment (2025b), p. 21.</ref> The commentary explains that storage up to 5.0 m is treated as ultra-fast following NFPA 72 and NFPA 204, and that growth increases further with taller vertical surfaces.<ref name="MBIE13-55" />

As a worked example, take a store with goods stacked 4 m high. With α = 0.188 kW/s², the heat release rate after 2 min is 0.188 × 120² = 2,707 kW, or about 2.7 MW. After 5 min it is 0.188 × 300² = 16,900 kW. The 50 MW peak is reached after √(50,000 / 0.188) = 516 s, or about 8.6 min. For comparison, the general design fire for most other buildings in C/VM2 grows at 0.0469 kW/s² to 20 MW, which takes 653 s.<ref name="MBIE25-20" /> The book uses slightly different reference values: it defines the growth time as the time to reach 1 MW, 75 s for ultra-fast growth.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref>

[[File:fse-warehouse-fire-v1.svg|thumb|upright=1.5|alt=Line chart: storage fire grows as 0.188 t squared to 50 MW at 516 s; general fire as 0.0469 t squared to 20 MW at 653 s.|Design fires of New Zealand's C/VM2 (2025): storage 3.0 to 5.0 m high (ultra-fast, peak 50 MW) and most other buildings (peak 20 MW). Based on Ministry of Business, Innovation and Employment (2025b), p. 20.]]

Measurements show how fast warehouse goods burn. According to NUREG-1805, most warehouse materials in a table taken from NFPA 72 fall in the fast or ultra-fast range.<ref name="IS-B-6">Iqbal and Salley (2004), p. B-6.</ref> Stacks of wood pallets 3 m high reach about 1,055 kW in 80 to 110 s, and vertical rolls of paper 6 m high in only 15 to 28 s.<ref name="NFPA72-B6">NFPA 72 (1999), as cited in Iqbal and Salley (2004), p. B-6.</ref><ref name="NFPA72-B7">NFPA 72 (1999), as cited in Iqbal and Salley (2004), p. B-7.</ref> Wood pallets stacked to 3 m release about 7 MW, and polystyrene jars in cartons stacked 4.9 m high about 30 to 40 MW.<ref name="KQ-3-2">Karlsson and Quintiere (1999), as cited in Iqbal and Salley (2004), p. 3-2.</ref>

Peak heat release rates per unit floor area of stored commodities, analysed by Heskestad from Factory Mutual tests, range widely. Cardboard cartons with a metal liner stacked 2.95 m high gave about 1,490 to 1,680 kW/m², while polyethylene bins in cardboard cartons stacked 4.51 m high gave 28,900 kW/m².<ref name="Hes-18">Heskestad (1997), as cited in Babrauskas (2002b), p. 3-18.</ref> These values cannot be scaled: they may be applied conservatively to lower stacks, but not extrapolated to higher ones.<ref name="Bab-17">Babrauskas (2002b), p. 3-17.</ref> Factory Mutual classifies stored goods for sprinkler protection by how much heat they release in the presence of water. Raising the share of polystyrene in cardboard boxes from about 15 % to 100 % increases the heat release rate exponentially and raises the water demand.<ref name="Tew-153">Tewarson (2002), p. 3-153.</ref><ref name="Tew-154">Tewarson (2002), p. 3-154.</ref>

[[File:fse-warehouse-fire-v3.svg|thumb|upright=1.5|alt=Bars on a logarithmic scale from 250 kW per square metre for an average building to 28,900 kW per square metre for plastic bins in cartons.|Peak heat release rate per unit floor area of stored commodities from Factory Mutual tests, compared with 250 kW/m² for a developed fire in an average building. Based on Heskestad (1997), as cited in Babrauskas (2002b), p. 3-18, and Van Rossum (2027), §4.5.]]

== Sprinkler protection ==
Classifying the occupancy and the stored commodity is the most critical step in sprinkler design. If the hazard is underestimated, the fire can overpower the sprinklers.<ref name="Fle-73" /> This step is described under [[sprinkler hazard classification]]. Sprinkler design for fire suppression is largely empirical. The criteria for rack storage and for large-drop and early suppression sprinklers are based on full-scale tests, while most other criteria rest on experience and judgement.<ref name="Fle-73" />

Ordinary sprinklers are designed to control a fire. An ESFR sprinkler, short for early suppression fast response, combines a fast response with large water drops and a high velocity, so that it can extinguish a high-challenge fire. Its installation rules are strict, and in-rack sprinklers are a separate type placed within the racks.<ref name="IS-10-3">Iqbal and Salley (2004), p. 10-3.</ref> The variables of storage protection include the water application rate, the response time index, the temperature rating and in-rack protection, and the storage arrangement matters as well.<ref name="Sch-113">Scheffey (2002), p. 4-113.</ref> Water from sprinklers also wets the goods, which helps to stop the fire from jumping across the aisles of a warehouse.<ref name="Tew-151">Tewarson (2002), p. 3-151.</ref>

Sprinklers in storage buildings perform slightly below average.<ref name="ABCB-C2-76">Australian Building Codes Board (2020a), Data Sheet C2, p. 76.</ref> The Australian data sheets give a reliability of 84 %, an efficacy of 97 % and an effectiveness of 83 % for storage buildings.<ref name="ABCB-C2-71">Australian Building Codes Board (2020a), Data Sheet C2, p. 71.</ref> United States data for 2010 to 2014 show that wet-pipe sprinklers in warehouses, excluding cold storage, operated in 84 % of fires and were effective in 82 %.<ref name="Ahr-C2-78">Ahrens (2017), as cited in Australian Building Codes Board (2020a), Data Sheet C2, p. 78.</ref>

== Smoke and heat venting ==
[[Smoke and heat exhaust ventilation]] in a warehouse aims to support escape and firefighting, so that firefighters can enter and see the seat of the fire, and to reduce property damage. A typical arrangement is a large space with vents in the roof, often divided by draft curtains into separate smoke reservoirs.<ref name="Coo-219">Cooper (2002b), p. 3-219.</ref> Without venting, smoke fills such a space quickly. Cooper considers goods that reach about 1 MW in 100 s, in a warehouse 6 m high with a floor area of 1,500 m². He calculates that the smoke layer becomes untenable at 183 °C after about 350 s. At that moment its lower edge is 2.7 m above the floor, and after about 600 s the layer fills the whole warehouse at about 430 °C.<ref name="Coo-265">Cooper (2002a), p. 3-265.</ref><ref name="Coo-266">Cooper (2002a), p. 3-266.</ref>

[[File:fse-warehouse-fire-v2.svg|thumb|upright=1.5|alt=Cross-section of a warehouse with high racks, a fire in one rack, a smoke layer under the roof, roof vents, draft curtains above the aisles and sprinklers.|Cross-section of a racked warehouse with a fire in one rack: smoke layer, roof vents, draft curtains above the aisles, ceiling and in-rack sprinklers. Based on Cooper (2002b), pp. 3-219 and 3-237, and Iqbal and Salley (2004), p. 10-3.]]

Roof vents rely mainly on the buoyancy of the smoke. Strong wind can create suction over the roof and increase the extraction, but the vent may then draw in clear air from below the smoke layer, so that a critical vent area exists.<ref name="Kan-24">Kandola (2002), p. 1-24.</ref><ref name="Kan-25">Kandola (2002), p. 1-25.</ref> Cooper gives a worked example for a 5 m × 5 m fire in a warehouse with a ceiling at 9 m and draft curtains reaching down to 6 m. To keep the smoke above the bottom of the curtains, each curtained space needs a total vent area of 18.6 m².<ref name="Coo-235">Cooper (2002b), p. 3-235.</ref>

The combination of vents and sprinklers was long controversial, and no generally accepted design guidelines existed when Cooper's chapter was written.<ref name="Coo-236">Cooper (2002b), p. 3-236.</ref> A review of 34 position papers, as cited by Cooper, concluded that venting does not harm sprinkler performance. It has no effect on the activation of the first sprinklers or on the total number activated, although a vent directly above the fire may slightly delay the first sprinklers. The review also advised placing draft curtains in aisles rather than over storage.<ref name="BC-237">Beyler and Cooper (in press), as cited in Cooper (2002b), p. 3-237.</ref> The Australian data sheets warn, on the other hand, that a vent may remove hot gases before sprinklers activate, which could compromise early suppression systems.<ref name="ABCB-B1-21">Australian Building Codes Board (2020a), Data Sheet B1, p. 21.</ref>

Sprinkler spray can drag the smoke layer down and mix it with the air below, an effect called smoke logging. Once this happens, the benefits of venting are lost, even with very large vents.<ref name="Coo-237">Cooper (2002b), p. 3-237.</ref><ref name="Coo-238">Cooper (2002b), p. 3-238.</ref> In the Netherlands, the book describes the criteria of the standard NEN 6093 for fire service intervention in a space with smoke and heat exhaust. Visibility up to a height of 1.8 m must be at least 100 m, and radiation from the smoke layer at that height at most 3.5 kW/m². The layer temperature may be at most 200 °C if goods are stored in the smoke layer and 500 °C otherwise.<ref name="VR-9.3" />

== Detection and other measures ==
Detection in high warehouses is a design problem of its own. In a design example for a furniture warehouse, Schifiliti and co-workers show that heat detectors must be spaced more closely as the distance from the fire to the ceiling grows. For a floor area of 5,000 m², about 48 fixed-temperature detectors or about 8 rate-of-rise detectors were needed to detect a fire of about 2,000 kW.<ref name="Sch-17">Schifiliti et al. (2002), p. 4-17.</ref><ref name="Sch-18">Schifiliti et al. (2002), p. 4-18.</ref> For a storage room of 50 m × 75 m × 10 m, a projected beam smoke detector had to be set to respond at about 30 % total obscuration or less.<ref name="Sch-26">Schifiliti et al. (2002), p. 4-26.</ref> Such detectors typically respond at 20 to 70 % total obscuration.<ref name="MBIE25-28">Ministry of Business, Innovation and Employment (2025b), p. 28.</ref>

In New Zealand, C/VM2 (second edition, 2025) allows manual activation of the fire alarm in buildings such as warehouses, where the ceiling is high and the occupant load is low. The conditions are an average ceiling height of at least 5 m and fewer than 50 occupants who are awake and familiar with the building.<ref name="MBIE25-26">Ministry of Business, Innovation and Employment (2025b), p. 26.</ref><ref name="MBIE25-28" /> The rule rests on 34 simulations with the Fire Dynamics Simulator. In these, the 12 m high building had the fastest ceiling jet, because the growth of a rack fire increases with rack height.<ref name="MBIE13-109">Ministry of Business, Innovation and Employment (2013), p. 109.</ref>

Fire spread can also be limited by the way goods are stored. The International Fire Engineering Guidelines mention changing from rack storage to palletised storage and storing items horizontally rather than vertically.<ref name="IFEG-1.4-7">National Research Council of Canada et al. (2005), p. 1.4-7.</ref> Another approach is to lower the oxygen level, the principle behind an oxygen reduction system. Air contains 23.3 % oxygen by mass.<ref name="Klo-279">Klote (2002), p. 4-279.</ref> Tewarson shows that flames of PMMA, a plastic, go out at an oxygen mass fraction of about 0.18 under normal conditions. When the fuel receives an external heat flux of 65 kW/m², it keeps burning down to 0.128.<ref name="Tew-155">Tewarson (2002), p. 3-155.</ref>

== Regulation and limits ==
Building codes set limits on large stores. In New Zealand, C/VM2 (second edition, 2025) sets conditions for unsprinklered firecells within 15 m of a relevant boundary that have a fire load above 20 TJ or a floor area above 5,000 m². When firefighters first apply water, the radiation at 1.5 m above the floor must not exceed 4.5 kW/m², and the smoke layer must be at least 2 m above the floor.<ref name="MBIE25-53">Ministry of Business, Innovation and Employment (2025b), p. 53.</ref> The commentary explains that the 5,000 m² limit was based on 800 MJ/m² per metre of storage height and a storage height of 5.0 m.<ref name="MBIE13-23">Ministry of Business, Innovation and Employment (2013), p. 23.</ref> With these values, 5,000 m² corresponds to 20 TJ.

The commentary works this out for an unsprinklered warehouse of 1,200 m² and 8.0 m high, with goods stored to 6.0 m. With an ultra-fast fire to 50 MW and water applied after 1,200 s, the criteria were met with automatic make-up air and 22 roof vents of 2.0 m², 3.7 % of the floor area.<ref name="MBIE13-150">Ministry of Business, Innovation and Employment (2013), p. 150.</ref> The Building Code of Australia, as described in the commentary, requires sprinklers where more than 1,000 m³ of combustible goods are stored higher than 4.0 m.<ref name="BCA-25">Building Code of Australia, as cited in Ministry of Business, Innovation and Employment (2013), p. 25.</ref> In the Netherlands, buildings with large fire compartments outside the scope of NEN 6060 are a typical field for fire safety engineering.<ref name="VR-1.5">Van Rossum (2027), §1.5.</ref>

The data behind warehouse design are limited. The heat release rates per unit area apply only to the tested storage heights, the Australian growth rate statistics for storage rest on only six fires, and full-scale burnout tests are almost never done.<ref name="Bab-17" /><ref name="Hol-B2-4">Holborn et al. (2004), as cited in Australian Building Codes Board (2020a), Data Sheet B2, p. 4.</ref><ref name="MBIE13-73" /> A common misconception is that a store full of goods burns like an office with a higher fire load. In reality, tall vertical fuel surfaces make the growth much faster, and the fire spreads upwards through the racks rather than only across the floor.<ref name="MBIE13-55" /><ref name="VR-8.6" />

== See also ==
* [[Beam smoke detector]]
* [[Sprinkler-vent interaction]]
* [[Car park fire]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Babrauskas, V. (2002b). Heat release rates. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association; Society of Fire Protection Engineers.
* Cooper, L. Y. (2002a). Compartment fire-generated environment and smoke filling. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-243–3-267). National Fire Protection Association; Society of Fire Protection Engineers.
* Cooper, L. Y. (2002b). Smoke and heat venting. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-219–3-242). National Fire Protection Association; Society of Fire Protection Engineers.
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Kandola, B. S. (2002). Introduction to mechanics of fluids. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-1–1-26). National Fire Protection Association; Society of Fire Protection Engineers.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Scheffey, J. L. (2002). Foam agents and AFFF system design considerations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-88–4-122). National Fire Protection Association; Society of Fire Protection Engineers.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association; Society of Fire Protection Engineers.
* Tewarson, A. (2002). Generation of heat and chemical compounds in fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-82–3-161). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Special Hazards & Building Types]]

Ventilation factor

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Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

The '''ventilation factor''' is the product of an enclosure opening's area and the square root of its height. It expresses the combined influence of opening size and vertical extent in simplified calculations of naturally ventilated compartment fires. With area in square metres and height in metres, its unit is m<sup>5/2</sup>. The factor appears in approximate air-inflow relations, burning-rate estimates and correlations for compartment temperature and flashover.<ref name="definition">Walton and Thomas (2002), pp. 3-174–3-176, 3-184–3-186.</ref>

The related ''opening factor'' divides this quantity by the enclosure's bounding surface area and has units of m<sup>1/2</sup>. The two quantities must be distinguished because they serve different roles in fire calculations. Neither determines fire severity alone. Fuel properties, available fuel, enclosure heat losses and the location of combustion remain relevant, while the simple ventilation relations presume an applicable opening arrangement and established buoyancy-driven exchange.<ref name="distinction">Lie (2002), pp. 4-202–4-203; Walton and Thomas (2002), pp. 3-173–3-174.</ref>

== Definition and geometric interpretation ==

For a single vertical opening, the ventilation factor is written below. Opening area includes both the incoming and outgoing portions of the exchange opening. The height is the opening height, rather than the height of the room or the elevation of its centre above the floor.<ref name="geometry">Walton and Thomas (2002), p. 3-174.</ref>

<div class="fse-equation">F<sub>v</sub> = A<sub>o</sub> √H<sub>o</sub></div>

{| class="wikitable"
! Symbol !! Meaning !! Unit
|-
| F<sub>v</sub> || Ventilation factor as defined here || m<sup>5/2</sup>
|-
| A<sub>o</sub> || Opening area || m²
|-
| H<sub>o</sub> || Opening height || m
|-
| A<sub>T</sub> || Enclosure bounding surface area under the selected method's convention || m²
|-
| O || Normalised opening factor as defined here || m<sup>1/2</sup>
|}

The square-root height term reflects the role of the vertical opening in buoyancy-driven exchange. Openings with the same area can have different ventilation factors if their heights differ. Conversely, increasing the width while keeping the height unchanged increases the factor directly with the area. The quantity therefore preserves a geometric influence that would be lost by reporting opening area alone.<ref name="geometry" />

The notation F<sub>v</sub> is used here to distinguish the unnormalised factor from the opening factor. Source documents do not always use the same letters or terminology. The defining expression and dimensions are more reliable identifiers than the symbol by itself. Confusing m<sup>5/2</sup> with m<sup>1/2</sup> changes the quantity being entered into a correlation.<ref name="definition" /><ref name="distinction" />
[[File:fse-ventilation-factor-v1.svg|thumb|upright=1.5|alt=A room opening defines area times square-root height, which is divided by enclosing area to obtain the opening factor.|The ventilation factor and the normalised opening factor have different dimensions. Based on Walton and Thomas (2002), p. 3-174, and Lie (2002), p. 4-203.]]

For several openings, their heights, positions and pressure relationships require attention. Lie refers to separate procedures for openings of unequal height rather than supplying a universal replacement height in the basic definition. An arbitrary average can therefore conceal an additional modelling assumption. The aggregation method should follow the particular compartment model or correlation being used.<ref name="multiple">Lie (2002), p. 4-203.</ref>

The geometric factor is also distinct from aerodynamic free area. Detailed opening-flow calculations include a discharge coefficient and a pressure distribution. Those effects enter the simplified ventilation relation through its assumptions and fitted coefficient; they do not make the geometric opening area a directly measured flow capacity. Changing the opening construction can consequently require reconsideration of the flow representation.<ref name="flowbasis">Walton and Thomas (2002), p. 3-174.</ref>

== Approximate air supply and ventilation control ==

A [[Ventilation-controlled fire|ventilation-controlled fire]] releases heat internally at a rate restricted by the available oxygen supply. For developed compartment burning, the incoming air flow can be approximated using the ventilation factor. Walton and Thomas present the commonly used relation below, with the stated metre and kilogram units.<ref name="airflow">Walton and Thomas (2002), p. 3-174, equation 5.</ref>

<div class="fse-equation">ṁ<sub>air</sub> ≈ 0.5 A<sub>o</sub> √H<sub>o</sub></div>

Here ṁ<sub>air</sub> is the incoming air mass flow in kilograms per second. The coefficient is dimensional and belongs to this unit system. It is an approximation to the more detailed exchange-flow calculation, which depends on temperature, layer-interface height, neutral-plane height and opening discharge behaviour. The simplified relation should not be read as an exact flow measurement.<ref name="flowbasis" /><ref name="airflow" />

The source associates this approximation with fires approaching flashover or undergoing developed burning, when the layer interface is low. Temperature dependence becomes relatively weak above about 150 °C under the analysed conditions. The coefficient still depends on opening-flow assumptions: the chapter reports calculated values from 0.40 to 0.61 before identifying 0.5 as the commonly used estimate.<ref name="limits">Walton and Thomas (2002), p. 3-174.</ref>

A [[Post-flashover fire|post-flashover fire]] can therefore be described partly through opening-controlled air supply, but its fuel mass loss need not equal complete internal combustion. Heated fuel can produce more volatiles than the incoming oxygen can burn. The excess may leave and burn outside the enclosure. A calculation must distinguish incoming air, fuel pyrolysis and the energy actually released inside.<ref name="combustion">Walton and Thomas (2002), pp. 3-172–3-175.</ref>

Initial smoke filling is a different condition. The neutral plane, layer interface and opening exchange are still developing, and the room's initial oxygen inventory can contribute to burning. Walton and Thomas restrict their mid-opening approximations to conditions after exchange flow has become established. Applying the developed-fire air-supply relation from ignition would discard that transient behaviour.<ref name="limits" /><ref name="oxygen">Cadorin and Franssen (2003), pp. 419–421.</ref>

== Heat release and burning-rate interpretations ==

For many common fuels, the heat released per mass of air consumed is approximately 3,000 kJ/kg in the simplified stoichiometric treatment. Combining that value with the approximate incoming air flow gives a reference heat release rate of 1,500 times the ventilation factor. The result is expressed in kilowatts.<ref name="stoich">Walton and Thomas (2002), pp. 3-173–3-174, 3-184–3-185.</ref>

<div class="fse-equation">Q̇<sub>stoich</sub> ≈ 1500 A<sub>o</sub> √H<sub>o</sub></div>

This is a reference based on oxygen consumption, not a prediction that every fire reaches that power. A small fuel package may release substantially less heat even when the opening could supply more air. Conversely, a high pyrolysis rate can send combustible material outside without increasing internal combustion in the same proportion. The fuel and ventilation constraints must be considered together.<ref name="combustion" /><ref name="stoich" />
[[File:fse-ventilation-factor-v3.svg|thumb|upright=1.5|alt=Opening geometry informs air supply and flashover estimates, while actual internal combustion also depends on fuel and energy released outside.|The same opening geometry supports several different estimates with distinct physical meanings. Based on Walton and Thomas (2002), pp. 3-173–3-175, 3-184–3-186.]]

Walton and Thomas also describe an early empirical wood-burning relation in which mass loss is proportional to 0.09 times the ventilation factor. Much of its supporting evidence involved cellulosic fuel and wood cribs. The chapter explains that enclosure area and the fuel's response to heating modify this simple proportionality. The relation should therefore not be generalised into a fuel-independent mass-loss law.<ref name="wood">Walton and Thomas (2002), p. 3-174.</ref>

The energy location is especially important when interpreting a temperature calculation. Only heat released inside contributes directly to the internal combustion term of the room energy balance. Increased production of volatiles can produce lower internal temperatures while increasing exterior burning. Thus, a larger total fuel-energy stream need not produce the internal temperature suggested by assuming complete combustion in the room.<ref name="combustion" />

The OZone paper makes this distinction explicit through alternative combustion assumptions. Its external-flaming option preserves the prescribed pyrolysis while limiting internal combustion according to oxygen supply. Its extended-duration option instead reduces pyrolysis and burns the fuel internally over a longer period. Both respond to ventilation limitation, but they allocate fuel energy differently and cannot be treated as equivalent consequences of one geometric factor.<ref name="models">Cadorin and Franssen (2003), pp. 419–423.</ref>

== Opening factor and temperature calculations ==

Dividing the ventilation factor by the bounding area relates opening-controlled exchange to the area available for enclosure heat transfer. This normalised quantity is commonly called the opening factor. Its definition is shown below, with the notation O used to avoid confusion with the unnormalised factor.<ref name="opening">Lie (2002), p. 4-203, equation 1.</ref>

<div class="fse-equation">O = A<sub>o</sub> √H<sub>o</sub> / A<sub>T</sub></div>

The surface-area convention must accompany the calculation. In the compartment examples used by Walton and Thomas and by Iqbal and Salley, the relevant enclosure area excludes openings. Other formulations should be checked against their own definitions. Floor area alone is not a substitute for the total enclosing area when the correlation requires walls, floor and ceiling.<ref name="area">Walton and Thomas (2002), pp. 3-175–3-177; Iqbal and Salley (2004), p. 13-9.</ref>

A [[Parametric fire curve|parametric fire curve]] can use opening geometry alongside fuel load and thermal boundary properties to describe a compartment heating history. Lie's characteristic temperature curves demonstrate this dependence on both opening factor and the enclosing materials. The opening factor does not independently determine peak temperature or fire duration. Its meaning comes from the complete temperature-time formulation in which it appears.<ref name="curves">Lie (2002), pp. 4-201–4-203.</ref>

The [[MQH correlation|MQH correlation]] uses the unnormalised ventilation factor together with heat release, surface area and effective heat transfer. An increased opening can alter both oxygen supply and energy loss through escaping gases. The net effect cannot be inferred from the geometric factor alone. Iqbal and Salley describe how restricted ventilation can prevent development, while extensive ventilation can increase cooling and raise the power needed for a critical layer temperature.<ref name="mqh">Walton and Thomas (2002), pp. 3-175–3-176; Iqbal and Salley (2004), pp. 13-5–13-6.</ref>

The enclosing material changes the amount of heat absorbed during the fire. Thermal conductivity, density, heat capacity and lining thickness influence that process. Two rooms with identical opening factors can therefore develop different temperature histories when their boundaries differ. Lie's distinction between representative light and heavy boundary materials makes this limitation explicit in the characteristic-curve method.<ref name="curves" />

The same distinction applies to [[Flashover criteria|flashover criteria]]. The Babrauskas threshold correlation uses 750 times the ventilation factor, based on compartment test data. That threshold differs from the 1,500 multiplier used for the stoichiometric reference. The coefficients describe different quantities and purposes. Substituting one for the other would conflate an estimated transition condition with a reference oxygen-limited heat release.<ref name="flashover">Walton and Thomas (2002), pp. 3-184–3-186.</ref>

The empirical support also has a defined range. Walton and Thomas report 33 fires behind the Babrauskas fit, primarily involving wood and polyurethane. Their ventilation factors ranged from 0.03 to 7.51 m<sup>5/2</sup>. The ratio of enclosing area to ventilation factor varied as well. A geometry far outside those conditions requires justification beyond the ability to substitute its dimensions into the equation.<ref name="flashover" />

== Worked geometric comparison ==

The SFPE example compartment is 3.0 m by 3.0 m in plan and 2.4 m high, with a 0.60 m by 1.80 m door. Its opening area is 1.08 m², and the enclosing area excluding the door is 45.72 m². The calculated ventilation factor is 1.449 m<sup>5/2</sup>. Normalising by the enclosing area gives an opening factor of 0.03169 m<sup>1/2</sup>.<ref name="example">Walton and Thomas (2002), pp. 3-177, 3-185–3-186.</ref>

For that geometry, the approximate developed-fire air inflow is 0.7245 kg/s. The corresponding stoichiometric heat-release reference is 2,173 kW, and the Babrauskas flashover estimate is 1,087 kW. These are separate model quantities calculated from the same geometry. They do not show that the source room actually undergoes a particular fire or reaches both values during its development.<ref name="airflow" /><ref name="stoich" /><ref name="flashover" />

Two hypothetical opening changes illustrate the geometric dependence. First, doubling the door width to 1.20 m while retaining its 1.80 m height doubles the ventilation factor to 2.898 m<sup>5/2</sup>. The approximate incoming air flow also doubles within the same relation. The enclosing area decreases slightly because the larger opening replaces part of a wall, so the normalised opening factor changes by a different proportion.<ref name="geometry" /><ref name="area" />

Second, an opening 1.20 m wide and 0.90 m high has the same area as the original door. Its ventilation factor is only 1.025 m<sup>5/2</sup>, and its approximate incoming flow is 0.5123 kg/s. Equal opening area therefore does not imply equal flow under this model. The height term distinguishes the two geometries.<ref name="geometry" /><ref name="airflow" />
[[File:fse-ventilation-factor-v2.svg|thumb|upright=1.5|alt=The original factor is 1.449, the wider opening gives 2.898, and an equal-area lower opening gives 1.025.|Equal opening areas can give different ventilation factors when their heights differ. Based on Walton and Thomas (2002), pp. 3-174, 3-177.]]

{| class="wikitable"
! Opening !! Area !! Ventilation factor !! Approximate air inflow
|-
| Source example, 0.60 × 1.80 m || 1.08 m² || 1.449 m<sup>5/2</sup> || 0.7245 kg/s
|-
| Wider opening, 1.20 × 1.80 m || 2.16 m² || 2.898 m<sup>5/2</sup> || 1.4490 kg/s
|-
| Equal-area lower opening, 1.20 × 0.90 m || 1.08 m² || 1.025 m<sup>5/2</sup> || 0.5123 kg/s
|}

The variants are arithmetic illustrations of the geometric formula, not independently validated fire experiments. Changing the physical opening can change flow patterns, fuel development and heat losses as well as the factor itself. The comparison demonstrates the sensitivity built into the expression while leaving those additional effects for a suitable compartment analysis.<ref name="flowbasis" /><ref name="mqh" />

== Limitations and reporting ==

The factor describes opening geometry under a particular model. It does not replace a full [[Vent flow|vent-flow]] calculation where separate openings, differing elevations or forced ventilation dominate. Detailed flow relations retain the pressure distribution, gas density and discharge behaviour. A simple geometric expression should therefore be used only where those effects are represented adequately by its assumptions.<ref name="flowbasis" /><ref name="multiple" />

An opening may also change during the fire. Cadorin and Franssen identify glazing breakage, automatic opening and firefighting actions as possible causes and allow time- or temperature-dependent vent sizes in their model. A single fixed ventilation factor then represents only one assumed opening state. The analysis should state whether that state is maintained or whether a sequence of geometries is being assessed.<ref name="change">Cadorin and Franssen (2003), p. 417.</ref>

A report should identify the opening dimensions, height reference, surface-area convention and units. It should distinguish the unnormalised ventilation factor from the normalised opening factor and state the relation using it. If an air-flow estimate is converted into heat release, the oxygen-consumption and combustion assumptions should accompany the result. This preserves the connection between geometry and the physical quantity actually estimated.<ref name="definition" /><ref name="opening" /><ref name="stoich" />

Fire load and ventilation factor describe different aspects of an exposure. Fire load supplies information about the fuel energy available, whereas the ventilation approximation concerns the rate at which air can support internal combustion. A temperature-time calculation must connect those quantities through its burning and decay assumptions. Reducing a rate while retaining the fuel inventory can change duration without eliminating the total potential energy.<ref name="severity" />

Finally, a smaller ventilation factor does not establish a less severe structural exposure in every respect. Restricted burning can extend the duration of a fire when fuel remains available, while a larger opening changes both combustion and heat loss. Lie and Walton and Thomas treat duration, temperature and boundary heat absorption together. Judging severity from the ventilation factor alone would omit those coupled effects.<ref name="severity">Lie (2002), pp. 4-202–4-203; Walton and Thomas (2002), p. 3-184.</ref>

== See also ==
* [[External flaming]]
* Glass breakage in fire
* [[Time equivalence]]

== Notes ==
<references />

== References ==
* Cadorin, J.-F., & Franssen, J.-M. (2003). A tool to design steel elements submitted to compartment fires: OZone V2. Part 1: Pre- and post-flashover compartment fire model. ''Fire Safety Journal, 38'', 395–427.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Lie, T. T. (2002). Fire temperature-time relations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-201–4-208). National Fire Protection Association.
* Walton, W. D., & Thomas, P. H. (2002). Estimating temperatures in compartment fires. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-171–3-188). National Fire Protection Association.

[[Category:Enclosure Fires]]

Timber in fire

2026-11-02T21:35:35Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Timber in fire''' describes the heating, decomposition, charring and structural response of wood members and assemblies during fire exposure. Timber can supply fuel to a fire while an interior portion continues to carry load. Its endurance depends on protective layers, the extent of charring and the capacity of the remaining uncharred section.<ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="W_4-257">White (2002), p. 4-257.</ref>

The charred surface and the intact-looking interior perform different roles. Char has very little load-bearing capacity, while the remaining wood can also lose performance as it heats. Charring rates depend on exposure, grain direction and material properties. A single rate therefore describes a particular approximation rather than every timber fire.<ref name="W_4-260_4-261">White (2002), pp. 4-260–4-261.</ref>

Assessment connects these material changes to the whole construction. Membranes and their attachments affect heating, while member geometry and loading determine the significance of section loss. Standard furnace results provide evidence for specified assemblies. Applying them to another arrangement requires attention to the conditions and limits of the test or calculation method.<ref name="W_4-257_4-259">White (2002), pp. 4-257–4-259.</ref>

== Heating, decomposition and combustion ==

Heating initially raises the temperature of the exposed timber surface and then affects material farther inside. Moisture evaporation absorbs some of the incoming energy. At higher temperatures, [[Pyrolysis]] breaks down the wood and releases gases while leaving a carbon-rich char. These processes change both the material properties and the geometry of the remaining solid.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="W_4-260">White (2002), p. 4-260.</ref>

The released gases can burn in flames outside the timber surface, and the char can also react with oxygen through glowing combustion. White explains that oxidation and mechanical disintegration can progressively erode the outer char layer. The surface is therefore not a permanent, unchanged insulating shell throughout every exposure.<ref name="W_4-260" />

[[Smouldering]] differs from pyrolysis alone. Ohlemiller defines it as flameless combustion sustained by heat from oxygen reacting with the solid fuel; a material can release smoke while externally heated without sustaining that oxidation process. The appearance of smoke therefore does not, by itself, identify the combustion mechanism taking place.<ref name="O_2-200">Ohlemiller (2002), p. 2-200.</ref>

White distinguishes an outer char layer, a zone undergoing decomposition and the inner wood. The base of the char layer is commonly associated with a temperature around 300 °C in the methods he describes. This boundary is useful for discussing section loss. It is not a statement that every point inside the remaining wood retains its original properties.<ref name="W_4-260" />

[[File:fse-timber-in-fire-v1.svg|thumb|upright=1.5|alt=Timber section with uncharred core, pyrolysis zone and char, with combustible gases leaving.|Timber develops an uncharred core, pyrolysis zone and char. Based on White (2002), p. 4-260, Figure 4-11.2, redraw, do not copy.]]

== Charring rate and grain direction ==

[[Charring rate]] describes how rapidly the boundary between char and uncharred wood advances. White explains that the rate can be relatively high initially and then become approximately steady during a standard exposure. A constant-rate description is therefore an empirical approximation. It represents a selected exposure and material response rather than a universal chemical constant.<ref name="W_4-260" />

For transverse-to-grain charring under the standard ASTM E119 exposure, White describes a commonly used approximation of 0.6 mm/min. He also reports that charring parallel to the grain is approximately twice as fast, and these are historical modelling conventions in the 2002 handbook. They are not complete contemporary design rules for every timber product.<ref name="W_4-260" />

[[File:fse-timber-in-fire-v2.svg|thumb|upright=1.5|alt=Transverse charring 0.6 mm/min and parallel charring about 1.2 mm/min.|Standard charring-rate convention by grain direction. Based on Kodur and Harmathy (2002), p. 1-164 and White (2002), p. 4-260.]]

Density, moisture, species, chemical composition and permeability affect charring. Greater moisture also changes the energy needed before the wood decomposes. Kodur and Harmathy report study values spanning approximately 0.137 to 0.85 mm/min under differing conditions. That range demonstrates variation across evidence; it is not an uncertainty band to apply around every design value.<ref name="KH_1-164_1-165">Kodur and Harmathy (2002), pp. 1-164–1-165.</ref>

[[File:fse-timber-in-fire-v3.svg|thumb|upright=1.5|alt=Study range 0.137 to 0.85 mm/min with the standard average 0.6 marked.|Reported charring rates vary around a standard average. Based on Kodur and Harmathy (2002), p. 1-164.]]

The direction and number of exposed faces change the shape of the remaining section. Corners exposed from adjacent faces become rounded as charring proceeds. White describes an approximate corner radius related to the char depth along the sides. Simply subtracting a rectangular layer can therefore miss geometry relevant to the residual section.<ref name="W_4-260" />

== A worked charring example ==

For a deliberately simplified constant-rate calculation, char depth is the rate multiplied by exposure time. The relationship describes advance from one exposed face in the selected direction, but it does not calculate the load capacity of the remaining section. Its applicability depends on whether the assumed rate continues to represent the exposure and member.<ref name="W_4-260_4-261" />

<math display="block">d_{\mathrm{char}}=\beta t</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>d_{\mathrm{char}}</math> || Depth of char measured from the original exposed face || mm
|-
| <math>\beta</math> || Assumed constant charring rate || mm/min
|-
| <math>t</math> || Time under the assumed exposure || min
|}

Using White's transverse-to-grain approximation of 0.6 mm/min for an illustrative 60 min exposure gives a char depth of 36 mm. This is the arithmetic consequence of the adopted constant rate. It is not a measured result for a particular beam, nor does it establish a 60 min structural rating. The remaining section and its temperature-dependent capacity still require assessment.<ref name="W_4-257" /><ref name="W_4-259_4-261">White (2002), pp. 4-259–4-261.</ref>

The same calculation cannot be extended indefinitely into a small member. White explains that heating of the centre can increase the charring rate as the residual section becomes thin. The approximation also omits corner rounding and any change in the exposed surface. Those effects can become influential before a simple geometric subtraction predicts complete consumption.<ref name="W_4-260" /><ref name="W_4-264">White (2002), p. 4-264.</ref>

Protection introduces another limit. If a membrane delays the onset of charring, total furnace time and actual charring time differ, and the membrane can also affect the subsequent heating rate after decomposition begins. Subtracting one assumed delay from every protected assembly does not reproduce all the protective behaviour described in the handbook.<ref name="W_4-257" /><ref name="W_4-259_4-260">White (2002), pp. 4-259–4-260.</ref>

== The remaining section and structural capacity ==

Char has very little load-bearing capacity in the structural assessment described by White. Resistance therefore depends primarily on the remaining uncharred wood and its condition, and the [[Reduced cross-section method]] expresses the related idea of evaluating a section after fire-related losses. A geometric char-depth estimate supplies only part of that assessment.<ref name="W_4-257" /><ref name="W_4-260" />

The residual section can be warm even where it has not converted to char. Under natural exposure, White notes that heating during the cooling period can affect more than a narrow outer layer. Residual dimensions and temperature consequently describe different aspects of the member. Treating all uncharred wood as unchanged would omit that thermal history.<ref name="W_4-264" />

Member size influences the relationship between those effects. Large solid and glued timber members can retain a substantial interior while their exposed surfaces char. These members connect the subject to Mass timber, although a calculation for one solid or glued member does not establish every assembly's behaviour. White's example methods specify material, dimensional and exposure limits.<ref name="W_4-261_4-264">White (2002), pp. 4-261–4-264.</ref>

Loading remains part of the structural problem. White identifies the capacity of the remaining wood as a separate contribution from the membrane and the char depth. A member can lose structural function before all its wood is consumed. Conversely, visible charring does not by itself specify the time at which the applied load can no longer be carried.<ref name="W_4-257" /><ref name="W_4-260" />

== Heat penetration is not char depth ==

Van Rossum uses thermal diffusivity to illustrate how a temperature disturbance penetrates a thick wall. Diffusivity combines conductivity, density and specific heat, and the characteristic depth grows with the square root of time when those properties are held constant. This thermal estimate differs from the constant-rate char-depth model because it describes another physical quantity.<ref name="VR_5.2" />

The source's timber example uses conductivity of 0.13 W/(m·K), density of 500 kg/m³ and specific heat of 1,600 J/(kg·K). Their combination gives a diffusivity of 1.63 × 10⁻⁷ m²/s. After 3,600 s, the characteristic thermal penetration depth is about 24 mm. The calculation is a simplified comparison using fixed properties, not a prediction of the char boundary.<ref name="VR_5.2" />

That 24 mm result and the earlier 36 mm char estimate should not be combined as if they described one tested member. They come from different simplifying models with different purposes; the penetration model does not include the changing geometry and properties caused by charring. A model intended to follow both processes requires additional treatment of decomposition and heat transfer.<ref name="VR_5.2" /><ref name="W_4-264" />

The physical distinction also explains why a cool interior can coexist with a damaged surface. Timber does not heat uniformly through a thick section at the beginning of an exposure. However, the depth and magnitude of that temperature gradient change with time. The available interior cannot be characterised solely by its original dimensions or by a surface-temperature observation.<ref name="VR_5.2" /><ref name="W_4-264" />

== Membranes and protected assemblies ==

A protective membrane is the first thermal barrier in many timber assemblies. White describes gypsum wallboard and plywood panelling as examples within historical test and calculation methods, and their type and thickness influence how long they remain effective. The performance of their fasteners and joints is part of the assembled construction.<ref name="W_4-257_4-258">White (2002), pp. 4-257–4-258.</ref>

White's component additive method assigns contributions to specified membranes, framing and other permitted features. The assignments come from correlations with ASTM E119 assembly tests; they are not independently measured endurance times that can be added for arbitrary products. The method includes construction details and limits on the assemblies to which it applies.<ref name="W_4-258_4-259">White (2002), pp. 4-258–4-259.</ref>

Adding a layer or filling a cavity can change heat transfer and attachment behaviour. White notes that insulation may improve some wall assemblies while producing different effects in floors or roofs. Changes in member spacing, internal finish and membrane arrangement can also fall outside the tested configuration. More material does not therefore create an automatic increase in the established rating.<ref name="W_4-257_4-259" />

Protective effects can continue after the onset of charring. White reports experiments in which gypsum board both delayed charring and reduced its subsequent extent, and this distinction matters when representing a membrane by a simple time delay. A delay-only model can omit part of the interaction between the board, the timber and the developing fire exposure.<ref name="W_4-260" />

== Reaction to fire and fire resistance ==

Timber's contribution as fuel and its performance as a structural member are separate questions. [[Fire resistance]] concerns maintaining specified assembly functions during a defined exposure. Surface burning behaviour concerns the contribution to developing fire conditions. A material can therefore require assessment for both its combustion behaviour and its remaining structural capacity.<ref name="KH_1-157" /><ref name="W_4-257" />

A fire-retardant surface treatment does not automatically provide structural protection. White distinguishes treatments aimed at surface flame spread from protection that reduces the heating of a member. Some treatments can change decomposition behaviour without producing the expected structural benefit. The relevant evidence depends on which outcome is being claimed.<ref name="W_4-259">White (2002), p. 4-259.</ref><ref name="W_4-261">White (2002), p. 4-261.</ref>

Regulatory treatment also depends on the use of the timber. New Zealand's C/VM2, second edition of 2025, lists specific exceptions within its internal surface-lining scenario. Its distinction between certain structural timber elements and exposed timber panels is part of that defined scope. It does not remove the separate need to evaluate the structural fire performance of an assembly.<ref name="CVM_50">Ministry of Business, Innovation and Employment (2025), p. 50.</ref>

The same New Zealand document uses ordinary timber products as examples associated with lining Group 3. Many fire-retardant-treated timbers are examples associated with Group 2. Those explanatory groups concern surface-lining performance within that method. They are not charring rates or structural endurance ratings for every product within either description.<ref name="CVM_52">Ministry of Business, Innovation and Employment (2025), p. 52.</ref>

Natural-fire calculations also require attention to the period after the highest gas temperature. White discusses changes in the residual timber section during cooling, when the interior temperature distribution continues to evolve. The mechanical condition cannot therefore be inferred solely from the time of the external temperature peak. A model following the complete exposure addresses a different question from one stopping at that peak.<ref name="W_4-264" />

This distinction separates extinguishing flames from completing a structural assessment. The source's nonstandard-fire discussion considers the subsequent temperature history within the remaining section, and its implications depend on the member, exposure and adopted material model. A calculation of maximum char depth alone does not describe every temperature-dependent change in the uncharred wood.<ref name="W_4-264" />

== Exposure limits and model evidence ==

The standard furnace exposure provides a repeatable heating history, while a natural compartment fire instead depends on combustible contents, openings and enclosure behaviour. Van Rossum explains that a standard temperature curve does not reproduce every real fire's growth and decay. A charring model calibrated to one exposure consequently needs justification before being transferred to another.<ref name="VR_8.6">Van Rossum (2027), §8.6.</ref><ref name="W_4-261_4-262">White (2002), pp. 4-261–4-262.</ref>

White describes empirical models for nonstandard exposure with explicit limits on duration, member dimensions and fire conditions. Such limits are part of the equations, not optional additions to them. His worked example checks whether the calculated depth remains within the model's dimensional range. Once the residual section heats more widely, the earlier approximation can cease to apply.<ref name="W_4-262_4-264">White (2002), pp. 4-262–4-264.</ref>

More detailed models follow energy storage, conduction and the energy effects of decomposition. Some also represent the movement of decomposition gases or moisture, and their flexibility allows a wider range of exposure histories, but it increases the demand for suitable physical data. White identifies both modelling the interacting processes and obtaining those data as difficulties in predicting timber behaviour.<ref name="W_4-264" />

Assembly evidence remains specific to the tested construction. A membrane, adhesive system or arrangement of timber pieces can change the sequence of heating and section loss. White's descriptions of solid and glued members therefore support the conditions he specifies. They do not establish a universal response for every later timber product or composite assembly.<ref name="W_4-257" /><ref name="W_4-261_4-264" />

== See also ==

* [[Structural fire engineering]]
* [[Strength reduction at elevated temperatures]]
* [[Fire testing]]

== Notes ==

<references />

== References ==

* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Ohlemiller, T. J. (2002). Smoldering combustion. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-200–2-210). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* White, R. H. (2002). Analytical methods for determining fire resistance of timber members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-257–4-273). National Fire Protection Association.

[[Category:Structural Fire Engineering]]

Tunnel fire

2026-11-02T21:35:32Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''tunnel fire''' is a fire in a road, rail or service tunnel, usually involving one or more vehicles or the installations in the tunnel. Because a tunnel is enclosed, the smoke of the fire stays around the people inside it, and their ability to move away from the fire is restricted.<ref name="Buk-229">Bukowski (2002), p. 5-229.</ref> Temperatures can become far higher than in an ordinary room fire: in the Summit rail tunnel fire on British Railways in 1984, the faces of brick-lined ventilation shafts fused.<ref name="DoT-13-7">Department of Transport (1984), as cited in Iqbal and Salley (2004), p. 13-7.</ref>

In the Netherlands, tunnels do not fit well into the building regulations, which are written mainly for buildings in which people stay. Fire safety engineering is therefore applied to tunnels on several aspects, and tunnels are usually fitted with a smoke management system.<ref name="VR-11.2">Van Rossum (2027), §11.2.</ref> Tunnel ventilation can keep part of a tunnel free of smoke by blowing air against the smoke, but the same airflow brings oxygen to the fire.<ref name="Klo-279">Klote (2002), p. 4-279.</ref> In fire tests, the peak heat release rate of vehicles ranged from about 1.5 MW for an older car to about 120 MW for a loaded truck.<ref name="Bab-27">Babrauskas (2002b), p. 3-27.</ref><ref name="Bab-28">Babrauskas (2002b), p. 3-28.</ref>

== Why tunnels differ from buildings ==
Bukowski describes the special hazards of rail tunnels in his chapter on transportation vehicles. In an accident in a tunnel, the fire effluent stays around the train and keeps exposing passengers and crew who have left the vehicles. Tunnels, bridges and elevated track also restrict how far people can move away from the train, which must be addressed for long tunnels.<ref name="Buk-229" /> Some fire scenarios are a threat to passengers only when they occur in a tunnel, because the tunnel increases the exposure to smoke.<ref name="Buk-231">Bukowski (2002), p. 5-231.</ref>

Most fire scenarios in trains lead to short exposures, mainly to heat. The exceptions are sleeping cars without fire detection and incidents in a long tunnel. For this reason, the operating procedure is that a train in which an emergency occurs keeps moving until it is out of the tunnel, if possible.<ref name="Buk-230">Bukowski (2002), p. 5-230.</ref> Trains are long and narrow spaces, so some assumptions of zone models may not be appropriate for them.<ref name="Buk-229" />

The temperatures in a tunnel fire can be extreme. A post-flashover compartment fire typically reaches about 1,100 °C, according to Drysdale as cited by Iqbal and Salley, but temperatures of 1,300 to 1,400 °C occasionally occur.<ref name="Dry-13-7">Drysdale (1998), as cited in Iqbal and Salley (2004), p. 13-7.</ref> Such temperatures are enough to fuse the surface of bricks, as happened in the ventilation shafts of the Summit tunnel.<ref name="DoT-13-7" /> For comparison, the cellulosic fire curves used for ordinary fire resistance tests reach a maximum of just over 900 °C.<ref name="IS-F-13">Iqbal and Salley (2004), p. F-13.</ref>

Regulation treats tunnels as special structures. The book ''Introduction to Fire Safety Engineering'' lists tunnels among the examples of buildings for which the Dutch building regulations are not effective. Other examples are public transport terminals and towers with a floor above 200 m. For such buildings, fire safety engineering is used.<ref name="VR-1.5">Van Rossum (2027), §1.5.</ref>

In New Zealand, Verification Method C/VM2 (second edition, 2025) names tunnels as an example of buildings outside its scope. Their compliance can be shown with an alternative solution.<ref name="MBIE-6">Ministry of Business, Innovation and Employment (2025b), p. 6.</ref> The International Fire Engineering Guidelines (2005) were written for buildings, but state that their concepts may also help in the design of ships and tunnels.<ref name="IFEG-0.1-3">National Research Council of Canada et al. (2005), Part 0 (Australia), p. 0.1-3.</ref> In the United States, road tunnels are covered by NFPA 502, listed in its 2001 edition in NUREG-1805.<ref name="IS-E-8">Iqbal and Salley (2004), p. E-8.</ref>

== Design fires ==
The design fire of a tunnel is usually a vehicle fire. The book gives a peak [[heat release rate]] of 8.5 MW for a car, and an energy content of 6,000 to 12,000 MJ per car and 19,000 MJ for an unloaded truck.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref><ref name="VR-4.4">Van Rossum (2027), §4.4.</ref> Measured peaks for single cars vary widely. Tests at the Fire Research Station in the United Kingdom gave 8.5 MW for an Austin Maestro and 4.5 MW for a Citroën BX. Finnish tests of cars from the late 1970s gave about 1.5 to 2.0 MW.<ref name="Bab-27" />

Larger vehicles release much more heat. In a European research programme, nearly two dozen vehicles were burnt, including cars, buses, trams, trucks and rail vehicles. Many of the peak heat release rates lay between about 10 and 35 MW. One test involved a truck loaded with 2 tonnes of modern upholstered furniture, which reached about 120 MW.<ref name="Bab-27" /><ref name="Bab-28" /> That is about 14 times the peak of a car fire of 8.5 MW. Truck tyres can ignite from an overheated axle and release a substantial amount of heat.<ref name="Bab-27" />

[[File:fse-tunnel-fire-v3.svg|thumb|upright=1.5|alt=Bars of peak heat release rates: cars 1.5 to 8.5 MW, electric car about 8 MW, large vehicles 10 to 35 MW, furniture truck about 120 MW.|Peak heat release rates of vehicle fires from tests and reviews. Based on Babrauskas (2002b), pp. 3-27–3-28, and Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 25.]]

In the Netherlands, the car fire curve in the standard NEN 6098 for mechanically ventilated car parks is based on a TNO design fire from 1999. In those tests, fire could spread to neighbouring cars 10 to 15 min after the first car, and the curve assumes three burning cars after 15 min.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> Modern cars, with their high plastic content, have a larger fire load and a higher heat release rate than older steel models.<ref name="VdG-11">Van der Graaf et al. (2021/2023), p. 11.</ref> The book therefore advises checking whether such curves still fit current vehicles.<ref name="VR-8.6" />

An [[electric vehicle fire]] has a similar peak to a conventional car fire, about 6 MW according to a review by Sun and co-workers. Vehicles with batteries of more than 100 kWh reach about 8 MW.<ref name="Sun-25">Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 25.</ref> Without intervention, an electric car burns out in about 90 min, and after extinguishing the battery can keep reigniting for several hours.<ref name="NFPA-26">NFPA (2013) and Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 26.</ref> A battery pack of 100 kWh can also release 2 to 20 kg of hydrogen fluoride, a toxic gas.<ref name="Lar-26">Larsson et al. (2017), as cited in Van der Graaf et al. (2021/2023), p. 26.</ref>

== Smoke control and critical velocity ==
Smoke can be stopped from flowing through an opening, such as a doorway or a corridor, by an airflow against it.<ref name="Klo-279" /> One criterion for the design air velocity is that no smoke flows back during the evacuation.<ref name="Klo-286">Klote (2002), p. 4-286.</ref> If the airflow is too weak, smoke flows back against it, a phenomenon known as backlayering.<ref name="Klo-278">Klote (2002), p. 4-278.</ref> The lowest air velocity that prevents this is the [[critical velocity]]. Thomas developed an empirical relation for this velocity in a corridor, which Klote gives in a simplified form for normal air properties:<ref name="Klo-279" />

[[File:fse-tunnel-fire-v1.svg|thumb|upright=1.5|alt=Two longitudinal tunnel sections with a burning vehicle: weak airflow lets smoke flow back upstream; stronger airflow keeps all smoke downstream.|Airflow below the critical velocity (top): smoke flows back upstream against the air. Airflow at or above the critical velocity (bottom): the upstream side stays free of smoke. Based on Klote (2002), pp. 4-278–4-279.]]

<math display="block">V_k = 0.292 \left( \frac{\dot{Q}}{W} \right)^{1/3}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>V_k</math> || critical air velocity to prevent smoke backflow || m/s
|-
| <math>\dot{Q}</math> || heat release rate of the fire || kW
|-
| <math>W</math> || width of the corridor || m
|}

The coefficient 0.292 follows from an air density of 1.3 kg/m³, a specific heat of 1.005 kJ/(kg·K), a downstream temperature of 27 °C and a constant of 1. The results are approximate, because the constant is known only approximately, but they show the size of the air velocity needed for different fires.<ref name="Klo-279" /> The relation was developed for corridors. Klote's design chart covers widths of 1 to 4 m and fires of 500 to 2,000 kW, far below the tens of megawatts of a truck fire.<ref name="Klo-280">Klote (2002), p. 4-280.</ref> It is not appropriate for sprinklered fires in which the smoke is barely warmer than the air.<ref name="Klo-279" /> For tunnels it therefore illustrates the principle rather than giving design values.

Klote's worked example is a wastebasket fire of 150 kW in a corridor 1.22 m wide. The relation gives 0.292 × (150 / 1.22)<sup>1/3</sup> = 0.292 × 4.97 = 1.45 m/s.<ref name="Klo-280" /> Doubling the heat release rate raises the critical velocity by only 26 %, because of the cube root. Within the range of the chart, a fire of 2,000 kW in a corridor 4 m wide needs 2.32 m/s. The cube root explains why larger fires need only moderately higher air speeds.

[[File:fse-tunnel-fire-v2.svg|thumb|upright=1.5|alt=Line chart of critical velocity rising slowly with heat release rate from 150 to 2,000 kW for widths of 1, 2 and 4 m.|Critical velocity from Thomas's corridor relation for three widths, within the range of Klote's design chart. Based on Klote (2002), pp. 4-279–4-280.]]

The airflow has a side effect: it brings oxygen to the fire. One cubic metre of air per second at 21 °C contains enough oxygen for a fire of 3,660 kW. In the worked example, the airflow of 4.3 m³/s that stops the smoke could support a fire of 15,800 kW, more than 100 times the wastebasket fire, so Klote advises extreme caution.<ref name="Klo-279" /><ref name="Klo-280" /> Strong ventilation also affects suppression and detection, as an example from a cable tunnel in the next section shows.<ref name="MB-328">Mawhinney and Back (2002), p. 4-328.</ref>

The same principle is used in some Dutch car parks. Displacement ventilation creates a high air speed over the whole cross-section, for example 1.5 m/s according to NEN 6098, which can easily mean 40 air changes per hour. It gives firefighters a clear view of the fire, but it works only in tunnel-shaped car parks and usually starts only after people have escaped.<ref name="VdG-38">Van der Graaf et al. (2021/2023), p. 38.</ref>

== Fire exposure of the tunnel structure ==
A tunnel lining must resist fires that are more severe than the standard fire of a building test. The book names two less common temperature–time curves that are more severe than the standard fire curve. One is the Rijkswaterstaat curve for tunnels, known as the RWS fire curve; the other is the hydrocarbon curve, which simulates an oil or gas fire.<ref name="VR-8.6" /> Fire curves are agreed temperature histories used to compare tested constructions; they do not reproduce the heat development of a real fire.<ref name="VR-8.6" /> Most furnace tests simulate a cellulosic fire, which grows more slowly than a hydrocarbon fire. In the United States, exposure ratings for hydrocarbon fires are given as H ratings under UL 1709.<ref name="IS-C-8">Iqbal and Salley (2004), p. C-8.</ref><ref name="IS-C-9">Iqbal and Salley (2004), p. C-9.</ref>

Concrete linings can suffer from [[spalling]], in which layers or pieces of concrete break off the heated surface, sometimes violently. Spalling is caused by a build-up of pore pressure from water vapour during heating, although some researchers attribute it to restrained thermal expansion near the surface. Extensive spalling can lead to early loss of stability and integrity, because it exposes the reinforcement.<ref name="KH-163">Kodur and Harmathy (2002), p. 1-163.</ref>

[[File:fse-tunnel-fire-v4.svg|thumb|upright=1.5|alt=Two cross-sections of a heated concrete lining: left, pieces break off and expose the reinforcement; right, melted fibres leave channels for steam.|Spalling of a heated concrete lining (left) and the effect of polypropylene fibres that melt at about 170 °C and let steam escape (right). Based on Kodur and Harmathy (2002), pp. 1-163 and 1-171.]]

The risk grows with a high moisture content, rapid heating, slender members and high stresses during the fire. Most members of normal-weight concrete withstand severe fires without spalling, but high-strength concrete of 50 to 120 MPa is more susceptible.<ref name="FB-255">Fleischmann and Buchanan (2002), p. 4-255.</ref> Design methods for concrete assume that the concrete stays intact, which no longer holds if the cover spalls off.<ref name="FB-255" />

A common remedy is to add polypropylene fibres to the concrete. The fibres melt at about 170 °C and leave channels through which steam can escape. Kodur and Harmathy give about 0.1 to 0.25 % by volume as the amount needed.<ref name="KH-171">Kodur and Harmathy (2002), p. 1-171.</ref> The International Fire Engineering Guidelines, citing Kodur, give 0.15 to 0.3 % without stating whether this is by volume or by mass.<ref name="IFEG-2.6-9">Kodur (1997), as cited in National Research Council of Canada et al. (2005), p. 2.6-9.</ref>

== Suppression and detection ==
A [[water mist system]] uses fine sprays in which no drop is larger than 1.0 mm.<ref name="MB-311">Mawhinney and Back (2002), p. 4-311.</ref> Test programmes for water mist have been carried out for high-voltage cable tunnels and for railway tunnels, including full-scale suppression tests for Eurotunnel and an onboard system for its shuttle trains for heavy goods vehicles.<ref name="MB-325">Mawhinney and Back (2002), p. 4-325.</ref> In Germany, VdS has test protocols for local application systems in electric cable tunnels.<ref name="MB-328" />

A cable tunnel of 9 km in Auckland shows the practical problems. Opening all nozzles along the tunnel at once would need very large water mains and pumps, and costly pumping out afterwards. The chosen solution released water in zones upstream and downstream of the fire.<ref name="MB-328" /> The ventilation air of 5 m/s would carry the heat along the tunnel, away from the nozzles closest to the fire, so individually heat-activated nozzles would not work. Turbulence under normal ventilation also made smoke and heat detection difficult. The detection system and the hydraulic system therefore had to be tested together.<ref name="MB-328" />

Vehicles with lithium-ion batteries raise further questions. A sprinkler or water mist system cannot extinguish a fire in an electric car, because the water droplets cannot reach the cells inside the closed battery pack. It can, however, reduce the chance that the fire grows and spreads to other vehicles and the structure.<ref name="VdG-37">Van der Graaf et al. (2021/2023), p. 37.</ref> For firefighting with hoses, the NIPV report gives two rules of thumb. A high-pressure jet of 125 L/min is generally sufficient for fires of up to 2.5 MW, and a low-pressure jet of 450 L/min for fires of up to 10 MW.<ref name="VdG-45">Van der Graaf et al. (2021/2023), p. 45.</ref> A truck fire of 120 MW is far beyond these values.<ref name="Bab-28" />

== Modelling ==
[[Computational fluid dynamics]] can be used to study how effective the smoke management system of a tunnel is.<ref name="VR-11.2" /> The book warns that the fire and its heat release rate must be prescribed by the modeller and that CFD is mainly reliable for qualitative comparisons of situations.<ref name="VR-11.4">Van Rossum (2027), §11.4.</ref> Cox and Kumar describe the King's Cross underground station fire, where CFD predicted that the flames would lie down in the trench of the escalator instead of rising. Physical tests confirmed this, and the authors stress that simple calculations should always shadow such simulations.<ref name="CK-207">Cox and Kumar (2002), p. 3-207.</ref>

Tunnels are numerically demanding. The Fire Dynamics Simulator notes that its standard pressure solver is excessively slow for tunnels made of dozens of computational meshes placed end to end, and offers an optional method for such geometries.<ref name="McG-43">McGrattan et al. (2026), p. 43.</ref> Its documentation also refers to work that couples a three-dimensional model of the fire region with a one-dimensional network model of the ventilation of a tunnel.<ref name="McG-111">McGrattan et al. (2026), p. 111.</ref> An older network program, the Subway Environment Simulation from the early 1970s, is used to size and locate ventilation shafts, evaluate tunnel geometry and fan size, and model heat and smoke from fires.<ref name="IS-B-83">Iqbal and Salley (2004), p. B-83.</ref>

== Limitations ==
The critical velocity relation was developed for corridors and covers fires up to 2,000 kW. The vehicle data come from a limited number of tests, and the book names the RWS fire curve without giving its values.<ref name="Klo-280" /><ref name="Bab-27" /><ref name="VR-8.6" /> Fire curves describe a test exposure, not a real fire, and CFD results depend on the prescribed fire.<ref name="VR-8.6" /><ref name="VR-11.4" /> A common misconception is that a tunnel fire can be treated as a room fire. The long geometry, the limited escape routes and the effect of ventilation on both smoke and fire make it a different problem.<ref name="Buk-229" /><ref name="Klo-279" />

== See also ==
* [[Car park fire]]
* [[Thermal runaway]]
* [[Lithium-ion battery fire]]

== Notes ==
<references />

== References ==
* Babrauskas, V. (2002b). Heat release rates. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association; Society of Fire Protection Engineers.
* Bukowski, R. W. (2002). Fire hazard assessment for transportation vehicles. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-227–5-233). National Fire Protection Association; Society of Fire Protection Engineers.
* Cox, G., & Kumar, S. (2002). Modeling enclosure fires using CFD. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-194–3-218). National Fire Protection Association; Society of Fire Protection Engineers.
* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association; Society of Fire Protection Engineers.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association; Society of Fire Protection Engineers.
* Mawhinney, J. R., & Back, G. G., III. (2002). Water mist fire suppression systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-311–4-337). National Fire Protection Association; Society of Fire Protection Engineers.
* McGrattan, K., Hostikka, S., Floyd, J., McDermott, R., Vanella, M., Mueller, E., & Paul, C. (2026). ''Fire Dynamics Simulator technical reference guide: Vol. 1. Mathematical model'' (6th ed., NIST Special Publication 1018-1). National Institute of Standards and Technology. https://doi.org/10.6028/NIST.SP.1018
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Special Hazards & Building Types]]

Thermal runaway

2026-11-02T21:35:29Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Thermal runaway''' is the uncontrolled rise in temperature of a reacting material or device when the heat produced by its own chemical reactions exceeds the heat it can lose to its surroundings. The higher temperature speeds up the reactions, which produce still more heat, until the material ignites or its reactive content is used up.<ref name="Gray-212">Gray (2002), p. 2-212.</ref><ref name="Kan-196">Kanury (2002b), p. 2-196.</ref> In the SFPE Handbook the term is used as a synonym of ''runaway reaction'', originally for chemical reactors.<ref name="Gray-212" /> Today it is best known as the failure mechanism behind a [[lithium-ion battery fire]], in which a battery cell heats itself and can set fire to its neighbours.<ref name="Col-22">Colella et al. (2016), as cited in Van der Graaf et al. (2021/2023), p. 22.</ref><ref name="VdG-22">Van der Graaf et al. (2021/2023), p. 22.</ref>

The same physics explains the [[self-heating]] of haystacks, oily rags and coal piles, so the general theory of self-heating is the starting point for understanding batteries.<ref name="Gray-211">Gray (2002), p. 2-211.</ref><ref name="Gray-223">Gray (2002), p. 2-223.</ref> In an electric vehicle, thermal runaway can start at temperatures of about 70 to 250 °C, depending on the type of battery.<ref name="Sun-22">Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 22.</ref> It releases flammable and toxic gases and can make the fire reignite until the battery's energy is used up.<ref name="VdG-22" /> The peak heat release rate of an [[electric vehicle fire]] is similar to that of a petrol or diesel car. Its slow start, long duration and the difficulty of extinguishing it are what set it apart.<ref name="Sun-25">Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 25.</ref><ref name="VdG-26">Van der Graaf et al. (2021/2023), p. 26.</ref><ref name="VdG-30">Van der Graaf et al. (2021/2023), p. 30.</ref>

== Definition ==
Gray describes spontaneous combustion as the reaction of an unstable, usually oxidisable, material that releases heat. Much of this heat stays inside the material because it, or its container, conducts heat poorly. If the process ends in flaming, it is called spontaneous ignition.<ref name="Gray-211" />

Mild self-heating that settles at a slightly raised temperature is called ''subcritical''. Self-heating that ends in ignition is called ''supercritical'', and the sharp boundary between the two is the ''critical condition''.<ref name="Gray-211" /> Runaway reaction and thermal runaway are the names used for supercritical behaviour in a chemical reactor, which is almost always well stirred.<ref name="Gray-212" /> Other chapters of the SFPE Handbook use the term in the same sense. In the thermal theory of autoignition, ignition is taken as the instant at which the temperature in the reacting mixture rises rapidly. This event is called thermal runaway and also marks the start of a rapid consumption of the reactants.<ref name="Kan-196" />

In the theory of heat conduction, thermal runaway is the case in which the temperature of a heat-generating solid grows exponentially with time and no steady state exists.<ref name="RM-36">Rockett and Milke (2002), p. 1-36.</ref> For batteries, a report by the Dutch Institute for Public Safety (NIPV) on car parks quotes a definition by Colella and co-workers. In that definition, thermal runaway is a failure mechanism that leads to self-heating in a battery or battery cell and that can result in fire.<ref name="Col-22" /> The NIPV report notes that thermal runaway and the burning of the released gases are different processes, and that the link between them is not yet well understood.<ref name="VdG-55">Van der Graaf et al. (2021/2023), p. 55.</ref>

== Heat generation and heat loss ==
The mechanism is a competition between two heat flows. Most chemical reaction rates increase almost exponentially with temperature, while heat loss by conduction increases only linearly. Once the heat production grows faster than the loss, the temperature can only rise.<ref name="Gray-212" /> A larger body and a higher ambient temperature both reduce the relative heat loss and so favour ignition. Inside a self-heating body the temperature profile is roughly parabolic, so runaway starts at the centre, where the temperature is highest.<ref name="Gray-212" />

Semenov's theory, the simplest description, writes this competition as a heat balance for a body with a uniform temperature. The body stores heat according to its heat capacity, gains heat from the reaction in its whole volume and loses heat through its surface. The rate of change of the stored heat equals the heat generated minus the heat lost:<ref name="Gray-216">Gray (2002), p. 2-216.</ref>

<math display="block">C_v \rho V \frac{dT}{dt} = V Q f(c)\, e^{-E/RT} - S \chi \left( T - T_a \right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>C_v</math> || heat capacity at constant volume, per unit mass || J/(kg·K)
|-
| <math>\rho</math> || density of the material || kg/m³
|-
| <math>V</math> || volume of the body || m³
|-
| <math>T</math> || temperature of the reacting material || K
|-
| <math>t</math> || time || s
|-
| <math>Q</math> || heat of reaction per unit concentration of fuel || J/mol
|-
| <math>f(c)</math> || kinetic rate law, a function of the fuel concentration <math>c</math> || mol/(m³·s)
|-
| <math>E</math> || activation energy of the reaction || J/mol
|-
| <math>R</math> || universal gas constant, 8.314 || J/(mol·K)
|-
| <math>S</math> || surface area across which heat is lost || m²
|-
| <math>\chi</math> || heat transfer coefficient || W/(m²·K)
|-
| <math>T_a</math> || ambient temperature, constant in time || K
|}

The first term on the right is the heat generated by the self-heating reaction, and the second is the heat lost to the surroundings. Their difference drives the change in temperature.<ref name="Gray-216" /> The equation cannot be solved by classical methods, but the critical condition can be found from it exactly.<ref name="Gray-216" />

The relation assumes a uniform temperature, a single reaction of simple order, and a heat of reaction and activation energy large enough to give ignition behaviour. It suits well-stirred liquids and gases. It is a poor approximation for poorly conducting materials such as cellulose, with a conductivity of about 0.05 W/(m·K), although it still gives semi-quantitative results there.<ref name="Gray-215">Gray (2002), p. 2-215.</ref><ref name="Gray-216" /> It is a general model of self-heating and not a model of a battery.

The balance is easiest to understand as two curves of heat flow against temperature, the Semenov diagram. At a low ambient temperature the straight heat-loss line cuts the curved heat-generation curve twice. The lower crossing is a stable state, usually 5 to 20 °C above ambient, in which the material may degrade or discolour but does not ignite.<ref name="Gray-214">Gray (2002), p. 2-214.</ref>

[[File:fse-thermal-runaway-v1.svg|thumb|upright=1.5|alt=Semenov diagram: a steeply rising heat generation curve and three parallel straight heat loss lines for low, critical and high ambient temperature.|Semenov diagram: heat generated by the reaction (curve) and heat lost to the surroundings (straight lines) for three ambient temperatures. Based on Gray (2002), pp. 2-213–2-214.]]

At the critical ambient temperature the line just touches the curve. Above it there is no balance point at all, and the temperature rises until ignition, at a rate proportional to the imbalance between heat production and loss.<ref name="Gray-214" /> The slope of the loss line depends on the ratio of surface area to volume. For a given ambient temperature there is therefore also a critical size, above which a body will run away.<ref name="Gray-214" />

A worked example shows why the critical point lies close to ambient conditions. Many spontaneous combustion reactions, in particular those of cellulosic materials, have activation energies of around 100 kJ/mol.<ref name="Gray-221">Gray (2002), p. 2-221.</ref> Gray shows that criticality exists only if the activation energy is at least four times the product of the gas constant and the critical ambient temperature.<ref name="Gray-217">Gray (2002), p. 2-217.</ref> At an ambient temperature of 30 °C (303 K) this product is 8.314 × 303 = 2.52 kJ/mol, so four times it is 10.1 kJ/mol. The activation energy of 100 kJ/mol is about ten times larger, so the reaction accelerates strongly enough for a sharp critical condition.

The ratio of the gas constant times the squared temperature to the activation energy is 8.314 × 303² / 100,000 = 7.6 K. Kanury points out that this ratio is generally small, which is why the critical temperature of a reacting mass lies close to the temperature of its surroundings.<ref name="Kan-196" /> As a rule of thumb for materials with an unknown activation energy, self-heating of more than 30 °C above ambient, typically a body temperature above 60 to 70 °C, indicates imminent spontaneous ignition.<ref name="Gray-217" />

== Size, storage and time to ignition ==
Because heat loss depends on surface area and heat generation on volume, size matters as much as temperature. Bodies placed in contact act as one larger body. Two bales that touch have a considerably lower critical ambient temperature than a single bale, so a test on one item says little about a stack unless a theory is used to scale it up.<ref name="Gray-215" /> Bodies that are not in contact can still interact by heating the air around them. In tests with kegs of 14 kg in still air, the critical ambient temperature fell from 62.5 °C for a single keg to 54 °C for 18 kegs packed in a steel box.<ref name="Gray-223" />

The time to ignition is very hard to predict. It becomes infinite at the critical condition and is extremely sensitive to conditions close to it.<ref name="Gray-223" /> Larger bodies generally take longer: oily rags in a wastepaper basket may ignite within a few hours, haystacks after a few weeks and coal stockpiles after a few months. Bodies that are stacked while still hot ignite much sooner.<ref name="Gray-223" /><ref name="Gray-224">Gray (2002), p. 2-224.</ref> Deep-seated burning that starts by spontaneous ignition is difficult to extinguish completely and often reignites days after it seemed to be out.<ref name="Gray-212" />

The International Fire Engineering Guidelines note that self-heating depends not only on the chemical nature of a substance but also on the size and shape of the aggregation.<ref name="IFEG-3.3-2">National Research Council of Canada et al. (2005), p. 3.3-2.</ref> In continuously stirred chemical reactors, the scale-up from a prototype to a commercial size has led to the critical condition being exceeded.<ref name="Gray-219">Gray (2002), p. 2-219.</ref> The same lesson applies to stacks and stores: the critical condition belongs to the whole assembly, not to a single item.<ref name="Gray-215" />

== Thermal runaway in lithium-ion batteries ==
A battery pack in an electric vehicle is built up in steps. Cells deliver about 4 V, cells are combined into modules of up to 60 V, and modules are connected into packs of 300 to 1,000 V. Packs in passenger cars can store 100 kWh or more.<ref name="VdG-21">Van der Graaf et al. (2021/2023), p. 21.</ref> Packs can also be connected into larger battery systems of 10 to 400 kWh, for example for trucks and electric ships.<ref name="VdG-21" /> Stationary installations of this kind are described under battery energy storage system.

Each battery pack has its own safety window. If it is exceeded, the pack can heat up further and thermal runaway can occur.<ref name="ARB-22">Air Resources Board (2015), as cited in Van der Graaf et al. (2021/2023), p. 22.</ref> The onset temperature depends on the type of battery and ranges from 70 to 250 °C.<ref name="Sun-22" /> Elsewhere the NIPV report gives a range of 50 to 270 °C, and it stresses that "lithium-ion" covers many battery types with different fire behaviour.<ref name="VdG-18">Van der Graaf et al. (2021/2023), p. 18.</ref> A battery management system monitors the cells. When a threshold is exceeded it can apply active cooling during charging, stop the charging or disconnect the whole pack, and a fault in the system itself also switches the pack off.<ref name="VdG-23">Van der Graaf et al. (2021/2023), p. 23.</ref>

The causes can be internal or external. Internal causes are rare design or manufacturing errors in the electrode, separator or electrolyte, which can lead to failures of the management system and to overcharging; such errors usually lead to recalls. External causes include outside heat, misuse and extreme conditions such as a collision that damages the battery.<ref name="VdG-23" /> In car parks, damaged charging cables or stations, vehicles that hit a charging station and vehicles with an unnoticed defective pack add to these causes.<ref name="Sun-29">Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 29.</ref>

Published failure probabilities differ widely, from one in a million or lower to about one in 100 million.<ref name="Lar-23">Larsson et al. (2017) and Bullis (2013), as cited in Van der Graaf et al. (2021/2023), p. 23.</ref> Overall the probability of battery failure seems relatively low. The NIPV report adds, however, that no lithium-ion battery is intrinsically safe. The design of a pack cannot completely prevent the release of enough energy for thermal runaway.<ref name="VdG-23" />

Once a cell runs away, the process can spread. Heat from one cell warms the adjacent cells, which then also go into thermal runaway, in a chain reaction through the pack.<ref name="VdG-22" /> As the battery heats up it releases flammable gases, which ignite if enough oxygen is present and the ignition temperature is reached; the hot cell housing may be enough. Gases trapped in a pouch or cartridge can escape when the enclosure or a pressure valve fails. In the right mixture with air they can cause a flare fire or a gas cloud [[explosion]], and mechanical damage can throw out burning fragments.<ref name="VdG-22" />

[[File:fse-thermal-runaway-v2.svg|thumb|upright=1.5|alt=Battery pack with modules of cells; one cell in thermal runaway heats its neighbours and releases gas through a vent.|Structure of an electric vehicle battery pack and spread of thermal runaway from cell to cell. Based on Van der Graaf et al. (2021/2023), pp. 21–22.]]

Ageing changes the behaviour. As a battery ages, its maximum state of charge falls, and since the intensity of thermal runaway depends on the state of charge, the intensity decreases.<ref name="Essl-28">Essl et al. (2021), as cited in Van der Graaf et al. (2021/2023), p. 28.</ref> An older battery in thermal runaway also produces fewer flammable gases than a new one.<ref name="VdG-28">Van der Graaf et al. (2021/2023), p. 28.</ref>

== Fire behaviour of electric vehicles ==
A battery fire develops in two stages. While the cells warm up and start to release gas, the temperature rises slowly, at about 0.2 °C per minute. Once thermal runaway occurs, the rise becomes exponential, at more than 10 °C per minute.<ref name="VdG-26" /> A conventional car fire burns for just over half an hour and peaks at about 5 MW after 10 to 15 min.<ref name="VdG-26" /> Without intervention an electric vehicle burns out in about 90 min.<ref name="NFPA-26">NFPA (2013), as cited in Van der Graaf et al. (2021/2023), p. 26.</ref> After extinguishing, the energy remains in the battery and the fire can keep reigniting for several hours.<ref name="Sun-26">Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 26.</ref>

[[File:fse-thermal-runaway-v3.svg|thumb|upright=1.5|alt=Schematic temperature-time line: a long shallow rise of about 0.2 °C per minute, then a steep rise of more than 10 °C per minute after thermal runaway.|Schematic development of a battery fire: a slow rise while the cells warm up and release gas, then a steep rise once thermal runaway occurs. Based on Van der Graaf et al. (2021/2023), p. 26.]]

The peak heat release rate is not much different from that of a conventional car. A review by Sun and co-workers found a similar peak of about 6 MW for both. The time to the peak was 6 to 40 min for electric vehicles and 6 to 35 min for conventional cars. The total heat released was 4.7 to 8.5 GJ and 3.3 to 10 GJ respectively.<ref name="Sun-25" /> Vehicles with packs of 15 to 25 kWh give about 4 to 6 MW, and the growth of packs to more than 100 kWh has raised this to about 8 MW.<ref name="Sun-25" />

[[File:fse-thermal-runaway-v4.svg|thumb|upright=1.5|alt=Dot plot of peak heat release rates of car fire tests: electric 4.2 to 7 MW, hybrid 6 to 8 MW, conventional 2.1 to 10.8 MW.|Peak heat release rate in full-scale fire tests of battery electric, plug-in hybrid and conventional cars. Based on Sun et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 24.]]

Measured flame temperatures do not differ significantly either. In tests by Lam and co-workers, electric and conventional vehicles both reached about 800 ± 100 °C over periods of 5 to 30 min.<ref name="Lam-23">Lam et al. (2016), as cited in Van der Graaf et al. (2021/2023), p. 23.</ref> In the Netherlands, the car fire curve in the standard NEN 6098 for car parks is based on a TNO design fire from 1999. In those tests, fire could spread to neighbouring cars 10 to 15 min after the first car. The book ''Introduction to Fire Safety Engineering'' notes that these curves may be less conservative for modern cars with more plastics.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref>

The gases differ more than the heat. Burning batteries release methane, carbon monoxide, carbon dioxide and hydrogen, as well as the toxic gases hydrogen fluoride and hydrogen chloride.<ref name="Sun-26" /> A burning pack releases about 20 to 200 mg of hydrogen fluoride per Wh of capacity. For a 100 kWh pack, that amounts to 2 to 20 kg, depending on the state of charge.<ref name="Lar-26">Larsson et al. (2017), as cited in Van der Graaf et al. (2021/2023), p. 26.</ref> Hydrogen fluoride is a strong irritant. Purser lists 200 ppm as the concentration predicted to impair escape in half of the population and 900 ppm as the concentration predicted to incapacitate half.<ref name="Pur-121">Purser (2002), p. 2-121.</ref>

For people escaping, smoke from any vehicle fire is already very toxic because of the burning plastics. On that basis the extra hydrogen fluoride from the battery is considered to have no effect on escape safety.<ref name="RISE-30">RISE (2020), as cited in Van der Graaf et al. (2021/2023), p. 30.</ref> Smoke with more hydrogen fluoride can still spread from the car park to escape routes and stairs of buildings above it.<ref name="VdG-30" />

The released gases also create an explosion hazard. If they do not ignite at once, an explosive mixture can build up in a confined or poorly ventilated space.<ref name="Bis-27">Bisschop et al. (2020), as cited in Van der Graaf et al. (2021/2023), p. 27.</ref> When it reaches the lower explosion limit and meets an ignition source, a fire gas explosion can follow.<ref name="VdG-27">Van der Graaf et al. (2021/2023), p. 27.</ref> Hydrogen, one of these gases, has a very wide flammable range: at room temperature a flame can propagate upwards through mixtures with 4.1 to 74 % hydrogen by volume in air.<ref name="IS-16-2">Iqbal and Salley (2004), p. 16-2.</ref> Zalosh describes explosion protection as breaking the chain of events: preventing a fuel-air mixture by ventilation or inerting, removing ignition sources, or limiting the pressure rise by venting or suppression.<ref name="Zal-402">Zalosh (2002), p. 3-402.</ref> Fires of electric vehicles can involve repeated small explosions, flying parts and flash fires.<ref name="VdG-29">Van der Graaf et al. (2021/2023), p. 29.</ref>

== Firefighting and design measures ==
A fire in which the battery pack is involved is very difficult or impossible to extinguish. The pack is closed, and the gases released by the self-propagating thermal runaway keep reigniting.<ref name="VdG-30" /> The coolant, often water, cannot reach the cells directly because the pack is sealed against moisture and dirt.<ref name="IFV-22">IFV (2021b), as cited in Van der Graaf et al. (2021/2023), p. 22.</ref> Cooling therefore needs a lot of water for a long time, and the situation is safe only when all electrical and chemical energy in the battery has been used up.<ref name="VdG-22" /> Putting out the flames needs no more capacity than for a conventional car, but long-term cooling to prevent reignition needs much more water.<ref name="NFPA-46">NFPA (2013), as cited in Van der Graaf et al. (2021/2023), p. 46.</ref>

At present, an immersion container is the best available method for the long-term cooling of a battery pack.<ref name="IFV-46">IFV (2021b), as cited in Van der Graaf et al. (2021/2023), p. 46.</ref> Blanketing the vehicle with foam is not yet a useful tactic, because laboratory studies show that packs can reignite during thermal runaway even with little oxygen.<ref name="VdG-47">Van der Graaf et al. (2021/2023), p. 47.</ref> Sprinklers and water mist cannot extinguish a burning electric vehicle, because the droplets cannot enter the pack. They do reduce the probability that the fire grows and spreads to nearby vehicles and to the structure.<ref name="VdG-37">Van der Graaf et al. (2021/2023), p. 37.</ref>

Ways to bring water into the pack are being studied. One is a sprinkler inside the pack, which could cool the cells in thermal runaway more effectively and possibly extinguish them.<ref name="RISE-56">RISE (2019a), as cited in Van der Graaf et al. (2021/2023), p. 56.</ref> Another is a hose connection in the casing of the pack, tested by a car manufacturer.<ref name="VdG-56">Van der Graaf et al. (2021/2023), p. 56.</ref> In a study of several detector types, carbon monoxide detectors gave the fastest alarm.<ref name="DNV-37">DNV-GL (2019), as cited in Van der Graaf et al. (2021/2023), p. 37.</ref>

A fire in the Singelgarage in Alkmaar on 1 July 2020 illustrates these problems. A police robot was used to tow an electric vehicle out of the car park because its battery pack kept reigniting, and the pack was then cooled for a long time in an immersion container.<ref name="VdG-12">Van der Graaf et al. (2021/2023), p. 12.</ref> For indoor car parks in the Netherlands, the NIPV report suggests, among other measures, not placing charging bays near pedestrian escape routes, because toxic and caustic products of thermal runaway can spread there. It also suggests a means of switching off all charging points at once.<ref name="VdG-35">Van der Graaf et al. (2021/2023), p. 35.</ref><ref name="VdG-36">Van der Graaf et al. (2021/2023), p. 36.</ref>

== Limits and misconceptions ==
The theory of thermal runaway is well developed for self-heating materials and chemical reactors, but it rests on simplifications. Semenov's model assumes a uniform temperature and a single simple reaction, and the classical corrections are often impossible to apply because data are lacking or uncertain.<ref name="Gray-212" /><ref name="Gray-216" /> No formula is available in these sources for the runaway of a battery cell or for its spread from cell to cell. For batteries, the NIPV report lists open questions: the relation between thermal runaway and fire development, the conditions for reignition, the effect and duration of external cooling, and the thermal load on car park structures.<ref name="VdG-55" />

A common misconception is that electric vehicles burn hotter or with a much larger peak heat release rate than conventional cars. The data summarised by NIPV show similar peaks and similar flame temperatures.<ref name="Sun-25" /><ref name="Lam-23" /> The differences lie in the slow start, the long duration, the risk of reignition and explosion, and the larger amount of hydrogen fluoride.<ref name="VdG-26" /><ref name="VdG-29" /> Another misconception is that a fire that seems to be out is safe. Both in self-heating stockpiles and in battery packs, deep-seated reactions can restart hours or days later.<ref name="Gray-212" /><ref name="Sun-26" />

== See also ==
* [[Car park fire]]
* [[Tunnel fire]]
* [[Warehouse fire]]

== Notes ==
<references />

== References ==
* Gray, B. (2002). Spontaneous combustion and self-heating. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-211–2-228). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Kanury, A. M. (2002b). Ignition of liquid fuels. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-188–2-199). National Fire Protection Association; Society of Fire Protection Engineers.
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-83–2-171). National Fire Protection Association; Society of Fire Protection Engineers.
* Rockett, J. A., & Milke, J. A. (2002). Conduction of heat in solids. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-27–1-43). National Fire Protection Association; Society of Fire Protection Engineers.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-402–3-421). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Special Hazards & Building Types]]

Thermal radiation

2026-11-02T21:35:26Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Thermal radiation''' is heat transfer by electromagnetic waves emitted because of the temperature of matter. It can occur through a vacuum and does not require a transporting medium between source and receiver. In fires, radiation comes from flames, hot soot, combustion gases and heated solid or liquid surfaces.<ref name="VR-5.4">Van Rossum (2027), §5.4.</ref><ref name="Tien-1-73">Tien, Lee, and Stretton (2002), p. 1-73.</ref>

This mechanism can heat objects at a distance, support ignition and contribute to fire spread within and between enclosures. Its importance increases strongly with temperature and can also change with fire scale. Radiation therefore forms a distinct part of [[Heat transfer]], alongside conduction and convection.<ref name="VR-5.4" /><ref name="Tien-1-73" />

The heat flux received by an object is not determined by source temperature alone. Emission, absorption, reflection, geometry, orientation and the medium between the surfaces can all influence the result. A useful assessment identifies both the radiant source and the receiving surface.<ref name="Tien-1-75">Tien, Lee, and Stretton (2002), p. 1-75.</ref>

== Electromagnetic energy and temperature ==

Every material above absolute zero emits radiation. The relevant energy can be described using electromagnetic waves or photons, and its distribution varies with wavelength. At temperatures relevant to buildings and fires, the dominant thermal-radiation range lies mainly in infrared, with some visible contribution at higher temperatures.<ref name="VR-5.4" />

Tien and colleagues identify a major thermal-radiation spectrum of 1 to 100 micrometres for the fire applications discussed. Water vapour and carbon dioxide can absorb and emit strongly in parts of this range. Hydrocarbon gases and soot also participate, with soot often contributing more than gases in the situations described.<ref name="Tien-1-73" />
[[File:fse-thermal-radiation-v1.svg|thumb|upright=1.5|alt=Hot source emitting infrared through gas to a receiver with absorption and reradiation.|Thermal radiation involves source, medium and receiver. Based on Van Rossum (2027), §5.4 and Tien, Lee, and Stretton (2002), p. 1-73.]]

Visible glow is only one part of radiant emission. Van Rossum notes that a surface at approximately 550 °C can emit enough visible radiation to appear red-hot, with colour changing as temperature rises further. Infrared energy can nevertheless be transferred without a surface appearing luminous to human vision.<ref name="VR-5.4" />

The wavelength of maximum blackbody emission shifts towards shorter wavelengths as temperature increases. This relationship, known as Wien's displacement law, shows why the spectral distribution changes with temperature. It does not mean that all energy moves to the visible range at fire temperatures.<ref name="Tien-1-74">Tien, Lee, and Stretton (2002), p. 1-74.</ref>

Radiation can be absorbed or emitted by gases between surfaces. Van Rossum notes that these gases can warm and reradiate, or absorb part of the energy passing through them. A clear line of sight therefore does not guarantee that the intervening medium has no effect.<ref name="VR-5.4" />

== Emission, absorption and reflection ==

[[Emissivity]] describes how strongly a real surface emits compared with an ideal blackbody under corresponding conditions. A blackbody is an idealised perfect absorber and emitter. Real materials have emissivities that can depend on wavelength, surface condition and temperature.<ref name="VR-5.4" /><ref name="Tien-1-74" />

Engineering calculations often use one emissivity value rather than a full wavelength-dependent description. Van Rossum explains that this grey-surface simplification avoids integrating detailed properties across the spectrum, which are difficult to determine. The simplification is practical but remains an approximation.<ref name="VR-5.4" />
[[File:fse-thermal-radiation-v3.svg|thumb|upright=1.5|alt=Emissivity values: polished aluminium 0.04, anodised aluminium 0.9 and rough concrete 0.91.|Emissivity varies with material and surface finish. Based on Van Rossum (2027), §5.4.]]

Surface finish can make a substantial difference. The example table in Van Rossum lists polished aluminium at 0.04 and anodised aluminium at 0.9, while rough concrete is listed at 0.91 and human skin at 0.97 to 0.999. These values demonstrate why identical substrate names or colours do not establish radiant behaviour.<ref name="VR-5.4" />

Kirchhoff's law connects absorptivity and emissivity under specified equilibrium and spectral conditions. It supports the intuitive relationship that good absorbers can also be good emitters. Applying total rather than spectral properties requires additional assumptions about the incident radiation and surface behaviour.<ref name="Tien-1-75" />

Incoming radiation can be absorbed, reflected or transmitted. Solids and liquids commonly absorb within a very small surface depth, while porous insulation can also transfer energy internally through radiation. Van Rossum notes that this contribution is commonly included in an effective conductivity rather than calculated separately.<ref name="VR-5.4" />

== Temperature and emitted power ==

The [[Stefan-Boltzmann law]] relates ideal blackbody emission per unit area to the fourth power of absolute temperature. Real-surface calculations include emissivity, and net exchange also accounts for radiation received from the surroundings. Kelvin, not degrees Celsius, must be used for the absolute-temperature relationship.<ref name="VR-5.4" /><ref name="Tien-1-74" />

For a source represented by a single temperature and emissivity, emitted power per unit area is calculated from the following expression. Setting emissivity to one gives the blackbody limit. The source's emissivity scales that maximum emission. This is an emission calculation, before the distance and orientation of a receiver are considered.<ref name="VR-5.4" />

<math display="block">E_s=\varepsilon_s\sigma T_s^4</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>E_s</math> || Source radiant emission per unit area || W/m²
|-
| <math>\varepsilon_s</math> || Effective source emissivity || Dimensionless
|-
| <math>\sigma</math> || Stefan–Boltzmann constant, <math>5.67\times10^{-8}</math> || W/(m²·K⁴)
|-
| <math>T_s</math> || Absolute source temperature || K
|}

This fourth-power dependence explains why radiation becomes increasingly important at high temperature. Van Rossum gives a broad transition in which convection tends to dominate at lower temperatures and radiation becomes particularly important from around 400 °C. This is guidance rather than a sharp universal boundary.<ref name="VR-5.4" />

Net exchange differs from gross emission. A hot surface emits towards a cooler one, but the cooler surface also emits back. When the receiver temperature is not negligible relative to the source, considering both temperatures gives a more appropriate description of net transfer.<ref name="VR-5.4" />

The same principle applies to hot smoke layers and flames. Their emission depends on temperature and radiative properties, while receiving objects have their own temperature and properties. A calculation based only on flame temperature cannot describe the entire exchange.<ref name="Tien-1-73" /><ref name="VR-5.4" />

Temperature distribution within a flame is not uniform. Different regions and soot concentrations can produce different emission, and small flames may lose a larger proportion through convection. Radiative source models therefore simplify a spatially varying physical system.<ref name="Simmons-1-145">Simmons (2002), p. 1-145.</ref><ref name="Tien-1-73" />

== Geometry and view between surfaces ==

[[View factor]] is a geometric fraction describing the radiation leaving one surface that is intercepted by another. It depends on size, separation and orientation. It does not include emissivity, temperature or absorption by an intervening gas, which must be treated separately.<ref name="Tien-1-75" />

Two surfaces facing each other directly have a different radiant relationship from surfaces at an angle or partly screened by obstacles. Moving a receiver can consequently change heat flux even when the source remains unchanged. The physical arrangement belongs in the radiation model.<ref name="Tien-1-75" />
[[File:fse-thermal-radiation-v2.svg|thumb|upright=1.5|alt=Three receivers with different distance, angle and shielding from one source.|View factor depends on geometry, not source temperature. Based on Tien, Lee, and Stretton (2002), p. 1-75.]]

A diffuse source emits with equal intensity per apparent surface area in each outward direction. For a uniform diffuse source, its direct contribution to receiver irradiation follows from a view factor. This assumes the gap neither absorbs, emits nor scatters radiation. The factor is defined from the receiver towards the source, describing the source's share of the receiver's radiative view. Reflections and other emitting surfaces are excluded from this direct contribution.<ref name="Tien-1-75" /><ref name="Tien-1-76">Tien, Lee, and Stretton (2002), p. 1-76.</ref>

<math display="block">G_{\mathrm{direct}}=F_{r\rightarrow s}E_s</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>G_{\mathrm{direct}}</math> || Direct source radiation incident on the receiver || W/m²
|-
| <math>F_{r\rightarrow s}</math> || View factor from receiver to source || Dimensionless
|}

The direction of the view factor matters. The fraction of a large source's radiation reaching a small target is generally different from the target's view of that source. The two factors are related through the areas of the surfaces. Using the wrong direction can therefore give the wrong flux per unit receiver area.<ref name="Tien-1-76" />

=== Emitted and received radiation in a source example ===

Van Rossum considers a square smoke layer measuring 49 m by 49 m in a 16 m high space. The layer is 2 m deep, at 400 °C, with an assumed emissivity of 0.9. A small upward-facing target is located centrally at a height of 1.75 m. These conditions provide a worked illustration of emission and geometric interception.<ref name="VR-5.4" />

The separation between the target and the layer underside is 12.25 m. Dividing the layer into four equal rectangles gives the source's tabulated view factor of 0.208 per rectangle, totalling 0.832. The source temperature is 673.15 K. Using those inputs gives the following emitted and direct incident fluxes, calculated without intermediate rounding.<ref name="VR-5.4" />

<math display="block">E_s=0.9\times5.67\times10^{-8}\times673.15^4\approx10.5\ \mathrm{kW/m^2}</math>

<math display="block">G_{\mathrm{direct}}=0.832E_s\approx8.72\ \mathrm{kW/m^2}</math>

The second result is radiation arriving from the layer, before accounting for receiver absorption and emission. It is not the net heat gained by the target. Van Rossum's separate net-exchange calculation also includes a receiver temperature and therefore gives a different quantity. Other emitting surfaces, reflections or absorption in the intervening gas would require additional terms.<ref name="VR-5.4" /><ref name="Tien-1-76" />

For an opaque receiver, net radiative heating is absorbed irradiation minus the receiver's own emission. The total incident irradiation includes every relevant source and reflection. Absorptivity describes the fraction absorbed from that incident radiation, while emissivity describes emission at the receiver temperature. They are not interchangeable without the appropriate spectral assumptions.<ref name="Tien-1-75" /><ref name="Tien-1-76" />

<math display="block">\dot q''_{\mathrm{rad,net}}=\alpha_rG_{\mathrm{total}}-\varepsilon_r\sigma T_r^4</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot q''_{\mathrm{rad,net}}</math> || Net radiative heat flux into the receiver || W/m²
|-
| <math>\alpha_r</math> || Effective receiver absorptivity for the incident radiation || Dimensionless
|-
| <math>G_{\mathrm{total}}</math> || Total radiation incident on the receiver || W/m²
|-
| <math>\varepsilon_r</math> || Receiver emissivity || Dimensionless
|-
| <math>T_r</math> || Absolute receiver temperature || K
|}

Geometry also affects how radiation contributes to compartment feedback. Hot upper gases and heated boundaries can expose many lower surfaces simultaneously. An object need not be above the flame or in the convective plume to receive this energy.<ref name="VR-4.3">Van Rossum (2027), §4.3.</ref><ref name="Tien-1-75" />

== Flame radiation and fire spread ==

[[Flame radiation]] arises from luminous gases, soot and the hot reaction region. Hot soot particles are responsible for much of the yellow or orange light in many diffusion flames, but low luminosity does not imply negligible thermal radiation. Source temperature, soot and gas properties all contribute.<ref name="VR-4.3" /><ref name="Tien-1-73" />

Radiative feedback supports evaporation and pyrolysis, allowing flames to sustain or extend fuel production. Along a vertical surface, heating above the burning region can accelerate upward spread. Radiation is therefore part of the coupling between the flame and its fuel.<ref name="VR-4.3" /><ref name="Beyler-Hirschler-1-110">Beyler and Hirschler (2002), p. 1-110.</ref>

[[Fire spread between buildings]] can occur when radiant energy from one fire heats combustible material across a separation. The receiving exposure depends on source size and properties, distance, orientation and screening. A gap alone does not quantify safety, and radiation need not require smoke or flames to cross it.<ref name="Tien-1-75" /><ref name="IFEG-2.6">Australian Building Codes Board et al. (2005), pp. 2.6-11–2.6-12.</ref>

Scale changes the radiative share. Tien and colleagues state that radiation is dominant in flames with characteristic lengths exceeding 0.2 m in their discussed context, while convection is more significant below that scale. Reduced-scale tests can therefore underrepresent full-scale radiant exposure if this difference is ignored.<ref name="Tien-1-73" />

Radiation can also expose people and structural elements without direct flame contact. Assessment needs the receiver's response to heat flux and exposure duration, rather than an assumption that distance alone removes the hazard.<ref name="Tien-1-73" /><ref name="VR-5.1">Van Rossum (2027), §5.1.</ref>

== Compartment fires and flashover ==

In an enclosure, flames, hot gases and heated boundaries exchange radiation with contents. Heat retained by the compartment raises surface and gas temperatures, increasing the potential for further radiative heating. This feedback can involve objects well beyond the first burning item.<ref name="VR-4.3" />

[[Flashover]] is associated with the transition to widespread involvement of combustible surfaces in a compartment. Radiation from the hot upper region and boundaries is one heat-transfer mechanism that can preheat those surfaces. The transition still depends on the complete fire scenario, including fuel and ventilation.<ref name="VR-4.7">Van Rossum (2027), §4.7.</ref><ref name="VR-4.3" />

A post-flashover environment can subject structural boundaries to sustained high temperatures. Radiative exchange then acts together with convection and conduction. Considering only internal solid conduction would omit the boundary exposure driving that temperature rise.<ref name="VR-5.2">Van Rossum (2027), §5.2.</ref><ref name="Tien-1-73" />

Radiation also leaves through openings and can heat external surfaces. Fuel volatiles burning outside an enclosure can create an additional radiant source outside the original compartment. The location of heat release and exposure therefore changes with ventilation and mixing.<ref name="Drysdale-1-95">Drysdale (2002), p. 1-95.</ref>

== Measurement and engineering use ==

Radiative heat-flux measurement addresses energy arriving at a surface per unit area and time. This differs from measuring total fire heat release rate. The same fire can produce different receiver readings at different distances and orientations.<ref name="Tien-1-75" /><ref name="VR-5.4" />

A radiation calculation should state the source model, temperature, emissivity, geometry and treatment of intervening gases. Receiver temperature and properties may also be required for net exchange. Omitting these inputs makes a result difficult to reproduce or apply elsewhere.<ref name="VR-5.4" />

Material data should be checked against surface condition. Polished, oxidised, coated and rough surfaces can have very different emissivities. Values also need an appropriate spectral and temperature basis rather than selection by material name alone.<ref name="VR-5.4" /><ref name="Tien-1-75" />

The result should be combined with other heat-transfer pathways on a consistent basis. A receiver can experience radiation and convection simultaneously while conducting energy inwards. Adding these contributions requires matching area, timing and reference conditions.<ref name="VR-5.3">Van Rossum (2027), §5.3.</ref><ref name="Rockett-Milke-1-29">Rockett and Milke (2002), p. 1-29.</ref>

== Limits and common misunderstandings ==

Thermal radiation is not simply visible light. Infrared energy can dominate the transfer, and a weakly luminous flame can still present a radiant hazard. Appearance cannot substitute for temperature, property and geometry data.<ref name="VR-5.4" /><ref name="Tien-1-73" />

A blackbody is not merely a surface coloured black. It is an idealised perfect absorber and emitter used as a reference. Real surfaces with the same visible colour can have different radiative properties.<ref name="VR-5.4" /><ref name="Tien-1-74" />

View factor does not describe how hot a source is or how strongly it emits. It describes only geometric interception. Multiplying unrelated source and receiver properties without preserving that distinction can conceal incorrect assumptions.<ref name="Tien-1-75" />

Radiative losses can cool flames and hot surfaces, contributing to extinction when heat production falls below losses. The safety effect depends on the direction, receiver and timing of the exchange.<ref name="Drysdale-1-97">Drysdale (2002), p. 1-97.</ref>

Radiative properties introduce uncertainty into engineering estimates. Real surfaces can have complex directional and wavelength-dependent behaviour, while measured property data may be incomplete. Tien and colleagues describe the grey diffuse approximation as a way to manage this complexity. Its suitability still depends on the surfaces and conditions represented.<ref name="Tien-1-76" />

Spectral detail presents a related choice. A grey-surface model may be adequate for an engineering estimate, but it hides wavelength-dependent absorption and emission. Where gases or selective surfaces are important, the simplified property basis should be checked against the source conditions.<ref name="VR-5.4" /><ref name="Tien-1-75" />

Receiver response adds a separate time dependence. A surface can absorb radiation while its temperature, emissivity and conductive losses change. Repeated or prolonged exposure therefore cannot always be represented by one unchanged receiver.<ref name="Rockett-Milke-1-29" /><ref name="VR-5.4" />

== See also ==

* [[Effects of heat on people]]
* [[Fire-resistant glazing]]
* [[Flame detector]]
* Glass breakage in fire
* [[Radiative fraction]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Beyler, C. L., & Hirschler, M. M. (2002). Thermal decomposition of polymers. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-110–1-131). National Fire Protection Association.
* Drysdale, D. D. (2002). Thermochemistry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-90–1-98). National Fire Protection Association.
* Rockett, J. A., & Milke, J. A. (2002). Conduction of heat in solids. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-27–1-43). National Fire Protection Association.
* Simmons, R. F. (2002). Premixed burning. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-144–1-154). National Fire Protection Association.
* Tien, C. L., Lee, K. Y., & Stretton, A. J. (2002). Radiation heat transfer. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-73–1-89). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Physics & Heat Transfer]]

Sprinkler head

2026-11-02T21:35:22Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''Sprinkler head''' is the outlet of an automatic sprinkler that normally closes a water-filled or pressurised pipe and opens in response to heat. It combines a heat-sensitive element, a seal and a water-distribution arrangement. In a conventional automatic system, the head acts as both a heat detector and a nozzle.<ref name="Fleming-4-85">Fleming (2002), p. 4-85.</ref><ref name="NUREG-10-3">Iqbal and Salley (2004), pp. 10-3–10-4.</ref>

Heating releases the element and opens the waterway. Water then strikes a deflector and forms a spray over the protected area. Activation time depends on the hot-gas flow, element temperature, response characteristics and installation, while suppression also depends on droplet motion and the fuel arrangement.<ref name="NUREG-10-11">Iqbal and Salley (2004), p. 10-11.</ref>

Different heads are made for different orientations, response speeds, coverage patterns and fire challenges. A head cannot be selected by temperature rating alone. Its listed application, position relative to the ceiling, obstructions, water pressure and compatibility with the system all influence performance.<ref name="NUREG-10-2">Iqbal and Salley (2004), pp. 10-2–10-3.</ref>

== Components and heat operation ==

The frame connects the head to the piping and supports the operating assembly. A cap or seal retains water until the heat-sensitive arrangement releases it. The deflector then shapes the discharged water into the spray pattern intended for that product.<ref name="NUREG-10-3" />

A fusible-link sprinkler uses a metallic alloy with a predetermined melting condition. Levers and struts can reduce the force carried by the solder, allowing a relatively small heat-sensitive mass. When the link releases, the assembly no longer holds the seal closed.<ref name="NUREG-10-3" />

A glass-bulb sprinkler uses liquid that expands as it warms. At the predetermined condition the bulb shatters and releases the seal. The liquid type and quantity establish the operating temperature, while the glass arrangement provides resistance to atmospheric corrosion in the cited description.<ref name="NUREG-10-4">Iqbal and Salley (2004), p. 10-4.</ref>
[[File:fse-sprinkler-head-v1.svg|thumb|upright=1.5|alt=A glass bulb releases a seal and water passes through the orifice to a deflector.|A sprinkler head combines heat detection and water distribution. Based on Iqbal and Salley (2004), pp. 10-3–10-4.]]

Other heat-sensitive forms include bimetallic discs, fusible-alloy pellets and chemical pellets. These arrangements perform the same basic function of retaining and then releasing a closure. Their specific response cannot be inferred without product evidence.<ref name="NUREG-10-4" />

Open sprinklers and nozzles used on deluge systems do not contain this individual heat-operated closure. A separate detection arrangement opens a valve and permits discharge through the open outlets. This distinction separates head activation from system-valve activation.<ref name="Fleming-4-73">Fleming (2002), p. 4-73.</ref>

== Heating and activation ==

The element exchanges heat with hot combustion products. NUREG-1805 identifies convection from heated gas, radiation from the fire and conduction through surrounding parts. Heat also conducts from the element into the sprinkler frame, so the response includes losses as well as gains.<ref name="NUREG-10-4" />

A [[Ceiling jet]] forms when the rising fire plume turns and spreads beneath a ceiling. It transports hot gas to heads located away from the plume centreline. Both its temperature and velocity influence convective heating, making location relative to the fire important.<ref name="NUREG-10-10">Iqbal and Salley (2004), p. 10-10.</ref>

The sensing element does not instantly adopt the surrounding gas temperature. Its thermal mass and heat-transfer conditions produce a lag. NUREG-1805 treats activation as the time needed for the difference between heat inflow and outflow to raise the element to its operating condition.<ref name="NUREG-10-4" />

The [[Response time index|Response time index (RTI)]] characterises sprinkler thermal response in the calculation methods described by NUREG-1805. A lower response index represents a faster-responding element under comparable conditions. It does not remove the effects of ceiling-jet velocity, activation temperature, starting temperature or distance from the fire.<ref name="NUREG-10-9">Iqbal and Salley (2004), pp. 10-9–10-10.</ref>
[[File:fse-sprinkler-head-v2.svg|thumb|upright=1.5|alt=A ceiling jet heats a sprinkler while frame conduction removes heat and the element warms gradually.|Sprinkler activation is a heat-transfer process with a time lag. Based on Iqbal and Salley (2004), pp. 10-9–10-12.]]

New Zealand's C/VM2, second edition, 2025, lists calculation inputs for extended-coverage, standard-response and quick-response categories. The table uses an activation temperature of 68 °C and different response parameters. Those values belong to that verification method and do not replace product-specific installation data.<ref name="CVM2-27">Ministry of Business, Innovation and Employment (2025), p. 27.</ref>

=== Simplified thermal-response equation ===

For constant gas temperature and velocity, a simplified model estimates the time needed to heat the element to its release temperature. A larger response time index increases this time, while higher gas velocity increases convective heating. NUREG-1805 gives the following expression for a uniform-temperature element heated by convection.<ref name="NUREG-10-9" />

<math display="block">t_{\mathrm{act}}=\frac{\mathrm{RTI}}{\sqrt{u}}\ln\left(\frac{T_g-T_0}{T_g-T_{\mathrm{act}}}\right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_{\mathrm{act}}</math> || Heating time to activation || s
|-
| <math>\mathrm{RTI}</math> || Response time index || (m s)<sup>1/2</sup>
|-
| <math>u</math> || Gas velocity at the element || m/s
|-
| <math>T_g,T_0,T_{\mathrm{act}}</math> || Gas, initial element and activation temperatures || °C
|}

The expression assumes gas hotter than the release temperature and an element initially below that temperature. It excludes heat lost to the frame and direct radiation from the flame. A growing fire requires changing gas conditions to be represented over time, rather than applying this constant-condition result as an exact prediction.<ref name="NUREG-10-9" /><ref name="NUREG-10-12">Iqbal and Salley (2004), p. 10-12.</ref>

== Position and spray distribution ==

Upright, pendant and sidewall are three basic installation configurations. Their names describe orientation and arrangement rather than different extinguishing chemicals. Each requires a compatible deflector and listing so that water reaches the intended area.<ref name="NUREG-10-3" />

Distance below the ceiling affects both heating and spray development. NUREG-1805 cautions against placing a head too far below the ceiling on a heat collector, because hot gas can pass above it. A suitable position supports activation and allows the intended spray pattern to develop.<ref name="NUREG-10-12" />

Conduction into the frame and airflow deflection around the installation can alter response. Fleming notes that some models omit these effects, along with orientation and radiation. Calculated activation is therefore most useful for comparison when its assumptions match the installation.<ref name="Fleming-4-85" />

The [[Sprinkler design density]] describes water applied over an area in a design method. It is not simply the flow leaving one head divided by an arbitrary room area. Pressure, spacing, spray distribution and the design area determine how the system delivers water to the fuel.<ref name="Fleming-4-73" />

Water must reach burning surfaces despite the rising plume. Droplets that are too small can evaporate or be carried upward before reaching the fuel. Larger droplets and sufficient velocity can improve penetration, particularly for rapidly growing, high-energy fires.<ref name="NUREG-10-11" />

=== Discharge and a worked pressure example ===

After opening, the flow through the sprinkler depends on pressure and the tested discharge coefficient, called its K-factor. Fleming relates flow to the square root of pressure. Rearranging the relation gives the pressure required for a specified flow, with consistent units for the coefficient.<ref name="Fleming-4-75">Fleming (2002), p. 4-75.</ref>

<math display="block">q=K\sqrt{p},\qquad p=\left(\frac{q}{K}\right)^2</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>q</math> || Water flow through the head || L/min
|-
| <math>p</math> || Pressure at the sprinkler || kPa
|-
| <math>K</math> || Discharge coefficient for these units || L/(min kPa<sup>1/2</sup>)
|}

Fleming's worked example requires approximately 95.4 L/min from one head. Converting its K-factor into the units used here gives approximately 8.07 L/(min kPa<sup>1/2</sup>). The calculated pressure is about 140 kPa, with rounding applied after the conversion and calculation.<ref name="Fleming-4-75" />

<math display="block">p=\left(\frac{95.4}{8.07}\right)^2\approx140\ \mathrm{kPa}</math>

This is the pressure at the head, not the complete pressure required at a pump. Pipe friction and elevation add further requirements upstream. The calculation also leaves the product's spray distribution, minimum listed flow and suitability for the fuel to separate evidence.<ref name="Fleming-4-75" />

== Response categories and special heads ==

Fast-response products reduce thermal lag, while other designs alter droplet size, distribution or protected area. These features address different parts of performance. Faster activation alone does not establish adequate spray penetration or sufficient water at the burning surface.<ref name="NUREG-10-3" /><ref name="NUREG-10-11" />

An ESFR sprinkler is an early-suppression, fast-response sprinkler intended for high-challenge fires. NUREG-1805 describes its combination of rapid response, large droplets and velocity. It is designed for suppression rather than only control, subject to strict design and installation conditions.<ref name="NUREG-10-3" />

Extended-coverage products can protect a larger listed area than conventional arrangements. This can reduce branch piping, but the wider coverage must remain within the product's tested conditions. Extended coverage is not permission to increase spacing independently of pressure and obstruction requirements.<ref name="NUREG-10-3" />

In-rack, dry, corrosion-resistant, concealed and recessed heads address particular installation needs. Their physical arrangement responds to storage, temperature, environment or appearance requirements. Each remains part of a specific tested assembly rather than a cosmetic variation of a standard head.<ref name="NUREG-10-3" />

== Interactions and delayed operation ==

[[Sprinkler skipping]] is delayed activation of a downstream head after water from an earlier head cools its sensing element. Droplets carried by the ceiling jet can reduce heating of the later link or bulb. This can change the sequence and number of heads that operate.<ref name="Cooper-3-239">Cooper (2002), p. 3-239.</ref>
[[File:fse-sprinkler-head-v3.svg|thumb|upright=1.5|alt=Large droplets penetrate a plume while an earlier spray cools a downstream element.|Sprays interact with the plume and nearby sprinkler elements. Based on Iqbal and Salley (2004), p. 10-11 and Cooper (2002), p. 3-239.]]

Skipping is not simply a defective head. It results from interaction among spray, hot-gas flow and the thermal element. Its timing can be uncertain because fire location, plume motion and droplet trajectories vary, even between nominally similar installations.<ref name="Cooper-3-239" />

Traditional sprinkler criteria account for such effects through empirical development and the number of installed heads. This does not make activation sequence irrelevant in special interactions with smoke vents. Cooper distinguishes the extensive sprinkler array from a smaller number of vents when discussing combined operation.<ref name="Cooper-3-239" />

Water discharge can also cool nearby smoke and alter the upper layer. Fleming's review describes convective heat transfer to droplets and, for small droplets, evaporation. These effects can assist fire control while also changing conditions for other heat-operated devices.<ref name="Fleming-4-86">Fleming (2002), p. 4-86.</ref>

== Installation and reliability ==

A head must remain physically and thermally connected to the conditions assumed in its design. Storage, ceiling services and other obstructions can intercept the spray or change hot-gas movement. Commodity height and arrangement can also change the fire challenge after installation.<ref name="NUREG-10-2" />

Paint, corrosion and mechanical damage can prevent normal operation or alter spray distribution. A painted bulb or link should not be treated as merely an appearance issue. NUREG-1805 includes corroded or painted heads among possible causes of sprinkler failure.<ref name="NUREG-10-2" />

An operational head still requires a functioning [[Sprinkler system]]. Closed valves, inadequate supplies, obstructed piping and pump failures can prevent useful discharge after the seal opens. Component reliability therefore cannot be separated from the supporting network.<ref name="NUREG-10-2" />

Different system arrangements create different discharge delays. A wet system has water at the head, whereas a dry system must exhaust gas and fill the piping. Preaction and deluge arrangements also depend on separate detection and valve functions.<ref name="Fleming-4-73" />

== Calculation and application limits ==

Activation correlations in NUREG-1805 assume an unobstructed, smooth, flat, horizontal and unconfined ceiling. The fire is away from walls and corners, and the cited steady-fire method does not include a developing smoke layer below the ceiling jet. Actual rooms can depart from all these conditions.<ref name="NUREG-10-12" />

The simplified calculation considers convective heating and treats the element as having a uniform internal temperature. It does not explicitly include direct flame radiation. Results should not be presented as exact activation predictions where those omitted processes matter.<ref name="NUREG-10-12" />

Suppression models have additional fuel limitations. Fleming describes a wood-crib-based method that does not represent every fuel's resistance to suppression or individual sprinkler distributions. A heat-response calculation consequently cannot be used as a complete extinction calculation.<ref name="Fleming-4-87">Fleming (2002), pp. 4-86–4-87.</ref>

Product listings and full-scale test evidence provide the application context for special heads. Pressure, spacing, ceiling, storage and obstruction details belong to that evidence. Substituting a head with the same nominal temperature but different spray or response characteristics can change the design.<ref name="NUREG-10-3" /><ref name="Fleming-4-73" />

Temperature rating and response speed answer different questions. The rating concerns the condition at which the operating element releases, while response concerns how quickly heat transfer brings it to that condition. Two heads with the same nominal temperature can therefore activate at different times in the same hot-gas flow.<ref name="NUREG-10-9" /><ref name="Fleming-4-85" />

C/VM2's 2025 table illustrates this distinction with standard-response and quick-response model inputs. It assigns different response indices and conduction factors to those categories while retaining the same nominal activation temperature. These parameters must be used with the method's prescribed geometry and radial distances.<ref name="CVM2-27" />

Fleming compares response time indices of 221 and 55 (m s)<sup>1/2</sup> for standard- and quick-response arrangements. The modelled activation times are 200 and 172 s under the example's particular fire and mounting conditions. Different element characteristics and positions are part of that comparison, so the times are not generic product ratings.<ref name="Fleming-4-85" />

A head's spray cannot be inferred solely from its orifice. Fleming relates droplet size to orifice and pressure in geometrically similar sprinklers, but droplet trajectories also depend on gas motion. The spray reaching fuel reflects the interaction of water momentum and the rising plume.<ref name="Fleming-4-86" />

Droplet surface area affects heat absorption from hot gases. Smaller droplets offer more total surface for a given water flow, while larger droplets can better resist plume deflection. Head design consequently balances gas cooling and delivery to the fuel rather than maximising one isolated property.<ref name="Fleming-4-86" /><ref name="NUREG-10-11" />

The protected area also influences the activation sequence. A remote head experiences different ceiling-jet conditions from one above the fire, and earlier sprays can cool it. This makes the number and location of operating heads a coupled fire-and-water problem.<ref name="Cooper-3-239" />

Heat collectors installed far below a ceiling illustrate an installation error rather than a faster-response accessory. NUREG-1805 warns that rising heat can pass above such arrangements. Placement must maintain contact with the hot ceiling flow without sacrificing the intended spray development.<ref name="NUREG-10-12" />

Sidewall and other directional patterns require attention to the room surfaces that shape distribution. A deflector designed for one orientation cannot simply be turned to another orientation while retaining its tested pattern. Product orientation and room geometry therefore remain linked.<ref name="NUREG-10-3" />

Dry and concealed constructions introduce additional physical parts around the basic release mechanism. Their response and spray must be assessed as the complete listed assembly. The visible cover or barrel should not be treated as independent of activation and water distribution.<ref name="NUREG-10-3" />

A sprinkler head differs from a standalone heat detector because it also controls water distribution. Detection criteria alone cannot describe droplet size, velocity or protected area. Conversely, an adequate spray pattern does not demonstrate timely heat response in the intended ceiling jet.<ref name="Fleming-4-85" />

The activation model and the suppression model should consequently be evaluated as separate stages. The first estimates when the closure releases under stated thermal conditions. The second addresses what the resulting water spray does to a particular fuel and enclosure.<ref name="NUREG-10-12" /><ref name="Fleming-4-87" />

== See also ==

* [[Dry pipe sprinkler system]]
* [[Wet pipe sprinkler system]]
* [[Critical water application rate]]

== Notes ==

<references />

== References ==

* Cooper, L. Y. (2002). Smoke and heat venting. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-219–3-242). National Fire Protection Association.
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.). New Zealand Government.

[[Category:Fire Suppression]]

Standard fire curve

2026-11-02T21:35:19Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

The '''standard fire curve''' is an agreed relation between time and gas temperature that a furnace follows when building elements are tested for fire resistance. The best-known versions are the curve of the international standard ISO 834 and the curve of the American standard ASTM E119.<ref name="Lie-4-206">Lie (2002), p. 4-206.</ref><ref name="Ozone2-431">Cadorin et al. (2003), p. 431.</ref> ''Introduction to Fire Safety Engineering'' calls it the standard ISO cellulosic curve and notes that construction elements are tested for fire resistance against it.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> The temperature rises quickly in the first minutes, passes about 840 °C after 30 minutes and keeps rising slowly for as long as the test lasts.<ref name="Lie-4-206" /><ref name="NUREG-17-2">Iqbal and Salley (2004), p. 17-2.</ref>

The curve was chosen to represent a severe, fully developed room fire, but it is not a model of any real fire.<ref name="Milke-4-210">Milke (2002a), p. 4-210.</ref> Its main value is that every test follows the same heating, so that results of different products can be compared.<ref name="VR-8.2">Van Rossum (2027), §8.2.</ref> Fire resistance ratings in minutes, such as 60 or 120 minutes, therefore refer to exposure to such a standard curve.<ref name="ABCB-C6-172">Australian Building Codes Board (2020a), Data Sheet C6, p. 172.</ref> Engineering methods such as [[time equivalence]] translate the severity of a real fire into an equivalent duration of the standard curve.<ref name="IFEG-2.6-3">National Research Council of Canada et al. (2005), p. 2.6-3.</ref>

== Purpose and origin ==
The temperature course of a real fire cannot be known when a building is designed. It depends on parameters such as the amount, surface area and arrangement of the fuel, which change with time and vary from room to room.<ref name="Lie-4-201">Lie (2002), p. 4-201.</ref> Surveys show that deviations of 50 % or more from the most probable fire load are common. This alone can shift fire temperatures by hundreds of degrees and fire durations by 50 % or more.<ref name="Lie-4-202">Lie (2002), p. 4-202.</ref> It is possible, however, to give a temperature–time curve that will probably not be exceeded during the life of the building. Such curves are a useful basis for fire-resistive design.<ref name="Lie-4-201" />

Lie divides a fire into a growth period, a fully developed period and a decay period. During growth the temperatures are relatively low, and their influence on the fire resistance of structural members is negligible. The real risk to structural members and fire separations begins in the fully developed stage, the [[post-flashover fire]], when temperatures of about 1,000 °C or higher can be reached.<ref name="Lie-4-201" /> Because ventilation-controlled fires are usually the more severe and quite likely to occur, fire resistance requirements are commonly based on the assumption that fire severity is controlled by ventilation.<ref name="Lie-4-202" />

Lie also shows that the exact shape of a design curve matters less than its total heating effect. In his example, a theoretical fire curve for a building with a chance of being exceeded once in 50 years is replaced by a simpler curve. That curve assumes a constant burning rate until the fuel is consumed, followed by a linear fall to room temperature.<ref name="Lie-4-203">Lie (2002), p. 4-203.</ref> Although the two shapes differ, their heating effect is about the same, so they provide virtually the same fire safety. The simpler curve has the advantage of being easier to define.<ref name="Lie-4-203" />

In a [[fire resistance test]], gas burners heat the furnace so that its temperature follows the standard curve.<ref name="Milke-4-210" /> Under ASTM E119, the furnace temperature is taken as the average of at least eight thermocouples, read at intervals of no more than 1 minute.<ref name="NUREG-17-2" /> Milke notes that the ASTM E119 curve is intended to relate to a severe exposure from a room fire. Its use for structural members outside a building, exposed to fires outside it, is therefore questionable.<ref name="Milke-4-210" /> Versions of the American test method are also published as NFPA 251 and UL 263.<ref name="Milke-4-210" />

[[File:fse-standard-fire-curve-v2.svg|thumb|upright=1.5|alt=Section through a wall furnace: gas burners heat the chamber, thermocouples measure the gas temperature, and a wall specimen closes one side.|Principle of a furnace test: burners are controlled so that the average furnace temperature follows the standard curve. Based on Milke (2002a), p. 4-210, and Iqbal and Salley (2004), p. 17-2.]]

== The ISO 834 relation ==
The curve of ISO 834 has a simple analytical form. The rise of the furnace temperature above its starting value grows with the logarithm of time. The factor 8 in the logarithm makes the temperature rise steeply in the first minutes, and the curve then flattens without ever reaching a maximum.<ref name="Lie-4-206" />

<math display="block">T - T_0 = 345\,\log_{10}(8t + 1)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>T</math> || fire (furnace gas) temperature || °C
|-
| <math>T_0</math> || initial temperature || °C
|-
| <math>t</math> || time from the start of the test || min
|}

The relation applies to the furnace gas temperature in the standard test. It does not describe the temperature of the tested element, and it does not include a decay phase.<ref name="Lie-4-206" /> With an initial temperature of 20 °C, the curve gives about 576 °C after 5 minutes and 678 °C after 10 minutes. After 30, 60 and 120 minutes the temperature is about 842 °C, 945 °C and 1,049 °C.<ref name="Calc-SFC">Calculated from Lie (2002), p. 4-206, Equation 9.</ref> After 4 hours, the longest period usually required, it reaches about 1,153 °C.<ref name="Calc-SFC" /><ref name="MBIE13-75">Ministry of Business, Innovation and Employment (2013), p. 75.</ref>

As a worked example, a wall is required to achieve a rating of 60 minutes. With an initial furnace temperature of 20 °C, the term 8t + 1 equals 481 at 60 minutes. Its logarithm is 2.682, so the temperature rise is 345 × 2.682 = 925 K. The furnace must therefore be at about 945 °C at the end of the required period.<ref name="Calc-SFC" /> In the first 3 minutes alone the temperature already climbs to about 500 °C.<ref name="Calc-SFC" />

The American ASTM E119 curve is defined by a table of points rather than one formula. NUREG-1805 lists 704 °C at 10 minutes, 843 °C at 30 minutes, 927 °C at 1 hour, 1,010 °C at 2 hours and 1,093 °C at 4 hours. The curve ends at 1,260 °C after 8 hours.<ref name="NUREG-17-2" /> Compared with the ISO formula, the American curve is about 26 K hotter at 10 minutes and nearly equal at 30 minutes. At 1 hour it is about 18 K cooler and at 4 hours about 60 K cooler.<ref name="Calc-SFC" />

[[File:fse-standard-fire-curve-v1.svg|thumb|upright=1.5|alt=Line chart of furnace temperature against time: the ISO 834 curve rises steeply to about 680 °C at 10 minutes and slowly to about 1150 °C at 4 hours; ASTM E119 points lie close to it.|The ISO 834 standard fire curve (T0 = 20 °C) with the ASTM E119 points. Based on Lie (2002), p. 4-206, and Iqbal and Salley (2004), p. 17-2.]]

Lie concludes that there are no significant differences between the standard curves used in various countries.<ref name="Lie-4-206" /> In his comparison, Australia, Great Britain and New Zealand share one curve, and Belgium, France, the Netherlands, Sweden and several other European countries share another. Canada and the United States share one curve, and the Japanese curve levels off at a lower temperature than the others in long tests.<ref name="Lie-4-207">Lie (2002), p. 4-207.</ref> For the North American curve, Lie also gives analytical approximations. One of them, a sum of three exponential terms, deviates from the tabulated values by at most −26 °C at 45 minutes, +48 °C at 3.5 hours and −78 °C at 8 hours.<ref name="Lie-4-206" />

== Other nominal curves ==
The standard curve is one of several agreed temperature–time curves. ''Introduction to Fire Safety Engineering'' names the external fire exposure curve, used to test facade elements against a fire in the open air. It also names two less frequently used curves that are more intense than these two. These are the Rijkswaterstaat curve for tunnels and the hydrocarbon fire curve, which simulates an oil or gas fire.<ref name="VR-8.6" /> The book stresses that such curves are only agreed temperature courses and in principle do not correspond to the heat development in a real fire.<ref name="VR-8.6" />

A temperature–time curve can also be used inside calculation models. The Eurocodes offer a choice between a temperature–time curve and a natural fire, whose temperature course follows from the characteristics of the fire and the room.<ref name="VR-8.6" /> A [[parametric fire curve]] is one form of such a design fire. In a worked example in the Australian Fire Safety Verification Method Data Sheets, a design fire produced a parametric curve that was closely aligned with the hydrocarbon heating regime.<ref name="ABCB-C8-233">Australian Building Codes Board (2020a), Data Sheet C8, p. 233.</ref>

== Use in design and regulation ==
Many national fire safety codes express the required performance of fire barriers as a fire resistance time or rating.<ref name="ABCB-C6-172" /> In Australia, the fire resistance level is defined as the grading period in minutes obtained by subjecting a specimen to the standard time–temperature curve of AS 1530.4.<ref name="ABCB-AppB-290">Australian Building Codes Board (2020a), Appendix B, p. 290.</ref> In the United States, ratings of floors, roofs, beams, walls and columns are based on ASTM E119.<ref name="NUREG-17-1">Iqbal and Salley (2004), p. 17-1.</ref> Such a rating describes the [[fire resistance]] of an element under this one heating regime, and its behaviour under other heating is generally not determined directly.<ref name="ABCB-C6-173">Australian Building Codes Board (2020a), Data Sheet C6, p. 173.</ref>

Required ratings rarely exceed 4 hours. NUREG-1805 notes that no jurisdiction demands fire endurance periods of more than 4 hours.<ref name="NUREG-3-14">Iqbal and Salley (2004), p. 3-14.</ref> The 2013 commentary to the New Zealand verification method C/VM2 calls ratings above 4 hours in the NZS/ISO 834 test unusual and very expensive.<ref name="MBIE13-75" /> C/VM2 (second edition, 2025) offers several ways to set the rating of an element that must resist a fully developed fire, with a minimum of 20 minutes. One option is an equivalent time of exposure in a standard fire resistance test assuming full burnout.<ref name="CVM2-18">Ministry of Business, Innovation and Employment (2025b), p. 18.</ref>

Time equivalence links real fires to the standard curve. The International Fire Engineering Guidelines (2005) define the equivalent structural fire severity as the time of exposure to the standard test that gives the same thermal impact as a complete burnout of the compartment.<ref name="IFEG-2.6-3" /> The New Zealand formula finds the time on the ISO 834 curve that produces the same maximum temperature in a protected steel member as a post-flashover fire in the space.<ref name="MBIE13-79">Ministry of Business, Innovation and Employment (2013), p. 79.</ref> In the Australian worked example, an element reached 454 °C after 63 minutes in the standard test but after 45 minutes in the design fire. Its failure time in that scenario was therefore taken as 45 minutes.<ref name="ABCB-C8-233" />

For separating elements, a different equivalence has been proposed. The International Fire Engineering Guidelines (2005) describe a method by Nyman, which assumes that a barrier fails when it receives the same cumulative radiation dose as at failure in the standard test. The method suits failure by heat conduction through the barrier.<ref name="IFEG-2.6-11">National Research Council of Canada et al. (2005), p. 2.6-11.</ref>

The standard curve also underlies some design values that are not fire resistance ratings. For fire spread to neighbouring buildings, C/VM2 (second edition, 2025) assumes that unprotected areas of an unsprinklered building emit 83, 103 or 144 kW/m<sup>2</sup>, depending on the fire load energy density.<ref name="CVM2-44">Ministry of Business, Innovation and Employment (2025b), p. 44.</ref> The 2013 commentary explains that this exposure corresponds to radiation from fire gases at the temperatures reached in a standard fire resistance test after 30, 45 or 90 minutes. The emissivity was raised from 0.95 to 1.0 while keeping the same incident radiation.<ref name="MBIE13-133">Ministry of Business, Innovation and Employment (2013), p. 133.</ref>

[[File:fse-standard-fire-curve-v4.svg|thumb|upright=1.5|alt=ISO curve with points at 30, 45 and 90 minutes labelled with the matching emitted heat fluxes of 83, 103 and 144 kW/m².|Emitted heat fluxes of C/VM2 for unsprinklered firecells and the points on the standard curve they correspond to. Based on Ministry of Business, Innovation and Employment (2013), p. 133, and (2025b), p. 44.]]

The ISO curve indeed gives 842 °C, 902 °C and 1,006 °C at these times. Black-body radiation at these temperatures, multiplied by 0.95, gives 83, 103 and 144 kW/m<sup>2</sup>.<ref name="Calc-SFC" /><ref name="VR-5.4">Van Rossum (2027), §5.4.</ref> The commentary adds that actual gas temperatures in a fire may differ from those in the standard test.<ref name="MBIE13-133" />

== Comparison with real fires ==
Real fires differ from the curve in several ways. A typical post-flashover room fire reaches a peak temperature of 900 to 1,000 °C, with a maximum of around 1,200 °C. The ASTM E119 curve, by contrast, keeps rising and reaches 1,260 °C after 8 hours.<ref name="NUREG-3-14" /> A real fire also decays when the fuel is consumed, which the standard curve does not.<ref name="Lie-4-201" /><ref name="Lie-4-206" /> ''Introduction to Fire Safety Engineering'' explains that the temperature of a room fire depends on the size of the room, its openings, its insulation and the heat release rate. The temperature is a result of a fire scenario and not a starting point for one.<ref name="VR-8.6" />

[[File:fse-standard-fire-curve-v3.svg|thumb|upright=1.5|alt=Chart with a continuously rising standard curve and an idealised real fire that grows, stays near 900 to 1000 °C and then decays.|The standard curve keeps rising, while a real fire grows, burns fully developed and then decays. Based on Lie (2002), p. 4-201, and Iqbal and Salley (2004), p. 3-14.]]

For this reason the International Fire Engineering Guidelines (2005) warn that ratings from ISO 834, ASTM E119 or AS 1530.4 may not represent the actual fire conditions in a building. They should be used in fire engineering only together with a fire severity analysis.<ref name="IFEG-2.6-2">National Research Council of Canada et al. (2005), p. 2.6-2.</ref> The authors of the OZone design tool observed that structural specialists long represented the fire by a single nominal curve, either ISO 834 or ASTM E119. Fire modellers, in turn, thought of the structure only in terms of a critical temperature.<ref name="Ozone2-431" />

The investigation of the World Trade Center collapses drew similar conclusions. In four standard tests of the floor system, it took about 90 minutes of furnace heating before the steel trusses exceeded 600 °C.<ref name="NCSTAR1-149">National Institute of Standards and Technology (2005), p. 149.</ref> The investigators noted that the standard test does not capture important thermally induced interactions between structural subsystems, elements and connections, because these are tested separately.<ref name="NCSTAR1A-67">National Institute of Standards and Technology (2008), p. 67.</ref> They concluded that a performance objective of burnout without collapse will require standard fire exposures that differ from those currently used.<ref name="NCSTAR1-212">National Institute of Standards and Technology (2005), p. 212.</ref>

== Common misconceptions ==
A rating of 60 minutes does not mean that an element will survive 60 minutes in a real fire. The test is comparative, and furnace size limits the dimensions of specimens, so it cannot be used to assess actual performance.<ref name="Milke-4-210" /> ''Introduction to Fire Safety Engineering'' adds that the curve suits the testing of a construction from a standardised starting point but is not suitable for simulating a fire in a room.<ref name="VR-8.6" />

Another misconception is that the standard curve is the worst case. More intense nominal curves exist for tunnels and for hydrocarbon fires.<ref name="VR-8.6" /> A short, hot design fire can also bring an element to its critical temperature sooner than the standard test does, as in the Australian example of 45 instead of 63 minutes.<ref name="ABCB-C8-233" />

Readers of the third edition of the SFPE Handbook should also note a labelling problem. The table captioned as the ISO 834 relation lists 538 °C at 5 minutes, 704 °C at 10 minutes and 927 °C at 1 hour.<ref name="Lie-4-206" /> These are the ASTM E119 values given in NUREG-1805.<ref name="NUREG-17-2" /> The table captioned as the North American relation lists temperature rises that match the ISO formula, for example 925 K at 60 minutes.<ref name="Lie-4-207" /><ref name="Calc-SFC" /> The two captions therefore appear to be interchanged.

== See also ==
* [[Structural fire engineering]]
* [[Charring rate]]
* RWS fire curve
* [[Eurocodes]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Cadorin, J.-F., Pintea, D., Dotreppe, J.-C., & Franssen, J.-M. (2003). A tool to design steel elements submitted to compartment fires – OZone V2. Part 2: Methodology and application. ''Fire Safety Journal'', ''38'', 429–451. https://doi.org/10.1016/S0379-7112(03)00015-8
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Lie, T. T. (2002). Fire temperature-time relations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-201–4-208). National Fire Protection Association; Society of Fire Protection Engineers.
* Milke, J. A. (2002a). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Institute of Standards and Technology. (2005). ''Final report on the collapse of the World Trade Center towers'' (NIST NCSTAR 1).
* National Institute of Standards and Technology. (2008). ''Final report on the collapse of World Trade Center Building 7'' (NIST NCSTAR 1A).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Structural Fire Engineering]]

Sprinkler hazard classification

2026-11-02T21:35:16Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Sprinkler hazard classification''' is the assignment of a protected occupancy or stored commodity to a category used to select sprinkler protection criteria. In an area/density design, the occupancy category determines the required water application and assumed operating area. Fleming identifies classification as a critical judgement made before hydraulic calculations establish whether the system can supply those requirements.<ref name="F-73-74">Fleming (2002), pp. 4-73–4-74.</ref>

Classification concerns the fire challenge presented by the contents and their use or arrangement. It is not established solely by a building's name, the installed pipe size or the amount of water already available. The NIST account of the historical NFPA method considers the quantity and combustibility of contents and the expected rate of heat release. Stored commodities require additional attention to packaging and configuration.<ref name="H-16-17">Hopkins et al. (2005), pp. 16–17.</ref><ref name="T-153-154">Tewarson (2002), pp. 3-153–3-154.</ref>

The category has meaning within a particular protection method and source edition. The categories discussed below illustrate the historical approaches described in the supplied handbook and NIST investigation. They do not establish a current classification schedule or a direct conversion between different national sprinkler standards. The selected criteria and the evidence describing the protected hazard must remain consistent.<ref name="F-73-74" /><ref name="H-18">Hopkins et al. (2005), p. 18.</ref>

== Purpose within the design process ==

Classification translates an understanding of the protected hazard into a suitable protection basis. In the conventional occupancy approach, that basis includes [[Sprinkler design density|sprinkler design density]] and a design area. These quantities are then used to determine individual sprinkler flows and the required supply. The sequence matters because hydraulic calculation checks delivery against criteria that have already been selected.<ref name="F-73-75">Fleming (2002), pp. 4-73–4-75.</ref>
[[File:fse-sprinkler-hazard-classification-v1.svg|thumb|upright=1.5|alt=A flow diagram begins with the protected contents and ends with verification of water delivery.|Classification establishes the protection basis before hydraulic delivery is checked. Based on Fleming (2002), pp. 4-73–4-75.]]

A calculation cannot independently establish that the chosen criteria suit the fuel and activity. Fleming warns that underestimating the hazard can allow a fire to overpower the sprinkler protection. Adequate pressure at a sprinkler would then demonstrate compliance with an unsuitable requirement. Classification and hydraulic adequacy are therefore separate questions that must both be resolved.<ref name="F-73">Fleming (2002), p. 4-73.</ref>

The [[Sprinkler system|sprinkler system]] also has characteristics that are not hazard categories. Wet pipe, dry pipe and preaction describe how the piping and water admission operate. They do not, by themselves, state how combustible the protected contents are. System type can influence additional design provisions, but it does not replace the assessment of the occupancy or commodity.<ref name="H-14-17">Hopkins et al. (2005), pp. 14–17.</ref>

Similarly, a sprinkler's thermal sensitivity or discharge coefficient describes aspects of the device. Classification describes the challenge for which protection is being selected. A fast operating sprinkler or a large discharge opening cannot establish a category for the surrounding contents. The device and system must instead be evaluated within the protection method appropriate to that challenge.<ref name="F-73-75" /><ref name="N-10-3">Iqbal and Salley (2004), p. 10-3.</ref>

The empirical basis of the criteria is important. Fleming describes protection requirements developed from both fire testing and accumulated experience. Classification connects an actual application with the conditions represented by that evidence. A category label used without its associated limits can lose the relationship between the protected hazard and the demonstrated performance.<ref name="F-73" />

== Occupancy categories in the historical NFPA approach ==

The NIST investigation describes Light Hazard, Ordinary Hazard Groups 1 and 2, and Extra Hazard Groups 1 and 2. These names belong to the occupancy hazard approach used for the systems examined in that report. They should be read as categories within that documented method. The report also notes changes to the groups and design curves between editions.<ref name="H-16-18">Hopkins et al. (2005), pp. 16–18.</ref>

Light Hazard describes spaces with relatively low quantities and combustibility of contents, where fires with relatively low heat release are expected. The report identifies ordinary office spaces and restaurant seating areas among its examples. The definition concerns the contents and expected fire behaviour, rather than an assertion that ignition is impossible or that no consequential fire can occur.<ref name="H-16">Hopkins et al. (2005), p. 16.</ref>

Ordinary Hazard covers a greater challenge and is subdivided into two groups in the account. The report gives restaurant service areas and laundries as examples associated with Group 1, and library stack areas and repair garages with Group 2. These examples illustrate why the activity within a space matters. They are not a replacement for examining the actual contents and applicable classification rules.<ref name="H-16" />

Extra Hazard addresses conditions capable of rapidly developing fires with high heat release. The report distinguishes its two groups partly through the presence of flammable or combustible liquids and shielding of combustibles. Group 1 involves little or no such liquid; Group 2 includes more substantial liquid involvement or shielding. These distinctions concern the challenge presented to water application as well as the potential intensity of burning.<ref name="H-17">Hopkins et al. (2005), p. 17.</ref>

The groups are not simply points on a universal numerical scale of danger. A category selects a package of protection assumptions and criteria. Two spaces with similar total combustible energy can differ in fire growth or accessibility to water. Conversely, an example occupancy name does not establish that every room bearing that name has identical contents or needs identical protection.<ref name="F-73" /><ref name="H-16-17" />

== Contents, activity and the protected area ==

The [[Fire load|fire load]] is relevant because the amount of combustible material contributes to the hazard. Classification also considers combustibility and expected heat release, which are not described by combustible quantity alone. The NIST definitions expressly combine these characteristics. An inventory of fuel energy is therefore useful evidence, but it is not by itself the complete classification decision.<ref name="H-16-17" />

The category can apply to a building portion rather than the entire building. The historical distinction between restaurant seating and service areas provides a useful example. These activities can coexist within one establishment while presenting different contents and operations. Describing the premises only as a restaurant would omit information needed to understand that distinction.<ref name="H-16" />

The same principle appears in the NIST investigation of office towers. Most areas were treated as Light Hazard, while specified areas used Ordinary Hazard criteria. The report documented the systems and associated design information for the particular locations examined. Its analysis therefore preserved local differences instead of assuming that every sprinkler in the same building served an identical hazard.<ref name="H-16" /><ref name="H-91-93">Hopkins et al. (2005), pp. 91–93.</ref>

A design record consequently needs to identify what the selected category applies to. Relevant evidence includes the contents, activities and their location within the protected area. Without that description, later changes cannot be compared with the assumptions supporting the original selection. A category written on a drawing is useful only when its connection to the protected conditions can be understood.<ref name="F-73-74" /><ref name="H-91-93" />

The classification also remains distinct from the assumed area of sprinkler operation. The latter is a hydraulic design quantity selected through the protection method. It does not necessarily equal the whole area occupied by that category or the eventual burned area. Keeping these areas separate avoids turning a classification boundary into an unsupported prediction of fire extent.<ref name="F-74">Fleming (2002), p. 4-74.</ref>

== Commodity classification for storage ==

A [[Warehouse fire|warehouse fire]] introduces a further distinction between occupancy classification and commodity classification. Tewarson describes a stored commodity as a configuration of goods, packaging and supporting materials. Its protection challenge depends on how that configuration burns in the presence of water. The product inside a carton is therefore only part of the information required.<ref name="T-153-154" />

Noncombustible goods can still form part of a combustible commodity arrangement. The handbook's historical examples include noncombustible products on wooden pallets or inside ordinary corrugated packaging. More substantial combustible packaging can increase the classification challenge even when the enclosed product remains noncombustible. Treating the product's material designation as the whole storage classification would miss that contribution.<ref name="T-153">Tewarson (2002), p. 3-153.</ref>
[[File:fse-sprinkler-hazard-classification-v2.svg|thumb|upright=1.5|alt=Three storage arrangements show combustible packaging and pallets added around a noncombustible product.|Packaging and pallets contribute to the storage protection challenge. Based on Tewarson (2002), p. 3-153.]]

The historical commodity examples progress through configurations involving cellulosic products and increasing involvement of synthetic materials. The handbook compares simulated commodities containing paper products with those containing polystyrene. The latter produce a greater heat-release challenge in the tests discussed and require greater water application for suppression. Those findings illustrate the physical basis for distinguishing commodities, without establishing a universal rule for every plastic product.<ref name="T-153-154" />

Arrangement is also part of the evidence. Tewarson describes test arrays assembled from pallet loads and cartons with specified dimensions and separation. Their three-dimensional configuration influences heat feedback and water access. Results from those arrays cannot be treated as measurements of an isolated material independent of geometry. A storage description therefore needs more detail than a list of product names.<ref name="T-153-154" />

The commodity classes described in that discussion are not synonyms for Light, Ordinary or Extra Hazard occupancy groups. They arise within a storage protection framework with their own examples and evidence. The supplied texts do not establish a simple one-to-one conversion between the two sets of names. A protection assessment must use the classification system applicable to the method being employed.<ref name="T-153-154" /><ref name="F-73" />

== Suppression method and special applications ==

The intended protection outcome also matters when interpreting a classification. The NIST report distinguishes fire control from suppression-oriented performance. Control aims to limit growth and spread, and final extinguishment may require fire service action. The existence of an occupancy category does not imply that every fire under that protection will be completely extinguished by the first operating sprinkler.<ref name="H-15-16">Hopkins et al. (2005), pp. 15–16.</ref>

An ESFR sprinkler is a particular suppression technology, rather than another occupancy hazard class. NUREG-1805 describes fast response, large droplets and discharge velocity as features intended for demanding fires. It also stresses strict design and installation requirements. The technology's name cannot replace information about the storage or the conditions under which its protection is supported.<ref name="N-10-3" />

Special sprinkler criteria can specify flows and pressures that differ from a conventional area/density approach. Fleming explains that such sprinklers are approved for particular protection goals and are not generally interchangeable. A change of sprinkler type must therefore retain the connection between the hazard, the relevant approval and the hydraulic conditions. A similar nominal flow is not sufficient evidence of equivalent application.<ref name="F-73" /><ref name="F-75">Fleming (2002), p. 4-75.</ref>

Water access provides another reason to preserve configuration details. Tewarson distinguishes simple burning surfaces from heterogeneous three-dimensional commodities and discusses the effects of water application on their burning. Shielding can affect whether water reaches the surfaces that need cooling. A classification decision that ignores the physical arrangement can omit a key part of the challenge faced by the selected protection.<ref name="T-151-154">Tewarson (2002), pp. 3-151–3-154.</ref>

== Interpreting existing design records ==

Older design records may use the same broad occupancy names within a different design procedure. The NIST report describes the pipe schedule method, which selected pipe sizes from tables according to the occupancy hazard and number of sprinklers served. That method differs from calculating individual flows and pressure losses for a selected density and operating area. The category name alone does not identify which procedure produced an existing installation.<ref name="H-17" />

The report also explains that historical Ordinary Hazard groups and area/density curves changed between editions. A classification written on an old drawing should therefore be read with the edition and design method used at the time. Otherwise, an apparent match of labels can conceal different underlying requirements. Historical documentation is evidence of a design basis, not an automatic statement of its relationship to a later method.<ref name="H-16-18" />

A review of an existing system needs both that documentary basis and evidence of its actual configuration. The NIST investigation used drawings to identify sprinkler spacing, piping and the criteria assigned to particular floors. Where exact layouts were unavailable, the report identified representative arrangements used for analysis. Maintaining that distinction prevents assumed configuration details from being reported as verified features of the original installation.<ref name="H-91-93" />

== Worked comparison of historical design inputs ==

The NIST report illustrates a Light Hazard calculation using 0.10 US gal/(min·ft²) over 1,500 ft². It separately documents a particular WTC 2 drawing specifying 0.16 US gal/(min·ft²) over the same area. That drawing concerned an Ordinary Hazard Group 1 installation. These two historical inputs provide an arithmetic comparison of downstream hydraulic consequences.<ref name="H-87">Hopkins et al. (2005), p. 87.</ref><ref name="H-91">Hopkins et al. (2005), p. 91.</ref>

<div class="fse-equation">Q<sub>nom</sub> = dA<sub>d</sub></div>

{| class="wikitable"
! Symbol !! Meaning !! Units for this comparison
|-
| Q<sub>nom</sub> || Nominal density-area product || US gal/min
|-
| d || Density specified in the historical example || US gal/(min·ft²)
|-
| A<sub>d</sub> || Associated design area || ft²
|}

The products are 150 US gal/min and 240 US gal/min respectively, equivalent to approximately 568 and 908 L/min. The second is sixty per cent greater because the comparison retains the same area. This arithmetic isolates the effect of the specified density. It does not demonstrate that these are generic requirements for the two categories in every source edition.<ref name="H-87" /><ref name="H-91" />
[[File:fse-sprinkler-hazard-classification-v3.svg|thumb|upright=1.5|alt=Two bars compare nominal products of one hundred and fifty and two hundred and forty US gallons per minute.|The two documented density inputs give different nominal flow products. Based on Hopkins et al. (2005), pp. 87 and 91.]]

Neither product is the completed system demand. Individual sprinklers can discharge more than their minimum flow because available pressures differ. Pipe friction, fittings and elevation also affect the supply pressure required. The classification thus initiates a chain of design decisions and calculations; the simple product cannot confirm the capacity of the installed system.<ref name="F-75-76">Fleming (2002), pp. 4-75–4-76.</ref>

The comparison should not be used to classify an unknown building by its existing water supply. A supply capable of the larger flow does not establish that the contents belong to the associated category. The direction of reasoning remains from protected hazard to suitable criteria, followed by verification that the proposed protection can deliver them.<ref name="F-73-75" />

== See also ==
* [[Hydraulic calculation]]

== Notes ==
<references />

== References ==
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 4-3, pp. 4-72–4-87). National Fire Protection Association.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Tewarson, A. (2002). Generation of heat and chemical compounds in fires. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-4). National Fire Protection Association.

[[Category:Fire Suppression]]

Sprinkler design density

2026-11-02T21:35:13Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Sprinkler design density''' is the specified minimum water discharge rate per unit protected area used in an area/density sprinkler design. It is paired with a design area representing the group of sprinklers assumed to operate. Fleming describes these quantities as inputs to calculations demonstrating that the system can deliver the required water to the selected sprinklers.<ref name="F-73-75">Fleming (2002), pp. 4-73–4-75.</ref>

Density connects a protection criterion with an individual sprinkler's required flow. Multiplying the density by the sprinkler's assigned coverage area gives a minimum discharge rate. The sprinkler discharge coefficient then relates that rate to pressure. The complete system calculation must also account for piping losses, elevation and the different pressures available at operating sprinklers.<ref name="F-75-78">Fleming (2002), pp. 4-75–4-78.</ref>

Design density is therefore a hydraulic requirement within a defined protection method. It is not a stand-alone prediction of extinguishment or a complete water-supply specification. Its meaning depends on the hazard, selected sprinkler, coverage arrangement and associated design area. The historical methods discussed here illustrate those relationships; their numerical examples do not establish requirements for a particular installation.<ref name="F-73">Fleming (2002), p. 4-73.</ref><ref name="H-16-18">Hopkins et al. (2005), pp. 16–18.</ref>

== Density, units and the design basis ==

The word density refers here to water flow divided by area. Common expressions include litres per minute per square metre and millimetres per minute. These are numerically equivalent because one litre spread over one square metre represents a depth of one millimetre. The depth unit expresses a rate of water application, rather than a prediction that a uniform layer accumulates on the floor.<ref name="F-74-75">Fleming (2002), pp. 4-74–4-75.</ref>

A value expressed in gallons per minute per square foot uses a different unit system. Its numerical value cannot be inserted unchanged into a calculation using litres and square metres. The sprinkler discharge coefficient also has units tied to the chosen flow and pressure units. Consistent units are required through the entire conversion from density to flow and then to pressure.<ref name="F-75">Fleming (2002), p. 4-75.</ref>

[[Sprinkler hazard classification|Sprinkler hazard classification]] precedes selection of the applicable density and area. Fleming emphasises that hydraulic calculations do not determine the correct hazard category. They establish whether the selected delivery requirement can be met. If the protected contents or activities have been underestimated, a mathematically correct calculation can still evaluate an unsuitable protection criterion.<ref name="F-73" />

The density must also be read with its associated design area. Historical area/density curves offered combinations of a higher density over a smaller area and a lower density over a larger area. A point could not be selected by treating the two coordinates as unrelated choices. The combination expresses the protection basis used to determine the expected operating group.<ref name="F-74">Fleming (2002), p. 4-74.</ref>

These curves are empirical design tools. Fleming explains that some sprinkler criteria arose from full-scale testing, while others developed through accumulated experience and judgement. The density value consequently carries the assumptions of the method that supplied it. It should not be treated as a universal material property or derived solely from a building's floor area.<ref name="F-73" />

== Converting density into sprinkler flow ==

For a sprinkler evaluated by the area/density method, the minimum flow is the product of the design density and its assigned coverage area. The corresponding pressure follows from the discharge relationship of the [[Sprinkler head|sprinkler head]]. These expressions describe the local discharge requirement before the upstream piping losses are added.<ref name="F-75" />
[[File:fse-sprinkler-design-density-v1.svg|thumb|upright=1.5|alt=A twelve square metre coverage rectangle requires seventy-two litres per minute at the illustrative design density.|Illustrative conversion from assigned coverage area to required flow. Based on Fleming (2002), p. 4-75.]]

<div class="fse-equation">Q = dA<sub>s</sub>;   Q = K√P;   P = (dA<sub>s</sub> / K)<sup>2</sup></div>

{| class="wikitable"
! Symbol !! Meaning !! Units used here
|-
| Q || Water discharge from one sprinkler || L/min
|-
| d || Specified design density || L/(min·m²)
|-
| A<sub>s</sub> || Assigned coverage area of that sprinkler || m²
|-
| K || Sprinkler discharge coefficient || L/(min·bar<sup>1/2</sup>)
|-
| P || Pressure used in the sprinkler discharge relationship || bar
|}

Coverage area is a calculation quantity determined from the layout and the applicable method. In a regular arrangement, spacing along the branch line and spacing between branch lines provide the relevant dimensions. Irregular spacing and proximity to walls need additional care. An apparent floor patch bounded by nearby walls is not automatically the area that the calculation assigns to a sprinkler.<ref name="F-75" /><ref name="H-92">Hopkins et al. (2005), p. 92.</ref>

The pressure relationship is nonlinear. For the same sprinkler coefficient, doubling required flow requires four times the pressure at that sprinkler. Increasing pressure also increases the discharge of sprinklers that already meet their minimum flow. This behaviour explains why balancing the network requires more than dividing a total flow equally between all operating sprinklers.<ref name="F-75-76">Fleming (2002), pp. 4-75–4-76.</ref>

The density-area product may not be the governing requirement for every sprinkler. Fleming notes that special and residential sprinklers can have minimum listed flows related to their approved spacing. A minimum pressure may also govern. Such requirements must be considered alongside the area/density calculation, rather than replaced by a smaller result from the simple multiplication.<ref name="F-75" />

The coefficient describes discharge through the sprinkler, but it does not alone establish suitable spray performance for every application. The handbook explains that special sprinklers are approved for particular protection goals and are not freely interchangeable. Matching a flow at a calculated pressure is therefore a necessary hydraulic consideration within the selected design basis, not proof of equivalent fire performance.<ref name="F-73" />

== Worked example in consistent SI units ==

Consider an illustrative density of 6 L/(min·m²), with one sprinkler assigned a rectangular area measuring 3 m by 4 m. The coverage area is 12 m², giving a minimum flow of 72 L/min. Assume a sprinkler coefficient of 80 L/(min·bar<sup>1/2</sup>). The discharge equation then gives a required sprinkler pressure of 0.81 bar.<ref name="F-75" />

These values are selected only to demonstrate the calculation. They do not specify a hazard category, a permitted spacing or a product's operating requirements. A real design would first establish those constraints and determine whether another minimum flow or pressure controls. It would also include the pressure required to transport water to this sprinkler.<ref name="F-73-75" />

Now increase the assigned coverage area to 16 m² while retaining the same illustrative density and coefficient. The required flow becomes 96 L/min and the calculated pressure becomes 1.44 bar. The larger area has increased flow by one third but pressure by more than three quarters. This result follows directly from the squared relationship between pressure and required flow.<ref name="F-75" />
[[File:fse-sprinkler-design-density-v2.svg|thumb|upright=1.5|alt=Two panels compare flows of seventy-two and ninety-six litres per minute and pressures of 0.81 and 1.44 bar.|Larger coverage requires more flow and a disproportionately larger discharge pressure. Based on Fleming (2002), p. 4-75.]]

For a nominal design area of 144 m², dividing by the original 12 m² coverage gives twelve sprinklers. Multiplying the design density by that area gives 864 L/min. This is a useful initial product, but it is not the completed supply demand. The shape of the operating group and actual individual discharges still have to be established.<ref name="F-74-76">Fleming (2002), pp. 4-74–4-76.</ref>

In particular, the arithmetic does not establish that twelve sprinklers form the required hydraulic design arrangement. The governing method can prescribe the design area's shape and its orientation relative to branch lines. Boundary conditions can also increase the number of sprinklers included. The example deliberately stops before that network and layout assessment.<ref name="F-74" /><ref name="H-92" />

== Design area and hydraulic demand ==

The design area represents an assumed operating group within the [[Sprinkler system|sprinkler system]]. It does not imply that every sprinkler in the building opens whenever fire occurs. The NIST discussion describes individual operation in response to sufficient heat, with further sprinklers opening if fire growth continues. The calculation tests an identified group against its required water supply.<ref name="F-74" /><ref name="H-14">Hopkins et al. (2005), p. 14.</ref>

The group's location matters because flow paths, elevation and pipe dimensions affect the available pressure. In a simple tree arrangement, the most remote end sprinkler commonly provides a starting point for calculation. Looped and gridded systems provide more than one flow path and require the flow distribution to be solved. Distance alone is therefore not a complete hydraulic description of a difficult operating area.<ref name="F-74-78">Fleming (2002), pp. 4-74–4-78.</ref>

A [[Hydraulic calculation|hydraulic calculation]] proceeds from the required sprinkler conditions through the network. Pressure must cover discharge at the sprinklers, losses along the pipes and fittings, and the effect of elevation. Flow accumulates as additional operating sprinklers join the calculation. Any applicable hose-stream allowance is a further demand, separate from the density assigned to sprinkler coverage.<ref name="F-75-78" />

Sprinklers at higher available pressure discharge more water than their minimum requirement. Fleming calls this hydraulic increase and explains why total system demand is not simply design density multiplied by design area. The additional discharge must itself pass through upstream pipes and therefore affects losses. Ignoring it can understate the supply required to maintain the minimum conditions at the limiting sprinklers.<ref name="F-75-76" />

Irregular layouts provide a related complication. The NIST investigation describes calculations in which sprinklers near an external wall retained an assigned coverage larger than their apparent share of the actual floor area. This increased the number and discharge of sprinklers in the design calculation. The case illustrates why the individual coverage rules and selected operating area must be retained through the analysis.<ref name="H-92" />

== Required density and available supply ==

A demand calculation starts with the minimum sprinkler conditions and determines the required supply pressure and flow. A supply calculation starts with an available water supply and predicts the discharges it can produce through a specified network. Hopkins and colleagues distinguish these approaches because they answer different questions. The design density is an input in one and a comparison benchmark in the other.<ref name="H-87-89">Hopkins et al. (2005), pp. 87–89.</ref>
[[File:fse-sprinkler-design-density-v3.svg|thumb|upright=1.5|alt=Opposing arrows show a demand calculation working towards the supply and a supply calculation working towards the sprinklers.|Demand and supply calculations answer different questions. Based on Hopkins et al. (2005), pp. 87–89.]]

Comparing calculated demand with a supply characteristic establishes whether that supply can support the selected operating condition. The comparison must use pressure and flow together. A supply capable of a large flow at insufficient pressure may fail to maintain the required end-sprinkler discharge. Conversely, a static pressure value alone does not state what remains available while the system flows.<ref name="H-88">Hopkins et al. (2005), p. 88.</ref>

Averaging total sprinkler flow over the operating area can help describe a case, but it does not remove the need to examine individual sprinklers. The NIST analysis reports differences between maximum and minimum discharge within the same operating group. Remote sprinklers typically discharged less because of branch-line pressure losses. A satisfactory average therefore cannot automatically prove that each assigned coverage area receives its required discharge.<ref name="H-94">Hopkins et al. (2005), p. 94.</ref>

The number of operating sprinklers influences the result. The NIST study examined groups smaller than, comparable with and larger than the nominal design area. It also examined different floors and primary or secondary supplies. Those calculations demonstrated the dependence of delivered density on a defined operating scenario; they did not turn design density into an unlimited guarantee for any number of simultaneously open sprinklers.<ref name="H-89-94">Hopkins et al. (2005), pp. 89–94.</ref>

Water quantity and duration form another part of the supply assessment. A tank may support a specified flow only for a limited time. The NIST study calculated durations from available stored volume and predicted flow, stating whether refill was included. A density figure without a duration and supply basis therefore leaves part of the system's capability unspecified.<ref name="H-90">Hopkins et al. (2005), p. 90.</ref>

== Changes to the protected arrangement ==

A change in system type can affect the operating area even when the specified density remains unchanged. The historical dry pipe discussion in the NIST report explains that delayed water delivery permits additional sprinklers to operate. The associated design approach compensates by increasing the assumed operating area. The larger operating group requires water for more simultaneous discharges. This illustrates why density alone cannot describe the difference between two otherwise similar system designs.<ref name="H-15">Hopkins et al. (2005), p. 15.</ref>

Changes during installation can also affect hydraulic demand without changing the written density requirement. Added pipe or fittings introduce losses that the final network calculation must represent. The NIST report identifies such changes as one reason for retaining a margin between required demand and available supply. That margin belongs to the supply comparison; it is not a substitute for identifying the protected hazard correctly.<ref name="H-88" /><ref name="F-73" />

== Relation to fire control and extinction ==

The [[Critical water application rate|critical water application rate]] for extinguishing a particular burning fuel is a different kind of quantity from a prescribed sprinkler design density. Tewarson describes experiments applying water to specified burning surfaces under controlled heat exposure. Their results depend on the material, geometry and exposure. Transferring such a rate directly to a floor-area sprinkler design would change the basis of the measurement.<ref name="T-151-154">Tewarson (2002), pp. 3-151–3-154.</ref>

Water reaching a fuel surface can cool it, alter heat feedback and impede release of combustible vapours. The relative importance of these effects differs between horizontal and vertical surfaces and between simple specimens and stored commodities. Tewarson's discussion demonstrates why the same nominal application rate can produce different outcomes. Actual delivery to the burning surfaces remains part of the suppression problem.<ref name="T-152-154">Tewarson (2002), pp. 3-152–3-154.</ref>

Fleming similarly cautions against interpreting a simple suppression correlation as a general design method. The particular wood-crib model described in the handbook assumes unshielded fuel and has limits on its application. It does not represent all spray distributions or the possibility of continued fire growth after initial operation. Specifying a density does not by itself justify a chosen heat-release decay curve.<ref name="F-86-87">Fleming (2002), pp. 4-86–4-87.</ref>

The intended outcome must remain explicit. Control-mode systems aim to limit fire growth and spread; final extinguishment may require further intervention. The NIST account distinguishes that objective from suppression-oriented protection. Assessment of a density requirement should preserve the outcome and hazard conditions on which the applicable protection method is based.<ref name="H-15-16">Hopkins et al. (2005), pp. 15–16.</ref>

== See also ==
* ESFR sprinkler

== Notes ==
<references />

== References ==
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 4-3, pp. 4-72–4-87). National Fire Protection Association.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Tewarson, A. (2002). Generation of heat and chemical compounds in fires. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-4). National Fire Protection Association.

[[Category:Fire Suppression]]

Spalling

2026-11-02T21:35:10Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Spalling''' is the breaking away of layers or pieces of concrete from the surface of a concrete element that is exposed to high and rapidly rising temperatures, as in a fire.<ref name="KH-1-163">Kodur and Harmathy (2002), p. 1-163.</ref> It can happen soon after the start of heating and can be violent and explosive. It can also happen later, when heating has weakened the concrete so much that pieces fall off as cracks develop.<ref name="KH-1-163" /> Spalling matters because most design methods for [[concrete in fire]] assume that the concrete stays in place. When the cover concrete falls away, the reinforcing steel is exposed to the fire and heats much faster than the design expects.<ref name="FB-4-255">Fleischmann and Buchanan (2002), p. 4-255.</ref>

[[File:fse-spalling-v1.svg|thumb|upright=1.5|alt=Cross-section of a concrete slab heated from below: a piece of cover concrete breaks away and leaves a reinforcing bar exposed to flames.|Spalling of the cover concrete exposes the reinforcement to the fire, so that it heats much faster than assumed in design. Based on Kodur and Harmathy (2002), pp. 1-163–1-164, and Fleischmann and Buchanan (2002), p. 4-255.]]

Two mechanisms are usually put forward. Water vapour trapped in the pores can build up a pressure that exceeds the tensile strength of the concrete. Restrained thermal expansion near the hot surface can also cause compressive stresses that are released by brittle fracture.<ref name="KH-1-163" />

Normal-weight concrete members usually withstand severe fires without spalling, but spalling does sometimes occur.<ref name="FB-4-255" /> High-strength concrete, which is denser and less permeable, is more susceptible and often spalls explosively in tests.<ref name="KH-1-163" /> The best-known remedy is to add fine polypropylene fibres to the mix. These melt in a fire and leave channels through which the steam can escape.<ref name="FB-4-255" /><ref name="IFEG-2.6-9">National Research Council of Canada et al. (2005), p. 2.6-9.</ref>

== Forms of spalling ==
The SFPE Handbook distinguishes two ways in which spalling develops. In the first, pieces break away soon after exposure to heat, sometimes accompanied by violent explosions. In the second, the concrete has become so weak after heating that pieces fall off the surface once cracks form.<ref name="KH-1-163" /> A glossary entry quoted in NUREG-1805 describes spalling in general terms as the breaking away or explosion of concrete under fire exposure.<ref name="Nolan">Nolan (2000), as cited in Iqbal and Salley (2004), p. F-56.</ref> The same glossary links thermal expansion to surface chipping and scaling.<ref name="NUREG-F-64">Iqbal and Salley (2004), p. F-64.</ref>

Spalling is not limited to structural concrete. It is also known to occur in fire-resistant protective coatings for steel, where asbestos or other fibre fillers are added to concrete or other cementitious materials to improve insulation.<ref name="Nolan" /> NUREG-1805 notes that cementitious sprayed coatings can spall during a fire and have had adhesion problems in practice. Effective application, complete coverage and long-term maintenance therefore have to be checked.<ref name="NUREG-17-10">Iqbal and Salley (2004), p. 17-10.</ref>

The extent of the damage varies widely. The consequences may be limited as long as only small areas spall. Extensive spalling, however, can lead to early loss of stability and integrity, because the reinforcement is exposed and partitions can be penetrated.<ref name="KH-1-163" /> The glossary lists four consequences: exposure of structural steel, reinforcement or prestressing cables, more heat transmission through a thinner section, fire passage through openings and reduced bending capacity.<ref name="Nolan" />

== Causes ==
The most common explanation is pore pressure. When concrete is heated, water in the cement paste turns into vapour. In dense concrete this vapour cannot escape fast enough, and the pressure rises towards the saturation vapour pressure.<ref name="KH-1-163" /> At 300 °C this pressure reaches about 8 MPa, while high-strength concrete has a tensile strength of only about 5 MPa.<ref name="KH-1-163" /> Because the heated surface is drained and the concrete has a low permeability, strong pressure gradients develop close to the surface, in what is called a moisture clog. Pieces break off when the vapour pressure exceeds the tensile strength.<ref name="KH-1-163" />

Fleischmann and Buchanan state that it is generally agreed that spalling most often occurs when water vapour is driven from the cement paste. The high pore pressures then create high tensile stresses in the concrete. In some cases spalling is related to the type of aggregate, but it is more often linked to the behaviour of the cement paste.<ref name="FB-4-255" /> The pore pressure is considered to drive a progressive failure, and the SFPE Handbook links greater spalling to a lower permeability of the concrete.<ref name="KH-1-163" />

Other researchers explain spalling with fracture mechanics. Thermal expansion close to the heated surface is restrained by the cooler concrete behind it. This creates compressive stresses parallel to the surface, which are released by brittle fracture.<ref name="KH-1-163" /> The NUREG-1805 glossary combines both views. It names stresses from a steep temperature gradient, expanding aggregate and trapped moisture that vaporises without a safe means of venting.<ref name="Nolan" />

[[File:fse-spalling-v2.svg|thumb|upright=1.5|alt=Two close-ups of heated concrete: left, vapour pressure behind the surface; right, compression along the hot surface breaking off a flake.|Two explanations of spalling: pore pressure from trapped water vapour (left) and restrained thermal expansion near the heated surface (right). Based on Kodur and Harmathy (2002), p. 1-163.]]

== Factors that increase the risk ==
Several conditions make spalling more likely. Fleischmann and Buchanan list a high moisture content, as in fresh concrete, rapid rates of heating, slender members and high stresses at the time of the fire.<ref name="FB-4-255" /> The International Fire Engineering Guidelines (2005) note that spalling is more common in new concrete with a high moisture content.<ref name="IFEG-2.6-9" /> The NUREG-1805 glossary adds permeability, porosity, restraint and reinforcement to moisture content and the rate of temperature rise.<ref name="Nolan" />

High-strength concrete is especially sensitive. It contains additives such as silica fume and water-reducing admixtures and reaches compressive strengths of 50 to 120 MPa.<ref name="FB-4-255" /> Its smaller free-pore volume fills with high-pressure vapour more quickly, and its low porosity slows the escape of that vapour.<ref name="FB-4-255" /> For high-strength concrete, the SFPE Handbook names strength, porosity, density, load intensity, fire intensity, aggregate type and relative humidity as the main parameters.<ref name="KH-1-164">Kodur and Harmathy (2002), p. 1-164.</ref> In full-scale fire tests on loaded columns, spalling was quite significant in a high-strength concrete column compared with a normal-strength one.<ref name="KH-1-163" /> High-strength concrete also tends to lose strength faster than normal concrete at temperatures up to 400 °C.<ref name="FB-4-255" />

The rate of heating links spalling to the choice of design fire. ''Introduction to Fire Safety Engineering'' notes that the RWS fire curve for tunnels and the hydrocarbon fire curve for oil and gas fires are more intense than the standard fire curve.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> Because a rapid rate of heating is one of the listed risk factors, spalling is a particular concern under these more intense exposures.<ref name="FB-4-255" /><ref name="VR-8.6" /> Tunnels are also among the structures for which the book expects a fire safety engineering approach instead of prescriptive rules. The wider hazards of a [[tunnel fire]] are treated in a separate article.<ref name="VR-1.5">Van Rossum (2027), §1.5.</ref>

== Heating depth and structural effects ==
In a fire, the heat stays near the surface of a concrete element for a long time. ''Introduction to Fire Safety Engineering'' gives a rule of thumb for the depth to which heat penetrates in a given time. If an element is thicker than about twice the characteristic penetration depth, it behaves as thermally thick and its back stays relatively cool.<ref name="VR-5.2">Van Rossum (2027), §5.2.</ref>

<math display="block">L \approx 2\sqrt{\alpha\, t}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>L</math> || indicative boundary thickness between thermally thick and thermally thin behaviour || m
|-
| <math>\alpha</math> || thermal diffusivity of the material || m<sup>2</sup>/s
|-
| <math>t</math> || duration of heating || s
|}

The book stresses that this is a practical rule and not a sharp physical boundary, because a heat front has no abrupt edge.<ref name="VR-5.2" /> In its worked example, concrete with a diffusivity of 9.88 × 10<sup>−7</sup> m<sup>2</sup>/s gives a depth of about 0.060 m after 15 minutes. A wall of 200 mm therefore behaves as thermally thick during the first quarter of an hour.<ref name="VR-5.2" /><ref name="VR-5.5">Van Rossum (2027), §5.5.</ref> With the same formula the depth grows to about 84 mm after 30 minutes and about 120 mm after 60 minutes.<ref name="Calc-Sp">Calculated from Van Rossum (2027), §5.2 and §5.5.</ref> The heating, and with it the steep temperature and pressure gradients, are thus concentrated in the outer few centimetres.<ref name="Calc-Sp" /><ref name="KH-1-163" /> This outer zone includes the cover concrete that protects the reinforcement.<ref name="FB-4-255" />

[[File:fse-spalling-v3.svg|thumb|upright=1.5|alt=Line chart of indicative heat penetration depth in concrete rising from 0 to about 170 mm over 120 minutes, with a marked point of 60 mm at 15 minutes.|Indicative heat penetration depth L ≈ 2√(αt) for concrete (α = 9.88 × 10⁻⁷ m²/s). Based on Van Rossum (2027), §5.2 and §5.5.]]

When spalling removes this cover, deeper layers of concrete are then exposed to fire temperatures and heat reaches the reinforcement much faster.<ref name="KH-1-164" /> When the reinforcement is exposed directly, its temperature rises at a very high rate and the member loses strength quickly. The loss of strength in the steel, added to the loss of concrete, significantly reduces the fire resistance of the member.<ref name="KH-1-164" /> The [[strength reduction at elevated temperatures]] of reinforcing and prestressing steel is therefore the main reason why spalling can lead to structural failure.

The concrete itself also weakens. Concrete with siliceous aggregate keeps nearly its full compressive strength up to about 500 °C, but has lost about half of it at 650 °C.<ref name="FB-4-240">Fleischmann and Buchanan (2002), p. 4-240.</ref> Prestressed concrete is particularly sensitive, because failure modes such as debonding, shear and spalling are more critical there.<ref name="FB-4-254">Fleischmann and Buchanan (2002), p. 4-254.</ref>

== Observations in fire tests ==
The fire resistance tests on World Trade Center floor assemblies, carried out to ASTM E119 in 2004, give a documented example. During the tests, loud reports were heard, often together with movement of the steel deck and dislodging of the sprayed fire protection. The investigators assumed that these signalled explosive spalling, although its exact location and extent could not be determined.<ref name="NCSTAR-49">Gross et al. (2005), p. 49.</ref> The relative humidity of the concrete slabs met the requirements of the standard.<ref name="NCSTAR-49" /> All four tests produced extensive spalling on the underside of the floor slab.<ref name="NCSTAR6-lxxii">Gross and McAllister (2005), p. lxxii.</ref>

The underside spalling began early. In the first three tests, the metal deck under the slab started to bulge within the first 15 minutes because concrete was spalling above it.<ref name="NCSTAR6-47">Gross and McAllister (2005), p. 47.</ref> Sections cut through the slabs after the tests confirmed delamination. The depth varied, but the remaining slab was about 2 to 3 in thick, essentially up to the double layer of welded wire fabric.<ref name="NCSTAR6-50">Gross and McAllister (2005), p. 50.</ref> In the first test the depth of the delamination spalling was of the order of 2 in, about 50 mm.<ref name="NCSTAR-57">Gross et al. (2005), p. 57.</ref> The temperatures on the unexposed surface of all four assemblies were similar until significant spalling began at around 50 minutes.<ref name="NCSTAR-104">Gross et al. (2005), p. 104.</ref>

Restraint made a clear difference on the top surface. The three restrained specimens showed significant cracking and explosive spalling at the top of the slab, while the unrestrained specimen of the same span showed no explosive spalling there.<ref name="NCSTAR6-51">Gross and McAllister (2005), p. 51.</ref> In the restrained 17 ft specimen with 1/2 in of fire protection, concrete fragments flew through the air and left a hole about 2 ft long through which hot gases escaped.<ref name="NCSTAR6-51" /> This happened at about 55 minutes, and the opening had to be covered with ceramic fibre insulation so that the test could continue.<ref name="NCSTAR-83">Gross et al. (2005), p. 83.</ref> Such a hole is the kind of integrity failure that extensive spalling can cause.<ref name="KH-1-163" />

The investigators concluded that the different results of the two 17 ft specimens were due mainly to the performance of the concrete slab, through spalling and cracking, and to fire protection overspray on the deck. The thickness of the fire protection on the trusses was not the main cause. Differences in spalling were possibly due to differences in moisture content and slab cracking.<ref name="NCSTAR6-lxxiii">Gross and McAllister (2005), p. lxxiii.</ref> The later computer models of the towers did not include concrete spalling.<ref name="NCSTAR6-xlvi">Gross and McAllister (2005), p. xlvi.</ref>

== Prevention and design ==
Polypropylene fibres are the most widely recommended measure. The fibres melt at a relatively low temperature of about 170 °C and create channels through which the steam can escape. This prevents the small explosions that cause spalling.<ref name="KH-1-171">Kodur and Harmathy (2002), p. 1-171.</ref> The SFPE Handbook gives a dosage of about 0.1 to 0.25 % by volume, most effective for high-strength concrete with normal-weight aggregate.<ref name="KH-1-171" /> The International Fire Engineering Guidelines (2005) give 0.15 to 0.3 % and call the fibres the most economic way to reduce the likelihood of spalling.<ref name="IFEG-2.6-9" />

[[File:fse-spalling-v4.svg|thumb|upright=1.5|alt=Two close-ups of concrete with thin fibres: intact before the fire, melted into channels for escaping steam during the fire.|Polypropylene fibres melt at about 170 °C and leave channels through which water vapour can escape. Based on Kodur and Harmathy (2002), p. 1-171, and National Research Council of Canada et al. (2005), p. 2.6-9.]]

Calculation methods need care when spalling is possible. The design methods in the concrete chapter of the SFPE Handbook assume that the concrete remains intact for the whole fire. This assumption is invalid if the cover spalls off during the fire.<ref name="FB-4-255" /> For high-strength concrete, Tomasson suggests a simple method that ignores concrete hotter than 500 °C in slabs and beams and hotter than 400 °C in columns.<ref name="Tomasson">Tomasson (1998), as cited in Fleischmann and Buchanan (2002), p. 4-255.</ref> The International Fire Engineering Guidelines (2005) also note that the cross-section of a member in fire may be smaller because of charring or spalling.<ref name="IFEG-2.6-7">National Research Council of Canada et al. (2005), p. 2.6-7.</ref>

Tests therefore remain important. The Australian Fire Safety Verification Method Data Sheets name materials prone to spalling among the components that are too complex to model from material properties alone without full-scale supporting data.<ref name="ABCB-C8-227">Australian Building Codes Board (2020a), Data Sheet C8, p. 227.</ref> A thermal-only method for converting fire resistance times does not directly account for spalling, shrinkage or thermal shock. This limitation is accepted only where the construction is not particularly sensitive to the heating rate.<ref name="ABCB-C8-233">Australian Building Codes Board (2020a), Data Sheet C8, p. 233.</ref>

== See also ==
* [[Fire resistance criteria]]
* [[Standard fire curve]]
* [[Structural fire engineering]]
* [[Fire resistance]]
* [[Restrained thermal expansion]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association; Society of Fire Protection Engineers.
* Gross, J., Hervey, F., Izydorek, M., Mammoser, J., & Treadway, J. (2005). ''Fire resistance tests of floor truss systems'' (NIST NCSTAR 1-6B). National Institute of Standards and Technology.
* Gross, J. L., & McAllister, T. P. (2005). ''Structural fire response and probable collapse sequence of the World Trade Center towers'' (NIST NCSTAR 1-6). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association; Society of Fire Protection Engineers.
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Structural Fire Engineering]]

Societal risk

2026-11-02T21:35:06Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Societal risk''' is the relationship between the frequency of harmful events and the number of people harmed in each event, within a given population.<ref name="HB-143">Australian Building Codes Board (2020b), p. 143.</ref> The term is used for hazards, such as large fires and explosions, that can harm many people at once. It takes account of the likelihood of multiple casualties, which a single risk value for one person does not show.<ref name="HB-22">Australian Building Codes Board (2020b), p. 22.</ref><ref name="BA-210">Barry (2002), p. 5-210.</ref> [[Individual risk]] describes the risk to a person at a specified location, whether or not anyone is present there. Societal risk, by contrast, depends on how many people are present and how likely they are to be exposed.<ref name="BA-210" /><ref name="BA-211">Barry (2002), p. 5-211.</ref>

Societal risk is often presented as an F-N curve, a plot of the frequency of exceeding a given number of fatalities against that number, as part of a [[quantitative risk assessment]].<ref name="BA-210" /> Australian building codes have evolved partly in response to loss of life, and their requirements tend to reflect community values about both individual and societal risk.<ref name="HB-146">Australian Building Codes Board (2020b), p. 146.</ref> Whether a given societal risk is acceptable remains a value judgement, because a universally acceptable level of fire risk does not exist.<ref name="WH-4">Watts and Hall (2002), p. 5-4.</ref>

== Definition and scope ==
Barry describes societal risk, sometimes called population risk, as a measure of human risk that takes into account the likelihood of multiple casualties from fires or explosions.<ref name="BA-210" /> The Fire Safety Verification Method handbook of the Australian Building Codes Board defines it as the relationship between frequency and the number of people suffering a specified level of harm in a given population. The harm results from the realisation of specified hazards.<ref name="HB-143" /> In that handbook, the given population is normally the population of the building under study, and of adjacent buildings where appropriate. The specified hazard is a fire within or involving these buildings.<ref name="HB-143" />

Individual risk and societal risk answer different questions. In the same handbook, individual risk is the frequency at which an individual may be expected to sustain a given level of harm from a fire in the building.<ref name="HB-22" /> Barry notes that individual risk contours show the expected frequency of harm at a location regardless of whether anyone is there to suffer it.<ref name="BA-210" /> A societal risk estimate, in contrast, needs a definition of the population at risk, the likelihood that people are present and the reliability of measures such as evacuation.<ref name="BA-211" />
[[File:fse-societal-risk-v1.svg|thumb|upright=1.5|alt=Two identical hazard sites with the same risk contours; left, three people inside the contour; right, a crowd of thirty people inside it.|The same individual risk contours around a hazard (left and right) with few and with many people present. Individual risk is the same; the risk of multiple casualties is not. Based on Barry (2002), pp. 5-210 to 5-211.]]

Both measures describe parts of the same underlying [[fire risk]]. Watts and Hall define the risk of a building as the full probability distribution of fire events and their consequences. They regard the many published definitions of risk as summary measures taken from that distribution.<ref name="WH-3">Watts and Hall (2002), p. 5-3.</ref> It follows from these definitions that societal risk keeps the information on the size of each event, which an average value would hide.

Barry's example of an individual risk profile shows how individual risk falls with distance from a source. At the nearest plotted point, about 125 ft (40 m) from the liquefied petroleum gas (LPG) tanks of a plant, the fatality probability is 7.43 × 10<sup>−4</sup> per year. At 650 to 700 ft from the tanks, about 200 m, it has fallen to 7.7 × 10<sup>−6</sup> per year.<ref name="BA-210" /> How much societal risk such a profile implies depends on how many people live or work at each distance, which the profile itself does not show.<ref name="BA-211" />
[[File:fse-societal-risk-v2.svg|thumb|upright=1.5|alt=Step chart of fatality probability per year falling from about 7.4 times ten to minus four near LPG tanks to 7.7 times ten to minus six at about 700 ft.|Individual risk profile: fatality probability per year against distance north from the LPG tanks of an example plant. Based on Barry (2002), p. 5-210.]]

== F-N curves and risk indices ==
An F-N curve plots the cumulative frequency <math>F</math> of multiple fatalities against the number <math>N</math> of fatalities. The vertical axis gives the frequency of events that exceed a specified number of fatalities.<ref name="BA-210" /> Barry gives this definition in words. In formula form, in the notation of this article, the curve value at <math>N</math> for a set of possible events is the sum of the frequencies of all events that harm more than <math>N</math> people:

<math display="block">F(N) = \sum_{i:\, N_i > N} f_i</math>

A logarithmic plot is usually used, because the frequencies of different numbers of fatalities may range over several orders of magnitude.<ref name="BA-211" /> The contributions of different parts of a facility can be shown as separate curves in the same graph. Barry's example shows a total facility curve together with curves for shore-based operations and marine transfer operations.<ref name="BA-210" /><ref name="BA-211" /> Such curves give insight into the risk of a facility both to the employees on the site and to the community beyond its boundaries.<ref name="BA-211" />

A second way to summarise societal risk is a single number. Societal risk can be expressed as risk indices, which sum the risks from each accident and give an annual predicted fatality rate. Such an index gives a single number that is easy to understand and useful for comparing design and protection options.<ref name="BA-211" /> In the notation of this article, the annual predicted number of fatalities is:

<math display="block">E = \sum_i f_i \, N_i</math>

Barry lists examples of such indices, including the fatal accident rate, the average rate of death, the equivalent social cost index and the mortality index.<ref name="BA-211" /> A ranking of the events that contribute most to the total risk is also useful, because it directs attention to the most critical failures.<ref name="BA-211" /> It follows from the two formulas that an index such as the annual rate of death treats ten small events like one large event with the same total. The F-N curve keeps them apart.

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>F(N)</math> || frequency of events that harm more than <math>N</math> people || year<sup>−1</sup> (or per fire, in a conditional analysis)
|-
| <math>N</math> || number of people harmed (usually fatalities) || persons
|-
| <math>f_i</math> || frequency of event <math>i</math> || year<sup>−1</sup> (or per fire)
|-
| <math>N_i</math> || number of people harmed in event <math>i</math> || persons
|-
| <math>E</math> || expected number of people harmed (annual predicted fatality rate) || persons per year (or per fire)
|}

Both forms rest on consequence models that translate exposure into harm. Most quantifications of human risk are based on fatalities. Barry stresses that it is uncertain what exactly constitutes a fatal dose of thermal radiation, blast or toxic chemicals, so every assumption must be documented.<ref name="BA-211" /> For people in buildings, exposure models range from simple tenability limits to fractional effective dose models and [[probit function]]s.<ref name="HB-110">Australian Building Codes Board (2020b), p. 110.</ref>

== Societal risk in building fire safety ==
The Australian handbook requires designers to consider both individual and societal risk. A proposed performance solution must achieve a fire safety level at least equivalent to that of a reference building that complies with the deemed-to-satisfy provisions.<ref name="HB-22" /> The choice of reference building is therefore critical, because it is the basis for quantifying the acceptance criteria for both measures.<ref name="HB-44">Australian Building Codes Board (2020b), p. 44.</ref> The reference building indirectly defines the acceptable levels of individual and societal risk, and its choice needs the consensus of the stakeholders.<ref name="HB-46">Australian Building Codes Board (2020b), p. 46.</ref> Where appropriate, the surrounding land use is also considered.<ref name="HB-27">Australian Building Codes Board (2020b), p. 27.</ref>

The handbook warns that the impact of this choice on societal risk may not be apparent from a superficial review.<ref name="HB-46" /> Its example is an apartment building in which the travel distance from an apartment door to a single fire-isolated stair is extended from 6 m to 12 m. With the same footprint and number of occupants, a deemed-to-satisfy layout would need two stairs. A smaller single-stair reference building with a 6 m travel distance would have half the population. The proposed building would then have twice the population at risk and twice the number of fire starts, with a significant effect on societal risk.<ref name="HB-47">Australian Building Codes Board (2020b), p. 47.</ref>
[[File:fse-societal-risk-v3.svg|thumb|upright=1.5|alt=Two floor plans: left, twelve apartments, one stair, 12 m travel distance; right, a smaller one-stair building with six apartments and 6 m travel.|Proposed apartment floor with one stair and 12 m travel distance (left) and an unsuitable smaller reference with half the apartments (right). Based on Australian Building Codes Board (2020b), pp. 46 to 47.]]

The size and form of a building can also call for more analysis. For high-rise buildings above an effective height of 60 m, the handbook suggests a more extensive analysis of structural behaviour in fire. This addresses the potential increase in societal risk from a catastrophic collapse. For some very large buildings with large populations, a more detailed analysis of the risk of unexpected catastrophic failure may also be appropriate.<ref name="HB-94">Australian Building Codes Board (2020b), p. 94.</ref>

Codes can also link requirements directly to the number of people at risk. In New Zealand, C/VM2 (second edition, 2025) contains a design scenario, RC, that tests a design for the failure of key fire safety systems. The scenario applies where such a failure could expose more than 150 people to untenable conditions. Lower thresholds apply to sleeping occupancies, at more than 50 people, and to people who are detained, receiving treatment or care, or in early childhood centres, at more than 20 people.<ref name="MBIE-58">Ministry of Business, Innovation and Employment (2025b), p. 58.</ref>

Care settings show how one fire can harm several people. Beard developed a stochastic model for the number of deaths in a fire and applied it to a fire starting on a bed in a hospital ward. The model gave a likelihood of more than 80% of multiple fatalities once the fire exceeded 50 kW. The model assumed that the fire did not spread beyond the ward.<ref name="BE-389">Beard (1981/1982), as cited in Ramachandran (2002c), p. 3-389.</ref>

== Worked example ==
The handbook's comparison of two fire safety systems can be read as a small societal risk calculation.<ref name="HB-118">Australian Building Codes Board (2020b), p. 118.</ref> In both designs, nobody is exposed to untenable conditions if the system works, and 2 people are exposed if it fails. The probability of failure per fire is 0.1 for system A, in the reference building, and 0.3 for system B, in the proposed design.<ref name="HB-118" /> Each design therefore has one harmful event per fire, with <math>N_i = 2</math>.

Per fire, the F-N curve of each design is a single step. Events exceeding one person occur with a frequency of 0.1 for A and 0.3 for B, and no event exceeds two people. The expected number of people exposed per fire follows from the second equation:<ref name="HB-119">Australian Building Codes Board (2020b), p. 119.</ref>

<math display="block">E_\mathrm{A} = 0.1 \times 2 = 0.2, \qquad E_\mathrm{B} = 0.3 \times 2 = 0.6</math>

Design B carries three times the risk of the reference design, although a deterministic analysis of the same two scenarios would find them equivalent.<ref name="HB-119" /> The apartment example adds a further effect.<ref name="HB-47" /> If a building has twice the fire starts of its reference, and a failure is assumed to expose twice as many people, the step moves from 2 to 4 people and its height doubles. The expected number exposed then rises fourfold, from 0.2 to 0.8 per reference fire, although the fire development is unchanged.
[[File:fse-societal-risk-v4.svg|thumb|upright=1.5|alt=Log-log F-N chart with three step curves: A at 0.1 up to 2 people, B at 0.3 up to 2 people, A doubled at 0.2 up to 4 people.|F-N curves per fire for the worked example: reference system A, proposed system B, and system A with twice the fire starts and twice the people exposed. Based on Australian Building Codes Board (2020b), pp. 47 and 118 to 119.]]

== Acceptability and risk aversion ==
Acceptable risk is a value judgement applied to a chosen scale of risk. It requires a decision on how risk is measured and on whose views of acceptability are used. For an authority, acceptable risk is meant to be acceptable to society in general or to a particular community.<ref name="WH-4" /> In a fire and explosion risk assessment, these limits are set at the start as severity limits, likelihood limits and the risk tolerance of management.<ref name="BA-177">Barry (2002), p. 5-177.</ref> Results can also be ranked against other voluntary and involuntary risks. If the risk is unacceptable or uncertain, cost-effective options for reducing it are identified and selected.<ref name="BA-211" />

Watts and Hall ask whether the recent fire losses of a country represent a level of risk that its citizens accept. If they do not, it is unclear why so little attention is paid to the problem; if they do, it is unclear why every serious fire is followed by a great clamour for change.<ref name="WH-1">Watts and Hall (2002), p. 5-1.</ref> They distinguish technical, societal, enforcer and managerial value judgements, which can rate the same measure, such as residential sprinklers, quite differently.<ref name="WH-1" /><ref name="WH-2">Watts and Hall (2002), p. 5-2.</ref>

People do not judge equal calculated risks equally. Studies of risk perception have found preferences for more certainty over less, for familiar over unfamiliar risks and for voluntary over involuntary risks. They have also found preferences for common or ordinary risks over dramatic or memorable ones.<ref name="WH-3" /> Individuals and organisations are inconsistent in their risk aversion, and the view that the present level of public fire risk must be acceptable is not a fully reliable generalisation.<ref name="WH-4" />

Zero risk is not an achievable goal. Watts and Hall describe the goal that comes closest to it as risk as low as is technically possible: the residual risk after all identified risk reduction measures have been adopted.<ref name="WH-4" /> Australian safe design practice follows a related test. Under the code of practice of Safe Work Australia, control measures should eliminate risks or, if this is not reasonably practicable, minimise them.<ref name="SW-25">Safe Work Australia (2012), as cited in Australian Building Codes Board (2020b), p. 25.</ref> Where risk reduction is weighed against its cost, human risk may have to be converted into equivalent monetary terms.<ref name="BA-211" />

The Netherlands shows the problem of implicit acceptance levels. Dutch building regulations do not state how many deaths or injuries a fire may cause. Their requirements grew partly from consensus and history rather than from quantified goals.<ref name="VR-1.2">Van Rossum (2027), §1.2.</ref> Van Rossum notes that the chance of dying in a fire, per hour of stay, is much greater in a residential building than in an assembly building. Yet the requirements for fire detection are stricter for assembly buildings.<ref name="VR-1.2" />

== Limitations and uncertainty ==
A societal risk estimate is only as good as its population data. The number of people present, their location over time and the reliability of evacuation all enter the calculation, and each is uncertain.<ref name="BA-211" /> Barry recommends presenting results with an uncertainty bandwidth. This is especially important for rare events with large consequences, whose likelihood may be highly uncertain.<ref name="BA-209">Barry (2002), p. 5-209.</ref>

The consequence side adds further uncertainty, because the doses that cause death or injury are themselves uncertain.<ref name="BA-211" /> Comparative methods carry their own risk. A reference building with a different population or number of fire starts can distort the societal risk comparison, without this being apparent at first sight.<ref name="HB-46" /><ref name="HB-47" />

Finally, a societal risk estimate does not settle acceptability. The acceptable level depends on the problem context, on the alternatives and on the person or group that judges it.<ref name="WH-4" /> The reference-building approach defines acceptable levels only indirectly, by comparison with a building that complies with the regulations.<ref name="HB-46" /> In the Netherlands, Van Rossum observes that fire safety engineering has no risk-based limit values at all.<ref name="VR-1.4">Van Rossum (2027), §1.4.</ref>

== See also ==
* [[Event tree analysis]]
* [[Fire risk assessment]]
* [[Fire statistics]]
* [[Uncertainty analysis]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-176–5-213). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* Ramachandran, G. (2002c). Stochastic models of fire growth. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-381–3-401). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Watts, J. M., Jr., & Hall, J. R., Jr. (2002). Introduction to fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-1–5-7). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Risk Analysis]]

Sprinkler-vent interaction

2026-11-02T21:35:03Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Sprinkler-vent interaction''' is the mutual influence of automatic sprinklers and smoke and heat vents that are installed in the same space.<ref name="C-236">Cooper (2002b), p. 3-236.</ref> Vents can change the flow of hot gases that should trigger the sprinklers, while sprinkler sprays cool the smoke that the vents must remove and mix it with cleaner air.<ref name="ABCB-B1">Australian Building Codes Board (2020a), Data Sheet B1, pp. 20–21.</ref><ref name="C-236" /><ref name="C-237">Cooper (2002b), p. 3-237.</ref> Simply combining both systems, each designed as if the other were absent, therefore does not guarantee that their benefits add up.<ref name="C-236" />

The subject has long been controversial. When the third edition of the ''SFPE Handbook of Fire Protection Engineering'' was prepared, no generally accepted technical guidelines for combined designs existed.<ref name="C-236" /> A review of 34 position papers concluded that venting does not harm sprinkler performance and does not change the number of sprinklers that operate.<ref name="C-236" /><ref name="BC-237">Beyler and Cooper (in press), as cited in Cooper (2002b), p. 3-237.</ref> The main design concerns are the cooling of smoke by sprinkler sprays, which reduces the flow through vents, and vigorous mixing of the smoke layer, which can fill the whole space with smoke.<ref name="C-237" /><ref name="C-238">Cooper (2002b), p. 3-238.</ref> Cooper's example guidelines therefore include the early, coordinated opening of all vents in the compartment of fire origin.<ref name="C-240">Cooper (2002b), p. 3-240.</ref>

== Two systems with different aims ==
[[Smoke and heat exhaust ventilation]], or smoke and heat venting, removes hot smoky gases from the upper part of a space and lets cooler, clean air into the lower part.<ref name="C-219">Cooper (2002b), p. 3-219.</ref> The flow can be driven by buoyancy through vents, by fans, or by both, and roof vents may be opened by fusible links.<ref name="C-219" /> Venting aims to help people escape, to let fire fighters enter and see the seat of the fire, and to limit damage from smoke and heat.<ref name="C-219" /> A typical setting is a large, open warehouse-type space with roof vents, possibly divided into compartments by draft curtains that hang from the ceiling.<ref name="C-219" />

A [[sprinkler system]] has a different aim. Control-mode sprinkler systems are designed to control the growth and spread of a fire, and full extinguishment may need the fire service.<ref name="H-16">Hopkins et al. (2005), pp. 15–16.</ref> In a [[warehouse fire]], the wetting of stored goods by sprinkler water also resists the jump of fire across aisles.<ref name="T-151">Tewarson (2002), p. 3-151.</ref> Cooper notes that venting becomes significantly more complex when sprinklers operate in the same space.<ref name="C-220">Cooper (2002b), p. 3-220.</ref>

Both systems may be found in the same building. In the Netherlands, indoor car parks larger than 1,000 m² generally have facilities that limit fire spread, such as sprinklers, and/or facilities that help an interior attack, such as smoke and heat removal.<ref name="VdG-52">Van der Graaf et al. (2021/2023), p. 52.</ref> The Dutch standard NEN 6093 contains calculation models and design and installation guidelines for smoke and heat exhaust systems.<ref name="VR-9.3">Van Rossum (2027), §9.3 (Results from zone models).</ref> For a fire service attack in a space with such a system, it sets limits such as a visibility of at least 100 m to light-emitting objects up to a height of 1.8 m.<ref name="VR-9.3" /> The calculated smoke layer may then not exceed 200 °C where goods are stored in the layer, or 500 °C otherwise.<ref name="VR-9.3" />

== How the two systems influence each other ==
Sprinklers and fusible-link vents respond to the same flow. Both are triggered when the hot [[ceiling jet]] heats their fusible links or glass bulbs.<ref name="C-239">Cooper (2002b), p. 3-239.</ref> The physical phenomena behind each system can be expected to interact, to a greater or lesser extent, when both are present.<ref name="C-236" /> Vent design can therefore change sprinkler performance, and sprinkler design can change vent performance.<ref name="C-236" />
[[File:fse-sprinkler-vent-interaction-v1.svg|thumb|upright=1.5|alt=Cross-section of a storage building with roof vents, draft curtains, a smoke layer, a fire plume and two operating sprinklers.|Sprinklers and roof vents in one curtained compartment. The ceiling jet triggers both; the sprays cool and mix the smoke layer that the vents remove. Based on Cooper (2002b), pp. 3-219, 3-236 to 3-237 and 3-239.]]

In one direction, sprinkler sprays cool the smoke that rises from the fire and fills the space.<ref name="C-236" /> A vent design based only on the hot, uncooled smoke does not account for this cooling, so less smoke flows out of the vents than intended.<ref name="C-236" /> If the reduction is significant, the vents must be larger.<ref name="C-236" />

In the other direction, ventilation can change where the hot gases go. The data sheets of the Australian Building Codes Board note that air flows can direct combustion products towards or away from detection devices, including sprinkler heads.<ref name="ABCB-B1-20">Australian Building Codes Board (2020a), Data Sheet B1, p. 20.</ref> They also warn that a vent or exhaust system may remove hot gases before the sprinklers activate.<ref name="ABCB-B1-21">Australian Building Codes Board (2020a), Data Sheet B1, p. 21.</ref> This could compromise the sprinkler system, especially one designed for early suppression.<ref name="ABCB-B1-21" /> Fast make-up air inlets close to a fire may increase its heat release rate or deflect its plume.<ref name="ABCB-B1-21" />

== Effect of sprinkler cooling on vent flow ==
Flow through a roof vent is driven by the buoyancy of the smoke layer.<ref name="C-223">Cooper (2002b), p. 3-223.</ref> The hot layer creates a higher pressure at the ceiling than outside, and this pressure difference grows with the depth and temperature of the layer.<ref name="C-223" /> A hotter layer pushes harder but is also less dense, so the mass of smoke removed does not keep rising with temperature.<ref name="C-224">Cooper (2002b), p. 3-224.</ref> Cooper combines these effects into one expression for the mass flow per unit vent area.<ref name="C-223" /> It assumes negligible pressure losses at the inlets, which typically holds if the low-level inlet openings are at least 1.5 to 2 times the vent area.<ref name="C-223" />

<math display="block">\frac{\dot{m}_\mathrm{vent}}{A_\mathrm{vent}} = 0.61\, \rho_\mathrm{amb} \sqrt{\frac{g\, h}{2}} \left[ 4 \left( 1 - \frac{T_\mathrm{amb}}{T_\mathrm{lay}} \right) \frac{T_\mathrm{amb}}{T_\mathrm{lay}} \right]^{1/2}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot{m}_\mathrm{vent}</math> || mass flow of smoke through the vent || kg/s
|-
| <math>A_\mathrm{vent}</math> || area of the ceiling vent || m²
|-
| <math>\rho_\mathrm{amb}</math> || density of ambient air || kg/m³
|-
| <math>g</math> || acceleration of gravity || m/s²
|-
| <math>h</math> || depth of the smoke layer below the ceiling || m
|-
| <math>T_\mathrm{amb}</math> || absolute ambient temperature || K
|-
| <math>T_\mathrm{lay}</math> || absolute temperature of the smoke layer || K
|}

The factor 0.61 is the flow coefficient of the vent.<ref name="C-222">Cooper (2002b), p. 3-222.</ref> The term in square brackets reaches its maximum of one when the absolute layer temperature is twice the ambient temperature, which is 586 K for an ambient temperature of 293 K.<ref name="C-224" /> If the layer is more than about 90 K hotter than ambient, the flow stays within 80 percent of this maximum.<ref name="C-224" /> Much cooler layers lead to significant reductions in vent flow.<ref name="C-224" />
[[File:fse-sprinkler-vent-interaction-v2.svg|thumb|upright=1.5|alt=Curve of relative vent mass flow against layer to ambient temperature ratio, peaking at 2; points mark 100 K and 20 K above ambient.|Relative mass flow through a roof vent as a function of the ratio of absolute layer and ambient temperature, with the layer at 100 K and, after spray cooling, 20 K above 293 K. Based on Cooper (2002b), pp. 3-223 to 3-224.]]

=== Worked example ===
Cooper considers a smoke layer 3 m deep and 100 K above an ambient temperature of 293 K.<ref name="C-224" /> The pressure difference across a roof vent is then 9.0 Pa, the smoke leaves at 2.7 m/s, and each square metre of vent removes 2.4 kg of smoke per second.<ref name="C-224" /> Suppose that sprinkler sprays cool the same layer to 20 K above ambient without changing its depth. The term in square brackets then falls from 0.76 to 0.24. Its square root, which is the fraction of the maximum possible flow, falls from 0.87 to 0.49, and the vent removes only about 1.4 kg/s per square metre, or 56 percent of the original flow. To remove the same mass of smoke, the vent area would have to grow by a factor of about 1.8.
[[File:fse-sprinkler-vent-interaction-v3.svg|thumb|upright=1.5|alt=Bar chart: vent mass flow per square metre falls from 2.4 to 1.0 kg/s as the layer cools from 100 K to 10 K above ambient.|Mass flow per square metre of roof vent for a 3 m deep smoke layer at different temperatures above an ambient 293 K, and the vent area factor needed to keep the flow of the 100 K case. Based on Cooper (2002b), pp. 3-223 to 3-224.]]

== Spray-driven mixing and smoke logging ==
Sprinkler sprays act on the smoke layer in two ways: they cool it by evaporation, and they dilute it by mixing cooler air from below into the layer.<ref name="C-237" /> As long as the loss of temperature and buoyancy is not too great, Cooper judges that additional vent capacity can offset moderate cooling and mixing.<ref name="C-237" /> He adds that spray-driven mixing can apparently be so effective, even without much cooling, that the volume of smoke grows very rapidly while its temperature drops.<ref name="C-237" /> If that happens, even impractically large increases in vent area would bring little benefit.<ref name="C-237" />

The extreme result is smoke logging, in which the sprays mix the fresh smoke from the fire plume continuously with all the gas in the space.<ref name="C-238" /> In preliminary tests in a large shopping mall, a manually operated sprinkler spray could, under some conditions, bring a smoke layer down, after which smoke logging occurred rapidly.<ref name="Bullen">Bullen (1977), as cited in Cooper (2002b), p. 3-238.</ref> Under other conditions, however, the smoke layer was not disturbed by the spray.<ref name="Bullen" /> A vent design that meets its aims must therefore be based on an analysis that accounts for smoke logging and avoids it.<ref name="C-238" />

A model of a single spray in a two-layer fire environment identified six possible configurations of spray and smoke layer.<ref name="C-238" /> Which one occurs depends mainly on the thickness and temperature of the layer and on the momentum, spread angle and droplet size of the spray.<ref name="C-238" /> Four configurations favour a combined design, provided the vents keep the layer relatively thin and not too buoyant.<ref name="C-238" /> The spray then carries the limited amount of smoke it entrains into the lower layer, where it becomes highly diluted.<ref name="C-238" /> Two configurations could lead to vigorous mixing, rapid growth of the smoke layer and possibly smoke logging.<ref name="C-238" /> Shortly after the first rapid-response sprinklers discharge, the layer is still thin and not too hot, and smoke logging is then never observed.<ref name="C-238" /><ref name="C-239" />

== Effect of vents on sprinkler operation ==
Studies and opinions on combined systems have produced claims in both directions. In favour, it is claimed that vents limit the spread of combustion products, reduce the number of sprinklers that operate and help fire fighters locate the fire.<ref name="BC-237" /> Against, it is claimed that vents increase the burning rate, delay sprinkler activation, increase the number of operating sprinklers and remove too little smoke to matter.<ref name="BC-237" />

After evaluating the evidence, Beyler and Cooper concluded that venting has no negative effect on sprinkler performance.<ref name="BC-237" /> Sprinklers do not depend on reduced oxygen concentrations, and venting changes neither the activation times of early sprinklers nor the total number activated.<ref name="BC-237" /> A fire directly beneath a vent may slightly delay the first sprinkler activations, but there is no evidence that this will have a significant impact on sprinkler performance.<ref name="BC-237" /> Venting does limit the spread of smoke and heat, which improves visibility for occupants and fire fighters and reduces damage.<ref name="BC-237" /> If the sprinklers fail, venting remains a valuable aid to manual fire fighting.<ref name="BC-237" />

The same review notes that in many fires, current design practice such as the guide NFPA 204 of the National Fire Protection Association is likely to limit the vents that open to one.<ref name="BC-237" /> In a successful sprinkler operation, the vents may not open at all.<ref name="BC-237" /> Vents with fusible links also suffer from vent skipping, the counterpart of [[sprinkler skipping]]: a random delay caused when water droplets in the ceiling jet cool their links.<ref name="C-239" /> Because far fewer vents than sprinklers are installed per unit floor area, Cooper suggests a safety factor on the total vent area.<ref name="C-239" /> The Australian data sheets are more cautious: they warn that venting before sprinklers activate could compromise early suppression systems.<ref name="ABCB-B1-21" /> They ask for special attention wherever a design departs from the standards for suppression and detection systems.<ref name="ABCB-B1-21" />

== Sprinkler activation in performance-based design ==
Some performance-based methods tie the design fire to the moment of sprinkler activation. In New Zealand, the Verification Method C/VM2 (second edition, 2025) lets the design fire for life safety (ASET) analysis in sprinklered buildings grow only until the sprinklers activate.<ref name="NZ-20">Ministry of Business, Innovation and Employment (2025b), p. 20.</ref> After activation the fire is assumed to be controlled, with a constant heat release rate.<ref name="NZ-20" /> Activation is calculated with values prescribed in a table of C/VM2.<ref name="NZ-27">Ministry of Business, Innovation and Employment (2025b), p. 27.</ref> For a standard response sprinkler these are an RTI of 135 (m·s)<sup>1/2</sup>, a C-factor of 0.85 (m/s)<sup>1/2</sup> and an activation temperature of 68 °C.<ref name="NZ-27" /> If the chosen sprinkler standard requires a higher activation temperature, that temperature must be used.<ref name="NZ-27" />

In Australia, the data sheets of the Australian Building Codes Board take the maximum heat release rate of a controlled fire as the rate when the last sprinkler within the assumed area of operation activates.<ref name="ABCB-C2-74">Australian Building Codes Board (2020a), Data Sheet C2, p. 74.</ref> In both methods the moment of sprinkler activation fixes the size of the design fire. A consequence not stated in either document is that any delay in activation would enlarge the design fire, and with it the smoke that a vent design must handle.

== Design approaches ==
Beyler and Cooper recommend design methods that make vents open early, with all vents operating together as a group.<ref name="BC-237" /> Sprinkler designs must treat draft curtains as obstructions, and the curtains should hang over aisles rather than over storage.<ref name="BC-237" /> Cooper suggests two general criteria for a successful vent design. The vents must remove the hottest and most hazardous smoke and slow or stop the descent of the smoke layer, for example above eye level.<ref name="C-237" /> Where draft curtains are used, a significant additional benefit is possible to the extent that the venting keeps the smoke within the curtained compartment of fire origin.<ref name="C-237" />

Cooper also gives example guidelines for a design on which all parties could agree.<ref name="C-240" /> The sprinkler design is first established in the traditional way, from full-scale tests without vents.<ref name="C-240" /> Where the sprinklers are expected to control the fire, the vent objective is to keep the smoke within the curtained compartment indefinitely.<ref name="C-240" /> If that is too ambitious, or the sprinklers only slow the fire, it is to do so for a set time, for example until the fire service attacks.<ref name="C-240" /> All vents of the compartment then open early, for example together after the first sprinkler activates.<ref name="C-240" /> The vent area is designed with a compartment fire model of proven capability for sprinklers, vents and draft curtains together.<ref name="C-240" />
[[File:fse-sprinkler-vent-interaction-v4.svg|thumb|upright=1.5|alt=Flowchart of four steps from sprinkler design by full-scale tests to vent design with a compartment fire model.|Example guidelines for a combined sprinkler and vent design: sprinklers first, then the vent objective, ganged early opening and a model-based vent design. Based on Cooper (2002b), p. 3-240.]]

Both zone models and field models can support such designs.<ref name="C-240" /> Zone models suit parametric studies and practical design, while field models suit the detailed study of specific scenarios.<ref name="C-240" /> Examples include a draft curtain almost directly above the fire, or the sequence in which sprinklers discharge.<ref name="C-240" />

== Limits and practical points ==
The evidence on combined systems is incomplete. Cooper wrote that no generally accepted guidelines existed at the time, and that past experiments had not tried to isolate the effects of sprinkler cooling.<ref name="C-236" /><ref name="C-238" /> Knowledge of spray-driven mixing and smoke logging rests partly on visual observations that were reported only anecdotally.<ref name="C-238" /> The vent flow expression above also assumes generous inlet openings and a well-defined smoke layer.<ref name="C-223" />

Three practical points follow from the sources. Vents and sprinklers designed each by their own rules do not necessarily combine their benefits.<ref name="C-236" /> Extra vent area can offset moderate cooling of the smoke, but according to Cooper it would bring little benefit once vigorous mixing occurs.<ref name="C-237" /> At the same time, there is experimental evidence that venting can control smoke logging.<ref name="C-238" /> Finally, the review of Beyler and Cooper found that venting affects neither the activation times of early sprinklers nor the total number activated.<ref name="BC-237" /> The only exception noted was a possible slight delay of the first activations when the fire is directly beneath a vent.<ref name="BC-237" />

== See also ==
* ESFR sprinkler
* [[Response time index]]
* [[Sprinkler hazard classification]]
* [[Hydraulic calculation]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Cooper, L. Y. (2002b). Smoke and heat venting. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-219–3-242). National Fire Protection Association; Society of Fire Protection Engineers.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* Tewarson, A. (2002). Generation of heat and chemical compounds in fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-82–3-161). National Fire Protection Association; Society of Fire Protection Engineers.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Fire Suppression]]

Stair pressurisation

2026-11-02T21:35:00Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Stair pressurisation''' is a [[smoke control]] method in which fans blow outside air into a stair enclosure, so that the air pressure in the stair is slightly higher than on the floors around it. Air then leaks out of the stair through the gaps around closed doors, and this outward flow stops smoke from leaking in.<ref name="Klo-278">Klote (2002), p. 4-278.</ref><ref name="Iq-F61">Iqbal and Salley (2004), p. F-61.</ref> The main goal is a smoke-free escape route; a second goal is a smoke-free staging area for firefighters.<ref name="Klo-286">Klote (2002), p. 4-286.</ref> It is a positive pressure system, and building codes in the United States require it in high-rise buildings.<ref name="Evans-70">Evans et al. (2005), p. 70.</ref><ref name="FS-10">Ferreira and Strege (2005), p. 10.</ref>

The system has to work against the natural forces that move smoke through a building, above all the stack effect in tall shafts. A pressure difference that is too small lets smoke in, while one that is too large makes the doors too heavy to open.<ref name="Klo-281">Klote (2002), p. 4-281.</ref> For closed doors, minimum design values of about 5 to 25 Pa are suggested, depending on the fire and on sprinklers. In the United States, the Life Safety Code limits the force needed to open an escape door to 133 N.<ref name="Klo-285">Klote (2002), p. 4-285.</ref> Open doors are the weak point. When many people leave a building at once, many stair doors stand open and the pressure in the stair collapses, as studies of the World Trade Center towers showed.<ref name="FS-60">Ferreira and Strege (2005), p. 60.</ref>

== Purpose and principle ==
Smoke is a major threat in building fires, and it often travels far from the fire itself. Stairs and lift shafts frequently fill with smoke, which blocks or slows evacuation. In the late 1960s the idea of pressurising stairs to keep smoke out began to attract attention. The term smoke control was later coined for systems that use pressure produced by mechanical fans to limit smoke movement.<ref name="Klo-274">Klote (2002), p. 4-274.</ref> A glossary of the US Nuclear Regulatory Commission describes stair pressurisation as increasing the air pressure in stair wells, usually with fan systems, to provide a refuge area from fire and smoke.<ref name="Iq-F61" /> The book ''Introduction to Fire Safety Engineering'' likewise notes that a smoke management system can keep an area free of smoke by overpressure.<ref name="VR-6.6">Van Rossum (2027), §6.6.</ref>

Smoke control rests on two principles. First, airflow by itself can control smoke if its average velocity is high enough. Second, a pressure difference across a barrier, such as a wall with a door, can stop smoke from crossing it.<ref name="Klo-278" /> Pressurisation creates small airflows through the cracks around closed doors and through gaps in the construction, and these flows keep smoke out of the high-pressure side.<ref name="Klo-278" />

[[File:fse-stair-pressurisation-v1.svg|thumb|upright=1.5|alt=Cross-section of a five-storey building with a pressurised stair; air leaks out of the stair at each closed door and keeps smoke on the fire floor out.|A fan supplies outside air to the stair. The higher pressure in the stair drives air out through the gaps around the closed doors, which keeps smoke on the fire floor out of the stair. Based on Klote (2002), pp. 4-278 and 4-286.]]

For a closed door the velocity in the gaps is hard to determine, so the pressure difference is the quantity used in design. For an open door the air velocity is the relevant quantity.<ref name="Klo-279">Klote (2002), p. 4-279.</ref> A pressurised stair therefore has two tasks: keep a positive pressure across each closed stair door and, ideally, push enough air through the door on the fire floor when it is opened.<ref name="Klo-286" />

The World Trade Center investigation describes stair pressurisation as a positive pressurisation system that limits smoke spread into the stairways of buildings such as [[High-rise building|high-rise buildings]]. Its aim is to keep the primary escape routes of the building clear of smoke.<ref name="Evans-70" /> Positive pressure systems also have drawbacks. Too much pressure, or unbalanced pressure, may push smoke from the fire zone into other parts of the building, and such systems do not remove smoke from the building.<ref name="FS-10" /> A pressurised stair is a special form of [[protected escape route]]: the walls and doors form the barrier, and the fans make that barrier work even when it leaks.<ref name="Klo-279" />

== Forces that the system must overcome ==
The main forces that drive smoke through a building are the stack effect, the buoyancy of hot smoke, expansion, wind and the ventilation system.<ref name="Klo-274" /><ref name="VR-6.6" /> The [[stack effect]] is the vertical movement of a gas caused by a difference in density, as in a chimney.<ref name="VR-6.6" /> In cold weather the warm air inside a building rises through shafts such as stairs and lift shafts. Klote gives the example of a building 60 m tall with the neutral plane at mid-height. With −18 °C outside and 21 °C inside, the stack effect alone gives a pressure difference of up to 55 Pa between a shaft and the outside.<ref name="Klo-275">Klote (2002), p. 4-275.</ref>

Hot smoke adds its own buoyancy. In a fire room at 800 °C, the pressure difference 1.52 m above the neutral plane is about 13 Pa. In a series of full-scale fire tests, the largest pressure difference measured across the wall of the burn room was 16 Pa, at the ceiling.<ref name="Klo-276">Klote (2002), p. 4-276.</ref> Wind can produce much larger pressures on the outside of a building. A wind of 15.6 m/s with a pressure coefficient of 0.8 gives about 117 Pa. Its effect inside a tight building with closed windows is small, but it becomes important once a window in the fire room breaks.<ref name="Klo-277">Klote (2002), p. 4-277.</ref>

In field tests of smoke control systems, pressure differences across closed doors often fluctuated by as much as 5 Pa, probably because of the wind. A stair pressurisation system must therefore produce a pressure difference large enough not to be overcome by these fluctuations, by the stack effect, by smoke buoyancy or by the wind.<ref name="Klo-281" /> Weather matters too. A smoke control system has no thermal time lag, so it meets the full stack effect of the moment it starts. If the outside temperature is below the winter temperature used in design, stack effect problems may result.<ref name="Klo-285" />

== Airflow through door gaps ==
The amount of air a fan must supply follows from the leakage of the stair. Air flows from the stair through every gap, and the flow through each gap grows with the square root of the pressure difference across it. Klote takes a flow exponent of 0.5 as reasonable for all flow paths except extremely narrow cracks.<ref name="Klo-280">Klote (2002), p. 4-280.</ref> With a flow coefficient of 0.65 and an air density of 1.2 kg/m³, the volume flow through a gap is:<ref name="Klo-280" />

<math display="block">\dot{V} = K_f\, A \sqrt{\Delta P}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot{V}</math> || volume flow of air through the gap || m³/s
|-
| <math>K_f</math> || coefficient, 0.839 for a flow coefficient of 0.65 and an air density of 1.2 kg/m³ || m/(s·Pa<sup>0.5</sup>)
|-
| <math>A</math> || flow area of the gap (leakage area) || m²
|-
| <math>\Delta P</math> || pressure difference across the gap || Pa
|}

The flow coefficient depends on the shape of the gap and is generally between 0.6 and 0.7.<ref name="Klo-280" /> A closed door with a crack area of 0.01 m² leaks about 0.013 m³/s at 2.5 Pa and 0.073 m³/s at 75 Pa.<ref name="Klo-281" /> Leakage areas depend mainly on workmanship, for example on how well a door is fitted. For the walls of an average stairwell, Klote gives a leakage area of 0.11 × 10<sup>−3</sup> times the wall area, excluding the gaps around doors.<ref name="Klo-282">Klote (2002), p. 4-282.</ref> For an open stair door, a flow area of half the door area is recommended, because the flow pattern through a real doorway is complex.<ref name="Klo-282" /> In New Zealand, C/VM2 (second edition, 2025) likewise treats an open egress door as half its width for smoke flow calculations.<ref name="MBIE-15">Ministry of Business, Innovation and Employment (2025b), p. 15.</ref>

[[File:fse-stair-pressurisation-v2.svg|thumb|upright=1.5|alt=Line chart: airflow through a door gap against pressure difference, two rising curves that flatten, for gaps of 0.01 and 0.024 square metres.|Air leakage through the gap of a closed door against the pressure difference, for gap areas of 0.01 m² and 0.024 m². Based on Klote (2002), pp. 4-280 and 4-288.]]

A worked example uses the stair of Klote's design example: 20 floors, each with a leakage area of 0.030 m² between stair and floor, made up of the door gap and the stair wall.<ref name="Klo-288">Klote (2002), p. 4-288.</ref> The pressure difference is taken as 20 Pa, the bottom value of that example. One floor then leaks 0.839 × 0.030 × √20 = 0.11 m³/s, and 20 floors leak about 2.3 m³/s.

This simple estimate assumes the same pressure difference on every floor. Klote's full analysis includes the stack effect for an outside temperature of −10 °C and a stair at 21 °C. The pressure difference then rises from 20 Pa at the bottom of the stair to 106 Pa at the top, and the fan must supply 3.9 m³/s.<ref name="Klo-288" /> Hand calculations of this kind assume no vertical leakage between floors. For vertical leakage and open stair doors, computer analysis is recommended.<ref name="Klo-287">Klote (2002), p. 4-287.</ref>

[[File:fse-stair-pressurisation-v3.svg|thumb|upright=1.5|alt=Line chart: pressure difference between stair and building rising in a straight line from 20 Pa at the bottom to 106 Pa at the top of a 66 m stair.|Pressure difference between a pressurised 20-storey stair and the building, with −10 °C outside and 21 °C in the stair. Based on Klote (2002), p. 4-288.]]

The result is sensitive to leakage. If the leakage area per floor in the same example were 0.050 m² instead of 0.030 m², the required supply would be 6.5 m³/s. In practice these areas are difficult to estimate and even more difficult to control. A fan with an adjustable drive is one way to match the supply to the real leakage of the finished building.<ref name="Klo-288" /> Network computer programs such as CONTAM model each stair as a vertical series of spaces, one per floor, and can include wind, stack effect and open doors.<ref name="Klo-290">Klote (2002), p. 4-290.</ref>

== Design criteria ==
Klote names five groups of design parameters for smoke control: leakage areas, weather data, pressure differences, airflow and the number of open doors.<ref name="Klo-285" /> The minimum pressure difference follows from the criterion that no smoke should leak in during the evacuation. To withstand an intense fire next to a door, a minimum of 20 to 25 Pa is suggested, slightly above the 16 Pa measured in fire tests. For hot smoke from a remote fire, 15 to 20 Pa is suggested. In a sprinklered building the smoke is cooled, and 5 to 10 Pa is suggested to allow for pressure fluctuations.<ref name="Klo-285" />

The maximum pressure difference is set by the force needed to open a door. A person's physical condition largely determines what force is reasonable, so the limit is hard to define. The US Life Safety Code (NFPA 101), as cited by Klote, limits the force to open any door in a means of escape to 133 N.<ref name="Klo-285" /> The total opening force is the force of the door closer plus the force needed to overcome the pressure difference. The closer alone usually needs more than 13 N and sometimes as much as 90 N. For a door 2.13 m high and 0.91 m wide, a pressure difference of 75 Pa with a closer force of 53 N gives a total of 133 N.<ref name="Klo-282" />

Where stair doors are [[fire door|fire doors]] with self-closers, C/VM2 (New Zealand, second edition, 2025) assumes them to be closed unless occupants are using them. During egress it treats each door as open for three seconds per person, or for the whole queuing time when people queue.<ref name="MBIE-15" /> In Australia, the 2020 data sheets for the Fire Safety Verification Method note that pressurisation can push opening forces above the permitted limits and can stop fire and smoke doors from closing automatically.<ref name="ABCB-132">Australian Building Codes Board (2020a), Data Sheet C4, p. 132.</ref>

Open doors need an air velocity criterion. Klote estimates about 4 m/s to stop smoke from an intense fire of 2.4 MW and 1.5 m/s for a fire of 125 kW. Where sprinklers cool the smoke, 0.25 to 1.25 m/s may be used.<ref name="Klo-286" />

In Australia, the deemed-to-satisfy provisions of the National Construction Code reference AS 1668.1. According to the 2020 data sheets, this standard requires an airflow of at least 1 m/s through each open doorway to the fire floor. That applies when all doors to that floor are open together with the main discharge doors of all fire-isolated exits.<ref name="ABCB-127">Australian Building Codes Board (2020a), Data Sheet C4, p. 127.</ref> For a door of 0.91 m by 2.13 m, 1 m/s means 1.94 m³/s through a single doorway. That is about half the supply in Klote's whole closed-door example. Because such flows are large, pressure relief is needed, so that excessive pressures do not make doors hard to open or stop them from closing.<ref name="ABCB-127" />

How many doors will be open at the same time depends on the use of the building. In a densely occupied building it is very likely that all doors will be opened during evacuation. With a staged evacuation plan, a refuge area concept or sparse occupation, only a few doors may be open at once.<ref name="Klo-286" /> Designing for all doors open makes sure the system always works, but it probably adds to the cost.<ref name="Klo-286" />

== System types ==
Stair pressurisation systems are divided into single and multiple injection systems. A single injection system supplies air at one point, most often at the top of the stair.<ref name="Klo-286" /> If smoke reaches the fan intake, the system can blow smoke into the stair it is meant to protect. Automatic shutdown should therefore be considered for that event. In tall stairs, single injection can fail when a few doors near the injection point are open, because all the supply air escapes through them. This failure is especially likely with injection at the bottom while the ground floor door is open.<ref name="Klo-286" />

Multiple injection systems supply air at several points over the height of the stair, with the fan at ground level or on the roof. The supply duct can run in a separate shaft or inside the stair itself. In that case the duct must not obstruct the evacuation.<ref name="Klo-287" /> An alternative is to divide a tall stair into compartments of a few floors, each with its own injection point. The benefit is lost when the doors between compartments are open. Compartmentation is therefore unsuitable for densely occupied buildings where everyone leaves by the stair at once, but it can work with a staged evacuation.<ref name="Klo-287" />

[[File:fse-stair-pressurisation-v4.svg|thumb|upright=1.5|alt=Three stair cross-sections: one with a single roof fan, one with a duct feeding air at several floors, one divided into sections each with its own supply.|Three ways to supply air to a tall stair: single injection at the top, multiple injection through a duct, and a stair divided into compartments. Based on Klote (2002), pp. 4-286 and 4-287.]]

Stair pressurisation is often combined with other measures. Lift shafts can be pressurised in the same way, and the same analysis applies with the lift shaft in place of the stair.<ref name="Klo-289">Klote (2002), p. 4-289.</ref> A protected lift shaft matters for the fire service, because firefighters use lifts with special keys for rescue and to bring equipment to the fire floor.<ref name="Klo-289" /> This is the role of a [[firefighting lift]]. A building with only stair pressurisation can still suffer smoke spread through floors and other shafts. Zone smoke control, in which the fire floor is exhausted and other floors are supplied with air, is meant to limit that spread.<ref name="Klo-289" />

== Reliability and testing ==
A smoke control system must be tested after installation, because many problems have been found in practice. Klote mentions fans running backwards, fans without electrical power and controls that did not work. The first test is functional and checks each component. The second checks the performance of the system as a whole, usually by measuring pressure differences across doors and, where needed, air velocities through open doors.<ref name="Klo-290" /> Chemical smoke from smoke candles is not recommended for performance tests, because it lacks the buoyancy of real hot smoke.<ref name="Klo-290" /> Pressure difference testing is therefore the most practical performance test.<ref name="Klo-291">Klote (2002), p. 4-291.</ref>

The International Fire Engineering Guidelines (2005) state that for smoke control, greater complexity means lower reliability.<ref name="IFEG-3.5-3">National Research Council of Canada et al. (2005), p. 3.5-3.</ref> The Australian data sheets of 2020 summarise studies of stair pressurisation in service. Audits of Australian buildings found that the fans failed to start on alarm in 10 % of office buildings and 8 % of retail premises.<ref name="ABCB-137">Australian Building Codes Board (2020a), Data Sheet C4, p. 137.</ref> A detailed study by Fazio treated door forces above 110 N or air velocities below 1 m/s as failure. On that basis the effectiveness for airflow was between 30 % and 63 % and that for door forces only 8 % to 10 %.<ref name="ABCB-137" /> The data sheets note that smoke may still be held back at lower velocities, and that some people can open doors with forces above 110 N.<ref name="ABCB-137" />

Fazio attributed these low values to systems that were never commissioned, were not maintained, or had faults that were not repaired.<ref name="ABCB-138">Australian Building Codes Board (2020a), Data Sheet C4, p. 138.</ref> The data sheets adopt a typical reliability of 50 % for Australian fire-isolated exit pressurisation systems, with a low value of 30 % and a high value of 60 %. For comparison, they give 70 % for lift shaft pressurisation.<ref name="ABCB-134">Australian Building Codes Board (2020a), Data Sheet C4, p. 134.</ref> They add that most of the data predate the current design and servicing standards, so newer systems may perform better.<ref name="ABCB-134" />

== Limits in tall buildings and mass evacuation ==
The World Trade Center towers in New York illustrate the limits of the method. Between 1976 and 1979 the Port Authority tested a prototype system in one stair of WTC 1, the north tower. The criteria of New York City Local Law 5 were 12.5 Pa across closed stair doors with three doors open, 25 Pa with all doors closed, and a maximum door opening force of 156 N.<ref name="FS-59">Ferreira and Strege (2005), p. 59.</ref> With three doors open the pressure differences were generally low, and with all doors closed the opening forces approached the limit.<ref name="FS-59" /> Sprinklered existing buildings were later exempted, and the towers were never fitted with stair pressurisation.<ref name="FS-60" />

After the bombing of 1993, many stair doors were held open by people leaving the building. This increased the airflow up the stairs caused by the stack effect, and much smoke spread through the stairs.<ref name="FS-59" /> The stairs met the code requirements for exit capacity, but they could not take all occupants quickly, so the doors stayed open.<ref name="FS-59" />

A later computer study found stair pressurisation feasible with the doors closed. It also found that relief venting was needed at the top of each stair section to keep door forces acceptable under stack effect. With several doors open a slightly positive pressure could be kept, but not with all doors open, as in a mass evacuation.<ref name="FS-60" /> A review committee concluded that stair pressurisation would not work in a mass evacuation with more than three stair doors open at once. It also found that the New York code lacked rules for periodic testing and maintenance.<ref name="FS-xxxiv">Ferreira and Strege (2005), p. xxxiv.</ref>

For the events of 11 September 2001, the investigation concluded that stair pressurisation would have been ineffective. The stairs ran through 110 storeys and changed position through transfer corridors, and the full evacuation of the undamaged floors would have lowered the stair pressure below the required value.<ref name="FS-111">Ferreira and Strege (2005), p. 111.</ref> In the impact zone the stairs were damaged and smoke entered them directly. Stair pressurisation is designed to keep smoke out of a stair, and its supply air would have been ineffective in diluting such large amounts of smoke.<ref name="FS-111" /> At the time, the main US building codes required stair pressurisation in new high-rise buildings.<ref name="FS-109">Ferreira and Strege (2005), p. 109.</ref> Full-scale tests in the 1970s had shown such systems to be effective against unsprinklered test fires.<ref name="Evans-71">Evans et al. (2005), p. 71.</ref>

== See also ==
* [[Evacuation lift]]
* Positive pressure ventilation
* [[Network model]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Evans, D. D., Peacock, R. D., Kuligowski, E. D., Dols, W. S., & Grosshandler, W. L. (2005). ''Active fire protection systems'' (NIST NCSTAR 1-4). National Institute of Standards and Technology.
* Ferreira, M. J., & Strege, S. M. (2005). ''Smoke management systems'' (NIST NCSTAR 1-4D). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Smoke Control]]

Sprinkler skipping

2026-11-02T21:34:57Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Sprinkler skipping''' is an unpredictable delay in the operation of sprinklers near a fire, caused by water droplets from sprinklers that have already opened.<ref name="C-239">Cooper (2002b), p. 3-239.</ref> The fire plume carries some of these droplets up to the ceiling, where the hot ceiling jet takes them past the sprinklers that should open next.<ref name="C-239" /> Droplets that strike the heat-sensitive link or glass bulb of such a sprinkler cool it by evaporation, so it heats more slowly and discharges later.<ref name="C-239" /> Smoke vents that open on fusible links suffer from the same effect, which Cooper calls vent skipping.<ref name="C-239" />

Conventional sprinkler design accounts for skipping only empirically, through the experimental basis of its design rules.<ref name="C-239" /> A sprinkler system has many heads and only a few are likely to be skipped, which makes such systems naturally tolerant of the effect.<ref name="C-239" /> Vent systems have far fewer units, so skipping matters more where sprinklers and vents are combined.<ref name="C-239" /> The Fire Dynamics Simulator (FDS) adds a droplet-cooling term to the equation that predicts when a sprinkler link reaches its operating temperature.<ref name="M-107">McGrattan et al. (2026), p. 107.</ref>

== What skipping is ==
In the ''SFPE Handbook of Fire Protection Engineering'', Cooper defines sprinkler skipping as the unpredictable and harmful delay in sprinkler discharge that results when droplets carried by the ceiling jet strike a link or bulb.<ref name="C-239" /> The term therefore describes a delay in operation, not a defect of the sprinkler itself.<ref name="C-239" /> A sprinkler spray consists of droplets of many sizes and velocities, and it varies even between nominally identical [[sprinkler head]]s.<ref name="C-239" /> A full description of such a spray is beyond current technology.<ref name="C-239" />

The droplets of the first sprinklers to open meet the vigorous upward flow of the fire plume.<ref name="C-239" /> Droplets that leave a sprinkler slowly are accelerated by the plume until they move with it, and the larger of them follow the plume well before they evaporate.<ref name="C-239" /> The plume then turns into the ceiling jet, which carries random numbers of droplets past the sprinklers further away.<ref name="C-239" /> This is the same flow that should heat those sprinklers until their links fuse or their bulbs break.<ref name="C-239" />
[[File:fse-sprinkler-skipping-v1.svg|thumb|upright=1.5|alt=Cross-section of a room: a fire plume rises under an operating sprinkler; the ceiling jet carries droplets to a second sprinkler that stays closed.|How skipping arises: small droplets from the first operating sprinkler are carried up by the plume and along the ceiling jet, where they strike and cool the link of the next sprinkler. Based on Cooper (2002b), p. 3-239, and Iqbal and Salley (2004), p. 10-11.]]

Iqbal and Salley explain why small droplets behave in this way. Water from an operating sprinkler must penetrate the rising plume to reach the burning fuel, so its droplets need enough size and velocity.<ref name="N-10-11">Iqbal and Salley (2004), p. 10-11.</ref> Droplets that are too small evaporate or are carried upward by the plume.<ref name="N-10-11" /> For fast-growing fires with a high heat release rate, large drop sprinklers are therefore sometimes needed.<ref name="N-10-11" />

== How a sprinkler is triggered ==
An automatic sprinkler serves two functions: it is a heat detector as well as a nozzle that distributes water.<ref name="F-85">Fleming (2002), p. 4-85.</ref> Experiments show that convective heating by hot gases is the most important factor in its activation.<ref name="N-10-9">Iqbal and Salley (2004), p. 10-9.</ref> The hot gases rise from the fire as a plume, strike the ceiling and spread out as a [[ceiling jet]], a relatively fast and shallow flow driven by buoyancy.<ref name="N-10-9" /> This jet is about 5 to 12 percent as thick as the height of the ceiling above the fire, with its highest temperature and velocity close to the ceiling.<ref name="N-10-9" />

The sensitivity of a sprinkler is expressed by its [[response time index]] (RTI), a concept developed by Factory Mutual Research Corporation.<ref name="N-10-7">Iqbal and Salley (2004), p. 10-7.</ref> The index is measured in plunge tests with a gas flow of constant temperature and velocity, and it assumes that heat conduction to the sprinkler frame is negligible.<ref name="N-10-7" /> It depends on the mass and surface area of the heat-sensitive element, and elements with little mass per unit area respond quickly.<ref name="N-10-7" /> Typical values are 130 (m·s)<sup>1/2</sup> for a standard response link and 34 (m·s)<sup>1/2</sup> for a quick response link.<ref name="N-10-8">Iqbal and Salley (2004), p. 10-8.</ref> Sprinklers with an ordinary temperature rating operate at 57 to 77 °C.<ref name="N-10-6">Iqbal and Salley (2004), p. 10-6.</ref>

For a steady fire, the time needed to heat the element from room temperature to its operating temperature grows with the RTI and falls with the square root of the gas velocity.<ref name="N-10-9" /> It also grows as the operating temperature approaches the temperature of the ceiling jet.<ref name="N-10-9" /> A low RTI and a hot, fast ceiling jet therefore give early operation.<ref name="N-10-9" />

<math display="block">t_\mathrm{act} = \frac{\mathrm{RTI}}{\sqrt{u_\mathrm{jet}}} \ln \left( \frac{T_\mathrm{jet} - T_a}{T_\mathrm{jet} - T_\mathrm{act}} \right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_\mathrm{act}</math> || activation time of the sprinkler || s
|-
| <math>\mathrm{RTI}</math> || response time index of the sprinkler || (m·s)<sup>1/2</sup>
|-
| <math>u_\mathrm{jet}</math> || velocity of the ceiling jet at the sprinkler || m/s
|-
| <math>T_\mathrm{jet}</math> || temperature of the ceiling jet at the sprinkler || °C
|-
| <math>T_a</math> || ambient temperature || °C
|-
| <math>T_\mathrm{act}</math> || operating temperature of the sprinkler || °C
|}

The temperature and velocity of the ceiling jet come from correlations based on large-scale fires of 668 kW to 98,000 kW.<ref name="N-10-10">Iqbal and Salley (2004), p. 10-10.</ref> Separate expressions apply where the plume strikes the ceiling and where the flow has become horizontal further out.<ref name="N-10-10" /> The method assumes a smooth, flat and unconfined ceiling, considers only convective heating and ignores radiation from the flames.<ref name="N-10-12">Iqbal and Salley (2004), p. 10-12.</ref> It does not apply to sprinklers installed far below the ceiling on heat collectors, flat shields above the sprinkler, because most of the heat then rises past them and they may not activate.<ref name="N-10-12" />

=== Worked example ===
Iqbal and Salley consider a steady fire of 1,000 kW, 3.0 m below a ceiling, with a standard response link sprinkler 3.0 m from the axis of the plume.<ref name="N-10-15">Iqbal and Salley (2004), p. 10-15.</ref><ref name="N-10-16">Iqbal and Salley (2004), p. 10-16.</ref> The sprinkler has an RTI of 130 (m·s)<sup>1/2</sup> and an operating temperature of 74 °C.<ref name="N-10-15" /> Their spreadsheet uses an ambient temperature of 20 °C and a convective heat release rate of 700 kW for the jet temperature.<ref name="N-10-17">Iqbal and Salley (2004), pp. 10-17 to 10-18.</ref> The ceiling jet at the sprinkler then reaches 88 °C at 1.35 m/s, and the sprinkler operates after about 2.9 min.<ref name="N-10-17" /><ref name="N-10-16" /> Under the same conditions, a quick response link with an RTI of 34 (m·s)<sup>1/2</sup> would operate after about 45 s.

== How water droplets delay operation ==
The Fire Dynamics Simulator estimates the link temperature from an equation by Heskestad and Bill, with an added term for cooling by water droplets from previously activated sprinklers.<ref name="M-107" /> In words, the link gains heat from the hot gas in proportion to the square root of the gas velocity and loses some heat by conduction to its mount. It loses further heat in proportion to the amount of liquid water carried in the gas.<ref name="M-107" /> The constant of the droplet term comes from experiments by DiMarzo and co-workers and is relatively constant for different types of sprinkler.<ref name="M-107" />

<math display="block">\frac{\mathrm{d}T_l}{\mathrm{d}t} = \frac{\sqrt{|u|}}{\mathrm{RTI}} \left( T_g - T_l \right) - \frac{C}{\mathrm{RTI}} \left( T_l - T_m \right) - \frac{C_2}{\mathrm{RTI}} \left( T_g - T_l \right) \beta \, |u|</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>T_l</math> || temperature of the sprinkler link || °C
|-
| <math>T_g</math> || gas temperature near the link || °C
|-
| <math>T_m</math> || temperature of the sprinkler mount (ambient) || °C
|-
| <math>u</math> || gas velocity at the link || m/s
|-
| <math>C</math> || conduction factor (C-factor) of the sprinkler || (m/s)<sup>1/2</sup>
|-
| <math>\beta</math> || volume fraction of liquid water in the gas || none
|-
| <math>C_2</math> || droplet cooling constant, 2.23 × 10<sup>5</sup> (the source prints the unit as (ms)<sup>−1/2</sup>; the equation is consistent only with (m/s)<sup>−1/2</sup>) || (m/s)<sup>−1/2</sup>
|}

The source prints the unit of the constant as (ms)<sup>−1/2</sup>, but the equation is dimensionally consistent only with (m/s)<sup>−1/2</sup>, which is used here.<ref name="M-107" /> If conduction to the mount is ignored, as in the activation time equation above, it follows from the equation that the droplet term reduces the heating of the link by the fraction <math>C_2 \beta \sqrt{|u|}</math>. When this fraction reaches one, the link stops heating at all, however hot the gas. Because the constant is large, the equation implies that very small amounts of water can slow a link.

=== Worked example, continued ===
At the jet velocity of 1.35 m/s from the example above, the link stops heating at a liquid volume fraction of only 3.9 × 10<sup>−6</sup>.<ref name="M-107" /><ref name="N-10-17" /> That is about 4 cm³ of water in each cubic metre of gas. For an assumed volume fraction of 1 × 10<sup>−6</sup>, the heating slows by 26 percent and operation is delayed from 2.9 to 3.9 min. For an assumed 2 × 10<sup>−6</sup>, the heating falls by 52 percent, and the sprinkler operates only after about 6.0 min.
[[File:fse-sprinkler-skipping-v2.svg|thumb|upright=1.5|alt=Line chart: link temperature rising towards 88 °C; it reaches 74 °C at 174 s without droplets, 234 s and 361 s with droplets.|Calculated temperature of a standard response sprinkler link in a 1,000 kW fire, without droplets and with liquid volume fractions of 1 and 2 millionths in the ceiling jet. Based on Iqbal and Salley (2004), pp. 10-15 to 10-18, and McGrattan et al. (2026), p. 107.]]

The heating term and the droplet term are both divided by the RTI, so it follows from the equation that a quick response link is slowed by the same fraction. At 1 × 10<sup>−6</sup> its operation moves from about 45 s to 61 s. The two volume fractions are assumed values chosen for illustration, not measurements, so the results show how sensitive a link is to wetting rather than what happens at a real sprinkler. The volume of water that reaches a particular link remains unknown in practice.<ref name="C-239" /> The FDS model also ignores thermal radiation to the link.<ref name="M-107" />
[[File:fse-sprinkler-skipping-v3.svg|thumb|upright=1.5|alt=Line chart: activation time against liquid volume fraction, rising steeply towards 3.9 millionths for standard and quick response links.|Calculated activation time against the volume fraction of liquid water in the ceiling jet, for a standard (RTI 130) and a quick response (RTI 34) link in the 1,000 kW example. Based on Iqbal and Salley (2004), pp. 10-15 to 10-18, and McGrattan et al. (2026), p. 107.]]

== Skipping in sprinkler design ==
Sprinklers are designed to control a fire. If the first sprinkler cannot control it, a second one opens and adds cooling, and the process continues until the fire is under control.<ref name="N-10-1">Iqbal and Salley (2004), p. 10-1.</ref> Design areas usually include 10 to 15 sprinklers, while incident data show that more than half of all fires are controlled or extinguished by one or two.<ref name="H-18">Hopkins et al. (2005), p. 18.</ref> Cooper notes that traditional sprinkler design accounts for skipping empirically, through the experimental basis of the design rules.<ref name="C-239" /> The large number of heads in a typical installation, compared with the few sprinklers likely to be skipped, makes sprinkler systems naturally tolerant of the effect.<ref name="C-239" />

Many factors influence how sprinklers respond. They include the temperature rating, spacing and depth of the sprinklers below the ceiling, and the ceiling height.<ref name="N-10-2">Iqbal and Salley (2004), p. 10-2.</ref> Openings, joists and air currents at ceiling level also change the flow of hot gases.<ref name="N-10-2" /> Fleming adds that heat conduction to the sprinkler frame and the distance of the element below the ceiling have a significant effect on response.<ref name="F-85" /> In one of his examples, a computer model shows that quick response sprinklers 0.46 m below a basement ceiling keep a sensitivity comparable to standard sprinklers at the usual maximum of 0.30 m.<ref name="F-85" /> For the chosen fire, the standard sprinkler operates after 200 s and the quick response sprinkler after 172 s.<ref name="F-85" />

An ESFR sprinkler (early suppression fast response sprinkler) is designed to extinguish high-challenge fires, not only to control them.<ref name="N-10-3">Iqbal and Salley (2004), p. 10-3.</ref> It combines a fast response with large droplets and a high droplet velocity.<ref name="N-10-3" /> Its element has an RTI of 50 (m·s)<sup>1/2</sup> or less, against 80 (m·s)<sup>1/2</sup> or more for standard sprinklers.<ref name="N-F-21">Iqbal and Salley (2004), p. F-21.</ref> Large drop ESFR sprinklers protect high-piled storage in wet pipe systems and were developed by Factory Mutual Research Corporation in the late 1970s and early 1980s.<ref name="N-F-21" /> Their design criteria come from full-scale testing, and very strict design and installation rules apply to them.<ref name="F-73">Fleming (2002), p. 4-73.</ref><ref name="N-10-3" />

== Skipping in performance-based analysis ==
Performance-based analyses can use sprinkler activation times to estimate the size of a controlled fire. The data sheets of the Australian Building Codes Board are an example from Australia. They take the maximum heat release rate of a controlled fire as the rate at the activation of the last sprinkler within the assumed area of operation.<ref name="ABCB-74">Australian Building Codes Board (2020a), Data Sheet C2, p. 74.</ref> They assume that the fire activates no more than the design number of sprinklers for the hazard, or the number in the room if that is smaller.<ref name="ABCB-74" /> In a growing fire, any delay in the activation of these sprinklers therefore raises such an estimate.

CFAST (Consolidated Fire and Smoke Transport) is a two-zone fire model.<ref name="P-1">Peacock et al. (2026), p. 1.</ref> Its suppression model records the activation of every sprinkler but ignores the effect of a second sprinkler on the fire.<ref name="P-37">Peacock et al. (2026), p. 37.</ref> Fleming warns that the use of such calculations for sprinkler actuation times has not been fully established.<ref name="F-85" /> He considers them useful mainly on a comparative basis.<ref name="F-85" />

== Vent skipping and combined systems ==
Smoke vents that open when a fusible link melts work on the same principle as sprinklers, so they suffer from the same random delays.<ref name="C-239" /> Cooper calls this vent skipping, and it is a central problem of [[sprinkler-vent interaction]].<ref name="C-239" /> Unlike sprinkler design, the design of automatic vent systems does not account for it.<ref name="C-239" /> Far fewer vents than sprinklers are installed per unit floor area, so Cooper suggests increasing the total vent area of a compartment by a safety factor.<ref name="C-239" />

A more reliable alternative is to open all vents of the fire compartment together, triggered by smoke detectors or by a signal that a sprinkler has discharged.<ref name="C-239" /> One strategy opens every vent of the compartment immediately after the first sprinkler discharges.<ref name="C-239" /> A refined strategy opens at once all vents beyond the first or second ring of sprinklers around the first one.<ref name="C-239" /> The other vents then open when the sprinklers have controlled the fire, and extra vent area compensates for the vents that stay closed at first.<ref name="C-239" />
[[File:fse-sprinkler-skipping-v4.svg|thumb|upright=1.5|alt=Plan of a roof with a sprinkler grid and vents; vents beyond the second ring of sprinklers around the first sprinkler are marked open.|Vent ganging after the first sprinkler discharge: vents beyond the second ring of sprinklers open at once, the vents closer to the fire after the sprinklers have controlled it. Based on Cooper (2002b), p. 3-239.]]

Sprinkler sprays also stir the smoke layer, and this mixing can lead to smoke logging, in which the smoke is mixed through the whole space.<ref name="C-238">Cooper (2002b), p. 3-238.</ref> Cooper identifies six configurations of spray and smoke layer, of which four favour a combined design and two do not.<ref name="C-238" /> Which one occurs depends mainly on the thickness and temperature of the layer and on the momentum, spread angle and droplet size of the spray.<ref name="C-238" /> Shortly after rapid-response sprinklers discharge, the layer is still thin and not too hot, and smoke logging is then never observed.<ref name="C-238" /><ref name="C-239" />

== Limits and practical points ==
Skipping cannot be predicted for a particular sprinkler. The droplet paths depend on the fire plume, which varies with the location and growth of the fire.<ref name="C-239" /> Even a perfect knowledge of the spray as it leaves the sprinkler would therefore be of little use in practice.<ref name="C-239" /> Activation models add their own simplifications: the method of Iqbal and Salley treats the element as a single lumped mass and ignores radiation.<ref name="N-10-12" />

Three practical points follow. First, a skipped sprinkler has not failed: Cooper describes a delay in discharge caused by cooling, not a fault in the sprinkler.<ref name="C-239" /> Second, quick response sprinklers are not protected against skipping. As derived above from the link equation of FDS, droplets slow a quick response link by the same fraction as a standard link when conduction to the mount is ignored.<ref name="M-107" /> Third, where the first sprinkler cannot control a fire, control depends on further sprinklers opening in turn, and these are the ones exposed to droplets from the first.<ref name="N-10-1" /><ref name="C-239" />

== See also ==
* [[Wet pipe sprinkler system]]
* [[Sprinkler design density]]
* [[Hydraulic calculation]]
* [[Critical water application rate]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Cooper, L. Y. (2002b). Smoke and heat venting. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-219–3-242). National Fire Protection Association; Society of Fire Protection Engineers.
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association; Society of Fire Protection Engineers.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* McGrattan, K., Hostikka, S., Floyd, J., McDermott, R., Vanella, M., Mueller, E., & Paul, C. (2026). ''Fire Dynamics Simulator technical reference guide: Vol. 1. Mathematical model'' (6th ed., NIST Special Publication 1018-1). National Institute of Standards and Technology. https://doi.org/10.6028/NIST.SP.1018
* Peacock, R. D., McGrattan, K. B., Forney, G. P., & Reneke, P. A. (2026). ''CFAST – Consolidated Fire and Smoke Transport: Vol. 1. Technical reference guide'' (Version 7, NIST Technical Note 1889v1). National Institute of Standards and Technology. https://doi.org/10.6028/NIST.TN.1889v1

[[Category:Fire Suppression]]

Smouldering

2026-11-02T21:34:54Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Smouldering''' is slow, relatively low-temperature and flameless [[Combustion]] sustained by heat released when oxygen reacts directly with a fuel surface. The reaction occurs on the material itself, unlike a flame in which gaseous fuel reacts. It commonly occurs in porous, char-forming materials and can spread within a fuel bed with little external sign. This can significantly delay recognition.<ref name="Ohlemiller-2-200">Ohlemiller (2002), p. 2-200.</ref>

The process presents two principal fire hazards. It can convert a relatively large proportion of fuel into toxic compounds, although more slowly than many flaming fires. It can also provide a pathway to flaming from an initial heat source too weak to ignite a flame directly. These hazards can develop over long periods and in concealed locations.<ref name="Ohlemiller-2-200" />

Smouldering should not be confused with smoke produced by forced thermal decomposition. [[Pyrolysis]] can gasify an organic material with little or no oxidation, whereas smouldering requires surface oxidation. The presence of smoke alone therefore does not establish which process is occurring. Assessment has to address hidden reaction zones, accumulated exposure, fuel-bed geometry and possible later flaming, rather than relying on visible flame or one universal spread rate for every material and airflow condition.<ref name="Ohlemiller-2-200" /><ref name="Ohlemiller-2-209">Ohlemiller (2002), p. 2-209.</ref>

== Conditions that sustain smouldering ==

Finely divided fuel provides a large surface area per unit mass, which facilitates oxygen attack. A permeable aggregate allows oxygen to reach the reaction zone by diffusion and convection. If the aggregate also resists heat loss, the limited energy released by surface oxidation can maintain the reaction.<ref name="Ohlemiller-2-200" />

Char formation is central for many cellulosic fuels. Char is typically richer in carbon and has greater surface area per unit mass than the original material. Oxygen can react with this porous residue to produce mainly carbon monoxide and carbon dioxide, supplying much of the heat for sustained smoulder propagation.<ref name="Ohlemiller-2-200" />

A burning cigarette combines several favourable features: finely divided fuel, a permeable structure and thermal insulation. It can also initiate smouldering in upholstery and bedding. These composite products involve both fabric and filling, so their combined response can differ from either material tested alone.<ref name="Ohlemiller-2-200" /><ref name="Ohlemiller-2-206">Ohlemiller (2002), p. 2-206.</ref>

The conditions needed to initiate smouldering are not necessarily sufficient for it to spread away from the initiation region. Continued propagation depends on heat generation, oxygen transport and heat transfer to adjacent fuel. The factors controlling a later transition to flaming are different again.<ref name="Ohlemiller-2-200" />

[[Self-heating]] can contribute to the initial temperature rise when oxidation within a material releases energy faster than it is lost. Fuel size and shape influence this balance by changing heat retention. Self-heating describes energy accumulation, while smouldering describes the sustained surface-combustion process that can follow under suitable conditions.<ref name="IFEG-3.3-2">Australian Building Codes Board et al. (2005), p. 3.3-2.</ref>

== Propagation and oxygen supply ==

After initiation, the smouldering zone often consumes oxygen as quickly as it reaches the reaction region. Propagation is then strongly controlled by oxygen transport. Thick fuel layers slow oxygen delivery but also retain heat, allowing very slow reaction zones to persist.<ref name="Ohlemiller-2-201">Ohlemiller (2002), p. 2-201.</ref>

In reverse smouldering, oxygen moves opposite to the direction of front propagation. It can reach the reaction zone by diffusion or by forced airflow through unburnt fuel. In forward smouldering, oxygen and the front move in the same general direction. These relative directions change preheating, heat retention and product composition.<ref name="Ohlemiller-2-201" /><ref name="Ohlemiller-2-203">Ohlemiller (2002), p. 2-203.</ref>
[[File:fse-smouldering-v1.svg|thumb|upright=1.5|alt=Two fuel beds with opposite and matching oxygen-flow and front-direction arrows.|Forward and reverse smouldering differ in relative oxygen-flow direction. Based on Ohlemiller (2002), pp. 2-201–2-203.]]

Ohlemiller describes sawdust experiments in which smouldering took about two weeks to move upwards through a layer 1 m deep. In another set of reverse-smoulder experiments, velocities were of the order of 0.0001 m/s across several fuels under the stated airflow conditions. These results illustrate possible timescales but do not provide a universal smouldering speed.<ref name="Ohlemiller-2-201" /><ref name="Ohlemiller-2-202">Ohlemiller (2002), p. 2-202.</ref>

The diffusion-controlled sawdust case has a useful scaling relation. As the front advances through unburnt fuel towards the surface, the distance through which oxygen must travel changes. Ohlemiller reports that the penetration time is approximately proportional to the square of the layer depth. The proportionality constant must be obtained from a measurement on the fuel configuration being considered:<ref name="Ohlemiller-2-202" />

<math display="block">t_L=A L^2</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_L</math> || Time for the front to penetrate the fuel layer || s
|-
| <math>L</math> || Layer depth || m
|-
| <math>A</math> || Empirical coefficient fitted to the same fuel and oxygen-supply conditions || s/m²
|}

For an illustrative scaling calculation, represent the reported two weeks at 1 m as 14 days. Keeping the same coefficient, a layer half as deep gives one quarter of that penetration time: 3.5 days. The result follows from the source's square-law model, rather than from a separate test of that shallower layer:<ref name="Ohlemiller-2-201" /><ref name="Ohlemiller-2-202" />

<math display="block">t_{0.5\,\mathrm{m}}=14\left(\frac{0.5}{1.0}\right)^2=3.5\ \mathrm{days}</math>

This estimate applies to approximately one-dimensional, diffusion-dominated propagation under comparable conditions. A non-uniform deposit can contain easier airflow paths, and buoyancy can introduce convection through the fuel. The fitted constant and square-law assumption cannot then be transferred automatically. The calculation illustrates the importance of oxygen transport and depth; it does not predict an incident's duration or extinction time.<ref name="Ohlemiller-2-202" />

Deep reaction zones can remain hidden until they approach a free surface. Oxygen access increases near that surface, while buoyancy and local airflow change heat and mass transfer. A fire can consequently show little sign internally before becoming more obvious at the exterior.<ref name="Ohlemiller-2-202" />

Real fuel beds often have two- or three-dimensional temperature and composition gradients. The upper part of a horizontal layer usually receives oxygen more readily than deeper material, producing an inclined reaction zone. Simple one-dimensional descriptions therefore apply only to selected configurations.<ref name="Ohlemiller-2-204">Ohlemiller (2002), p. 2-204.</ref>

== Heat loss, airflow and fuel-bed size ==

A self-sustaining reaction requires heat generation to keep pace with heat loss. Thin layers have a large surface relative to their volume and can lose energy too rapidly. Below a minimum thickness, smouldering therefore stops. That thickness depends on fuel type, particle size, bulk density and oxygen supply.<ref name="Ohlemiller-2-205">Ohlemiller (2002), p. 2-205.</ref>
[[File:fse-smouldering-v2.svg|thumb|upright=1.5|alt=Thin layer losing heat and thick layer retaining heat around a slow reaction zone.|Fuel-bed thickness affects the heat balance for sustained smouldering. Based on Ohlemiller (2002), pp. 2-201–2-205.]]

Airflow can either strengthen or weaken the process. Increased oxygen supply can raise heat release and accelerate spread, but sufficiently strong flow can add cooling and disrupt the reaction zone. The response depends on flow direction, fuel-bed geometry and whether propagation is forward or reverse.<ref name="Ohlemiller-2-205" />

Fuel particle size affects more than chemical surface area. It changes permeability, insulation and the minimum layer depth needed for sustained spread. In the sawdust and cork experiments described by Ohlemiller, particle size had less influence on velocity than flow configuration, but it strongly affected limiting thickness.<ref name="Ohlemiller-2-205" />

Scale can also allow smouldering to pass beneath an intended barrier. In laboratory studies of deep fuel beds, heated and partly decomposed material below an initial reaction zone supported a second wave moving in the opposite direction. Ohlemiller warns that inert covering layers may slow rather than stop such fires.<ref name="Ohlemiller-2-206" />

== Smoke, carbon monoxide and detection ==

Smouldering can produce substantial [[Carbon monoxide]] relative to the fuel converted. The yield and concentration vary with fuel and airflow, so a single value cannot represent all smouldering fires. The slow release rate does not remove the hazard because exposure can accumulate over a long period in an enclosure.<ref name="Ohlemiller-2-200" /><ref name="Ohlemiller-2-202" />

In one flexible-polyurethane-foam experiment, carbon monoxide comprised 6% to 7% of evolved gases on a molar basis at an imposed air velocity of 0.0015 m/s. Cellulosic insulation in another test varied from about 10% to 22% as airflow changed. These are configuration-specific measurements, not safe-exposure criteria or universal material yields.<ref name="Ohlemiller-2-202" />

The aerosol from smouldering differs from sooty flaming smoke. For the cellulosic-insulation source studied by Ohlemiller, the mass mean particle size was 2 to 3 micrometres, larger than cigarette smoke and much larger than particles from the flaming source used for comparison. The fuel bed also filtered part of the aerosol before it escaped.<ref name="Ohlemiller-2-203" />

This behaviour affects [[Smoke detector]] response. Ohlemiller links the large aerosol particles with relatively poor sensitivity of ionisation detectors to the realistic smouldering source examined. Deep smouldering may also remain undetectable until it nears an exposed surface because the fuel bed traps products.<ref name="Ohlemiller-2-203" />

The weak heat source presents a further detection problem. Reverse-smoulder sources discussed in the handbook produced only a few hundredths of a kilowatt in the stated configurations. Their buoyant plumes might not reach the ceiling of a room, limiting the transport of combustion products to ceiling-mounted devices.<ref name="Ohlemiller-2-203" />

== Transition to flaming ==

[[Smouldering-to-flaming transition]] requires a flammable mixture of pyrolysis gases and air and sufficient heat to ignite it at the same place and time. Increased oxygen supply, larger scale and reduced heat losses can promote both conditions. The transition is therefore possible but not inevitable.<ref name="Ohlemiller-2-208">Ohlemiller (2002), p. 2-208.</ref>

Forward smouldering can be particularly favourable in some fuel beds because heat transfer intensifies the reaction near its leading edge. Cavities formed there can collect fuel gases and stabilise initial flames. Different materials and configurations produce other mechanisms, so there is no single transition temperature or airflow for all smouldering fires.<ref name="Ohlemiller-2-208" />

Experiments with upholstered furniture demonstrate the wide time range. In a survey cited by Ohlemiller, about two thirds of tested chairs and beds made the transition, with reported times from 22 to 306 minutes after smouldering began. These results describe the tested objects and should not be used as a countdown for an actual incident.<ref name="Ohlemiller-2-208" />
[[File:fse-smouldering-v3.svg|thumb|upright=1.5|alt=Observed range from 22 to 306 minutes for tested chairs and beds.|Reported smouldering-to-flaming times in a furniture-test survey. Based on Ohlemiller (2002), p. 2-208.]]

Neighbouring materials can change the outcome. Retardants that prevented transition in an isolated cellulosic insulation layer became less effective when that layer touched unretarded wood. Heat from the smouldering zone could ignite the adjacent material even when the original fuel did not flame.<ref name="Ohlemiller-2-208" />

== Detection, extinction and reignition ==

Effective extinction requires more than suppressing visible glow. Oxygen exclusion can stop reaction temporarily, but oxygen readmission can cause reignition while the fuel remains hot. Ohlemiller states that oxygen removal may have to continue until cooling is sufficient, and that obtaining this cooling can be exceptionally difficult in a large porous bed.<ref name="Ohlemiller-2-206" />

Extinguishing agents can also miss concealed reaction zones. In grain silos, higher-permeability channels can allow an agent to bypass significant smouldering regions. Emptying before complete extinction introduces another hazard because combustible dust can become dispersed. The source treats this as a practical configuration problem rather than a simple choice of agent.<ref name="Ohlemiller-2-207">Ohlemiller (2002), p. 2-207.</ref>

Assessment after an intervention therefore includes the temperature and location of remaining fuel, not only the atmosphere above it. A deep bed can retain reactive material for long periods. Restored airflow can then change both oxygen supply and heat loss, with outcomes that depend on the new conditions.<ref name="Ohlemiller-2-205" /><ref name="Ohlemiller-2-206" />

== Buildings and outdoor fuel beds ==

Upholstery and bedding combine fabrics, fillings and crevices, producing behaviour that a single-material specimen may not reproduce. A cellulosic fabric can supply heat to polyurethane foam while both compete for oxygen. Ohlemiller reports that this combination can smoulder over a wider range of conditions than the foam alone.<ref name="Ohlemiller-2-206" />

Closed-room mattress experiments show why slow development still requires attention. In two of five cigarette-initiated cotton-mattress tests described in the handbook, flaming followed smouldering after 65 to 80 minutes. In other bedding and upholstery tests, flaming usually required two to three hours of prior smouldering. These observations belong to the tested products and rooms, and are not general predictions.<ref name="Ohlemiller-2-206" />

Solid wood presents a different configuration from loose fibres. Its lower permeability limits oxygen access to the decomposition region, and a single layer may lose too much heat to sustain smouldering without additional exposure. Ohlemiller reports a requirement of about 10 kW/m² of external heat input in the cited solid-wood configuration. Other wood forms and arrangements can behave differently.<ref name="Ohlemiller-2-204" />

Peat and organic material on a forest floor can retain smouldering after a flaming front has passed. The process is spatially irregular and can later support renewed flaming. This outdoor example involves a porous fuel bed with oxygen entering largely from above, rather than a manufactured uniform specimen.<ref name="Ohlemiller-2-206" />

== Engineering use and uncertainty ==

Design-fire descriptions sometimes include a smouldering phase. The 2005 International Fire Engineering Guidelines distinguish smouldering fires that remain flameless from those that later become flaming. The transition remains difficult to predict from fuel identity alone because airflow, geometry and heat losses affect its onset.<ref name="IFEG-1.2-29">Australian Building Codes Board et al. (2005), p. 1.2-29.</ref><ref name="Ohlemiller-2-208" />

The same older guidelines use a notional maximum heat release rate below 5 kW for an illustrated smouldering design fire. This is a modelling choice in that guidance, not a universal physical maximum. Experimental source strengths and spread rates need to be tied to the fuel bed and airflow from which they were obtained.<ref name="IFEG-1.2-29" /><ref name="Ohlemiller-2-203" />

Ohlemiller concludes that quantitative guidance for realistic smoulder propagation, detection, toxic production and transition remains limited. Experimental results can support closely analogous situations, but dissimilar materials and geometries require caution. Fuel chemistry alone is not enough to predict spread when oxygen transport and heat retention dominate.<ref name="Ohlemiller-2-209" />

Toxic assessment needs the material and combustion mode as well as carbon monoxide. The 2005 guidelines identify carbon monoxide as the principal toxic species for many fires, but caution that atypical materials require broader analysis. They specifically note that smouldering polyurethane foam can yield significant hydrogen cyanide.<ref name="IFEG-2.4-12">Australian Building Codes Board et al. (2005), p. 2.4-12.</ref>

Source terms should therefore be based on appropriate experimental data for the combustible and the smouldering condition. A flaming-fire yield cannot be substituted automatically, and a slow source can continue for much longer than the test used to characterise it. Both yield and duration influence the exposure calculated for an enclosure.<ref name="IFEG-2.4-12" /><ref name="Ohlemiller-2-209" />

== See also ==

* [[Fire development stages]]
* [[Firebrands]]
* [[Hot work]]
* Mass timber
* [[Timber in fire]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Ohlemiller, T. J. (2002). Smoldering combustion. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-200–2-210). National Fire Protection Association.

[[Category:Combustion]]

SFPE

2026-11-02T21:34:50Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''SFPE''', the Society of Fire Protection Engineers, is an organisation in the United States that represents fire protection engineers.<ref name="NIST-201">National Institute of Standards and Technology (2005), p. 201.</ref> It is based in Bethesda, Maryland.<ref name="DiNenno-iii">DiNenno et al. (2002), pp. iii–iv.</ref> The International Fire Engineering Guidelines (IFEG, 2005) list SFPE among the organisations that publish and provide knowledge for fire engineering.<ref name="IFEG-US-05">National Research Council of Canada et al. (2005), Part 0 (United States), pp. 0.5-6–0.5-10.</ref> Its publications include the ''SFPE Handbook of Fire Protection Engineering'', engineering guides on subjects such as performance-based design, and engineering standards such as one on calculating fire exposures to structures.<ref name="DiNenno-iii" /><ref name="Notarianni-42">Notarianni (2002), p. 5-42.</ref><ref name="ABCB-B1">Australian Building Codes Board (2020a), Data Sheet B1, p. 12.</ref>

SFPE has also developed a Canon of Ethics for Fire Protection Engineers, to which the IFEG refer for professional issues outside their own scope.<ref name="IFEG-US-01">National Research Council of Canada et al. (2005), Part 0 (United States), pp. 0.1-1–0.1-4.</ref> Its publications are used well beyond the United States. In New Zealand, Verification Method C/VM2 (second edition, 2025) refers to the SFPE Handbook for evacuation calculations.<ref name="MBIE-26">Ministry of Business, Innovation and Employment (2025b), pp. 26, 33.</ref> In Australia, the 2020 handbook for the Fire Safety Verification Method cites SFPE engineering standards.<ref name="ABCB-H">Australian Building Codes Board (2020b), pp. 109, 113.</ref> SFPE is a separate body from the National Fire Protection Association, which publishes the SFPE Handbook and develops codes and standards of its own.<ref name="DiNenno-iii" /><ref name="Iqbal-E1">Iqbal and Salley (2004), p. E-1.</ref>

== Fire protection engineering and the society ==

SFPE describes fire protection engineering as the application of science and engineering principles to protect people and their environment from destructive fire.<ref name="IFEG-US-03">National Research Council of Canada et al. (2005), Part 0 (United States), pp. 0.3-1–0.3-2.</ref> In this description the field includes the analysis of fire hazards. It also covers reducing fire damage through the design, construction, arrangement and use of buildings, materials, structures, industrial processes and transport systems.<ref name="IFEG-US-03" /> A third part is the design, installation and maintenance of fire detection, suppression and communication systems, and a fourth is investigation and analysis after a fire.<ref name="IFEG-US-03" /> In the SFPE wording, a fire protection engineer knows through education, training and experience how fires start and spread, and how they can be detected, controlled or extinguished.<ref name="IFEG-US-03" /> Such an engineer can also anticipate how materials, structures and processes behave in fire.<ref name="IFEG-US-03" />

The term "fire protection engineer" is common in the United States, but the IFEG mainly use "fire engineer", which they consider a better international description of the engineer who applies their design methods.<ref name="IFEG-US-01" /> The guidelines take their definition of [[Fire safety engineering|fire engineering]] from the International Organization for Standardization (ISO).<ref name="IFEG-US-03" /> In it, fire engineering is the application of engineering principles, rules and expert judgement based on a scientific appreciation of fire, its effects and the behaviour of people.<ref name="IFEG-US-03" /> Its aims include saving life, protecting property, preserving the environment and heritage, quantifying the hazards and risk of fire, and evaluating the measures needed to limit its consequences to prescribed levels.<ref name="IFEG-US-03" />

NIST, the US National Institute of Standards and Technology, counts SFPE among the organisations that represent engineers, such as the National Society of Professional Engineers.<ref name="NIST-201" /> It distinguishes these groups from the organisations that develop codes and standards, and notes that they also provide training, especially where training affects how code provisions are applied in practice.<ref name="NIST-201" /> SFPE also carries out periodic surveys of the industry to understand what roles fire protection engineers play.<ref name="IFEG-US-01" /> The IFEG list two SFPE periodicals, the ''Journal of Fire Protection Engineering'' and the ''SFPE Journal'', among the journals useful to fire engineering professionals.<ref name="IFEG-US-05" /> In New Zealand, the IFEG note that fire engineers may be approved for full membership of bodies such as SFPE once they have shown appropriate qualifications and experience. Membership of an institution does not, however, necessarily prove the competence of an individual.<ref name="IFEG-NZ-04">National Research Council of Canada et al. (2005), Part 0 (New Zealand), p. 0.4-2.</ref>

== The SFPE Handbook ==

The third edition (2002) of the ''SFPE Handbook of Fire Protection Engineering'' is copyrighted by SFPE and published by the [[NFPA|National Fire Protection Association]] (NFPA) in Quincy, Massachusetts.<ref name="DiNenno-iii" /> Philip J. DiNenno was editor-in-chief, with six section editors from consultancies, a university, NIST, NFPA and The Fire Safety Institute.<ref name="DiNenno-iii" /> Its 72 chapters, each written by named authors, are grouped into five sections: Fundamentals, Fire Dynamics, Hazard Calculations, Design Calculations and Fire Risk Analysis.<ref name="DiNenno-v">DiNenno et al. (2002), pp. v–viii.</ref> Appendices then give data such as conversion factors, thermophysical properties of materials and fuel properties.<ref name="DiNenno-v" />
[[File:fse-sfpe-v1.svg|thumb|upright=1.5|alt=Fundamentals and hazard methods support design and risk analysis in the handbook.|The handbook combines specialist technical subjects. Based on DiNenno et al. (2002), pp. iii–vii.]]

In the preface, DiNenno describes the handbook as a contribution towards documenting and integrating the theoretical and applied bases of fire safety engineering.<ref name="DiNenno-ix">DiNenno et al. (2002), pp. ix–x.</ref> According to the preface, the rapid assimilation of performance-based design had underscored its importance.<ref name="DiNenno-ix" /> The third edition added chapters on heat fluxes from fires to surfaces, water mist systems and computer field modelling, and more material on risk assessment.<ref name="DiNenno-ix" /> Part of the new material on radiation heat transfer came from an SFPE technical committee working towards consensus on engineering methods.<ref name="DiNenno-ix" /> The editors expected future editions to include the work of several engineering consensus groups aiming at a consensus-based standard of care in fire safety engineering.<ref name="DiNenno-ix" />

Other documents draw on the handbook as well. NUREG-1805, a 2004 report for the US Nuclear Regulatory Commission, derived the technical basis of its Fire Dynamics Tools primarily from the SFPE Handbook and the NFPA Fire Protection Handbook.<ref name="Iqbal-xxxvii">Iqbal and Salley (2004), p. xxxvii.</ref> The IFEG name the SFPE Handbook among the textbooks that give methods for smoke production, smoke layer height, upper layer temperature and smoke movement.<ref name="IFEG-2-5">National Research Council of Canada et al. (2005), p. 2.5-2.</ref> In New Zealand, C/VM2 (2025) refers readers to Section 3, Chapter 13 of the fourth edition (2008) for more information on calculating the required safe egress time and on egress calculation procedures.<ref name="MBIE-26" /><ref name="MBIE-61">Ministry of Business, Innovation and Employment (2025b), p. 61.</ref>

The textbook ''Introduction to Fire Safety Engineering'' also takes values from the handbook. Its walking speeds for different groups, for example, range from 0.58 m/s for people with a walking frame to 1.25 m/s for healthy, unimpeded people.<ref name="VR-7.4">Van Rossum (2027), §7.4.</ref> From the same source it takes the smoke potential, which expresses how much light the smoke from one kilogram of burnt material blocks.<ref name="VR-6.4">Van Rossum (2027), §6.4.</ref> In fires this is usually 3,300 m²/kg, a generic average for burning building and furnishing materials.<ref name="VR-6.4" />

== Engineering guides and standards ==

Besides the handbook, SFPE publishes engineering guides that evaluate calculation methods for particular problems. In the handbook chapter on large hydrocarbon fires, Beyler explains that the methods for radiation from pool fires were evaluated and included in an SFPE engineering guide.<ref name="Beyler-272">Beyler (2002a), p. 3-272.</ref> In that guide the methods are described in full, their assumptions are identified and their limits of applicability are assessed.<ref name="Beyler-272" /> The guide also lists available input data and compares the accuracy of the methods with experimental data.<ref name="Beyler-272" /> These [[Hand calculations|hand calculations]] range from very crude initial hazard assessments to detailed methods that need more engineering effort.<ref name="Beyler-272" /> Where a simple method shows that a separation distance is far larger than needed for safety, a more rigorous analysis may not be necessary.<ref name="Beyler-272" />

A related SFPE guide of 2000 treats skin burns from thermal radiation in more detail than the handbook.<ref name="Beyler-308">Beyler (2002a), pp. 3-308, 3-313.</ref> In New Zealand, C/VM2 (2025) points to that guide where occupants escape past more than one window, because the time-dependent build-up of radiation must then be calculated.<ref name="MBIE-34">Ministry of Business, Innovation and Employment (2025b), pp. 34–35.</ref> For computer fire models, SFPE published Guidelines for Substantiating a Fire Model for a Given Application (2011). A 2016 validation study for the NRC names them as a useful reference next to the ASTM standard that the study follows.<ref name="Stroup">Stroup et al. (2016), p. 1-3.</ref>

Such guidance does not make a calculation tool self-validating. NUREG-1805 asks first-time users to read the whole report before an analysis and to apply its spreadsheet tools only within the limits of their validity.<ref name="Iqbal-xxxix">Iqbal and Salley (2004), p. xxxix.</ref> The IFEG add that even an expensive and highly sophisticated computer model does not guarantee accurate results, so all model output must be reviewed and verified.<ref name="IFEG-2-8">National Research Council of Canada et al. (2005), p. 2.8-4.</ref> They also describe a hydraulic method for evacuation from the SFPE Handbook, which assumes among other things that all occupants start to leave at the same time.<ref name="IFEG-2-8" />
[[File:fse-sfpe-v2.svg|thumb|upright=1.5|alt=Scenario inputs pass through a bounded hand calculation and independent plausibility review.|Hand calculations require valid inputs and critical review. Based on Iqbal and Salley (2004), p. xxxix and National Research Council of Canada et al. (2005), p. 2.8-4.]]

SFPE also issues engineering standards. The Australian data sheets for the Fire Safety Verification Method (2020) cite SFPE S.01 (2011), a standard on calculating fire exposures to structures, as a standardised approach to predicting flashover.<ref name="ABCB-B1" /> For fire models, it gives as criteria for flashover an upper layer temperature above 600 °C or a heat flux to the floor above 20 kW/m².<ref name="ABCB-B1" /> The accompanying handbook lists S.01 among the methods for fully developed fires.<ref name="ABCB-H" /> It names SFPE S.02 (2015) as a source of examples for checking heat transfer models, a process known as validation and verification.<ref name="ABCB-H" /> In the United States, NIST recommended in 2005 that standards committees draw on the ASCE/SFPE 29 standard for fire resistance design when they address progressive collapse under fire conditions.<ref name="NIST-206">National Institute of Standards and Technology (2005), pp. 206, 212.</ref>

== Performance-based design ==

For [[Performance-based design|performance-based design]], SFPE published its Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings in 2000.<ref name="IFEG-US-01" /> The guide is meant for both design engineers and approving authorities.<ref name="Notarianni-42" /> Its stated intent is to help them determine and document that agreed levels of fire safety are achieved for a particular project.<ref name="Notarianni-42" /> Its steps are to define the project scope, identify goals, define objectives, develop performance criteria, develop fire scenarios, develop and evaluate candidate designs, and select and document the final design.<ref name="Notarianni-42" /> The documentation has four parts: a fire protection engineering design brief, a performance design report, detailed specifications and drawings, and a building operations and maintenance manual.<ref name="Notarianni-60">Notarianni (2002), p. 5-60.</ref>

The guide also gives a method for quantifying the fire risk from several fire scenarios. The total risk is the sum, over all fire scenarios considered, of the loss in each scenario multiplied by how often that scenario occurs.<ref name="Meacham">Meacham (2002), p. 5-161.</ref> Watts and Hall (2002) note that SFPE addresses the basics of fire risk analysis in its publications on performance-based design, and that SFPE task groups were adding further detail.<ref name="WattsHall">Watts and Hall (2002), pp. 5-6–5-7.</ref>

Other guidance builds on this work. The IFEG drew on the 2000 SFPE guide and on a Code Officials Guide to Performance-Based Design Review that SFPE produced with the International Code Council in 2004.<ref name="IFEG-US-01" /> For the United States, the IFEG call both documents good resources for deriving goals and objectives where no performance code has been adopted.<ref name="IFEG-US-02">National Research Council of Canada et al. (2005), Part 0 (United States), p. 0.2-9.</ref> They also mention SFPE work towards a consistent method for determining design fires.<ref name="IFEG-US-02" /> In addition, the IFEG recommend both guides as a benchmark for third-party reviewers of fire engineering reports.<ref name="IFEG-US-03-9">National Research Council of Canada et al. (2005), Part 0 (United States), pp. 0.3-8–0.3-9.</ref> In New Zealand, C/VM2 (2025) lists SFPE, with the IFEG and British Standards, among the publishers of internationally recognised documents on the fire engineering brief process.<ref name="MBIE-7">Ministry of Business, Innovation and Employment (2025b), p. 7.</ref>

== Uncertainty and limits ==

SFPE guidance does not remove uncertainty from performance-based design. Notarianni (2002) describes a review of the design process in the SFPE guide and of several case studies of real designs.<ref name="Notarianni-42" /> The review found seven barriers to documenting that agreed levels of fire safety had been reached.<ref name="Notarianni-42" /> The first two are performance criteria that are not established or agreed, and an unspecified process for choosing design fires.<ref name="Notarianni-43">Notarianni (2002), pp. 5-43–5-44.</ref> Others are assumptions about human behaviour, poorly documented limits of fire models and model outputs given as single values.<ref name="Notarianni-43" /> The last two are engineers working beyond their expertise and the lack of a standard way to include the reliability of fire protection systems.<ref name="Notarianni-43" />

Each barrier can lead to switchover, in which reasonable changes in inputs, scenarios or parameters change the decision on whether a design is acceptable.<ref name="Notarianni-42" /> In one example, two engineers who had both followed the current design guidelines for real buildings chose very different performance criteria.<ref name="Notarianni-43" /> Because model predictions are compared with such criteria, the same design can pass under one set and fail under another.<ref name="Notarianni-43" />
[[File:fse-sfpe-v3.svg|thumb|upright=1.5|alt=Changed criteria, scenarios, behaviour and model assumptions lead to different acceptability outcomes.|Uncertainty can change a design from acceptable to unacceptable. Based on Notarianni (2002), pp. 5-43–5-44.]]

Human behaviour is a particular source of uncertainty. Proulx (2002) warns that research has shown some traditional assumptions about behaviour in fires to be wrong.<ref name="Proulx">Proulx (2002), pp. 3-342–3-343.</ref> She also cites the observation that the hydraulic model of evacuation assumes occupants who are alert, able-bodied and ambulatory, and deals only with movement, not with the time people take to start.<ref name="Proulx" /> Notarianni adds that one internationally used egress model assumes that all occupants are readily mobile and leave as soon as they hear an alarm.<ref name="Notarianni-43" /> Experience shows that this is often not the case.<ref name="Notarianni-43" />

The handbook also has practical limits. Some of its equations, tables and charts keep US customary units because their data were originally developed in those units.<ref name="DiNenno-ix" /> Its notice states that neither the publisher nor the authors guarantee the accuracy or completeness of the contents, and that they supply information and opinion rather than engineering services.<ref name="DiNenno-iii" /> Where such services are needed, the notice advises seeking the help of an appropriate professional.<ref name="DiNenno-iii" />

== Ethics and professional practice ==

One of SFPE's contributions to [[Ethics in fire safety engineering|ethics in fire safety engineering]] is its Canon of Ethics for Fire Protection Engineers, which the IFEG quote in part.<ref name="IFEG-US-04">National Research Council of Canada et al. (2005), Part 0 (United States), p. 0.4-2.</ref> Its preamble calls fire protection engineering an important learned profession whose work has a direct and vital impact on the quality of life of all people.<ref name="IFEG-US-04" /> The services of fire protection engineers therefore require honesty, impartiality, fairness and equity, and must be dedicated to protecting and enhancing public safety, health and welfare.<ref name="IFEG-US-04" /> Engineers are expected to maintain and constantly improve their competence and to act with balanced regard for the interests of the public, clients, employers, colleagues and the profession.<ref name="IFEG-US-04" />

Three fundamental principles follow from the preamble. Fire protection engineers use their knowledge and skill for the enhancement of human welfare.<ref name="IFEG-US-04" /> They are honest and impartial and serve the public, their employers and their clients with fidelity.<ref name="IFEG-US-04" /> They also strive to increase the competence and prestige of their profession.<ref name="IFEG-US-04" /> The IFEG state that the canon deals with professional issues outside their own scope and should be consulted as appropriate.<ref name="IFEG-US-01" />

SFPE also has a role in education. After its World Trade Center investigation, NIST named SFPE in 2005 among the organisations affected by its recommendation to develop continuing education for fire protection engineers, structural engineers and architects.<ref name="NIST-222">National Institute of Standards and Technology (2005), pp. 222–223.</ref> It also named SFPE for training material on computational fire dynamics and thermostructural analysis tools.<ref name="NIST-222" /> For NIST's report on the active fire protection systems of the World Trade Center, an SFPE engineering programmes manager supplied introductory and summary material.<ref name="Evans">Evans et al. (2005), p. xxvii.</ref> Its purpose was to give all readers a common basis for understanding the results.<ref name="Evans" />

== Relationship with NFPA and with regulation ==

SFPE and NFPA are separate organisations with different roles. NFPA develops and publishes consensus codes and standards, whereas NIST groups SFPE with the organisations that represent engineers.<ref name="Iqbal-E1" /><ref name="NIST-201" /> The IFEG list the two as distinct bodies that publish fire engineering knowledge.<ref name="IFEG-US-05" /> They work together on publications: SFPE holds the copyright of the SFPE Handbook and NFPA publishes it.<ref name="DiNenno-iii" /> NIST also named both in 2005 for work on standard methods for multi-floor design fire scenarios.<ref name="NIST-206" />

SFPE guides and standards are not regulations in themselves. A NIST report on the World Trade Center explains that trade associations and professional societies develop practices that may guide how buildings are designed and built.<ref name="Lew">Lew et al. (2005), p. 142.</ref> Such practices are not strictly enforceable unless a code refers to them, but they represent a consensus of what is reasonable or prudent.<ref name="Lew" /> Where a regulatory document does refer to SFPE material, it does so selectively. C/VM2 (2025), for example, cites the SFPE Handbook and an SFPE guide only in particular comments and clauses.<ref name="MBIE-61" /> Showing compliance with the New Zealand Building Code through C/VM2 still requires each of its ten design scenarios to be satisfied.<ref name="MBIE-7" />

C/VM2 is meant for professional fire engineers who are proficient in fire engineering modelling methods.<ref name="MBIE-7" /> They are expected to apply appropriate judgement to model inputs and results.<ref name="MBIE-7" /> The IFEG likewise allow engineering judgement where valid methods or verified data are not available, but require all quantification based on it to be justified in detail.<ref name="IFEG-1-8">National Research Council of Canada et al. (2005), p. 1.8-10.</ref> For the United States, they give the fire engineer the task of evaluating a performance design and the authority having jurisdiction the task of assessing and approving it.<ref name="IFEG-US-0211">National Research Council of Canada et al. (2005), Part 0 (United States), p. 0.2-11.</ref>

== See also ==

* [[Acceptance criteria]]
* [[Fire scenario]]
* [[Fire safety objectives]]
* Qualitative design review
* [[Building regulations]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Beyler, C. L. (2002a). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-268–3-314). National Fire Protection Association; Society of Fire Protection Engineers.
* DiNenno, P. J., Drysdale, D., Beyler, C. L., Walton, W. D., Custer, R. L. P., Hall, J. R., Jr., & Watts, J. M., Jr. (Eds.). (2002). ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association; Society of Fire Protection Engineers.
* Evans, D. D., Peacock, R. D., Kuligowski, E. D., Dols, W. S., & Grosshandler, W. L. (2005). ''Active fire protection systems'' (NIST NCSTAR 1-4). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Lew, H. S., Bukowski, R. W., & Carino, N. J. (2005). ''Design, construction, and maintenance of structural and life safety systems'' (NIST NCSTAR 1-1). National Institute of Standards and Technology.
* Meacham, B. J. (2002). Building fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-153–5-175). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Institute of Standards and Technology. (2005). ''Final report on the collapse of the World Trade Center towers'' (NIST NCSTAR 1).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Notarianni, K. A. (2002). Uncertainty. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-40–5-64). National Fire Protection Association; Society of Fire Protection Engineers.
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association; Society of Fire Protection Engineers.
* Stroup, D., Lindeman, A., McGrattan, K., Peacock, R., Overholt, K., Joglar, F., LeStrange, S., & Montanez, S. (2016). ''Verification and validation of selected fire models for nuclear power plant applications: Supplement 1'' (NUREG-1824, Supplement 1; EPRI 3002002182). U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research; Electric Power Research Institute.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Watts, J. M., Jr., & Hall, J. R., Jr. (2002). Introduction to fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-1–5-7). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Safety Design & Regulation]]

Smoke control

2026-11-02T21:34:47Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Smoke control''' is the deliberate limitation and direction of smoke movement during a fire. It can use physical barriers, natural ventilation, mechanical extraction, pressurisation or a combination of these measures. The objective is to protect particular spaces or routes for a required period, rather than to remove every trace of smoke from a building.<ref name="IFEG-2-5-7">Australian Building Codes Board et al. (2005), p. 2.5-7.</ref><ref name="Cooper-3-219">Cooper (2002), p. 3-219.</ref>

Smoke control works with the processes that transport combustion products. Hot gases rise, ceiling jets spread sideways, and pressure differences drive flow through openings. Fans, vents and barriers can change those flows, but outdoor conditions, building leakage and other fire systems also influence the result.<ref name="IFEG-2-5-6">Australian Building Codes Board et al. (2005), p. 2.5-6.</ref><ref name="Evans-70">Evans et al. (2005), pp. 69–71.</ref>

The design must therefore state where smoke is intended to go, which spaces must remain usable and what conditions could defeat the system. Detection, make-up air, equipment operation and maintenance belong to the assessment. A fan or vent installed without those supporting functions does not establish smoke control.<ref name="ABCB-128">Australian Building Codes Board (2020), pp. 128–129.</ref>

== Objectives and protected spaces ==

The 2005 International Fire Engineering Guidelines (IFEG) describe the general objective as removing heat and minimising smoke concentration in designated areas. This focuses attention on selected locations rather than an undefined whole-building outcome. The relevant locations might include escape routes, occupied zones or areas needed for firefighting.<ref name="IFEG-2-5-7" />

Cooper identifies three objectives for designed smoke and heat venting. These are supporting escape, helping firefighters enter and see the fire, and reducing smoke and heat damage to property. A system may address more than one objective, but the corresponding conditions and duration must be made explicit.<ref name="Cooper-3-219" />

A smoke-control zone provides a defined boundary for that objective. It can be separated from adjacent zones by partitions, floors, doors and dampers. NUREG-1805 notes that a smoke compartment is enclosed on all sides, including the top and bottom.<ref name="NUREG-F50">Nolan (2000), as cited in Iqbal and Salley (2004), pp. F-50–F-51.</ref>

Protection of a boundary is not the same as maintaining clear air throughout the fire room. Pressurisation can restrict smoke entering a stair while leaving severe conditions in the fire compartment. The location of people and the intended place of safety determine whether that outcome is useful.<ref name="Evans-70" />

Extraction has a different spatial aim. It removes smoke from the hot layer to slow descent or reduce concentration in the protected volume. Its effectiveness depends on the incoming smoke flow and replacement air, so a rated fan capacity alone cannot specify the resulting layer height.<ref name="ABCB-128" /><ref name="IFEG-2-5-4">Australian Building Codes Board et al. (2005), p. 2.5-4.</ref>

== Smoke movement as the design basis ==

[[Smoke movement]] begins with the fire plume and its entrainment of surrounding air. The rising products carry smoke into an upper layer, after which ceiling flows and openings distribute it. The amount entering a smoke-control system therefore depends on fire size, plume geometry and air supply.<ref name="IFEG-2-5-2">Australian Building Codes Board et al. (2005), pp. 2.5-1–2.5-2.</ref>

Pressure differences govern horizontal flow through openings. They can arise from hot gases, wind, building services or differences between indoor and outdoor temperatures. Smoke-control pressures act within that combined field rather than replacing all other influences.<ref name="IFEG-2-5-6" /><ref name="Evans-70" />

The fire scenario must include the fuel and the geometry that shapes entrainment. IFEG notes that walls and corners restrict air entrainment into a plume. A model developed for an unrestricted fire may consequently misrepresent smoke production near such boundaries.<ref name="IFEG-2-5-3">Australian Building Codes Board et al. (2005), pp. 2.5-3–2.5-4.</ref>

Layer behaviour provides another design condition. Smoke-layer height varies with time, fire size and exhaust rate. A calculated clear height belongs to those inputs and cannot be treated as a fixed property of a ventilation unit.<ref name="IFEG-2-5-4" />

A mass balance explains why the smoke layer can continue growing while an exhaust fan runs. Over a short interval, the change in stored gas mass equals the mass entering minus the mass leaving. This form assumes that the stated flows remain constant over the interval.<ref name="VR-3.7">Van Rossum (2027), §3.7.</ref>

<math display="block">\Delta m=(\dot m_{\mathrm{in}}-\dot m_{\mathrm{out}})\Delta t</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\Delta m</math> || Change in gas mass stored in the layer || kg
|-
| <math>\dot m_{\mathrm{in}},\dot m_{\mathrm{out}}</math> || Mass flow entering and leaving || kg/s
|-
| <math>\Delta t</math> || Time interval || s
|}

Van Rossum illustrates this with 10 kg/s entering a smoke layer and 8 kg/s leaving. During 1 s, the layer gains 2 kg of gas. Extraction reduces accumulation in this example but does not balance the incoming plume.<ref name="VR-3.7" />

<math display="block">\Delta m=(10-8)\times1=2\ \mathrm{kg}</math>

The calculation concerns the entire smoky gas mixture, including entrained air, rather than soot mass alone. Converting accumulated mass into layer depth also requires density and enclosure geometry. Temperature changes and heat losses can change that density, so equal volume flows do not necessarily represent equal mass flows.<ref name="VR-3.6">Van Rossum (2027), §3.6.</ref><ref name="VR-3.7" />

A stationary layer requires a balance over the relevant interval. A growing fire changes the plume supply, and an opening or fan change can alter the removal rate. The simple balance is therefore an explanation of accumulation, not a complete transient smoke-exhaust design method.<ref name="VR-3.7" /><ref name="IFEG-2-5-4" />

== Natural and mechanical ventilation ==

[[Smoke and heat exhaust ventilation|Smoke and heat exhaust ventilation (SHEV)]] can remove hot gases through openings near the ceiling or roof. Cooper distinguishes natural buoyancy-driven removal, fan-driven removal and combined arrangements. The system must also introduce relatively cool, uncontaminated air at a lower level.<ref name="Cooper-3-219" />

Natural ventilation uses the buoyancy of the hot layer and the pressure conditions across vents. It does not require a fan to create every part of the flow, but it still depends on effective vent area, layer conditions and replacement air. Wind and external temperatures can alter those conditions.<ref name="ABCB-128" /><ref name="Evans-70" />

Mechanical extraction uses fans to remove smoke from the upper part of a space. Australian Building Codes Board (ABCB) guidance describes extraction at or near the roof or ceiling, with make-up air at low level. That guidance concerns its national context and does not provide a universal design arrangement.<ref name="ABCB-128" />

Make-up air replaces gases removed by the exhaust or vent. Insufficient replacement air can restrict the intended flow and change pressure conditions. It should be treated as part of the smoke-control system rather than as an unrelated opening.<ref name="ABCB-128" />
[[File:fse-smoke-control-v1.svg|thumb|upright=1.5|alt=Two rooms show roof-vent and fan extraction with low-level replacement air.|Natural and mechanical venting both need a coherent airflow path. Based on Cooper (2002), p. 3-219 and Australian Building Codes Board (2020), p. 128.]]

Airflow paths should not short-circuit the intended smoke movement. Supply at low level and exhaust near the layer serve different functions in the cited venting approach. Their locations and operation must support a coherent flow from clean inlet to smoky outlet.<ref name="Cooper-3-219" /><ref name="ABCB-128" />

An exhaust inlet can also draw relatively clear air from below a thin smoke layer. This effect is called plugholing. The extracted mixture then contains less smoke than a calculation assuming pure layer extraction would suggest.<ref name="VR-6.8">Van Rossum (2027), §6.8.</ref>

Van Rossum describes several ways of addressing this flow pattern. These include spreading extraction over more outlets, reducing flow per outlet, or allowing a deeper layer where the design permits it. Outlet orientation also matters, because the local suction flow determines whether air is drawn from beneath the layer.<ref name="VR-6.8" />

Plugholing also changes the interpretation of an exhaust measurement. The total flow through a duct includes any clear air drawn into it. Only the part taken from the smoke layer contributes directly to removal in the layer mass balance.<ref name="VR-6.8" /><ref name="VR-3.7" />

== Pressure differences and containment ==

[[Stair pressurisation]] supplies air to protect an escape stair from smoke infiltration. It creates a pressure difference between the stair and adjoining spaces. Open doors change the airflow and pressure, so the design must consider the relevant door conditions.<ref name="Evans-70" /><ref name="ABCB-127">Australian Building Codes Board (2020), p. 127.</ref>

Zone pressurisation uses different pressures between a fire zone and adjacent zones. Supply to non-fire zones and extraction from the fire zone can both contribute. The intended direction is from protected spaces towards less protected spaces through leakage paths.<ref name="ABCB-127" /><ref name="Evans-70" />
[[File:fse-smoke-control-v2.svg|thumb|upright=1.5|alt=Fresh air pressurises a stair and adjacent zone, directing leakage flow towards the fire zone.|Pressurisation protects boundaries by controlling flow direction. Based on Evans et al. (2005), p. 70 and Australian Building Codes Board (2020), p. 127.]]

Excessive pressure is not a universal improvement. ABCB guidance explains that relief may be needed to avoid excessive door-opening forces or interference with automatic closing. The system must protect against smoke while preserving the operation of the escape route.<ref name="ABCB-127" />

A [[Smoke barrier]] restricts smoke passage through a continuous construction or closure. NUREG-1805 notes that such a barrier may or may not also have fire resistance. Smoke containment and fire resistance are related building functions but are not interchangeable labels.<ref name="NUREG-F50" />

Dampers can complete a smoke boundary within ventilation ducts. Shutdown of air handling can limit recirculation and smoke transfer between compartments. A stopped fan alone may not seal an open duct, so the damper arrangement and its control still matter.<ref name="ABCB-126">Australian Building Codes Board (2020), p. 126.</ref><ref name="Evans-70" />

== Reservoirs, boundaries and special volumes ==

A [[Smoke reservoir]] is a volume in which smoke can collect above the space being protected. Its boundaries help define where the layer is retained and from which region extraction occurs. Reservoir behaviour must be analysed together with incoming plume flow and replacement air.<ref name="IFEG-2-5-4" /><ref name="Cooper-3-219" />

Large open spaces differ from subdivided office floors. Cooper describes warehouse spaces that may be divided by ceiling screens and atrium-like spaces connected to adjacent rooms. These geometries affect smoke accumulation and the paths between the fire and occupied areas.<ref name="Cooper-3-219" />

[[Atrium smoke control]] must account for the connected volume and the locations requiring protection. Smoke can collect above an atrium fire or arrive from an adjoining space. The relevant plume and layer model therefore depends on the actual fire location.<ref name="Cooper-3-219" /><ref name="IFEG-2-5-2" />

Tunnel ventilation is another application of smoke control. Van Rossum identifies tunnels as spaces in which fire-engineering analysis addresses conditions that differ from ordinary occupied buildings. Computational fluid dynamics, which calculates gas movement through a divided modelled space, can investigate the effectiveness of the proposed system.<ref name="VR-11.2">Van Rossum (2027), §11.2.</ref>

== System interaction and reliability ==

Smoke control often relies on detection to select the correct fire mode. Zone systems may need the alarm location as well as confirmation that a fire exists. An incorrect zone signal could produce pressure or airflow patterns that do not match the fire location.<ref name="ABCB-131">Australian Building Codes Board (2020), p. 131.</ref>

Sprinkler operation can reduce heat and buoyancy while disturbing the smoke layer. The US National Institute of Standards and Technology (NIST) describes cooling and mixing in its discussion of building smoke management. This interaction can change the conditions assumed for smoke transport and heat-operated vents.<ref name="Evans-70" />

Cooper describes delayed activation of later sprinklers or vents when earlier sprays cool their elements. Such skipping makes the sequence less predictable. Interactions should be evaluated rather than assuming that each system reaches its design state independently.<ref name="Cooper-3-239">Cooper (2002), p. 3-239.</ref>

Active systems can contain many components in series. ABCB gives illustrative reliability calculations using assigned component values, but these are simplified examples rather than universal system probabilities. Their purpose is to show how complexity and dependencies can reduce availability.<ref name="ABCB-129">Australian Building Codes Board (2020), p. 129.</ref>

Normal building ventilation can either support or oppose the fire-mode arrangement. Recirculation can distribute smoke if the system does not change to its intended state. The design should document fan, damper and control positions for each relevant operating mode.<ref name="ABCB-126" /><ref name="Evans-70" />

== Commissioning and design limits ==

Commissioning should include an installation check, performance tests in all operating modes, repair of defects and retesting. ABCB presents this sequence because a completed installation is not necessarily a functioning system. Repeated testing may be needed to close identified defects.<ref name="ABCB-130">Australian Building Codes Board (2020), pp. 129–130.</ref>

Access for inspection and maintenance affects reliability over the system's life. Components that cannot be reached safely are harder to test and service. Documentation should identify required inspections and the mode in which each component is expected to operate.<ref name="ABCB-130" />

Calculations carry uncertainty from the fire, geometry and flow paths. IFEG notes that smoke-spread calculations beyond the enclosure of origin are more difficult and uncertain than those within it. Results should not be given more precision than those inputs support.<ref name="IFEG-2-5-6" />

Dilution alone should not be confused with every definition of smoke control. NUREG-1805's cited glossary definition distinguishes pressure- and airflow-based control from simple supply-and-extract dilution within an enclosure. Broader smoke-management classifications nevertheless include dilution as one technique.<ref name="NUREG-F50" /><ref name="IFEG-2-5-7" />

== Performance assessment ==

Performance should be assessed against the sequence of system states. Detection must select the intended mode, fans and dampers must respond, and airflow must then develop through the actual openings. Treating the final airflow as immediate would hide delays and incorrect intermediate states.<ref name="ABCB-126" /><ref name="ABCB-131" />
[[File:fse-smoke-control-v3.svg|thumb|upright=1.5|alt=Detection leads through fan and damper states to boundary airflow and acceptance tests.|Smoke-control acceptance covers the complete operating sequence. Based on Australian Building Codes Board (2020), pp. 129–131.]]

Different door positions can create different smoke-control problems. A closed door may preserve a pressure boundary, while an open door requires airflow through its opening. Pressure relief and door operation therefore need to be tested for the scenarios used in design.<ref name="ABCB-127" />

Mechanical equipment also has dependencies. A fan needs a suitable control signal and operating condition, while a damper must reach its intended position. Verification should follow those functions through to airflow at the protected boundary instead of stopping at an electrical signal.<ref name="ABCB-130" />

Exhaust capacity and fire size are coupled design inputs. ABCB warns that smoke-control performance can be compromised if sprinklers fail to limit the fire as assumed. A larger smoke source may exceed the exhaust arrangement or damage exposed components.<ref name="ABCB-132">Australian Building Codes Board (2020), p. 132.</ref>

Maintenance should preserve both airflow hardware and the physical building boundary. Later alterations to partitions, doors, ducts or ventilation can change the smoke-control zones. Those changes require comparison with the design basis even when the original fans remain in place.<ref name="ABCB-130" /><ref name="Evans-70" />

A pressure measurement and a layer-height measurement answer different questions. The first helps establish flow direction across a boundary, while the second describes smoke accumulation in a volume. The acceptance record should use observations that correspond to the actual design objective rather than treating either as a universal indicator.<ref name="ABCB-127" /><ref name="IFEG-2-5-4" />

== See also ==

* [[Smoke]]
* [[Protected escape route]]
* [[Fire safety strategy]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Australian Building Codes Board. (2020). ''Fire safety verification method data sheets'' (Version 1.1).
* Cooper, L. Y. (2002). Smoke and heat venting. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-219–3-242). National Fire Protection Association.
* Evans, D. D., Peacock, R. D., Kuligowski, E. D., Dols, W. S., & Grosshandler, W. L. (2005). ''Active fire protection systems'' (NIST NCSTAR 1-4). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Smoke Control]]

Reaction to fire

2026-11-02T21:34:44Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Reaction to fire''' describes how a material or product contributes to the development of a fire under specified exposure conditions. It includes the behaviour leading to ignition and the subsequent release of heat and combustion products. Heat release rate is a central measure because it links burning material to the thermal conditions developing around it.<ref name="J_3-38_3-39">Janssens (2002), pp. 3-38–3-39.</ref>

The response depends on more than the material's name. Thickness, orientation, mounting, incident heat and the surrounding enclosure can change the observed behaviour. Results from a small specimen therefore need interpretation before they are applied to a complete product or room. A test classification retains meaning through the conditions and application rules attached to it.<ref name="J_3-39">Janssens (2002), p. 3-39.</ref><ref name="J_3-56">Janssens (2002), p. 3-56.</ref>

Reaction to fire is distinct from the ability of an assembly to maintain its function during fire exposure. A combustible material can form part of a fire-resisting assembly, while a noncombustible material can lose mechanical performance when heated. The two assessments describe different parts of building fire safety.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref>

== Contribution to a developing fire ==

A material can have several roles in the same building, and it may carry loads, insulate another component, and supply fuel when heated. Kodur and Harmathy distinguish these functions because a useful structural material can become an additional fire source. A description of its room-temperature strength therefore says little about its contribution to fire development.<ref name="KH_1-157" />

[[Combustibility]] concerns whether a material can burn. Reaction to fire examines a wider sequence, including the exposure needed for ignition and the subsequent rate of energy release. A combustible product that releases energy slowly can produce a different fire from one that burns rapidly. Material mass alone cannot describe that difference.<ref name="KH_1-157" /><ref name="B_3-1">Babrauskas (2002), p. 3-1.</ref><ref name="B_3-32">Babrauskas (2002), p. 3-32.</ref>

[[Fire resistance]] addresses another question: how long a building assembly maintains specified functions during a defined fire exposure. These functions include carrying loads and limiting heat transmission or the passage of flames. Reaction-to-fire evidence characterises the product's contribution to the fire; it does not establish the endurance of a complete wall, floor or protected member.<ref name="KH_1-155" /><ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref>

== Heating, ignition and flame spread ==

Before a solid ignites, incoming heat raises its surface temperature and penetrates its interior. Some energy returns to the surroundings through radiation and convection. Moisture evaporation can absorb further energy before substantial decomposition occurs. The resulting balance depends on the exposure, material thickness and thermal properties.<ref name="K_2-231_2-232">Kanury (2002), pp. 2-231–2-232.</ref>

Heating can produce combustible gases through thermal decomposition, also called pyrolysis, and these gases mix with surrounding air and may ignite when suitable conditions develop. Piloted ignition involves an external ignition source, such as a small flame or spark. Ignition without such a pilot requires the gas mixture itself to reach conditions that sustain the reaction.<ref name="K_2-232">Kanury (2002), p. 2-232.</ref>

[[Flame spread]] extends burning into previously unburned material. Heat from the advancing flame prepares the next surface region to release combustible gases. The flame front and the boundary of the decomposing solid are related, but they are not identical physical boundaries. Surface orientation and airflow affect the heat transferred ahead of the flame.<ref name="Q_2-246_2-247">Quintiere (2002), pp. 2-246–2-247.</ref>

Spread and burnout compete during fire growth. If new surface becomes involved before the earlier region stops burning, the active burning area can increase. If the earlier fuel burns out faster than the flame advances, growth can slow or stop. This explains why a spread measurement requires an account of both material behaviour and the surrounding exposure.<ref name="Q_2-246">Quintiere (2002), p. 2-246.</ref>

[[File:fse-reaction-to-fire-v1.svg|thumb|upright=1.5|alt=Exposure leads to ignition, heat release, flame spread, smoke and toxic products.|Reaction to fire covers several material responses. Based on Janssens (2002), pp. 3-38–3-39 and Quintiere (2002), p. 2-247.]]

== Heat release and mass loss ==

Heat release rate measures the rate of thermal energy production, expressed in kilowatts. Mass loss rate measures how quickly the specimen loses mass, expressed in kilograms per second, and the effective heat of combustion connects these quantities under the particular burning conditions. It represents the energy released per unit mass lost, rather than a complete description of the fuel's chemistry.<ref name="B_3-1" /><ref name="J_3-39" />

Multiplying the mass loss rate by the effective heat of combustion gives the corresponding heat release rate. The following form uses kilojoules per kilogram, so that the result is directly in kilowatts. Both quantities must refer to the same specimen and stage of burning.<ref name="B_3-1" /><ref name="J_3-39" />

<math display="block">\dot Q=\dot m\,\Delta h_{c,\mathrm{eff}}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot Q</math> || Heat release rate || kW
|-
| <math>\dot m</math> || Mass loss rate || kg/s
|-
| <math>\Delta h_{c,\mathrm{eff}}</math> || Effective heat of combustion || kJ/kg
|}

The effective heat of combustion need not remain constant during a test. Babrauskas describes a 17 mm Western red cedar specimen exposed to an irradiance of 65 kW/m². Its effective heat of combustion was approximately 12 MJ/kg during the earlier period and approximately 30 MJ/kg during later char burning. Using one fixed value throughout would conceal this change.<ref name="B_3-1_3-2">Babrauskas (2002), pp. 3-1–3-2.</ref>

A unit-rate calculation illustrates the consequence without reconstructing that experiment. At an assumed mass loss rate of 0.001 kg/s, the two source values give 12 kW and 30 kW. The second result is 2.5 times the first, despite identical assumed mass loss rates. These calculated powers are illustrative normalisations, not measured powers from the cedar test.<ref name="B_3-1_3-2" />

The effective value also differs from a calorific value measured in an oxygen bomb calorimeter. That apparatus burns a small specimen under high-pressure oxygen. Janssens explains that these conditions differ from practical fires, and that effective values for many solids are lower. Substituting a bomb-calorimeter value into a fire model can therefore change the predicted energy release.<ref name="J_3-39" />

Quintiere gives a simple illustration of surface spread on an upholstered chair. A burning region initially 6 cm across grows to 18 cm across after one minute at the stated radial spread rate. The corresponding circular area becomes nine times larger. This is a geometric illustration using the source's dimensions, rather than a prediction for every upholstered product.<ref name="Q_2-246" />

The distinction between spread distance and burning area matters when interpreting such an example: a front advances along a boundary, while energy release comes from the active burning surface. Growth in that surface can provide more heat feedback and accelerate further involvement. The material's burning duration determines whether the earlier regions remain active as the boundary advances.<ref name="Q_2-246" />

== What tests measure ==

[[Fire testing]] can examine a small specimen, a complete product or an assembly in a room, and these scales expose different parts of the burning process. A specimen test offers controlled exposure and detailed measurements, while a room test includes interactions with the enclosure. Neither description alone establishes that one test can replace the other.<ref name="J_3-38_3-39" />

In a room-corner test, lining materials are mounted on the walls or ceiling of a small enclosure. A burner near a rear corner provides the ignition exposure. Combustion products leave through the opening and enter a collection hood. Measurements in the exhaust can include gas concentrations, flow and smoke obscuration, alongside the information needed to determine heat release.<ref name="J_3-39" />

The Single Burning Item test uses two wall panels arranged as a corner without a ceiling. Babrauskas describes it as a European regulatory heat-release test in the 2002 handbook, and its geometry differs from the enclosed room-corner arrangement. The [[Euroclass system]] is the related classification topic; the historical test description alone does not provide a complete classification procedure.<ref name="B_3-32" />

Calorimeter results depend on specimen mounting, orientation, geometry and exposure. Janssens reports comparisons in which different apparatuses produced different peaks or time-dependent heat-release behaviour. Agreement for an average value did not necessarily imply agreement for the peak. The measured quantity and averaging period therefore belong with any reported result.<ref name="J_3-56" />

[[File:fse-reaction-to-fire-v2.svg|thumb|upright=1.5|alt=Four test scales from small cone specimen to room and facade systems.|Reaction-to-fire tests address different scales and feedback. Based on Janssens (2002), p. 3-39 and Babrauskas (2002), p. 3-33.]]

Oxygen-consumption calorimetry estimates heat release through the oxygen consumed during combustion. Babrauskas reports a commonly used conversion of 13.1 MJ per kilogram of oxygen consumed. He also notes that some substances differ substantially from that convention. Knowing the composition can support a correction, so the conversion is an approximation with a physical basis rather than an exact constant for every fuel.<ref name="B_3-32" />

The gas measurement belongs to a complete collection and flow-measurement arrangement. In the room-corner description, the exhaust carries combustion products into the instrumented duct. Gas concentration and total flow are therefore connected parts of the measurement. A concentration by itself does not specify how much material or energy passes through the system per unit time.<ref name="J_3-39" />

== Why total energy and peak power differ ==

The total heat released describes energy over the complete burning period. Peak heat release rate describes the largest rate observed during that period. A large total energy does not necessarily imply the highest peak power. Babrauskas illustrates this distinction through wardrobe tests involving different panel materials and thicknesses.<ref name="B_3-32_3-33">Babrauskas (2002), pp. 3-32–3-33.</ref>

One tested wardrobe used unpainted plywood panels 3.2 mm thick, with 36.0 kg of combustible construction and 1.93 kg of contents. Its reported peak was 6,400 kW and its total heat release was 590 MJ. A 19 mm particleboard wardrobe contained 120.3 kg of combustible construction and 0.81 kg of contents. Its reported peak was 1,900 kW, while its total heat release was 1,349 MJ.<ref name="B_3-33">Babrauskas (2002), p. 3-33.</ref>

The thinner plywood package therefore produced approximately 3.4 times the peak power of the particleboard package. The particleboard package nevertheless released approximately 2.3 times as much total energy, and these ratios are calculated from the reported tests, whose constructions and contents differed. They illustrate package behaviour and cannot establish a universal ranking of plywood against particleboard.<ref name="B_3-32_3-33" />

The enclosure can further alter burning. Radiation from hot gases and surrounding surfaces supplies additional energy to the fuel, while ventilation can restrict combustion. A product burning freely in an open calorimeter may therefore behave differently inside a compartment. Babrauskas specifically cautions against extrapolating a room-test result to rooms with larger ventilation openings.<ref name="B_3-1_3-2" />

== Classification and use in buildings ==

Classification connects specified test results with a defined regulatory framework. The intended use matters because a wall lining, floor covering and structural member serve different functions. New Zealand's C/VM2, second edition of 2025, treats rapid spread over internal surface linings as a specific design scenario. Its criteria depend on location, building use and importance level.<ref name="CVM_50_52">Ministry of Business, Innovation and Employment (2025), pp. 50–52.</ref>

In that New Zealand method, exposed internal wall and ceiling surfaces receive material Group Numbers. The commentary associates ordinary timber products with Group 3 and many fire-retardant-treated timbers with Group 2, and it identifies exposed polyurethane foams as examples associated with Group 4. These are explanatory examples, rather than classifications transferable to every product bearing the same material name.<ref name="CVM_50_52" />

Flooring is assessed through critical radiant flux in the same document. A higher critical flux corresponds to better performance in the specified flooring assessment. For sleeping areas and exitways in care or detention buildings, the 2025 table gives 4.5 kW/m² without sprinklers and 2.2 kW/m² with sprinklers. These are New Zealand scenario requirements, not general ignition thresholds for all materials.<ref name="CVM_52">Ministry of Business, Innovation and Employment (2025), p. 52.</ref>

[[File:fse-reaction-to-fire-v3.svg|thumb|upright=1.5|alt=Critical radiant flux values 4.5, 2.2 and 1.2 kW/m² for three C/VM2 situations.|C/VM2 critical radiant flux depends on occupancy and sprinklers. Based on Ministry of Business, Innovation and Employment (2025), p. 52.]]

The distinctions reflect the role of the space. C/VM2 gives greater emphasis to linings along escape routes, where they may form a substantial part of the available fuel. Occupants' ability to evacuate and the presence of sprinklers also affect the specified criteria. Applying one classification requirement throughout every occupancy would remove these distinctions.<ref name="CVM_52" />

== Smoke production and treatment effects ==

Heat release and smoke-related hazards are connected but are not interchangeable measurements. Janssens expresses the production rate of a toxic gas as its yield multiplied by the mass loss rate. A high yield alone does not establish the largest total release. The burning rate and its variation during the exposure are also part of the assessment.<ref name="J_3-38">Janssens (2002), p. 3-38.</ref>

A fire-retardant treatment can change more than one measured property. Janssens discusses treatments that increase a toxic-gas yield while reducing mass loss sufficiently to reduce the assessed hazard. That example explains why treatment performance cannot be judged from one isolated number. Its interpretation depends on the complete combination of burning rate, yields and exposure conditions.<ref name="J_3-38" />

Smoke obscuration is another measurement available in calorimetry. It describes the effect of suspended products on transmitted light, rather than directly measuring structural endurance or the complete toxic hazard. A test reporting smoke obscuration therefore answers a different question from a furnace test of a separating assembly. The measurements become useful when each remains connected to its own physical quantity.<ref name="J_3-39" /><ref name="M_4-209_4-210" />

== Evidence and uncertainty ==

Heat-release measurements contain both systematic bias and random variation. Babrauskas describes calibration with a metered gas supply as one means of addressing bias. Comparisons between laboratories reveal variability that a single test cannot show. The historical interlaboratory results in the handbook are evidence about those apparatuses and trials, rather than permanent uncertainty allowances for every later test.<ref name="B_3-32_3-33" />

A model that uses small-specimen results introduces a further step between measurement and application. Material properties derived from those results must reproduce the processes relevant to the larger fire. Janssens describes approaches ranging from full-scale experiments to calculations using bench-scale data. Their suitability depends on the fire scenario, the available measurements and the treatment of enclosure feedback.<ref name="J_3-38_3-39" />

Even the same product can present different exposed areas and orientations in different applications. A room-corner arrangement provides different heat feedback from an isolated specimen, while a mounting method can alter burning. A defensible comparison consequently identifies the product, construction, exposure, measured quantity and test configuration together. Removing those conditions can turn a valid measurement into an unsupported prediction.<ref name="J_3-39" /><ref name="J_3-56" />

== See also ==

* [[Flame retardant]]
* [[Heat release rate]]
* [[Ignition]]

== Notes ==

<references />

== References ==

* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-38–3-62). National Fire Protection Association.
* Kanury, A. M. (2002). Flaming ignition of solid fuels. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-229–2-245). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Quintiere, J. G. (2002). Surface flame spread. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-246–2-257). National Fire Protection Association.

[[Category:Materials & Fire Testing]]

Response time index

2026-11-02T21:34:41Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Response time index''' ('''RTI''') is a measure of the thermal sensitivity of a sprinkler or heat detector sensing element. In the conventional convective model, it equals the element's thermal time constant multiplied by the square root of the surrounding gas speed. A lower RTI produces faster heating under otherwise identical conditions. Its SI unit is (m·s)<sup>1/2</sup>.<ref name="S-5-6">Schifiliti et al. (2002), pp. 4-5–4-6.</ref>

RTI connects a measured device characteristic with a model of the local fire environment. Calculating operation also requires the gas temperature and velocity history, the initial element temperature and the operating criterion. The resulting time belongs to that combination of device and exposure. RTI itself is neither a number of seconds nor the temperature at which the element operates.<ref name="S-6-7">Schifiliti et al. (2002), pp. 4-6–4-7.</ref><ref name="I-3">Australian Building Codes Board et al. (2005), p. 2.7-3.</ref>

The usual model treats the element as a small body with one representative temperature. More detailed treatments can account for heat conducted into the sprinkler mounting and cooling by discharged water. The usefulness of an RTI calculation consequently depends on both the thermal model and the accuracy of the gas conditions supplied to it.<ref name="S-6">Schifiliti et al. (2002), p. 4-6.</ref><ref name="FDS-107">McGrattan et al. (2026), p. 107.</ref>

== Physical meaning of thermal sensitivity ==

An automatic [[Sprinkler head|sprinkler head]] combines a heat-sensitive operating mechanism with a water-discharge function. RTI characterises the heating response of that mechanism. It does not describe the amount of water passing through an opened sprinkler or the distribution of its spray. Those functions require additional hydraulic and discharge information.<ref name="F-85">Fleming (2002), p. 4-85.</ref><ref name="F-75">Fleming (2002), p. 4-75.</ref>

The basic heat balance compares convective heat input with energy stored in the sensing element. Increasing the element's mass or heat capacity increases the energy required for a given temperature rise. Increasing exposed area or the heat-transfer coefficient increases the rate at which that energy can enter. The thermal time constant combines these influences into one quantity for the assumed exposure.<ref name="S-5">Schifiliti et al. (2002), p. 4-5.</ref>
[[File:fse-response-time-index-v1.svg|thumb|upright=1.5|alt=Hot gas flows over a sensing element while arrows distinguish convective heating from heat lost to its mounting.|RTI relates convective exposure to the heating response of a sensing element. Based on Schifiliti et al. (2002), pp. 4-5–4-6.]]

<div class="fse-equation">τ = mc / (hA);   RTI = τ√u</div>

{| class="wikitable"
! Symbol !! Meaning !! SI unit
|-
| τ || Thermal time constant at gas speed u || s
|-
| m || Effective mass of the heated element || kg
|-
| c || Specific heat of the element || J/(kg·K)
|-
| h || Convective heat-transfer coefficient || W/(m²·K)
|-
| A || Effective area exposed to convective heating || m²
|-
| u || Gas speed at the element || m/s
|-
| RTI || Response time index || (m·s)<sup>1/2</sup>
|}

The characteristic time changes with gas speed because convective heat transfer changes. With RTI held constant, the expression gives τ = RTI/√u. Faster gas flow therefore produces a smaller time constant in this model. RTI is used to transfer information between different flow conditions without assigning a new time constant at every velocity.<ref name="S-5-6" />

That transfer is approximate. Real elements have complex shapes, and their heat transfer does not follow an exact square-root relationship across every flow regime. The handbook discusses variation with Reynolds number and differences observed during testing. A quoted RTI should therefore be understood as an experimentally based model parameter with an applicable range.<ref name="S-6" />

== Measuring RTI in a plunge test ==

In a plunge test, the sprinkler or detector is suddenly introduced into a stream of hot gas. Gas temperature and velocity are known and remain approximately constant during the exposure. The elapsed time to operation is measured. The convective response equation can then be rearranged to determine the RTI associated with that test.<ref name="S-6" />

The test also requires the initial temperature and the temperature associated with operation. If these quantities are omitted, a measured response time cannot uniquely determine RTI. A short time in a very hot, fast stream is not directly comparable with the same time in a cooler, slower stream. The calculation separates those exposure conditions from the inferred sensitivity.<ref name="S-6" />

The test arrangement can affect how well the result transfers to a fire environment. The handbook notes that high test velocities can make conductive heat loss relatively small compared with convective heating. At a different velocity, heat conducted into the mounting may have greater influence. An RTI derived under one condition does not establish that neglected heat losses remain negligible elsewhere.<ref name="S-6" />

Device geometry can also direct gas towards or away from the sensing element. Orientation and nearby mounting components therefore matter when relating a laboratory result to installation conditions. Fleming identifies sprinkler orientation, flow deflection, frame conduction and position below the ceiling among the influences on predicted response. An appropriate device input cannot compensate for an incorrectly represented local environment.<ref name="S-6" /><ref name="F-85" />

The inverse calculation also provides a useful interpretation of the measurement. For a specified test stream, the logarithmic temperature ratio converts the measured operating time into a thermal time constant. Multiplication by the square root of test velocity then gives RTI. A reported result should retain the temperature and velocity conditions so that the inferred parameter can be interpreted correctly.<ref name="S-6" />

Repeating a test at different velocities can reveal whether one RTI adequately describes the observed response. The handbook discusses measurements showing variation and considers reporting more than one time constant. Such variation need not mean that a stopwatch measurement was wrong. It can indicate that a single simplified heat-transfer parameter does not capture the device equally well across the tested conditions.<ref name="S-6" />

== Convective response and operating temperature ==

For a [[Heat detector|heat detector]] or sprinkler represented by a single thermal mass, the simplest response equation is:<ref name="S-6" /><ref name="I-3" />

<div class="fse-equation">dT<sub>l</sub>/dt = (√u / RTI)(T<sub>g</sub> − T<sub>l</sub>)</div>

{| class="wikitable"
! Symbol !! Meaning !! Unit
|-
| T<sub>l</sub> || Temperature of the link or sensing element || °C
|-
| T<sub>g</sub> || Local gas temperature || °C
|-
| t || Time after the specified exposure begins || s
|-
| u || Local gas speed || m/s
|-
| RTI || Response time index || (m·s)<sup>1/2</sup>
|}

The temperature difference drives heating, while RTI and gas speed determine the rate of response. If the element and gas have the same temperature, this model predicts no net convective heating. When the gas becomes hotter, the element approaches the gas temperature progressively. It does not instantaneously acquire the temperature predicted by a fire model.<ref name="S-5-6" />

For a fixed-temperature device, [[Detector activation time|detector activation time]] is found when the calculated element temperature reaches the operating temperature. RTI and operating temperature are separate inputs to that calculation. Changing either can alter the result, but they do so in different ways. A lower operating temperature changes the threshold; a lower RTI changes the speed of heating towards it.<ref name="S-6-7" />

This interpretation does not transfer unchanged to every heat detector mechanism. Rate-of-rise devices can depend on air expansion within a chamber, while rate-compensated devices involve differential heating of several components. The handbook explains why a single lumped element may not represent those mechanisms adequately. Their operation requires a model appropriate to the device rather than an assumed universal RTI threshold.<ref name="S-7">Schifiliti et al. (2002), p. 4-7.</ref>

== Worked example under constant conditions ==

If gas temperature and velocity remain constant, the convective equation has an exponential solution. Let the element initially be at the ambient temperature T<sub>a</sub>. For an operating temperature T<sub>r</sub> between T<sub>a</sub> and T<sub>g</sub>, rearrangement gives the following response time.<ref name="S-6" />

<div class="fse-equation">T<sub>l</sub>(t) = T<sub>a</sub> + (T<sub>g</sub> − T<sub>a</sub>)[1 − exp(−t√u / RTI)]</div>
<div class="fse-equation">t<sub>r</sub> = (RTI / √u) ln[(T<sub>g</sub> − T<sub>a</sub>) / (T<sub>g</sub> − T<sub>r</sub>)]</div>

Here T<sub>a</sub> is the initial element temperature, T<sub>r</sub> is the operating temperature and t<sub>r</sub> is the calculated response time in seconds. The logarithm uses a dimensionless ratio of temperature differences. The stated condition T<sub>g</sub> > T<sub>r</sub> > T<sub>a</sub> ensures a finite positive heating time in this example.<ref name="S-6" />

Consider hypothetical gas at 150 °C moving at 1 m/s, with the element initially at 20 °C and operating at 68 °C. For RTI = 50 (m·s)<sup>1/2</sup>, the time constant is 50 s. Substitution gives approximately 23.0 s to operation. These are illustrative inputs selected to demonstrate the equation, rather than the declared characteristics of a particular product.<ref name="S-6" />

Doubling RTI to 100 (m·s)<sup>1/2</sup>, with every other input unchanged, doubles the calculated time to approximately 46.1 s. Alternatively, retaining RTI at 50 while increasing gas speed to 4 m/s halves the time to approximately 11.5 s. The square root of speed explains why a fourfold velocity increase produces a twofold change in this particular response calculation.<ref name="S-5-6" />
[[File:fse-response-time-index-v2.svg|thumb|upright=1.5|alt=Three exponential temperature curves cross 68 °C after about 11.5, 23.0 and 46.1 seconds.|Illustrative RTI responses to a constant 150 °C gas stream. Based on Schifiliti et al. (2002), p. 4-6, Equations 11–15; article calculation.]]

The comparison isolates thermal sensitivity because the exposure remains fixed. It does not say that a real sprinkler with half the RTI always operates in half the time after ignition. In a growing fire, the earlier and later devices encounter different portions of the changing gas history. The response equation must then be integrated over that history.<ref name="S-8-9">Schifiliti et al. (2002), pp. 4-8–4-9.</ref>

The time origin also matters. The example begins when the constant hot stream reaches the element. It includes neither the time for a fire to develop nor the transport time before hot gases arrive. Treating its 23.0 s result as a prediction from ignition would therefore introduce a delay assumption absent from the calculation.<ref name="S-8-9" />

The logarithmic expression also shows why the temperature margin above the operating threshold matters. As the constant gas temperature approaches the operating temperature from above, the predicted heating time increases strongly. If the gas remains below the required operating temperature, the convection-only model cannot heat an initially cooler element to that threshold. A low RTI does not remove this limit.<ref name="S-6" />

The constant-exposure solution provides a check on a numerical implementation. With the same fixed inputs, numerical integration should approach the exponential temperature history as numerical error decreases. Agreement checks the calculation under those assumptions. It does not validate the assumed gas conditions or establish that conduction and radiation are negligible in a particular installation.<ref name="S-6" /><ref name="S-8-9" />

== Obtaining the local fire environment ==

A fire plume and [[Ceiling jet|ceiling jet]] transport heat towards a ceiling-mounted device. Predicting the element response requires conditions at that device, rather than only the fire's total heat release rate. Ceiling height, radial position and the fire's development influence the local temperature and velocity. These environmental inputs are independent of the device RTI.<ref name="S-7" /><ref name="I-3" />

The [[Alpert correlations|Alpert correlations]] provide one approach to estimating ceiling-jet conditions under their assumptions. The handbook describes a quasi-steady method that divides a changing fire into short intervals. Within each interval, gas conditions are calculated and the element temperature is advanced from its previous value. The thermal history is therefore carried forward rather than restarted at ambient temperature.<ref name="S-8-9" />

A small numerical time step cannot correct an unsuitable environmental model. The handbook discusses errors associated with ignoring gas transport and treating the ceiling as effectively unbounded. Walls and an accumulated hot layer can alter the conditions surrounding a detector. Position below the ceiling also matters because a sensing element may lie outside the region represented by a correlation.<ref name="S-7" /><ref name="S-9-10">Schifiliti et al. (2002), pp. 4-9–4-10.</ref>

The supplied CFAST technical guide illustrates another implementation. It obtains device conditions from plume, ceiling-jet or compartment-layer calculations according to location. For some locations it uses an estimated gas speed. Thus, even when two models contain the same RTI response equation, different representations of local gas conditions can give different operating times.<ref name="CFAST-35">Peacock et al. (2026), p. 35.</ref>

== Heat losses and interaction with water ==

Heat conducted from the element into its mounting can delay its temperature rise. The supplied FDS technical guide represents this influence with an experimentally determined conduction parameter, usually called the C-factor. RTI describes the convective sensitivity, while the C-factor describes a separate heat-loss pathway. Setting the latter to zero is a modelling choice with a physical consequence.<ref name="FDS-107" />

The same FDS formulation includes an empirical term for cooling by water droplets from previously operating sprinklers. This recognises that operation of one sprinkler can change the exposure of another sensing element. The handbook also cautions that activation calculations omitting spray cooling can misrepresent subsequent sprinkler operation. A first-operation calculation and a sequence of operating sprinklers therefore require different consideration of their surroundings.<ref name="FDS-107" /><ref name="S-7" />

Radiation is another distinct heat-transfer mechanism. The simple handbook treatment neglects it when convective heating dominates the early fire conditions being considered. The supplied FDS guide states that its sprinkler and heat-detector activation models do not account for thermal radiation. Model output consequently remains subject to that limitation even when a detailed gas-flow calculation supplies the temperature and velocity.<ref name="S-5" /><ref name="FDS-107" />

== Interpretation in sprinkler design ==

Fast thermal response is one feature of an ESFR sprinkler, but it does not establish the complete suppression performance of that sprinkler. NUREG-1805 also identifies droplet size and discharge velocity, together with strict design and installation requirements. A suitable RTI value cannot replace evidence that the sprinkler and its water supply suit the protected hazard.<ref name="N-10-3">Iqbal and Salley (2004), p. 10-3.</ref>

Operation of a thermal element is also distinct from water arrival. In a dry pipe system, valve operation and movement of water through the piping introduce additional delay after a sprinkler opens. Fleming separates this water-delivery time into trip and transit components. These delays do not become part of RTI merely because they influence the eventual application of water.<ref name="F-85" />
[[File:fse-response-time-index-v3.svg|thumb|upright=1.5|alt=An unscaled timeline separates heating to operation from dry-valve trip and water transit.|RTI governs thermal response, while dry pipe water delivery introduces additional delays. Based on Fleming (2002), p. 4-85; Schifiliti et al. (2002), pp. 4-6–4-7.]]

An RTI result is most useful when the analysis states the operating temperature, local exposure model and included heat-transfer mechanisms. Sensitivity to uncertain gas conditions can then be examined alongside sensitivity to the device parameter. Reporting excessive numerical precision would obscure uncertainties that the handbook identifies in activation temperature, ambient conditions and ceiling-jet predictions.<ref name="S-9-10" />

The overall response objective can extend beyond operation of the device. The detection-system chapter separates detection, signal processing and subsequent actions needed to meet a safety objective. An RTI calculation addresses only the thermal part of that sequence. This separation preserves the distinction between device sensitivity and complete system response. Any assumed processing or response delay must be accounted for separately when comparing a predicted operation time with the required outcome.<ref name="S-2-3">Schifiliti et al. (2002), pp. 4-2–4-3.</ref>

== See also ==
* [[Sprinkler skipping]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing. (2005). ''International fire engineering guidelines''.
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 4-3, pp. 4-72–4-87). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* McGrattan, K., Hostikka, S., Floyd, J., McDermott, R., Vanella, M., Mueller, E., & Paul, C. (2026). ''Fire Dynamics Simulator technical reference guide: Volume 1, Mathematical model'' (6th ed., NIST SP 1018-1; supplied revision FDS-6.11.1). National Institute of Standards and Technology.
* Peacock, R. D., McGrattan, K. B., Forney, G. P., & Reneke, P. A. (2026). ''CFAST: Consolidated Fire and Smoke Transport (Version 7), Volume 1: Technical reference guide'' (NIST TN 1889v1; supplied revision CFAST-7.7.7). National Institute of Standards and Technology.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 4-1). National Fire Protection Association.

[[Category:Fire Suppression]]

Sandwich panel

2026-11-02T21:34:38Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''sandwich panel''' is a building panel made of two thin facings, usually metal sheets, with a layer of insulation as its core.<ref name="Tew-3-96">Tewarson (2002), p. 3-96.</ref><ref name="MBIE13-159">Ministry of Business, Innovation and Employment (2013), p. 159.</ref> A typical example in ''Introduction to Fire Safety Engineering'' is an insulated steel roof with 100 mm of polyurethane foam between two steel sheets of 0.5 mm.<ref name="VR-5.2">Van Rossum (2027), §5.2.</ref> For such products, fire performance can be dominated by construction details rather than by the surface material.<ref name="MBIE13-159" /> New Zealand guidance therefore names metal-faced sandwich panels among the products that are not suitable for small-scale testing in the cone calorimeter.<ref name="MBIE13-141">Ministry of Business, Innovation and Employment (2013), p. 141.</ref> Panels with a combustible core are instead tested as full assemblies, for example in a room test or in a large corner test.<ref name="MBIE13-159" /><ref name="Tew-3-96" />

[[File:fse-sandwich-panel-v1.svg|thumb|upright=1.5|alt=Cross-section of a roof panel: thin steel sheet, thick foam core, thin steel sheet, with hot smoke below and outside air above.|Cross-section of a metal-faced sandwich panel as in the insulated steel roof example: two steel sheets of 0.5 mm with 100 mm of polyurethane foam between them. Based on Van Rossum (2027), §5.2, and Tewarson (2002), p. 3-96.]]

The core can be a foamed plastic, a light material with many fine voids that heats quickly at its surface and is therefore easy to ignite.<ref name="CVM2-65">Ministry of Business, Innovation and Employment (2025b), p. 65.</ref><ref name="NUREG-2-10">Iqbal and Salley (2004), pp. 2-10–2-11.</ref> Polyurethanes do not break down below about 475 K, and when they do they release hydrogen cyanide, carbon monoxide and isocyanates.<ref name="BH-1-128">Beyler and Hirschler (2002), p. 1-128.</ref> At the same time the core supplies most of the thermal insulation of the panel, which slows the passage of heat to the unexposed side.<ref name="VR-5.2" /><ref name="Calc-SP">Calculated from Van Rossum (2027), §5.2 and §5.5.</ref>

== Construction and materials ==
A sandwich panel combines a thin, stiff skin on each side with a thick, light core. In the large corner test used by Factory Mutual Research Corporation, the wall and ceiling materials tested are typically panels with a metal skin over an insulation core material.<ref name="Tew-3-96" /> The first edition of the New Zealand verification method C/VM2 describes the same product as a metal-skin panel assembly with a combustible core material.<ref name="MBIE13-159" /> Sandwich construction is not limited to metal skins. In one series of corner fire tests, an 88 mm sandwich composite consisted of 76 mm of balsa wood between two facings of 6 mm fire-retarded glass-fibre-reinforced vinyl ester.<ref name="Lat-2-291">Lattimer (2002), p. 2-291.</ref>

Insulating cores such as the polyurethane foam of the book's example belong to the group that New Zealand regulation calls foamed plastics. C/VM2 (second edition, 2025) defines these as combustible polymeric materials of low density, typically below 100 kg/m<sup>3</sup>. Fine voids typically make up 90 to 98 % of their volume.<ref name="CVM2-65" /> The listed examples include expanded or extruded polystyrene, phenolic, polyurethane and polyethylene foams.<ref name="CVM2-65" /> The 2013 commentary also refers to Australian standards for rigid cellular polyurethane, polyisocyanurate and polystyrene sheets for thermal insulation.<ref name="MBIE13-3">Ministry of Business, Innovation and Employment (2013), p. 3.</ref> The general fire behaviour of such polymers is treated in the article on [[plastics in fire]].

Polyurethanes are made by the condensation of polyisocyanates and polyols. Their main use is as flexible or rigid foams or as thermal insulation.<ref name="BH-1-111">Beyler and Hirschler (2002), p. 1-111.</ref> ''Introduction to Fire Safety Engineering'' gives polyurethane foam a thermal conductivity of 0.034 W/(m·K), a density of 20 kg/m<sup>3</sup> and a specific heat of 1,400 J/(kg·K). Steel has a conductivity of 45.8 W/(m·K) and a density of 7,850 kg/m<sup>3</sup>.<ref name="VR-5.5">Van Rossum (2027), §5.5.</ref> With these values, a square metre of the book's roof example contains about 7.9 kg of steel and only 2.0 kg of foam.<ref name="Calc-SP" />

== Fire behaviour of the core ==
The fire hazard of a sandwich panel lies mainly in its core. A material with low thermal inertia heats up quickly at its surface, and light insulation materials are an example. If such a material is combustible, the fast rise in surface temperature can contribute to fast ignition.<ref name="VR-5.2" /> NUREG-1805 explains that good insulators of low density typically ignite more quickly than poor insulators of high density. It names this as the main reason why foamed plastics are so dangerous in fires.<ref name="NUREG-2-10" /> Calculated with the book's property table, the thermal inertia of polyurethane foam is about 31 J/(m<sup>2</sup>·K·s<sup>1/2</sup>), against about 2,000 for concrete.<ref name="Calc-SP" /><ref name="VR-5.5" />

When the core heats up, it decomposes. As a class, polyurethanes do not break down below 475 K, which is about 200 °C. The production of hydrogen cyanide and carbon monoxide increases with the pyrolysis temperature.<ref name="BH-1-128" /> Other toxic products include nitrogen oxides, nitriles and isocyanates. A major breakdown step splits the bond between polyol and isocyanate. The isocyanate vaporises and condenses again as smoke, while the liquid polyol remains and decomposes further.<ref name="BH-1-128" />

Burning foam also produces heat and soot. The Australian Fire Safety Verification Method Data Sheets list rigid polyurethane foam with a soot yield of 0.118 kg/kg and a chemical heat of combustion of 16.9 MJ/kg. Polystyrene foam has a soot yield of 0.194 kg/kg and 25.5 MJ/kg.<ref name="ABCB-B2-21">Australian Building Codes Board (2020a), Data Sheet B2, p. 21.</ref> These values come from bench-scale tests in well-ventilated conditions. Under the ventilation-controlled conditions of many fully developed fires, the soot yield rises substantially and the effective heat of combustion falls.<ref name="ABCB-B2-21" />

The metal facings change how this fuel takes part in a fire. Guidance on the New Zealand lining tests notes that the cone calorimeter is unsuitable when the fire performance of an assembly is dominated by construction details rather than by the flammability of the surface. It is also unsuitable when significant mechanical damage occurs at full scale but not in small horizontal samples.<ref name="MBIE13-159" /> For such products the commentary requires the ISO 9705 room test or another large-scale test.<ref name="MBIE13-159" />

== Heat transfer through a panel ==
The insulating core also determines how much heat a panel passes from a fire to the other side. ''Introduction to Fire Safety Engineering'' gives a steady-state relation for a wall or roof of several layers. The heat flow per square metre equals the difference between the air temperatures on both sides, divided by the sum of all thermal resistances. Each solid layer adds its thickness divided by its thermal conductivity. Each surface adds a surface resistance, which is the inverse of its convective heat transfer coefficient.<ref name="VR-5.2" />

<math display="block">\dot q'' = \frac{T_1 - T_4}{R_{si} + \dfrac{L_1}{\lambda_1} + \dfrac{L_2}{\lambda_2} + \dfrac{L_3}{\lambda_3} + R_{se}}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot q''</math> || heat flow per unit area (heat flux) through the panel || W/m<sup>2</sup>
|-
| <math>T_1</math>, <math>T_4</math> || air or smoke temperature on the heated side and on the cool side || K
|-
| <math>R_{si}</math>, <math>R_{se}</math> || surface resistance on the heated side and on the cool side || m<sup>2</sup>·K/W
|-
| <math>L_1</math>, <math>L_2</math>, <math>L_3</math> || thickness of facing, core and facing || m
|-
| <math>\lambda_1</math>, <math>\lambda_2</math>, <math>\lambda_3</math> || thermal conductivity of each layer || W/(m·K)
|}

The relation assumes a steady state, with constant temperatures on both sides. In a real fire the smoke temperature changes and the construction warms up gradually, so the heat flow in the first minutes can differ considerably.<ref name="VR-5.2" /> The result is therefore an estimate for prolonged exposure and an upper value rather than a prediction over time.<ref name="VR-5.2" /> For a fully developed fire the book gives guide values of 20 to 25 W/(m<sup>2</sup>·K) for the convective heat transfer coefficient. For a standard fire 25 W/(m<sup>2</sup>·K) is usually taken, which gives a surface resistance of 0.04 m<sup>2</sup>·K/W.<ref name="VR-5.2" />

In the book's worked example, a smoke layer of 400 °C lies under the insulated steel roof and the outside air is 10 °C. Both surfaces have a resistance of 0.04 m<sup>2</sup>·K/W. The foam layer of 0.1 m adds 2.94 m<sup>2</sup>·K/W and each steel sheet adds only about 0.00001 m<sup>2</sup>·K/W. The heat flow is then about 129 W/m<sup>2</sup>.<ref name="VR-5.2" /> The core supplies about 97 % of the total resistance. Without it, the two steel sheets would pass about 4,900 W/m<sup>2</sup>, roughly 38 times as much.<ref name="Calc-SP" />

The book also shows that the temperature drop over each layer is proportional to its share of the total resistance.<ref name="VR-5.2" /> Applied to the roof example, almost the whole drop of 390 K occurs inside the foam. In the steady state, the face of the core behind the hot steel sheet would therefore reach about 395 °C.<ref name="Calc-SP" /> That is well above the temperature of about 200 °C below which polyurethanes do not break down.<ref name="BH-1-128" /> A good insulation value thus keeps the cool side cool, but it also concentrates the heating in the combustible core on the fire side.

[[File:fse-sandwich-panel-v2.svg|thumb|upright=1.5|alt=Line chart of temperature through the roof panel: about 395 °C at the hot face of the core, falling almost linearly to about 15 °C at the cool face.|Steady-state temperature profile through the insulated steel roof of the worked example (400 °C smoke, 10 °C outside). Based on Van Rossum (2027), §5.2 and §5.5.]]

== Fire testing ==
Small-scale tests can rank many lining materials, but sandwich panels need large-scale tests. In New Zealand, results from the ISO 5660 cone calorimeter have been correlated with the time to flashover in the ISO 9705 room test. The 2013 commentary names metal-faced sandwich panels and foil-faced combustible insulation as products for which this correlation is not suitable.<ref name="MBIE13-141" /> In the ISO 9705 [[room corner test]], the linings are exposed to a burner of 100 kW for 10 minutes and then 300 kW for a further 10 minutes. Flashover is taken as a heat release rate of 1.0 MW.<ref name="MBIE13-141" />

A test standard written specifically for these products is ISO 13784 Part 1 (2002). Its title describes reaction-to-fire tests for sandwich panel building systems, with a test method for small rooms.<ref name="MBIE13-4">Ministry of Business, Innovation and Employment (2013), p. 4.</ref> The first edition of C/VM2 required metal-skin panel assemblies with combustible cores to be assessed only with ISO 9705 or ISO 13784 Part 1.<ref name="MBIE13-159" /> In general, a product must be tested in a configuration that resembles its actual end use as closely as possible.<ref name="MBIE13-141" />

Factory Mutual Research Corporation has used a 25-ft corner test since 1971. The test structure is 7.6 m high, 15.2 m long and 11.6 m wide. It is exposed to a growing fire of about 340 kg of oak pallets stacked 1.5 m high, with a peak heat release rate of about 3 MW.<ref name="Tew-3-96" /> A panel fails if, within 15 minutes, fire spreads to the limits of the structure or flames extend outside it through the ceiling smoke layer.<ref name="Tew-3-96" /> In the FMRC Class No. 4880 standard for insulated wall or wall and ceiling panels, this corner test has been replaced by bench-scale tests in the ASTM E2058 fire propagation apparatus. Materials with a convective flame spread parameter of up to 0.39 pass, values from 0.47 fail, and the range between is uncertain.<ref name="Tew-3-97">Tewarson (2002), p. 3-97.</ref>

[[File:fse-sandwich-panel-v4.svg|thumb|upright=1.5|alt=Line drawing of a large building corner with two panel walls and a ceiling, and a stack of wood pallets burning at the base of the corner.|The Factory Mutual 25-ft corner test: two panel walls and a ceiling exposed to about 340 kg of burning oak pallets in the corner. Based on Tewarson (2002), p. 3-96.]]

In Europe, the Single Burning Item test is a regulatory heat release rate test for building products. It uses two wall panels in a corner configuration without a ceiling.<ref name="Bab-3-32">Babrauskas (2002b), p. 3-32.</ref> The way its results are classified is described in the article on the [[Euroclass system]]. Corner tests on sandwich construction can produce high heat fluxes. In open corner tests with combustible linings, including the balsa sandwich composite, heat fluxes to the ceiling as high as 130 kW/m<sup>2</sup> were measured.<ref name="Lat-2-291" /><ref name="Lat-2-292">Lattimer (2002), p. 2-292.</ref>

== Regulation in New Zealand ==
The New Zealand verification method gives the most detailed rules on panels in the source documents used here. Under the first edition of C/VM2, as explained in the 2013 commentary, linings are classified with Group Numbers from 1 (best) to 4 (worst). The classification is based on their measured time to flashover in the ISO 9705 test.<ref name="MBIE13-141" /> A Group Number 3 material has a total heat release of no more than 1 MW after 2 minutes at 100 kW. A Group Number 4 material exceeds 1 MW within those 2 minutes.<ref name="MBIE13-159" /> Group Number 4 includes exposed polyurethane foams, which are not acceptable as linings in occupied spaces.<ref name="MBIE13-141" />

[[File:fse-sandwich-panel-v3.svg|thumb|upright=1.5|alt=Step chart of burner output: 100 kW from 0 to 10 minutes, 300 kW from 10 to 20 minutes, with Group Number markers at 2, 10 and 20 minutes.|Burner programme of the ISO 9705 room test and the times that define material Group Numbers under the first edition of C/VM2. Based on Ministry of Business, Innovation and Employment (2013), pp. 141 and 159.]]

Where foamed plastics or combustible insulation form part of an element, the completed assembly must achieve the required Group Number. The foam itself must also meet the flame propagation criteria of AS 1366.<ref name="MBIE13-138">Ministry of Business, Innovation and Employment (2013), p. 138.</ref> Without a protective lining, the foam tested alone must reach Group Number 3. Normally a protective barrier between the foam and the room side is needed.<ref name="MBIE13-138" /><ref name="MBIE13-145">Ministry of Business, Innovation and Employment (2013), p. 145.</ref> According to the commentary, fire-retardant grades of foamed plastics are already generally used in the construction industry.<ref name="MBIE13-145" />

C/VM2 (second edition, 2025) refers to the separate Building Product Specifications for Group Numbers, surface linings and cladding. References to test standards such as ISO 9705, ISO 13784 and BS EN 13501 have been removed from the verification method itself.<ref name="CVM2-3">Ministry of Business, Innovation and Employment (2025b), p. 3.</ref> Material Group Numbers apply to the exposed surface of the wall or ceiling lining.<ref name="CVM2-50">Ministry of Business, Innovation and Employment (2025b), p. 50.</ref> In C/VM2, a combustible material is one that is neither non-combustible nor of limited combustibility.<ref name="CVM2-62">Ministry of Business, Innovation and Employment (2025b), p. 62.</ref> The wider meaning of these classes is discussed under [[combustibility]].

Panels used as external walls also fall under the rules for vertical fire spread, the subject of the article on [[facade fire]]. For multi-level buildings taller than 10 m, C/VM2 (second edition, 2025) uses a design fire that exposes the cladding to 50 kW/m<sup>2</sup> for 15 minutes for importance levels 2 and 3. For importance level 4 the exposure is 90 kW/m<sup>2</sup>.<ref name="CVM2-48">Ministry of Business, Innovation and Employment (2025b), p. 48.</ref> The entire external wall cladding system must either consist of non-combustible or limited combustible materials, or meet the acceptance criteria of the Building Product Specifications. Cavity barriers are required at each floor level.<ref name="CVM2-48" />

== Limits of current knowledge ==
The source documents used for this article contain no systematic data on the fire behaviour of complete sandwich panels. They give no measured times to failure of joints or facings and no account of fire spread hidden inside the core. They also give no data on panel roofs that carry solar installations, which are treated under photovoltaic system fire. The steady-state heat transfer calculation describes only the insulation of an intact panel. It does not show when a facing deforms, opens at a joint or lets flames reach the core.<ref name="VR-5.2" />

Large single-storey buildings raise a further question. In a distribution centre with high racking, fuel at height can ignite as a secondary fire once the smoke layer exceeds 200 °C. Most materials ignite at temperatures between about 200 °C and 500 °C.<ref name="VR-9.3b">Van Rossum (2027), §9.3 (Results from zone models).</ref> How a panel roof above such storage contributes to a [[warehouse fire]] cannot be quantified from the sources available here.

== See also ==
* [[Reaction to fire]]
* Single Burning Item test
* [[Cone calorimeter]]
* Large-scale facade fire test
* [[Fire resistance test]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Babrauskas, V. (2002b). Heat release rates. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association; Society of Fire Protection Engineers.
* Beyler, C. L., & Hirschler, M. M. (2002). Thermal decomposition of polymers. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-110–1-131). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Lattimer, B. Y. (2002). Heat fluxes from fires to surfaces. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-269–2-296). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* Tewarson, A. (2002). Generation of heat and chemical compounds in fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-82–3-161). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Materials & Fire Testing]]

Quantitative risk assessment

2026-11-02T21:34:34Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Quantitative risk assessment''' ('''QRA''') is the estimation of risk in numerical terms, by combining the frequency of undesired events with the size of their consequences.<ref name="BA-176">Barry (2002), p. 5-176.</ref> It answers three questions: what could happen, how bad would it be, and how likely is it to happen.<ref name="WH-1">Watts and Hall (2002), p. 5-1.</ref> The results support decisions, either through comparison with acceptable risk levels or through a ranking of the options for reducing risk.<ref name="BA-177">Barry (2002), p. 5-177.</ref> A QRA identifies hazards and scenarios, estimates their frequencies with methods such as [[event tree analysis]] and [[fault tree analysis]], and models their consequences. It presents the outcome in measures such as [[individual risk]] and [[societal risk]].<ref name="BA-188">Barry (2002), p. 5-188.</ref><ref name="BA-210">Barry (2002), p. 5-210.</ref>

In the process industries, QRA supports decisions on plant siting, protection options and regulatory compliance.<ref name="BA-177" /> In nuclear power, the same method is called probabilistic risk assessment (PRA), and fire PRA studies have shown that fire can be a significant or even dominant contributor to the risk of a plant.<ref name="SIU-214">Siu (2002), p. 5-214.</ref> In building design, a full QRA is the most complete way to compare a design with a code-compliant reference building. It needs substantial resources, however, so simpler event tree comparisons are often used.<ref name="HB-119">Australian Building Codes Board (2020b), p. 119.</ref>

== Definition and terminology ==
Watts and Hall define risk as the potential for unwanted, adverse consequences to human life, health, property or the environment. They note that risk is usually estimated as the expected value of the probability of an event times its consequence.<ref name="WH-3">Watts and Hall (2002), p. 5-3.</ref> Strictly, the risk of a building is the whole probability distribution of its fire events and their consequences. The many published definitions of risk can be seen as summary measures of that distribution, and a committee of the Society for Risk Analysis identified 17 of them.<ref name="WH-3" /> Barry expresses fire and explosion risk as the product of the frequency of an undesired event and its expected consequences:<ref name="BA-176" />

<math display="block">R = F \times C</math>

To reduce the risk of a defined fire or explosion, the frequency, the consequences or both must therefore be reduced.<ref name="BA-176" /> The terms risk analysis and risk assessment are used interchangeably by some authors and distinguished sharply by others.<ref name="WH-3" /> In the definitions of Watts and Hall, risk analysis includes the quantification of the probabilities and expected consequences of identified risks, while risk evaluation judges their significance and acceptability. Barry describes risk assessment as the use of quantitative risk estimates to support risk management decisions, and he names decision support as its key purpose.<ref name="BA-177" />

In nuclear power, the same work is called probabilistic risk assessment or probabilistic safety assessment (PSA).<ref name="SIU-214" /> More broadly, a quantitative approach is one of two families of fire safety engineering methods. The qualitative approach relies on expert judgement, experience and descriptive risk classes, while the quantitative approach uses measurements and statistical analyses and suits complex scenarios with several variables.<ref name="VR-1.4">Van Rossum (2027), §1.4.</ref> Watts and Hall noted in 2002 that probabilistic analysis was not yet well established in fire protection engineering, where empiricism, heuristics and physics-based modelling dominated.<ref name="WH-3" />

== Steps of an assessment ==
Barry divides a fire and explosion risk assessment into seven steps.<ref name="BA-177" /> The analyst first defines the objectives, then identifies the hazards and describes the loss event scenarios. The consequences and the probabilities of these scenarios are assessed next, with a risk screening step alongside. The results are then presented. If the risk is not acceptable, risk reduction is analysed and the assessment is repeated, while an acceptable risk is followed by monitoring.<ref name="BA-177" />
[[File:fse-quantitative-risk-assessment-v1.svg|thumb|upright=1.5|alt=Flowchart of seven QRA steps from objectives to risk presentation, with a decision on acceptability leading to risk reduction or monitoring.|The steps of a fire and explosion risk assessment. An unacceptable risk leads to risk reduction and a new assessment; an acceptable risk to monitoring. Based on Barry (2002), p. 5-177.]]

The objectives determine the rest of the work. They state the decision to be supported, such as plant siting, protection options or regulatory compliance. They also state the focus, such as casualties, property damage, lost production or environmental damage.<ref name="BA-177" /> Finally, they fix the level of detail, relative or absolute, and the acceptable risk limits, including severity limits, likelihood limits and the risk tolerance of management.<ref name="BA-177" />

Event trees are the most widely used technique for structuring fire scenarios, because they follow the initiation, propagation and consequences of a fire in time.<ref name="BA-180">Barry (2002), p. 5-180.</ref> An event tree may lack detail on the causes of a particular branch. In that case fault trees supplement it and provide detail on the events that lead to the final consequence.<ref name="BA-180" />

Consequence assessment estimates the intensity of fires and explosions and their effects on equipment and people. Barry gives generic damage levels for thermal radiation, based on observations of large fires. An incident heat flux of 37.5 kW/m² damages process equipment and causes 100% lethality within 1 min. At 12.5 kW/m² the lethality is 1% in 1 min, and 4.0 kW/m² causes pain if exposure lasts longer than 20 s.<ref name="BA-186">Barry (2002), p. 5-186.</ref>
[[File:fse-quantitative-risk-assessment-v5.svg|thumb|upright=1.5|alt=Horizontal scale of incident heat flux from 1.6 to 37.5 kW/m2 with effects on people, from no discomfort to 100 percent lethality in 1 min.|Generic damage levels for incident thermal radiation used in consequence assessment, based on observations of large fires. Based on Barry (2002), p. 5-186.]]

Such generic thresholds give a good first-order review but are weak in their treatment of time. Detailed heat transfer or structural models are used where time matters.<ref name="BA-186" /> For people in buildings, exposure models range from simple tenability limits to fractional effective dose models and [[probit function]]s.<ref name="HB-110">Australian Building Codes Board (2020b), p. 110.</ref>

== Frequency and probability ==
The frequency of a scenario follows its path through an event tree. The frequency of the initiating event is combined with the conditional probabilities of the intermediate events that increase or mitigate the spread of the fire.<ref name="BA-188" /> Barry names two ways to obtain these numbers: relevant historical data, and synthesis with fault trees, human reliability analysis and expert judgement. The two are often used together, each as a check on the other.<ref name="BA-188" />

Historical frequencies represent only average values and suit simple systems best.<ref name="BA-188" /> Barry also reports that human error is the leading cause of fires and explosions in industry. The quoted shares are 70% to 85% for human factors, 10% to 20% for equipment failures and 10% to 20% for external factors such as earthquakes and floods.<ref name="SL-188">Slater et al. (1990), as cited in Barry (2002), p. 5-188.</ref>

Fire PRA of nuclear power plants writes the same logic as a formula. Siu divides the core damage frequency contribution of a fire scenario into three parts. They are the frequency of the fire, the conditional probability of damage to critical equipment, and the conditional probability of core damage given that damage:<ref name="SIU-216">Siu (2002), p. 5-216.</ref>

<math display="block">\mathrm{CDF} = \sum_i \lambda_i \left[ \sum_j p_{\mathrm{ed},j \mid i} \left( \sum_k p_{\mathrm{CD},k \mid i,j} \right) \right]</math>

The three terms correspond to the three layers of fire protection defence in depth: fire prevention, fire detection and suppression, and fire mitigation.<ref name="SIU-216" /> Fire frequencies are generally estimated with simple statistical models, damage with deterministic and probabilistic models of the physical processes, and core damage with conventional PRA system models.<ref name="SIU-216" /> In the methodology of the Electric Power Research Institute (EPRI) and the U.S. Nuclear Regulatory Commission (NRC), the frequency of a single fire scenario is itself a product of four factors:<ref name="NO-11-2">Nowlen et al. (2005b), p. 11-2.</ref>
[[File:fse-quantitative-risk-assessment-v2.svg|thumb|upright=1.5|alt=Event tree from fire frequency through equipment damage and core damage branches; brackets mark prevention, detection and suppression, mitigation.|The three terms of the fire risk equation: fire frequency, conditional probability of equipment damage, and conditional probability of core damage, matched to the layers of defence in depth. Based on Siu (2002), p. 5-216.]]

<math display="block">\lambda_k = \lambda_{i,k} \cdot W_{g,k} \cdot \mathit{SF}_k \cdot P_{\mathrm{ns},k}</math>

The ignition frequency of the source is multiplied by a floor area ratio for transient fires, a severity factor and the probability that the fire is not suppressed in time.<ref name="NO-11-2" /> The scenario frequency is then combined with the conditional core damage probability of the scenario, and the core damage frequency of a compartment is the sum over its scenarios.<ref name="NO-11-31">Nowlen et al. (2005b), p. 11-31.</ref> Many studies start with conservative screening values, for example a damage probability of one, and refine only the scenarios that matter.<ref name="SIU-216" />

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>R</math> || risk of a defined fire or explosion || consequence per year
|-
| <math>F</math> || frequency of the undesired event || year<sup>−1</sup>
|-
| <math>C</math> || expected consequences of the event (e.g. fatalities, damage) || consequence per event
|-
| <math>\mathrm{CDF}</math> || core damage frequency || year<sup>−1</sup>
|-
| <math>\lambda_i</math> || frequency of fire scenario <math>i</math> || year<sup>−1</sup>
|-
| <math>p_{\mathrm{ed},j \mid i}</math> || conditional probability of damage to critical equipment set <math>j</math>, given fire scenario <math>i</math> || dimensionless
|-
| <math>p_{\mathrm{CD},k \mid i,j}</math> || conditional probability of core damage through plant response <math>k</math>, given scenario <math>i</math> and damage <math>j</math> || dimensionless
|-
| <math>\lambda_{i,k}</math> || ignition frequency of the ignition source of scenario <math>k</math> || year<sup>−1</sup>
|-
| <math>W_{g,k}</math> || floor area ratio for a transient fire scenario (1.0 for fixed sources) || dimensionless
|-
| <math>\mathit{SF}_k</math> || severity factor of scenario <math>k</math> || dimensionless
|-
| <math>P_{\mathrm{ns},k}</math> || probability that the fire of scenario <math>k</math> is not suppressed in time || dimensionless
|-
| <math>R_\mathrm{A}</math>, <math>R_\mathrm{B}</math> || expected number of people exposed to untenable conditions per fire, for systems A and B (worked example) || persons per fire
|}

== Risk measures and presentation ==
Results are presented in forms that suit the decision. A risk profile plots the expected frequencies of incidents against their consequences, for example property damage, business interruption or fatalities.<ref name="BA-209">Barry (2002), p. 5-209.</ref> Barry adds that the presentation should include an uncertainty bandwidth, which matters most for rare events with large consequences.<ref name="BA-209" />

Individual risk is the probability of injury or death to a person at a specified location within the effect zone of a fire or explosion.<ref name="BA-210" /> It is often drawn as risk contours, which are closed lines of constant risk around a facility. A contour shows the expected frequency of events that can cause a specified harm at a location, whether or not anyone is present there.<ref name="BA-210" />
[[File:fse-quantitative-risk-assessment-v3.svg|thumb|upright=1.5|alt=Plan view of a petrochemical plant with three nested closed risk contours of 10^-6, 10^-7 and 10^-8 per year reaching towards nearby housing.|Schematic individual risk contours around a petrochemical plant. Each line joins points of equal individual risk; inside a line the risk is at least that value. Based on Barry (2002), p. 5-210.]]

Societal risk takes account of the likelihood of multiple casualties. It is usually presented as an F-N curve, which plots the cumulative frequency of events with N or more fatalities against N on logarithmic scales.<ref name="BA-210" /><ref name="BA-211">Barry (2002), p. 5-211.</ref> An F-N curve for people beyond a plant boundary needs a definition of the population at risk, the likelihood that people are present and the reliability of mitigation such as evacuation. Risk indices, such as the fatal accident rate, give single numbers for comparing design options.<ref name="BA-211" />

The Fire Safety Verification Method of the Australian Building Codes Board uses similar definitions. Individual risk is the frequency at which an individual may be expected to sustain a given level of harm from a fire in the building. Societal risk is the relationship between frequency and the number of people harmed in a given population, usually the occupants of the building and its surroundings.<ref name="HB-22">Australian Building Codes Board (2020b), p. 22.</ref> Most human risk quantification is based on fatalities, and Barry stresses that the fatal doses of thermal radiation, blast and toxic chemicals are themselves uncertain.<ref name="BA-211" />

== Worked example ==
The handbook of the Australian Building Codes Board shows why a purely deterministic comparison can mislead.<ref name="HB-118">Australian Building Codes Board (2020b), p. 118.</ref> Two fire safety systems give the same deterministic result. If they work as designed, nobody is exposed to untenable conditions, and if they fail, 2 people are exposed. System A, in the code-compliant reference building, has a reliability of 90%, and system B, in the proposed design, has a reliability of 70%.<ref name="HB-118" /> A deterministic analysis alone would therefore judge the two systems equivalent. A simple risk calculation multiplies the probability of failure by the number of people exposed:<ref name="HB-119" />

<math display="block">R_\mathrm{A} = 0.1 \times 2 = 0.2, \qquad R_\mathrm{B} = 0.3 \times 2 = 0.6</math>

System B exposes the occupants to three times the risk of the reference solution, so the two designs are not equivalent.<ref name="HB-119" /> The handbook concludes that a risk assessment is generally required whenever the reliabilities of the fire safety systems differ appreciably between the proposed design and the reference building.<ref name="HB-118" /> The results are expected numbers of people exposed per fire. A full QRA would also account for the frequency of fires and repeat the calculation over many scenarios.<ref name="BA-176" /><ref name="HB-119" />
[[File:fse-quantitative-risk-assessment-v4.svg|thumb|upright=1.5|alt=Bar chart: system A failure probability 0.1 and risk 0.2 people per fire; system B failure probability 0.3 and risk 0.6 people per fire.|Probability of failure and expected number of people exposed per fire for the reference system A and the proposed system B. Based on Australian Building Codes Board (2020b), pp. 118 to 119.]]

== Use in fire safety engineering and regulation ==
Barry lists five reasons why companies use QRA.<ref name="BA-176" /> It helps to reduce design risks to in-house standards and to evaluate code equivalency or the relative risk of design options. It can also show a community or an insurer that a large hazard carries a small risk. Other uses are the prediction of effect zones for emergency planning and compliance with government requirements. In the United States, Barry noted in 2002 that rules under the 1990 Clean Air Act Amendments may require risk assessment and risk management programmes from facilities that hold threshold amounts of hazardous materials. Several states also required QRA.<ref name="BA-176" />

In the nuclear industry, PRA has been used since the Reactor Safety Study of 1975, and studies had been performed for all operating nuclear power plants in the United States by 2002.<ref name="SIU-214" /> Fire PRA determines the contribution of fires to plant risk, and its results are used to decide whether and how the fire protection programme of a plant should change.<ref name="SIU-214" /> Because the main concern is the health and safety of the public, fire PRA focuses on scenarios that lead to core damage and uses the core damage frequency as its principal measure.<ref name="SIU-215">Siu (2002), p. 5-215.</ref>

For buildings in Australia, the International Fire Engineering Guidelines (2005) explain that the performance requirements of the Building Code of Australia set a benchmark for the risk of fatality, injury and loss of adjacent structures. That benchmark is not zero risk, but its level is not stated explicitly, so acceptance criteria are agreed for each project.<ref name="IFEG-0.2-3">National Research Council of Canada et al. (2005), Part 0 (Australia), p. 0.2-3.</ref> The Fire Safety Verification Method handbook (2020) uses a comparative approach, in which a code-compliant reference building indirectly defines the acceptable levels of individual and societal risk.<ref name="HB-46">Australian Building Codes Board (2020b), p. 46.</ref>

A detailed QRA is the most complete way to make this comparison in the Australian method. Because of the time-dependent interactions between fire, fire safety systems, occupants and fire services, it often needs substantial resources and multi-scenario analysis.<ref name="HB-119" /> For designs with only minor differences from the reference building, simple event trees for the probabilities and deterministic analysis of the critical branches are considered reasonable and conservative.<ref name="HB-124">Australian Building Codes Board (2020b), p. 124.</ref>

In the Netherlands, building regulations set limits on measures, such as walking distances and fire resistance in minutes. They do not state how many casualties or how much fire spread to neighbouring plots is acceptable.<ref name="VR-1.2">Van Rossum (2027), §1.2.</ref> Van Rossum notes that the lack of risk-based limit values is a drawback of a quantitative approach in Dutch fire safety engineering.<ref name="VR-1.4" /> The acceptable residual risk then has to be agreed in advance, for example by comparison with a reference situation based on the regulations. Some standards for large fire compartments are partly based on this method.<ref name="VR-1.2" />

== Uncertainty and limitations ==
Siu distinguishes two kinds of uncertainty in fire PRA. Aleatory uncertainty describes random variation, such as the number of fires in a room over a given period, which is modelled with a Poisson distribution. Epistemic uncertainty describes limited knowledge, such as the uncertain value of the room fire frequency itself, and it can be reduced with more data.<ref name="SIU-215" /> In the EPRI/NRC methodology, the epistemic distributions are propagated through the risk model with [[Monte Carlo simulation]] or Latin hypercube sampling. The result is a probability distribution of the core damage frequency instead of a single value.<ref name="NO-14-5">Nowlen et al. (2005b), p. 14-5.</ref>

Data are a common weak point. Fire records for homes in the United States are numerous but thin on detail, nuclear plants have few fires but detailed records, and a single building has very few relevant events of its own.<ref name="WH-3" /> Watts and Hall add that no totally objective way to measure fire risk exists, because problem identification, data collection and the integration of information all involve subjective judgement.<ref name="WH-3" /> The International Fire Engineering Guidelines note that probabilistic methods need much statistical data that are not always available. They also involve time-consuming calculations and are harder to validate, so deterministic methods are used more often.<ref name="IFEG-1.2-22">National Research Council of Canada et al. (2005), p. 1.2-22.</ref>

Finally, the numbers do not decide acceptability by themselves. Accepting a level of risk is a value judgement, and the result depends on whose values are applied, such as those of a client, an authority or the general public.<ref name="WH-1" /><ref name="WH-4">Watts and Hall (2002), p. 5-4.</ref> Watts and Hall treat it as an axiom of fire risk analysis that zero risk is not an achievable goal.<ref name="WH-4" />

== See also ==
* [[Fire risk assessment]]
* ALARP
* [[TNT equivalence]]
* [[Common cause failure]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-176–5-213). National Fire Protection Association; Society of Fire Protection Engineers.
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Nowlen, S. P., Najafi, B., Wyant, F. J., Forester, J., Kazarians, M., Kolaczkowski, A., Joglar, F., Funk, D., Hannaman, G., & Anoba, R. (2005b). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Vol. 2. Detailed methodology'' (NUREG/CR-6850; EPRI 1011989). Electric Power Research Institute; U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research.
* Siu, N. (2002). Fire risk assessment for nuclear power plants. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-214–5-226). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Watts, J. M., Jr., & Hall, J. R., Jr. (2002). Introduction to fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-1–5-7). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Risk Analysis]]

Room corner test

2026-11-02T21:34:31Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Room corner test''' is a fire experiment in which an ignition source exposes products installed inside a room, commonly at a corner. It measures how those products contribute to fire development under defined enclosure and exposure conditions. The ISO 9705 arrangement described in the ''SFPE handbook'' uses a gas burner and measures heat release through the combustion products leaving the doorway.<ref name="J-57-58">Janssens (2002), pp. 3-57–3-58.</ref>

For wall and ceiling linings, the test captures interactions between spreading flames, the growing burning area and heating from the enclosure. These interactions are difficult to represent using a small material specimen alone. The measured [[Heat release rate|heat release rate]] includes the ignition burner as well as burning products when the reported quantity is total room output.<ref name="B-30-31">Babrauskas (2002), pp. 3-30–3-31.</ref><ref name="NZ-159">Ministry of Business, Innovation and Employment (2013), p. 159, reproduced C/VM2 Appendix A, p. 66.</ref>

The result depends on the test geometry, burner programme and product installation. It can support product classification or an engineering model, but does not automatically predict every room containing the product. Different room-test protocols can use different exposures and acceptance rules. Their results therefore require identification of the particular method and its intended application.<ref name="J-57-58" /><ref name="B-3">Babrauskas (2002), pp. 3-2–3-3.</ref>

== Why the room matters ==

An interior lining can cover a large area without all of that area burning at the same time. Fire first involves part of the surface, then may spread to additional areas. The developing fire consequently depends on both the local burning behaviour and the changing area of involvement. Babrauskas identifies this spreading area as a central difficulty in predicting lining heat release from small specimens.<ref name="B-30-31" />

The enclosure also changes the exposure received by the product. Heated walls, the ceiling and accumulated gases can return radiation to burning surfaces. This feedback can increase fuel decomposition and change the heat release compared with open burning. The room test includes these interactions within its own geometry, although another enclosure may produce different feedback and ventilation conditions.<ref name="J-38">Janssens (2002), p. 3-38.</ref><ref name="B-3" />

The connection with [[Flashover|flashover]] is particularly useful for evaluating interior finishes. The New Zealand C/VM2 commentary describes time to flashover as the principal parameter in its lining-group approach. For that reference test, the commentary takes total output reaching 1.0 MW as the flashover criterion. This is a test-specific operational criterion, not a universal power threshold for every room.<ref name="NZ-139-141">Ministry of Business, Innovation and Employment (2013), pp. 139–141.</ref>

A room experiment can also reveal behaviour that depends on assembly details. A small coupon may preserve its shape while a complete panel assembly opens, separates or otherwise changes during exposure. The 2013 New Zealand commentary specifically identifies cases where construction details dominate performance. These are reasons to evaluate the installed arrangement rather than infer its behaviour solely from the surface material.<ref name="NZ-159" />

Large-scale measurements serve two related purposes in the handbook's account. They can evaluate products or assemblies that small specimens cannot represent, and they can test the predictive performance of fire models. The second purpose requires the experimental boundary conditions to be known. Otherwise, a difference between calculation and measurement may reflect different assumed exposures rather than the particular physical model under examination.<ref name="J-57-58" />

== Room, burner and collection system ==

The ISO arrangement described in the sources is 3.6 m long, 2.4 m wide and 2.4 m high. A doorway in a short wall is 0.8 m wide and 2.0 m high. The burner occupies a corner opposite that opening. Combustion products leaving the doorway enter a hood connected to the exhaust measurement system.<ref name="B-geometry">Babrauskas (2002), p. 3-3, Figure 3-1.3.</ref><ref name="NZ-139">Ministry of Business, Innovation and Employment (2013), p. 139.</ref>
[[File:fse-room-corner-test-v1.svg|thumb|upright=1.5|alt=Plan and section of a room corner test with burner, doorway and collection hood.|Reference room and exhaust arrangement. Based on Babrauskas (2002), p. 3-3, and Ministry of Business, Innovation and Employment (2013), p. 139.]]

The New Zealand commentary describes lining the walls and ceiling with the same material when determining the material Group Number. This classification arrangement does not necessarily reproduce the combination of wall and ceiling products in a particular building. The distinction matters when interpreting the result as a reference scenario. The tested product configuration and the proposed end-use arrangement remain separate pieces of information.<ref name="NZ-139" />

Gas burners provide a controllable and repeatable ignition exposure. Janssens identifies their development, together with oxygen calorimetry, as central to standardising room tests. The primary ISO burner programme described in the handbook supplies 100 kW for ten minutes, followed by 300 kW for another ten minutes. The higher second stage challenges products that withstand the first exposure without extensive fire growth.<ref name="J-57-58" />

The collection system measures the combined products from burner combustion and product burning. The [[Oxygen consumption principle|oxygen consumption principle]] allows chemical heat release to be derived from exhaust-flow and gas-composition measurements. This differs from estimating fire power solely from room temperature. The hood and instruments make the room a calorimeter, while the room itself establishes the exposure and ventilation environment.<ref name="J-57-58" /><ref name="NZ-139" />

== Interpreting output and burner contribution ==

The total measured output includes energy released by the exposure source. In the historical New Zealand Group Number procedure, the 1 MW comparison explicitly includes the burner contribution. Interpreting a total curve as though it represented only the lining would therefore overstate the material contribution. Conversely, comparing a burner-subtracted curve directly with that total-output criterion would use inconsistent quantities.<ref name="NZ-159" />

The relationship can be expressed as an energy-rate balance between the burner and lining contributions. The accumulated burner energy is obtained by multiplying each constant power level by its duration and adding the stages. These expressions describe the stated reference programme. They do not predict how much energy the installed lining releases or when its flame spread accelerates.<ref name="NZ-159" /><ref name="AB-48">Australian Building Codes Board (2020), p. 48.</ref>

<div class="fse-equation">Q̇<sub>total</sub> = Q̇<sub>burner</sub> + Q̇<sub>lining</sub></div>
<div class="fse-equation">E<sub>burner</sub> = Σ Q̇<sub>burner,i</sub> Δt<sub>i</sub></div>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| Q̇<sub>total</sub> || Total chemical heat release rate || kW
|-
| Q̇<sub>burner</sub> || Ignition-source heat release rate || kW
|-
| Q̇<sub>lining</sub> || Lining contribution to heat release rate || kW
|-
| E<sub>burner</sub> || Energy released by the burner || kJ
|-
| Δt<sub>i</sub> || Duration of burner stage i || s
|}

For the specified exposure history, the first 600 s at 100 kW release 60 MJ from the burner. The second 600 s at 300 kW release a further 180 MJ. The complete programme therefore supplies 240 MJ, calculated from the source powers and durations. This value describes the ignition source over a completed programme; it is not the total fire energy or a specimen's measured combustion energy.<ref name="J-57-58" />
[[File:fse-room-corner-test-v2.svg|thumb|upright=1.5|alt=Step chart of 100 kW for ten minutes followed by 300 kW for ten minutes.|The two burner stages release 240 MJ over a completed programme. Based on Janssens (2002), pp. 3-57–3-58.]]

At a total output of 1,000 kW, the corresponding lining contribution would be 900 kW during the first burner stage. During the second stage, the same total corresponds to 700 kW from the lining. These calculated differences explain why the output curve and burner history are interpreted together. They are arithmetic illustrations at the criterion, rather than observations from a particular product test.<ref name="NZ-159" />

Heat release rate and accumulated heat release also require different interpretations. The first describes power at a particular stage, whereas the second adds energy released over a period. A lining that releases energy rapidly can influence early fire development differently from one releasing the same energy over a longer period. The reference classification therefore uses the timed development of output, while later design-fire assessment separately considers fuel load.<ref name="B-30-31" /><ref name="AB-47-52" />

== Classification and product configuration ==

The 2013 New Zealand commentary describes a system running from Group Number 1 to Group Number 4. Its classification uses how the tested lining behaves during successive parts of the reference exposure. Products that avoid the defined flashover condition throughout the complete test perform differently from products that exceed it early. The classification therefore retains information about the development of fire, not simply whether ignition occurred.<ref name="NZ-139-141" /><ref name="NZ-159" />

These historical rules distinguish the first two minutes, the first ten minutes and the complete twenty-minute exposure. They also distinguish heat-release performance from additional smoke criteria. The commentary explains that product composition, thickness and additives can affect the assigned group. Broad material descriptions therefore do not replace a result for the product and configuration actually tested.<ref name="NZ-139-141" /><ref name="NZ-159" />

A [[Sandwich panel|sandwich panel]] with metal faces and a combustible core illustrates the difficulty of relying only on small samples. The 2013 New Zealand provisions reproduced in the commentary require specified larger-scale methods for these assemblies. They also identify foil-faced combustible products and other arrangements unsuitable for cone-based assessment. These are requirements of that named historical New Zealand document, not universal requirements imposed by the room test itself.<ref name="NZ-159" />

The Single Burning Item test is another arrangement used to evaluate building products. Babrauskas describes it as two wall panels forming a corner without a ceiling. That geometry differs from an enclosed room with wall and ceiling linings. Similar use of heat-release measurements therefore does not make the two test configurations or their classification systems interchangeable.<ref name="B-32">Babrauskas (2002), p. 3-32.</ref>

A group classification also does not specify a universal outcome for every proposed installation. The New Zealand commentary relates required lining performance to occupancy, escape routes, occupant evacuation ability and sprinkler protection. These considerations determine where a classified product is acceptable within the stated framework. The experiment supplies product evidence; the framework connects that evidence to the building conditions and fire-safety purpose.<ref name="NZ-139" />

== From measurements to design fires ==

Australian guidance provides an example of using room-test behaviour in engineering comparisons. The ABCB 2020 Data Sheets discuss comparing wall and ceiling linings with different Group Numbers. Their reference scenario follows the 100 kW and 300 kW burner stages. The guidance links the time to exceed 1,000 kW total output with an assumed design-fire growth description.<ref name="AB-47-50">Australian Building Codes Board (2020), pp. 47–50.</ref>

The same guidance distinguishes known product results from generic lining assumptions. Where the relevant test result is available, it permits a system-specific growth description within its method. Where generic Group 3 linings are used, it assigns different growth assumptions to the reference building and proposed solution. This is an explicit modelling convention for that Australian comparison process, rather than a measured property shared by every Group 3 product.<ref name="AB-50-51">Australian Building Codes Board (2020), pp. 50–51.</ref>

Changing a lining can also change more than the early growth rate. The ABCB document identifies potential effects on fire load, the fraction of fires reaching full development and the severity of later exposure. It discusses modifications for suppression interventions and the contribution of combustible linings to fuel load. Thus the room-test classification is one input to the comparison, rather than a complete building-fire calculation.<ref name="AB-47-52">Australian Building Codes Board (2020), pp. 47–52.</ref>
[[File:fse-room-corner-test-v3.svg|thumb|upright=1.5|alt=Diagram connecting lining-test evidence to growth, fire load, fire development and intervention assumptions.|Lining changes can affect several parts of an engineering comparison. Based on Australian Building Codes Board (2020), pp. 47–52.]]

The guidance calls for case-specific consideration of whether its simple design fires represent the proposed application. A more detailed analysis may be necessary where the assumed growth and spread relationships are unsuitable. This connects experimental evidence with the scenario being analysed. A classification derived from one reference room does not, by itself, supply every condition required for another building.<ref name="AB-48" /><ref name="B-3" />

== Smoke measurements and their meaning ==

Room tests can record smoke production alongside heat release. The 2013 New Zealand commentary expresses optical smoke production rate as the exhaust extinction coefficient multiplied by its volumetric flow. Extinction coefficient describes how strongly smoke attenuates light along a path. Combining this quantity with flow describes the rate of optical smoke production leaving the test system.<ref name="NZ-143">Ministry of Business, Innovation and Employment (2013), p. 143.</ref>

The same commentary distinguishes room-test smoke production from the specific extinction area measured in a cone calorimeter. The former is expressed in square metres per second; the latter is normalised by the mass consumed. Their different units reflect different measured quantities. The commentary reports that scaling and ventilation complicate correlation between the two forms of smoke result.<ref name="NZ-143" />

Its historical lining classification adds an S designation when the relevant smoke criterion is met. That designation accompanies a material Group Number rather than replacing the heat-release assessment. The commentary also discusses the basis and limitations of the selected smoke limits. A smoke classification consequently requires both the test method and the particular regulatory framework to be identified.<ref name="NZ-143" />

The smoke limits described in the historical commentary concern averages over defined test periods. The reproduced Appendix A associates those periods with the relevant Group Number exposure. A short high smoke-production episode and a period average are consequently different descriptions of the same test. The averaging interval remains part of the reported result when comparing it with the named classification requirement.<ref name="NZ-159" />

== Limits of extrapolation ==

The value of [[Fire testing|fire testing]] depends on matching the experiment to the question being asked. A room test provides evidence for its product arrangement and exposure, while an engineering model may address a different geometry. Babrauskas warns that measured room-fire output cannot simply be transferred to rooms with different ventilation. Test scale alone does not remove the need to examine representativeness.<ref name="B-3" />

Models that infer room behaviour from cone data also have defined limits. The EUREFIC model discussed by Babrauskas uses the standard room, doorway and burner programme with material on both walls and ceiling. Its burning-area treatment and empirical constants were developed for that configuration. Applying those relationships to different burners, installations or rooms requires more than substituting another surface area.<ref name="B-30-31" />

Even within room testing, exposure details can influence the ordering of results. Janssens describes experiments where burner size and output changed the severity experienced by wall linings. He also describes different historical room protocols with different burner positions and power histories. A comparison of product results therefore retains those protocol details instead of treating every corner ignition as an identical challenge.<ref name="J-57-58" />

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020). ''Fire safety verification method data sheets: Handbook annex'' (Version 1.1).
* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-38–3-62). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for verification method C/VM2'' (Amendment 2).

[[Category:Materials & Fire Testing]]

Reduced cross-section method

2026-11-02T21:34:28Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

The '''reduced cross-section method''' is a calculation method for the fire resistance of timber members.<ref name="W-267">White (2002), p. 4-267.</ref> The charred layer and an extra zero-strength layer are removed from the cross-section, and the remaining section is checked with the strength and stiffness of wood at room temperature.<ref name="W-267" /> The name ''reduced cross-section method'' is not used in the sources cited here. White describes the approach under the heading ''effective cross-sectional area method'', and Eurocode 5, in the version ENV 1995-1-2:1994 that he cites, calls it the ''effective cross-section method''.<ref name="W-267" /><ref name="W-271">White (2002), p. 4-271.</ref>

The method rests on two observations. Char has virtually no load-bearing capacity, and the wood just below the char is heated and weakened.<ref name="W-260">White (2002), p. 4-260.</ref><ref name="W-265">White (2002), p. 4-265.</ref> Instead of modelling this weakened zone, the method treats it as an equivalent layer of wood without any strength, 7 mm thick in ENV 1995-1-2:1994.<ref name="W-267" /><ref name="W-271" /> Besides the original dimensions of the member and its room-temperature strength, the method needs only a charring rate and the thickness of this layer.<ref name="W-267" /> White calls models that divide the uncharred wood into layers at different temperatures the most complex approach. Compared with them, the zero-strength layer approach is a simple method for [[timber in fire]].<ref name="W-267" />

== Charring and the residual cross-section ==
When wood is heated, it decomposes by pyrolysis: large molecules break down into smaller ones and form combustible pyrolysis gases.<ref name="VR-3.1">Van Rossum (2027), §3.1.</ref> The solid residue is char, which consists mainly of carbon and has a black, porous structure.<ref name="VR-3.1" /> Because wood turns into char and gas, its density drops.<ref name="W-260" /> In a fire, the pyrolysis gases burn as flames at the surface, while glowing combustion and mechanical breakdown eventually erode the outer char layer.<ref name="W-260" /> The boundary between char and uncharred wood is distinct and lies at a temperature of about 300 °C.<ref name="W-260" /><ref name="IFEG-10">National Research Council of Canada et al. (2005), p. 2.6-10.</ref>

The [[charring rate]] is the linear rate at which wood is converted to char.<ref name="W-260" /> Under standard fire exposure, it is fairly constant after a higher rate at the start.<ref name="W-260" /> The empirical model used most widely assumes a rate of 0.6 mm/min perpendicular to the grain for all woods in the ASTM E119 standard fire test.<ref name="W-260" /> Actual rates differ between species, with density, chemical composition, permeability and moisture content.<ref name="W-260" /> Denser wood chars more slowly, and moisture slows charring but also lowers the strength of the wood.<ref name="W-269">White (2002), p. 4-269.</ref> Parallel to the grain, wood chars about twice as fast as across it.<ref name="W-260" />

Charring removes material from every exposed face, so the cross-section shrinks as the fire goes on. The International Fire Engineering Guidelines describe this as a reduction of the effective section dimensions with a consequent loss of load-bearing ability.<ref name="IFEG-9">National Research Council of Canada et al. (2005), p. 2.6-9.</ref> The corners of a charring beam or column become rounded, with a radius about equal to the char depth on the sides.<ref name="W-260" /> In ENV 1995-1-2:1994, Part 1-2 of Eurocode 5 on the design of timber structures and one of the [[Eurocodes]], this rounding is covered by a higher design charring rate.<ref name="W-261">White (2002), p. 4-261.</ref><ref name="W-271" /> The design rates in that document are 0.7 mm/min for glued laminated softwood and 0.8 mm/min for solid softwood, both with a characteristic density of 290 kg/m³.<ref name="W-261" /> For hardwood with a characteristic density of 450 kg/m³, the design rate is 0.5 mm/min.<ref name="W-261" />

== The heated layer below the char ==
The uncharred wood next to the char is not at room temperature. Because wood conducts heat poorly, the temperature gradient below the char is steep. Once charring has become steady, the wood about 6 mm below the char base is still at about 180 °C.<ref name="W-265" /> The moisture content peaks where the wood is at about 100 °C, roughly 13 mm below the char base.<ref name="W-265" />

In this zone, the strength and stiffness of the wood are reduced, which is a form of [[strength reduction at elevated temperatures]].<ref name="W-265" /><ref name="W-266">White (2002), p. 4-266.</ref> Schaffer and colleagues combined strength and stiffness relations with the temperature and moisture gradients in a fire-exposed slab to calculate how these properties vary below the char layer.<ref name="W-265" /><ref name="W-266" /> Their graphs for softwood, valid for fire exposures of 20 minutes or more, show the losses of stiffness, compressive strength and tensile strength fading out over a few centimetres.<ref name="W-266" />

White gives a simple profile for the temperature in a thick piece of wood below the char front. It is based on a power term, one of the two forms that White names, the other being an exponential term.<ref name="W-266" /> The profile reads:
<math display="block">T = T_i + (300 - T_i)\left(1 - \frac{x}{d_p}\right)^2</math>
Here the char front sits at 300 °C, and the temperature falls to the initial value at the thermal penetration depth. In White's tests, the penetration depth averaged 33 mm, and European tests led to a more conservative recommended value of 40 mm.<ref name="W-266" /> With an initial temperature of 25 °C and a penetration depth of 40 mm, the formula gives about 94 °C at 20 mm and 42 °C at 30 mm below the char front. The profile does not show the plateau near 100 °C that often occurs in moist wood.<ref name="W-266" />
[[File:fse-reduced-cross-section-method-v2.svg|thumb|upright=1.5|alt=Two curves of wood temperature falling from 300 °C at the char front to 25 °C at 33 mm and at 40 mm depth, with the first 7 mm shaded.|Temperature in the uncharred wood below the char front from the power-law profile, for thermal penetration depths of 33 mm and 40 mm and an initial temperature of 25 °C. The shaded band is the 7 mm zero-strength layer. Based on White (2002), pp. 4-266 to 4-267.]]

The heated zone is therefore several centimetres deep, and the loss of strength within it is gradual rather than complete.<ref name="W-266" /> White's effective cross-sectional area method replaces the gradual loss of strength by an equivalent layer of zero strength.<ref name="W-267" /> In a model for glued-laminated beams, Schaffer and colleagues estimated this layer at about 8 mm and added it to the char depth.<ref name="W-267" /> The same approach was used in a reliability-based model of glued-laminated beams made of laminates of different grades.<ref name="W-267" />

== Calculation steps ==
The calculation starts from the char depth, which equals the charring rate multiplied by the time of fire exposure. The method then adds the zero-strength layer to obtain the effective depth that is removed from each exposed face.<ref name="W-267" /> For ENV 1995-1-2:1994, White prints the rule as "7 mm after 2 min (linear fraction of 7 mm up to 20 min)". Read consistently with the parenthesis, the layer grows linearly to its full 7 mm over the first 20 minutes of exposure.<ref name="W-267" />
<math display="block">d_\mathrm{ef} = \beta\, t + \delta</math>
For a rectangular beam heated on both sides and on the bottom, the breadth loses two layers and the depth one. For a member heated on all four sides, the depth also loses two layers.<ref name="W-266" /> White gives the section modulus of the charred member with the char depths <math>\beta t</math>. Replacing them by the effective depth gives:<ref name="W-266" /><ref name="W-267" />
<math display="block">S_\mathrm{ef} = \frac{1}{6}\,\left(B - 2 d_\mathrm{ef}\right)\left(D - j\, d_\mathrm{ef}\right)^2</math>
The rest of the section keeps its room-temperature properties.<ref name="W-267" /> The member therefore passes the check as long as the bending moment in the fire does not exceed the room-temperature bending strength times the effective section modulus.<ref name="W-266" /> In symbols, the condition reads:
<math display="block">M \le f_m\, S_\mathrm{ef}</math>
[[File:fse-reduced-cross-section-method-v1.svg|thumb|upright=1.5|alt=Cross-section of a timber beam heated on both sides and the bottom, showing the char layer, a 7 mm zero-strength layer and the smaller effective section.|Cross-section of a beam heated on three sides. The char depth βt and the zero-strength layer δ are removed from each exposed face; the effective section keeps room-temperature properties. Based on White (2002), pp. 4-260 and 4-266 to 4-267.]]

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>d_\mathrm{ef}</math> || effective depth removed from each exposed face || mm
|-
| <math>\beta</math> || charring rate perpendicular to the grain || mm/min
|-
| <math>t</math> || time of fire exposure || min
|-
| <math>\delta</math> || thickness of the zero-strength layer || mm
|-
| <math>B</math> || original breadth of the member || mm
|-
| <math>D</math> || original depth of the member || mm
|-
| <math>j</math> || number of exposed faces across the depth: 1 for three-sided, 2 for four-sided exposure || –
|-
| <math>S_\mathrm{ef}</math> || elastic section modulus of the effective cross-section || mm³
|-
| <math>M</math> || bending moment from the loads during the fire || N·mm
|-
| <math>f_m</math> || bending strength of the wood at room temperature || N/mm²
|-
| <math>T</math> || temperature of the wood || °C
|-
| <math>T_i</math> || initial temperature of the wood || °C
|-
| <math>x</math> || distance below the char front || mm
|-
| <math>d_p</math> || thermal penetration depth || mm
|}

The strength value must match the method. Calculations of the residual section are normally made with ultimate strength values, while Eurocode 5 uses design or characteristic values.<ref name="W-267" /> White warns that design values and methods must be compatible.<ref name="W-267" /> The performance of the member depends on the ratio between the applied load and the ultimate capacity of the residual member.<ref name="W-267" />

== Worked example ==
White's chapter contains a glued-laminated beam of 130 mm × 533 mm, exposed to fire on three sides.<ref name="W-268">White (2002), p. 4-268.</ref> White's example does not state the species or density, so the beam is assumed here to be glued-laminated softwood with a characteristic density of 290 kg/m³. The example applies the zero-strength layer approach to it, with the ENV 1995-1-2:1994 design charring rate of 0.7 mm/min for that class and a zero-strength layer of 7 mm.<ref name="W-261" /><ref name="W-267" /> Before the fire, the section modulus is 130 × 533² / 6 = 6.16 × 10⁶ mm³.

After 30 minutes, the effective depth is 0.7 × 30 + 7 = 28 mm.<ref name="W-261" /><ref name="W-267" /> The effective breadth is then 130 − 2 × 28 = 74 mm, and the effective depth of the section is 533 − 28 = 505 mm. The effective section modulus is 74 × 505² / 6 = 3.15 × 10⁶ mm³, or 51 % of the original value. Without the zero-strength layer, 62 % would remain, so the 7 mm layer removes about 18 % of the remaining bending capacity.

After 60 minutes, the effective depth is 0.7 × 60 + 7 = 49 mm, and only 32 mm of the original 130 mm breadth still counts. The effective section modulus drops to 1.25 × 10⁶ mm³, or 20 % of the original value. A constant charring rate is reasonable only while a member behaves as a thick slab.<ref name="W-261" /> Once the temperature at the centre of the member starts to rise, the charring rate increases, so results for such thin remaining sections are doubtful.<ref name="W-261" />

Suppose the bending moment during the fire is half of the moment the original section could carry, and the same bending strength applies before and during the fire. The beam then fails when the effective section modulus falls below half of its original value. The calculation gives 31.0 minutes, and rounded down to the safe side, the beam has a fire resistance of 30 minutes under these assumptions. White notes that the performance of a member in a fire depends on the ratio of the applied load to the ultimate capacity of the residual member.<ref name="W-267" />
[[File:fse-reduced-cross-section-method-v3.svg|thumb|upright=1.5|alt=Line chart of remaining section modulus of a 130 by 533 mm glulam beam over 60 minutes, with and without the zero-strength layer, crossing 50 % near 31 minutes.|Remaining section modulus of a 130 mm × 533 mm glued-laminated beam heated on three sides, with a charring rate of 0.7 mm/min, with and without the zero-strength layer. Based on White (2002), pp. 4-261, 4-266 to 4-268.]]

== Alternative methods ==
White distinguishes two ways to assess the load-carrying capacity of the wood that remains. The remaining section can be treated as a single homogeneous material, or as a composite of layers with different properties.<ref name="W-266" /> In the homogeneous approach, the analyst uses either reduced material properties or room-temperature properties. If the properties are not reduced, a larger part of the cross-section has to be removed, which is the role of the zero-strength layer.<ref name="W-266" /><ref name="W-267" />

The reduced properties approach keeps the charred section but multiplies the room-temperature strength and stiffness of all uncharred wood by a factor α.<ref name="W-266" /> Proposed values of α ranged from 0.5 in New Zealand to 0.83 in France, reflecting uncertainty, different design loads and different levels of safety.<ref name="W-267" /> Eurocode 5 calls this the reduced strength and stiffness method, and its reduction factors depend on the fire-exposed perimeter of the residual section divided by its area.<ref name="W-267" /> In light-frame members, α would be substantially lower than in large members.<ref name="W-267" />

Other simplified approaches handle the heated layer differently. Technical Report 10 of the American Wood Council does not use a zero-strength layer but increases the charring rate by 20 %.<ref name="W-267" /> For large beams and columns, Lie's formulas give the fire resistance directly from the member size and a load factor, and they are recognised by building codes in the United States and Canada.<ref name="W-268" /> For White's 130 mm × 533 mm beam at 75 % of its allowable load, Lie's formula gives 53.8 minutes.<ref name="W-268" /> For members damaged in a fire, Williamson recommended a zero-strength layer of 6 mm where compression governs and 16 mm where tension governs.<ref name="W-267" />

The most complex approach divides the uncharred wood into layers or elements at different temperatures and moisture contents.<ref name="W-267" /> Each layer receives its own strength and stiffness, and Eurocode 5 refers to such models as general calculation methods.<ref name="W-267" /> White notes that Eurocode 5 offers calculation methods at three levels of complexity.<ref name="W-257" />

== Use in codes and design ==
Fire resistance ratings of timber members have traditionally come from furnace tests to ASTM E119. Listed ratings are limited to the assembly that was tested and normally do not permit modifications.<ref name="W-257">White (2002), p. 4-257.</ref> Calculation procedures for wood beams and columns have been accepted by building codes in the United States and Canada, and Eurocode 5 provides calculation methods in Europe.<ref name="W-257" /> White identifies three factors that set the fire endurance of a wood member: the protective membrane, if there is one, the extent of charring, and the load-carrying capacity of the uncharred wood.<ref name="W-257" /> The zero-strength layer approach deals with the last two.

The International Fire Engineering Guidelines (2005) define heavy timber as large sawn or glue-laminated members with a smallest dimension of at least 80 mm, citing Buchanan.<ref name="IFEG-9" /> For such members, the guidelines refer to White's chapter and to the Australian Standard AS 1720.4 for methods to determine fire resistance.<ref name="IFEG-10" /> In Australia, the data sheets of the Fire Safety Verification Method (2020) list AS 1720.4 among the structural design codes that provide methods for calculating the fire resistance level of an element.<ref name="ABCBD-33">Australian Building Codes Board (2020a), Data Sheet B3, p. 33.</ref> They cite the 2006 edition of this standard.<ref name="ABCBD-44">Australian Building Codes Board (2020a), Data Sheet B3, p. 44.</ref>

White's remark on member size concerns the related reduced-properties equations. Their application is generally limited to large wood members, and in light-frame members the α values would be substantially lower.<ref name="W-267" /> None of the sources cited here deals specifically with mass timber products.

Connections need separate attention. Where a fire endurance of 1 hour is required, connectors and fasteners must be protected by 38 mm of wood, fire-rated gypsum board of suitable thickness, or a coating approved for a 1-hour rating.<ref name="W-268" /> Glued-laminated beams often have a high-strength tension laminate at the bottom. Under the North American procedure for exposed members with a 1-hour rating, a core lamination is removed and an extra outer tension lamination added. A high-strength laminate then remains after charring.<ref name="W-268" />

== Limits and uncertainty ==
The charring equations given above apply to the standard ASTM E119 fire exposure.<ref name="W-261" /> In a real fire, the charring rate depends on the heat flux to the surface. In tests on spruce, rates of 0.56, 0.80 and 1.02 mm/min were measured at external heat fluxes of 25, 50 and 75 kW/m².<ref name="W-261" /> For natural fires, Eurocode 5 gives a parametric charring rate, and the International Fire Engineering Guidelines point to the 2003 final draft of Eurocode 5 for charring in realistic parametric fires.<ref name="W-264">White (2002), p. 4-264.</ref><ref name="IFEG-10" />

The cooling phase of a natural fire brings a further complication. Tests on glued-laminated beams showed that the temperature of the residual cross-section keeps changing during the cooling period.<ref name="W-264" /> The influence of high temperature is then no longer concentrated in the outer layer of the residual section, unlike under standard exposure.<ref name="W-264" /> The Australian data sheets add a related caution about simple equivalence methods. Their empirical formulae were mostly validated on steel members with insulation that stays in place, so they should be applied with caution to exposed timber.<ref name="ABCBD-33" />

The value of the zero-strength layer itself varies between models, from 7 mm in ENV 1995-1-2:1994 to about 8 mm in the model of Schaffer and colleagues.<ref name="W-267" /> Property data for wood are often limited to temperatures below 100 °C.<ref name="W-270">White (2002), p. 4-270.</ref> In small members or thin remaining sections, the charring rate increases once the centre of the member heats up.<ref name="W-261" /> For the reduced-properties equations, White adds that the α values would be substantially lower in light-frame members.<ref name="W-267" />

== See also ==
* [[Fire resistance]]
* [[Fire resistance criteria]]
* [[Parametric fire curve]]
* [[Standard fire curve]]
* [[Time equivalence]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* White, R. H. (2002). Analytical methods for determining fire resistance of timber members. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-257–4-273). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Structural Fire Engineering]]

Pool fire

2026-11-02T21:34:25Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''pool fire''' is a fire burning on a horizontal, upward-facing layer of fuel, usually a flammable or combustible liquid in a container, a bund or a spill on the ground.<ref name="IS-3-5">Iqbal and Salley (2004), p. 3-5.</ref> The liquid itself does not burn: heat from the flames evaporates it, and the vapour burns above the surface.<ref name="VR-4.1">Van Rossum (2027), §4.1.</ref> The term can also cover flat slabs of solids that decompose much like liquids, such as polymethylmethacrylate and polyethylene.<ref name="IS-3-5" />

In United States nuclear power plants, for example, liquid spill fires are among the most commonly assumed fires of transient fuels.<ref name="IS-3-3" /> Such pool fires can result from leaking pump seals, oil spills from transformers, fuel spray from diesel generators, and liquids used for cleaning and painting.<ref name="IS-3-6">Iqbal and Salley (2004), p. 3-6.</ref> They can be large: a burning pool of gasoline of 1 m² releases about 2.5 MW, about the same as an average burning living-room sofa.<ref name="IS-3-2">Iqbal and Salley (2004), p. 3-2.</ref><ref name="VR-4.5">Van Rossum (2027), §4.5.</ref> The size of the fire follows mainly from the area of the pool and the burning rate of the fuel, and the main hazard to the surroundings is thermal radiation from the large, sooty flames.<ref name="GW-2-297">Gottuk and White (2002), p. 2-297.</ref><ref name="Bey-3-268">Beyler (2002a), p. 3-268.</ref> Engineers estimate the heat release rate, burning duration, flame height and radiant heat flux with simple correlations that rest on large-scale tests.<ref name="IS-3-3">Iqbal and Salley (2004), p. 3-3.</ref><ref name="Bey-3-269">Beyler (2002a), p. 3-269.</ref>

== Pools and spills ==
Gottuk and White distinguish two situations. A pool is a confined body of fuel, typically more than 1 cm deep, that forms when a release collects in a low spot such as a trench, or that exists in tanks and containers.<ref name="GW-2-297" /> A spill is a thin layer of fuel from an unconfined release, and its fire is highly variable, depending on the source, the surface it spreads over and the moment of ignition.<ref name="GW-2-297" /> Spill depths for liquid spill fires range from 0.7 mm to 4 mm, depending mainly on the quantity released.<ref name="GW-2-299">Gottuk and White (2002), p. 2-299.</ref>

The difference matters for the burning rate. In tests with jet fuel spilled on concrete, unconfined spill fires larger than about 1 m in diameter burned at roughly one fifth of the maximum burning rate of confined pool fires.<ref name="GW-2-311">Gottuk and White (2002), p. 2-311.</ref> The authors attribute this to greater heat loss from the thin fuel layer, about 1 mm deep, to the concrete.<ref name="GW-2-311" /> For a given amount of fuel, a spill with a large area burns with a high heat release rate for a short time. A spill with a small area burns with a lower rate for longer.<ref name="IS-3-5" />

In the event tree of Beyler for a release of flammable material, a pool fire follows when a spill accumulates and is ignited locally after a delay.<ref name="Bey-3-269" /> The geometry of the containment, or the lack of it, strongly influences its characteristics.<ref name="Bey-3-269" /> A pool fire can also follow a vapour cloud fire that burns back to the release point.<ref name="Bey-3-269" /> In quantitative risk assessment it is one of the radiant heat outcomes, defined as a fire involving a pool of confined or spreading flammable material.<ref name="Bar-5-184">Barry (2002), p. 5-184.</ref>

== How a pool fire burns ==
A liquid has to turn into vapour before it can burn.<ref name="VR-4.1" /> Part of the heat of the flames therefore has to return to the liquid surface to keep the evaporation going. The balance between that heat and the energy needed to evaporate the fuel controls how fast the fuel burns.<ref name="VR-4.3">Van Rossum (2027), §4.3.</ref> The [[burning rate]] is usually given as the mass of fuel burned per square metre of pool surface per second.<ref name="IS-3-3" />

[[File:fse-pool-fire-v1.svg|thumb|upright=1.5|alt=Cross-section of a burning liquid pool in a bund: vapour rises from the liquid, a tall flame burns above it with black smoke, arrows show heat back to the pool and radiation to a target.|A pool fire: heat fed back from the flame evaporates the liquid, the vapour burns above the pool, and the flame radiates heat to its surroundings. Based on Van Rossum (2027), §4.1 and §4.3, and Beyler (2002a), pp. 3-270 and 3-277.]]

The [[flash point]] is the lowest temperature at which a flammable mixture of vapour and air exists at the surface of a liquid.<ref name="IS-6-1">Iqbal and Salley (2004), p. 6-1.</ref> At that temperature the vapour pressure is just high enough to give a mixture at the lower flammability limit.<ref name="S-1-147">Simmons (2002), p. 1-147.</ref> In the NIST experiments for the World Trade Center investigation, for example, jet fuel with a flash point of 43 to 66 °C did not at first form a flammable vapour layer at room temperature.<ref name="Ohl-42">Ohlemiller et al. (2005), p. 42.</ref> The radiant heat of the burner first had to warm the fuel.<ref name="Ohl-42" /> Once ignited, flames spread over flammable and combustible liquids at about 10 cm/s to 2 m/s.<ref name="IS-3-6" />

The way a pool fire burns changes with its diameter. NUREG-1805, after Babrauskas, distinguishes four modes: convective and laminar below 0.05 m, convective and turbulent below 0.2 m, radiative and optically thin from 0.2 to 1.0 m, and radiative and optically thick above 1.0 m.<ref name="IS-3-5" /> In pools larger than about 1 m, radiation from the optically thick flame dominates the heat transfer to the surface.<ref name="IS-3-5" /> Above a diameter of about 0.2 m the burning rate per unit area increases with diameter, and it approaches a maximum value for very large pools.<ref name="GW-2-310">Gottuk and White (2002), p. 2-310.</ref> Fuel blends with components of very different volatility do not burn at a constant rate. The most volatile components burn first, and later the burning resembles that of the heavier components that remain.<ref name="GW-2-310" />

== Heat release rate ==
The heat release rate of a pool fire is found from the burning rate per unit area, the effective heat of combustion and the area of the pool.<ref name="IS-3-3" /> A correction factor accounts for the lower burning rate of smaller pools: it is close to zero for very small pools and approaches one for large ones.<ref name="IS-3-3" /><ref name="GW-2-310" /> NUREG-1805 gives the relation as follows.<ref name="IS-3-3" />

<math display="block">\dot Q = \dot m''\, \Delta H_\mathrm{c,eff}\, A_\mathrm{f} \left(1 - e^{-k\beta D}\right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot Q</math> || heat release rate of the pool fire || kW
|-
| <math>\dot m''</math> || mass burning rate per unit area of a large pool || kg/(m²·s)
|-
| <math>\Delta H_\mathrm{c,eff}</math> || effective heat of combustion || kJ/kg
|-
| <math>A_\mathrm{f}</math> || horizontal burning area of the fuel || m²
|-
| <math>k\beta</math> || empirical constant of the fuel || m<sup>−1</sup>
|-
| <math>D</math> || diameter of the burning area || m
|}

For a pool that is not circular, an equivalent diameter is used: the diameter of a circle with the same area.<ref name="GW-2-310" /> The relation applies to confined pools burning in the open, in still air, in a pan or tank without an excessive lip height.<ref name="GW-2-311" /> The fuel data come from large-pool tests compiled by Babrauskas. For gasoline the burning rate is 0.055 kg/(m²·s), the effective heat of combustion 43,700 kJ/kg and ''kβ'' 2.1 m<sup>−1</sup>. For transformer oil the values are 0.039 kg/(m²·s), 46,400 kJ/kg and 0.7 m<sup>−1</sup>.<ref name="IS-3-4">Iqbal and Salley (2004), p. 3-4.</ref> Where the constant ''kβ'' is unknown, NUREG-1805 advises a conservative value of 100 m<sup>−1</sup>, which sets the bracket to one.<ref name="IS-3-6" />

[[File:fse-pool-fire-v2.svg|thumb|upright=1.5|alt=Two rising curves of heat release rate per square metre against pool diameter; gasoline levels off near 2,400 kW/m² by 2 m, transformer oil rises more slowly.|Heat release rate per square metre of pool surface against pool diameter for gasoline and transformer oil, from the large-pool data and the diameter correction. Based on Iqbal and Salley (2004), pp. 3-3 to 3-4.]]

'''Worked example.''' NUREG-1805 considers a spill of 5 US gallons (18.9 L) of lubricating oil that covers 9.0 ft² (0.836 m²) of a concrete floor. It uses the properties of transformer oil, with an effective heat of combustion of 46,000 kJ/kg.<ref name="IS-3-6" /><ref name="IS-3-22">Iqbal and Salley (2004), p. 3-22.</ref> The equivalent diameter is 1.03 m, so the bracket is 1 − e<sup>−0.7 × 1.03</sup> ≈ 0.514. Then:

<math display="block">\dot Q = 0.039 \times 46{,}000 \times 0.836 \times 0.514 \approx 771\ \mathrm{kW}</math>

This agrees with the 772 kW in the NUREG-1805 solution; the small difference comes from rounding.<ref name="IS-3-23">Iqbal and Salley (2004), p. 3-23.</ref> Without the diameter correction the result would be about 1.5 MW, so for a pool of this size the correction roughly halves the heat release rate. For a large gasoline pool the burning rate and heat of combustion give about 2.4 MW per square metre, consistent with the 2.5 MW quoted for a 1 m² pool.<ref name="IS-3-4" /><ref name="IS-3-2" /> Inside a room, the heat release rate can differ from these free-burn values. Radiation from the hot smoke layer and the heated ceiling and walls increases the burning rate, while small openings limit the oxygen supply and reduce it.<ref name="IS-3-5" />

== Burning duration and flame height ==
A fire that burns at a constant heat release rate consumes the fuel at a constant rate, so the burning duration follows from the amount of fuel and the burning rate.<ref name="IS-3-7">Iqbal and Salley (2004), p. 3-7.</ref> For a liquid pool, the fuel surface drops at the regression rate, which is the mass burning rate per unit area divided by the density of the liquid.<ref name="IS-3-8">Iqbal and Salley (2004), p. 3-8.</ref> In the lubricating oil example the regression rate is about 0.05 mm/s, and the 18.9 L spill burns for about 7.35 minutes.<ref name="IS-3-23" /> The same volume spread over a larger area would burn more intensely for a shorter time.<ref name="IS-3-8" />

The flame height matters because it shows whether flames reach objects above the pool and because it sets the size of the radiating flame.<ref name="Bey-3-270">Beyler (2002a), p. 3-270.</ref> Several correlations exist, based on the pool diameter and the burning rate or the heat release rate; the Heskestad correlation is used in both NUREG-1805 and the SFPE handbook.<ref name="Bey-3-270" /><ref name="Bey-3-274">Beyler (2002a), p. 3-274.</ref> For the lubricating oil fire it gives a flame height of 2.31 m, and the Thomas correlation gives 2.67 m.<ref name="IS-3-23" /> Both exceed the 8 ft (2.4 m) to a cable tray above the pool, so the example concludes that the flames impinge on the tray.<ref name="IS-3-23" /><ref name="IS-3-22" /> Pool fire flames fluctuate, so the flame tip moves well beyond the continuous luminous region, and flame height is defined in different ways in different studies.<ref name="Bey-3-270" /> Wind tilts the flame and changes its visible length.<ref name="Bey-3-270" /><ref name="Bey-3-271">Beyler (2002a), p. 3-271.</ref>

== Thermal radiation ==
Thermal radiation is the main way in which large open hydrocarbon fires injure people and damage property.<ref name="Bey-3-268" /> The [[flame radiation]] comes mainly from water vapour, carbon dioxide and soot.<ref name="Bey-3-270" /> Fires of flammable liquids typically have higher heat release rates per unit area than fires of ordinary combustibles, taller flames and more luminous soot. An observer near a liquid fire therefore feels more heat than near an ordinary fire of similar size.<ref name="IS-5-2">Iqbal and Salley (2004), p. 5-2.</ref>

Estimating the radiation involves three steps: describing the size of the fire, describing its radiative properties, and calculating the heat flux at the target.<ref name="Bey-3-269" /> The simplest method treats the flame as a point source at the centre of the fire, radiating a fraction of the heat release rate.<ref name="IS-5-3">Iqbal and Salley (2004), p. 5-3.</ref> That fraction ranges from about 0.15 for low-sooting fuels such as alcohol to 0.60 for high-sooting hydrocarbons, and cold soot around large flames can reduce it considerably.<ref name="IS-5-3" /> The point source method is accurate at large distances, but it is not a good choice where ignition of nearby combustibles must be assessed.<ref name="Bey-3-275">Beyler (2002a), p. 3-275.</ref>

The [[solid flame model]] represents the flame as a cylinder with the pool diameter and the flame height, whose surface radiates with an average emissive power.<ref name="Bey-3-276">Beyler (2002a), p. 3-276.</ref> The heat flux at a target equals that emissive power times the view factor between flame and target.<ref name="Bey-3-276" /> Shokri and Beyler found that the effective emissive power falls as the pool gets larger, because black smoke outside the flame increasingly hides the luminous flame.<ref name="Bey-3-277">Beyler (2002a), p. 3-277.</ref> Their correlation gives about 57 kW/m² for a 1 m pool, 48 kW/m² for a 10 m pool and 22 kW/m² for a 50 m pool.<ref name="Bey-3-277" /> Most of the uncertainty lies in the emissive power, not in the view factor.<ref name="Bey-3-277" />

[[File:fse-pool-fire-v3.svg|thumb|upright=1.5|alt=Falling curve of effective emissive power from about 57 kW/m² at 1 m pool diameter to about 22 kW/m² at 50 m.|Effective emissive power of large hydrocarbon pool fire flames against pool diameter, after the correlation of Shokri and Beyler. Based on Beyler (2002a), p. 3-277.]]

For quick screening, Shokri and Beyler also correlated the radiant heat flux to a vertical target at ground level with the distance from the pool centre divided by the pool diameter.<ref name="Bey-3-273">Beyler (2002a), p. 3-273.</ref> Above ground level the heat flux is expected to be higher than the correlation gives, because the radiation is strongest near the mid-height of the flame.<ref name="Bey-3-273" /> A safety factor of 2 is recommended for design use with this correlation, but not where a realistic estimate is needed.<ref name="Bey-3-273" />

== Protection and firefighting ==
Containment limits the size of a pool fire. A dike or curbing confines a spill to a known area, and the area, together with the burning rate, sets the heat release rate.<ref name="IS-3-5" /><ref name="IS-3-6" /><ref name="GW-2-297" /> A pool in a bund therefore burns longer than an unconfined spill of the same volume, but with a smaller fire.<ref name="IS-3-8" />

Water is often a poor extinguishing agent for these fires. A liquid that is lighter than water and does not mix with it floats on the water and keeps burning.<ref name="IS-B-58">Iqbal and Salley (2004), p. B-58.</ref> [[Firefighting foam]] is therefore widely used for fires of flammable and combustible liquids: it keeps air from the fuel, cools as the water drains from it, and protects surfaces that are not yet burning.<ref name="IS-B-58" /> It must be applied in sufficient volume and at a sufficient rate to make up for the foam destroyed by heat and flames.<ref name="IS-B-59">Iqbal and Salley (2004), p. B-59.</ref> Fixed foam systems are used in bunds and on spills, and subsurface injection of low-expansion foam into hydrocarbon storage tanks is a recognised design method in the NFPA standards.<ref name="IS-B-60">Iqbal and Salley (2004), p. B-60.</ref>

Tank fires carry a further hazard. When water penetrates a hot oil whose temperature is well above the boiling point of water, it turns into steam below the surface and causes an eruption of burning oil, called boilover.<ref name="IS-B-58" /> NUREG-1805 describes boilover as a phenomenon of fires in open tanks containing blends such as crude oil, which requires water at the bottom of the tank.<ref name="IS-F-9">Iqbal and Salley (2004), p. F-9.</ref> Foam applied to a liquid at 100 °C or above can also cause boilover, because the steam formed expands the foam fourfold.<ref name="IS-B-60" />

Fire resistance tests for structures near pool fires need a different exposure. Most standard tests simulate a cellulosic fire, which grows more slowly than a hydrocarbon fire, although it may ultimately become hotter; specific hydrocarbon fire exposures for pool and jet fires were developed later.<ref name="IS-C-8">Iqbal and Salley (2004), p. C-8.</ref> In the United States, UL 1709 rates barriers for a hydrocarbon fire exposure, with H ratings for 120 minutes against the passage of flame and heat.<ref name="IS-C-9">Iqbal and Salley (2004), p. C-9.</ref> In Australia, the Fire Safety Verification Method data sheets (2020) refer to results of hydrocarbon fire tests and to a hydrocarbon heating regime alongside the standard one.<ref name="ABCB-233">Australian Building Codes Board (2020a), p. 233.</ref>

== Limits and uncertainty ==
The methods for pool fires are largely semi-empirical and rest on experimental data, so they carry uncertainties.<ref name="Bey-3-269" /> The burning rate correlations come from confined pools in the open and in still air. There are very few data for unconfined spills, and wind and lip height can change the burning rate in either direction.<ref name="GW-2-311" /><ref name="GW-2-313">Gottuk and White (2002), p. 2-313.</ref> The radiation methods assume a circular or nearly circular pool.<ref name="IS-5-17">Iqbal and Salley (2004), p. 5-17.</ref> The emissive power correlation was developed from fires of kerosene, fuel oil, gasoline, jet fuels and liquefied natural gas, with pool diameters from 1 to 50 m.<ref name="IS-5-17" />

Inside a building, the free-burn values are only a starting point. Feedback from the smoke layer and the walls, and the supply of air through openings, change the burning rate.<ref name="IS-3-5" /> The heat release rate is not a fundamental property of a fuel and is usually determined from tests.<ref name="IS-3-1">Iqbal and Salley (2004), p. 3-1.</ref>

== See also ==
* [[Aqueous film-forming foam]]
* [[BLEVE]]
* [[Jet fire]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-176–5-213). National Fire Protection Association; Society of Fire Protection Engineers.
* Beyler, C. L. (2002a). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-268–3-314). National Fire Protection Association; Society of Fire Protection Engineers.
* Gottuk, D. T., & White, D. A. (2002). Liquid fuel fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-297–2-316). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Ohlemiller, T. J., Mulholland, G. W., Maranghides, A., Filliben, J. J., & Gann, R. G. (2005). ''Fire tests of single office workstations'' (NIST NCSTAR 1-5C). National Institute of Standards and Technology.
* Simmons, R. F. (2002). Premixed burning. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-144–1-154). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Explosions & Industrial Fires]]

Performance-based design

2026-11-02T21:34:22Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Performance-based design''' is an approach to fire safety design in which measures are chosen for a specific building and then shown by engineering analysis to meet stated objectives or performance requirements.<ref name="HB-12">Australian Building Codes Board (2020b), p. 12.</ref><ref name="IFEG-1221">National Research Council of Canada et al. (2005), p. 1.2-21.</ref> It is the alternative to following a prescribed set of rules. Building codes that allow this approach state what a building must achieve and leave open how it is achieved.<ref name="HB-12" /> In Australia, a design developed this way is called a Performance Solution, and it is unique to each situation.<ref name="HB-13">Australian Building Codes Board (2020b), p. 13.</ref>

Performance-based design grew out of the limits of prescriptive codes, which cannot cover emerging technologies and every combination of circumstances.<ref name="IFEG-021">National Research Council of Canada et al. (2005), p. 0.2-1 (Part 0, Australia).</ref> It is applied through [[fire safety engineering]]. The engineer and the stakeholders agree the objectives, [[fire scenario|fire scenarios]], design fires and acceptance criteria. One or more trial designs are then analysed until one meets the criteria.<ref name="IFEG-122">National Research Council of Canada et al. (2005), p. 1.2-2.</ref>

The analysis may show that a design is at least equivalent to a design that complies with the prescriptive provisions, or that it meets the performance requirements directly.<ref name="IFEG-1221" /> The freedom of the approach comes with costs. The performance requirements of many codes are not quantified, the results are hard for authorities to check, and the design depends on the building being managed as assumed.<ref name="IFEG-023">National Research Council of Canada et al. (2005), p. 0.2-3 (Part 0, Australia).</ref><ref name="VR-2.1">Van Rossum (2027), §2.1.</ref>

== Principle and terminology ==
The core idea is to regulate the outcome rather than the means. The International Fire Engineering Guidelines (IFEG, 2005) explain that the intent of building regulations is to reduce risks to a level that the community tolerates.<ref name="IFEG-021" /> Traditional codes did this with prescriptive rules. Because such rules constrained designs in ways that did not always suit the building, codes became performance-based, to free designers, increase innovation and facilitate trade.<ref name="IFEG-021" /> The opposite approach is described in the article on [[prescriptive design]].

Performance-based codes are usually arranged as a hierarchy. In the Building Code of Australia described by the IFEG, objectives and functional statements state in general terms what the community expects and how a building could satisfy it.<ref name="IFEG-022">National Research Council of Canada et al. (2005), p. 0.2-2 (Part 0, Australia).</ref> Below them are the performance requirements, which every design must meet but which are not quantified.<ref name="IFEG-023" /> A design that complies with the deemed-to-satisfy (DTS) provisions is deemed to meet the performance requirements. A design that differs and is shown by analysis to comply was called an Alternative Solution.<ref name="IFEG-023" />

[[File:fse-performance-based-design-v1.svg|thumb|upright=1.5|alt=Pyramid: objectives, functional statements, performance requirements; below, two routes: deemed-to-satisfy solution and performance solution.|Hierarchy of a performance-based building code: the performance requirements are met either by deemed-to-satisfy provisions or by a performance solution shown to comply by analysis. Based on National Research Council of Canada et al. (2005), pp. 0.2-2–0.2-3 and Australian Building Codes Board (2020b), p. 13.]]

The terms differ between countries. The current National Construction Code (NCC) of Australia uses Performance Solution for what earlier editions called an Alternative Solution.<ref name="HB-16">Australian Building Codes Board (2020b), p. 16.</ref> The NCC is performance-based, and a design may use a Performance Solution, a DTS Solution, or a combination of both.<ref name="HB-12" />

In New Zealand, the Building Code sets objectives, functional requirements and performance criteria. Compliance can be shown with an acceptable solution, a verification method such as C/VM2, or another means.<ref name="CVM2-2">Ministry of Business, Innovation and Employment (2025b), p. 2.</ref> In the Netherlands, a risk-based alternative to the prescribed measures of the building regulations is usually called equivalence. It must achieve at least the same level of fire safety as the measure it replaces.<ref name="VR-1">Van Rossum (2027), §1.</ref>

== Reasons for using it ==
The main advantage is freedom of design. The Australian handbook for the Fire Safety Verification Method (FSVM) points out that a performance-based code imposes no obligation to use any particular material, component or construction method. The only condition is that the performance requirements are met.<ref name="HB-12" /> Performance Solutions are often flexible in achieving the outcomes and encourage innovative design and use of technology.<ref name="HB-13" /> A DTS Solution, by contrast, follows a set recipe of what, when and how to build.<ref name="HB-13" />

The IFEG list further benefits. They include a disciplined approach to fire safety design and a better understanding of how the parts of a fire safety system interact. Others are a method for comparing alternative solutions, monetary savings, and guidance for construction, commissioning and maintenance.<ref name="IFEG-033">National Research Council of Canada et al. (2005), p. 0.3-3 (Part 0, Australia).</ref> Fire engineering can also assess existing buildings when their use changes and propose solutions for upgrading them.<ref name="IFEG-033" />

Some buildings fall outside what prescriptive rules can handle. ''Introduction to Fire Safety Engineering'' notes that in the Netherlands, fire safety engineering is applied mainly to buildings that deviate from the norm. Examples are public transport terminals, tunnels, towers with a floor above 200 m, buildings with large atria, and large compartments outside the scope of the Dutch standards.<ref name="VR-1.5">Van Rossum (2027), §1.5.</ref> Even in ordinary buildings, an analysis may address a single aspect to represent reality better than the standard rules do.<ref name="VR-1.5" />

New Zealand gives an example of why a structured performance framework was introduced. A review of its Building Code found that the fire safety performance requirements were not clear or precise enough.<ref name="MBIE13-11">Ministry of Business, Innovation and Employment (2013), p. 11.</ref> The lack of a consistent approach led to disputes over designs, stifled innovation, more conservative designs, and lengthy and costly debates about compliance.<ref name="MBIE13-11" /> The response was C/VM2, a verification method with prescribed design scenarios for complex buildings. Simple buildings remained covered by acceptable solutions.<ref name="MBIE13-11" />

== The design process ==
The IFEG describe a typical process in five stages: preparing a fire engineering brief (FEB), carrying out the analysis, collating and evaluating the results, drawing conclusions, and preparing the report.<ref name="IFEG-112">National Research Council of Canada et al. (2005), p. 1.1-2.</ref> The FEB defines the scope of work and the basis for the analysis, as agreed by the relevant stakeholders.<ref name="IFEG-122" /> For a simple departure from a prescriptive provision it may be a short document, but for a large or complex project it can be a major one.<ref name="IFEG-122" />

[[File:fse-performance-based-design-v2.svg|thumb|upright=1.5|alt=Five boxes from fire engineering brief to report, with a loop from the conclusions back to the brief when a trial design fails.|The fire engineering process: if a trial design does not meet the criteria, the brief is revisited and a new trial design analysed. Based on National Research Council of Canada et al. (2005), pp. 1.1-2 and 1.2-2.]]

The FEB covers the scope, stakeholders, building and occupant characteristics, objectives, hazards and available measures, and the trial designs.<ref name="IFEG-1232">National Research Council of Canada et al. (2005), p. 1.2-32.</ref> It also records the non-compliance issues, the approaches and methods of analysis, the [[acceptance criteria]] and factors of safety, and the fire scenarios and design occupant groups.<ref name="IFEG-1232" /> In principle, the objectives, trial designs, methods and criteria are all agreed before the analysis starts.<ref name="IFEG-122" /> At this stage the [[design fire|design fires]] are described as far as possible without calculation, so the brief works as a qualitative review of the design.<ref name="IFEG-1229">National Research Council of Canada et al. (2005), p. 1.2-29.</ref> If analysis later shows that a trial design is unacceptable, the brief is revisited and a further trial design is developed.<ref name="IFEG-122" />

Australian practice uses a performance-based design brief (PBDB), followed by a performance-based design report.<ref name="HB-125">Australian Building Codes Board (2020b), p. 125.</ref> The report lists all variations from the DTS provisions and the performance requirements they affect. For each design scenario it states whether the proposal reached at least the safety level of a reference building that complies with the DTS provisions.<ref name="HB-125" /> In New Zealand, C/VM2 (second edition, 2025) describes an example process. It runs from concept design and FEB to a trial design tested against ten design scenarios, which is revised until all of them are satisfied.<ref name="CVM2-9">Ministry of Business, Innovation and Employment (2025b), p. 9.</ref>

== Comparative and absolute approaches ==
A key decision in the brief is how compliance will be shown. In a comparative approach, the fire safety of the trial design is compared with that of an identical building designed to the DTS or prescriptive provisions.<ref name="IFEG-1221" /> Both are analysed with the same assumptions, models and input data, and the trial design must be equivalent or better. This is often called an equivalence approach.<ref name="IFEG-1221" /> In an absolute approach, the results are compared directly with the objectives or performance requirements using the agreed acceptance criteria, without a benchmark design.<ref name="IFEG-1221" />

[[File:fse-performance-based-design-v3.svg|thumb|upright=1.5|alt=Two panels: left, trial design and DTS design analysed the same way and compared; right, trial design results compared with fixed criteria.|Comparative approach (left): the trial design must perform at least as well as an identical DTS design. Absolute approach (right): the results must meet agreed acceptance criteria. Based on National Research Council of Canada et al. (2005), p. 1.2-21.]]

The Australian FSVM requires a comparison with a reference building that complies with the DTS provisions.<ref name="HB-16" /> The handbook explains that the reference building indirectly defines the acceptable individual and societal risk levels, so its choice must be agreed by all stakeholders.<ref name="HB-46">Australian Building Codes Board (2020b), p. 46.</ref> An example shows why this matters. A Performance Solution for an apartment building extends the travel distance from an apartment door to a fire-isolated stair from the DTS limit of 6 m to 12 m.<ref name="HB-46" /> A fair reference building with the same footprint and number of occupants would need two stairs under the DTS provisions. The proposal therefore both lengthens the travel distance and removes an exit, which changes the scenarios that must be analysed.<ref name="HB-46" />

[[File:fse-performance-based-design-v5.svg|thumb|upright=1.5|alt=Two floor plans of 12 apartments: left, one central stair with 12 m travel distance; right, the same floor with two stairs and 6 m limit.|Proposed design with one stair and a 12 m travel distance (left) and a reference building of the same size that complies with the DTS provisions with two stairs (right). Based on Australian Building Codes Board (2020b), pp. 46–48.]]

Analyses also differ in method. Qualitative analysis is used only in a minority of cases, for example for a single non-compliance issue, and its logic must be documented.<ref name="IFEG-1221" /> Most cases need a quantitative approach.<ref name="IFEG-1221" /> Deterministic methods, which always give the same outcome for the same inputs, are the most common. Probabilistic methods assign reliabilities and frequencies and combine many scenarios, but they need much statistical data.<ref name="IFEG-1222">National Research Council of Canada et al. (2005), p. 1.2-22.</ref> ''Introduction to Fire Safety Engineering'' adds that both approaches have their own strengths and are often used together.<ref name="VR-1.4">Van Rossum (2027), §1.4.</ref>

== Acceptance criteria and safety margins ==
Acceptance criteria turn the general objectives into tests that an analysis can pass or fail. The IFEG require them to be appropriate to the objectives and the methods, numerical unless the analysis is qualitative, and realistic.<ref name="IFEG-1225">National Research Council of Canada et al. (2005), p. 1.2-25.</ref> Zero risk, for example, is not an appropriate criterion.<ref name="IFEG-1225" /> Typical parameters for protecting occupants are the expected risk to life, the margin between available and required escape time, smoke layer height, layer temperature, radiant heat, smoke optical density and carbon monoxide level.<ref name="IFEG-1225" />

For life safety, the most common deterministic test is a timeline comparison. The [[available safe egress time]] (ASET) is compared with the required safe egress time (RSET), and ASET must exceed RSET by a margin agreed in the brief.<ref name="IFEG-1222" /> In a comparative evaluation, the margin of the trial design must be the same as or greater than that of the DTS design.<ref name="IFEG-1222" /> ''Introduction to Fire Safety Engineering'' notes that many inputs to both times are uncertain, so the safety margin is important. It can be expressed either as a factor on RSET or as a minimum difference between ASET and RSET.<ref name="VR-7.1">Van Rossum (2027), §7.1.</ref> The more reliable the inputs, the smaller the margin needs to be.<ref name="VR-7.1" />

[[File:fse-performance-based-design-v4.svg|thumb|upright=1.5|alt=Timeline from ignition: RSET bar ends before ASET bar; the gap between them is the safety margin.|The available safe egress time must exceed the required safe egress time by an agreed safety margin. Based on National Research Council of Canada et al. (2005), p. 1.2-22 and Van Rossum (2027), §7.1.]]

Factors of safety should reflect the redundancy and reliability of the design, the methods and assumptions, the uncertainty and the consequences of a fire.<ref name="IFEG-1226">National Research Council of Canada et al. (2005), p. 1.2-26.</ref> They should be applied only at the end of a calculation, because applying them at every step leads to overly conservative results.<ref name="IFEG-1226" /> In a comparative evaluation, explicit factors are usually unnecessary because both designs are analysed in the same way.<ref name="IFEG-1226" /> Sensitivity studies test how the result changes when key inputs vary. Examples are a fire growth rate several times greater, partial failure of smoke exhaust, lower walking speeds or fewer available exits.<ref name="IFEG-1224">National Research Council of Canada et al. (2005), p. 1.2-24.</ref>

== Verification, competence and the building life cycle ==
Performance-based designs are harder to check than prescriptive ones. ''Introduction to Fire Safety Engineering'' points out that the justification can be so complex that the approving authority cannot easily verify it, unlike a rule-based design.<ref name="VR-2.1" /> Computational fluid dynamics is given as an example: authorities often have no specialist in it, so the integrity of the fire safety engineer must be relied upon.<ref name="VR-2.1" /> A second opinion is advised where results are unexpected or the party is unknown, but it is not economically feasible for every project.<ref name="VR-2.1" /> The book also notes incentives, such as obtaining a permit or saving on construction and installations, that can make certain outcomes attractive to the parties involved.<ref name="VR-2.2">Van Rossum (2027), §2.2.</ref>

Regulators therefore restrict who may use the formal methods. In Australia, the FSVM must only be used by a professional engineer or other suitably qualified person recognised as competent in fire safety engineering.<ref name="HB-6">Australian Building Codes Board (2020b), p. 6.</ref> C/VM2 is intended for professional fire engineers who are proficient in fire engineering modelling methods.<ref name="CVM2-7">Ministry of Business, Innovation and Employment (2025b), p. 7.</ref> The IFEG describe third-party review by an independent peer or specialist, including check calculations, as a constructive way to support approval.<ref name="IFEG-038">National Research Council of Canada et al. (2005), p. 0.3-8 (Part 0, Australia).</ref>

A performance-based design is specific to its building, occupants and site. The IFEG call this both a strength and a weakness. It allows the fire safety system best suited to the building, but changes to the building, its occupants or its site may require a new evaluation.<ref name="IFEG-037">National Research Council of Canada et al. (2005), p. 0.3-7 (Part 0, Australia).</ref> Such a re-evaluation might not have been needed if the broader DTS provisions had been followed.<ref name="IFEG-037" />

== Limits and criticism ==
The main weakness is the lack of quantified targets. The IFEG note that the level of safety intended by the Australian building code is not stated explicitly, so acceptance criteria must be developed for each design.<ref name="IFEG-023" /> Because the link between criteria and performance requirements is a matter of engineering judgement, it varies between practitioners and projects. Involving all stakeholders reduces this variation.<ref name="IFEG-023" /> The Australian handbook calls unquantified performance requirements a recognised limitation of performance-based codes and a barrier to their use.<ref name="HB-14">Australian Building Codes Board (2020b), p. 14.</ref>

The Netherlands faces the same problem. ''Introduction to Fire Safety Engineering'' states that Dutch regulations do not lay down how many casualties are acceptable or how large the risk of fire spread to a neighbouring plot may be.<ref name="VR-1.2">Van Rossum (2027), §1.2.</ref> There are also no risk-based limit values, and the limits in the rule-based approach cannot be translated into them unambiguously.<ref name="VR-1.4" /> Benchmarks themselves can be weak: the commentary to C/VM2 notes that many values in international codes are commonly accepted but have no technical basis.<ref name="MBIE13-12">Ministry of Business, Innovation and Employment (2013), p. 12.</ref>

Tools and data are a further limit. The IFEG were deliberately written as guidelines rather than as a mandatory code, because fire engineering was judged to lack the necessary validated tools and data.<ref name="IFEG-012">National Research Council of Canada et al. (2005), p. 0.1-2 (Part 0, Australia).</ref> Fire engineering designs therefore rely heavily on engineering judgement, and approving authorities need to understand the process to assess them.<ref name="IFEG-012" />

== See also ==
* [[Building regulations]]
* [[SFPE]]
* [[Ethics in fire safety engineering]]
* [[Sensitivity analysis]]
* [[Equivalency]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Fire Safety Design & Regulation]]

Probit function

2026-11-02T21:34:18Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''probit function''' is one of the more complex models of human exposure that can be used in fire safety engineering to estimate how people are affected by a fire.<ref name="AU-110">Australian Building Codes Board (2020b), p. 110.</ref> Another such model is the [[fractional effective dose]] (FED).<ref name="AU-110" /> Human exposure models range from simple tenability limits to such more complex models. For fire safety engineering in buildings, either simple tenability limits or FED models are generally adopted.<ref name="AU-110" /> Simpler exposure criteria, used alongside or instead of probit functions, include tenability limits, lethal concentrations of toxic gases, thresholds for pain and burns, and tables of percentage lethality for thermal radiation and explosion overpressure.<ref name="P-87">Purser (2002), p. 2-87.</ref><ref name="BY-309b">Beyler (2002a), p. 3-309.</ref><ref name="B-186">Barry (2002), p. 5-186.</ref>

Exposure criteria face a common difficulty: people do not respond in the same way to the same exposure. A tenability value represents the most frequent response in a population, and some groups, such as elderly people and people with asthma, are more sensitive than others.<ref name="P-90">Purser (2002), p. 2-90.</ref> In [[quantitative risk assessment]] (QRA) of fires and explosions, the effect of an exposure on people is expressed as the likelihood of death and of different degrees of injury at different levels of exposure.<ref name="B-186" />

== Place among human exposure models ==
In its simplest form, a human exposure model is a tenability limit, such as a minimum visibility or a maximum thermal FED.<ref name="AU-110" /> The FED is a step up from such a limit. During the exposure, the fractional doses received are added until their sum reaches 1.<ref name="P-88">Purser (2002), p. 2-88.</ref> In the ISO definition quoted by the Australian Building Codes Board, the FED compares the dose received with the dose expected to produce a specified effect. The reference is an exposed subject of average susceptibility.<ref name="AU-140">Australian Building Codes Board (2020b), p. 140.</ref>

The same handbook names probit functions, together with the FED, among the more complex human exposure models, without describing them further. For the estimation of the time to compromised tenability in fires, it refers to ISO 13571 and ISO TR 13571-2, which give guidelines, a methodology and examples of tenability assessments.<ref name="AU-110" /> For buildings, it notes that simple tenability limits or FED models are generally adopted, so these simpler criteria are the ones most often used in building design.<ref name="AU-110" />
[[File:fse-probit-function-v2.svg|thumb|upright=1.5|alt=Three rising steps: simple tenability limits, fractional effective dose, and more complex models such as probit functions.|Human exposure models from simple tenability limits to more complex models such as probit functions; for buildings, simple limits or FED models are generally adopted. Based on Australian Building Codes Board (2020b), p. 110.]]

== Variation between people ==
A tenability dose or concentration is the most frequent value in a statistical distribution of responses. The responses of individuals are spread around it in a probability curve.<ref name="P-90" /> The data behind these values mostly come from healthy young adult animals or humans. Groups with weaker hearts or lungs, such as the elderly and the roughly 15 per cent of children and 5 per cent of adults with asthma, may be affected at much lower exposures.<ref name="P-90" />

For irritant gases the spread is wide. The toxicity chapter of the SFPE Handbook expects most people to be affected by hydrogen chloride at about 200 parts per million (ppm), and some already at about 100 ppm. Others tolerate more than 500 ppm without serious effects on escape.<ref name="P-120">Purser (2002), p. 2-120.</ref> The sensitivity to irritants is probably distributed on a logarithmic scale, in humans as in rodents. For hydrogen chloride, the handbook gives the proportions of a population expected to suffer severe irritancy, impaired escape and incapacitation at different concentrations. These proportions are based partly on human and animal data and partly on the judgement of the author.<ref name="P-120" />

== Criteria for toxic gases ==
For toxic gases, effect data from animal tests are commonly reported as an LC<sub>50</sub>, the concentration that kills half of the exposed animals.<ref name="P-87" /><ref name="N-B66">Iqbal and Salley (2004), p. B-66.</ref> NUREG-1805, the fire hazard analysis guide of the U.S. Nuclear Regulatory Commission, explains this as the concentration that causes a 50 per cent probability of lethality. The value is only meaningful together with the exposure time, which is generally 30 minutes, followed by an observation period of 14 days.<ref name="Bab">Babrauskas et al. (1991), as cited in Iqbal and Salley (2004), p. B-66.</ref>

Lethal concentrations measured over different times are often converted to a common 30-minute exposure with [[Haber's rule]], which treats the product of concentration and time as constant for a given effect.<ref name="P-87" /><ref name="P-92">Purser (2002), p. 2-92.</ref> For hydrogen chloride, for example, a 30-minute lethal concentration for rats of 3800 ppm corresponds to an exposure dose of 114,000 ppm·min.<ref name="P-119">Purser (2002), p. 2-119.</ref> Incapacitation is predicted at around a third of the lethal exposure dose of the smoke from a burning material.<ref name="P-93">Purser (2002), p. 2-93.</ref>

== Criteria for thermal radiation ==
For thermal radiation, fire safety engineering uses thresholds for pain and burns and tabulated levels of percentage lethality. Thermal radiation from a fire can burn bare skin if the radiation is intense enough and lasts long enough.<ref name="BY-308">Beyler (2002a), p. 3-308.</ref> Burns form a continuous range of severity. A first-degree burn reddens the skin without blisters, a second-degree burn forms blisters, and a third-degree burn destroys all layers of the skin.<ref name="BY-309">Beyler (2002a), pp. 3-308–3-309.</ref> Healthy adults and teenagers can normally be expected to survive if less than 20 per cent of the body surface has second- and third-degree burns. Survival becomes unlikely when more than 50 per cent of the body is covered by full-thickness burns, even with intensive medical care.<ref name="BY-309" />

Pain and tissue damage are both related to the heating of the skin. Pain is felt when the skin at a depth of 0.1 mm reaches about 45 °C.<ref name="BY-309b" /> The time to pain can be estimated from the incident radiation with a simple correlation, Equation 84 of the hydrocarbon fire chapter of the SFPE Handbook:<ref name="BY-309b" />
<math display="block">t_p = \left( \frac{35}{\dot{q}''} \right)^{1.33}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_p</math> || time until pain is felt || s
|-
| <math>\dot{q}''</math> || incident thermal radiation on the skin || kW/m²
|}

No pain was observed below 1.7 kW/m², however long the exposure lasted.<ref name="BY-309b" /> Blisters form when the skin surface reaches about 55 °C, and the severity of the burn then depends on the energy absorbed after that moment. About 41.8 kJ/m² gives pain or a mild second-degree burn, a further 83.6 kJ/m² a severe second-degree burn, and more than 162.2 kJ/m² a severe third-degree burn.<ref name="BY-309b" /> These effects are described in more detail under [[effects of heat on people]].

Data on deaths from thermal radiation are much scarcer than data on pain and burns. The only large source is the analysis of fatalities from nuclear weapons, where exposure times were very short and interpretation is somewhat subjective.<ref name="BY-310">Beyler (2002a), p. 3-310.</ref> Eisenberg and co-workers used these data to relate radiation intensity and exposure time to four levels of harm. These are a threshold for significant injury, 1 per cent lethality, about 50 per cent lethality and nearly 100 per cent lethality.<ref name="Eis">Eisenberg et al. (1975), as cited in Beyler (2002a), p. 3-310.</ref> On logarithmic axes of time and incident flux, each level appears as a straight line, and the time needed for a given level falls as the flux rises. Based on these data, an exposure of about 40 s at about 10 kW/m² can be taken as a threshold for fatality.<ref name="BY-310" />

A table in the SFPE Handbook chapter on risk assessment in the chemical process industries lists effect levels based on observations of large fires.<ref name="B-186" /> At 37.5 kW/m² it gives 1 per cent lethality after 10 s and 100 per cent after one minute. At 12.5 kW/m² it gives 1 per cent lethality after one minute, and at 4.0 kW/m² pain after more than 20 s without likely blistering. At 1.6 kW/m² no discomfort is expected, even for a long exposure.<ref name="B-186" /> The two combinations for 1 per cent lethality, 37.5 kW/m² for 10 s and 12.5 kW/m² for one minute, deliver 375 and 750 kJ/m². The same tabulated effect thus corresponds to very different amounts of radiant energy.
[[File:fse-probit-function-v1.svg|thumb|upright=1.5|alt=Log-log chart of exposure time against radiation intensity with points for pain, burns, injury and 1 and 100 per cent lethality.|Exposure times for pain, burns, injury and death at different levels of thermal radiation, with the calculated time to pain. Based on Barry (2002), p. 5-186, and Beyler (2002a), pp. 3-309–3-310.]]

In the Netherlands, the publication PGS 1, Part 1A, gives a relation between radiation dose and first-degree burns, second-degree burns and lethality. In practice, Dutch fire safety engineering mostly uses 2.5 kW/m² for escape and 1 kW/m² for long stays.<ref name="VR-7.7">Van Rossum (2027), §7.7.</ref> ''Introduction to Fire Safety Engineering'' stresses that the effect of radiation depends strongly on the duration of the exposure, which has to be taken into account when judging whether radiation actually causes problems.<ref name="VR-7.7" />

== Criteria for explosion overpressure ==
For explosions, effect levels are likewise stated as percentages of people affected.<ref name="B-186" /> At an overpressure of 2.5 to 5 psig, the table in the SFPE Handbook gives 1 per cent deaths from lung damage. At the same overpressure, more than half of the people suffer eardrum rupture, and more than half suffer serious wounds from flying objects. At 1 to 2.4 psig it gives 1 per cent eardrum rupture and 1 per cent serious wounds from flying objects.<ref name="B-186" /> With 1 psi equal to about 6.89 kPa, these ranges correspond to about 17 to 34 kPa and about 7 to 17 kPa.<ref name="A-12">DiNenno et al. (2002), p. A-12.</ref>
[[File:fse-probit-function-v4.svg|thumb|upright=1.5|alt=Two horizontal bars on an overpressure axis in kPa: 7 to 17 kPa for 1 per cent eardrum rupture, 17 to 34 kPa for 1 per cent deaths.|Overpressure ranges with their effects on people: 1 per cent eardrum rupture and serious wounds at about 7 to 17 kPa, and 1 per cent deaths with more than half injured at about 17 to 34 kPa. Based on Barry (2002), p. 5-186.]]

== Use in quantitative risk assessment ==
In a quantitative risk assessment, risk is the product of the frequency of an undesired event and its expected consequences.<ref name="B-176">Barry (2002), p. 5-176.</ref> The assessment proceeds in steps: defining the objectives, identifying hazards, describing loss scenarios, assessing consequences and probabilities, presenting the risk and analysing ways to reduce it.<ref name="B-177">Barry (2002), p. 5-177.</ref> Consequence assessment estimates the harm to a target, usually expressed as effects on people, loss of property or business interruption. It combines the vulnerability of the target with the way the hazardous environment develops in intensity, distance and time.<ref name="B-182">Barry (2002), p. 5-182.</ref>
[[File:fse-probit-function-v3.svg|thumb|upright=1.5|alt=Flowchart: release and fire or explosion, then exposure, then vulnerability of people, then individual and societal risk.|Place of effect models for people in a quantitative risk assessment, from the fire or explosion to individual and societal risk. Based on Barry (2002), pp. 5-182, 5-186 and 5-210.]]

Vulnerability can be assessed at two levels.<ref name="B-186" /> The first level uses general tables of damage criteria, such as the tables for radiation and overpressure described above. This gives a good first review but deals poorly with the duration of exposure, so many projects use generic threshold levels. The second level applies detailed heat transfer or structural models where the time or the specific conditions justify the extra effort.<ref name="B-186" />

The results feed two common measures of human risk. [[Individual risk]] is the probability of injury or death to a person at a specified location relative to a defined point within the fire or explosion effect zone.<ref name="B-210">Barry (2002), p. 5-210.</ref> Societal risk takes into account the likelihood of multiple casualties and is often shown as a curve of the frequency of exceeding a given number of fatalities.<ref name="B-210" /> Most of this quantification is based on fatalities. There is uncertainty about what exactly constitutes a fatal dose of thermal radiation, blast or toxic chemicals, so all assumptions and judgements have to be documented.<ref name="B-211">Barry (2002), p. 5-211.</ref>

== Worked example: time to pain ==
This example applies the time-to-pain correlation for thermal radiation given above; it is a threshold calculation, not a probit calculation. The United States federal safety standards for liquefied natural gas facilities suggest 5 kW/m² as an acceptable level for direct exposure of people, and this level can be used as a criterion for injury.<ref name="BY-310" /> With the correlation, the time to pain at this level is:
<math display="block">t_p = \left( \frac{35}{5} \right)^{1.33} = 7^{1.33} \approx 13\ \mathrm{s}</math>

For the same level, the handbook gives about 13 s before unbearable pain, and second-degree burns may occur in about 40 s.<ref name="BY-310" /> The correlation itself describes the threshold of pain, so the two values refer to different degrees of pain although the numbers coincide.<ref name="BY-309b" /> At 2.5 kW/m², the level used for escape in the Netherlands, the correlation gives about 33 s.<ref name="VR-7.7" /> At 10 kW/m² it gives about 5 s, so doubling the intensity from 5 to 10 kW/m² shortens the time to pain to about 40 per cent. At about 10 kW/m², an exposure of about 40 s is taken as a threshold for fatality.<ref name="BY-310" />

== Limits and uncertainty ==
The data behind effect levels for fatalities are limited. For thermal radiation they come mainly from nuclear weapons, with exposures much shorter than in most fires.<ref name="BY-310" /> Tables of damage criteria are weak on the effect of exposure time, and the exact fatal dose of radiation, blast or toxic chemicals is uncertain.<ref name="B-186" /><ref name="B-211" /> For the time to pain, no pain was observed below 1.7 kW/m², and different studies diverge at high fluxes, although the correlation predicts the time to pain with reasonable accuracy.<ref name="BY-309b" />

For toxic and irritant gases, the spread of sensitivity within a population is partly based on expert judgement, because experiments with humans at dangerous exposures cannot be done.<ref name="P-120" /> Sensitive groups may respond far below the typical values.<ref name="P-90" /> For buildings, fire safety engineering generally uses simple tenability limits or FED models.<ref name="AU-110" />

== See also ==
* [[Societal risk]]
* [[Event tree analysis]]
* [[Fire risk assessment]]
* ALARP
* [[Uncertainty analysis]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-176–5-213). National Fire Protection Association; Society of Fire Protection Engineers.
* Beyler, C. L. (2002a). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-268–3-314). National Fire Protection Association; Society of Fire Protection Engineers.
* DiNenno, P. J., Drysdale, D., Beyler, C. L., Walton, W. D., Custer, R. L. P., Hall, J. R., Jr., & Watts, J. M., Jr. (Eds.). (2002). ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-83–2-171). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Fire Risk Analysis]]

Minimum ignition energy

2026-11-02T21:34:15Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Minimum ignition energy''' is the smallest spark energy capable of igniting a specified combustible mixture under the conditions of a test. Commonly abbreviated MIE, it describes sensitivity to an electrical discharge. The value depends on the material, mixture composition and discharge characteristics, rather than being an unrestricted constant for every situation involving that substance.<ref name="B-181">Beyler (2002), p. 2-181.</ref><ref name="Z-405">Zalosh (2002), p. 3-405.</ref>

The quantity helps assess whether an [[Ignition source|ignition source]] can initiate combustion. It is distinct from the minimum temperature needed for ignition and from the pressure developed after an explosion. Those properties require different measurements and answer different safety questions.<ref name="Z-404-406">Zalosh (2002), pp. 3-404–3-406.</ref> A comparison between a possible spark and a measured MIE therefore retains the type of discharge, the fuel concentration and the surrounding conditions. Gas mixtures near their flammability boundaries generally require more ignition energy than more readily ignited compositions within the flammable range.<ref name="B-181" /><ref name="N-4">Iqbal and Salley (2004), p. 16-4.</ref>

== What the measured quantity describes ==

Ignition energy concerns the initiation of combustion by a particular source. The experimental arrangement supplies energy to a prepared mixture and determines whether ignition occurs. For dust clouds, Zalosh describes a standardised electrical-spark test. For gases, Beyler relates the required energy to mixture composition and to the loss of heat near surrounding surfaces.<ref name="Z-405" /><ref name="B-181-182">Beyler (2002), pp. 2-181–2-182.</ref>

The energy is commonly reported in millijoules, where one millijoule is one thousandth of a joule. Electrical energy calculations often use joules with capacitance, voltage, inductance and current in their corresponding SI units. Converting the measured threshold before making that comparison prevents a thousandfold unit error. The handbook's worked example explicitly converts millijoules to joules.<ref name="Z-405" />

The word minimum refers to the conditions examined in obtaining the value. The most readily ignited concentration can differ between materials. Zalosh states that his tabulated dust results represent the most sensitive concentration for each tested sample. A result for another concentration can therefore exceed the reported minimum without contradicting it.<ref name="Z-405" />

An ignition-energy result is not an explosion-severity measurement. The pressure following ignition depends on flame propagation, confinement and the thermal state of the burned gases. Zalosh treats that pressure calculation separately from the ignition-source assessment. A material that is easily ignited does not have its eventual pressure determined by MIE alone.<ref name="Z-402">Zalosh (2002), p. 3-402.</ref><ref name="Z-406">Zalosh (2002), p. 3-406.</ref>

The distinction also separates energy from ignition temperature. Dust-cloud temperature tests expose dispersed material in a heated apparatus, while dust-layer tests use a heated surface. An electrical spark delivers energy through a different exposure. The resulting values cannot be substituted for each other simply because all concern ignition.<ref name="Z-404">Zalosh (2002), p. 3-404.</ref>

== Gas concentration and surrounding conditions ==

A gas must be mixed with oxidant in suitable proportions for a flame to propagate. [[Flammability limits]] identify the boundaries of that range under specified conditions. Inside the range, the energy needed for ignition still varies with composition. Being within the flammable range therefore does not imply that every possible electrical disturbance will ignite the mixture.<ref name="B-181" />

Beyler reports ignition energies of the order of a few tenths of a millijoule for many near-stoichiometric mixtures in air. Stoichiometric composition supplies fuel and oxygen in the proportions required by the combustion reaction. The minimum does not necessarily occur exactly at that composition. The source discusses shifts towards richer mixtures associated with preferential diffusion for certain fuels.<ref name="B-181" />

As a mixture approaches either flammability boundary, its required ignition energy rises sharply. This dependence means that one measured minimum cannot reproduce the complete concentration-dependent response. It is useful for identifying a sensitive condition, while a particular scenario still needs its actual mixture considered. The nuclear inspection guidance describes the same general trend for hydrogen in air.<ref name="B-181" /><ref name="N-4" />
[[File:fse-minimum-ignition-energy-v1.svg|thumb|upright=1.5|alt=A qualitative curve shows higher required spark energy near the lean and rich boundaries and a lower intermediate region.|Required ignition energy changes within the flammable concentration range. Based on Beyler (2002), p. 2-181, and Iqbal and Salley (2004), p. 16-4.]]

The oxidant mixture also influences ignition. Beyler notes much smaller energy scales for mixtures in oxygen than for corresponding discussions of mixtures in air. NUREG-1805 describes increased ignition energy when a diluent such as steam is added to hydrogen and air. A threshold therefore needs the oxidant and diluent conditions alongside the fuel name.<ref name="B-181" /><ref name="N-4" />

Pressure is another part of the reported experimental condition. The hydrogen figure reproduced in NUREG-1805 presents separate ignition-energy curves for different pressures. These curves vary with hydrogen concentration and do not collapse into one fixed threshold. The figure supports retaining pressure when interpreting its data, without supplying a universal correction for every gas and discharge.<ref name="N-4" />

== Hydrogen as an ignition-sensitivity example ==

The importance of low-energy sparks is evident in [[Hydrogen safety|hydrogen safety]]. NUREG-1805 identifies electrical equipment and small static discharges as possible ignition sources when a hydrogen-air mixture becomes flammable. Its discussion concerns dry, relatively still mixtures and shows how required energy changes with composition. These conditions remain part of the evidence.<ref name="N-4" />

The same report distinguishes hydrogen's low spark-energy requirement from its comparatively high ignition temperature. The properties describe different ignition mechanisms. A relatively high temperature criterion therefore does not mean that small electrical sparks can be disregarded. Conversely, a spark-energy value does not specify the temperature of every surface capable of initiating combustion.<ref name="N-2">Iqbal and Salley (2004), p. 16-2.</ref><ref name="N-4" />

Hydrogen flammability limits also depend on the flame-propagation direction used in the test. NUREG-1805 distinguishes upward, horizontal and downward propagation. This illustrates that ignition and sustained propagation are evaluated within a defined experimental arrangement. Combining an ignition-energy measurement with unrelated mixture limits can conceal differences in what the experiments actually assessed.<ref name="N-2" /><ref name="N-4" />

The report's plotted curves and approximate prose statement serve different purposes. The curves show concentration and pressure dependence, while the prose conveys the small energy scale. Treating the approximate statement as one exact minimum for every hydrogen mixture would discard the variation shown on the same page. The article therefore does not assign a universal hydrogen threshold.<ref name="N-4" />

== Dust-cloud tests and sample dependence ==

For a [[Dust explosion|dust explosion]] assessment, the relevant fuel is a suspended particulate cloud. Zalosh describes measuring MIE in a 1.2 litre cylindrical apparatus, commonly called a modified Hartmann tube. An electrical discharge is applied to the prepared cloud. The account refers to the historical test method described in the 2002 handbook.<ref name="Z-405" />

The tested powder is more specific than its commercial material name. The handbook reports particle-size information with the results and identifies concentration, temperature and mixture motion as influences. These conditions can differ between a laboratory sample and a process cloud. A tabulated value consequently requires the associated sample and test description.<ref name="Z-404" /><ref name="Z-405" />

The following examples retain the median particle sizes reported in Zalosh's table. The MIE results were obtained using relatively long inductive discharges and the most sensitive dust concentration. They demonstrate variation among particular tested powders. They are not universal constants for all sugar, milk powder or starch products.<ref name="Z-table">Zalosh (2002), pp. 3-404–3-405, Table 3-16.2.</ref>

{| class="wikitable"
! Tested material !! Reported median particle size !! Minimum ignition energy
|-
| Sugar || 10 μm || 14 mJ
|-
| Milk powder || 165 μm || 75 mJ
|-
| Corn starch || Less than 10 μm || 300 mJ
|}

Differences between these rows cannot isolate a particle-size effect because the materials also differ. The table combines several characteristics of each sample. An assessment of one influence would require otherwise comparable test conditions and material. The numbers support sample-specific comparison, rather than a simple ranking based only on the displayed particle diameters.<ref name="Z-table" /><ref name="Z-405" />

Minimum explosible concentration is a separate dust property. Its test examines whether a cloud of a given concentration supports the relevant combustion response, using an ignition source specified by that method. Zalosh notes that those results can themselves be sensitive to igniter energy and turbulence. A concentration test does not automatically determine the material's minimum spark energy.<ref name="Z-404" />

The milk-powder row also reports a cloud ignition temperature of 460 °C and a layer ignition temperature of 330 °C. These temperatures accompany an MIE of 75 mJ for the stated sample. The three numbers describe different experimental exposures. Their different units and test arrangements prevent interpreting one as a direct conversion of another.<ref name="Z-table" />
[[File:fse-minimum-ignition-energy-v2.svg|thumb|upright=1.5|alt=Three test concepts distinguish the milk-powder sample’s spark energy, cloud ignition temperature and layer ignition temperature.|The same powder sample has distinct energy, cloud-temperature and layer-temperature results. Based on Zalosh (2002), pp. 3-404–3-405.]]

Zalosh attributes lower layer ignition temperatures to reduced heat dissipation within deposited material compared with a dispersed cloud. The distinction helps explain why a hot deposited layer can present a different ignition problem from the same material suspended in air. A spark-energy result for the cloud consequently does not evaluate sustained heating of the deposit.<ref name="Z-404-406" />

Temperature and motion can also change the spark test itself. Zalosh reports decreasing dust MIE with increasing mixture temperature and increasing MIE with greater dust-air velocity. Those influences are separate from the choice of powder and concentration. A result obtained in one prepared cloud therefore does not establish the same threshold under every hotter or faster-moving process condition.<ref name="Z-405" />

The test record consequently needs more than a material label and an energy number. Sample description, concentration, temperature and discharge duration identify what was actually assessed. Keeping these details together permits a meaningful comparison with a proposed ignition scenario.<ref name="Z-405" />

== Discharge duration and stored energy ==

The duration of an electrical spark affects its ability to ignite a dust cloud. Zalosh describes lower measured MIE values for longer discharges produced by adding inductance or resistance to a capacitive circuit. The total energy and its release history are therefore related but distinct characteristics. Comparing only the energy numbers can overlook the duration difference.<ref name="Z-405" />

This matters when laboratory results are compared with electrostatic discharges. The source distinguishes relatively short capacitive sparks from longer discharges associated with electrical equipment. A dust threshold obtained with a long inductive spark cannot automatically be treated as the matching threshold for every capacitive spark. The discharge type accompanies the reported MIE.<ref name="Z-405" />

Theoretical stored energies for ideal capacitive and inductive circuits follow the equations below. Their variables use SI units so that the calculated energy is in joules. These expressions describe the stated ideal electrical storage. They do not independently establish the fraction of that energy transferred to a real combustible mixture.<ref name="Z-405" />

<div class="fse-equation">E<sub>C</sub> = ½ C U²</div>
<div class="fse-equation">E<sub>L</sub> = ½ L I²</div>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| E<sub>C</sub> || Ideal capacitive stored energy || J
|-
| E<sub>L</sub> || Ideal inductive stored energy || J
|-
| C || Capacitance || F
|-
| U || Potential difference before discharge || V
|-
| L || Inductance || H
|-
| I || Current || A
|}

The square dependence means that voltage and energy do not change in direct proportion at fixed capacitance. Halving the voltage gives one quarter of the stored energy. The corresponding inductive expression has the same square dependence on current at fixed inductance. These mathematical relationships help interpret changes within the stated circuit model.<ref name="Z-405" />

Mechanical sparks require another assessment. Zalosh states that their associated energy is much more difficult to determine than energy in simple electrical circuits. Hot spots produced by sustained friction also differ from brief impact sparks. The capacitive formula therefore cannot be used as a complete description of every possible ignition source.<ref name="Z-405" />

== A worked comparison of discharge types ==

Zalosh gives an illustrative powder silo with a capacitance of 500 picofarads. The stated powder has a minimum ignition energy of 10 mJ for inductive sparks and 50 mJ for capacitive sparks. The question concerns a capacitive discharge, so the matching comparison uses 50 mJ. The lower inductive result describes a different discharge history.<ref name="Z-405" />
[[File:fse-minimum-ignition-energy-v3.svg|thumb|upright=1.5|alt=The capacitive threshold connects to the stored-energy calculation, while the inductive threshold is shown as an incompatible input.|The theoretical electrostatic comparison uses the threshold for the same discharge type. Based on Zalosh (2002), p. 3-405.]]

Rearranging the capacitive equation gives U = √(2E<sub>C</sub>/C). Converting the inputs gives an energy of 0.050 J and a capacitance of 500 × 10⁻¹² F. The calculated voltage is approximately 14,100 V, or 14 kV to two significant figures. This reproduces the handbook's rounded theoretical result.<ref name="Z-405" />

Using the 10 mJ inductive threshold in that capacitive calculation would instead give approximately 6.3 kV. This is a calculated illustration of the error introduced by changing the threshold definition. It does not establish a second valid capacitive ignition criterion. The difference arises from comparing unlike discharge conditions.<ref name="Z-405" />

The source connects the example to charge generation during powder handling. It also notes that grounding the silo addresses charge on that conductive object. Isolated objects inside it and a sufficiently resistive powder can retain their own charge hazards. The energy calculation therefore identifies one mechanism without demonstrating that every electrostatic source has been controlled.<ref name="Z-405" /><ref name="Z-406" />

== Engineering use and limits ==

One prevention approach is to limit electrical equipment so that its worst fault condition cannot supply sufficient ignition energy for the specified gas. Beyler describes this as intrinsic safety. Another approach contains an internal ignition and prevents its flame from propagating outside the enclosure. These approaches address ignition in different ways and require their own design basis.<ref name="B-181" />

Flame quenching depends on heat lost as a flame passes through a sufficiently small gap. Beyler distinguishes the quenching distance from the minimum experimental safe gap, which also reflects possible ignition outside by emerging hot gases. Neither distance is simply an energy value. Their relationship to ignition sensitivity does not make them interchangeable equipment parameters.<ref name="B-181-182" />

These source-control concepts are relevant to the separate topic Hazardous area classification. The ignition-energy discussion here does not establish a zone or division, an equipment category or a permissible installation. It describes the physical basis for comparing certain ignition sources with specified combustible mixtures.<ref name="B-181" /><ref name="Z-402" />

Finally, an assessment retains both the ignition conditions and the consequences if ignition occurs. Mixture formation, electrical or mechanical source characteristics and subsequent flame propagation are separate parts of that sequence. A favourable comparison with one measured MIE does not evaluate every alternative source or mixture state. The source data remain conditional on their material and experimental context.<ref name="Z-402" /><ref name="Z-405" /><ref name="N-4" />

== See also ==
* [[Deflagration index]]

== Notes ==
<references />

== References ==
* Beyler, C. (2002). Flammability limits of premixed and diffusion flames. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 2-7). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-16). National Fire Protection Association.

[[Category:Explosions & Industrial Fires]]

Oxygen consumption principle

2026-11-02T21:34:12Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

The '''oxygen consumption principle''' states that the burning of organic fuels releases a nearly constant amount of heat per unit mass of oxygen consumed, about 13.1 kJ per gram of oxygen.<ref name="JA-45">Janssens (2002), p. 3-45.</ref> Thornton found this regularity in 1917 for organic liquids and gases. Huggett later showed that it also holds for organic solids, with an average value that is accurate within ±5 % with very few exceptions.<ref name="TH">Thornton (1917) and Huggett (1980), as cited in Janssens (2002), p. 3-45.</ref> The [[heat release rate]] of a fire can therefore be determined by measuring how much oxygen the fire removes from the air, without knowing exactly what is burning.<ref name="JA-45" />

This idea is the basis of oxygen consumption calorimetry. The method is regarded as the most accurate and practical technique for measuring heat release rates in fire experiments, at bench scale and at large scale.<ref name="JA-46">Janssens (2002), p. 3-46.</ref> The [[cone calorimeter]], the [[room corner test]] and the Single Burning Item test all rely on it.<ref name="BA-64">Babrauskas (2002a), p. 3-64.</ref><ref name="JA-58">Janssens (2002), p. 3-58.</ref><ref name="BB-32">Babrauskas (2002b), p. 3-32.</ref> The heat release rate is the single most important parameter characterising a fire, and in many fire experiments it is measured by oxygen consumption calorimetry.<ref name="HM-31">Hamins and McGrattan (2007), p. 3-1.</ref><ref name="HM-32">Hamins and McGrattan (2007), p. 3-2.</ref>

== Principle ==
The [[heat of combustion]] of a fuel is the heat released when it burns completely. Expressed per gram of fuel, it differs strongly between materials, from about 16 kJ/g for cellulose to 50 kJ/g for methane. Expressed per gram of oxygen consumed, it is approximately constant for most fuels, with an average of 13.1 kJ/g. Per gram of air consumed, the average is about 3 kJ/g.<ref name="DR-93">Drysdale (2002), p. 1-93.</ref> Thornton's rule implies that it is enough to measure the oxygen consumed in a combustion system to determine the net heat released.<ref name="JA-45" />

Perhaps the first application of the principle in fire research was made by Parker on the ASTM E-84 tunnel test. The technique was then refined at the National Bureau of Standards, now the National Institute of Standards and Technology, in the late 1970s and early 1980s.<ref name="JA-46" /> Since then it has become routine in fire research and fire testing. It is used for small samples as well as for items of furniture and wall lining materials.<ref name="DR-96">Drysdale (2002), p. 1-96.</ref>

The constancy can be checked with [[stoichiometry]], which gives the amounts of substances consumed and formed in a reaction. One mole of methane, about 16 g, burns completely with two moles of oxygen, about 64 g.<ref name="VR-3.3">Van Rossum (2027), §3.3.</ref> With a heat of combustion of 800 kJ/mol, methane therefore releases 800/64 = 12.5 kJ per gram of oxygen.<ref name="DR-93" /> Propane releases 2,044 kJ/mol and needs five moles, or 160 g, of oxygen, which gives 12.8 kJ/g. Both values lie within 5 % of the average of 13.1 kJ/g.<ref name="DR-93" />
[[File:fse-oxygen-consumption-principle-v1.svg|thumb|upright=1.5|alt=Two bar charts for nine fuels: heat per gram of fuel ranges from 10 to 50 kJ, heat per gram of oxygen stays near 13 kJ except for CO.|Heat of combustion per gram of fuel (left) and per gram of oxygen consumed (right), with the average of 13.1 kJ/g. Based on Drysdale (2002), p. 1-93.]]

{| class="wikitable"
|+ Heat of combustion per gram of fuel and per gram of oxygen consumed, at 25 °C<ref name="DR-93" />
! Fuel !! kJ per g of fuel !! kJ per g of oxygen
|-
| Methane || 50.00 || 12.54
|-
| Propane || 46.45 || 12.80
|-
| Ethanol || 26.78 || 12.88
|-
| Cellulose || 16.09 || 13.59
|-
| Polyethylene || 43.28 || 12.65
|-
| Polystyrene || 39.85 || 12.97
|-
| Polymethylmethacrylate || 24.89 || 12.98
|-
| Polyoxymethylene || 15.46 || 14.50
|-
| Carbon monoxide || 10.10 || 17.69
|}

Other sources give slightly different averages. Tewarson found an average of 12.8 kJ/g with a spread of ±7 % for a large set of materials. He notes that this is close to the 13.4 kJ/g used in the heating and power industries and to Huggett's 13.1 kJ/g.<ref name="TE-104">Tewarson (2002), p. 3-104.</ref> For most testing, the standard value of 13.1 MJ per kilogram of oxygen is used. A small number of substances differ substantially from it, and if their composition is known, the value can be corrected.<ref name="BB-32" />

A related technique uses the carbon dioxide and carbon monoxide generated instead of the oxygen consumed. Tewarson reports average values of 13.3 kJ per gram of carbon dioxide generated, with a spread of ±11 %, and 11.1 kJ per gram of carbon monoxide, with a spread of ±18 %.<ref name="TE-103">Tewarson (2002), p. 3-103.</ref> Both spreads are wider than the ±7 % of the oxygen-based value.<ref name="TE-103" /><ref name="TE-104" />

== Measuring the heat release rate ==
The basic requirement is that all combustion products are collected and removed through an exhaust duct. Far enough downstream for the gases to be well mixed, both the flow rate and the composition of the gases are measured. The inflow of air does not have to be measured, as long as the flow in the exhaust duct is known.<ref name="JA-46" /> Applying Thornton's rule to such a system gives a simple oxygen balance:<ref name="JA-46" />
[[File:fse-oxygen-consumption-principle-v2.svg|thumb|upright=1.5|alt=Fire under a hood connected to an exhaust duct with a fan; flow and oxygen are measured in the duct.|An oxygen consumption calorimeter: all products are collected in a hood; flow rate and oxygen concentration are measured in the exhaust duct. Based on Janssens (2002), p. 3-46.]]

<math display="block">\dot{q} = E \left( \dot{m}_a \, Y^a_{\mathrm{O_2}} - \dot{m}_e \, Y^e_{\mathrm{O_2}} \right)</math>

Here <math>E</math> is about 13.1 kJ per gram of oxygen, and the mass fraction of oxygen in dry incoming air is 0.232.<ref name="JA-46" /> In practice the equation cannot be used directly, for three reasons. Oxygen analysers measure mole fractions rather than mass fractions. Water vapour is removed from the gas sample before it reaches the analyser, so the reading is on a dry basis. Flow measurements give the volume flow rather than the mass flow, and the combustion reactions change the volume of the gas slightly.<ref name="JA-46" /> For the common case in which only oxygen is measured, after water vapour and carbon dioxide have been removed from the sample, Janssens gives the working equations:<ref name="JA-47">Janssens (2002), p. 3-47.</ref>

<math display="block">\dot{q} = E \, \frac{\phi}{1 + \phi (\alpha - 1)} \, \dot{m}_e \, \frac{M_{\mathrm{O_2}}}{M_a} \left( 1 - X^a_{\mathrm{H_2O}} - X^a_{\mathrm{CO_2}} \right) X^{A,a}_{\mathrm{O_2}}</math>

<math display="block">\phi = \frac{X^{A,a}_{\mathrm{O_2}} - X^{A,e}_{\mathrm{O_2}}}{\left( 1 - X^{A,e}_{\mathrm{O_2}} \right) X^{A,a}_{\mathrm{O_2}}}</math>

{| class="wikitable"
|+ Symbols used in the oxygen consumption equations
! Symbol !! Description !! Unit
|-
| <math>\dot{q}</math> || heat release rate || kW
|-
| <math>E</math> || heat released per mass of oxygen consumed (about 13,100) || kJ/kg
|-
| <math>\dot{m}_a</math>, <math>\dot{m}_e</math> || mass flow rate of incoming air and of exhaust gas || kg/s
|-
| <math>Y^a_{\mathrm{O_2}}</math>, <math>Y^e_{\mathrm{O_2}}</math> || mass fraction of oxygen in the incoming air and in the exhaust gas || –
|-
| <math>\phi</math> || oxygen depletion factor || –
|-
| <math>\alpha</math> || volumetric expansion factor (recommended average 1.105) || –
|-
| <math>M_{\mathrm{O_2}}</math>, <math>M_a</math> || molar mass of oxygen (32)<ref name="VR-3.3" /> and of dry air (29)<ref name="JA-47" /> || g/mol
|-
| <math>X^a_{\mathrm{H_2O}}</math>, <math>X^a_{\mathrm{CO_2}}</math> || mole fraction of water vapour and of carbon dioxide in the incoming air || –
|-
| <math>X^{A,a}_{\mathrm{O_2}}</math>, <math>X^{A,e}_{\mathrm{O_2}}</math> || measured (dry) mole fraction of oxygen in the incoming air and in the exhaust gas || –
|}

The expansion factor depends on the fuel. It equals 1 for the complete combustion of carbon in dry air and 1.21 for pure hydrogen, and an average of 1.105 is recommended when the fuel is unknown. Dry air contains about 330 ppm of carbon dioxide, and in a temperature-controlled laboratory the water vapour content is typically less than a few percent.<ref name="JA-47" /> With these generic values, the equations are expected to be accurate within ±10 % if the combustion is complete. The error can be larger when much carbon monoxide or soot forms, or when the products include other species such as hydrogen chloride.<ref name="JA-47" />

Adding analysers for carbon dioxide, carbon monoxide and water vapour improves the accuracy. Burning carbon monoxide to carbon dioxide releases about 17.6 kJ per gram of oxygen, so a correction term accounts for carbon that leaves as carbon monoxide.<ref name="JA-47" /> Even under the worst conditions considered by Janssens, ignoring the carbon monoxide causes an error of less than 5 %.<ref name="JA-48">Janssens (2002), p. 3-48.</ref>

High-quality work requires a paramagnetic oxygen analyser. The standards for the cone calorimeter allow at most 50 ppm of noise and drift, and the best instruments reach 20 ppm.<ref name="BA-64" /><ref name="BA-65">Babrauskas (2002a), p. 3-65.</ref> Because a paramagnetic analyser responds to the partial pressure of oxygen, changes in atmospheric pressure must be compensated. Otherwise the calculated heat release rate can contain a significant error. Carbon dioxide in the sample causes an error of less than 0.3 % in the oxygen reading.<ref name="BA-65" />

== Worked example: a cone calorimeter test ==
The cone calorimeter draws air through its exhaust system at 24 L/s.<ref name="BA-69">Babrauskas (2002a), p. 3-69.</ref> At 20 °C, air has a density of about 1.2 kg/m³, so the exhaust mass flow is about 0.024 × 1.2 = 0.0288 kg/s.<ref name="VR-3.2">Van Rossum (2027), §3.2.</ref> Air contains 21 % oxygen by volume.<ref name="VR-4.2">Van Rossum (2027), §4.2.</ref> Suppose that, during a test, the dry oxygen reading in the exhaust falls from 21.0 % to 20.5 %. The depletion factor and the heat release rate then follow from the equations above. The calculation uses the expansion factor of 1.105, dry incoming air with 330 ppm of carbon dioxide and molar masses of 32 and 29 g/mol:<ref name="JA-47" /><ref name="VR-3.3" />

<math display="block">\phi = \frac{0.210 - 0.205}{(1 - 0.205) \times 0.210} \approx 0.0300</math>

<math display="block">\dot{q} = 13{,}100 \times \frac{0.0300}{1 + 0.0300 \times 0.105} \times 0.0288 \times \frac{32}{29} \times (1 - 0.00033) \times 0.210 \approx 2.6\ \mathrm{kW}</math>

The specimen in a cone calorimeter measures 100 mm by 100 mm, or 0.01 m², so this corresponds to about 261 kW/m².<ref name="BA-63">Babrauskas (2002a), p. 3-63.</ref> The result lies well within the normal calibrated range of the instrument, 0 to 12 kW.<ref name="BA-63" /> The example also shows why the analyser must be so precise. A drop of 0.5 percentage points equals 5,000 ppm, so an analyser noise of 20 to 50 ppm corresponds to 0.4 to 1 % of the signal.<ref name="BA-65" />

== Calorimeters based on the principle ==
The cone calorimeter is the preferred instrument for measuring the heat release rate at bench scale. A specimen of 100 mm by 100 mm, 6 to 50 mm thick, is exposed to a radiant heat flux of up to 110 kW/m² and ignited by an electric spark.<ref name="BA-63" /> The instrument has been designed to use only oxygen consumption as its measuring principle. Besides the heat release rate, it measures the effective heat of combustion, the mass loss rate, ignitability, smoke and toxic gases.<ref name="BA-63" /><ref name="BA-64" />
[[File:fse-oxygen-consumption-principle-v3.svg|thumb|upright=1.5|alt=Cross-section of a cone calorimeter: specimen on a load cell under a conical heater, with hood, exhaust duct, gas sampling and blower above.|Main parts of the cone calorimeter. Based on Babrauskas (2002a), pp. 3-63 and 3-64.]]

The room corner test is a standardised large-scale test for wall and ceiling linings. Specimens line the walls and ceiling of a small room, and a gas burner in one rear corner ignites them. All combustion products leave through the doorway into a hood, where the gases are analysed.<ref name="JA-39">Janssens (2002), p. 3-39.</ref>

In the international version, ISO 9705 of 1992, the room is about 2.4 m wide, 3.7 m deep and 2.4 m high, with a single doorway of about 0.8 m by 2.0 m. A sand burner of 0.17 m by 0.17 m releases 100 kW for 10 minutes and then 300 kW for another 10 minutes.<ref name="JA-58" /> The American room test standard NFPA 286 uses a nearly identical room with a burner output of 40 kW for 5 minutes, followed by 160 kW for 10 minutes. In one series of room tests, a total heat release rate of 1 MW served as one of the criteria for [[flashover]].<ref name="JA-58" />

The Single Burning Item test is a European regulatory heat release test for building products. It uses two wall panels in a corner configuration, without a ceiling.<ref name="BB-32" /> Larger set-ups follow the same principle. Furniture calorimeters measure the heat release rate of chairs, sofas and mattresses placed on a load cell beneath a hood.<ref name="JA-57">Janssens (2002), p. 3-57.</ref> Industrial-size calorimeters reach into the megawatt range, and measurements from fires of a few kilowatts up to 100 MW have been reported.<ref name="JA-58" /> For comparison, an average living room sofa burns with a heat release rate of about 2.5 MW.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref>

== Accuracy and uncertainty ==
Uncertainty arises from both bias and random error. The fixed value of 13.1 MJ/kg is one source of bias, and calibration with a metered flow of pure gas reduces bias in general.<ref name="BB-32" /> NUREG-1824 summarises several uncertainty studies of oxygen consumption calorimetry. For the Single Burning Item test and the room corner test, the relative expanded uncertainty ranged from 0.07 to 0.14, and for the cone calorimeter from 0.10 to 0.12.<ref name="HM-32" /> The oxygen measurement and the exhaust mass flow were consistently identified as major sources of uncertainty, and the heat release factor also contributed. Larger oxygen deficits give smaller combined uncertainties.<ref name="HM-32" />

Interlaboratory trials, known as round robins, show the random error separately. They quantify the repeatability within one laboratory and the reproducibility between laboratories. For the peak heat release rate, both limits are much wider for the larger apparatus than for the cone calorimeter.<ref name="BB-33">Babrauskas (2002b), p. 3-33.</ref>
[[File:fse-oxygen-consumption-principle-v4.svg|thumb|upright=1.5|alt=Bar chart of 95 % limits for peak heat release rate: cone 17 and 23 %, SBI 38 and 54 %, room calorimeter 65 and 79 %.|Repeatability (r) and reproducibility (R) of the peak heat release rate in round robins, as 95 % confidence limits. Based on Babrauskas (2002b), p. 3-33.]]

{| class="wikitable"
|+ 95 % confidence limits of the peak heat release rate from round robin tests (r = repeatability, R = reproducibility)<ref name="BB-33" />
! Apparatus !! Year of round robin !! r (%) !! R (%)
|-
| Cone calorimeter || 2000 || 17 || 23
|-
| Single Burning Item test || 1997 || 38 || 54
|-
| Room calorimeter || 1994 || 65 || 79
|}

== Use in fire safety engineering ==
The heat release rate is the primary variable that determines how much a material contributes to the hazard of a compartment fire.<ref name="JA-38">Janssens (2002), p. 3-38.</ref> It controls how strongly a fire heats its surroundings, and it is the most significant input uncertainty of fire models.<ref name="HM-31" /> The fire models evaluated in NUREG-1824 do not predict the heat release rate but take it as an input. In the experiments used for that evaluation, it was determined from the fuel mass loss rate or by oxygen consumption calorimetry.<ref name="HM-31" /><ref name="HM-32" /> Data from furniture calorimeters serve as input to compartment fire and smoke transport models.<ref name="JA-57" /> Bench-scale data can also be used with calculation methods to predict the behaviour of linings in the room corner test.<ref name="JA-39" />

The principle also appears inside fire models. CFAST takes the heat of combustion based on oxygen consumption as 13.1 MJ/kg, representative of typical hydrocarbon fuels, when it limits burning by the available oxygen.<ref name="PE-13">Peacock et al. (2026), p. 13.</ref> The Fire Dynamics Simulator uses about 13,100 kJ/kg for most fuels in its extinction model.<ref name="MG-62">McGrattan et al. (2026), p. 62.</ref>

Building regulations refer to test methods based on the principle. In Australia, the non-mandatory data sheets for the Fire Safety Verification Method of the Australian Building Codes Board (2020a) define a reference design scenario closely aligned to ISO 9705.<ref name="AB-B2">Australian Building Codes Board (2020a), Data Sheet B2, p. 1.</ref><ref name="AB-48" /> A corner fire burns at 100 kW for 10 minutes and then at 300 kW for 10 minutes, unless the wall and ceiling linings become involved.<ref name="AB-48">Australian Building Codes Board (2020a), Data Sheet B4, p. 48.</ref> The group number of the lining, determined in accordance with AS 5637, then sets the growth of the design fire.<ref name="AB-48" /> In New Zealand, Building Code clause C3.4 as reproduced in the 2013 commentary to C/VM2 specified internal surface linings by material group numbers determined under ISO 9705.<ref name="NZ-18">Ministry of Business, Innovation and Employment (2013), p. 18.</ref> The second edition of C/VM2 (2025) has removed its references to product test standards such as ISO 5660 and ISO 9705, which now appear in separate Building Product Specifications.<ref name="NZ-3">Ministry of Business, Innovation and Employment (2025b), p. 3.</ref>

== Limitations and misconceptions ==
The method only works if all combustion products reach the exhaust duct.<ref name="JA-46" /> The standard exhaust flow of the cone calorimeter, 24 L/s, is about twice the minimum flow at which no gases spill out of the hood.<ref name="BA-69" /> The constant of 13.1 kJ/g is an average. Fuels such as polyoxymethylene, at 14.50 kJ/g, and carbon monoxide, at 17.69 kJ/g, deviate considerably from it.<ref name="DR-93" />

Oxygen consumption gives the total heat release rate, not how that heat is divided between convection and radiation. The convective fraction depends on the design of the apparatus and on the size of the specimen, so it is not a material property. The cone calorimeter was therefore deliberately designed without a separate measurement of the convected heat.<ref name="BA-64" />

The measured heat release also differs from what a bomb calorimeter suggests. The effective heat of combustion is the ratio of the heat release rate to the mass loss rate. For most solid materials it is significantly lower than the heat of combustion measured in pure oxygen at high pressure in a bomb calorimeter. The effective value is the one to use in fire hazard assessment.<ref name="JA-39" /> A single test result is not an exact number either, given the reproducibility of 23 to 79 % between laboratories for the peak heat release rate.<ref name="BB-33" />

== See also ==
* [[Effective heat of combustion]]
* [[Equivalence ratio]]
* [[Adiabatic flame temperature]]
* [[Incomplete combustion]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Babrauskas, V. (2002a). The cone calorimeter. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-63–3-81). National Fire Protection Association; Society of Fire Protection Engineers.
* Babrauskas, V. (2002b). Heat release rates. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association; Society of Fire Protection Engineers.
* Drysdale, D. D. (2002). Thermochemistry. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-90–1-98). National Fire Protection Association; Society of Fire Protection Engineers.
* Hamins, A., & McGrattan, K. (2007). ''Verification and validation of selected fire models for nuclear power plant applications: Vol. 2. Experimental uncertainty'' (NUREG-1824; EPRI 1011999). U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research; Electric Power Research Institute.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-38–3-62). National Fire Protection Association; Society of Fire Protection Engineers.
* McGrattan, K., Hostikka, S., Floyd, J., McDermott, R., Vanella, M., Mueller, E., & Paul, C. (2026). ''Fire Dynamics Simulator technical reference guide: Vol. 1. Mathematical model'' (6th ed., NIST Special Publication 1018-1). National Institute of Standards and Technology. https://doi.org/10.6028/NIST.SP.1018
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* Peacock, R. D., McGrattan, K. B., Forney, G. P., & Reneke, P. A. (2026). ''CFAST – Consolidated Fire and Smoke Transport: Vol. 1. Technical reference guide'' (Version 7, NIST Technical Note 1889v1). National Institute of Standards and Technology. https://doi.org/10.6028/NIST.TN.1889v1
* Tewarson, A. (2002). Generation of heat and chemical compounds in fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-82–3-161). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Combustion]]

Oxygen depletion

2026-11-02T21:34:09Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Oxygen depletion''' is the fall of the oxygen concentration in the air of a room or building below its normal value of about 21 per cent by volume. It is caused by a fire that consumes oxygen or by gases that displace it.<ref name="VR-4.2">Van Rossum (2027), §4.2.</ref><ref name="P-107">Purser (2002), p. 2-107.</ref> It affects both the fire and the people exposed to it. A fire that runs short of oxygen burns less efficiently, produces more carbon monoxide and smoke, and may die down or go out.<ref name="P-136">Purser (2002), p. 2-136.</ref><ref name="P-155">Purser (2002), p. 2-155.</ref> People who breathe air with too little oxygen suffer hypoxia, a lack of oxygen in the body that can lead to loss of consciousness and death.<ref name="P-106">Purser (2002), p. 2-106.</ref>

Low oxygen is one of the asphyxiant effects in [[fire toxicity]], together with carbon monoxide and hydrogen cyanide.<ref name="P-91">Purser (2002), p. 2-91.</ref> Its effect on people is usually small down to about 15 per cent oxygen and becomes severe at about 10 per cent.<ref name="P-106" /> The SFPE Handbook gives a simple equation for the time to loss of consciousness at a given oxygen concentration, which can be combined with the doses of other gases in a [[fractional effective dose]] calculation.<ref name="P-107" /><ref name="P-110">Purser (2002), p. 2-110.</ref> The same physics is used on purpose by extinguishing systems that lower the oxygen concentration with inert gas, which raises the question of how long people may stay in such an atmosphere.<ref name="DN-174">DiNenno (2002), p. 4-174.</ref><ref name="DN-184">DiNenno (2002), p. 4-184.</ref>

== Oxygen in air and in a fire ==
Air consists of about 78 per cent nitrogen, 21 per cent oxygen and 1 per cent other gases, all by volume.<ref name="VR-4.2" /> The SFPE Handbook uses 20.9 per cent as the normal oxygen concentration at sea level.<ref name="P-107" /> Oxygen is one side of the fire triangle. When the oxygen level falls, a fire stops spreading and may eventually go out, depending on the exact concentration reached.<ref name="VR-4.2" />

The amount of oxygen a fire needs follows from [[stoichiometry]], the fixed ratio between fuel and oxygen in a complete reaction. ''Introduction to Fire Safety Engineering'' expresses this as a stoichiometric constant. About 1.25 kg of oxygen is needed per kilogram of cellulose fuel such as wood, and about 3.46 kg per kilogram of hydrocarbon fuel such as petrol or diesel.<ref name="VR-3.3">Van Rossum (2027), §3.3.</ref> With this constant, an engineer can estimate how much oxygen a fire consumes and when it may smother for lack of oxygen. Some zone models use the constant as the starting point of this calculation.<ref name="VR-3.3" />

The oxygen in a closed room runs out quickly. According to the SFPE Handbook, a typical domestic room with the doors and windows shut will not support the complete combustion of more than about 1 kg of fuel. After that, the oxygen concentration has fallen to about 10 per cent and the fire goes out or dies down.<ref name="P-155" /> In a small bedroom, the decomposition of about 0.5 kg of material was calculated to be enough to lower the oxygen concentration to 10 per cent.<ref name="P-136" /> In a full-scale test in a furnished lounge, the oxygen concentration started to fall after about 5 minutes and the fire went out by itself at around 9 minutes.<ref name="P-137">Purser (2002), p. 2-137.</ref>

[[File:fse-oxygen-depletion-v3.svg|thumb|upright=1.5|alt=Two room cross-sections: a closed room with a small dying fire and oxygen at 10 per cent; an open room with air flowing in low and smoke flowing out high.|In a closed room, burning about 1 kg of fuel lowers the oxygen to about 10 per cent and the fire dies down; with an open door, inflowing air sustains the fire. Based on Purser (2002), p. 2-155, and Van Rossum (2027), §4.8.]]

== Effect on the fire ==
In the growth phase, a fire in a room is usually small compared with the room, and enough oxygen is present. Such a fire is fuel-controlled: its development depends on the rate at which the fuel releases combustible gases.<ref name="VR-4.8">Van Rossum (2027), §4.8.</ref> When the fire is large and the openings are small, the supply of air becomes the limit and the fire becomes a [[ventilation-controlled fire]]. The heat release rate then depends on the available oxygen rather than on the fuel. Unburnt pyrolysis gases can then leave the fire and form a flammable mixture where they meet fresh air.<ref name="VR-4.8" />

A fully developed fire is usually ventilation-controlled, and part of its gases burn as flames outside the openings.<ref name="VR-4.8" /><ref name="VR-4.11">Van Rossum (2027), §4.11.</ref> The hot gases of a ventilation-controlled fire typically contain almost no oxygen.<ref name="NUREG-2-4">Iqbal and Salley (2004), p. 2-4.</ref> Measurements in flashover experiments, quoted in the technical guide of the Fire Dynamics Simulator, show that the oxygen concentration in the upper layer drops to zero once its temperature exceeds about 600 °C.<ref name="FDS-63">McGrattan et al. (2026), p. 63.</ref>

Oxygen depletion also changes what the fire produces. In closed-room fires, the combustion becomes inefficient once the oxygen concentration falls after a minute or so of burning, and the result is a dense smoke rich in carbon monoxide and other toxic products.<ref name="P-136" /> In early flaming fires, the ratio of carbon dioxide to carbon monoxide is high at first and falls to about 50 to 100 as the oxygen concentration drops towards 15 per cent.<ref name="P-135">Purser (2002), p. 2-135.</ref> In hot post-flashover fires above 800 °C with low oxygen, the pyrolysis products break down into small molecules with high concentrations of carbon monoxide and hydrogen cyanide.<ref name="P-123">Purser (2002), p. 2-123.</ref> For most hydrocarbons, the oxygen concentration varies with the equivalence ratio, the ratio of fuel to air relative to the stoichiometric ratio, in much the same way.<ref name="GL-79">Gottuk and Lattimer (2002), p. 2-79.</ref>

A flame that burns in air diluted with combustion products goes out before all the oxygen has been used. The classic example is a candle under an inverted jar.<ref name="FDS-62">McGrattan et al. (2026), p. 62.</ref> This is a form of [[flame extinction]]. Experiments by Morehart, Zukoski and Kubota found that flames went out at oxygen concentrations of 12.4 to 14.3 per cent. The lower value applied to a 50 cm pool burner and the higher value to a 9 cm burner.<ref name="B-184">Beyler (2002b), p. 2-184.</ref>

In diesel pool fire tests in a compartment, oxygen concentrations below 14 per cent could not be reached while the pool was burning. In water mist tests, the average oxygen concentration at extinction was 14.5 per cent for heptane spray fires and 13.5 per cent for pool fires.<ref name="B-184" /> These values hold for fairly calm conditions; at higher strain rates in the flow, the oxygen concentration at extinction rises.<ref name="B-184" />

Oxygen depletion does not always end the hazard. In a closed space, a fire can consume oxygen while flammable gases build up at a high temperature. If a door is then opened and fresh air flows in, the gases can ignite suddenly, which is called a [[backdraft]].<ref name="VR-4.9">Van Rossum (2027), §4.9.</ref> The Australian Fire Safety Verification Method data sheets note that a fire without an adequate air supply will put itself out. For design, however, they consider it generally conservative to assume that the air supply does not limit fire growth or the progress to flashover.<ref name="ABCB-B1-20">Australian Building Codes Board (2020a), Data Sheet B1, p. 20.</ref>

== Effects on people ==
The body can compensate for a moderate drop in the oxygen concentration of the inhaled air. When a person is exposed to low oxygen, the blood flow to the brain increases by reflex, and the blood releases its oxygen more efficiently.<ref name="P-106" /> In tests with monkeys, 15 per cent oxygen caused no harmful effects beyond a slight rise in heart rate, while 10 per cent caused a marked depression of brain function. In humans, too, there is little effect down to 15 per cent oxygen apart from a slightly reduced tolerance for exercise, but at about 10 per cent the effects suddenly become severe.<ref name="P-106" /> Much of the human data come from studies at high altitude, where the low air pressure has similar effects to a low oxygen concentration at sea level.<ref name="P-107" /> On this basis the SFPE Handbook describes four phases of hypoxia, each with an equivalent oxygen concentration at sea level:<ref name="P-106" />

{| class="wikitable"
! Phase !! Oxygen concentration (per cent) !! Main effects
|-
| Indifferent phase || 20.9 to 14.4 || minor effects on adjustment of the eyes to darkness; first effects on exercise tolerance towards 15 per cent
|-
| Compensated phase || 14.4 to 11.8 || slightly faster breathing and heart rate; some loss of performance in complex tasks, short-term memory and judgement
|-
| Manifest hypoxia || 11.8 to 9.6 || loss of critical judgement, dulled senses, poorer muscle control; behaviour may vary from indifference to euphoria
|-
| Critical hypoxia || 9.6 to 7.8 || rapid loss of judgement, then unconsciousness, followed by arrest of breathing and death
|}

The manifest phase is particularly dangerous in fires. The handbook calls the passage into the critical phase, at about 10 per cent oxygen, the catastrophe point.<ref name="P-106" /> Up to this point the compensating mechanisms hide most of the effect, so performance hardly declines. Beyond it, the condition of the victim deteriorates very quickly, usually to unconsciousness, and escape is no longer possible.<ref name="P-106" /> Loss of consciousness occurs when the partial pressure of oxygen in the venous blood of the brain falls below 20 mmHg.<ref name="P-106" />

[[File:fse-oxygen-depletion-v1.svg|thumb|upright=1.5|alt=Vertical oxygen scale from 21 to 7.8 per cent with four hypoxia phases and a band where flames go out between 12.4 and 14.3 per cent.|Oxygen concentration scale with the four phases of hypoxia in people and the range in which diffusion flames went out in experiments. Based on Purser (2002), p. 2-106, and Beyler (2002b), p. 2-184.]]

== Time to incapacitation ==
When a person suddenly enters air with less oxygen, it takes some time before the blood reaches equilibrium with the new air. During this time a kind of dose of hypoxia is taken up. Once equilibrium is reached, usually within a few minutes, the effect depends on the oxygen concentration and hardly changes with time.<ref name="P-88">Purser (2002), p. 2-88.</ref> The time to loss of consciousness depends on how far the oxygen concentration falls, on the activity of the person and on the volume of air breathed per minute.<ref name="P-107" />

From altitude data for people at rest, the SFPE Handbook derives an equation for the time to loss of consciousness in a fire atmosphere with low oxygen.<ref name="P-107" /> The time is an exponential function of the oxygen vitiation, which is the drop of the oxygen concentration below the normal 20.9 per cent. Each extra percentage point of vitiation shortens the time by a fixed factor:<ref name="P-107" />
<math display="block">t_\mathrm{IO} = \exp\left[8.13 - 0.54\left(20.9 - \%\mathrm{O_2}\right)\right]</math>

[[File:fse-oxygen-depletion-v2.svg|thumb|upright=1.5|alt=Curve of time to loss of consciousness against oxygen concentration, rising from under 3 minutes at 7.8 per cent to about 28 minutes at 12 per cent.|Time to loss of consciousness for a person at rest against the oxygen concentration, calculated with the SFPE Handbook equation; the solid part covers the range of the underlying data. Based on Purser (2002), p. 2-107.]]

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_\mathrm{IO}</math> || time to incapacitation (loss of consciousness) by low oxygen || min
|-
| <math>\%\mathrm{O_2}</math> || oxygen concentration in the inhaled air || per cent by volume
|-
| <math>20.9 - \%\mathrm{O_2}</math> || oxygen vitiation, the drop below normal air || percentage points
|}

The equation is based on the time of useful consciousness of resting people after a sudden drop in pressure, with data spanning sea-level equivalent oxygen concentrations of about 3.9 to 9.6 per cent.<ref name="P-107" /> Values calculated for higher oxygen concentrations lie outside the range of these data. The time also depends on the activity of the person, which raises the oxygen demand, and on the volume of air breathed per minute.<ref name="P-107" />

For a varying oxygen concentration, the handbook divides the exposure into periods of one minute and adds the fractions <math>1/t_\mathrm{IO}</math> of each minute. Loss of consciousness is predicted when the sum reaches 1.<ref name="P-107" /> In the handbook's example, a person breathes air with 10 per cent oxygen for 5 minutes, followed by 7.8 per cent for 1.5 minutes. At 10 per cent, <math>t_\mathrm{IO}</math> is exp(8.13 − 0.54 × 10.9), or about 9.43 minutes, so each minute adds 0.106. At 7.8 per cent, <math>t_\mathrm{IO}</math> is 2.87 minutes and each minute adds 0.348.<ref name="P-107" /> The sum is 0.106 × 5 + 0.348 × 1.5 = 1.05, so loss of consciousness is predicted at 6.5 minutes.<ref name="P-107" />

The equation also shows that oxygen depletion does not follow [[Haber's rule]], which assumes a constant product of concentration and time. At 17 percentage points of vitiation, the dose to incapacitation is about 5.6 per cent·min, but at 11.3 percentage points it is about 87 per cent·min.<ref name="P-107" /> A short exposure to severe hypoxia therefore incapacitates very quickly, while a long exposure to moderate hypoxia has little effect.<ref name="P-107" /> Applied to moderate values, the equation gives about 140 minutes at 15 per cent oxygen and about 28 minutes at 12 per cent (calculated with the handbook's equation).<ref name="P-107" />

== Use in tenability analysis ==
In an analysis of the time available for escape, low oxygen is one of several effects of smoke on people. The International Fire Engineering Guidelines (2005) note that life safety criteria often consider carbon monoxide, [[carbon dioxide]] and hydrogen cyanide, and also low oxygen.<ref name="IFEG-1.5-4">National Research Council of Canada et al. (2005), p. 1.5-4.</ref> In the incapacitation model of the SFPE Handbook, the fraction of an incapacitating dose of low oxygen is added to the fractions for carbon monoxide and hydrogen cyanide.<ref name="P-110" /> The fractions for these gases are first multiplied by a factor for the faster breathing caused by carbon dioxide. Incapacitation is predicted when the total reaches 1, and a total of 0.1 should allow nearly all exposed people, including sensitive groups, to escape safely.<ref name="P-110" />

The gases interact. Carbon monoxide and low oxygen both reduce the oxygen carried by the blood, so some addition of their effects is expected.<ref name="P-109">Purser (2002), p. 2-109.</ref> Carbon dioxide, by contrast, has been shown to increase the resistance to incapacitation by low oxygen. It makes people breathe faster, which increases the uptake of oxygen, and it helps the blood release oxygen to the tissues.<ref name="P-109" /> In most practical fires, carbon monoxide is the most important asphyxiant, while hydrogen cyanide and low oxygen add to its effect and may shorten the time to incapacitation in some situations.<ref name="P-110" />

Regulations take this into account in different ways. In New Zealand, Verification Method C/VM2 (second edition, 2025) requires the fractional effective dose for carbon monoxide to be calculated with ISO 13571 and to include the contributions of carbon monoxide, carbon dioxide and oxygen.<ref name="CVM2-17">Ministry of Business, Innovation and Employment (2025b), p. 17.</ref> The commentary on the first edition explains that other species were left out because the data for them were considered unreliable.<ref name="CVM2C-43">Ministry of Business, Innovation and Employment (2013), p. 43.</ref> ''Introduction to Fire Safety Engineering'' notes that people usually spend less than 30 to 60 seconds in smoke during escape, so the dose of toxic gases is often not decisive.<ref name="VR-7.7">Van Rossum (2027), §7.7.</ref>

== Lowering oxygen on purpose ==
Some extinguishing systems use oxygen depletion as their working principle. In the Fire Dynamics Tools report of the U.S. Nuclear Regulatory Commission (NUREG-1805), inert gas agents, such as nitrogen and mixtures containing argon, are described as acting mainly by depleting oxygen.<ref name="NUREG-B41">Iqbal and Salley (2004), p. B-41.</ref> According to the SFPE Handbook, an inert gas lowers the flame temperature by reducing the oxygen concentration and by raising the heat capacity of the atmosphere. Adding enough inert gas to bring the oxygen concentration below 12 per cent extinguishes flaming fires.<ref name="DN-174" />

For inert gases, the main health concern is the reduced oxygen concentration.<ref name="DN-182">DiNenno (2002), p. 4-182.</ref> The SFPE Handbook gives the exposure limits that applied at the time of writing. Up to 43 per cent agent, which leaves 12 per cent oxygen, exposure is limited to 5 minutes. Between 43 and 52 per cent agent, or between 12 and 10 per cent oxygen, the limit is 3 minutes, and above 52 per cent agent it is 30 seconds.<ref name="DN-184" /> Small amounts of carbon dioxide added to some inert gas blends appear to reduce the effects of hypoxia.<ref name="DN-184" />

Water mist can also deplete oxygen. When droplets turn to steam in a hot enclosure, the steam dilutes the oxygen, while the fire continues to consume it. If the combined effect brings the oxygen concentration below the limiting value, the fire goes out; for most hydrocarbon fuels this value is about 13 per cent.<ref name="MB-314">Mawhinney and Back (2002), p. 4-314.</ref> The oxygen available depends on the size of the fire, the volume of the compartment and its ventilation. Enclosure effects increase the benefit of oxygen depletion for a [[water mist system]], because the spray drives the hot, oxygen-poor gases of the upper layer down to the fire.<ref name="MB-314" />

Deliberate oxygen reduction can affect people outside the protected room. In 1992, at the Duane Arnold nuclear power plant in the United States, a test discharge of carbon dioxide into the cable spreading room leaked into the control room above it. Within a few minutes, oxygen levels of 17 per cent at chest height and 15 per cent at floor level were recorded. Both were below the plant's acceptance criterion of 19.5 per cent, and the operators put on breathing apparatus.<ref name="NUREG-B52">Iqbal and Salley (2004), p. B-52.</ref>

== Modelling oxygen depletion ==
Fire models handle oxygen depletion in different ways. ''Introduction to Fire Safety Engineering'' notes that most models deal poorly with a ventilation-controlled fire, so the user often has to specify what happens when oxygen runs short. The options are that all gases still burn in the fire room, that the surplus burns outside as external flames, or that combustion stops.<ref name="VR-8.4">Van Rossum (2027), §8.4.</ref> The [[zone model]] OZone, for example, offers a choice between ignoring the shortage, external flaming and an extended fire duration.<ref name="VR-9.3a">Van Rossum (2027), §9.3 (How a zone model works).</ref> Zone models and CFD models can report the oxygen consumption in the fire room as a result.<ref name="VR-9.3b">Van Rossum (2027), §9.3 (Results from zone models).</ref><ref name="VR-11.2">Van Rossum (2027), §11.2.</ref>

The zone model CFAST limits burning with a lower oxygen limit. By default, combustion stops when the oxygen mass fraction in the layer containing the fire falls to 0.15, a value that does not depend on temperature.<ref name="CFAST-13">Peacock et al. (2026), p. 13.</ref> The Fire Dynamics Simulator uses a limiting oxygen volume fraction of 0.135 at an ambient temperature of 20 °C, consistent with the measurements of Morehart and co-workers.<ref name="FDS-63" /> In coarse simulations, the model also lets the fire burn at any oxygen level once the gas temperature exceeds a default of 600 °C, in line with the experiments described above.<ref name="FDS-63" />

== Limits and common misconceptions ==
A common misconception is that a fire in a closed room is harmless because it will soon go out. Closed-room fires can in fact produce a rapidly lethal atmosphere, because the low oxygen concentration comes together with dense smoke rich in carbon monoxide.<ref name="P-136" /> For the people in the room, carbon monoxide usually matters more than the lack of oxygen itself.<ref name="P-110" />

A second misconception is that the oxygen concentration alone tells whether a flame can survive. The measured extinction limits range from about 12 to 15 per cent and depend on the size of the fire, the flow conditions and the gas that dilutes the air.<ref name="B-184" /> CFAST and the Fire Dynamics Simulator also express their limits differently, as a mass fraction and as a volume fraction.<ref name="CFAST-13" /><ref name="FDS-63" />

The equation for the time to incapacitation is based on healthy people at rest exposed to low air pressure at altitude, not on fire victims.<ref name="P-107" /> It does not include the effects of heat, irritant gases or carbon monoxide, which must be added separately.<ref name="P-110" /> The exposure limits for inert gases were set for extinguishing systems and cannot simply be transferred to an oxygen reduction system, for which the sources cited in this article give no data.<ref name="DN-184" />

== See also ==
* [[Gaseous extinguishing system]]
* [[Inerting]]
* [[Tenability criteria]]
* [[Carbon monoxide]]
* [[Hydrogen cyanide]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Beyler, C. L. (2002b). Flammability limits of premixed and diffusion flames. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-172–2-187). National Fire Protection Association; Society of Fire Protection Engineers.
* DiNenno, P. J. (2002). Halon replacement clean agent total flooding systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-173–4-200). National Fire Protection Association; Society of Fire Protection Engineers.
* Gottuk, D. T., & Lattimer, B. Y. (2002). Effect of combustion conditions on species production. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-54–2-82). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Mawhinney, J. R., & Back, G. G., III. (2002). Water mist fire suppression systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-311–4-337). National Fire Protection Association; Society of Fire Protection Engineers.
* McGrattan, K., Hostikka, S., Floyd, J., McDermott, R., Vanella, M., Mueller, E., & Paul, C. (2026). ''Fire Dynamics Simulator technical reference guide: Vol. 1. Mathematical model'' (6th ed., NIST Special Publication 1018-1). National Institute of Standards and Technology. https://doi.org/10.6028/NIST.SP.1018
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Peacock, R. D., McGrattan, K. B., Forney, G. P., & Reneke, P. A. (2026). ''CFAST – Consolidated Fire and Smoke Transport: Vol. 1. Technical reference guide'' (Version 7, NIST Technical Note 1889v1). National Institute of Standards and Technology. https://doi.org/10.6028/NIST.TN.1889v1
* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-83–2-171). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

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Lithium-ion battery fire

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A '''lithium-ion battery fire''' is a fire in a lithium-ion battery or battery pack that is driven by [[thermal runaway]]. Thermal runaway is a failure mechanism in which a battery cell heats itself up, and it can result in fire.<ref name="NIPV-22">Van der Graaf et al. (2021/2023), p. 22.</ref> Many electric cars store their energy in lithium-ion packs, which can hold 100 kWh or more.<ref name="NIPV-21">Van der Graaf et al. (2021/2023), p. 21.</ref> Once thermal runaway has started, heat can pass from cell to cell, flammable gases may be released and the fire keeps re-igniting until the energy in the pack is used up. The pack is sealed against moisture and dirt, so water cannot reach the cells directly and cooling needs a lot of water for a long time.<ref name="NIPV-22" />

In tests, burning electric cars reached temperatures and peak heat release rates similar to those of petrol and diesel cars.<ref name="NIPV-23">Van der Graaf et al. (2021/2023), p. 23.</ref><ref name="NIPV-25">Van der Graaf et al. (2021/2023), pp. 24–25.</ref> Their fires nevertheless develop more slowly, last longer, can involve repeated small explosions and flash fires, and release more hydrogen fluoride, a toxic and corrosive gas.<ref name="NIPV-29">Van der Graaf et al. (2021/2023), p. 29.</ref><ref name="NIPV-30">Van der Graaf et al. (2021/2023), p. 30.</ref> Together with high voltages, these risks are one reason why firefighting in indoor car parks may be limited or impossible.<ref name="NIPV-11">Van der Graaf et al. (2021/2023), p. 11.</ref> A 2021 study by the Netherlands Institute for Public Safety (NIPV) on indoor car parks with electric vehicles found that the probability of such fires could hardly be determined from empirical data.<ref name="NIPV-20">Van der Graaf et al. (2021/2023), p. 20.</ref>

== How thermal runaway starts ==

A battery pack in an electric car consists of cells of about 4 V, joined into modules of up to 60 V that together form a pack of 300 to 1,000 V.<ref name="NIPV-21" /> The SFPE Handbook explains the general principle of self-heating: heat produced by a chemical reaction competes with heat lost to the surroundings. Most reaction rates rise almost exponentially with temperature, but heat losses by conduction rise only linearly. Ignition, or thermal runaway, therefore begins where the temperature is highest, if it occurs at all.<ref name="Gray">Gray (2002), pp. 2-211–2-212.</ref>

In a battery, each pack has its own safety window, and beyond it the pack can heat up further and go into thermal runaway.<ref name="NIPV-22" /> The temperature at which this can start depends on the type of battery: the NIPV report gives 70 to 250 °C in one place and 50 to 270 °C in another.<ref name="NIPV-22" /><ref name="NIPV-18">Van der Graaf et al. (2021/2023), p. 18.</ref> Every electric car has a battery management system that monitors the individual cells.<ref name="NIPV-22" /> When limits are exceeded, it can switch on active cooling during charging, stop charging or disconnect the pack. The system is designed to be fail-safe, so a fault in the system itself also switches the pack off.<ref name="NIPV-23" />

A battery can fail because of a design or manufacturing error in the electrode, separator or electrolyte. This can lead to failures in the battery management system and to overcharging, but such errors are rare and, once detected, generally lead to a recall.<ref name="NIPV-23" /> Outside causes include external heat, misuse and damage in a collision.<ref name="NIPV-23" /> Parking and charging electric cars in car parks add causes that do not exist with petrol and diesel cars. Examples are a damaged cable or charging station, a fault in the battery management system, a collision with a charging station and a defective pack that has gone unnoticed.<ref name="NIPV-29" /> Radiant heat from a neighbouring burning car may also cause thermal runaway in an electric car parked next to it.<ref name="NIPV-32">Van der Graaf et al. (2021/2023), pp. 32–33.</ref>

How often batteries fail is uncertain. Estimates quoted in the NIPV report range from one failure in a million or fewer to about one in 100 million. The report concludes that the probability of battery failure seems relatively low. Still, no lithium-ion battery is intrinsically safe: no pack design can completely prevent the release of enough energy for thermal runaway.<ref name="NIPV-23" />

== Gases, chain reactions and explosions ==

A heating cell can release flammable gases. These may ignite if there is enough oxygen and the ignition temperature is reached, and the casing of the cell may be hot enough for this. The heat of one cell can also push the cells next to it into thermal runaway, so that the failure spreads through the pack as a chain reaction.<ref name="NIPV-22" /> Gases held in a pouch or cartridge can escape if the pack or its pressure valve fails under high pressure. If the pack is mechanically damaged, the pressure wave can throw out parts and fragments, which may be burning.<ref name="NIPV-22" />

Gas that does not ignite at once can build up into an explosive mixture in a confined or poorly ventilated space.<ref name="NIPV-27">Van der Graaf et al. (2021/2023), p. 27.</ref> If the mixture reaches its lower explosion limit, the lowest concentration at which a flame can spread through it, and is then ignited, a gas explosion can occur.<ref name="NIPV-27" /><ref name="NUREG-16">Iqbal and Salley (2004), p. 16-2.</ref> Among the gases that burning packs give off are hydrogen, methane and carbon monoxide.<ref name="NIPV-26">Van der Graaf et al. (2021/2023), p. 26.</ref> Hydrogen alone has a lower flammability limit in air of 4.1 per cent by volume, and its flame is often invisible in daylight.<ref name="NUREG-16" /> The NIPV report counts repeated small explosions, flying parts and flash fires among the ways in which fires in electric cars differ from other car fires.<ref name="NIPV-29" />
[[File:fse-lithium-ion-battery-fire-v1.svg|thumb|upright=1.5|alt=One hot cell heats neighbours, releasing gases that accumulate and can ignite or explode.|Thermal runaway can propagate and produce flammable gases. Based on Van der Graaf et al. (2021/2023), p. 22 and p. 27.]]

== Heat release and fire development ==

In terms of temperature, fires in electric cars do not differ significantly from those in conventional cars. Battery tests reviewed in the NIPV report measured maximum flame temperatures of 798 to 863 °C, rising with how fully the batteries were charged. Full-scale tests on both types of car measured 800 ± 100 °C.<ref name="NIPV-23" /> The heat radiation from an electric car with a fully charged pack was also similar to that from a conventional car.<ref name="NIPV-25" />

The heat release rate, the amount of heat a fire releases per second, largely determines how intense a fire is.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref> A review of published tests found similar peaks of about 6 MW for electric and fossil-fuelled cars. The total heat released was 4.7 to 8.5 GJ for electric cars and 3.3 to 10 GJ for the others.<ref name="NIPV-25" /> Larger batteries raise the peak: packs of about 15 to 25 kWh gave about 4 to 6 MW, while packs of more than 100 kWh give about 8 MW. That is significantly higher than the approximately 6.8 MW of an average mid-range conventional car.<ref name="NIPV-25" /> ''Introduction to Fire Safety Engineering'' gives a peak of 8.5 MW for a car and 2.5 MW for an average sofa.<ref name="VR-4.5" />

The course of the fire over time differs more. In a petrol or diesel car, the plastic tank can fail and suddenly release fuel that catches fire, so the temperature rises very rapidly in the first minutes. Battery cells first need time to warm up and give off gas. The temperature therefore rises evenly, at about 0.2 °C per minute, until thermal runaway makes it climb by more than 10 °C per minute.<ref name="NIPV-26" /> A normal passenger car fire generally burns for just over half an hour and peaks at about 5 MW after 10 to 15 minutes. An electric car left to burn without intervention burns out in about 90 minutes, and an extinguished one can keep re-igniting for several hours.<ref name="NIPV-26" />

An [[electric vehicle fire]] in a car park can spread from car to car as a travelling car fire. The NIPV report expects electric cars to make such fires more likely, because a long-burning pack radiates heat to its neighbours for longer.<ref name="NIPV-29" /> In 2021, Dutch building regulations, standards and guidelines were still based on fires in conventionally fuelled cars, and modern cars contain more plastic than older steel models.<ref name="NIPV-11" /> The car-fire curve in the Dutch standard NEN 6098 rests on a design fire set by TNO in 1999. In the TNO tests, fire could spread to the adjacent cars 10 to 15 minutes after the first one. With more plastics in modern cars, such curves may be less conservative in some situations.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref>

== Toxic and corrosive products ==

The toxic hazard of a fire, the subject of [[fire toxicity]], depends on how quickly and how much toxic products are produced, and on how potent they are.<ref name="Purser">Purser (2002), p. 2-91.</ref> Burning battery packs release corrosive substances from the electrolyte and combustion products from the plastics and packaging. Besides methane, carbon monoxide, carbon dioxide and hydrogen, they release the toxic gases hydrogen fluoride and hydrogen chloride.<ref name="NIPV-26" /> The SFPE Handbook counts these acid gases among the most important irritants in fire smoke. Irritants can impair escape or incapacitate people through pain and breathing difficulty.<ref name="Purser" />

A study cited in the NIPV report found about 20 to 200 mg of hydrogen fluoride per watt-hour of battery capacity. A 100 kWh pack can thus emit 2 to 20 kg, depending on its charge. Comparable tests on electric and conventional cars found hardly any difference in other toxic gases, but the electric cars appeared to produce about 1.8 times more hydrogen fluoride.<ref name="NIPV-26" /> Hydrogen fluoride binds to other substances and smoke particles and settles on floors, walls and ceilings. In one study this more than halved its concentration in the smoke within 10 to 20 minutes, but made firefighting clothing more contaminated.<ref name="NIPV-26" /> According to the report, a fire attack requires the clothing to be decontaminated because of the toxic and corrosive gases, unlike an attack on a conventional car fire.<ref name="NIPV-30" />
[[File:fse-lithium-ion-battery-fire-v2.svg|thumb|upright=1.5|alt=Battery smoke travels through air and deposits on clothing, walls, floors and residue.|Battery-fire contamination includes airborne and deposited hazards. Based on Van der Graaf et al. (2021/2023), pp. 26, 29–30, 39 and 47.]]

For people escaping, the extra hydrogen fluoride changes little. The plastic parts of any burning car already create severely toxic smoke, and the report puts the effect of the extra hydrogen fluoride on escape safety at zero. Systemic health effects seem unlikely, although slight exposure may irritate the skin and severe exposure may cause chemical burns.<ref name="NIPV-30" /> Research cited in the report found that firefighters in protective equipment can carry out a "safe" attack with proper hygiene if their exposure to the smoke lasts no more than 20 to 30 minutes.<ref name="NIPV-26" /> The report sees no reason to assume that they need more protective equipment than at a fire in a conventional car.<ref name="NIPV-47">Van der Graaf et al. (2021/2023), p. 47.</ref>

Smoke with extra hydrogen fluoride can spread from a car park through open doors into the escape routes and stairwells of buildings above.<ref name="NIPV-30" /> People who leave at once are exposed only briefly, but those who cannot escape or take longer are exposed for longer. For this reason the report advises against placing charging stations near pedestrian escape routes.<ref name="NIPV-39">Van der Graaf et al. (2021/2023), p. 39.</ref>

== Extinguishing and cooling ==

Fighting a battery fire involves two tasks: putting out the flames, and cooling the pack for a long time so that thermal runaway does not set it alight again. Putting out the flames needs no more capacity than for a conventional car.<ref name="NIPV-46">Van der Graaf et al. (2021/2023), p. 46.</ref> Stopping thermal runaway is much harder, because the closed construction of the pack keeps water away from the cells.<ref name="NIPV-22" /> According to the NIPV report, a burning pack can only be controlled by prolonged cooling with a lot of water, and extinguishing it requires water inside the pack.<ref name="NIPV-30" />

After the flames are out, the pack catches fire again within a short time. It therefore needs continuous cooling, and its temperature has to be monitored for a long time.<ref name="NIPV-46" /> Firefighters can extinguish continuously or each time the fire re-ignites, and the amount of water needed depends on the pack and how fully it is charged.<ref name="NIPV-46" /> For packs without special facilities, the most successful way to get water inside is to immerse the pack in water.<ref name="NIPV-30" /> An immersion container is currently the best method available for long-term cooling, but its effect depends on how far the water can reach the cells.<ref name="NIPV-46" />
[[File:fse-lithium-ion-battery-fire-v3.svg|thumb|upright=1.5|alt=Flames are knocked down before prolonged cooling, temperature monitoring and salvage.|Battery-fire response continues after visible flames disappear. Based on Van der Graaf et al. (2021/2023), pp. 45–47.]]

Fixed sprinkler or water mist systems cannot extinguish a fire in an electric car, because the water droplets cannot enter the pack. They can, however, reduce the probability that the fire grows and spreads to nearby structures and vehicles.<ref name="NIPV-37">Van der Graaf et al. (2021/2023), p. 37.</ref> Covering the car in foam is not a useful method for the time being. The fire can re-ignite under the foam, because packs in thermal runaway can re-ignite even when little oxygen is available.<ref name="NIPV-47" />

[[Fire classes]] sort fires by the type of fuel. In the US scheme of NFPA 10 (2002 edition), summarised in NUREG-1805, fires in energised electrical equipment form Class C, for which the agent must not conduct electricity.<ref name="NUREG-B">Iqbal and Salley (2004), p. B-13.</ref> The NIPV report, which deals with lithium-ion packs in cars, relies on water for cooling and extinguishing them.<ref name="NIPV-30" /> Although electric cars carry up to about 400 V, with peaks of up to 800 V, the probability of electrocution is negligible when the fire is fought from a distance.<ref name="NIPV-11" /><ref name="NIPV-43">Van der Graaf et al. (2021/2023), p. 43.</ref>

== Firefighting and salvage in car parks ==

In an indoor car park, a fire in an electric car adds several problems for the fire service. It is uncertain how the fire will develop and spread, and the pack can re-ignite and burn for longer. Explosions, flare fires and specific toxic gases can occur, and the deployment may be long and need a lot of water.<ref name="NIPV-43" /> The stability of the structure is uncertain, and a burning electric car may even start to move.<ref name="NIPV-30" /> The report concludes that the risks and uncertainties of an attack have increased compared with car parks without electric cars.<ref name="NIPV-43" />

Dutch fire services prefer to fight a fire from the outside. Before choosing an attack, they establish whether the location of the fire is known, whether it can be reached from outside and whether enough cooling capacity is available. Only if all three conditions are met can the fire be put out from the outside. Otherwise the attack becomes defensive, and a large structure such as a car park is in principle considered beyond saving.<ref name="NIPV-44">Van der Graaf et al. (2021/2023), p. 44.</ref> For car parks, the report concludes that an attack from inside is generally not safely possible, although the commanding officer may still decide on one.<ref name="NIPV-45">Van der Graaf et al. (2021/2023), p. 45.</ref> The fire service will not automatically enter, so a car park may burn out.<ref name="NIPV-47" />

Cooling capacity is estimated with rules of thumb. A high-pressure jet of 125 litres per minute is generally sufficient for a heat release rate of up to 2.5 MW. A low-pressure jet of 450 litres per minute generally suffices for up to 10 MW.<ref name="NIPV-45" /> Fires in electric cars call for low-pressure jets, and several burning cars will probably need several jets.<ref name="NIPV-44" /> ''Introduction to Fire Safety Engineering'' explains the idea behind such rules: the expected heat release rate of a fire indicates the cooling capacity needed to fight it.<ref name="VR-8.6" />

Because a pack can re-ignite after the fire is out, the report advises planning how an electric car can be removed from the car park. Together with a properly equipped salvage company, the fire service removes the car, which can then be left to react in a water tank until thermal runaway has stopped.<ref name="NIPV-42">Van der Graaf et al. (2021/2023), p. 42.</ref> Not every salvage company has the right equipment, and smoke or poor access can delay removal from an underground car park.<ref name="NIPV-46" /> In a fire in the Singelgarage car park in Alkmaar in 2020, the pack of one electric car kept re-igniting. A police robot towed the car out, and it was then cooled for a long time in an immersion container.<ref name="NIPV-12">Van der Graaf et al. (2021/2023), p. 12.</ref>

Ordinary extinguishing water from electric car fires harms the environment hardly more than that from other car fires and can go into the sewer.<ref name="NIPV-46" /> Cooling water in an immersion tank is different. Burnt packs contain lithium oxide, which reacts with water to form lithium hydroxide, so the pH of the water can keep rising.<ref name="NIPV-29" /> Such cooling water may not be discharged directly into the sewer, and a residue with a neutral pH on the outside may still contain heavy metals.<ref name="NIPV-47" />

== Prevention in car parks ==

In the Netherlands, the 2021 NIPV report discusses prevention against the Building Decree 2012, whose fire safety rules did not specifically address parking and charging electric cars.<ref name="NIPV-17">Van der Graaf et al. (2021/2023), p. 17.</ref> Under that decree, enclosed indoor car parks of more than 1,000 m² needed an automatic fire alarm system with full detection, and new indoor car parks had to have charging facilities.<ref name="NIPV-37" /><ref name="NIPV-10">Van der Graaf et al. (2021/2023), p. 10.</ref> Amendments proposed in 2021 for its successor, the Building Works and Living Environment Decree, would make sprinklers mandatory in certain car parks. They would also require a facility to switch off all charging points at once.<ref name="NIPV-18" />

The report offers its measures as a range from which to build a tailor-made set, not as a detailed standard.<ref name="NIPV-34">Van der Graaf et al. (2021/2023), p. 34.</ref> It sees a sprinkler or water mist system as the most obvious way to hold a fire to a few cars and so prevent a travelling fire.<ref name="NIPV-36">Van der Graaf et al. (2021/2023), p. 36.</ref><ref name="NIPV-49">Van der Graaf et al. (2021/2023), pp. 49–50.</ref> Fast detection helps, but its effect depends on prompt follow-up of the alarm.<ref name="NIPV-37" /><ref name="NIPV-40">Van der Graaf et al. (2021/2023), p. 40.</ref> Carbon monoxide detectors gave the fastest alert in one study, but in the Netherlands they are not used as fire detection.<ref name="NIPV-37" /> Collision protection for charging stations is a further measure.<ref name="NIPV-36" />

The report prefers parking spaces for electric cars near the vehicle entrances and at street level, so that a fire can be fought from outside and a car removed quickly.<ref name="NIPV-41">Van der Graaf et al. (2021/2023), pp. 41–42.</ref> It advises against places where ventilation air is supplied.<ref name="NIPV-39" /> Grouping charging points in one marked area helps the fire service find electric cars, but such clustering can also lead to a travelling car fire.<ref name="NIPV-42" /> Users can be told not to park a car whose battery management system reports a fault and to keep their distance if gases are released.<ref name="NIPV-40" />

== Uncertainties and limits ==

How often electric cars catch fire is largely unknown, because there are no reliable datasets.<ref name="NIPV-54">Van der Graaf et al. (2021/2023), p. 54.</ref> The report judges that a parked electric car is unlikely to catch fire more often than a fossil-fuelled car. Charging, however, is expected to raise the probability, because it adds an activity, the technology is still in its teething phase and existing electrical installations may not be safe enough.<ref name="NIPV-28">Van der Graaf et al. (2021/2023), p. 28.</ref> Ageing probably raises the internal resistance of the cells, which increases the heat they produce. An older battery also holds a lower maximum charge, however, so its thermal runaway is less intense and releases fewer flammable gases.<ref name="NIPV-28" />

The NIPV report covers only lithium-ion passenger cars in Dutch indoor car parks, and "lithium-ion" itself covers many kinds of lithium batteries that respond differently to fire.<ref name="NIPV-18" /> It warns that test results vary greatly with the amount of fuel, the battery capacity and the plastics in the car, so single studies cannot simply be generalised.<ref name="NIPV-20" /> Battery packs can also be combined into systems of 10 to 400 kWh, for example in trucks and electric ships. Stationary installations such as a battery energy storage system lie outside the report's scope.<ref name="NIPV-21" /><ref name="NIPV-18" /> Open questions include the exact process of thermal runaway, the conditions under which packs re-ignite and the best detection and suppression systems.<ref name="NIPV-55">Van der Graaf et al. (2021/2023), p. 55.</ref>

== See also ==

* [[Car park fire]]
* [[Tunnel fire]]
* [[Warehouse fire]]

== Notes ==

<references />

== References ==

* Gray, B. (2002). Spontaneous combustion and self-heating. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-211–2-228). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-83–2-171). National Fire Protection Association; Society of Fire Protection Engineers.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Special Hazards & Building Types]]

Ignition source

2026-11-02T21:33:59Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

An '''ignition source''' supplies energy capable of initiating combustion when it reaches a suitable fuel-oxidiser system. Flames, sparks, heated wires, incandescent particles and hot surfaces can act as sources. Chemical self-heating can also create an initiating condition inside a material. Effectiveness depends on the fuel, mixing, exposure and heat losses at the point of interaction.<ref name="Kanury-2-230">Kanury (2002), p. 2-230.</ref><ref name="Gray-2-211">Gray (2002), p. 2-211.</ref>

The source is only one part of [[Ignition]]. A flammable mixture and suitable thermal conditions must also be present. A source that is too small or loses energy too quickly can fail, while a modest flame or spark can initiate a much larger fire when the surrounding mixture is favourable.<ref name="Kanury-2-232">Kanury (2002), p. 2-232.</ref><ref name="IFEG-2.4-4">Australian Building Codes Board et al. (2005), p. 2.4-4.</ref>

Ignition sources can also occur in sequence. NUREG-1805 describes a burning wastebasket becoming a source for a chair, after which the chair can ignite other fuel. The initial device and subsequent burning objects therefore play different roles in the developing fire. Every later burning object must be assessed both as a target and as a potential new source.<ref name="NUREG-1805-F37">Iqbal and Salley (2004), p. F-37.</ref>
[[File:fse-ignition-source-v2.svg|thumb|upright=1.5|alt=Wastebasket ignites a chair and the chair becomes a source for another object.|Burning objects can become later ignition sources. Based on Iqbal and Salley (2004), p. F-37.]]

== Flames, sparks and hot surfaces ==

A small pilot flame initiates a reaction in an already suitable fuel-air mixture. Its role is not necessarily to heat the whole fuel body or generate all the pyrolysis gases. Once the reaction begins, it can propagate away from the pilot through the connected mixture.<ref name="Kanury-2-230" />

Sparks and heated filaments can perform a similar pilot function. Their effect depends on energy, size, exposure time and the thermal and chemical properties of the mixture. Heat loss to surrounding gas and surfaces can quench the initial reaction before propagation develops.<ref name="Kanury-2-232" />

Hot surfaces create a different exposure because they can heat a fuel continuously. Surface temperature alone does not determine ignition: contact area, airflow, fuel thickness and exposure duration affect the energy balance. A small hot object can therefore produce a different outcome from a large surface at the same nominal temperature.<ref name="Kanury-2-231">Kanury (2002), pp. 2-231–2-232.</ref>

Open flames introduce both a pilot and a heat source for further fuel production. They can ignite a gas mixture rapidly or heat liquids and solids until vapour and pyrolysis products become involved. These distinct roles should be identified when reconstructing a fire scenario.<ref name="Kanury-2-230" /><ref name="VR-4.1">Van Rossum (2027), §4.1.</ref>

Electrical faults can produce local overheating or arcing. In one NUREG-1805 case, improperly grounded equipment caused fault current to overheat conductors and ignite material in two locations. This nuclear-plant incident illustrates a specific electrical sequence, not a universal frequency for cable ignition.<ref name="NUREG-1805-H24">Iqbal and Salley (2004), pp. H-24–H-25.</ref>

[[Hot work]] includes activities using heat, sparks or open flame, such as cutting, welding and grinding. These activities can introduce an ignition source into areas where it is not normally present. Fuel arrangement and work procedures therefore form part of the source assessment.<ref name="NUREG-1805-F37" /><ref name="NUREG-6850-6-21">EPRI and NRC (2005), p. 6-21.</ref>

Oxygen-acetylene torches provide a particularly intense source. NUREG-1805 gives a hottest-flame value of approximately 3,500 °C for the torch conditions described. That value concerns the flame itself and does not equal the temperature reached by every target or the energy required for ignition.<ref name="NUREG-1805-3-9">Iqbal and Salley (2004), p. 3-9.</ref>

The Electric Power Research Institute (EPRI) and U.S. Nuclear Regulatory Commission (NRC) address welding and cutting in their 2005 nuclear fire-analysis methodology. They link frequency with maintenance activity, hot-work procedures and housekeeping. It treats these as plant-specific influences rather than fixed properties of a compartment. Similar reasoning applies to temporary work in other settings, although the numerical bins are specific to the nuclear method.<ref name="NUREG-6850-6-21" />

A continuous fire watch can shorten detection time when hot work ignites fuel. The same guidance states that such fires are likely to be detected quickly when a watch has been posted. This is a response measure, not proof that ignition has been prevented.<ref name="NUREG-6850-11-28">EPRI and NRC (2005), p. 11-28.</ref>

== Ignition energy and flammable atmospheres ==

[[Minimum ignition energy]] is the lowest energy associated with ignition of a specified fuel-oxidiser mixture under stated conditions. It is relevant when a spark or other short-duration source contacts a flammable atmosphere. Mixture composition, temperature and the nature of the discharge affect the requirement.<ref name="Kanury-2-232" /><ref name="Zalosh-3-405">Zalosh (2002), p. 3-405.</ref>

The 2005 International Fire Engineering Guidelines note that fuel-air mixtures within the flammable region can often be ignited by sources of only millijoules. The actual value depends on the mixture and test method. A small electrical or static source can therefore be significant even without a large hot surface.<ref name="IFEG-3.3-2">Australian Building Codes Board et al. (2005), p. 3.3-2.</ref>

Flammability limits remain essential when interpreting this energy. Outside the propagating range, a source can create local combustion without a flame travelling through the wider mixture. Beyler distinguishes this local effect from sustained flame propagation within the limits.<ref name="Beyler-2-172">Beyler (2002), pp. 2-172–2-173.</ref>

Prevention commonly keeps gas or vapour concentrations well below the lower flammable limit. The guidelines caution against relying on a mixture above the upper limit because subsequent dilution can return it to the flammable region. Ignition-source control works together with concentration control rather than replacing it.<ref name="IFEG-3.3-2" />

== Self-heating as an internal source ==

[[Self-heating]] occurs when chemical reactions inside a material generate energy faster than it can be lost. The material then supplies part of the initiating heat itself. Poor thermal conductivity and insulating containers can help retain this energy.<ref name="Gray-2-211" />

The critical condition depends on material chemistry, ambient temperature, size and shape. Larger bodies can favour runaway because heat is retained more effectively, while higher ambient temperature reduces the relative thermal driving force for cooling. No single external ignition device is required in these cases.<ref name="Gray-2-211" /><ref name="Gray-2-212">Gray (2002), p. 2-212.</ref>
[[File:fse-ignition-source-v3.svg|thumb|upright=1.5|alt=Heat generated inside a body exceeds losses and produces internal runaway.|Self-heating can create an internal ignition source. Based on Gray (2002), pp. 2-211–2-212.]]

Preheated products add another variable. Hot laundry, recently manufactured chipboard and hot porous food products require attention to the material's own stacking temperature as well as ambient conditions. Gray explains that time to ignition can be much shorter for preheated bodies than for material stacked at ambient temperature.<ref name="Gray-2-211" /><ref name="Gray-2-213">Gray (2002), p. 2-213.</ref>

Spontaneous runaway often begins at the centre of a low-conductivity body. Charring or ash can therefore be found inside while the exterior appears less affected. This evidence can inform investigation, but it must be assessed alongside other possible ignition sources and preheating.<ref name="Gray-2-212" />

== Source and target interaction ==

The target is the fuel exposed to the source. Its physical and chemical properties determine how it responds, including conductivity, heat capacity, decomposition behaviour and geometry. A source-target description should retain these properties rather than treating ignition as a property of the source alone.<ref name="Kanury-2-229">Kanury (2002), p. 2-229.</ref>
[[File:fse-ignition-source-v1.svg|thumb|upright=1.5|alt=Source heating a target while vapour, oxygen and heat losses shape ignition.|Ignition depends on source-target interaction and heat loss. Based on Kanury (2002), pp. 2-230–2-232.]]

For a solid, incoming energy is partitioned into internal conduction, reradiation and convection to adjacent gas. Moisture evaporation and pyrolysis then modify the response. The source can be steady in the model while the net heating of the target changes substantially over time.<ref name="Kanury-2-232" />

Mixing has a dual effect. It is necessary to bring fuel vapour and oxygen together, but it can also cool and dilute the mixture. Spontaneous ignition needs both suitable composition and sufficient thermal condition at the same location. More airflow is therefore not always more favourable.<ref name="Kanury-2-232" />

For piloted ignition, the pilot can be small relative to the target because it only initiates the reaction. It still cannot be infinitely small: reaction can be quenched if the source region does not exceed the mixture's critical dimensions and energy requirements. The relevant threshold belongs to the whole mixture-source arrangement.<ref name="Kanury-2-232" />

Source position can also change the fire that follows ignition. NUREG-1805 contrasts a pilot at the bottom of a curtain with the same pilot at the top. The first arrangement favours rapid upward flame spread, while the second produces slower downward spread. Source identification therefore includes its location relative to the fuel, as well as the device or energy type.<ref name="NUREG-1805-6-3">Iqbal and Salley (2004), p. 6-3.</ref>

== Fire statistics and frequency analysis ==

[[Fire statistics]] can show which sources and first-ignited materials occur in reported incidents. Such evidence helps prioritise prevention and estimate ignition frequencies. It does not by itself establish the cause of an individual fire or the probability of ignition during one particular exposure.<ref name="IFEG-2.4-4" /><ref name="NUREG-6850-6-21" />

Nuclear fire probabilistic risk analysis uses detailed ignition-source counts and weighting factors. The method considers equipment, maintenance, occupancy and storage when assigning compartment-specific influences. These categories belong to US nuclear power plant analysis and should not be presented as universal building values.<ref name="NUREG-6850-6-21" />

The 2005 guidance recommends work-order counts and staff information to assess maintenance-related transient fires. It separately addresses welding and cutting, including procedures that prohibit these activities during power operation. This demonstrates how administrative controls can alter the frequency assigned to a source scenario.<ref name="NUREG-6850-6-22">EPRI and NRC (2005), p. 6-22.</ref>

Data quality remains important. The 2005 guidelines note that ignition statistics can support quantitative frequency studies and qualitative comparisons, but general prediction of ignition potential remained uncertain. Source identification and statistical frequency answer different questions.<ref name="IFEG-2.4-4" />

== Hazardous areas and prevention ==

For Hazardous area classification, the source inventory has to be related to the potential presence of a flammable atmosphere. The IFEG gas and vapour discussion identifies mixture concentration as a separate part of ignition prevention. Removing one possible source does not establish that the atmosphere is outside its flammable range.<ref name="IFEG-3.3-2" />

Prevention can address an activity, the flammable atmosphere or the separation of fuel from energy. Detection and response act on a fire after ignition. The suitable combination depends on whether the source is permanent equipment, a temporary task or an internal reaction. One generic prohibition cannot cover all these mechanisms.<ref name="IFEG-2.4-4" /><ref name="NUREG-6850-6-21" />

Hot-work procedures provide a temporary-source example. Housekeeping addresses available fuel, work controls address source generation and a posted fire watch can shorten detection time. Evaluating only the torch or spark would miss the wider scenario that determines whether a small ignition becomes a damaging fire.<ref name="NUREG-6850-6-21" /><ref name="NUREG-6850-11-28" />

For self-heating storage, source prevention can involve size, stacking temperature and heat dissipation rather than electrical exclusion. The source is distributed within the fuel body, so separating it from the fuel is not a meaningful description. Geometry and storage conditions become the principal controls.<ref name="Gray-2-211" />

== Fire investigation ==

[[Fire investigation]] seeks to establish the sequence and conditions of ignition from evidence. Potential sources are evaluated together with target materials, heat transfer and subsequent fire development. Finding a device capable of ignition is not alone proof that it initiated the event.<ref name="Kanury-2-229" /><ref name="Gray-2-212" />

Electrical evidence can include fault paths and conductor damage. The Palo Verde incident in NUREG-1805 linked simultaneous fires to a common overheated conductor caused by grounding faults. The value of that example lies in tracing the complete sequence rather than assigning every cable fire to an electrical fault without evidence.<ref name="NUREG-1805-H24" />

Self-heating evidence can include deep central charring and a comparatively intact exterior. Gray nevertheless stresses the need to consider solar exposure, recent processing and other preheating. Unknown cause can also be more common in large destructive fires because evidence is lost.<ref name="Gray-2-211" /><ref name="Gray-2-212" />

A reliable investigation distinguishes initial ignition from later sources. A burning object found at one location may have started the fire there or may itself have been ignited by an earlier object. Reconstructing this order prevents the first discovered burning item from being misidentified as the original igniter.<ref name="NUREG-1805-F37" />

== Calculating electrical source energy ==

A theoretical energy calculation is useful when the source is a simple electrical discharge. It describes the energy associated with the circuit, which can be compared with ignition-test evidence for a specified mixture. The discharge type must match the test. Zalosh distinguishes capacitive electrostatic discharges from inductive sparks because their duration and ignition effectiveness differ.<ref name="Zalosh-3-405" />

For a purely capacitive discharge, energy depends on capacitance and the square of the voltage before discharge. Capacitance describes how much electrical charge a body stores for a given voltage. The equation is an idealised electrical relation, rather than a complete calculation of heat deposited in a particular fuel mixture.<ref name="Zalosh-3-405" />

<math display="block">E=\frac{1}{2}CV^2</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>E</math> || Theoretical energy of the capacitive discharge || J
|-
| <math>C</math> || Electrical capacitance || F
|-
| <math>V</math> || Voltage before discharge || V
|}

Zalosh's worked example considers an elevated powder silo with a capacitance of 500 pF. The example powder has an ignition energy of 10 mJ for inductive sparks and 50 mJ for capacitive sparks. The capacitive comparison therefore uses 50 mJ. These are the supplied example's values, not general properties of pharmaceutical powders or storage silos.<ref name="Zalosh-3-405" />

Rearranging the energy equation gives the voltage associated with that capacitive ignition energy. Converting picofarads to farads and millijoules to joules gives approximately 14 kV. The calculation retains the unrounded value until the final result. Its meaning is a threshold comparison for the idealised source and specified powder in the example.<ref name="Zalosh-3-405" />

<math display="block">V=\sqrt{\frac{2E}{C}}=\sqrt{\frac{2(50\times10^{-3})}{500\times10^{-12}}}=14142\ldots\;\mathrm{V}\approx14\;\mathrm{kV}</math>

Using the inductive value in this capacitive calculation would compare unlike discharge conditions. Zalosh explains that longer-duration sparks can ignite a dust cloud at lower energy than a short capacitive discharge. Dust concentration and mixture temperature also influence the measured threshold. The numerical energy alone therefore does not fully characterise the source's ignition capability.<ref name="Zalosh-3-405" />

The same equation does not quantify ignition by frictional sparks, glowing particles or hot surfaces. Their heating histories and contact mechanisms differ from a purely capacitive discharge. Zalosh notes that evaluating mechanical friction and impact sparks is more difficult. Kanury's source-target description likewise requires the thermal and chemical conditions at the actual interaction.<ref name="Zalosh-3-405" /><ref name="Kanury-2-232" />

== See also ==

* [[Fire triangle]]
* Photovoltaic system fire

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Beyler, C. L. (2002). Flammability limits of premixed and diffusion flames. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-172–2-187). National Fire Protection Association.
* Electric Power Research Institute, & U.S. Nuclear Regulatory Commission. (2005). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Volume 2: Detailed methodology'' (EPRI 1011989; NUREG/CR-6850).
* Gray, B. (2002). Spontaneous combustion and self-heating. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-211–2-228). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Kanury, A. M. (2002). Flaming ignition of solid fuels. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-229–2-245). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-402–3-421). National Fire Protection Association.

[[Category:Ignition & Flame Spread]]

Jet fire

2026-11-02T21:33:56Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''jet fire''' is a flame sustained by a directed release of combustible material that mixes with surrounding air as it burns. The release can arise from a pressurised leak or from an intentionally operated flare. Its momentum influences the flame's direction and shape, while buoyancy and the surrounding wind also affect its development. Beyler describes these fires as turbulent diffusion flames, meaning that fuel and air mix during combustion.<ref name="B291">Beyler (2002), pp. 3-291–3-292.</ref>

The distinction between exposure outside the flame and direct flame impingement is central to assessing the hazard. A distant surface may receive predominantly thermal radiation, whereas an engulfed target also experiences strong convective heating. The release direction, flame dimensions and target position therefore matter alongside the total heat release rate. A radiation calculation for a distant target cannot represent every consequence of a nearby jet.<ref name="B298">Beyler (2002), p. 3-298.</ref><ref name="B302">Beyler (2002), p. 3-302.</ref>

== Release conditions and possible fire sequences ==

Beyler's release event tree distinguishes immediate ignition from ignition after fuel has accumulated or dispersed. Immediate ignition of a release through a relatively small opening can produce a jet flame. The material can be gas or liquid, with a liquid release potentially involving flashing into vapour and accumulation. The flame representation must therefore match the state and behaviour of the released material.<ref name="Bevent">Beyler (2002), pp. 3-268–3-269.</ref>
[[File:fse-jet-fire-v1.svg|thumb|upright=1.5|alt=A release branches into jet, pool and cloud-fire pathways.|A release can lead to different fire types and a changing sequence. Based on Beyler (2002), pp. 3-268–3-269.]]

A [[Pool fire|pool fire]] involves burning associated with an accumulated liquid surface. A directed jet and an accumulated pool can arise within the same release sequence, but their geometries differ. Delayed ignition of a dispersed cloud can also propagate back towards the release and establish subsequent steady burning. Treating the initial event and the continuing fire as separate stages preserves these differences.<ref name="Bevent" />

An intentionally operated flare shares important flame characteristics with an accidental jet fire. However, flare composition, outlet diameter and stack height may be known design inputs. For an accidental release, those inputs can require estimation from the failed equipment and release conditions. Similar combustion physics does not mean that the source uncertainty is the same.<ref name="B291" />

The EPRI/NRC methodology provides examples involving hydrogen relief valves, valve packing and flange leaks. It distinguishes jet flames from tank explosions and delayed cloud ignition. The report was prepared for fire risk assessment at US nuclear power facilities. Its scenario categories can clarify the sequence being considered, while its numerical screening assumptions remain tied to that purpose.<ref name="N7">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-7–N-8.</ref>

The distinction also matters when considering a [[BLEVE|boiling liquid expanding vapour explosion]]. A sustained jet exposure and a sudden vessel failure are different stages or outcomes. Beyler describes accidents in which burning released fuel heated neighbouring liquefied-gas vessels before later failures. A calculation of the original jet therefore does not automatically describe every subsequent exposure.<ref name="B302" />

== Momentum, buoyancy and flame stability ==

Fuel emerging from an opening carries momentum. Mixing with surrounding air supports combustion and changes the moving stream, while hot gases experience buoyancy. Depending on their relative influence, the flame can be predominantly momentum-controlled or buoyancy-controlled. Beyler consequently separates the corresponding flame-length relationships instead of assigning one universal length to a given release diameter.<ref name="Bgeometry">Beyler (2002), pp. 3-291–3-293.</ref>

At relatively low release velocities, the flame can remain attached near the outlet. Increasing velocity can cause its base to lift away. At still higher conditions, a stable flame may cease to be maintained and blowout can occur. An obstruction can also stabilise a flame, so the arrangement around the release belongs in the assessment.<ref name="B291" /><ref name="Bstability">Beyler (2002), pp. 3-296–3-297.</ref>

A lifted flame does not mean that fuel has stopped being released. Its burning region is displaced from the opening. The handbook explains this position through the balance between local flow velocity and turbulent burning velocity. Changes in release conditions can move the flame base to another location where that balance is possible.<ref name="Bstability" />

These mechanisms limit simple comparisons based only on outlet velocity. The same velocity does not uniquely determine flame length, attachment or radiation for every fuel and opening. Density, burning characteristics and the flow regime also enter the cited relationships. A prediction should retain those conditions instead of treating a laboratory observation as a universal jet-fire rule.<ref name="Bgeometry" /><ref name="Bstability" />

== Wind, geometry and the location of exposure ==

Crosswind can bend a jet flame and change its length and width. The handbook reviews experiments with several fuels and distinguishes vertical flame height from distance along an inclined flame. These geometric quantities answer different questions. A height above the outlet cannot be used directly as the full length of a tilted flame.<ref name="Bwind">Beyler (2002), pp. 3-293–3-296.</ref>

The correlations described in the chapter have stated experimental ranges. One group of wind-tunnel tests used burner diameters from 6 to 22 mm, jet velocities from 13 to 200 m/s, and crosswinds from 2.6 to 8.1 m/s. These conditions identify the supporting evidence. They do not establish equal accuracy for every large accidental release.<ref name="B294">Beyler (2002), p. 3-294.</ref>

Release direction can determine which equipment lies within the flame path. The EPRI/NRC hydrogen assessment explicitly considers orientation relative to potential targets. For a relief valve, the discharge direction may constrain the possible flame direction. For a less clearly defined leak, the assumed direction requires its own scenario basis.<ref name="N7" />

Distance also requires a defined reference. In the point-source radiation model, it is measured from a representative point near the flame centre. Distance from the pipe opening is generally a different quantity. A long flame can therefore place the representative radiating region substantially closer to a target than the release point itself.<ref name="B298" />

The receiving surface orientation further affects radiation. A surface facing the representative source receives a different projected exposure from the same surface turned obliquely. This geometric effect is separate from any change in flame power. Source location and surface orientation both need definition before numerical distances can be compared.<ref name="B298" />

One historical hydrogen incident in the EPRI/NRC appendix illustrates the importance of localisation. Direct impingement severely damaged equipment near the release, while damage decreased farther away. A later release through an excess-flow valve directed flame towards a fence. The account identifies changing release geometry rather than a uniform exposure around the original source.<ref name="N6">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-6.</ref>

== Radiation models and their limits ==

[[Flame radiation|Flame radiation]] depends on the amount of energy emitted and the geometric relationship to the target. A simple model replaces the flame by a point at its centre. Beyler gives the following expression for a target outside the flame, together with the relation between radiated power and total heat release.<ref name="B298" />

<div class="fse-equation">q̇″ = Q̇<sub>r</sub> cos θ / (4πR²)</div>
<div class="fse-equation">Q̇<sub>r</sub> = χ<sub>r</sub> Q̇</div>

{| class="wikitable"
! Symbol !! Meaning !! Unit
|-
| q̇″ || Incident radiative heat flux in the simplified model || kW/m²
|-
| Q̇<sub>r</sub> || Total power emitted as radiation || kW
|-
| Q̇ || Total heat release rate || kW
|-
| χ<sub>r</sub> || Fraction of heat release emitted as radiation || dimensionless
|-
| R || Distance from the representative flame centre to the target || m
|-
| θ || Angle between the surface normal and direction towards the source || degrees, used consistently in the cosine
|}

This expression distributes radiant power over a spherical area and includes the receiving surface's projected orientation. It does not resolve how emission varies along the flame. The chapter reports useful comparisons for flare radiation, but also identifies errors close to the source. The point approximation therefore requires separation large enough for the finite flame geometry to be adequately represented.<ref name="B298" /><ref name="B301">Beyler (2002), pp. 3-301–3-302.</ref>

A solid-flame model retains a simplified emitting shape, such as a tilted cylinder. Its result depends on surface emissive power, a geometric configuration factor and atmospheric transmission. A line-source model instead sums contributions along the flame length. These approaches expose different geometric detail; none eliminates the need to justify the flame and emission inputs.<ref name="B301" />

The radiative fraction is not a universal constant for a fuel. Beyler reviews effects of combustion efficiency, soot, mixing and heat transferred to entrained air. The chapter also reports changes with jet velocity and crosswind. Laboratory trends provide evidence of these influences, but their quantitative transfer to large flames requires care.<ref name="Bfraction">Beyler (2002), pp. 3-299–3-301.</ref>

Atmospheric attenuation is another separate influence. The basic point expression shown here contains no transmission factor. Its use therefore embodies that simplification. A more detailed assessment must retain consistency between emitted power, any attenuation model and the incident quantity being reported.<ref name="Bfraction" /><ref name="B301" />

The spatial distribution of emission is another source of approximation. Propane experiments reviewed by Beyler found the strongest radiation near the flame centre, decreasing towards either end. A uniformly emitting cylinder discards that variation. A line representation can retain variation along its length, provided the assigned distribution has supporting evidence.<ref name="Bfraction" /><ref name="B301" />

The chapter also describes a three-dimensional model incorporating flow, turbulence, combustion and soot. Its reported comparison with field experiments used methane jets up to 254 mm in diameter and obtained heat-flux agreement within 15%. That result belongs to the identified model and experiments. It is not a general accuracy statement for every computational jet-fire model.<ref name="B301" />

== Worked radiation comparison ==

Consider an illustrative 10 MW jet with an assumed radiative fraction of 0.20. The handbook lists a value of 0.20 among the reported methane results, but also explains its dependence on operating conditions. It is selected here solely to demonstrate the equation. It is not a recommended fraction for every methane release.<ref name="Btable">Beyler (2002), p. 3-299, Table 3-11.12.</ref>
[[File:fse-jet-fire-v2.svg|thumb|upright=1.5|alt=Three assumed point-source cases show radiation decreasing with distance and oblique orientation.|Distance and orientation change the calculated far-field radiation. Based on Beyler (2002), pp. 3-298–3-299.]]

The assumed radiated power is 2,000 kW. For a target facing the representative source at 50 m, the equation gives approximately 0.0637 kW/m². At 100 m, the result is approximately 0.0159 kW/m². Doubling distance reduces the calculated flux to one quarter because the spherical area increases with the square of distance.<ref name="B298" />

Keeping the target at 50 m but turning its normal through 60° halves the result to approximately 0.0318 kW/m². The calculation uses the same emitted power and changes only projected orientation. These three cases demonstrate the distance and angular terms independently. All intermediate calculations retain unrounded values.<ref name="B298" />

The example does not establish that an actual 10 MW jet has a particular flame length. It assumes that the chosen positions are sufficiently far from the flame for the point representation. Nor does it calculate atmospheric attenuation, direct contact or the thermal response of a target. Those omissions define the scope of the reported values.<ref name="B298" /><ref name="B301" />

A numerical flux is also not automatically a consequence criterion. The target's material, duration of exposure and response require separate treatment. The handbook frames its radiation methods as inputs to an assessment of particular impacts. A distance derived from the equation needs that additional basis before it can be interpreted as a protection distance.<ref name="Bintro">Beyler (2002), p. 3-268.</ref>

== Direct impingement and structural exposure ==

An impinging jet heats the target through both radiation and convection. The handbook reports particularly severe exposures where large-scale jet flames engulfed cylindrical targets. In the cited tests, average heat fluxes over the impingement area were approximately 200 kW/m² for sonic natural gas and 150 kW/m² for two-phase liquefied petroleum gas. These are results for those experimental arrangements.<ref name="B302" />
[[File:fse-jet-fire-v3.svg|thumb|upright=1.5|alt=A remote target receives radiation while an engulfed target also receives strong convective heating.|Direct impingement combines radiative and convective heating. Based on Beyler (2002), pp. 3-301–3-302.]]

The corresponding reported peaks reached approximately 300 and 250 kW/m² respectively. A peak local value differs from an average over the target area. Neither value describes every location on a vessel or every release condition. Retaining the fuel state and target geometry prevents those measurements from becoming universal design inputs.<ref name="B302" />

Beyler describes roughly comparable radiative and convective contributions in some high-flux regions. Other gaseous propane tests reported a different balance. A radiation-only estimate therefore cannot generally reproduce total impingement heating. The relevant exposure includes the local gas motion and thermal environment as well as radiation.<ref name="B302" />

A prescribed hydrocarbon fire curve describes a temperature–time exposure associated with oil or gas fire testing. Van Rossum distinguishes such agreed histories from temperatures developing in an actual scenario. The curve and the local jet-impingement flux consequently describe different inputs. Substituting one for the other requires a thermal assessment rather than a change of label.<ref name="VR86">Van Rossum (2027), §8.6.</ref><ref name="B302" />

== Mitigation, continuing release and assessment scope ==

Water application can affect exposure without necessarily extinguishing the jet. Beyler reviews experiments showing reduced radiation at water-spray rates below complete suppression. Fleming likewise distinguishes cooling of exposed construction from successful extinction. A reduction in measured radiation is therefore a different result from stopping fuel flow or eliminating the flame.<ref name="Bwater">Beyler (2002), p. 3-300.</ref><ref name="F72">Fleming (2002), p. 4-72.</ref>

A [[Deluge system|deluge system]] supplies open discharge devices after a separate detection system operates its valve. That system description does not specify its effectiveness against a particular jet. Fleming emphasises the empirical basis and limits of suppression calculations. The cited jet-spray observations therefore cannot supply a general deluge application rate or guaranteed performance.<ref name="F72" /><ref name="F73">Fleming (2002), p. 4-73.</ref><ref name="Bwater" />

For [[Hydrogen safety|hydrogen safety]], continuing release and ignition sequence remain particularly relevant. The EPRI/NRC report explains that loss of a flame while gas continues escaping can permit a flammable cloud to form. Its discussion of source isolation reflects that change in scenario. Extinction and removal of the fuel source are consequently distinct outcomes in the hazard analysis.<ref name="N1">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-1–N-2.</ref>

The final assessment needs a defined release, flame representation, target geometry and exposure duration. It also needs the applicable model limitations and supporting experimental conditions. The EPRI/NRC report leaves selection and validation of detailed computational tools outside its hydrogen scenario rules. Its screening assumptions cannot replace a validated thermal model for a different application.<ref name="N11">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-11.</ref><ref name="Bintro" />

== See also ==
* [[Fireball]]

== Notes ==
<references />

== References ==
* Beyler, C. L. (2002). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-11). National Fire Protection Association.
* Electric Power Research Institute, & U.S. Nuclear Regulatory Commission. (2005). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Volume 2, Detailed methodology'' (EPRI 1011989; NUREG/CR-6850).
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''.

[[Category:Explosions & Industrial Fires]]

Inerting

2026-11-02T21:33:53Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Inerting''' is the addition of a suitable diluent to prevent a combustible mixture from supporting flame propagation. In common gas-purging applications, an inert gas reduces the oxygen concentration below the limit relevant to the fuel and conditions. The method changes the mixture's ability to burn, rather than relying solely on excluding ignition sources.<ref name="B-179">Beyler (2002), p. 2-179.</ref><ref name="N-27">Iqbal and Salley (2004), p. B-27.</ref>

The limiting oxygen concentration depends on the fuel, diluent, temperature and pressure. An inerted state therefore requires a defined mixture and operating condition. A concentration that prevents flame propagation in one system cannot automatically be transferred to another.<ref name="B-179" /> Mixing during gas replacement also matters: the path from the initial composition to the final composition can cross a flammable region even when the endpoints do not.<ref name="B-180">Beyler (2002), pp. 2-180–2-181.</ref> Inerting calculations consequently consider mixture composition, dilution history and the continued control of oxygen. Practical application also depends on concentration nonuniformity and the performance of monitoring instruments.<ref name="Z-403">Zalosh (2002), p. 3-403.</ref>

== Preventing a combustible mixture ==

A premixed fire requires fuel and oxidant in proportions that support flame propagation. [[Flammability limits]] describe the boundaries of that composition range under specified test conditions. Adding a diluent changes the concentrations and thermal behaviour of the mixture. Beyond a sufficient dilution, a flame cannot propagate away from the ignition source under those conditions.<ref name="B-178">Beyler (2002), pp. 2-178–2-179.</ref>

This provides one way to interrupt the sequence leading to an [[Explosion|explosion]]. Zalosh describes three broad protection approaches: preventing a flammable mixture, excluding ignition sources and limiting the pressure generated after ignition. Inerting belongs to the first approach. Explosion venting and suppression address different stages, so their mechanisms are not interchangeable with mixture control.<ref name="Z-402">Zalosh (2002), p. 3-402.</ref>

NUREG-1805 distinguishes oxygen control from fuel-concentration control. An inert purge gas reduces the oxidant available to a mixture. Air dilution instead reduces fuel concentration while introducing additional oxygen. These approaches can move the composition along different paths and require different evidence that the resulting mixtures remain outside the flammable region.<ref name="N-27" /><ref name="B-180" />

The word inert describes the diluent's role in the specified combustion problem. It does not mean that the resulting atmosphere is suitable for breathing. The handbook's discussion of inert-gas agents identifies reduced oxygen as their principal physiological hazard. Fire prevention and the assessment of human exposure therefore remain separate questions.<ref name="D-184">DiNenno (2002), p. 4-184.</ref>

The supplied vessel-purging methods also have a defined application scope. NUREG-1805 discusses tanks and process vessels, while Beyler examines fuel, oxidant and diluent mixtures. These calculations do not constitute a complete design description for an oxygen reduction system. The shared oxygen-control principle does not supply every installation-specific operating requirement.<ref name="N-27" /><ref name="B-179" />

== Limiting oxygen concentration ==

The limiting oxygen concentration is the oxygen boundary below which the specified mixture cannot support the relevant combustion process. Beyler discusses it in terms of preventing premixed flame propagation. Zalosh relates the limiting oxidant concentration to explosion prevention. The intended test criterion matters when interpreting values obtained from different experimental arrangements.<ref name="B-179" /><ref name="Z-402" />

The limit is different from a fuel's lower flammable limit in ordinary air. The lower fuel limit concerns insufficient fuel in a specified oxidising mixture. The oxygen limit concerns insufficient oxidant after dilution. Controlling one variable does not remove the need to identify the other constituents of the mixture.<ref name="B-178" /><ref name="B-179" />

Diluent choice affects the limiting condition. Beyler compares nitrogen and carbon dioxide and relates their different performance to heat capacity. The added gas absorbs energy during combustion, influencing whether a flame can sustain itself. Equal volume fractions of two different diluents therefore need not produce the same flammability boundary.<ref name="B-179" />

Fuel identity also matters. The handbook describes hydrogen and carbon monoxide as having lower limiting oxygen concentrations than many common hydrocarbon fuels. A value selected for one hydrocarbon therefore cannot be treated as an oxygen limit for every combustible gas. The relevant fuel data remain part of the inerting calculation.<ref name="B-179" />

Temperature and pressure accompany the composition data. Beyler states that the limiting concentration depends on both and identifies the conditions attached to his tabulated results. A value measured near normal atmospheric conditions is not an unrestricted limit for a heated or pressurised process. The data and the proposed operating state need a compatible basis.<ref name="B-179" />

The experimental limit is also distinct from an operating setpoint. Zalosh discusses margins for nonuniform mixtures and for instrument accuracy, response and reliability. His numerical examples refer to the historical standard edition cited in that chapter. The underlying distinction remains that a measured boundary alone does not specify the margin or monitoring arrangement for an installation.<ref name="Z-403" />

== Reading the composition path ==

A flammability diagram represents mixtures of fuel, oxygen and diluent. In a three-axis diagram, each constituent has an explicit concentration coordinate. The three fractions sum to the complete mixture. A two-axis representation can carry the same information by obtaining the third fraction from the difference between the other two and the total.<ref name="B-178" />

The flammable region occupies only part of that composition space. A mixture can lie outside it because it contains too little fuel, too little oxygen or too much fuel relative to oxidant. These are different starting states. Their subsequent response to added air cannot be inferred from the simple statement that the initial mixture is nonflammable.<ref name="B-178" /><ref name="B-180" />

Adding one constituent moves the overall composition towards the point representing that pure gas. Adding air instead moves it towards the air composition. Beyler uses these paths to examine the dilution of fuel-rich mixtures. A straight path between an initial mixture and air can pass through the flammable region even though the initial rich mixture lies outside it.<ref name="B-180" />
[[File:fse-inerting-v1.svg|thumb|upright=1.5|alt=Composition diagram shows a direct air-mixing path crossing a flammable region and an alternative path around it.|The path through composition space matters as well as its endpoints. Based on Beyler (2002), pp. 2-178–2-181.]]

Adding nitrogen first can change the starting point for later air dilution. In the handbook example, a graphical tangent identifies a diluted composition whose subsequent mixing line avoids the flammable region. The result depends on the complete diagram and its stated conditions. It cannot be obtained merely by assuming that any reduction in fuel concentration is protective.<ref name="B-180" />

The same reasoning applies to gas leaving the system. An exhaust mixture that cannot burn inside the inerted volume can mix with external air and enter a flammable range. Beyler explicitly identifies this issue in his room-purging example. The discharge boundary is therefore part of the combustion assessment, rather than the point at which consideration ends.<ref name="B-181">Beyler (2002), p. 2-181.</ref>

== A model for well-mixed purging ==

Purging replaces some of the original gas with an introduced gas while material leaves through an outlet. If the entire volume remains well mixed, the outlet contains the same mixture as the interior. Newly added inert gas consequently leaves alongside the original gas. This loss makes mixed purging different from replacing one unmixed volume with another.<ref name="B-180" />

Beyler describes the decline in fuel concentration using an exponential relationship. The model assumes a fixed enclosed volume and uniform concentration during the addition of nitrogen. Added and exhausted gas volumes are expressed on a consistent basis. The formula concerns the idealised dilution process and does not establish that an actual space mixes uniformly.<ref name="B-181" />

<div class="fse-equation">C = C<sub>0</sub> exp(−V<sub>N</sub>/V)</div>
<div class="fse-equation">V<sub>N</sub> = −V ln(C/C<sub>0</sub>)</div>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| C || Fuel concentration after the modelled purge || Volume fraction or volume percent
|-
| C<sub>0</sub> || Initial fuel concentration, on the same basis || Volume fraction or volume percent
|-
| V<sub>N</sub> || Nitrogen volume introduced at the stated gas conditions || m³
|-
| V || Fixed volume being purged || m³
|}

The concentration ratio is dimensionless, so both concentrations must use the same convention. Volume percent can be used in both numerator and denominator without converting them separately to fractions. The logarithm is the natural logarithm. Mixing a percentage with a fraction would produce a different ratio and an erroneous purge quantity.<ref name="B-181" />

The expression predicts progressively smaller concentration reductions for successive equal gas additions. As the original gas becomes more dilute, less of it leaves with each unit of exhaust. A later addition therefore removes less original fuel than an equally large initial addition. This is the physical meaning of the exponential decline under the complete-mixing assumption.<ref name="B-181" />

Other mixing patterns require other descriptions. Beyler contrasts complete mixing with an ideal replacement in which only the original mixture is removed. Neither idealisation proves the flow pattern in a particular room or vessel. The selected model has to retain its assumptions when its calculated gas quantity is interpreted for an actual installation.<ref name="B-180" />

== Worked examples from the handbook ==

Beyler considers a 200 m³ room initially containing 30% methane by volume. His flammability diagram gives a methane concentration of 13% for the selected nitrogen-diluted endpoint before subsequent air mixing. These are inputs to a particular theoretical example. They are not breathable-atmosphere criteria or a general procedure for clearing a methane-filled room.<ref name="B-180" /><ref name="D-184" />

Using the mixed-purge expression gives −200 ln(13/30), approximately 167 m³ of nitrogen. Direct calculation with the displayed inputs gives 167.25 m³, consistent with the handbook's rounded result. The volume exceeds the amount obtained by assuming that the incoming nitrogen replaces only original gas. Under complete mixing, some nitrogen also leaves through the outlet.<ref name="B-181" />
[[File:fse-inerting-v2.svg|thumb|upright=1.5|alt=Methane concentration falls from 30% to 13% as the model adds about 167 cubic metres of nitrogen.|Complete mixing causes an exponential decline in the modelled concentration. Based on Beyler (2002), pp. 2-180–2-181.]]

For the ideal unmixed replacement comparison, the expression 200(30 − 13)/30 gives approximately 113 m³. The mixed-purge result is about 48% greater, using unrounded values. This difference illustrates the influence of the mixing assumption. It does not supply an installation allowance for leaks, poor distribution or uncertain concentration measurements.<ref name="B-180" /><ref name="B-181" />

The source also considers a continuous methane stream released at 1 kg/s. Its graphical construction uses methane and nitrogen proportions of 18% and 82% by volume. Those proportions correspond to molar proportions for the stated gas treatment. The required mass-flow ratio therefore additionally depends on the molecular weights of the two gases.<ref name="B-181" />

Using molecular weights of 16 for methane and 28 for nitrogen gives a nitrogen flow of approximately 7.97 kg/s in that example. Simply multiplying the methane mass flow by 82/18 would omit the molecular-weight conversion. The worked result demonstrates why a volumetric or molar mixture specification cannot be treated as a mass fraction.<ref name="B-181" />

Both examples depend on their selected composition path. Neither the final methane percentage nor the nitrogen flow is a universal target for every methane system. The source's warning about flammable mixing at the exhaust remains relevant. The numerical exercises describe a model of the mixture, not proof of personnel safety or of field performance.<ref name="B-180" /><ref name="B-181" /><ref name="D-184" />

== Dusts and changing process conditions ==

Inerting can also address a [[Dust explosion|dust explosion]] hazard when suspended combustible particles are mixed with air. Zalosh describes reducing oxygen where dust concentration cannot reliably be maintained below its minimum explosible concentration. The control variable is then the oxidant available to the cloud. The relevant limiting concentration remains material-specific.<ref name="Z-404">Zalosh (2002), p. 3-404.</ref>

Dust concentrations observed during normal operation may not represent abnormal conditions. Zalosh gives examples in which vibration or air blasts used to dislodge obstructions produce substantially greater suspended concentrations. Such changes affect the potential combustible cloud. An assessment based only on a routine concentration measurement can therefore miss the state against which inerting is intended to provide protection.<ref name="Z-404" />

Different dusts do not have one common oxygen limit. The handbook distinguishes organic materials from some metal powders requiring substantially lower concentrations. Temperature also affects the reported dust limits. Gas-phase data for a convenient reference fuel cannot replace evidence for the actual powder and process conditions.<ref name="Z-403" /><ref name="Z-404" />

Dust testing and gas testing also use different experimental arrangements. Zalosh describes controlled dispersion, ignition and pressure measurement for dust-cloud assessment. The resulting boundary is associated with those material and test conditions. Its use requires understanding what the test establishes rather than treating a tabulated value as independent of the experiment.<ref name="Z-403" /><ref name="Z-404" />

== Monitoring and interpretation ==

Practical concentration fields can be stratified or otherwise nonuniform. A well-mixed calculation assigns one concentration to the whole volume, while a real process can contain regions with different mixtures. Zalosh identifies that difference as a central issue in applying flammability data. A favourable average does not establish the same composition at every location.<ref name="Z-403" />
[[File:fse-inerting-v3.svg|thumb|upright=1.5|alt=Uniform model and nonuniform vessel mixture are compared alongside the properties of concentration measurement.|Nonuniform mixtures and instrument performance affect the interpretation of an inerting calculation. Based on Zalosh (2002), p. 3-403.]]

Instrument performance introduces another limitation. Accuracy affects how closely the measured concentration represents the gas at the sensor. Response time affects whether changing conditions are detected promptly, while reliability concerns continued availability of the measurement. The source treats these as reasons that an experimental limiting concentration cannot simply become the operating boundary without further assessment.<ref name="Z-403" />

The intended [[Oxygen depletion|oxygen depletion]] also affects people independently of whether flame propagation is prevented. DiNenno identifies oxygen reduction as the physiological concern associated with inert-gas agents. His discussion concerns a specific suppression context; it does not establish safe occupancy for the purge examples above. A combustion calculation cannot substitute for an exposure assessment.<ref name="D-184" />

Finally, maintaining an inerted state is different from calculating an initial gas addition. NUREG-1805 describes control of oxygen in dynamic processing equipment, and Zalosh emphasises changing mixtures and monitoring. The assessment therefore retains the process conditions under which the selected mixture boundary remains applicable. A successful arithmetic dilution result alone does not demonstrate that those conditions persist.<ref name="N-27" /><ref name="Z-403" />

== See also ==
* [[Flame extinction]]

== Notes ==
<references />

== References ==
* Beyler, C. (2002). Flammability limits of premixed and diffusion flames. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 2-7). National Fire Protection Association.
* DiNenno, P. J. (2002). Halon replacement clean agent total flooding systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 4-7). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-16). National Fire Protection Association.

[[Category:Explosions & Industrial Fires]]

Hydraulic calculation

2026-11-02T21:33:50Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Hydraulic calculation''' is the method used to show that the pipes and water supply of a [[sprinkler system]] can deliver the required flow and pressure to every sprinkler expected to open in a fire.<ref name="F-74">Fleming (2002), p. 4-74.</ref> The designer starts from a prescribed water density over a design area and determines the flow and pressure needed at the most remote sprinkler.<ref name="F-74" /><ref name="F-75">Fleming (2002), p. 4-75.</ref> The calculation then works back towards the source, adding the pressure lost to pipe friction, fittings and differences in height.<ref name="F-75" /> The result, called the system demand, is a specific flow at a specific pressure.<ref name="F-76">Fleming (2002), p. 4-76.</ref> It must lie below the curve that describes the available water supply.<ref name="F-81">Fleming (2002), p. 4-81.</ref>

In the United States, the sprinkler standard NFPA 13 of the National Fire Protection Association (NFPA) requires the empirical Hazen–Williams formula for pipe friction.<ref name="F-76" /> Hydraulically calculated designs have been in common use since the early 1970s, as an alternative to the older pipe schedule method.<ref name="H-17">Hopkins et al. (2005), p. 17.</ref> Hydraulic calculation is the only part of sprinkler design that is widely calculated. The ability of a water spray to suppress a fire can only be estimated with very rudimentary methods.<ref name="F-73">Fleming (2002), p. 4-73.</ref>

== Purpose and history ==
The pipe schedule method uses predefined tables of pipe sizes for light, ordinary and extra hazard occupancies.<ref name="H-17" /> Each table lists the maximum number of sprinklers that a pipe of a given size may supply, which made design quick but subjective.<ref name="H-17" /> In the 1970s the capabilities of pipe schedule systems, proven over a hundred years, were codified into curves of water density against design area.<ref name="F-73" /> This step introduced hydraulic calculation into what had become a cookbook method of design.<ref name="F-73" />

Hydraulic calculation brought two practical gains. Designers could take advantage of strong water supplies to build more economical systems, and they could determine the flows and pressures available at points in the piping.<ref name="F-73" /> The second gain opened the way to special sprinklers, which are approved for specific protection goals.<ref name="F-73" /> The calculation only covers the flow of water through the pipes. Most protection criteria in NFPA 13 result from experience and judgement, and only some, such as those for early suppression fast response sprinklers, rest on full-scale tests.<ref name="F-73" />

Fleming distinguishes four basic types of system: wet pipe, dry pipe, deluge and preaction.<ref name="F-72">Fleming (2002), p. 4-72.</ref> A [[wet pipe sprinkler system]], by far the most common type, keeps water under pressure in its pipes.<ref name="F-72" /> Heat at one sprinkler then makes only that sprinkler discharge water over its own area.<ref name="F-72" /> A dry pipe system holds air or nitrogen in the pipes until a sprinkler opens, and is used where water in the pipes could freeze.<ref name="F-72" />

The first and most critical design step is the occupancy hazard classification.<ref name="F-73" /> If the hazard is underestimated, a fire may overpower the sprinklers, and no calculation method exists for this step.<ref name="F-73" /> [[Sprinkler hazard classification]] in NFPA 13 distinguishes light hazard, ordinary hazard groups 1 and 2, and extra hazard groups 1 and 2.<ref name="H-16">Hopkins et al. (2005), p. 16.</ref> Offices are examples of light hazard occupancies.<ref name="H-16" />

== Design density and design area ==
The hazard class determines the minimum water density and the minimum area of sprinkler operation, which are the inputs for the hydraulic calculation.<ref name="H-16" /> The density is a water flow per unit floor area, expressed in mm/min or L/(min·m²), or in gallons per minute per square foot (gpm/ft²).<ref name="H-17" /><ref name="F-74" /> The designer reads the [[sprinkler design density]] and design area from an area and density curve in NFPA 13.<ref name="F-74" /> Any point on or to the right of the curve is acceptable, so a high density over a small area and a low density over a large area are both possible.<ref name="F-74" /> In either case the fire is expected to be controlled by the sprinklers within the design area.<ref name="F-74" />

Fleming gives an example curve that allows anything from 0.1 gpm/ft² over 5,000 ft² to 0.17 gpm/ft² (6.9 mm/min) over 1,500 ft² (139 m²).<ref name="F-74" /> A designer might select 0.15 gpm/ft² (6.1 mm/min) over 2,400 ft², which is about 223 m².<ref name="F-74" /> Water is provided only for the sprinklers within this area, because the others are not expected to open.<ref name="F-74" /> NFPA 13 divides the design area by the area per sprinkler and rounds up.<ref name="F-74" /> With sprinklers spaced at 12 ft by 15 ft (3.66 m by 4.57 m), each covers 180 ft², and the design area holds 2,400 / 180 = 13.3, so 14 sprinklers.<ref name="F-74" />
[[File:fse-hydraulic-calculation-v2.svg|thumb|upright=1.5|alt=Chart of design area against water density: a falling straight line from 465 m2 at 4.1 mm/min to 139 m2 at 6.9 mm/min, region to its right shaded.|Sample area and density curve converted to SI units. Any point on or to the right of the line is acceptable; the marked point is the selection of 6.1 mm/min over 223 m². Based on Fleming (2002), p. 4-74.]]

The remote design area must be a rectangle with its long side along the branch lines.<ref name="F-74" /> Its length is 1.2 times the square root of the design area, here 1.2 × 49 = 59 ft, or five sprinklers spaced 12 ft apart along a branch line.<ref name="F-74" /> The 1999 edition of NFPA 13 modifies the design area for dry systems, for quick response sprinklers under flat smooth ceilings and for rooms in highly compartmented buildings.<ref name="F-74" /> Since 1985 it has also allowed a design area of four sprinklers for dwelling units with residential sprinklers.<ref name="F-74" />
[[File:fse-hydraulic-calculation-v1.svg|thumb|upright=1.5|alt=Plan of a sprinkler system: a riser and cross main feed six branch lines; a shaded rectangle of 14 sprinklers lies at the far end.|Plan of a tree sprinkler system with the remote design area of 14 sprinklers at the far end of the branch lines. The calculation starts at the most remote sprinkler and runs back to the supply. Based on Fleming (2002), pp. 4-74 to 4-75.]]

For light hazard occupancies, the 2002 edition of NFPA 13 requires 0.1 gpm/ft² over 1,500 ft², about 4.1 mm/min over 139 m².<ref name="H-87">NFPA (2002), as cited in Hopkins et al. (2005), p. 87.</ref> With sprinklers spaced 14 ft by 14 ft, each sprinkler covers 196 ft², and the design area needs eight sprinklers.<ref name="H-87" /> Each of them must then discharge at least 19.6 gpm, about 74 L/min.<ref name="H-87" />

== From the most remote sprinkler to the source ==
The calculation starts at the most remote sprinkler in the design area.<ref name="F-74" /> In a tree system, where each sprinkler is fed from one direction only, this is generally the end sprinkler on the branch line farthest from the riser.<ref name="F-74" /> The area that this sprinkler protects is taken as S × L. Here S is twice the larger distance to the next sprinkler on the line, and L is twice the larger distance to the next branch line.<ref name="F-75" /> The minimum flow from the sprinkler is this area multiplied by the required density.<ref name="F-75" />

The flow through a sprinkler orifice rises with the square root of the water pressure in the pipe. All other properties of the orifice are lumped into one experimental constant, the K-factor, which testing laboratories determine when they list a sprinkler model.<ref name="F-75" /> NFPA 13 sets a minimum pressure of 7 psi (0.48 bar) at the end sprinkler, to ensure a proper spray pattern.<ref name="F-75" />

<math display="block">Q = K \sqrt{P} \qquad \Leftrightarrow \qquad P = \left( \frac{Q}{K} \right)^2</math>

=== Worked example ===
Fleming considers a standard spray sprinkler that protects 12 ft by 14 ft, or 15.6 m², at a density of 6.1 mm/min (0.15 gpm/ft²).<ref name="F-75" /> The minimum flow is 15.6 × 6.11 ≈ 95.4 L/min (25.2 gpm). A standard sprinkler with a nominal orifice of half an inch has a K-factor of 5.6 gpm/psi<sup>1/2</sup>, which is 80.7 L/(min·bar<sup>1/2</sup>).<ref name="F-75" /> The required pressure is then (95.4 / 80.7)² = 1.40 bar, or 20.2 psi, well above the minimum of 0.48 bar.<ref name="F-75" />

From the end sprinkler the calculation proceeds backwards towards the source of supply.<ref name="F-75" /> At each point it adds the pressure needed to overcome friction and differences in height, while keeping the minimum pressure at the remote sprinkler.<ref name="F-75" /> A water column produces a pressure of 0.433 psi per foot of height, about 0.098 bar per metre.<ref name="F-78">Fleming (2002), p. 4-78.</ref> This follows from the specific weight of water, 9.81 kN/m³.<ref name="T-44">Titus (2002), p. 4-44.</ref> Beyond the design area no further sprinkler flow is added, only an allowance for hose streams.<ref name="F-75" />

Sprinklers closer to the supply receive a higher pressure, so each discharges more water than the minimum.<ref name="F-75" /> This effect is called hydraulic increase.<ref name="F-76" /> It explains why the total demand of a system is not simply the density multiplied by the design area.<ref name="F-76" /> At the end of the calculation, the demand is known as a specific flow at a specific pressure.<ref name="F-76" />

== Pipe friction and the Hazen–Williams formula ==
Water flowing through a pipe loses pressure through friction with the pipe wall and turbulence in the flow.<ref name="T-50">Titus (2002), p. 4-50.</ref> Flows in fire protection piping are almost always turbulent.<ref name="T-50" /> NFPA 13 prescribes the empirical Hazen–Williams formula to estimate this friction loss.<ref name="F-76" /> In words, the loss per metre of pipe grows with the flow to the power 1.85 and falls steeply with the internal diameter. A roughness coefficient C represents the condition of the pipe wall; smoother pipes have higher values. In SI units the formula reads:<ref name="T-52">Titus (2002), p. 4-52.</ref>

<math display="block">p = \frac{6.05 \times 10^5 \, Q^{1.85}}{C^{1.85} \, D^{4.87}}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>p</math> || friction loss per metre of pipe || bar/m
|-
| <math>Q</math> || flow rate through the pipe or sprinkler || L/min
|-
| <math>C</math> || Hazen–Williams roughness coefficient || none
|-
| <math>D</math> || internal pipe diameter || mm
|-
| <math>K</math> || K-factor of a sprinkler || L/(min·bar<sup>1/2</sup>)
|-
| <math>P</math> || water pressure at the sprinkler || bar
|}

The US form used in NFPA 13 is <math>p = 4.52\,Q^{1.85}/(C^{1.85} d^{4.87})</math>, with the loss in psi per foot, the flow in gpm and the diameter in inches.<ref name="F-76" /> NFPA 13 stipulates the C values, which are meant to represent the inside roughness of aged pipe.<ref name="F-76" /> Steel pipe in dry and preaction systems takes C = 100, and steel pipe in wet and deluge systems takes C = 120.<ref name="F-76" /> Cement-lined cast or ductile iron takes 140, and copper tube and listed plastic pipe take 150.<ref name="F-76" />

Fittings and valves cause extra losses through turbulence.<ref name="F-76" /> Designers usually express them as equivalent lengths of straight pipe, which are added to the real pipe length.<ref name="F-76" /> A standard elbow in 1 in. Schedule 40 steel pipe, for example, counts as 2 ft (0.61 m) of pipe.<ref name="F-76" /> The table of equivalent lengths assumes C = 120 and is multiplied by factors for other pipe materials.<ref name="F-76" />

In the continuation of the worked example, the second sprinkler is fed through 3.66 m (12 ft) of 1 in. Schedule 40 steel pipe with a bore of 26.6 mm and C = 120.<ref name="F-76" /> The formula gives 0.045 bar/m (0.20 psi/ft), so the pipe loses 0.17 bar (2.4 psi).<ref name="F-76" /> The second sprinkler therefore needs 1.56 bar (22.6 psi) and discharges about 101 L/min (26.6 gpm).<ref name="F-76" /> If four elbows were added to avoid a column, the pressure would rise to 24.2 psi and the flow to 27.5 gpm.<ref name="F-77">Fleming (2002), p. 4-77.</ref> NFPA 13 allows designers to ignore velocity pressure, because the effect is usually small and ignoring it gives a more conservative design.<ref name="F-77" />
[[File:fse-hydraulic-calculation-v3.svg|thumb|upright=1.5|alt=Side view of a pipe with two sprinklers 3.66 m apart: the end sprinkler gets 1.40 bar and 95 L/min, the second 1.56 bar and 101 L/min.|Two sprinklers at the end of a branch line. Friction in 3.66 m of pipe adds 0.17 bar, so the second sprinkler discharges more than the end sprinkler. Based on Fleming (2002), pp. 4-75 to 4-76.]]

== Looped and gridded systems ==
In a tree system each sprinkler is fed along a single path, so the calculation can follow the pipes in one direction.<ref name="F-74" /> In looped and gridded systems, water reaches a point along several paths, and the split of flow between them is unknown at the start.<ref name="F-79">Fleming (2002), p. 4-79.</ref> For grids, computers are generally used, because the problem becomes a set of non-linear equations.<ref name="F-79" /> By hand, the Hardy Cross method assumes a flow distribution and corrects it step by step until the pressure losses along different routes agree.<ref name="F-79" />

NFPA 13 requires the calculated pressures to balance within 0.5 psi (0.03 bar) at each hydraulic junction.<ref name="F-79" /> In practice this means repeating the corrections until the loss from the design area back to the supply is almost the same along any path.<ref name="F-79" /> Pipes in series or in parallel can first be replaced by one equivalent pipe, which reduces the work.<ref name="F-79" />

== Comparing demand with the water supply ==
The strength of a [[fire water supply]] is tested by measuring two pressures at a hydrant.<ref name="F-81" /> The static pressure is read with no extra flow, and the residual pressure is read while a known flow is taken from another hydrant.<ref name="F-81" /> The fall in pressure between the two readings reflects friction in the supply network, and it is proportional to the flow to the power 1.85.<ref name="F-81" /> The available pressure at any other flow can therefore be estimated from the two measurements, with the formula below; the formula follows from this proportionality but is not printed in the handbook. On graph paper with a flow scale to the power 1.85, the water supply curve becomes a straight line.<ref name="F-81" />

<math display="block">P_\mathrm{avail}(Q) = P_s - \left( P_s - P_r \right) \left( \frac{Q}{Q_r} \right)^{1.85}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>P_\mathrm{avail}</math> || pressure available from the supply at flow <math>Q</math> || bar
|-
| <math>P_s</math> || static pressure (no extra flow) || bar
|-
| <math>P_r</math> || residual pressure during the test flow || bar
|-
| <math>Q_r</math> || flow during the test || L/min
|}

Fleming describes a test with a static pressure of 6.9 bar (100 psi) and a residual pressure of 5.5 bar (80 psi) at 3,785 L/min (1,000 gpm).<ref name="F-81" /> Reading a sketch graph, the handbook gives about 90 psi (6.2 bar) available at 1,703 L/min (450 gpm).<ref name="F-81" /> This article's own calculation with the formula above gives 100 − 20 × 0.45<sup>1.85</sup> = 95.4 psi, or 6.58 bar, for the same flow. The system demand, including the hose stream allowance, should lie below the supply curve.<ref name="F-81" /> In a demand calculation the pressure and flow at the end sprinkler are related back to the supply and compared with this curve.<ref name="H-88">Hopkins et al. (2005), p. 88.</ref> If the demand lies above the curve, a pump, a tank or other provisions must be added.<ref name="H-88" />
[[File:fse-hydraulic-calculation-v4.svg|thumb|upright=1.5|alt=Line chart: available supply pressure falls from 6.9 bar at zero flow to 5.5 bar at 3785 L/min; a margin line lies 0.69 bar lower.|Water supply curve from a flow test with 6.9 bar static and 5.5 bar residual pressure at 3,785 L/min, with a margin of 10 percent of the static pressure. Based on Fleming (2002), p. 4-81, and Hopkins et al. (2005), p. 88.]]

Good practice leaves a margin of safety between demand and supply.<ref name="H-88" /> Hopkins et al. describe it as a fixed percentage of the static pressure, such as 10 or 20 percent, or a fixed pressure, such as 10 or 20 psi.<ref name="H-88" /> The margin covers fluctuations in the supply and later changes to the system, such as extra fittings and pipe added during tenant fit-outs.<ref name="H-88" />

Where the supply lacks pressure, a fire pump can make up the difference.<ref name="F-82">Fleming (2002), p. 4-82.</ref> In the United States, NFPA 20 requires a horizontal fire pump to deliver at least its rated pressure at its rated flow.<ref name="F-82" /> At 150 percent of the rated flow it must still deliver at least 65 percent of the rated pressure.<ref name="F-82" /> By interpolating between such points, Fleming shows that a pump rated at 500 gpm and 100 psi can be expected to give at least 86 psi at 600 gpm.<ref name="F-83">Fleming (2002), p. 4-83.</ref> Tanks must hold enough water for the minimum duration in NFPA 13, at the required pressure even when nearly empty.<ref name="F-83" />

== Use in fire investigation ==
Hydraulic calculation also works in the opposite direction. In a supply calculation, the water supply and the piping are given, and the flow is followed forward to find the largest density that the system can deliver.<ref name="H-88" /> The National Institute of Standards and Technology used this approach to assess the sprinkler water supplies of the World Trade Center buildings.<ref name="H-89">Hopkins et al. (2005), p. 89.</ref> Representative floors were analysed with 4, 8 to 15, and 18 to 25 open sprinklers.<ref name="H-89" />

For the 99th and 107th floors of the North Tower (WTC 1), up to 24 sprinklers could operate while keeping an average density of at least 0.1 gpm/ft².<ref name="H-138">Hopkins et al. (2005), p. 138.</ref> That is three times the number of sprinklers in the design area.<ref name="H-138" /> On the 98th floor the system could supply 17 sprinklers at 7 psi and 0.1 gpm/ft², over twice the design area.<ref name="H-138" /> In the mid-level zone, the flow to one supply riser was limited to about 440 gpm, which limited the systems on the 87th and 32nd floors to 19 and 17 sprinklers.<ref name="H-138" />

== Limits and common misconceptions ==
The Hazen–Williams formula has no sound theoretical basis and contains no properties of the fluid.<ref name="T-52" /> It applies only to water at about 15.6 °C and gives acceptable results only with a careful choice of C, which depends on pipe material, age and water quality.<ref name="T-52" /> It is not suitable for C values well below 100.<ref name="T-54">Titus (2002), p. 4-54.</ref> In rough pipes the loss rises with the flow to the power 2 rather than 1.85, which makes high flows in old pipes uncertain.<ref name="T-54" />

Titus compares both methods for 500 gpm (1,893 L/min) through 100 ft (30.5 m) of 4 in. (102 mm) steel pipe.<ref name="T-54" /><ref name="T-56">Titus (2002), p. 4-56.</ref> The more theoretical Darcy–Weisbach equation gives 5.98 psi, while Hazen–Williams gives 10.06 psi with C = 100 and 5.40 psi with C = 140.<ref name="T-56" /> The result therefore depends strongly on the chosen coefficient, whereas the Darcy–Weisbach result is far less sensitive to the assumed roughness.<ref name="T-56" />

A common misconception is that a hydraulically adequate system will suppress any fire. The calculation shows only that water is delivered; how well that water suppresses a fire is judged empirically.<ref name="F-73" /> Another misconception is that every sprinkler opens in a fire. In a wet pipe system, heat opens individual sprinklers, and incident data show that more than half of all fires are controlled or extinguished by one or two sprinklers.<ref name="F-72" /><ref name="H-18">Hopkins et al. (2005), p. 18.</ref> In Australia, the data sheets of the Australian Building Codes Board base their effectiveness estimates on wet pipe systems designed and installed to the Australian Standard AS 2118 and serviced to AS 1851. The edition that applies is the one prescribed by the National Construction Code at the time of installation.<ref name="ABCB-70">Australian Building Codes Board (2020a), Data Sheet C2, p. 70.</ref>

== See also ==
* [[Critical water application rate]]
* [[Dry pipe sprinkler system]]
* [[Deluge system]]
* ESFR sprinkler
* [[Sprinkler head]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association; Society of Fire Protection Engineers.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Titus, J. J. (2002). Hydraulics. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-44–4-71). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Suppression]]

Flashover

2026-11-02T21:32:52Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Flashover''' is the rapid transition in which combustible materials throughout an enclosure ignite or become involved, changing a local fire into a fully developed compartment fire. It is associated with accelerating heat feedback, especially radiation from the hot gas layer and heated boundaries. The transition changes both the scale of burning and the conditions throughout the enclosure.<ref name="VR-4.7">Van Rossum (2027), §4.7.</ref><ref name="Cadorin-Franssen-412">Cadorin and Franssen (2003), p. 412.</ref>

Before flashover, the fire is generally local and fuel controlled. Afterwards, most or all combustible surfaces can be involved and ventilation commonly restricts combustion. This change can produce abundant pyrolysis gases, external flaming and much higher exposure of boundaries and occupants.<ref name="VR-4.7" /><ref name="VR-4.11">Van Rossum (2027), §4.11.</ref>

Flashover is not defined by one universal temperature or heat release rate. Criteria based on upper-layer temperature, received heat flux, lower-zone temperature and fire power describe different measurements and models. Their source and location must accompany any threshold used in an assessment.<ref name="Cadorin-Franssen-412" /><ref name="Babrauskas-3-1">Babrauskas (2002), p. 3-1.</ref>

== Local fire to whole-compartment involvement ==

An early compartment fire can involve one object or a limited number of objects. Heat release depends largely on fuel-gas production while sufficient oxygen remains available. Hot gases rise in a plume and collect near the ceiling, forming an upper layer.<ref name="VR-4.8">Van Rossum (2027), §4.8.</ref><ref name="Quintiere-3-162">Quintiere (2002a), p. 3-162.</ref>

As that layer and surrounding surfaces become hotter, they radiate energy to contents below. Convective heating and direct flame contact can add to this exposure. Additional objects then begin to pyrolyse and ignite, increasing heat release and reinforcing the heating process.<ref name="VR-4.3">Van Rossum (2027), §4.3.</ref><ref name="Cadorin-Franssen-412" />

This feedback makes flashover a transition rather than merely one more object igniting. The enclosure becomes the driver of widespread involvement, and a local-fire description no longer represents the dominant conditions. The whole fuel inventory and its exposure become relevant.<ref name="VR-4.7" /><ref name="Drysdale-1-95">Drysdale (2002), p. 1-95.</ref>
[[File:fse-flashover-v1.svg|thumb|upright=1.5|alt=Local fire under a hot layer compared with widespread fire and external flames after flashover.|Flashover changes local burning into developed compartment fire. Based on Van Rossum (2027), §4.7 and §4.11.]]

[[Fire development stages]] commonly describe this as the change from growth to fully developed fire. The labels are useful for modelling, but the physical transition can be gradual in some scenarios and more abrupt in others. Ignition of every item at exactly the same instant is not required for engineering use of the concept.<ref name="VR-4.11" /><ref name="Cadorin-Franssen-412" />

== Hot gas layer and radiative feedback ==

The [[Hot gas layer]] accumulates combustion products and entrained air transported by the plume. Its temperature and depth influence the radiation received by the floor and lower objects. Heated walls and ceiling add further emission and change the net energy balance.<ref name="VR-6.7">Van Rossum (2027), §6.7.</ref><ref name="VR-5.4">Van Rossum (2027), §5.4.</ref>

Van Rossum uses an upper-layer temperature of 500 °C as one criterion, corresponding to radiation of approximately 20 kW/m² in his calculation. Many materials pyrolyse rapidly at that exposure. The example links layer temperature with floor-received heat flux rather than treating temperature as an isolated number.<ref name="VR-4.7" />

A second criterion in the same source concerns lower-zone temperatures of about 300 to 350 °C. At those conditions, many combustible materials in the lower layer can become hot enough to ignite. This describes a different measurement location from the upper-layer criterion.<ref name="VR-4.7" />

Radiation depends on more than gas temperature. Emissivity, view between surfaces, participating gases and receiver properties affect net exchange. The book's example assumes a view relationship in which upper-layer radiation also reaches floor materials, so the same temperature need not produce the same exposure in every geometry.<ref name="VR-4.7" /><ref name="VR-5.4" />

=== Relating temperature to radiant exposure ===

The Stefan–Boltzmann relation explains why radiant heating rises rapidly with temperature. For an ideal black emitting region and a black receiving surface with an unobstructed full view, net radiation is the difference between their fourth-power emissions. Temperatures in this equation are absolute temperatures in kelvin.<ref name="VR-5.4" />
<math display="block">\dot q^{\prime\prime}_{\mathrm{net}}=\sigma\left(T_h^4-T_s^4\right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot q^{\prime\prime}_{\mathrm{net}}</math> || Net radiant heat flux received || W/m²
|-
| <math>\sigma</math> || Stefan–Boltzmann constant, 5.67 × 10⁻⁸ || W/(m²·K⁴)
|-
| <math>T_h</math> || Absolute temperature of the hot emitting region || K
|-
| <math>T_s</math> || Absolute temperature of the receiving surface || K
|}

Using the 500 °C layer example and a 20 °C receiving surface gives 773.15 K and 293.15 K. Substitution gives approximately 19,800 W/m², or 19.8 kW/m². This explains the approximate 20 kW/m² association used in Van Rossum's introductory discussion.<ref name="VR-4.7" /><ref name="VR-5.4" />

The result depends on the idealised emitting and receiving conditions. A real smoke layer need not behave as a blackbody, and an object may see only part of it. Flames and heated walls can also contribute radiation, while convection adds a separate heat-transfer mechanism.<ref name="VR-5.4" /><ref name="VR-4.7" />

Consequently, the calculation does not establish that every room flashes over at 500 °C. Ignition also depends on the receiving materials and their preceding thermal exposure. The numerical example links temperature to an ideal radiant flux; a flashover criterion additionally defines which transition is being represented and where the temperature is measured.<ref name="VR-4.7" /><ref name="Cadorin-Franssen-412" />

== Flashover criteria ==

[[Flashover criteria]] are measurable conditions used to identify the transition in a test or model. They can include layer temperature, heat flux to fuel, lower-zone temperature and heat release rate. A criterion is a practical indicator of a complex process, not a separate law governing every compartment.<ref name="VR-4.7" /><ref name="Cadorin-Franssen-412" />

Cadorin and Franssen report upper-layer temperatures of 450 to 800 °C across collected studies, with most between 600 and 700 °C, and heat fluxes between 15 and 33 kW/m². They also note that 600 °C and about 20 kW/m² are commonly used. These ranges demonstrate uncertainty and differences between experimental definitions.<ref name="Cadorin-Franssen-412" />
[[File:fse-flashover-v2.svg|thumb|upright=1.5|alt=Temperature range 450 to 800 °C and heat-flux range 15 to 33 kW/m², with common values marked.|Collected flashover criteria and common model values. Based on Cadorin and Franssen (2003), p. 412.]]

Their OZone model uses 500 °C as its default average upper-layer criterion. The authors explain that temperatures near the ceiling can be higher than the volume-averaged layer temperature used by a two-zone model. Comparing a ceiling measurement directly with that average would mix different quantities.<ref name="Cadorin-Franssen-412" />

Heat-release criteria require equal caution. Babrauskas gives roughly 1.5 to 1.75 MW as the range where flashover can be reached for room fires ventilated through one normal-sized door. This example is tied to the test configuration and should not be treated as a universal fire-power threshold.<ref name="Babrauskas-3-1" />

== Fire growth and heat release ==

Heat release rate influences how quickly the plume and upper layer develop. Increasing power can raise gas temperature and radiative feedback, which then accelerates additional ignition. Fire growth and enclosure heating therefore form a coupled process.<ref name="Heskestad-2-2">Heskestad (2002), p. 2-2.</ref><ref name="VR-4.3" />

Design fires sometimes represent growth with a t-squared curve followed by fully developed burning and decay. These simplified curves are modelling choices for evaluation, not predictions of when flashover must occur. Incubation, object-to-object spread and changing combustion efficiency can alter the real sequence.<ref name="IFEG-1.2-29">Australian Building Codes Board et al. (2005), pp. 1.2-29–1.2-30.</ref><ref name="IFEG-2.4-11">Australian Building Codes Board et al. (2005), p. 2.4-11.</ref>

Fuel arrangement affects the transition. Thin or easily ignited objects can become involved earlier, while thick objects can absorb energy internally. Separation and orientation change received radiation and convective exposure, so identical total fire load can produce different development.<ref name="Kanury-2-231">Kanury (2002), pp. 2-231–2-232.</ref><ref name="Quintiere-2-247">Quintiere (2002b), p. 2-247.</ref>

Suppression during growth can prevent the developed stage. Van Rossum notes that active systems commonly intervene before flashover and can interrupt increasing heat release. Flashover is therefore not an inevitable stage of every compartment fire.<ref name="VR-4.11" />

== Rollover and backdraft ==

[[Rollover]] is a separate enclosure-fire term and should not be used interchangeably with flashover. Flashover describes widespread involvement of combustible materials, whereas the present article reserves backdraft for rapid ignition of accumulated combustible gases after oxygen enters. These labels address different mechanisms.<ref name="VR-4.7" /><ref name="VR-4.9">Van Rossum (2027), §4.9.</ref>

[[Backdraft]] requires a fuel-rich atmosphere created under oxygen restriction and a subsequent ventilation and mixing event. Flashover instead concerns the transition to widespread fuel involvement through enclosure heating. One can influence the conditions for the other, but their definitions remain distinct.<ref name="VR-4.9" /><ref name="NUREG-1805-15-4">U.S. Nuclear Regulatory Commission (2005), pp. 15-3–15-4.</ref>

A fully developed fire can have abundant pyrolysis gases and external burning, which makes these distinctions especially important. External flames alone do not identify whether the enclosure underwent flashover, backdraft or another process. The preceding history is needed.<ref name="VR-4.11" /><ref name="Drysdale-1-95" />

== Post-flashover conditions ==

A [[Post-flashover fire]] involves the whole compartment environment and is often ventilation controlled. Limited air supply can restrict internal combustion while pyrolysis continues. Unburnt gases can then burn outside openings after mixing with fresh air.<ref name="VR-4.8" /><ref name="VR-4.11" />

External flaming shifts part of the heat release to facades, adjacent spaces and neighbouring objects. It also means that heat release measured inside the compartment need not equal total heat generated by fuel originating there. System boundaries must be stated in the analysis.<ref name="Drysdale-1-95" />
[[File:fse-flashover-v3.svg|thumb|upright=1.5|alt=Pyrolysis gases leave a hot room and burn outside after mixing with fresh air.|Post-flashover combustion can occur inside and outside the room. Based on Van Rossum (2027), §4.11 and Drysdale (2002), p. 1-95.]]

Gas conditions can become more uniform, motivating one-zone rather than two-zone models. OZone switches between these representations while conserving mass and energy. The switch is a modelling approximation and does not mean that real compartment properties become perfectly uniform.<ref name="Cadorin-Franssen-399">Cadorin and Franssen (2003), pp. 399–400.</ref><ref name="Cadorin-Franssen-400">Cadorin and Franssen (2003), pp. 400–401.</ref>

High gas and surface temperatures can threaten structural elements and separating constructions. Sustained exposure after the transition can be more important for structural assessment than the short growth period. Fire resistance therefore needs the post-flashover temperature-time history.<ref name="Cadorin-Franssen-395">Cadorin and Franssen (2003), pp. 395–396.</ref><ref name="NUREG-1805-F45">U.S. Nuclear Regulatory Commission (2005), p. F-45.</ref>

== Modelling and testing ==

Zone models represent early development with hot and cool layers and developed fire with one mixed zone. Their results depend on the chosen flashover or switch criterion. Different criteria can change when the model transitions and what exposure it predicts.<ref name="Cadorin-Franssen-400" /><ref name="Cadorin-Franssen-412" />

Room-fire tests include enclosure effects that open-burning calorimetry does not capture. Hot-layer radiation and ventilation can change heat release rate significantly. Test enclosure size, openings and fuel arrangement must therefore accompany any reported flashover observation.<ref name="Babrauskas-3-1" /><ref name="Babrauskas-3-2">Babrauskas (2002), p. 3-2.</ref>

The [[Room corner test]] provides a standardised enclosure arrangement for evaluating fire development. Results from such tests belong to their method and cannot be transferred to every room without assessing scale, ventilation and fuel configuration. Flashover criteria should be identified within the test report.<ref name="Babrauskas-3-3">Babrauskas (2002), p. 3-3.</ref>

Glazing and openings can change during the transition. The 2005 International Fire Engineering Guidelines allow time of glass breakage to be estimated from fire severity or, in a simplified method, linked to flashover. Breakage affects both spread and ventilation, so it should not be treated as an isolated visual observation.<ref name="IFEG-1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

== Limits and common misunderstandings ==

Flashover is not a synonym for ignition. Ignition marks the start of self-sustaining combustion, while flashover is a later enclosure-scale transition. A room can have a sustained local fire for a substantial period without reaching flashover.<ref name="Kanury-2-229">Kanury (2002), p. 2-229.</ref><ref name="VR-4.7" />

It is also not the same as a backdraft or smoke explosion. Those events involve rapid combustion of a combustible gas atmosphere, while flashover concerns widespread involvement of fuel through heating. Their timing and required conditions differ.<ref name="VR-4.9" /><ref name="VR-4.10">Van Rossum (2027), §4.10.</ref>

No single temperature defines flashover in every enclosure. Average layer temperature, ceiling temperature, lower-zone temperature and received heat flux are different measurements. Reported thresholds must retain their source and measurement location.<ref name="Cadorin-Franssen-412" /><ref name="VR-4.7" />

flashover is not inevitable. Fuel depletion, suppression, insufficient heat feedback or unsuitable geometry can prevent it. Design scenarios should demonstrate why the transition is expected rather than inserting it automatically.<ref name="VR-4.11" /><ref name="IFEG-1.2-29" />

A criterion map can clarify what a model or test actually measures. Upper-layer average temperature, near-ceiling temperature, lower-zone temperature, received heat flux and total heat release rate occupy different places in the analysis. Treating them as interchangeable thresholds would confuse the evidence for the transition.<ref name="Cadorin-Franssen-412" /><ref name="Babrauskas-3-1" />

The averaging distinction is particularly relevant to two-zone models. Their upper-layer value is an average over the whole layer, not the hottest gas immediately beneath the ceiling. A criterion taken from a ceiling measurement should therefore be evaluated before being applied to that average.<ref name="Cadorin-Franssen-412" /><ref name="VR-9.2">Van Rossum (2027), §9.2.</ref>

Heat-flux criteria also depend on the receiver. View factor, surface orientation, emissivity and the temperature of surrounding surfaces affect net radiation at fuel. Two rooms with the same upper-layer temperature can therefore produce different ignition responses at their contents.<ref name="VR-5.4" /><ref name="Tien-1-75">Tien, Lee, and Stretton (2002), p. 1-75.</ref>

Fire-power criteria belong to their ventilation arrangement. Babrauskas's approximate 1.5 to 1.75 MW example concerns room flashover with one normal-sized door. Larger or smaller openings can change oxygen supply and external burning, so the same power has different implications elsewhere.<ref name="Babrauskas-3-1" /><ref name="Drysdale-1-95" />

Test selection should reflect the stage being examined. Open-burning data can describe early item behaviour without room feedback, while room tests are needed when layer radiation and ventilation alter heat release. Using only open data for a developed [[Compartment fire]] would omit a defining part of the problem.<ref name="Babrauskas-3-1" /><ref name="Babrauskas-3-3" />

Post-flashover analysis should state where combustion occurs. Fuel volatiles can burn inside, outside or in both regions, and external flames can expose facades and neighbouring objects. The model's heat-release boundary must include these locations consistently with the scenario.<ref name="Drysdale-1-95" /><ref name="VR-4.11" />

Opening changes can link several stages. Glass failure can create a new vent and flame path, alter oxygen supply and mark a change in external exposure. Using flashover as a simplified proxy for breakage is a modelling choice from the 2005 guidelines, not a universal physical equivalence.<ref name="IFEG-1.6-7" />

A final sensitivity review can vary layer criterion, fire growth, ventilation and fuel arrangement. This reveals whether the predicted transition is controlled by one assumption and whether the selected model remains valid after it occurs. The resulting time range is more informative than an unjustified single flashover time.<ref name="Cadorin-Franssen-412" /><ref name="VR-1.7">Van Rossum (2027), §1.7.</ref>

The review should also state whether flashover is an input or an output. A model can be told to switch at a selected criterion, while another analysis estimates when that criterion is reached. Confusing these approaches can make a chosen transition look like an independent prediction.<ref name="Cadorin-Franssen-400" /><ref name="Cadorin-Franssen-412" />

Evidence before and after the transition should remain separated. Pre-flashover plume and layer assumptions support local-fire analysis, while post-flashover conditions support developed exposure and external burning. Combining data from both without identifying the transition creates an inconsistent fire history.<ref name="VR-4.8" /><ref name="VR-4.11" />

A clear report therefore gives the selected criterion, its measurement basis and the resulting post-flashover treatment. It also states whether the criterion was varied and what happened to the outcome. This allows flashover to be assessed as an uncertain physical transition rather than an automatic stage label.<ref name="Cadorin-Franssen-412" /><ref name="VR-1.7" />

== See also ==

* [[Thermal radiation]]
* [[Fire spread]]
* [[Fire dynamics]]
* Glass breakage in fire

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Cadorin, J.-F., & Franssen, J.-M. (2003). A tool to design steel elements submitted to compartment fires: OZone V2. Part 1: Pre- and post-flashover compartment fire model. ''Fire Safety Journal, 38'', 395–427.
* Drysdale, D. D. (2002). Thermochemistry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Heskestad, G. (2002). Fire plumes, flame height, and air entrainment. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Kanury, A. M. (2002). Flaming ignition of solid fuels. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Quintiere, J. G. (2002a). Compartment fire modeling. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Quintiere, J. G. (2002b). Surface flame spread. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Tien, C. L., Lee, K. Y., & Stretton, A. J. (2002). Radiation heat transfer. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* U.S. Nuclear Regulatory Commission. (2005). ''Fire dynamics tools: Quantitative fire hazard analysis methods for the U.S. nuclear regulatory commission fire protection inspection program'' (NUREG-1805).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Enclosure Fires]]

Gaseous extinguishing system

2026-11-02T21:32:52Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''gaseous extinguishing system''' is a fixed [[fire suppression system]] that puts out a fire by discharging an [[extinguishing agent]] in gaseous form, usually into a closed room. A gaseous agent stays a gas at normal room temperature and pressure, spreads easily and distributes itself evenly through an enclosure.<ref name="IS-B41">Iqbal and Salley (2004), p. B-41.</ref> The agents fall into two classes: halocarbons, such as Halon 1301 and its replacements, and inert gases, such as nitrogen and mixtures containing argon. [[Carbon dioxide]] is a third, long-established agent.<ref name="IS-B41" /><ref name="DN-173">DiNenno (2002), p. 4-173.</ref>

Carbon dioxide systems are useful where an inert, electrically non-conductive, three-dimensional gas is needed and where clean-up must be minimal. Hazards protected include flammable liquids, electrical equipment such as transformers and switchgear, engines and computer rooms.<ref name="IS-B47">Iqbal and Salley (2004), p. B-47.</ref><ref name="HO-58">Hopkins et al. (2005), p. 58.</ref> An important advantage of gaseous agents is that no cleaning is needed after a release in the absence of a fire; a few minutes of venting is enough.<ref name="IS-B41" /> The protected room must be tight enough to hold the agent, and a halogenated system in most cases has only one chance to put the fire out. Several agents are also dangerous to people at the concentrations needed.<ref name="IS-B46">Iqbal and Salley (2004), p. B-46.</ref><ref name="IS-B49">Iqbal and Salley (2004), p. B-49.</ref>

Halon may contribute to the depletion of the Earth's ozone layer and is therefore considered harmful to the environment.<ref name="NO-F14">Nolan (2000), as cited in Iqbal and Salley (2004), p. F-14.</ref> Production of halons ended in developed countries on 31 December 1993 under the Montreal Protocol. Since then, several clean halocarbon and inert gas alternatives to Halon 1301 have been commercialised.<ref name="DN-173" />

== Agents and how they work ==
Gaseous agents extinguish fires by different mechanisms. Inert gases act mainly by [[oxygen depletion]], while halocarbon agents act largely by absorbing heat, with some chemical effect on the flame reactions.<ref name="IS-B41" /> Inert gases lower the flame temperature below the level needed to sustain the combustion reactions. They do so by reducing the oxygen concentration and by raising the heat capacity of the atmosphere.<ref name="DN-174">DiNenno (2002), p. 4-174.</ref> Adding enough inert gas to bring the oxygen concentration in air below 12 % leads to [[flame extinction]] in flaming fires.<ref name="DN-174" />

Carbon dioxide displaces the normal atmosphere and reduces the oxygen content below the 15 % that a report of the US Nuclear Regulatory Commission (NRC) gives as necessary for a diffusion flame.<ref name="IS-B46" /> Its action is mainly thermophysical: the reacting gases are prevented from reaching a temperature high enough to keep up the free radicals that sustain the flame.<ref name="IS-B46" /> It is colourless, odourless, electrically non-conductive and stored as a liquid. After release it becomes a gas, with some small solid particles, about 50 % heavier than air.<ref name="IS-B46" />

Halon 1301 works chemically. It inhibits the chain reaction of combustion and therefore suppresses a fire very quickly, unlike agents that remove heat or oxygen.<ref name="IS-B42">Iqbal and Salley (2004), p. B-42.</ref> On a weight basis it is about 2.5 times as effective as carbon dioxide.<ref name="IS-B42" /> Its replacements, the halocarbon clean agents, act by a mix of chemical and physical mechanisms. Compounds containing bromine or iodine scavenge flame radicals like Halon 1301, while most others work mainly by extracting heat from the flame zone.<ref name="DN-174" /> Clean agents are defined as extinguishants that vaporise readily and leave no residue.<ref name="DN-173" />

Inert gas agents can also be blends. In World Trade Center Building 7 (WTC 7), a room containing a 6,000 gal fuel oil tank was protected by Inergen, a proprietary mixture of 52 % nitrogen, 40 % argon and 8 % carbon dioxide by volume.<ref name="MA-73">McAllister et al. (2008), p. 73.</ref><ref name="HO-71">Hopkins et al. (2005), p. 71.</ref> A small amount of carbon dioxide in an inert gas mixture appears to reduce the effects of low oxygen on people substantially.<ref name="DN-184">DiNenno (2002), p. 4-184.</ref>

== System types and components ==
A gaseous system can protect a room or an object. In total flooding, the whole enclosure is filled with the agent to a prescribed concentration, through nozzles placed to give a uniform concentration everywhere.<ref name="IS-B47" /> Local application directs the agent at a localised hazard without filling the enclosure. It suits surface fires in flammable liquids, gases and very shallow solids, for example spray booths, printing presses and rolling mills.<ref name="IS-B47" /> Total flooding is the most common method for halogenated agents.<ref name="IS-B43">Iqbal and Salley (2004), p. B-43.</ref>

[[File:fse-gaseous-extinguishing-system-v1.svg|thumb|upright=1.5|alt=Cross-section of a room with agent cylinders, pipework to ceiling nozzles, detectors, control panel, warning device and closed door.|Main parts of a total flooding gaseous extinguishing system. Based on Iqbal and Salley (2004), pp. B-47 to B-48, Hopkins et al. (2005), p. 58 and DiNenno (2002), p. 4-187.]]

The agent is stored in containers and released through pipes and nozzles. Carbon dioxide is held either in high-pressure steel cylinders at room temperature, at about 850 psi (5.9 MPa) at 21 °C, or in refrigerated low-pressure vessels at about −18 °C and 300 psi (2.1 MPa).<ref name="IS-B48">Iqbal and Salley (2004), p. B-48.</ref> Cylinders hold 50 to 100 lb (23 to 45 kg) of agent each, so most high-pressure systems use several cylinders manifolded together.<ref name="IS-B48" /> Halon 1301 is stored as a liquid under pressure and released as a vapour.<ref name="IS-B42" />

Detection starts the system. In the World Trade Center towers, smoke and heat detectors actuated the release of carbon dioxide into the protected computer rooms.<ref name="HO-58" /> The Inergen system in WTC 7 was to be actuated by two heat detectors at the ceiling above the fuel tank.<ref name="HO-71" /> In the United States, NFPA 12A (1997) of the National Fire Protection Association (NFPA) required automatic actuation of Halon 1301 total flooding systems for ordinary combustible materials, unless the authority having jurisdiction accepted manual actuation.<ref name="IS-B43" />

The discharge must be fast. A Halon 1301 discharge must be substantially complete in a nominal 10 seconds, to prevent the fire from becoming deep-seated, to limit decomposition products and to disperse the agent throughout the enclosure.<ref name="IS-B43" /> For halocarbon clean agents, the maximum discharge time is also 10 seconds. For inert gases, the requirement is currently 60 seconds, and longer times are typically used in Europe.<ref name="DN-189">DiNenno (2002), p. 4-189.</ref> For carbon dioxide on deep-seated fires, NFPA 12 requires the design concentration within 7 minutes and 30 % within 2 minutes. For surface fires, it requires the design concentration within 1 minute.<ref name="IS-B49" />

== Design concentration and agent quantity ==
The design starts from the concentration needed to extinguish the fuel. For halocarbon agents, the minimum extinguishing concentration is measured with a laboratory cup burner and then checked in full-scale approval tests.<ref name="DN-188">DiNenno (2002), p. 4-188.</ref> Halon 1301 design concentrations were historically set at the cup burner value plus a 20 % safety factor, with a minimum of 5 %.<ref name="DN-187">DiNenno (2002), p. 4-187.</ref> Full-scale tests later suggested that 20 % might be insufficient. The first edition of ISO 14520-1, a standard of the International Organization for Standardization (ISO), therefore required a safety factor of at least 30 %. NFPA 2001 requires 30 % for Class B hazards and for systems actuated only by hand.<ref name="DN-188" />

Carbon dioxide needs much higher concentrations. NFPA 12 sets a minimum of 34 % by volume for surface fires such as liquid fuels and 50 % for deep-seated hazards such as electrical equipment. Bulk paper requires 65 % and some special hazards 75 %.<ref name="IS-B47" /> Most surface burning stops at about 20 % carbon dioxide or less, so these values include a large margin of safety.<ref name="IS-B47" /> For inert gases, IG-541 is used at a minimum design concentration of 37.5 % where ordinary combustible materials are involved.<ref name="DN-189" />

[[File:fse-gaseous-extinguishing-system-v2.svg|thumb|upright=1.5|alt=Bar chart of design concentrations: Halon 1301 5 %, HFC-227ea 8.6 %, CO2 surface fires 34 %, IG-541 37.5 %, CO2 deep-seated 50 %; line at 9 %.|Minimum design concentrations of gaseous agents, with the carbon dioxide level above which most people lose consciousness. Based on DiNenno (2002), pp. 4-176 to 4-189 and Iqbal and Salley (2004), pp. B-47 and B-49.]]

Once the design concentration is known, the quantity of agent follows.<ref name="DN-189" /> The protected volume is the net volume of the space.<ref name="DN-189" /> For a halocarbon agent, the mass needed to reach the design concentration in a closed room depends on the room volume and the specific volume of the agent vapour:<ref name="DN-189" />

<math display="block">w = \frac{V}{S} \cdot \frac{C}{100 - C}</math>

{| class="wikitable"
|+ Symbols
! Symbol !! Description !! Unit
|-
| <math>w</math> || mass of agent required || kg
|-
| <math>V</math> || net volume of the protected space || m³
|-
| <math>S</math> || specific volume of the agent vapour at the minimum expected room temperature, <math>S = k_1 + k_2 T</math> || m³/kg
|-
| <math>C</math> || design concentration || % by volume
|}

The factor C/(100 − C) assumes that the agent and air mixture that escapes during discharge is well mixed at concentration C. The formula makes no allowance for leakage after discharge.<ref name="DN-189" /> For inert gases, a logarithmic version is used, which is identical to the expression for carbon dioxide and assumes that the displaced atmosphere is freely vented.<ref name="DN-189" /> The minimum room temperature is used because a colder room needs more agent.<ref name="DN-189" />

=== Worked example ===
HFC-227ea is one of the halocarbon agents acceptable for normally occupied areas.<ref name="DN-184" /> Its cup burner extinguishing concentration for n-heptane is 5.8 to 6.6 %.<ref name="DN-176">DiNenno (2002), p. 4-176.</ref> With the upper value and the 30 % safety factor for Class B hazards, the design concentration is 1.3 × 6.6 ≈ 8.6 %.<ref name="DN-188" /> This lies below the no observed adverse effect level (NOAEL) of HFC-227ea, which is 9.0 %.<ref name="DN-183">DiNenno (2002), p. 4-183.</ref>

For a minimum room temperature of 20 °C, the constants for HFC-227ea give S = 0.1269 + 0.0005 × 20 = 0.137 m³/kg.<ref name="DN-189" /> Assume a closed room with a net volume of 100 m³. The agent mass is then:

<math display="block">w = \frac{100}{0.137} \cdot \frac{8.6}{100 - 8.6} \approx 69\ \mathrm{kg}</math>

If the room can cool to 0 °C, S falls to 0.127 m³/kg and the required mass rises to about 75 kg. The calculation gives only the agent for the design concentration. Leakage, unclosable openings and the required hold time must be assessed separately.<ref name="DN-187" /><ref name="DN-189" />

== Enclosure integrity and hold time ==
The enclosure is a critical part of the system. It must be tight enough to prevent preferential loss of agent during discharge and excessive loss of the agent and air mixture afterwards, so that the concentration is held long enough.<ref name="DN-187" /> Doors, ventilation fans and other openings must be secured before discharge. Systems should not be installed in rooms with unclosable openings unless test data show that adequate concentrations can be reached.<ref name="DN-187" />

The density of the agent and air mixture is the driving force for leakage in still air.<ref name="DN-198">DiNenno (2002), p. 4-198.</ref> Halon 1301 is about five times as heavy as air, so the agent and air mixture flows out through low openings while fresh air enters at the top.<ref name="IS-B45">Iqbal and Salley (2004), p. B-45.</ref> An interface forms and descends; the space above it is unprotected, while the space below keeps the original concentration.<ref name="IS-B46" /> The concentration at the height of the highest combustible therefore matters most.<ref name="IS-B45" />

[[File:fse-gaseous-extinguishing-system-v3.svg|thumb|upright=1.5|alt=Two room sections: just after discharge the room is uniformly filled; later, agent leaks out at the bottom, air enters at the top and an interface descends.|Leakage of a heavy agent and air mixture from an enclosure: the protected zone shrinks as the interface descends. Based on Iqbal and Salley (2004), pp. B-45 to B-46 and DiNenno (2002), p. 4-198.]]

If the extinguishing atmosphere is lost too quickly, glowing embers may reignite when air returns. Openings must then be closed, or extra agent must be discharged.<ref name="IS-B48" /> For rotating electrical equipment such as generators, an extended discharge at a reduced rate maintains the concentration while leakage continues.<ref name="IS-B48" />

Deep-seated fires need long soaking times. If a 5 % concentration of Halon 1301 does not extinguish a fire within 10 minutes, NFPA classes it as deep-seated.<ref name="IS-B43" /> Visible flames on solid materials go out at once, but glowing combustion can continue inside the material.<ref name="IS-B43" /> In full-scale tests on cable trays, a 6 % Halon 1301 concentration held for 10 minutes extinguished fires in unqualified cables, while qualified cables needed 15 minutes.<ref name="IS-B44">Iqbal and Salley (2004), p. B-44.</ref> For carbon dioxide on deep-seated fires, the design concentration must be held for at least 20 minutes.<ref name="IS-B49" />

== Safety of people ==
Several gaseous agents are dangerous at the concentrations needed to put out a fire. Carbon dioxide replaces the oxygen in the air; harmful effects become noticeable at 6 to 7 %, and most people lose consciousness quickly above 9 %.<ref name="IS-B49" /> Since the minimum extinguishing concentrations exceed 9 %, every carbon dioxide system needs adequate safety precautions.<ref name="IS-B49" /> According to the NRC report, carbon dioxide should not be used in occupied areas unless the documented fire risk is greater than the risk to personnel and no viable alternative exists.<ref name="IS-B50">Iqbal and Salley (2004), p. B-50.</ref> In the United States, the Occupational Safety and Health Administration (OSHA) requires a predischarge alarm with enough time delay for people to leave when the design concentration exceeds 4 %.<ref name="IS-B50" />

Accidents show why these rules exist. A US Environmental Protection Agency review found 51 incidents from 1975 onwards, with 72 deaths and 145 injuries from discharges of carbon dioxide systems. All deaths attributed to carbon dioxide were caused by asphyxiation.<ref name="IS-B50" /> In 1998, a total flooding system discharged without warning during maintenance at a US national laboratory, killing one worker.<ref name="IS-B51">Iqbal and Salley (2004), p. B-51.</ref> In 1992, a test discharge at the Duane Arnold nuclear plant let carbon dioxide leak into the control room. The oxygen level fell to 17 % at chest height and 15 % at floor level, below the plant's criterion of 19.5 %.<ref name="IS-B52">Iqbal and Salley (2004), p. B-52.</ref>

Clean agents are limited by toxicity data. For halocarbons, the NOAEL is the highest concentration at which no adverse effect on the heart was observed in animal tests. The lowest observed adverse effect level (LOAEL) is the lowest concentration at which an effect was measured.<ref name="DN-183" /> Where no further modelling data exist, the design concentration in occupied areas must be below the NOAEL. On this basis, HFC-227ea, HFC-23 and FC-3-1-10 are acceptable for normally occupied areas.<ref name="DN-184" />

Inert gases are physiologically inert; their hazard is the low oxygen concentration that they create. Exposure is limited to 5 minutes up to 43 % agent (12 % residual oxygen), to 3 minutes between 43 and 52 %, and to 30 seconds above 52 %.<ref name="DN-184" /> Keeping a room permanently at a reduced oxygen level is a different approach, described under oxygen reduction system.

[[File:fse-gaseous-extinguishing-system-v4.svg|thumb|upright=1.5|alt=Step chart of allowed exposure time against inert gas concentration: 5 min up to 43 %, 3 min from 43 to 52 %, 30 s above 52 %.|Exposure time limits for inert gas agents, with the corresponding residual oxygen concentration. Based on DiNenno (2002), p. 4-184.]]

== Reliability and performance ==
Gaseous systems are credited with a high, but not perfect, reliability. For fire risk studies of United States nuclear power plants, recommended unreliability values are 0.04 for carbon dioxide systems and 0.05 for halon systems.<ref name="PA-P6">Parkinson et al. (1994), as cited in Nowlen et al. (2005b), p. P-6.</ref> For a Halon 1301 system in a computer facility, Steciak and Zalosh estimated the probability that the system fails to protect against fire damage. They found 0.05 for an electrical cable fire, 0.13 for a waste paper fire and 0.08 for a fire outside the protected room.<ref name="SZ">Steciak and Zalosh (1992), as cited in National Research Council of Canada et al. (2005), p. 3.7-3.</ref>

A halogenated agent system in most cases has only a single chance to extinguish a fire. The NRC report therefore recommends testing systems and measuring concentrations at several heights, at least at the highest combustible.<ref name="IS-B46" /> Field experience includes both successes and failures. At Rancho Seco in 1984, a hydrogen fire at the main generator was extinguished by the fixed automatic carbon dioxide system within 14 minutes.<ref name="IS-H12">Iqbal and Salley (2004), p. H-12.</ref> At Millstone Unit 3 in 1999, an inadvertent carbon dioxide discharge in a cable spreading room migrated to other rooms. The control room reached more than 17,000 ppm, and operators wore breathing apparatus for about six hours.<ref name="IS-B51" />

Engineering analysis of these systems relies on standards rather than general methods. The International Fire Engineering Guidelines state that calculations for inert and chemical gaseous systems should be based on their design specifications and on standards such as AS 4214 and NFPA 2001. These calculations are not covered by the guidelines themselves.<ref name="IFEG-2.7-8">National Research Council of Canada et al. (2005), p. 2.7-8.</ref>

== See also ==
* [[Water mist system]]
* [[Extinguishing mechanisms]]
* [[Deluge system]]

== Notes ==
<references />

== References ==
* DiNenno, P. J. (2002). Halon replacement clean agent total flooding systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-173–4-200). National Fire Protection Association; Society of Fire Protection Engineers.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* McAllister, T. P., Gann, R. G., Averill, J. D., Gross, J. L., Grosshandler, W. L., Lawson, J. R., McGrattan, K. B., Pitts, W. M., Prasad, K. R., Sadek, F. H., & Nelson, H. E. (2008). ''Structural fire response and probable collapse sequence of World Trade Center Building 7'' (NIST NCSTAR 1-9, Vols. 1–2). National Institute of Standards and Technology.
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Nowlen, S. P., Najafi, B., Wyant, F. J., Forester, J., Kazarians, M., Kolaczkowski, A., Joglar, F., Funk, D., Hannaman, G., & Anoba, R. (2005b). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Vol. 2. Detailed methodology'' (NUREG/CR-6850; EPRI 1011989). Electric Power Research Institute; U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research.

[[Category:Fire Suppression]]

High-rise building

2026-11-02T21:32:52Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''high-rise building''' is, in fire protection engineering, a building that is nominally taller than about 25 m and from which occupants cannot be rescued from the outside during a fire.<ref name="NIST08-xxxv">National Institute of Standards and Technology (2008), p. xxxv.</ref> Because rescue from outside is not possible, occupants must leave by the stairs, and firefighters often have to climb the same stairs to reach the fire.<ref name="NIST05-169">National Institute of Standards and Technology (2005), p. 169.</ref> Height changes several parts of the fire problem at once. The [[stack effect]] drives smoke up through stairs and lift shafts to floors far from the fire.<ref name="Klo-276">Klote (2002), p. 4-276.</ref>

A full evacuation can take a long time, so many high-rise buildings use a staged or [[phased evacuation]] in which the floors most at risk leave first.<ref name="IFEG-2.8-2">National Research Council of Canada et al. (2005), p. 2.8-2.</ref> Firefighters who climb with breathing apparatus need about 2 min per floor, which has led to calls for protected lifts for the fire service.<ref name="NIST05-170">National Institute of Standards and Technology (2005), p. 170.</ref><ref name="NIST05-218">National Institute of Standards and Technology (2005), p. 218.</ref> The 2001 collapse of World Trade Center Building 7, a 47-storey office building, was the first known total collapse of a tall building primarily due to fires.<ref name="NIST08-xxxv" />

== Definition and characteristics ==
The investigation of World Trade Center Building 7 explains two terms that are often mixed up. Architects and structural engineers speak of a ''tall building'' when it is taller than its surroundings, slender, or needs technologies such as wind bracing, and is nominally taller than 15 to 20 storeys. Fire protection engineers use ''high-rise building'' for buildings nominally taller than 25 m (75 ft) from which external rescue from fires is not possible.<ref name="NIST08-xxxv" /> The fire definition therefore depends on whether rescue from outside is possible, not on the shape of the building.

The main consequence of height is that the risk to an occupant grows with the floor on which that person is. The National Institute of Standards and Technology (NIST) notes that fire rating requirements in the United States were originally developed from experience with buildings of less than 20 storeys. For tall buildings, the consequences of a given threat are more severe for an occupant on an upper floor than on the first floor. With lifts out of service, both full evacuation from upper floors and fire service access to those floors take much longer.<ref name="NIST05-208">National Institute of Standards and Technology (2005), p. 208.</ref>

The fire load in a high-rise office floor is not unusual in itself. A table of fire load densities from Swiss studies of 1967 to 1969, reproduced in the International Fire Engineering Guidelines, gives an average of 800 MJ/m² for a high-rise office building.<ref name="IFEG-3.4-2">National Research Council of Canada et al. (2005), p. 3.4-2.</ref><ref name="IFEG-3.4-5">National Research Council of Canada et al. (2005), p. 3.4-5.</ref> Some performance-based methods do not cover such buildings. In New Zealand, Verification Method C/VM2 (second edition, 2025) lists tall buildings of more than 60 m or 20 storeys as outside its scope, together with buildings that need a managed evacuation.<ref name="MBIE-6">Ministry of Business, Innovation and Employment (2025b), p. 6.</ref>

== Smoke movement and the stack effect ==
Smoke spreads through a building under several driving forces: expansion of heated gases, the stack effect, wind, building services and pressure differences caused by temperature differences.<ref name="VR-6.6">Van Rossum (2027), §6.6.</ref> In tall buildings, smoke movement can be dominated by the stack effect.<ref name="Klo-276" /> When it is cold outside, the warmer and lighter air inside rises through shafts such as stairs, lift shafts and service ducts. This is called the normal stack effect. When the outside air is warmer than the inside air, the flow in the shafts reverses and runs downwards.<ref name="Klo-274">Klote (2002), p. 4-274.</ref>

The size of the pressure difference depends on the difference in density between the cold and warm air columns and on the height considered.<ref name="VR-3.2">Van Rossum (2027), §3.2.</ref> Klote gives a relation for the pressure difference between a shaft and the outside, at standard atmospheric pressure. It uses absolute temperatures and the height above the ''[[neutral plane]]'', the level where the pressure inside equals the pressure outside:<ref name="Klo-274" /><ref name="Klo-275">Klote (2002), p. 4-275.</ref>

<math display="block">\Delta P = K_s \left( \frac{1}{T_0} - \frac{1}{T_I} \right) h</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\Delta P</math> || pressure difference between the shaft and the outside || Pa
|-
| <math>K_s</math> || coefficient, 3460 in SI units || Pa·K/m
|-
| <math>T_0</math> || absolute temperature of the outside air || K
|-
| <math>T_I</math> || absolute temperature of the air inside the shaft || K
|-
| <math>h</math> || distance above the neutral plane || m
|}

Above the neutral plane the shaft pressure is higher than outside, and below it the shaft pressure is lower. If air leakage paths are fairly uniform over the height, the neutral plane lies near mid-height. Vented shafts and other uneven leakage can move it considerably. In unusually airtight buildings with exterior stairs, reverse stack effect has even been seen in cold weather.<ref name="Klo-275" /> The relation describes the undisturbed building; the shape and position of openings, flow resistance, wind and mechanical ventilation all change the real pressure distribution.<ref name="VR-3.2" />

[[File:fse-high-rise-building-v1.svg|thumb|upright=1.5|alt=Two building sections with a central shaft: in cold weather air rises in the shaft, in warm weather it falls; a dashed neutral plane at mid-height.|Air movement caused by the normal stack effect (left, cold outside) and the reverse stack effect (right, warm outside). Based on Klote (2002), pp. 4-274–4-275.]]

Klote's worked example is a building 60 m tall with the neutral plane at mid-height, an outside temperature of −18 °C and an inside temperature of 21 °C. At the top, the shaft is 55 Pa above the outside pressure, and at the bottom it is 55 Pa below it.<ref name="Klo-275" /> A recalculation in SI units gives 1.80 Pa per metre and 54 Pa at 30 m above the neutral plane; Klote's 55 Pa (0.22 in. of water) follows from the rounded imperial temperatures. On a mild winter day of 0 °C outside, the same building gives about 27 Pa. A summer day of 30 °C with 21 °C inside gives about −10 Pa, a reverse stack effect. These are of the same order as the 13 Pa that Klote calculates for the buoyancy of an 800 °C fire room, 1.52 m above its neutral plane.<ref name="Klo-276" />

[[File:fse-high-rise-building-v2.svg|thumb|upright=1.5|alt=Line chart of pressure difference against height in a 60 m building: straight lines through zero at 30 m for three outside temperatures.|Pressure difference between a shaft and the outside in a 60 m building with the neutral plane at mid-height and 21 °C inside, for three outside temperatures. Based on Klote (2002), pp. 4-274–4-275.]]

The stack effect can carry smoke far from the fire. With a fire below the neutral plane, smoke moves with the building air into the shafts and up them, and flows out onto upper floors above the neutral plane. If leakage between floors is small, the floors below the neutral plane apart from the fire floor stay relatively free of smoke, until the smoke production exceeds what the stack flows can carry. Smoke from a fire above the neutral plane is carried to the outside through openings in the facade.<ref name="Klo-276" /> Hot smoke can also rise through buoyancy against a reverse stack effect.<ref name="Klo-276" />

Wind adds to these pressures. If a window of the fire room breaks on the windward side, the wind forces smoke through the fire floor and even to other floors, endangering occupants and hampering firefighting. A broken window on the leeward side tends to vent the smoke instead.<ref name="Klo-277">Klote (2002), p. 4-277.</ref> Kandola points out that a pressurisation system in a high-rise building must account for wind-induced pressures, or it may create overpressure that prevents escape or underpressure that makes it ineffective.<ref name="Kan-24">Kandola (2002), p. 1-24.</ref> In cold weather, a broken window on a lower fire floor also increases the stack effect pressures.<ref name="Klo-286">Klote (2002), p. 4-286.</ref>

== Evacuation strategies ==
In multi-storey office buildings, Proulx distinguishes two types of evacuation. An ''uncontrolled total evacuation'' sends everybody to the stairs at the same time. A ''controlled selective evacuation'' clears floors in a planned order and needs a voice communication system to manage it.<ref name="Pro-355">Proulx (2002), p. 3-355.</ref> The International Fire Engineering Guidelines describe the same idea. In high-rise buildings with suitable warning and intercommunication systems, trained staff may manage the evacuation, with floors furthest from the fire first put on alert and evacuated progressively only if the fire keeps developing.<ref name="IFEG-2.8-2" />

Canadian drills show how the two approaches compare. Consider a 15-storey office building with 70 people per floor and two stairs 1,120 mm wide. A total evacuation then gives a flow of about one person per second per exit and a descent speed of 3.6 floors per minute. In both strategies, about 9 min were needed to move everybody below the presumed fire floor. The selective evacuation moved 490 people to safety in that time, while the total evacuation brought all 980 occupants to the ground.<ref name="Pro-355" />

[[File:fse-high-rise-building-v3.svg|thumb|upright=1.5|alt=Two time-floor diagrams of a 15-storey building: all floors leave at once (left); the fire floor and floors above leave in sequence (right).|Schematic movement of the last person leaving each floor in an uncontrolled total evacuation (left) and a controlled selective evacuation with a fire on the 10th floor (right). Based on Proulx (2002), p. 3-355.]]

In the total evacuation, however, people from the most threatened floors would queue, and stair doors opened on the fire floor would let smoke into the stairs above it.<ref name="Pro-356">Proulx (2002), p. 3-356.</ref> On the other hand, a total evacuation is simple and needs no costly systems or training, whereas a controlled evacuation may delay the moment at which occupants who should leave are told to do so.<ref name="Pro-356" /> In a real fire, delays are longer, smoke may block exits and occupants above the fire floor may be unable to leave, which can change the total evacuation time entirely.<ref name="Pro-358">Proulx (2002), p. 3-358.</ref>

A controlled evacuation depends on clear communication. In a 1971 drill in a 21-storey office building in Ottawa, the planned sequence cleared the fire floor first and then the floors above it from the top down. The first public address announcement came almost 3 min late and was ambiguous, and as many as 350 people left their floors before their turn.<ref name="Pro-358" /> The World Trade Center towers used prepared announcements from a Fire Command Desk in each lobby, asking occupants to wait until their floor number was called.<ref name="NIST05-60">National Institute of Standards and Technology (2005), p. 60.</ref> In Australia, the 2020 data sheets for the Fire Safety Verification Method note that alarm systems for phased evacuation commonly have an alert tone and an evacuation tone. Where alarms to some areas are delayed, the delay must be included in the analysis.<ref name="ABCB-243">Australian Building Codes Board (2020a), p. 243.</ref>

The scale of a full evacuation is shown by the NIST simulations of the World Trade Center towers. A phased evacuation of 600 occupants to three floors below the fire floor took 3.5 to 4 min without delay and 11 to 11.5 min with random delays of up to 10 min.<ref name="Ave-160">Averill et al. (2005), p. 160.</ref> A full evacuation of a fully occupied tower of 19,800 people took about 112 min in the buildingEXODUS model, with each extra thousand occupants adding 5.2 min. NIST estimated that such an evacuation on the day of the attacks would have taken over 3 hours.<ref name="Ave-162">Averill et al. (2005), p. 162.</ref> About 87 % of the estimated 17,400 occupants of the towers evacuated successfully, and 99 % of those below the impact floors.<ref name="NIST05-xxxviii">National Institute of Standards and Technology (2005), p. xxxviii.</ref><ref name="NIST05-xxxviii">National Institute of Standards and Technology (2005), p. xxxviii.</ref> NIST recommended that tall buildings be designed for a timely full evacuation, with stairs wide enough for firefighters moving up against the flow.<ref name="NIST05-215">National Institute of Standards and Technology (2005), p. 215.</ref>

[[File:fse-high-rise-building-v4.svg|thumb|upright=1.5|alt=Horizontal bars: phased evacuation of 600 people 11 min, full evacuations of 8,800, 19,800 and 25,500 people 55, 112 and 142 min.|Simulated evacuation times for a World Trade Center tower: phased evacuation of the floors at risk compared with full building evacuations (models with delays of up to 10 min). Based on Averill et al. (2005), pp. 160–162.]]

Each tower had three stairs, two 44 in. (1.12 m) wide and one 56 in. (1.42 m) wide, for up to 365 people per floor. Neither the 1968 New York City Building Code nor the more recent codes that NIST compared made the number and width of stairs depend on the number of storeys.<ref name="NIST05-58">National Institute of Standards and Technology (2005), p. 58.</ref> People with reduced mobility need other solutions, and the use of refuges and lifts for their evacuation is a growing area of research.<ref name="IFEG-2.8-2" /> Evacuation models increasingly allow lifts to be used for escape.<ref name="VR-8.3">Van Rossum (2027), §8.3.</ref>

== Smoke control in stairs and shafts ==
Movement through smoke is common in high-rise fires. In the 1993 bombing of the World Trade Center, 94 % of the occupants of Tower 1 moved through smoke. In two high-rise residential fires, about 96 % of the occupants above the fire floor did so. Proulx explains that repeated opening of doors on the fire floor and on upper floors lets smoke into the stairs, even when they are pressurised. In that sense, the stairs of a high-rise building may be the most dangerous place in a fire after the room of origin and the fire floor.<ref name="Pro-362">Proulx (2002), p. 3-362.</ref>

[[Stair pressurisation]] aims to keep a stair free of smoke by supplying air so that it is at a higher pressure than the fire floor. Its main goal is a smoke-free escape route, and a secondary goal is a smoke-free staging area for firefighters. Air may be injected at one point, usually the top, or at several points over the height. In tall stairs, a single injection point can fail when a few doors near it are open, because all the air escapes there.<ref name="Klo-286" /> Dividing the stair into compartments is an alternative, but it suits only buildings with a staged evacuation, since open doors between compartments cancel the effect.<ref name="Klo-287">Klote (2002), p. 4-287.</ref> The number of doors that will be open at once also depends on the strategy: in a densely occupied building with a total evacuation, all doors may be open together.<ref name="Klo-286" />

Klote's design example for a 20-storey stair shows the role of temperature. With −10 °C outside and 21 °C in the stair, the temperature factor is 1.39 Pa per metre. A pressure difference of 20 Pa at the bottom of the stair grows to 106 Pa at the top. About 3.9 m³/s of supply air is needed, and 6.5 m³/s if the leakage area around the doors is larger than assumed.<ref name="Klo-288">Klote (2002), p. 4-288.</ref> Because the leakage areas are difficult to estimate and control, Klote mentions fans with adjustable supply as one way to correct the airflow after installation.<ref name="Klo-288" />

Lift shafts are a second vertical route. Using lift shafts as smoke shafts prevents their use for evacuation and often spreads smoke to floors far from the fire.<ref name="Klo-278">Klote (2002), p. 4-278.</ref> The MGM Grand Hotel fire in Clark County, Nevada, in 1980 stayed on the casino level. Its heat and smoke, however, spread through seismic joints, lift shafts and stairs to the residential floors above.<ref name="Bry-326">Bryan (2002), p. 3-326.</ref> Of the 85 fatalities, most were found between the 20th and 25th floors, including 9 people in stairs and 5 in lifts.<ref name="Bry-326" /> The lifts had no special smoke protection and were one of the main paths of smoke to the upper floors.<ref name="Klo-288" />

== Firefighting and water supply ==
Fighting fires on the upper floors of tall buildings is not the same as in buildings less than about 30 m (100 ft) high.<ref name="NIST05-169" /> In the World Trade Center, responders without breathing apparatus climbed at about 1.4 min per floor, and firefighters with protective clothing, breathing apparatus and equipment at about 2 min per floor. Evacuees coming down, including people with disabilities, slowed them further in the 44 in. stairs.<ref name="NIST05-170" /> At 2 min per floor, reaching the 60th floor from the ground would take about two hours. NIST found that climbing more than 10 to 12 floors makes it difficult to start aggressive firefighting and rescue at once.<ref name="NIST05-219">National Institute of Standards and Technology (2005), p. 219.</ref>

For this reason NIST recommended fire-protected and structurally hardened lifts in tall buildings. These would give emergency responders timely access and allow the evacuation of occupants with reduced mobility, and they would be reserved for responders during emergencies.<ref name="NIST05-218" /> Lifts of this kind for fire service use are described under [[firefighting lift]]. Rescue by helicopter is not a general alternative. At the MGM Grand Hotel, about 300 guests were evacuated by helicopter and the fire department rescued about 900 others.<ref name="Bry-327">Bryan (2002), p. 3-327.</ref> In the World Trade Center, the New York police and fire departments did not consider roof rescue a viable strategy for a general evacuation.<ref name="NIST05-169" />

Firefighting water must be brought to the upper floors through vertical pipes, called standpipes in the World Trade Center reports; such systems are described under [[dry and wet risers]]. Each World Trade Center tower had an alarm system, automatic sprinklers, a standpipe system and a smoke venting system.<ref name="NIST05-61">National Institute of Standards and Technology (2005), p. 61.</ref> Each tower also had six storage tanks of 5,000 gal (about 19 m³), three on the 110th floor and one each on the 20th, 41st and 75th floors. Water could flow by gravity to the sprinklers, building staff could start pumps, and the fire department could add water through fire department connections.<ref name="NIST05-62">National Institute of Standards and Technology (2005), p. 62.</ref> Although there were redundant vertical supply pipes, each floor had only one connection to its sprinklers.<ref name="NIST05-63">National Institute of Standards and Technology (2005), p. 63.</ref> The standpipes stood in the stairs, so where stairs were close together the spacing between standpipes exceeded the 140 ft (43 m) maximum of the 1968 New York City code.<ref name="Lew-154">Lew et al. (2005), p. 154.</ref>

The reliability of [[Sprinkler system|automatic sprinklers]] has been studied for this building type. In Australia, the 2020 data sheets summarise a fault tree study of wet-pipe sprinkler systems in Australian high-rise office buildings. The general sprinkler reliability of 90 % used in the data sheets lies within the range calculated for these buildings.<ref name="ABCB-81">Australian Building Codes Board (2020a), p. 81.</ref>

== Structural fire resistance and collapse ==
High-rise buildings in the United States are designed to withstand a sizeable fire and remain standing. Their elements receive fire resistance ratings in hours from standard furnace tests. These ratings are relative: they do not mean that a structure will last that long in a real fire, which may be more or less severe than the test.<ref name="NIST05-11">National Institute of Standards and Technology (2005), p. 11.</ref>

World Trade Center Building 7 shows what can happen when this protection is overwhelmed. Debris from the collapse of the north tower ignited fires on at least 10 floors, and the fires on six floors grew and burned until the collapse almost seven hours later. Their growth and spread were consistent with ordinary office contents fires. Had the sprinkler system had a water supply and operated as designed, the fires would likely have been controlled and the collapse prevented.<ref name="NIST08-xxxv" /><ref name="NIST08-xxxvi">National Institute of Standards and Technology (2008), p. xxxvi.</ref>

Local fire damage, made worse by the thermal expansion of long-span floors, led to a cascade of local floor failures, which left a critical interior column unsupported over nine storeys. Its buckling started a [[progressive collapse]], in which local damage spreads from element to element until the whole structure or a large part of it falls.<ref name="NIST08-xxxvi" /> NIST concluded that structures must be designed for situations where sprinklers are absent, do not work or are overwhelmed.<ref name="NIST08-xxxvi" />

Fire can also spread vertically outside the building. The Australian data sheets warn that a phased evacuation strategy may be sensitive to rapid fire spread to several floors over the facade, a [[facade fire]], and that this scenario may need its own evaluation. The evacuation plan should then describe what happens when a fire spreads to several floors at once.<ref name="ABCB-250">Australian Building Codes Board (2020a), p. 250.</ref>

== Limitations ==
Much of the detailed knowledge about high-rise fires comes from a few cases. The World Trade Center reports describe one event with unusual causes, and the evacuation models NIST used had not been validated for buildings as tall as 110 storeys.<ref name="Ave-160" /> The stack effect relation assumes uniform leakage and a known neutral plane, and the real distribution of pressures depends on openings, wind and ventilation systems.<ref name="Klo-275" /><ref name="VR-3.2" /> Drill data, such as the Canadian studies, describe evacuations without smoke, which may differ greatly from a real fire.<ref name="Pro-358" /> A common misconception is that a total evacuation is always the safest choice. The drill data show that it can expose people on the most threatened floors to queues and smoke in the stairs, while a phased approach depends on reliable communication and trained staff.<ref name="Pro-356" /><ref name="Pro-358" />

== See also ==
* [[Fire service access]]
* [[Stay-put strategy]]
* [[Evacuation lift]]
* Mass timber

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Averill, J. D., Mileti, D. S., Peacock, R. D., Kuligowski, E. D., Groner, N., Proulx, G., Reneke, P. A., & Nelson, H. E. (2005). ''Occupant behavior, egress, and emergency communications'' (NIST NCSTAR 1-7). National Institute of Standards and Technology.
* Bryan, J. L. (2002). Behavioral response to fire and smoke. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-315–3-341). National Fire Protection Association; Society of Fire Protection Engineers.
* Kandola, B. S. (2002). Introduction to mechanics of fluids. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-1–1-26). National Fire Protection Association; Society of Fire Protection Engineers.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association; Society of Fire Protection Engineers.
* Lew, H. S., Bukowski, R. W., & Carino, N. J. (2005). ''Design, construction, and maintenance of structural and life safety systems'' (NIST NCSTAR 1-1). National Institute of Standards and Technology.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Institute of Standards and Technology. (2005). ''Final report on the collapse of the World Trade Center towers'' (NIST NCSTAR 1).
* National Institute of Standards and Technology. (2008). ''Final report on the collapse of World Trade Center Building 7'' (NIST NCSTAR 1A).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Special Hazards & Building Types]]

Firefighting

2026-11-02T21:32:52Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Firefighting''' is the work of controlling and extinguishing fires, together with the rescue and protection tasks that go with it. A glossary published by the US Nuclear Regulatory Commission treats it as fire suppression, either manual, with hoses, portable extinguishers or manually operated fixed systems, or automatic, by systems using water, Halon or carbon dioxide.<ref name="NUREG-F29">Iqbal and Salley (2004), p. F-29.</ref> Besides attacking the fire, fire services search for and rescue occupants, protect property and limit harm to the environment.<ref name="IFEG-2.9-3">National Research Council of Canada et al. (2005), p. 2.9-3.</ref> Early action matters: an automatic extinguishing system generally intervenes while the fire is still in its growth stage, so the fire cannot become fully developed.<ref name="VR-4.11">Van Rossum (2027), §4.11.</ref> A fire service that arrives after flashover, by contrast, may have no effect on the fire itself.<ref name="IFEG-1.9-7">National Research Council of Canada et al. (2005), p. 1.9-7.</ref> Tactics differ between countries and situations; the Dutch fire service, for example, prefers to fight building fires from outside and attacks from inside only when an exterior attack fails and this can be done safely.<ref name="NIPV-43">Van der Graaf et al. (2021/2023), p. 43.</ref>

== Who fights fires and what they aim for ==

Many fires are fought first by the people who discover them. In the decision process that Bryan describes, an occupant who has recognised a fire chooses between flight, leaving the building, and fight, fetching an extinguisher or raising the alarm.<ref name="Bryan-3-318">Bryan (2002), p. 3-318.</ref> In a British study of 2,193 people at 952 fires, 14.9 % made fighting the fire their first action. In a US study of residential fires the share was 10.4 %, and in both studies men were more often active in fighting the fire.<ref name="Bryan-3-322">Bryan (2002), pp. 3-322–3-323.</ref> The Australian handbook to the Fire Safety Verification Method (print version 1.1, 2020) notes that many smouldering and small flaming fires are dealt with by occupants and never reported. Estimates of how often design fires occur are therefore commonly based on reported fires, ignoring suppression by occupants.<ref name="ABCBH-61">Australian Building Codes Board (2020b), pp. 61–62.</ref>

At industrial sites, trained staff and private fire brigades take part as well. The US glossary describes a fire watch: people trained to recognise fire hazards, to use fire extinguishers and to follow the proper notification procedures.<ref name="NUREG-F29" /> At US nuclear power plants, the fire brigade operates fixed systems by hand, removes fuel sources, switches off electrical systems and uses portable extinguishers and hose streams.<ref name="Nowlen-P5">Nowlen et al. (2005b), p. P-5.</ref> The International Fire Engineering Guidelines (2005 edition) include such private brigades, for example the brigade of an industrial complex, in their analysis of fire service intervention.<ref name="IFEG-1.9-1">National Research Council of Canada et al. (2005), p. 1.9-1.</ref>

The aims of firefighting go beyond putting out flames. According to the guidelines, fire services are commonly responsible for search and rescue, containing and extinguishing the fire and protecting property. They also protect the environment and the community, for example from contaminated firefighting water running off a chemical warehouse.<ref name="IFEG-2.9-3" /> Control means that the fire is kept from growing, for instance by wetting nearby combustibles and cooling the hot gases under the ceiling, while extinguishment is the complete suppression of all burning material.<ref name="NUREG-F25">Iqbal and Salley (2004), p. F-25.</ref> An attack can be offensive, applying water to the fire, or defensive, using hose streams to protect adjoining property, or both.<ref name="IFEG-1.9-4">National Research Council of Canada et al. (2005), p. 1.9-4.</ref>

== How fires are put out ==

[[Extinguishing mechanisms]] work by separating the fuel from the flame, removing or diluting the oxygen, cooling the fuel or the flame, or interfering with the chemistry of combustion. Several of them often act at once. Water on a burning solid cools the solid, so that it releases less flammable gas, and cools the flame, so that less heat reaches the fuel. Steam can keep oxygen away in some confined conditions, and a fog of fine droplets can block heat radiation.<ref name="NUREG-B15">Iqbal and Salley (2004), p. B-15.</ref> Water is the most common extinguishing agent because it is widely available, cheap and able to absorb a great deal of heat.<ref name="Fleming-4-72">Fleming (2002), p. 4-72.</ref> Fleming gives 9,280 Btu for one US gallon of water heated from 21 °C and turned into steam at 100 °C, which is about 2.6 MJ for every litre.<ref name="Fleming-4-72-SI">Fleming (2002), p. 4-72 (9,280 Btu per US gallon, converted to SI).</ref>
[[File:fse-firefighting-v1.svg|thumb|upright=1.5|alt=Control, extinction and exposure protection are supported by cooling, blanketing and chemical action.|Firefighting objectives and mechanisms must match the incident. Based on Iqbal and Salley (2004), p. B-15 and Fleming (2002), p. 4-72.]]

Water does not suit every fire. It is inappropriate for certain water-reactive materials, with which it can produce heat, flammable or toxic gases or explosions. Most hydrocarbon fuels are lighter than water and do not mix with it, so they float on the water and keep burning.<ref name="Fleming-4-72" /> On hot oil or fat, water can sink below the surface, turn to steam and throw out burning oil in a boilover.<ref name="NUREG-B58">Iqbal and Salley (2004), p. B-58.</ref> In the US classification of fires, water must never be used on Class D fires, which involve combustible metals such as magnesium, sodium and lithium.<ref name="NUREG-B16">Iqbal and Salley (2004), p. B-16.</ref>

Foam is the main alternative to water, used mostly on burning liquids.<ref name="NUREG-B58" /> Firefighting foam consists of air-filled bubbles made from water mixed with a foam concentrate, typically at 1, 3 or 6 percent. It floats on the fuel and forms a layer that keeps air out and stops the fuel from evaporating, so the fire goes out once the whole surface is covered. Low-expansion foam works well on a pool of liquid but much less well on running fuel or a pressurised spray, where an extra agent such as dry chemical is used.<ref name="Scheffey-4-88">Scheffey (2002), p. 4-88.</ref> Heat breaks foam down, so it must be applied fast enough and in large enough amounts to keep a layer over the fuel.<ref name="NUREG-B59">Iqbal and Salley (2004), p. B-59.</ref> A ruptured foam blanket can let the fire burn back and put firefighters at risk.<ref name="NUREG-B60">Iqbal and Salley (2004), p. B-60.</ref>

Dry chemical powders probably act mainly on the chemistry of the flame, and they also absorb heat, block radiation and, in one type, coat the burning surface. They leave residue that needs thorough cleaning and can corrode equipment.<ref name="NUREG-B55">Iqbal and Salley (2004), pp. B-55–B-56.</ref> In a 2001 fire at the Point Beach nuclear plant in the United States, the fire brigade discharged about 32 kg of dry chemical from three extinguishers without success. The fire was finally put out with 57 to 76 L of water, and white dust covered large parts of the containment building.<ref name="NUREG-H29">Iqbal and Salley (2004), p. H-29.</ref> Gaseous agents such as Halon 1301 put out visible flames almost at once, but glowing combustion inside a solid fuel can continue and re-ignite when air is let back in.<ref name="NUREG-B43">Iqbal and Salley (2004), pp. B-43–B-44.</ref>

== Manual firefighting: extinguishers, hoses and water ==

A [[Fire extinguisher]] is one of the means of manual suppression named in the US glossary, alongside hoses and manually operated fixed systems.<ref name="NUREG-F29" /> In the United States, its rating combines a number for relative effectiveness with a letter for each class of fire on which it has proved effective.<ref name="NUREG-F25" /> Class A covers ordinary combustibles such as wood and paper, B flammable liquids and gases, and C fires involving energised electrical equipment. Class D covers combustible metals and K cooking oils and fats.<ref name="NUREG-B16" /> Dry chemical agents are safe on electrical fires as far as electric shock is concerned, but they can damage delicate equipment.<ref name="NUREG-B55" />

Hose lines need a water supply that the fire service can reach. A [[Fire hydrant]] provides water to the pumpers of the fire department.<ref name="NUREG-F26">Iqbal and Salley (2004), p. F-26.</ref> In tall buildings, [[Dry and wet risers]] carry water to outlets on the floors, so firefighters can connect their hoses near the fire instead of laying them from the street.<ref name="NUREG-F61">Iqbal and Salley (2004), pp. F-61–F-62.</ref><ref name="Hopkins-21">Hopkins et al. (2005), p. 21.</ref> In New York City, supplying extra water to a building's fire protection systems is a routine fire department operation.<ref name="Hopkins-xlii">Hopkins et al. (2005), p. xlii.</ref> Reaching the hydrants, inlets and fire floor is a matter of [[fire service access]], which New Zealand's Verification Method C/VM2 (second edition, 2025) covers in its scenario for firefighting operations.<ref name="CVM2-53">Ministry of Business, Innovation and Employment (2025b), p. 53.</ref>

The water flow must match the size of the fire. The Netherlands Institute for Public Safety (NIPV) gives rules of thumb for cooling capacity. A high-pressure jet of 125 L/min is generally sufficient for a fire of up to about 2.5 MW, and a low-pressure jet of 450 L/min for up to about 10 MW.<ref name="NIPV-45">Van der Graaf et al. (2021/2023), p. 45.</ref> For comparison, Van Rossum gives about 2.5 MW for an average living-room sofa and a peak of 8.5 MW for a car.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref> He notes that such heat release data help the fire service judge whether a fire can still be fought with the flow its vehicle delivers at low, medium or high pressure.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref>

Time is often decisive. In an aircraft fuel spill fire, the aluminium skin of the aircraft can burn through in about 1 minute. The cabin becomes unsurvivable once the windows melt out after about 3 minutes.<ref name="Scheffey-4-103">Scheffey (2002), p. 4-103.</ref> Airport rescue and firefighting vehicles are designed to reach an incident on the airport within 2 to 3 minutes. Once there, they must apply agent to control the fire within 1 minute, a critical time recognised by US and international aviation and fire protection bodies.<ref name="Scheffey-4-103" />

== Automatic systems and the fire service ==

Automatic sprinklers often act long before firefighters can. Human response, from discovery of the fire to the travel of the fire brigade, usually takes much longer than the time sprinklers need to control a fire in its early stages. Sprinklers are designed to control a fire, but they often put it out, because the wetted materials around it can no longer heat up to their ignition temperature.<ref name="NUREG-10-1">Iqbal and Salley (2004), pp. 10-1–10-2.</ref> Even where sprinklers do not suppress a fire, their cooling can protect the structure until the fire is extinguished by other means.<ref name="Fleming-4-72" />

Manual and automatic firefighting both depend on the water supply. Sprinkler systems fail when a supply valve is closed, a water tank is empty, a fire pump does not start or loses its power, or the pipes and heads are blocked or corroded.<ref name="NUREG-10-2">Iqbal and Salley (2004), p. 10-2.</ref> At World Trade Center 7, the sprinklers on the lower 20 floors depended on one automatic fire pump and on the city main.<ref name="Hopkins-xli">Hopkins et al. (2005), p. xli.</ref> After the collapse of WTC 1, the fire department could not provide firefighting or supplementary water to the building.<ref name="Hopkins-xliv">Hopkins et al. (2005), p. xliv.</ref> In the SFPE Handbook, Siu warns that many fire risk studies for nuclear power plants ignore the reliance of automatic and manual suppression on a common water supply, which can make their results non-conservative.<ref name="Siu-5-221">Siu (2002), p. 5-221.</ref>
[[File:fse-firefighting-v2.svg|thumb|upright=1.5|alt=Extinguisher, hydrant and hose line, and automatic sprinkler have different operating chains.|Manual and automatic suppression have different dependencies. Based on Iqbal and Salley (2004), pp. F-25–F-26 and 10-1–10-2.]]

Risk studies of US nuclear power plants estimate from past events how long manual firefighting takes. For all fire types together, NUREG/CR-6850 (2005) gives a probability of 0.46 that a fire is still burning after 10 minutes of manual suppression, and 0.10 after 30 minutes.<ref name="Nowlen-P9">Nowlen et al. (2005b), pp. P-9–P-10.</ref> These curves leave out the time to detect the fire and the response time of the fire brigade. Both must be subtracted from the time before damage occurs to find the time that is actually available for suppression.<ref name="Nowlen-P9" />

== Tactics: inside or outside, offensive or defensive ==

Firefighting tactics weigh the chance of success against the risk to firefighters. The International Fire Engineering Guidelines note that a shortage of water or of firefighters for an interior attack can change the strategy from offensive, fighting the fire, to defensive. The defensive aim is to stop the fire spreading to adjoining buildings.<ref name="IFEG-2.9-4">National Research Council of Canada et al. (2005), p. 2.9-4.</ref>

The Dutch fire service arranges its tactics in a quadrant model. The goal is either to prevent fire growth or to extinguish the seat of the fire, and the attack is made either from inside or from outside the building. Firefighters prefer to fight a fire from outside, and they carry out an interior attack only in a small room or building when an exterior attack fails and it can be done safely. A smoke-filled space is entered only if the benefits outweigh the risks, and reducing material damage is not a reason to take risks.<ref name="NIPV-43" />

The Dutch basic principles start with taking time to stop and think, followed by a reconnaissance from outside, for example with a thermal imaging camera. Three questions then decide the type of attack: is it known where the fire is, can it be reached from outside, and is there enough cooling capacity.<ref name="NIPV-44">Van der Graaf et al. (2021/2023), p. 44.</ref> If the fire cannot be found, reached and cooled from outside, large buildings are fought defensively and considered beyond saving.<ref name="NIPV-44" /> In a small building an offensive interior attack may still be possible, with control of the doors, the building kept closed where possible and water on the fire as quickly as possible.<ref name="NIPV-63">Van der Graaf et al. (2021/2023), p. 63.</ref>

An interior attack also needs a short route through smoke and enough cooling capacity, and the commanding officer on site makes the final decision.<ref name="NIPV-45" /> Van Rossum stresses the same point for engineering studies: a positive result does not mean that the fire service will attack from inside, because that decision always rests with the fire service on site.<ref name="VR-9.3">Van Rossum (2027), §9.3 (Results from zone models).</ref> The Australian handbook, summarising limits from the Fire Brigade Intervention Model, adds that search and rescue cannot be carried out in a room that has reached flashover.<ref name="ABCBH-113">Australian Building Codes Board (2020b), p. 113.</ref>

== Ventilation, backdraft and smoke explosions ==

Firefighters also change the ventilation of a burning building. Positive pressure ventilation uses fans to blow fresh air into an enclosure, creating a pressure difference that drives the existing air and combustion products out through an exit opening. It is used to influence the degree of ventilation, to assist firefighting and to influence the burning itself.<ref name="NUREG-F46">Iqbal and Salley (2004), p. F-46.</ref>
[[File:fse-firefighting-v3.svg|thumb|upright=1.5|alt=Fan airflow changes smoke flow and can supply oxygen to hot unburned gases.|Ventilation can alter both visibility and combustion conditions. Based on Iqbal and Salley (2004), p. F-46 and Van Rossum (2027), §4.9.]]

Adding air is risky when a fire is short of oxygen. In a ventilation-controlled fire the oxygen supply limits the burning, so unburnt pyrolysis gases can build up, and mixed with oxygen they form a flammable mixture that needs only ignition energy.<ref name="VR-4.8">Van Rossum (2027), §4.8.</ref> A [[Backdraft]] is the explosive ignition of such gases when fresh air suddenly enters, for example when a door is opened, and it can produce a large fireball or a jet of flame. Van Rossum describes it as a dangerous phenomenon for the fire service.<ref name="VR-4.9">Van Rossum (2027), §4.9.</ref>

A [[smoke explosion]] is a different event. It is the very rapid burning of flammable gases that are already reasonably premixed with air within their explosion limits, set off by a spark, by glowing particles or by self-ignition.<ref name="VR-4.10">Van Rossum (2027), §4.10.</ref> The Dutch basic principles favour keeping a building closed where possible, which they call anti-ventilation, and controlling the doors during an interior attack.<ref name="NIPV-63" />

Ventilation, smoke control and sprinklers also affect one another. The NIPV study notes that smoke and heat removal can raise the chance of a successful interior attack in indoor car parks.<ref name="NIPV-6">Van der Graaf et al. (2021/2023), p. 6.</ref> Building ventilation systems that keep running during a fire, or that recirculate air, can themselves spread smoke through the building.<ref name="Evans-70">Evans et al. (2005), p. 70.</ref> Sprinkler sprays can also cool the heat-sensitive links of downstream sprinklers and smoke vents and delay their opening, effects known as sprinkler skipping and vent skipping.<ref name="Cooper-3-239">Cooper (2002b), p. 3-239.</ref>

== Firefighting in building design and regulation ==

The International Fire Engineering Guidelines state that evacuation analysis should not rely on fire service intervention, although the needs of fire services must not be discounted.<ref name="IFEG-1.9-1" /> In New Zealand, C/VM2 (second edition, 2025) sets out a design scenario for firefighting operations. It sets requirements for access, water supply, information for firefighters and structural stability.<ref name="CVM2-53" /> For large unsprinklered firecells near a boundary, it sets limits for the moment when firefighters first apply water. The radiation at 1.5 m above the floor may then not exceed 4.5 kW/m², and the smoke layer must be at least 2 m above the floor.<ref name="CVM2-53" /> That moment may be taken as 1,200 s, or 1,000 s with a fire alarm connected directly to a remote receiving centre.<ref name="CVM2-54">Ministry of Business, Innovation and Employment (2025b), p. 54.</ref>

In Australia, the Fire Safety Verification Method Standard 2022 includes a fire brigade intervention scenario, assessed with the Fire Brigade Intervention Model, that applies to buildings within 50 km road travel of a fire station.<ref name="FSVM-15">Australian Building Codes Board (2022), p. 15.</ref> The 2020 handbook shows how a design fire may be cut short by occupants, by sprinklers, or by fire brigade suppression before or after flashover.<ref name="ABCBH-61" /> The design fire is then modified for the automatic or fire brigade intervention that applies to the scenario.<ref name="ABCBH-61" />

In the Netherlands, an equivalent solution under the 2012 Building Decree cannot take credit for a fire service attack.<ref name="NIPV-15">Van der Graaf et al. (2021/2023), p. 15.</ref> The NIPV study stresses that the fire service has an obligation of best efforts rather than of result.<ref name="NIPV-41">Van der Graaf et al. (2021/2023), p. 41.</ref> Some Dutch design curves do include firefighting: the car fire curve in the car park standard NEN 6098, as described by Van Rossum, reflects the extinguishing action of the fire service.<ref name="VR-8.6" />

== Limits and common misconceptions ==

Putting out the visible flames does not always end a fire. Glowing combustion inside solids can survive a gaseous agent and re-ignite when air returns, and a damaged foam blanket can let a liquid fire burn back.<ref name="NUREG-B43" /><ref name="NUREG-B60" /> Battery packs of electric vehicles can catch fire again shortly after the flames are out. They therefore need continuous cooling and temperature monitoring, for example in a water-filled immersion container.<ref name="NIPV-46">Van der Graaf et al. (2021/2023), p. 46.</ref>

More agent is not automatically better. Water can spread a burning liquid that floats on it, and repeated discharges of dry chemical at Point Beach left residue across the containment building without putting the fire out.<ref name="Fleming-4-72" /><ref name="NUREG-H29" /> In enclosed spaces, dry chemical can also impair breathing and reduce visibility.<ref name="NUREG-H29" /> Firefighting itself exposes firefighters to heat, flame, smoke, explosion and structural collapse, as one of the US definitions of fire suppression states.<ref name="NUREG-F29" />

Engineering models cannot promise what firefighters will find. The International Fire Engineering Guidelines note that the effect of fire service activities does not lend itself easily to quantification, so many aspects rest on qualitative judgement.<ref name="IFEG-2.9-2">National Research Council of Canada et al. (2005), p. 2.9-2.</ref> C/VM2's limits apply only at the moment firefighters first apply water, and operations after that depend on the conditions they face at the time.<ref name="CVM2-54" />

== See also ==

* [[Hose reel]]
* [[Rollover]]
* [[Electric vehicle fire]]
* [[Critical water application rate]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Australian Building Codes Board. (2022). ''Fire Safety Verification Method Standard 2022''.
* Bryan, J. L. (2002). Behavioral response to fire and smoke. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-315–3-341). National Fire Protection Association; Society of Fire Protection Engineers.
* Cooper, L. Y. (2002b). Smoke and heat venting. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-219–3-242). National Fire Protection Association; Society of Fire Protection Engineers.
* Evans, D. D., Peacock, R. D., Kuligowski, E. D., Dols, W. S., & Grosshandler, W. L. (2005). ''Active fire protection systems'' (NIST NCSTAR 1-4). National Institute of Standards and Technology.
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association; Society of Fire Protection Engineers.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Nowlen, S. P., Najafi, B., Wyant, F. J., Forester, J., Kazarians, M., Kolaczkowski, A., Joglar, F., Funk, D., Hannaman, G., & Anoba, R. (2005b). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Vol. 2. Detailed methodology'' (NUREG/CR-6850; EPRI 1011989). Electric Power Research Institute; U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research.
* Scheffey, J. L. (2002). Foam agents and AFFF system design considerations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-88–4-122). National Fire Protection Association; Society of Fire Protection Engineers.
* Siu, N. (2002). Fire risk assessment for nuclear power plants. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-214–5-226). National Fire Protection Association; Society of Fire Protection Engineers.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Firefighting & Fire Service]]

Fire service access

2026-11-02T21:32:52Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Fire service access''' is the set of provisions that let the fire service reach a building, deliver water to every part of it, and carry out [[firefighting]] and rescue inside with reasonable safety.<ref name="CVM2-53">Ministry of Business, Innovation and Employment (2025b), p. 53.</ref><ref name="IFEG-1.2-10">National Research Council of Canada et al. (2005), p. 1.2-10.</ref> In New Zealand, the Building Code clauses restated in Verification Method C/VM2 (second edition, 2025) cover a hard-standing for fire vehicles, water throughout the building, routes to the fire floor and information for firefighters.<ref name="CVM2-53" /> The International Fire Engineering Guidelines (2005 edition) treat access to the site and to the building as part of fire services intervention, one of the six sub-systems of a fire safety design.<ref name="IFEG-1.2-10" /> Access matters because the time needed to bring water to a fire affects how far the fire develops and whether it can still be suppressed.<ref name="NIPV-66">Van der Graaf et al. (2021/2023), p. 66.</ref> A fire service that arrives after the fire has grown beyond flashover may have no effect on it at all.<ref name="IFEG-1.9-7">National Research Council of Canada et al. (2005), p. 1.9-7.</ref> Requirements differ between countries; in the Netherlands, for example, the Building Works and Living Environment Decree (Bbl) counts the preservation of fire service attack routes among its sub-goals.<ref name="VR-1.2">Van Rossum (2027), §1.2.</ref>

== What fire service access includes ==

New Zealand's Building Code clause C5 deals with access and safety for firefighting operations. Its functional requirements, as printed in the 2013 commentary, ask for a low probability that firefighters are delayed or impeded, and a low probability that they are injured or made ill.<ref name="Comm-32">Ministry of Business, Innovation and Employment (2013), p. 32.</ref> Verification Method C/VM2 (second edition, 2025) restates the performance clauses. Fire service vehicles need a hard-standing from which an unobstructed path leads to the building within 20 m of the firefighter entrance and of any sprinkler or hydrant inlets. Firefighters, with their protective equipment and standard training, must be able to reach the floor of fire origin, search the area around it and protect their way out.<ref name="CVM2-53" /> Clear information about the fire and the building is also required, and the structure that carries the access routes must stay stable during and after the fire.<ref name="CVM2-53" />
[[File:fse-fire-service-access-v1.svg|thumb|upright=1.5|alt=Arrival leads through hard-standing, connections and internal routes to firefighting and egress.|Fire service access connects vehicles, equipment, personnel and safe withdrawal. Based on Ministry of Business, Innovation and Employment (2025b), pp. 53–55.]]

In Australia, the handbook to the Fire Safety Verification Method (print version 1.1, 2020) lists facilities for firefighting among the broad fire safety objectives of the National Construction Code.<ref name="ABCBH-27">Australian Building Codes Board (2020b), p. 27.</ref> It calls for a firefighter strategy, a plan by which the fire brigade is notified of the fire and its location and gains access to the site. The brigade also receives the correct fire location and communication facilities on arrival, documents on the fire safety strategy, and a set-up area with facilities for firefighting and for search and rescue. The plan has to be developed with the fire authority, using the Fire Brigade Intervention Model where appropriate.<ref name="ABCBH-29">Australian Building Codes Board (2020b), p. 29.</ref>

The International Fire Engineering Guidelines cover public fire services as well as private ones, such as the fire brigade of an industrial complex.<ref name="IFEG-1.9-1">National Research Council of Canada et al. (2005), p. 1.9-1.</ref> For this sub-system they list measures such as the type of fire service, full-time or volunteer, its capability and resources, access to the site and the building, and water supplies.<ref name="IFEG-1.2-10" /> In the Netherlands, the Bbl keeps the attack routes of the fire service intact as one of its sub-goals.<ref name="VR-1.2" /> Under the Bbl, a non-enclosed space through which an escape route runs must also remove enough heat and smoke, and admit enough fresh air, to stay usable for escape, rescue and firefighting work.<ref name="VR-7.7">Van Rossum (2027), §7.7.</ref>

== How access affects the time to intervention ==

The International Fire Engineering Guidelines describe intervention as a sequence of steps, each of which takes time. The fire service has to be notified, dispatched and driven to the site, and a station with full-time paid firefighters is likely to respond faster than one run by volunteers.<ref name="IFEG-1.9-2">National Research Council of Canada et al. (2005), p. 1.9-2.</ref> On arrival, crews locate the fire from installed equipment, from occupants and from the sight of smoke and flames. They then move vehicles, hoses and other equipment into position, a step that fire conditions in or near the building may affect. Search and rescue and the attack follow, and the attack can be offensive, putting water on the fire, or defensive, protecting adjoining property with hose streams, or both.<ref name="IFEG-1.9-4">National Research Council of Canada et al. (2005), p. 1.9-4.</ref>

Access shapes several of these steps. The location of a building and the access to it affect the travel time, while its size, layout and signage affect investigation, search, rescue and firefighting. The location of hydrants, fire indicator panels and other fire service facilities affects how efficiently the fire is suppressed.<ref name="IFEG-1.9-5">National Research Council of Canada et al. (2005), p. 1.9-5.</ref> The guidelines also warn that this sub-system changes over the life of a building, as fire station locations, budgets, equipment and traffic density change.<ref name="IFEG-1.9-2" />

The arrival time largely decides what an attack can achieve, and the guidelines distinguish three outcomes: no effect, control and extinguishment. No effect fits a fire service that arrives after the fire has grown beyond flashover. Control, in which the fire burns at a steady size until the fuel is used up, is a conservative assumption often made when access to the fire is limited.<ref name="IFEG-1.9-7" /> A risk model in the SFPE Handbook likewise judges the effectiveness of firefighting from the time of flashover and the arrival time of the fire brigade.<ref name="Meacham-5-164">Meacham (2002), p. 5-164.</ref> Studies of fires in health care buildings, quoted by Bryan, single out the period between detection and the arrival of the fire department. They see it as the most important life-saving period for the area in direct contact with the room of origin.<ref name="Bryan-3-315">Lerup et al. (1978), as cited in Bryan (2002), p. 3-315.</ref>

In Australia the main tool for estimating these times is the Fire Brigade Intervention Model (FBIM) of the Australasian Fire Authorities Council (AFAC).<ref name="IFEG-2.9-2">National Research Council of Canada et al. (2005), p. 2.9-2.</ref> It is built from up to 16 flow charts for steps such as notification, dispatch, travel, putting on safety equipment and setting up the water supply.<ref name="IFEG-2.9-3">National Research Council of Canada et al. (2005), pp. 2.9-3–2.9-5.</ref> It can estimate, for example, how long firefighters need to reach a given location in a building.<ref name="IFEG-2.9-4">National Research Council of Canada et al. (2005), p. 2.9-4.</ref> Its numerical values were prepared solely from Australian data, but because no other country has compiled such a guide, they may have at least a semi-quantitative use elsewhere.<ref name="IFEG-3.9-2">National Research Council of Canada et al. (2005), p. 3.9-2.</ref>

== Vehicle access and hard-standing ==

New Zealand's C/VM2 (second edition, 2025) repeats clause C5.3: a hard-standing from which an unobstructed path leads to the building within 20 m of the firefighter entrance and any sprinkler or hydrant inlets. Under clause C5.4, firecells larger than 5,000 m² without sprinklers need such access on more than one side.<ref name="CVM2-53" /> The 2013 commentary adds that these access points should be spread around the building, not placed on both sides of one corner served by the same hard-standing. It also notes that the clauses use conventional methods that the Fire Service can easily anticipate, so unusual solutions should be agreed with it in advance.<ref name="Comm-33">Ministry of Business, Innovation and Employment (2013), p. 33.</ref> According to the commentary, clauses C5.3 to C5.8 do not apply to detached dwellings, the inside of household units in multi-unit dwellings, backcountry huts, outbuildings or ancillary buildings.<ref name="Comm-32" />

In Australia, the Fire Safety Verification Method Standard 2022 requires external fire brigade access and external hydrants for every building assessed under its fire brigade intervention scenario.<ref name="FSVM-16">Australian Building Codes Board (2022), p. 16.</ref> That scenario applies only to buildings within 50 km road travel of a fire station.<ref name="FSVM-15">Australian Building Codes Board (2022), p. 15.</ref> For buildings further away, the 2020 handbook states that fire brigade intervention should not be taken into account, and that the design brief should address its absence and any need for compensating measures.<ref name="ABCBH-86">Australian Building Codes Board (2020b), p. 86.</ref>

Indoor car parks show how access can limit firefighting in practice. A study by the Netherlands Institute for Public Safety (NIPV) names heat, loss of visibility, long hose distances and the difficulty of finding one's bearings. Together they make reconnaissance and firefighting in such car parks difficult and risky.<ref name="NIPV-11">Van der Graaf et al. (2021/2023), p. 11.</ref> It recommends placing charging spaces for electric vehicles near the vehicle entrances and exits and at street level where possible. This aids accessibility and raises the chance that a fire can be fought from outside or the vehicle removed more quickly.<ref name="NIPV-42">Van der Graaf et al. (2021/2023), p. 42.</ref> Higher decks are not always easy to reach, and a fire service entrance that is also an escape route creates conflicting safety interests.<ref name="NIPV-39">Van der Graaf et al. (2021/2023), p. 39.</ref>

== Water for firefighting: hydrants, inlets and risers ==

A [[Fire hydrant]] is a device that supplies water to fire department pumpers for fighting fires in buildings.<ref name="NUREG-F26">Iqbal and Salley (2004), p. F-26.</ref> A fire department connection is an inlet through which the fire service pumps water from its vehicles into the fire protection system of a building.<ref name="NUREG-F25">Iqbal and Salley (2004), p. F-25.</ref> Inside, a standpipe or riser system of pipes, valves and hose connections carries the water to the floors. Trained occupants can use its hoses until the fire department arrives, and firefighters can connect their own hoses to outlets near the fire.<ref name="NUREG-F61">Iqbal and Salley (2004), pp. F-61–F-62.</ref> [[Dry and wet risers]] differ in how they are filled. A wet system is always full of water and connected to an automatic supply, whereas a manual dry system has only fire department connections and relies on the fire service for water.<ref name="Hopkins-21">Hopkins et al. (2005), p. 21.</ref><ref name="NUREG-F61" />
[[File:fse-fire-service-access-v2.svg|thumb|upright=1.5|alt=Hydrant feeds a pumper, while an inlet feeds a riser and hose outlets inside a building.|Hydrants, inlets and internal risers have distinct functions. Based on Iqbal and Salley (2004), pp. F-25–F-26 and F-61–F-62, and Hopkins et al. (2005), pp. xxxiv–xxxv.]]

New Zealand and Australian rules also limit how far water may have to be carried. Under C/VM2, a pumping appliance parked close to the building must be able to reach any point inside within 75 m, about three hose lengths. Otherwise an internal hydrant is needed, designed to NZS 4510 or approved by the National Commander of Fire and Emergency New Zealand.<ref name="CVM2-54">Ministry of Business, Innovation and Employment (2025b), pp. 54–55.</ref> C/VM2 treats access to an intermediate floor as achieved when a hydrant in a safe path lies within 40 m of its most remote point, about two hose lengths.<ref name="CVM2-55">Ministry of Business, Innovation and Employment (2025b), p. 55.</ref> Australia's 2022 standard requires internal hydrants in a sprinklered building when reaching all points needs more than 100 m or the building has more than three levels. Without sprinklers the distance threshold is 70 m.<ref name="FSVM-16" />

Risers shorten the hose that firefighters must lay. The NIPV study notes that a dry riser can shorten the attack time because less hose has to be rolled out. Its most effective location is where the fire service enters the car park.<ref name="NIPV-66" /> A NIST report on the World Trade Center states that avoiding long hose lays from the fire engine to an upper floor of a tall building improves the initial attack. It adds that standpipes are not an alternative to automatic sprinklers.<ref name="Hopkins-21" />

An accessible inlet does not guarantee water. Sprinkler and pump systems can fail because of a closed supply valve, an empty tank, a fire pump that does not start or loses its power, or an inadequate supply.<ref name="NUREG-10-2">Iqbal and Salley (2004), p. 10-2.</ref> At World Trade Center 7, the sprinklers on floors 1 to 20 depended on one automatic fire pump and on the city main near the building.<ref name="Hopkins-xli">Hopkins et al. (2005), p. xli.</ref> After the collapse of WTC 1, the fire department could not provide firefighting or supplementary water to WTC 7.<ref name="Hopkins-xliv">Hopkins et al. (2005), p. xliv.</ref> C/VM2 asks that access and firefighter safety be designed with regard to the likelihood and consequences of failure of any fire safety system.<ref name="CVM2-53" />

== Reaching the fire floor: stairs, lifts and high-rise buildings ==

C/VM2 links the protection of the internal route to the height of the building. Where the escape height exceeds 10 m, floors that cannot be reached directly from street level must be served by fire-separated stairways that resist fire spread until burnout. In lower buildings these stairways must last 60 minutes from ignition or until burnout.<ref name="CVM2-55" /> Pressurised stairwells keep smoke out by holding the stair at a higher air pressure than the fire floor. Their main aim is a smoke-free escape route, and a secondary aim is a smoke-free staging area for firefighters.<ref name="Klote-4-286">Klote (2002), p. 4-286.</ref>

In a [[high-rise building]] the climb itself becomes a barrier. NIST's study of the emergency response at the World Trade Center notes that a New York firefighter in full protective clothing and breathing apparatus carries about 23 kg. Extra equipment can add another 23 kg or more.<ref name="Lawson-xliii">Lawson and Vettori (2005), p. xliii.</ref> Fully equipped firefighters climbed WTC 1 at about 2.0 minutes per floor, and their fitness for rescue and firefighting fell with every floor climbed.<ref name="Lawson-xliii" /><ref name="Lawson-xliv">Lawson and Vettori (2005), p. xliv.</ref> Another NIST report gives a typical pace of about one minute per floor, which is hard to sustain beyond about the first 20 storeys. Even at that pace, reaching the 60th floor would take about an hour.<ref name="Lew-191">Lew et al. (2005), p. 191.</ref>

A [[firefighting lift]] removes most of that climb. When a fire is detected, lifts are normally taken out of service and recalled to the ground floor. Fire services carry keys that let them run the lifts for rescue and to carry crews and equipment towards the fire.<ref name="Klote-4-289">Klote (2002), p. 4-289.</ref> In 2005, NIST found that US building codes, with a few exceptions, did not permit fire-protected lifts for routine access by first responders. The United Kingdom and other countries using British standards had required such firefighter lifts in protected shafts for a number of years.<ref name="Lew-191" /> NIST's final report recommended fire-protected and structurally hardened lifts in tall buildings, reserved for emergency responders during emergencies.<ref name="NIST-218">National Institute of Standards and Technology (2005), p. 218.</ref>

Each World Trade Center tower had four vertical water supply zones, with standpipes in the stairwells feeding hose stations on every floor. Manual fire pumps on the 7th, 41st and 75th floors boosted the pressure, and fourteen ground-level fire department connections served the complex.<ref name="Hopkins-xxxiv">Hopkins et al. (2005), pp. xxxiv–xxxv.</ref> New York City's 2003 building code requires emergency power in new high-rise office buildings for fire pumps, at least three lifts, alarms, emergency lighting and smoke control.<ref name="Razza-4">Razza and Grill (2005c), p. 4.</ref>

== Conditions firefighters can work in ==

Access is only useful if conditions at the end of the route allow work. New Zealand's clause C3.8 covers unsprinklered firecells within 15 m of a relevant boundary with a fire load above 20 TJ or a floor area above 5,000 m². When firefighters first apply water to such a fire, the radiation at 1.5 m above the floor may not exceed 4.5 kW/m², and the smoke layer must be at least 2 m above the floor.<ref name="CVM2-53" /> C/VM2 lets designers take the time until water is first applied as 1,200 s (20 minutes), or 1,000 s with an automatic alarm connected directly to a remote receiving centre. Another time may be used if a fire brigade intervention model supports it.<ref name="CVM2-54" /> The 2013 commentary on the first edition explains that the same values are rounded 95th percentiles from New Zealand industrial fires, about 1,240 s with a monitored alarm and 1,060 s with a direct connection.<ref name="Comm-149">Ministry of Business, Innovation and Employment (2013), p. 149.</ref>

Australia's 2020 handbook summarises firefighter limits from the FBIM manual, measured 1.5 m above the floor and to be confirmed with the fire brigade. In routine conditions firefighters may work for up to 25 minutes at up to 100 °C and 1 kW/m². In hazardous conditions the limits are 10 minutes, 120 °C and 3 kW/m².<ref name="ABCBH-112">Australian Building Codes Board (2020b), p. 112.</ref> Extreme conditions, such as a snatch rescue or a retreat from flashover, allow 1 minute at 160 °C and 4 to 4.5 kW/m². Above 235 °C or 10 kW/m² conditions are life-threatening, and no search and rescue is possible in a room after flashover.<ref name="ABCBH-112" /><ref name="ABCBH-113">Australian Building Codes Board (2020b), p. 113.</ref> Poor visibility is not a limit in itself, but it slows search and firefighting, and the air supply of the breathing apparatus may run out first.<ref name="ABCBH-111">Australian Building Codes Board (2020b), p. 111.</ref>

In the Netherlands, the standard NEN 6093 on smoke and heat exhaust systems sets limits for a fire service attack in a space with such a system. Visibility must be at least 100 m to light-emitting objects up to 1.8 m above the floor, and radiation from the smoke layer at most 3.5 kW/m² at that height. The smoke layer may reach 200 °C where goods are stored in it and 500 °C otherwise, and it must stay below the critical temperature of the structure.<ref name="VR-9.3">Van Rossum (2027), §9.3 (Results from zone models).</ref> Van Rossum adds that firefighters need to know whether the fire is still local or already a compartment fire, and whether they can attack with the fire in sight.<ref name="VR-9.3" />

The structure must also hold long enough. C/VM2 requires the structure that gives firefighters access to floors to remain stable during and after the fire, with its fire resistance derived from a full burnout design fire.<ref name="CVM2-53" /><ref name="CVM2-54" /> Australia's 2022 standard pairs its fire brigade intervention scenario with a scenario that guards against unexpected catastrophic structural failure.<ref name="FSVM-16" />

== Information, communication and upkeep ==

Firefighters arriving at a building need to know where the fire is and what they can use. New Zealand's clause C5.7 asks for clear information on the general location of the fire, the available fire safety systems and any hazardous substances or processes.<ref name="CVM2-53" /> Australia's 2022 standard asks for command and control provisions in unsprinklered buildings and in sprinklered buildings of more than three levels.<ref name="FSVM-16" /> New York City's 2003 code requires two-way voice communication and a fire command station in new office buildings over 75 ft (about 23 m).<ref name="Razza-4" />
[[File:fse-fire-service-access-v3.svg|thumb|upright=1.5|alt=Fire location, system status and hazardous materials inform access and suppression choices.|Responders need current information as well as physical access. Based on Ministry of Business, Innovation and Employment (2025b), p. 53.]]

Access provisions have to stay usable for the whole life of the building. The International Fire Engineering Guidelines list the items whose design and maintenance support intervention: perimeter roads, the access paths and lifts used by the fire service, and equipment such as hydrants. The list also includes protective measures such as structural stability, sprinklers, smoke management and emergency communication.<ref name="IFEG-1.9-8">National Research Council of Canada et al. (2005), p. 1.9-8.</ref> The New Zealand version of the guidelines adds that alterations or a change of use can compromise the original fire engineering design and may call for a new evaluation.<ref name="IFEG-0.3-8-NZ">National Research Council of Canada et al. (2005), Part 0 (New Zealand), p. 0.3-8.</ref>

== Limits and common misconceptions ==

Fire service access does not make the fire service part of the evacuation design. The International Fire Engineering Guidelines state that evacuation analysis should not rely on fire service intervention, although the needs of fire services must not be discounted.<ref name="IFEG-1.9-1" /> In the Netherlands, an equivalent solution under the 2012 Building Decree cannot take credit for a fire service attack.<ref name="NIPV-15">Van der Graaf et al. (2021/2023), p. 15.</ref> The fire service has an obligation of best efforts rather than of result, so its deployment cannot replace fire prevention measures.<ref name="NIPV-41">Van der Graaf et al. (2021/2023), p. 41.</ref>

A positive engineering result does not oblige firefighters to attack from inside the building. Van Rossum stresses that this decision always rests with the fire service on site.<ref name="VR-9.3" /> Likewise, the C/VM2 limits describe a single moment, and later operations are decided by the officer in charge according to the conditions found.<ref name="Comm-149" />

Fire service intervention is also hard to quantify. The International Fire Engineering Guidelines note that its effect does not lend itself easily to calculation, so many aspects rest on qualitative judgement.<ref name="IFEG-2.9-2" /> The FBIM values come from Australian data only.<ref name="IFEG-3.9-2" />

== See also ==

* [[Hose reel]]
* Positive pressure ventilation
* [[Fire extinguisher]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Australian Building Codes Board. (2022). ''Fire Safety Verification Method Standard 2022''.
* Bryan, J. L. (2002). Behavioral response to fire and smoke. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-315–3-341). National Fire Protection Association; Society of Fire Protection Engineers.
* Hopkins, M., Schoenrock, J., & Budnick, E. (2005). ''Fire suppression systems'' (NIST NCSTAR 1-4B). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association; Society of Fire Protection Engineers.
* Lawson, J. R., & Vettori, R. L. (2005). ''The emergency response operations'' (NIST NCSTAR 1-8). National Institute of Standards and Technology.
* Lew, H. S., Bukowski, R. W., & Carino, N. J. (2005). ''Design, construction, and maintenance of structural and life safety systems'' (NIST NCSTAR 1-1). National Institute of Standards and Technology.
* Meacham, B. J. (2002). Building fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-153–5-175). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Institute of Standards and Technology. (2005). ''Final report on the collapse of the World Trade Center towers'' (NIST NCSTAR 1).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Razza, J. C., & Grill, R. A. (2005c). ''Comparison of the 1968 and current (2003) New York City Building Code provisions'' (NIST NCSTAR 1-1F). National Institute of Standards and Technology.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Firefighting & Fire Service]]

Fire risk

2026-11-02T21:32:52Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Fire risk''' is the potential for a fire to cause unwanted, adverse consequences to human life, health, property or the environment.<ref name="WH-5-3">Watts and Hall (2002), p. 5-3.</ref> It brings together three questions: what could happen, how bad it would be, and how likely it is.<ref name="WH-5-1">Watts and Hall (2002), pp. 5-1–5-2.</ref> A fire risk therefore depends both on the consequences of possible fires and on the likelihood that they occur. It describes the uncertainty of a loss, not a loss that is certain to happen.<ref name="WH-5-1" /> Every decision related to fire safety is in effect a fire risk decision, whether or not it is treated as one.<ref name="WH-5-1" />
[[File:fse-fire-risk-v1.svg|thumb|upright=1.5|alt=What could happen, how likely and how severe lead to a risk evaluation.|Fire risk combines event scenarios, likelihood and consequences. Based on Watts and Hall (2002), pp. 5-1–5-3 and Meacham (2002), pp. 5-154–5-156.]]

Zero risk is not an achievable goal, because no technology is completely reliable and natural events such as lightning and earthquakes can also cause fires.<ref name="WH-5-4">Watts and Hall (2002), p. 5-4.</ref> The practical questions are how large the remaining risk is and whether it is acceptable. Accepting a level of risk requires a value judgement, and people make such judgements in different ways.<ref name="WH-5-1" /> Fire risk is estimated from [[Fire statistics|fire statistics]], usage data and laboratory tests, and the result is then judged for its acceptability.<ref name="HallAhrens-5-65">Hall and Ahrens (2002), p. 5-65.</ref><ref name="WH-5-3" />

== Hazard, consequence and probability ==

A hazard is a chemical or physical condition that has the potential to cause damage to people, property or the environment.<ref name="WH-5-3" /> An analysis of what could happen and how bad it would be, without considering how likely it is, is called a fire hazard analysis. A fire risk analysis adds the likelihood. A sequence of events that ends in a fire loss is called a scenario.<ref name="WH-5-1" /> For a whole building, the fire risk is the full spread of possible events and their consequences, not the outcome of one scenario.<ref name="WH-5-3" />

Consequences describe how bad a fire would be if it happened. They range from deaths and damage to property to intangible losses such as business interruption, environmental damage and the destruction of cultural objects. A consequence can be direct, such as damaged property, or indirect, such as a company that is out of business for several days. It can also be objective, such as a replacement cost, or subjective, such as the pain and suffering of an injury.<ref name="WH-5-1" /> In building fire risk analysis, the main things of value are life safety, property, business continuity, the environment and heritage.<ref name="Meacham-5-153">Meacham (2002), pp. 5-153–5-154.</ref>

Risk is usually estimated by combining the probability that an event occurs with the consequence of the event if it does occur.<ref name="WH-5-3" /> The terminology is not consistent: a committee of the Society for Risk Analysis found 17 different definitions of risk.<ref name="WH-5-3" /> The SFPE Handbook also describes fire risk as the possibility of an unwanted outcome in an uncertain situation, where fire may cause loss or harm to something that is valued.<ref name="Meacham-5-153" /> A related term is the fire safety level, which the Australian Fire Safety Verification Method handbook (2020) calls the reciprocal of fire risk: when the risk to occupants falls, the safety level rises.<ref name="ABCB-140">Australian Building Codes Board (2020b), p. 140.</ref>

== Frequency and probability ==

A frequency states how often an event occurs in a period, such as the number of fires per year. On its own it is not a probability, because the number of possible occurrences is also needed.<ref name="Meacham-5-159">Meacham (2002), p. 5-159.</ref> In a hypothetical example, 20 fires a year in toasters that are switched on 20 million times a year give a probability of one in a million per start.<ref name="Meacham-5-159" /> Fire incident data therefore have to be combined with usage or exposure data, such as the number of appliances in use or the floor area of a type of building.<ref name="HallAhrens-5-65" />

There are two views of probability. In the frequency view, probability is the proportion of the time that an event occurs in the long run. In the subjective view, it measures how strongly a person believes that an event will occur.<ref name="WH-5-3" /> Fires are relatively rare, and buildings and their contents change over time, so past losses are a limited guide to future ones. This is a strong argument for using subjective probabilities, based on current knowledge and judgement, in building fire risk analysis.<ref name="Meacham-5-159" />

The amount of available data differs widely. For US homes there are very many recorded fires with limited detail, while for US nuclear power plants there are far fewer fires but much more detail on each. For a single existing building there are very few fires at all. In fire safety engineering, risk analysis is therefore mostly used for an application or a class of facility with a considerable fire loss history.<ref name="WH-5-3" />

== Typical values ==

The frequency of fire depends strongly on the use of a building. In British Standards Institution data from 2001, quoted in the International Fire Engineering Guidelines (2005), a dwelling had about 0.003 fire starts per year and an office about 0.006. Schools and industrial buildings had about 0.04, entertainment venues about 0.12 and hospitals about 0.3 fire starts per building per year. The guidelines warn that such values may have changed with new technologies and materials.<ref name="IFEG-3-2-2">National Research Council of Canada et al. (2005), p. 3.2-2.</ref> Finnish data show that the number of fires per square metre falls as buildings get larger, while the number per building generally rises with floor area.<ref name="IFEG-3-2-3">National Research Council of Canada et al. (2005), p. 3.2-3.</ref>

Risk studies often sort frequencies into broad classes. One example in the SFPE Handbook calls events anticipated if they occur more often than once in 100 years. Events are unlikely between once in 100 and once in 10,000 years, and extremely unlikely between once in 10,000 and once in a million years. Rarer events are beyond extremely unlikely. Frequencies should be counted for a given loss rather than for a single scenario: 30 scenarios that each occur once in 10 million years together occur three times in a million years.<ref name="Meacham-5-166">Meacham (2002), pp. 5-166–5-167.</ref>

Reliability values are typical inputs as well. In reported US home fires, roughly one-third of smoke alarms were not working, but a general study of home installations found only one-fifth not working. Data from unreported fires suggest that the main reason is that working alarms keep many fires so small that the fire service is never called. Reported US fires suggest that sprinklers do not operate in one-sixth to one-fifth of the fires large enough to activate them, yet their real reliability could be well over 90 %.<ref name="HallAhrens-5-72">Hall and Ahrens (2002), p. 5-72.</ref>

== Individual and societal risk ==

Risk to people is often expressed in two complementary ways. [[Individual risk]] is the probability of injury or death to a person at a specified location relative to a fire or explosion source. It can be drawn as contour lines that connect points of equal risk, regardless of whether anyone is actually present there.<ref name="Barry-5-210">Barry (2002), p. 5-210.</ref> In the Australian Fire Safety Verification Method handbook (2020), individual risk is the frequency at which a person may be expected to suffer a given level of harm from a fire in the building.<ref name="ABCB-22">Australian Building Codes Board (2020b), p. 22.</ref>

[[Societal risk]] takes into account the likelihood of fires or explosions that cause multiple casualties. It is often shown as an F-N curve, which plots the frequency of events that exceed a given number of fatalities, N, against that number.<ref name="Barry-5-210" /> Such a curve requires the population at risk, the likelihood that people are present and the reliability of measures such as evacuation to be defined.<ref name="Barry-5-211">Barry (2002), p. 5-211.</ref> Barry (2002) describes these measures for the chemical process industries, where most calculations of risk to people are based on fatalities.<ref name="Barry-5-211" />
[[File:fse-fire-risk-v2.svg|thumb|upright=1.5|alt=Location-based individual contours contrast with cumulative frequency for multiple casualties.|Individual and societal risk answer different questions. Based on Barry (2002), pp. 5-210–5-211.]]

The two measures answer different questions. Individual risk shows how the risk to one person varies from place to place, while societal risk shows how often losses of many lives can occur.<ref name="Barry-5-210" /> Single-value risk indices, such as an annual predicted fatality rate, are easy to understand and useful for comparing design options. A ranking of the events that contribute most to the total helps to focus risk reduction.<ref name="Barry-5-211" /> In Australia, the Fire Safety Verification Method Standard 2022 accepts the deemed-to-satisfy provisions of the National Construction Code as reflecting societal expectations, including on individual and societal risk.<ref name="ABCB2022-7">Australian Building Codes Board (2022), p. 7.</ref>

== Acceptable risk ==

Acceptable risk is a value judgement applied to a chosen scale for measuring risk. It needs two prior decisions: how risk is measured, and whose views on acceptability count. For a practising engineer, acceptable risk is usually the risk acceptable to the client, while for an authority it is meant to be acceptable to society or to a particular community. A universally acceptable level of fire risk does not exist, because it depends on the problem and on the person judging it.<ref name="WH-5-4" />

People judge the same risk in different ways. Experts mainly weigh the calculated reduction in fire risk, while ordinary people also weigh costs and other needs. Enforcers act on behalf of society, and managers such as builders are most directly affected by the costs.<ref name="WH-5-1" /> The reduced fire risk of a home sprinkler system, for example, appears to be valued less by the average citizen than the benefit of a new car.<ref name="WH-5-1" /> Risks that are objectively equal are also perceived differently: people prefer certain over uncertain, familiar over unfamiliar, voluntary over involuntary and ordinary over dramatic risks.<ref name="WH-5-3" /> Dying in a fire is perceived as worse than dying in a car accident, and most people who die in fires die at home.<ref name="VR-7">Van Rossum (2027), §7.</ref>

Reducing fire risk may even increase other risks, as with the potential damage to the ozone layer from halon extinguishing agents. The goal that comes closest to zero risk is risk as low as is technically possible. In fire protection engineering, this may mean accepting the residual risk after all identified risk reduction measures have been adopted. A complication is that this residual risk may then be perceived as zero, although a non-zero risk remains.<ref name="WH-5-4" /> In Australia, workplace health and safety legislation also requires safe design, which a code of practice defines as eliminating risks to health and safety or, if this is not reasonably practicable, minimising them.<ref name="ABCB-25">Australian Building Codes Board (2020b), p. 25.</ref>

Building regulations rarely state an acceptable risk in numbers. The Australian Fire Safety Verification Method Standard 2022 notes that the National Construction Code contains no specific safety targets. A design assessed with this method must therefore be at least equivalent to the deemed-to-satisfy provisions.<ref name="ABCB2022-7" /> It adds that a full quantitative probabilistic risk assessment would ideally be used, but the tools and data for it are not included. The method instead permits a simple deterministic comparison of available and required escape times, with additional checks.<ref name="ABCB2022-18">Australian Building Codes Board (2022), p. 18.</ref>

In the Netherlands, where no risk-based limit values exist, the residual risk can be expressed as an acceptable probability of failure. One way to set it is by comparison with a reference situation that follows the rules.<ref name="VR-1-2">Van Rossum (2027), §1.2.</ref><ref name="VR-1-4">Van Rossum (2027), §1.4.</ref> In performance-based design, deciding which consequences matter is often described as setting fire safety goals, [[Fire safety objectives|fire safety objectives]] and criteria.<ref name="Meacham-5-155">Meacham (2002), p. 5-155.</ref>

== Fire statistics as evidence ==

Fire incident data show how often fires start and how severe they are. In the United States, the national fire incident reporting system collects roughly a million fires a year, but only about half of the fires reported to fire departments. A separate survey of fire departments is therefore used to scale the data up to national estimates. Fires with an unknown cause must be allocated over the known causes. If they are ignored while the share of unknowns falls, every known cause can appear to grow although the total number of fires stays the same.<ref name="HallAhrens-5-67">Hall and Ahrens (2002), pp. 5-67–5-68.</ref>

Not every fire appears in these statistics. Fires handled by the occupants or by private fire brigades are not reported, and fires in buildings with sprinklers or good detection are more likely to be controlled on site. Anecdotes show the range of fires that can happen but cannot be used to estimate rates or probabilities. Detailed databases that are not statistically representative can also mislead, so analysts should not give up statistical validity for detail.<ref name="HallAhrens-5-69">Hall and Ahrens (2002), pp. 5-69–5-70.</ref>

Data on the reliability of fire protection systems are scarce.<ref name="HallAhrens-5-69" /> Expert estimates tend to rate reliable systems even higher and unreliable systems even lower than they really are. Inspection and testing records usually come from well-maintained properties, so they show better reliability than typical buildings achieve. They can also miss short-lived failures, such as a door blocked open.<ref name="HallAhrens-5-71">Hall and Ahrens (2002), p. 5-71.</ref>

== Assessing and reducing fire risk ==

Fire risk analysis is a structured approach to decision making under uncertainty. A general procedure identifies the fire hazards, estimates their consequences and probabilities, identifies options to control them, estimates how each option changes the risk, and selects the protection.<ref name="WH-5-4" /> Methods of [[Fire risk assessment|fire risk assessment]] range from checklists and written recommendations through risk indexing to probabilistic methods.<ref name="WH-5-4" /> Checklists and written recommendations do not quantify risk: a design passes if it follows them, and the residual risk is never evaluated.<ref name="WH-5-5">Watts and Hall (2002), p. 5-5.</ref>

A risk matrix sorts hazards by classes of consequence and likelihood, and each cell can record whether such risks are acceptable or how they should be reduced. Probabilistic methods are the most informative, because their results can be traced back through explicit assumptions, data and relationships. Common tools are event trees, which follow the possible outcomes after an initiating event in time order, and fault trees, which show the combinations of system states that lead to an outcome.<ref name="WH-5-5" />

Risk can be reduced at several points in the chain from cause to consequence. The SFPE Handbook describes a causal sequence from an initiating event through its outcome and the exposure of people or property to the final consequences. The sequence can be interrupted at each of these points, by blocking the event, the outcome, the exposure or the consequence.<ref name="Meacham-5-157">Meacham (2002), p. 5-157.</ref> In the chemical process industries, some measures reduce how often incidents occur, such as preventive maintenance, control of ignition sources and operator training. Others reduce how severe they are, such as gas and fire detection, fireproofing of steel and water sprays.<ref name="Barry-5-211" />
[[File:fse-fire-risk-v3.svg|thumb|upright=1.5|alt=Ignition, fire development, exposure and consequences offer different intervention points.|Risk reduction can act at several points in the fire scenario. Based on Meacham (2002), pp. 5-157–5-159 and Barry (2002), p. 5-211.]]

Measures only reduce risk if they work when they are needed. Typical reliability questions are whether the battery in a smoke alarm works, whether a sprinkler valve is open and whether a fire door is blocked open.<ref name="WH-5-6">Watts and Hall (2002), p. 5-6.</ref> A US Nuclear Regulatory Commission guide lists causes of sprinkler failure. Examples are a closed water supply valve, an empty tank and a fire pump that fails to start, for instance after a power failure.<ref name="NUREG-10-2">Iqbal and Salley (2004), p. 10-2.</ref> Failures can also share a common cause, as when a failure of the fire detection system stops a smoke control system from working as intended.<ref name="ABCBDS-C4">Australian Building Codes Board (2020a), Data Sheet C4, p. 131.</ref>

== Uncertainty and variability ==

Fire risk estimates are always uncertain. Unwanted combustion is perhaps the least predictable common physical phenomenon, and uncertainty analysis should underpin the choice of safety factors and safety margins. This concerns the uncertainty of the engineer about how large a risk is, not the uncertainty of a potential victim about whether a fire loss will occur.<ref name="WH-5-6" /> A totally objective way to measure fire risk does not exist, because defining the problem, collecting data and combining information all involve subjective judgements.<ref name="WH-5-3" />

Uncertainty and variability are different things. It may not be known how many people will be exposed, which is uncertainty, while the people who are exposed differ from each other, which is variability.<ref name="Meacham-5-159" /> Scientific uncertainties come from theories and models, from data and inputs, from limits of the calculation, from the level of detail and from how well a model represents reality. Further uncertainty lies in human behaviour, in perceptions of risk and values, and in decision making itself.<ref name="Meacham-5-160">Meacham (2002), p. 5-160.</ref>

Calculations can hide much of this uncertainty. Fire models give single values, such as a detector activation time of 121 s, although the real time may be longer or shorter. One widely used egress model assumes that all occupants are readily mobile and start leaving as soon as they hear an alarm, which experience shows is often not the case. In a full uncertainty analysis, only the inputs that could change the decision on whether a design is acceptable, a change called switchover, need detailed quantitative treatment.<ref name="Notarianni-5-43">Notarianni (2002), pp. 5-43–5-44.</ref>

Design practice also handles variability and uncertainty in simpler ways. The Dutch national annex to Eurocode 1 (NEN-EN 1991-1-2/NB), for example, gives both average fire loads and 80 % fractiles for a more conservative approach. An 80 % fractile is a value that the actual fire load does not exceed in 80 % of cases.<ref name="VR-8-5">Van Rossum (2027), §8.5.</ref> An escape time analysis keeps a safety margin between the available and the required escape time, because many of the inputs are uncertain. The more reliable the inputs are, the smaller the margin needs to be.<ref name="VR-7-1">Van Rossum (2027), §7.1.</ref>

== See also ==

* [[Event tree analysis]]
* [[Fault tree analysis]]
* [[Quantitative risk assessment]]
* [[Reliability of fire protection systems]]
* [[Uncertainty analysis]]
* [[Fire safety concepts tree]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Australian Building Codes Board. (2022). ''Fire Safety Verification Method Standard 2022''.
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-176–5-213). National Fire Protection Association; Society of Fire Protection Engineers.
* Hall, J. R., Jr., & Ahrens, M. J. (2002). Data for engineering analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-65–5-78). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Meacham, B. J. (2002). Building fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-153–5-175). National Fire Protection Association; Society of Fire Protection Engineers.
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Notarianni, K. A. (2002). Uncertainty. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-40–5-64). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Watts, J. M., Jr., & Hall, J. R., Jr. (2002). Introduction to fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-1–5-7). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Risk Analysis]]

Fire safety objectives

2026-11-02T21:32:51Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Fire safety objectives''' are the specific fire safety goals that a building or facility is meant to achieve.<ref name="Watts-5-136">Watts (2002), pp. 5-136–5-137.</ref> Typical examples are life safety, property protection, continuity of operations, environmental protection and the preservation of heritage.<ref name="Watts-5-136" /> They state what a fire safety design has to achieve, and so explain why fire safety measures are taken at all.<ref name="VR-1">Van Rossum (2027), §1.</ref> Some objectives are set by law, such as protecting the occupants and preventing fire spread between buildings. Others are chosen by the client or by other stakeholders, for example an insurer.<ref name="IFEG-1-2-7">National Research Council of Canada et al. (2005), pp. 1.2-7–1.2-8.</ref> [[Fire safety engineering]] can itself be defined as applying all fire-related knowledge to achieve the relevant fire safety goals of a project, so the objectives come first.<ref name="VR-1-1">Van Rossum (2027), §1.1.</ref>

Objectives are normally written in general words, such as safeguarding people from an unacceptable risk of injury or illness caused by fire.<ref name="CVM2-37">Ministry of Business, Innovation and Employment (2025b), p. 37.</ref> Before a design can be checked, they are refined into numerical performance criteria, for example a maximum temperature or a limit on fire spread.<ref name="Notarianni-5-52">Notarianni (2002), pp. 5-52–5-53.</ref> Building regulations seldom state how safe is safe enough.<ref name="VR-1-2">Van Rossum (2027), §1.2.</ref><ref name="IFEG-NZ-0-2-5">National Research Council of Canada et al. (2005), Part 0 (New Zealand), p. 0.2-5.</ref> In a performance-based design, the objectives and criteria are therefore agreed between the parties involved before the analysis starts.<ref name="IFEG-1-2-2">National Research Council of Canada et al. (2005), p. 1.2-2.</ref><ref name="IFEG-US-0-2-8">National Research Council of Canada et al. (2005), Part 0 (United States), p. 0.2-8.</ref>

== Goals, objectives and criteria ==

In the SFPE Handbook, a common hierarchy of fire safety decisions has five levels, although a particular application may have more or fewer. Objectives form the second level.<ref name="Watts-5-136" /> Above them is the fire safety policy that an organisation adopts to achieve security against fire and its effects. Below them come strategies, each of which contributes wholly or partly to the objectives. The lowest levels are attributes and survey items, which can be measured or estimated in a real building.<ref name="Watts-5-136" /> Broad aims such as fire prevention, fire control and occupant protection usually appear in the introductory sections of building codes and fire safety laws.<ref name="Watts-5-136" />

The terms are not used consistently, and an objective is sometimes simply called a goal. The International Fire Engineering Guidelines (2005) define an objective as the desired overall safety outcome, expressed in qualitative terms.<ref name="IFEG-US-0-5-4">National Research Council of Canada et al. (2005), Part 0 (United States), pp. 0.5-4–0.5-5.</ref> A functional statement is more specific and states what the building, its systems or its occupants must achieve for an objective to be met. A performance requirement gives the criteria, in engineering terms, by which a trial design is judged.<ref name="IFEG-US-0-5-4" /> In the SFPE Handbook, stakeholders first identify broad goals, such as protecting people and property. These goals are then refined into objectives that can be quantified in engineering terms.<ref name="Notarianni-5-52" />

A simple chain shows how the levels connect, starting from the goal of protecting the occupants. A matching objective may be to keep the gas concentrations in a corridor tenable. The performance criterion then sets the numerical limit against which the expected performance of the design is compared.<ref name="Notarianni-5-52" /> New Zealand's Building Code uses the same ladder of objectives, functional requirements and performance criteria.<ref name="CVM2-2">Ministry of Business, Innovation and Employment (2025b), p. 2.</ref> A report for the US Nuclear Regulatory Commission notes that performance-based designs state their goals explicitly, whereas prescriptive requirements contain them only implicitly.<ref name="NUREG-1-9">Iqbal and Salley (2004), p. 1-9.</ref>

Objectives can be secured in two ways. In a rule-based approach, the design follows predefined rules and limit values, such as legislation, the conditions of an insurer or company rules. Such rules are generic and inflexible, and only partly tailored to the building, its users and its surroundings. In a risk-based or goal-based approach, fire safety is assessed for the specific project, so that more factors can be weighed together. In the Netherlands, such an alternative to the Dutch Buildings Decree (Bbl) is called equivalence. Article 4.7 of the Environment and Planning Act (Omgevingswet) allows it on condition that it achieves at least the same level of fire safety as the prescribed measure that it replaces.<ref name="VR-1" />

== Typical objectives ==

Most fire safety objectives trace back, directly or indirectly, to the protection of people.<ref name="HallAhrens-5-74">Hall and Ahrens (2002), p. 5-74.</ref> The safety of the people in a building when a fire breaks out is one of the most important objectives. Dying in a fire is also perceived as worse than dying in a car accident.<ref name="VR-7">Van Rossum (2027), §7.</ref> Keeping every occupied area completely free of fire effects would be a very conservative and generally unachievable objective. An engineering analysis therefore has to consider what happens to the occupants: how many there are, where they are, how they act and what they can do.<ref name="HallAhrens-5-74" />

Building codes commonly also aim to facilitate the work of the emergency services. Property objectives can concern the building itself, its contents and equipment, or neighbouring buildings. Other common objectives are business continuity and financial viability, corporate and public image, and community interests and infrastructure. Some projects also aim to protect heritage in older or significant buildings, or to limit the release of hazardous materials into the environment.<ref name="IFEG-1-2-7" /> The book ''Introduction to Fire Safety Engineering'' adds limiting the impact of a fire on society. It notes that its own list is an arbitrary and incomplete mix of public and private goals.<ref name="VR-1" />

It is not always clear how something is valued or how its loss should be described.<ref name="Meacham-5-153">Meacham (2002), pp. 5-153–5-154.</ref> For life safety, some people draw the line simply between life and death. Others also count quality of life, pain and suffering, and rehabilitation after an injury.<ref name="Meacham-5-155">Meacham (2002), p. 5-155.</ref> For property, smoke and water damage should be considered as well as damage by heat. For business continuity, a loss of image and market share can follow long after the short-term losses of downtime.<ref name="Meacham-5-153" />

Outside ordinary buildings, the objectives can be quite different. For US nuclear power plants, the primary objectives of fire protection programmes are to minimise both the probability and the consequences of fire. Through defence in depth, these programmes are designed to give reasonable assurance that a fire will not prevent a safe shutdown and that radioactive releases are minimised.<ref name="NUREG-1-1">Iqbal and Salley (2004), p. 1-1.</ref> Defence in depth aims at a balance between preventing fires from starting, detecting and suppressing fires quickly, and limiting the consequences of a fire.<ref name="NUREG-F-20">Iqbal and Salley (2004), p. F-20.</ref>

== Objectives in building regulations ==

[[Building regulations]] set the public objectives that every building must meet, usually in broad words rather than in numbers.<ref name="VR-1-4">Van Rossum (2027), §1.4.</ref><ref name="ABCB-14">Australian Building Codes Board (2020b), p. 14.</ref> In the Netherlands, the explanatory notes to the Dutch Buildings Decree (Bbl) give two aims for its fire safety rules. These are preventing casualties, both injured and dead, and preventing a fire from spreading to another plot. Preserving the building and preventing damage to the environment, monuments or social facilities or interests are explicitly not objectives of the decree. The rules work these aims out in sub-goals, such as keeping the structure standing, limiting fire and smoke spread, and keeping escape and firefighting routes usable.<ref name="VR-1-2" />

In New Zealand, Verification Method C/VM2 (second edition, 2025) relates all its design scenarios to three fire objectives of the Building Code.<ref name="CVM2-7">Ministry of Business, Innovation and Employment (2025b), pp. 7–8.</ref> They are to safeguard people from an unacceptable risk of injury or illness caused by fire, and to protect other property from damage caused by fire. The third is to facilitate firefighting and rescue operations.<ref name="CVM2-58">Ministry of Business, Innovation and Employment (2025b), pp. 58–59.</ref> In Australia, the 2020 handbook to the Fire Safety Verification Method, written for the 2019 edition of the National Construction Code (NCC 2019), summarises the broad fire objectives of that code.<ref name="ABCB-2">Australian Building Codes Board (2020b), p. 2.</ref> They are life safety of occupants, protection of other property, facilities for firefighting and fire safety during construction. The protection of the building itself and its contents is addressed only to a limited extent for some building classes.<ref name="ABCB-27">Australian Building Codes Board (2020b), pp. 27–28.</ref>

The International Fire Engineering Guidelines describe two further systems as they were in 2005. The 2005 National Building Code of Canada was the first edition in an objective-based format, in which every provision serves at least one stated objective. Its objectives are worded as limiting the probability of undesirable situations, because a code cannot prevent them completely. The risk that remains after the code is complied with is regarded as the acceptable risk.<ref name="IFEG-CA-0-2-2">National Research Council of Canada et al. (2005), Part 0 (Canada), p. 0.2-2.</ref> For the United States, the guidelines note that choosing the intended level of performance is a value judgement that should ultimately be made by policy makers rather than by designers.<ref name="IFEG-US-0-2-6">National Research Council of Canada et al. (2005), Part 0 (United States), p. 0.2-6.</ref>

The overall level of safety is rarely stated in numbers.<ref name="ABCB-14" /> The Dutch rules do not lay down how many deaths and injuries are acceptable, or how large the risk of fire spread to a neighbouring plot may be. Their measurable limits apply to the measures instead, such as walking distances, minutes of fire resistance and compartment areas. These limits grew partly from consensus and partly from history, not from a quantified goal.<ref name="VR-1-2" /> The 2005 guidelines note that in New Zealand, too, the level of safety of the Building Code is not always stated explicitly, which can make its requirements hard to interpret.<ref name="IFEG-NZ-0-2-5" />

== Objectives of owners and other stakeholders ==

In a performance-based project, the objectives are agreed in the fire engineering brief (FEB), the process in which the stakeholders set down the basis of the analysis.<ref name="IFEG-1-2-2" /><ref name="IFEG-1-2-7" /> The International Fire Engineering Guidelines suggest first identifying the objectives of each stakeholder, which may differ. These are then divided into building regulatory, other regulatory and non-regulatory objectives. Other regulatory objectives come from laws on matters such as the environment, occupational health and safety, the fire services, dangerous goods and planning. Non-regulatory objectives are set by the client or other stakeholders, for example to limit damage to the structure, contents and equipment.<ref name="IFEG-1-2-7" />
[[File:fse-fire-safety-objectives-v1.svg|thumb|upright=1.5|alt=Building law, other law and stakeholders contribute distinct objectives to one project.|Fire-safety objectives arise from different requirements and stakeholder goals. Based on National Research Council of Canada et al. (2005), pp. 1.2-7–1.2-8.]]

Complying with the code and protecting an owner's assets are not the same thing. Some owners do not realise that code compliance can differ significantly from protecting their building, process, contents or other assets of value. Such differences matter when tolerable damage and acceptance criteria are chosen, so the interested and affected parties must be involved.<ref name="Meacham-5-155" /> For New Zealand, the 2005 guidelines explain that the Building Act 2004 does not require anyone to exceed the performance criteria of the Building Code, so doing so is the owner's choice.<ref name="IFEG-NZ-0-3-6">National Research Council of Canada et al. (2005), Part 0 (New Zealand), p. 0.3-6.</ref>

Clients also have objectives that are not about fire but still affect fire safety. Examples are increased security, natural lighting, an open-plan layout, new materials, energy efficiency, flexibility for future uses and low life-cycle costs.<ref name="IFEG-1-2-7" /> In the New Zealand part of the guidelines, the fire engineer is responsible for ensuring that such objectives do not stop the design from meeting the fire requirements of the Building Code.<ref name="IFEG-NZ-0-3-3">National Research Council of Canada et al. (2005), Part 0 (New Zealand), p. 0.3-3.</ref> The engineer should also explain to the client the effect of adopting further objectives or not, and decline instructions where the objectives are unacceptable.<ref name="IFEG-NZ-0-4-1">National Research Council of Canada et al. (2005), Part 0 (New Zealand), p. 0.4-1.</ref> In Australia, the 2020 handbook likewise asks for client and end-user objectives to be identified early.<ref name="ABCB-22">Australian Building Codes Board (2020b), p. 22.</ref>

Stakeholders do not always value the same outcomes in the same way. Some people accept a higher risk to firefighters, who take on risk as part of their job, if this lowers the risk to the public, while others do not.<ref name="Notarianni-5-46">Notarianni (2002), p. 5-46.</ref> Stakeholders may want to protect historic features or to avoid business interruption, and those with different values may see these needs differently. The SFPE Handbook therefore advises identifying where value judgements enter a design and making these assumptions explicit.<ref name="Notarianni-5-52" />

== From objectives to acceptance criteria ==

Objectives are too broad to be checked directly, so [[Acceptance criteria|acceptance criteria]] are set for the analysis.<ref name="IFEG-CA-0-2-2" /> The criteria must suit the objectives, the performance requirements and the analysis methods. They must also be numerical, unless the analysis is qualitative, and realistic: zero risk is not an appropriate criterion.<ref name="IFEG-1-2-25">National Research Council of Canada et al. (2005), pp. 1.2-25–1.2-26.</ref> In the ten-step design process of the SFPE engineering guide, as tabulated in the SFPE Handbook, the scope, goals and objectives are defined before the performance criteria are developed. Design fire scenarios, candidate designs and their evaluation follow after that.<ref name="Notarianni-5-52" />

The guidelines give typical criteria for each general objective. Protecting occupants can be judged by the margin between the available and the required escape time, and by the smoke layer height. Other occupant criteria are the temperature and radiant heat of the hot layer, the smoke density and the carbon monoxide level. Facilitating the fire services can be judged by radiant heat, structural failure, water supply and resources at the fire scene. Protecting adjacent property uses the radiant heat from the fire and flame impingement, while limiting damage and keeping a business running use monetary loss, smoke release and corrosive gases. Environmental objectives use the toxicity of the fire gases, the containment of firefighting water and the expected risk to plants and animals.<ref name="IFEG-1-2-25" />
[[File:fse-fire-safety-objectives-v2.svg|thumb|upright=1.5|alt=Objective, exposed group, scenario, criterion and evidence form a traceable assessment chain.|Objectives must be translated into assessable criteria and evidence. Based on National Research Council of Canada et al. (2005), pp. 1.2-25–1.2-26.]]

Regulations sometimes fix the numbers themselves. In New Zealand, the objective of protecting other property is backed by limits on the radiation received from a fire. The radiation may not exceed 30 kW/m² at the boundary of the property, or 16 kW/m² at 1 m beyond it. These values belong to the New Zealand Building Code as applied in C/VM2 (second edition, 2025).<ref name="CVM2-43">Ministry of Business, Innovation and Employment (2025b), p. 43.</ref> In an absolute assessment, the values may instead be agreed in the fire engineering brief, and they should allow for uncertainty and safety factors.<ref name="IFEG-1-2-25" />

Two approaches are used to judge whether a design meets its objectives.<ref name="IFEG-1-2-21">National Research Council of Canada et al. (2005), p. 1.2-21.</ref> In a comparative approach, the trial design is compared with an otherwise identical building that follows the prescriptive rules.<ref name="IFEG-1-2-21" /> The same criteria are used for both, and the trial design should perform at least as well.<ref name="IFEG-1-2-25" /> In an absolute approach, the results are matched directly against the objectives using the agreed criteria.<ref name="IFEG-1-2-21" /> In Australia, the Fire Safety Verification Method compares the design with a reference building that follows the deemed-to-satisfy provisions. This can make the outcome less sensitive to the choice of inputs and methods.<ref name="ABCBDS-i">Australian Building Codes Board (2020a), p. i.</ref>

== How objectives guide the design ==

The Australian handbook defines a [[Fire safety strategy|fire safety strategy]] as a combination of physical and human measures, including maintenance and management, specified to achieve the nominated fire safety objectives.<ref name="ABCB-140">Australian Building Codes Board (2020b), p. 140.</ref> The design process normally starts by defining the relevant objectives, of the building code and any others, and then develops the strategy. The handbook describes fire safety engineering as a logical sequence from objectives and performance requirements to the strategy, fire scenarios, detailed analysis and the decision on compliance.<ref name="ABCB-20">Australian Building Codes Board (2020b), p. 20.</ref> The documented strategy should include a summary of the fire safety objectives.<ref name="ABCB-31">Australian Building Codes Board (2020b), p. 31.</ref>

Strategies link the objectives to concrete measures. Examples are ignition prevention, limitation of combustibles, compartmentation, detection and alarm, suppression and the protection of exposed people or things. A matrix of objectives against strategies shows how important each strategy is for each objective.<ref name="Watts-5-136" /> A single system can serve several objectives: smoke and heat venting is designed to help people escape, to let firefighters see the seat of the fire, and to reduce property damage.<ref name="Cooper-3-219">Cooper (2002b), p. 3-219.</ref> How well a system serves an objective depends on two factors. Efficacy is the degree to which it achieves a design objective when it works as specified, and reliability is the probability that it does work as specified.<ref name="ABCBDS-C4">Australian Building Codes Board (2020a), Data Sheet C4, p. 125.</ref>

The [[Fire safety concepts tree|fire safety concepts tree]], a diagram based on the judgements of an NFPA technical committee, starts from the fire safety objectives at its top. Below them, it splits into two branches: preventing fire ignition and managing the fire impact. One branch or the other must succeed for the objectives to be met. Ignition is prevented by controlling heat sources, their interaction with fuel, and the fuel itself. Fire impact is reduced either by managing the fire itself or by managing what is exposed to it. If ignition is not prevented, the tree helps to evaluate whether the systems of the building can manage the fire impact.<ref name="Meacham-5-158">Meacham (2002), p. 5-158.</ref>
[[File:fse-fire-safety-objectives-v3.svg|thumb|upright=1.5|alt=Fire-safety objectives branch into preventing ignition and managing fire impact.|Prevention and impact management provide complementary paths towards objectives. Based on Meacham (2002), p. 5-158.]]

In New Zealand, C/VM2 (second edition, 2025) tests a design against ten design scenarios that must each be satisfied separately. Each scenario is tied to one or more of the Building Code objectives.<ref name="CVM2-7" /> One scenario checks that the failure of a critical part of the fire safety system does not cause the design to miss those objectives. Each key system, such as smoke management or a fire door, is assumed to fail in turn, and the design is changed if the occupants could then no longer escape safely. Sprinklers and automatic fire alarms installed to a recognised standard are treated as reliable enough to be exempt.<ref name="CVM2-58" />

== Limits and common misconceptions ==

Fire safety objectives do not aim at absolute safety. For New Zealand and the United States, the International Fire Engineering Guidelines state that absolute safety and zero risk are not achievable. The accepted risk takes into account what the community expects and what safety costs the community.<ref name="IFEG-NZ-0-2-5" /><ref name="IFEG-US-0-2-8" /> The Australian handbook adds that removing all risk would bring the fire safety strategy into conflict with the function and use of the building.<ref name="ABCB-27" /> Objectives therefore aim at an acceptable or tolerable level of [[Fire risk|fire risk]], not at the absence of risk.<ref name="IFEG-CA-0-2-2" /><ref name="ABCB-27" />

Deriving that level from the regulations is difficult, because their actual outcomes differ widely between types of building. In the Netherlands, the chance of dying in a fire per hour of stay is much greater in a residential building than in an assembly building. Yet the requirements for fire detection are stricter for assembly buildings. For an engineering approach, the required performance or the accepted residual risk must therefore be agreed in advance, for example by comparison with a reference situation that follows the rules.<ref name="VR-1-2" /> The Netherlands has no risk-based limit values, a drawback for quantitative analysis there.<ref name="VR-1-4" />

Objectives also carry values and uncertainty. The SFPE Handbook (2002) notes that no significant work has been done to identify what fire safety is trying to achieve, so lists of objectives are very subjective.<ref name="Watts-5-136" /> Few studies show how society values fire safety risks at the level needed for performance-based trade-offs.<ref name="Notarianni-5-46" /> Uncertainty arises in the science, in human behaviour, in perceptions of risk and values, and in decision making itself. Some people are risk tolerant, while others are risk averse.<ref name="Meacham-5-160">Meacham (2002), p. 5-160.</ref>

Meeting one objective does not mean meeting the others. Two designs may be equivalent for life safety but not for property protection, business interruption or structural collapse. The conditions behind the objectives also change over the life of a building, because its use, its occupants and even the fire service may change.<ref name="Notarianni-5-46" /> The fire safety of a building depends on its fire safety system continuing to work and on management limits, such as fuel loads and free escape routes, being respected. When a building is altered or its use changes, the existing fire engineering evaluation may have to be re-examined to see whether it still applies.<ref name="IFEG-NZ-0-3-8">National Research Council of Canada et al. (2005), Part 0 (New Zealand), p. 0.3-8.</ref>

== See also ==

* Qualitative design review
* [[Performance-based design]]
* [[Prescriptive design]]
* [[Equivalency]]
* [[Fire scenario]]
* [[Fire safety management]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Cooper, L. Y. (2002b). Smoke and heat venting. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-219–3-242). National Fire Protection Association; Society of Fire Protection Engineers.
* Hall, J. R., Jr., & Ahrens, M. J. (2002). Data for engineering analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-65–5-78). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Meacham, B. J. (2002). Building fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-153–5-175). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Notarianni, K. A. (2002). Uncertainty. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-40–5-64). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Watts, J. M., Jr. (2002). Fire risk indexing. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-125–5-142). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Safety Design & Regulation]]

Firefighting foam

2026-11-02T21:32:51Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Firefighting foam''' is a mass of air-filled bubbles made from water and a foam concentrate. It is applied to a burning surface or used to fill a space. On a suitable liquid pool, the foam forms a floating blanket that limits vapour release, reduces heat feedback and separates the fuel from air.<ref name="Scheffey-4-88">Scheffey (2002), p. 4-88.</ref><ref name="NUREG-B58">Iqbal and Salley (2004), pp. B-57–B-58.</ref>

Foam is not simply soapy water or one standard chemical product. Different formulations have different flow, drainage, fuel resistance and film-forming behaviour. Concentrate must be mixed in the intended proportion, aerated and delivered in a way that creates and preserves the required blanket.<ref name="Scheffey-4-88" /><ref name="NUREG-B60">Iqbal and Salley (2004), p. B-60.</ref>

The principal use discussed in the sources is control and extinction of flammable-liquid pool fires. Foam can also be used for particular ordinary-combustible and space-filling applications. Its suitability is limited by fuel chemistry, surface shape, heat, water incompatibility and destruction of the blanket.<ref name="NUREG-B58" /><ref name="Scheffey-4-89">Scheffey (2002), p. 4-89.</ref>

== Formation and physical form ==

Producing foam starts with proportioning concentrate into water. Scheffey describes typical proportions of 1, 3 or 6 percent concentrate for the applications in his chapter, not as universal values for every product. The solution is then aerated to create bubbles.<ref name="Scheffey-4-88" />
[[File:fse-firefighting-foam-v1.svg|thumb|upright=1.5|alt=Concentrate and water are proportioned and aerated before foam spreads over liquid fuel.|Foam production ends with a blanket over the fuel surface. Based on Scheffey (2002), p. 4-88.]]

Expansion describes the increase from solution volume to foam volume. Low-expansion foams are relatively fluid and can spread across a liquid surface. Medium- and high-expansion foams can provide large bubble volumes for filling spaces, but these forms create different application and occupancy concerns.<ref name="NUREG-B61">Iqbal and Salley (2004), pp. B-60–B-61.</ref>

A useful blanket combines expansion, cohesion, stability and fluidity. Bubbles must adhere sufficiently to form a layer, while the foam must still flow around obstructions. It must also resist fuel pickup and thermal damage so that the blanket does not itself become contaminated and burn.<ref name="NUREG-B59">Iqbal and Salley (2004), p. B-59.</ref>

Drainage is the loss of liquid from the bubble structure. NUREG-1805 describes a 25 percent drainage measure as the time for one quarter of the liquid content to drain under standard conditions. The cited typical range of 2 to 5 minutes is a foam property under that test, not an extinction time.<ref name="NUREG-B59" />

Film formation is distinct from bubble coverage. Some solutions draining from foam spread as a thin aqueous film over hydrocarbon fuel. That film can help seal vapour, but it does not occur for every formulation or fuel.<ref name="Scheffey-4-89" />

=== Expansion and a worked flow example ===

Expansion ratio compares the volume of finished foam with the liquid solution used to make it. Both volumes refer to the same sample or to matching flow intervals. The ratio describes added air volume, rather than an increase in the amount of water or concentrate.<ref name="NUREG-B61" />

<math display="block">E=\frac{V_f}{V_s},\qquad \dot V_f=E\dot V_s</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>E</math> || Foam expansion ratio || 1
|-
| <math>V_f,V_s</math> || Finished foam and solution volumes || m³
|-
| <math>\dot V_f,\dot V_s</math> || Finished foam and solution volume flow rates || L/min
|}

The example in NUREG-1805 uses an expansion ratio of 8:1. Its solution application rate converts to approximately 4.07 L/(m² min). Multiplying by eight gives approximately 32.6 L/(m² min) of expanded foam, before accounting for losses between generation and useful coverage.<ref name="NUREG-B61" />

<math display="block">8\times4.07\approx32.6\ \mathrm{L/(m^2\,min)}</math>

This is a reproduction of the source's volume calculation, not a prescribed application rate for another fuel. The finished foam contains the same liquid quantity as the original solution, distributed through a larger bubble structure. Heat, drainage and mechanical damage then change the volume and condition that remain over the fuel.<ref name="NUREG-B59" /><ref name="NUREG-B61" />

Expansion and drainage are therefore reported together. Scheffey describes an early aqueous film-forming foam (AFFF) formulation with expansion of 8:1 and a 25% drainage time of 6 min. That historical result differs from the 2–5 min discussion in NUREG-1805 because the passages describe different foam evidence, rather than one universal pass criterion.<ref name="Scheffey-4-89" /><ref name="NUREG-B59" />

== Extinguishing action ==

The [[Extinguishing mechanisms]] of foam include blanketing, cooling and reduced vaporisation. A complete surface layer restricts air contact and interrupts the transfer of radiant heat that supports fuel evaporation. Less vapour then reaches the combustion zone.<ref name="NUREG-B15">Iqbal and Salley (2004), p. B-15.</ref>

Water draining from the foam provides additional cooling. If the liquid is water soluble, that water can also dilute the fuel and reduce its vapour pressure. Deep pools can require substantial dilution, so formulation and application remain important even for soluble fuels.<ref name="NUREG-B15" /><ref name="NUREG-B58" />

Foam is lighter than the aqueous solution draining from it and lighter than the hydrocarbon liquids described by Scheffey. It therefore floats and spreads over the fuel. Low-expansion foam is especially associated with two-dimensional [[Pool fire]] conditions rather than fuel running from an elevated leak.<ref name="Scheffey-4-88" />

The blanket can protect exposed surfaces that are not yet burning. Low surface tension can also help foam enter crevices. These benefits depend on reaching the surface and maintaining coverage under fire and wind conditions.<ref name="NUREG-B58" />

Visible flame knockdown does not guarantee lasting extinction. If the blanket is disrupted, vapour can again reach an ignition source and burnback can occur. The residual layer and continued control of the fuel surface are therefore central to performance.<ref name="NUREG-B60" />

== Foam types and fuel compatibility ==

Protein foam uses hydrolysed protein materials and forms a blanket without the aqueous surface film associated with AFFF. Fluoroprotein products add surface-active agents to alter fuel shedding and flow. These are separate formulations, not interchangeable descriptions of one concentrate.<ref name="Scheffey-4-89" />

[[Aqueous film-forming foam|Aqueous film-forming foam (AFFF)]] contains surface-active compounds that allow drained solution to form a film on suitable hydrocarbon fuels. The foam bubbles and draining film both contribute to vapour suppression. Excessive stiffness and slow drainage can hinder flow and film formation.<ref name="Scheffey-4-89" />

Alcohol-resistant concentrates are intended for water-miscible fuels such as the alcohols identified in the source. Scheffey describes a floating polymeric skin that protects the foam from polar-solvent breakdown. An ordinary hydrocarbon-fuel foam should not be assumed to survive on those fuels.<ref name="Scheffey-4-89" />

[[Fire classes]] provide selection categories, but their definitions depend on the national system. In the US table reproduced in NUREG-1805, foam is listed for ordinary combustibles and flammable-liquid fires. This does not imply that every foam is suitable for every fuel within those broad groups.<ref name="NUREG-B16">Iqbal and Salley (2004), p. B-16.</ref>

Foam remains principally water based. It can share water's incompatibility with reactive substances and energised electrical equipment. The chosen foam must be checked against the actual liquid, equipment and discharge arrangement rather than selected solely by its fire-performance label.<ref name="NUREG-B60" />

== Application and system design ==

Foam delivery has three stages: proportioning, foam generation and distribution. Air aspiration is a basic generation method. Fixed spray systems, monitors and mobile hose equipment can apply foam, but the final blanket depends on the operation of the complete chain.<ref name="NUREG-B60" />

Low-expansion foam is commonly associated with storage-tank tops, bunds and spills. Medium- and high-expansion foam can fill spaces such as basements. These applications differ in distribution, agent quantity and hazards to people within the foam-filled space.<ref name="NUREG-B61" />

Application must compensate for foam lost through heating, vaporisation and physical disruption. NUREG-1805 explains that a residual layer must remain over already extinguished portions while coverage advances. A nominal flow at the nozzle is therefore not the same as effective coverage at the fuel.<ref name="NUREG-B59" />
[[File:fse-firefighting-foam-v3.svg|thumb|upright=1.5|alt=Fresh foam enters a blanket while heat, drainage, fuel and rising gases remove or disrupt it.|A foam blanket needs continued protection against losses. Based on Iqbal and Salley (2004), pp. B-58–B-60.]]

Tank application can use foam chambers, internal distributors or subsurface injection, depending on tank form. Top application can be hindered by rising gases or damage from an initial explosion. Floating roofs introduce different distribution problems, so one tank arrangement cannot be transferred uncritically to another.<ref name="NUREG-B61" />

The fixed [[Extinguishing agent]] supply must include enough concentrate and water for the intended duration. Large tank fires can require substantial inventories and logistical arrangements. Disposal and containment of the resulting foam solution are part of the operational problem.<ref name="NUREG-B61" />

== Fire geometry and application method ==

A horizontal, immiscible hydrocarbon pool offers a surface on which foam can spread. Water alone may pass beneath the lighter liquid while the fuel continues to burn. The foam blanket addresses that geometry by remaining above the liquid and limiting vapour production.<ref name="Fleming-4-72">Fleming (2002), p. 4-72.</ref><ref name="Scheffey-4-88" />

Running fuel and pressurised sprays do not provide the same continuous horizontal surface. Scheffey describes these as three-dimensional fires for which low-expansion foam is less effective. The source discusses supplementary agents in such cases, subject to compatibility between the chosen products.<ref name="Scheffey-4-88" />
[[File:fse-firefighting-foam-v2.svg|thumb|upright=1.5|alt=A continuous pool blanket contrasts with foam failing to cover running fuel and a spray fire.|Fuel geometry changes the usefulness of a foam blanket. Based on Scheffey (2002), p. 4-88.]]

Water-soluble fuels alter the blanket's survival. Their ability to mix with the foam's liquid can destroy an unsuitable formulation, while drainage also changes fuel concentration. Alcohol-resistant products address this specific interaction rather than merely increasing the quantity of generic foam.<ref name="Scheffey-4-89" />

Tank-top application must overcome the size and conditions of the fuel surface. Strong upward gas flow can divert light foam, and explosion damage can impair fixed equipment. Distribution should therefore be assessed for the fire condition, not only for a calm commissioning demonstration.<ref name="NUREG-B58" /><ref name="NUREG-B61" />

Space-filling foam follows a different objective from pool coverage. Large bubble volumes inundate surfaces and cavities, making distribution through the volume central to the design. This introduces restricted visibility and movement, which are less prominent in a thin surface blanket.<ref name="NUREG-B60" /><ref name="NUREG-B61" />

== Testing, properties and records ==

Expansion ratio records how much foam is produced from a given solution volume, but a larger volume does not by itself establish better extinction. Flow, drainage and resistance to the fuel must remain suitable. The properties interact as the blanket spreads and ages.<ref name="NUREG-B59" />

Drainage influences both cooling and film formation. Liquid leaving the bubbles can spread on a suitable hydrocarbon, while excessive loss can weaken the remaining blanket. Test measurements therefore need the product, expansion condition and measurement method to be meaningful.<ref name="Scheffey-4-89" /><ref name="NUREG-B59" />

Foam shear properties affect its ability to flow and remain coherent. NUREG-1805 gives a torsional-viscometer example for fluidity, illustrating that foam is characterised by physical measurements as well as fire tests. Such a measurement is not a universal field-application rate.<ref name="NUREG-B59" />

Fire tests should represent the intended fuel's solubility, temperature and geometry. A hydrocarbon pool result cannot establish performance on a polar solvent or a pressurised discharge. The tested application rate and coverage period must also accompany any claim of extinction.<ref name="Scheffey-4-88" />

Records should preserve concentrate identity, intended proportion, compatible equipment and relevant water-quality conditions. Substitution in one part of this chain can alter the foam reaching the fuel. Test evidence belongs to the resulting formulation and application, not just to a product family name.<ref name="NUREG-B59" /><ref name="NUREG-B60" />

== Losses, hazards and limitations ==

Heat destroys bubbles and evaporates their water. Mechanical impact, incompatible chemical agents and rising combustion gases can also divert or disrupt foam. Simultaneous use of another agent must therefore be based on demonstrated compatibility rather than assumed additive benefit.<ref name="NUREG-B58" /><ref name="NUREG-B59" />

Water quality can influence foam properties. NUREG-1805 reports deleterious effects from contaminants such as corrosion inhibitors and anti-fouling agents in a cited study. Product testing with the intended supply and equipment provides more relevant evidence than a generic claim of water compatibility.<ref name="NUREG-B59" />

Hot fuel creates another limit. Applying water-based foam to liquid above water's boiling temperature can generate steam, expand the foam and eject burning liquid. The source gives particular warnings at temperatures of 100 °C or above and for hot oils or fats.<ref name="NUREG-B60" />

Medium- and high-expansion foam can obscure visibility and restrict movement. Filling an occupied space with foam also presents an asphyxiation concern in NUREG-1805. Space-filling performance must consequently be assessed together with the safety of anyone present.<ref name="NUREG-B60" />

Foam performance is largely established through empirical tests. Scheffey states that there was no general international agreement on all fire tests or a complete first-principles explanation of foam extinction in the cited handbook. Product claims must therefore retain their fuel, test and application context.<ref name="Scheffey-4-88" />

Environmental acceptability is not established by fire-test performance. Historical fluorinated-agent descriptions explain chemical behaviour but do not provide current regulatory approval. The supplied engineering sources do not support a general statement that every modern foam formulation has equivalent environmental effects.<ref name="Scheffey-4-89" />

Protein-based foam generally produces a relatively thick blanket. Film-forming foam can be less viscous and spread more rapidly, allowing its drained solution to contribute to vapour sealing. Those differences affect coverage speed and resistance to disruption rather than representing a simple ranking of all products.<ref name="Scheffey-4-88" />

AFFF requires a balance between expansion and drainage. Scheffey describes early tests in which very stiff, highly expanded foam resisted flow and slowed film formation. Lower expansion improved movement and drainage while retaining enough stability to resist burnback in the reported work.<ref name="Scheffey-4-89" />

Storage-tank design also depends on roof construction. Fixed-roof tanks can use chambers, distributors or subsurface injection, while a tilted or sunken floating roof can obstruct distribution. These examples show why a foam system's hardware must match the protected geometry.<ref name="NUREG-B61" />

Low-expansion foam can be injected below the liquid surface in suitable tank systems. This can reduce reliance on foam falling through rising combustion gases. It does not remove the need to check distribution throughout the tank or the condition of injection equipment after an explosion.<ref name="NUREG-B61" />

Mobile foam equipment adds proportioning and logistics to the fireground problem. Concentrate, water, hoses and generation equipment must remain available for the intended attack. A large inventory at a remote store does not establish sufficient delivered foam at the fuel surface.<ref name="NUREG-B61" />

The aftermath includes contaminated fuel, drained solution and damaged blanket material. Re-ignition protection depends on the condition of the surface after active application. Assessment must therefore include the persistence of coverage as well as the initial rate of flame reduction.<ref name="NUREG-B60" />

== See also ==

* [[Fire suppression system]]
* [[Deluge system]]
* Boilover

== Notes ==

<references />

== References ==

* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Scheffey, J. L. (2002). Foam agents and AFFF system design considerations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-88–4-122). National Fire Protection Association.

[[Category:Fire Suppression]]

Fire testing

2026-11-02T21:32:51Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Fire testing''' is the controlled evaluation of materials, products, components or systems under specified fire or thermal exposure. Tests provide measurements such as ignition time, heat release rate, mass loss, flame spread, smoke production and fire resistance. Their purpose is to characterise response under defined conditions rather than to reproduce every possible real fire.<ref name="Janssens-3-38">Janssens (2002), pp. 3-38–3-39.</ref><ref name="Babrauskas-3-3">Babrauskas (2002), p. 3-3.</ref>

Tests range from bench-scale material measurements to full-scale product and system experiments. Each scale addresses different controlling processes, including material decomposition, room feedback, ventilation and installation geometry. Results should therefore be applied only with a suitable model and a clear account of the test arrangement.<ref name="Babrauskas-3-1">Babrauskas (2002), p. 3-1.</ref><ref name="Babrauskas-3-3" />

Fire testing supports [[Reaction to fire]] and [[Fire resistance test]] assessments, design data, product comparison and model validation. It also reveals uncertainty from apparatus, specimen preparation, instrumentation and real-world variability.<ref name="Janssens-3-38" /><ref name="Babrauskas-3-33">Babrauskas (2002), pp. 3-32–3-33.</ref>

== Purposes and measurements ==

A test can establish whether and how a material ignites, how quickly it releases energy, how a flame spreads and how much smoke or toxic product is generated. Other tests evaluate whether a construction maintains integrity, insulation or structural adequacy. These are different performance questions and require different endpoints.<ref name="CVM2-64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref><ref name="Milke-4-209">Milke (2002), p. 4-209.</ref>

Heat release rate is central to many reaction-to-fire methods because it links material consumption with fire severity. Effective heat of combustion connects heat release and mass loss but can vary during a test. Bomb-calorimeter values alone therefore cannot represent all real burning behaviour.<ref name="Janssens-3-39">Janssens (2002), p. 3-39.</ref><ref name="Babrauskas-3-1" />

Smoke and toxic-product measurements add further dimensions. Soot yield affects optical density, while carbon monoxide and other species influence inhalation hazard. Their yields vary with combustion mode, so test ventilation and exposure must be reported.<ref name="Mulholland-2-259">Mulholland (2002), p. 2-259.</ref><ref name="Purser-2-96">Purser (2002), p. 2-96.</ref>

Tests can also provide model inputs. A heat-release curve, ignition criterion or material property can support calculations for a larger scenario, but the model still needs to represent scale, enclosure and installation. A measured result does not eliminate modelling assumptions.<ref name="Janssens-3-39" /><ref name="Babrauskas-3-3" />

== Bench-scale calorimetry ==

The [[Cone calorimeter]] exposes a small specimen to controlled radiant heat and measures heat release rate by oxygen consumption. Its conical heater, spark ignitor, specimen holder and load cell sit beneath a hood and exhaust duct. Air and combustion products are extracted while oxygen and other gas concentrations are measured.<ref name="Janssens-cone">Janssens (2002), p. 3-55.</ref>

The standard specimen is 0.1 m by 0.1 m, with horizontal and vertical orientations possible. Maximum irradiance can exceed 100 kW/m², and the heater can be positioned above or beside the specimen. The initial exhaust flow can be adjusted between 10 and 32 litres per second, with relatively constant volumetric flow during a test.<ref name="Janssens-cone" />
[[File:fse-fire-testing-v1.svg|thumb|upright=1.5|alt=Cone heater, specimen, spark, load cell and exhaust gas analysis in a cone calorimeter.|Cone-calorimeter setup and oxygen-consumption measurement. Based on Janssens (2002), p. 3-55.]]

Oxygen-consumption calorimetry estimates heat release from oxygen used, commonly using 13.1 MJ per kilogram of oxygen consumed. Corrections can be needed for carbon monoxide and for substances whose oxygen-consumption constant differs. This is a measurement method, not a universal conversion from mass loss alone.<ref name="Drysdale-1-96">Drysdale (2002), pp. 1-95–1-96.</ref><ref name="Babrauskas-3-33" />

Bench-scale tests are efficient for comparing materials and obtaining input curves, but specimen size and boundary conditions differ from installed products. Orientation, backing, thickness and mounting can change heat feedback and decomposition. Application to a full object requires those differences to be evaluated.<ref name="Janssens-3-39" /><ref name="Babrauskas-3-3" />

=== Converting oxygen consumption to power ===

Oxygen-consumption calorimetry estimates released heat from the oxygen consumed by combustion. Drysdale gives an approximate conversion of 13.1 MJ per kilogram of oxygen for many common fuels. The basic relationship multiplies oxygen-consumption rate by that energy per unit mass.<ref name="Drysdale-1-96" />
<math display="block">\dot Q\approx E_{\mathrm{O_2}}\dot m_{\mathrm{O_2,consumed}}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot Q</math> || Heat release rate || kW
|-
| <math>E_{\mathrm{O_2}}</math> || Energy released per mass of oxygen consumed; approximately 13,100 || kJ/kg
|-
| <math>\dot m_{\mathrm{O_2,consumed}}</math> || Oxygen consumption rate || kg/s
|}

For a 1 MW full-scale source, this simplified conversion gives 1,000/13,100 = 0.0763 kg/s of oxygen consumed. The calculation illustrates the principle at an item-fire scale; it is not a heat-release claim for a small cone-calorimeter specimen. The assumed conversion and the measured oxygen deficit must use compatible units.<ref name="Drysdale-1-96" /><ref name="VR-4.6">Van Rossum (2027), §4.6.</ref>

An oxygen concentration alone does not give this mass-consumption rate. The instrument also needs the exhaust flow and the incoming-air reference, with corrections appropriate to the apparatus and gas measurements. Incomplete combustion, including carbon-monoxide production, can require corrections to the simple heat-per-oxygen relation.<ref name="Drysdale-1-96" /><ref name="Janssens-3-38" />

Janssens describes the cone calorimeter with a 0.1 m × 0.1 m specimen under controlled irradiation. The measured heat release per specimen area can support comparisons between materials at that exposure. It does not by itself determine the burning area, ventilation or thermal feedback of a complete room fire.<ref name="Janssens-cone" /><ref name="Babrauskas-3-3" />

== Single Burning Item and room tests ==

The Single Burning Item test (SBI) uses two wall panels in a corner configuration without a ceiling and is a regulatory heat-release test for building products. It evaluates product response under that specified exposure. Results should not be interpreted as direct measurements of every wall or room installation.<ref name="Babrauskas-SBI">Babrauskas (2002), p. 3-32.</ref>

A [[Room corner test]] places materials in a small enclosure with a defined burner and opening, then collects combustion products in a hood and exhaust duct. It includes hot-layer and room-surface feedback that open-burning tests omit. This makes it useful when enclosure effects are expected to influence heat release.<ref name="Janssens-3-39" /><ref name="Babrauskas-3-1" />
[[File:fse-fire-testing-v2.svg|thumb|upright=1.5|alt=Two wall panels in an open corner and a burner in a room with a hot upper layer.|SBI and room-corner tests represent different boundary conditions. Based on Babrauskas (2002), p. 3-33 and Janssens (2002), p. 3-39.]]

Room tests can differ from open calorimetry as fire grows. Babrauskas reports limited augmentation for some upholstered chairs at lower heat release rates, but much stronger effects for mattresses and liquid pools. A single room correction is therefore not valid for every product.<ref name="Babrauskas-3-2">Babrauskas (2002), p. 3-2.</ref>

Room-fire data also cannot be extrapolated directly to rooms with larger ventilation. Open-burning data may instead suit well-ventilated conditions when the fuel package is comparable. The source test and intended enclosure must be matched explicitly.<ref name="Babrauskas-3-2" />

== Large-scale and system tests ==

A Large-scale facade fire test evaluates facade systems at a scale where joints, cavities, cladding layers and external flames can interact. Such tests are relevant to system behaviour that cannot be inferred reliably from small material specimens. The actual method and installation remain necessary when applying the result.<ref name="IFEG-1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref><ref name="CVM2-64" />

Fire-resistance tests expose structural and separating assemblies to a defined furnace curve. Milke explains that ASTM E119 addresses structural integrity, temperature, flame and hot-gas passage and, in some cases, hose-stream response. These criteria are distinct from reaction-to-fire measurements of a material's own combustion.<ref name="Milke-4-209" /><ref name="Milke-4-210">Milke (2002), pp. 4-209–4-210.</ref>

Large tests can still be comparative rather than literal full-scale reproductions. Furnace dimensions, loading and end restraints may differ from the built structure. Actual performance requires appropriate analytical extension and validation rather than assuming the test building is identical.<ref name="Milke-4-210" />

C/VM2 (second edition, 2025) determines fire resistance ratings from standard tests or calculation methods verified by experimental data from standard tests. Its ratings report structural adequacy, integrity and insulation in that order. This is a regulatory use of fire-test evidence within New Zealand.<ref name="CVM2-64" />

== Data quality and uncertainty ==

Measurement uncertainty includes bias and random error. Calibration with a metered high-purity gas can reduce bias in oxygen-consumption systems, while interlaboratory trials help quantify random error. The 95% confidence intervals reported for some tests should be retained when comparing results.<ref name="Babrauskas-3-33" />
[[File:fse-fire-testing-v3.svg|thumb|upright=1.5|alt=Calibration addresses bias, repeated trials show random error and a model adds extrapolation uncertainty.|Fire-test uncertainty comes from measurement and application. Based on Babrauskas (2002), pp. 3-32–3-33.]]

Apparatus features influence results. Heater spectrum and orientation, specimen mounting, exhaust flow and gas analysis can all affect the measured curve. Using different methods without checking those features can produce apparent material differences that are really method differences.<ref name="Janssens-3-56">Janssens (2002), p. 3-56.</ref><ref name="Janssens-3-39" />

Specimen selection adds uncertainty. Composite products may have varying layers, moisture and manufacturing quality, and a small specimen may not represent the whole. Full-scale tests reduce some of these issues but introduce cost, ventilation and installation variability.<ref name="Babrauskas-3-3" /><ref name="Kodur-Harmathy-1-156">Kodur and Harmathy (2002), p. 1-156.</ref>

Data should include the complete time history and its definitions. Peak heat release rate, an early average and a long-term average answer different questions, and their values need not agree. The averaging interval and ignition reference must be stated.<ref name="Babrauskas-3-3" /><ref name="Janssens-3-56" />

== Using results in engineering ==

Results can support material comparison, regulatory classification and design-fire selection. The intended use determines which measurements and acceptance criteria matter. A test that suits one purpose may not provide the data needed for another.<ref name="CVM2-52">Ministry of Business, Innovation and Employment (2025), p. 52.</ref><ref name="Janssens-3-39" />

For reaction-to-fire assessment, heat release, ignition, spread and smoke describe how a product contributes to fire. For fire resistance, the construction's ability to continue separating or supporting loads is central. Confusing these measures can lead to incorrect claims about a material or assembly.<ref name="CVM2-64" /><ref name="Milke-4-209" />

For modelling, bench-scale data can be extrapolated only with a defensible model. Full-scale data are stronger evidence when they match the actual fuel package and enclosure, but even then installation and ventilation differences need review. Similar product names are not enough.<ref name="Babrauskas-3-3" /><ref name="Janssens-3-39" />

For regulatory use, the applicable standard and edition must be identified. C/VM2 uses its 2025 second edition and New Zealand context, while ASTM E119 and ISO room tests have their own methods and criteria. A class or rating should not be transferred between systems without demonstrating equivalence.<ref name="CVM2-64" /><ref name="Milke-4-210" />

== Limits and common misunderstandings ==

A fire test does not prove performance in every real fire. It proves response under the reported exposure and arrangement. Extrapolation needs a model, compatible conditions and acknowledgment of uncertainty.<ref name="Babrauskas-3-3" /><ref name="Janssens-3-39" />

A larger test is not automatically a better test. Scale can introduce important room and system feedback, but it can also make results harder to reproduce and apply elsewhere. The appropriate scale depends on the decision and the controlling mechanisms.<ref name="Babrauskas-3-2" /><ref name="Janssens-3-39" />

A standard test is not a universal measure of noncombustibility or safety. It characterises particular properties, and other hazards such as toxicity, installation and changing ventilation may remain. All relevant performance criteria should be considered.<ref name="Purser-2-96" /><ref name="CVM2-64" />

test data are not free of error merely because they follow a standard. Calibration, specimen preparation, instrument response and averaging still matter. These details belong with the data used for design or publication.<ref name="Babrauskas-3-33" /><ref name="Janssens-3-56" />

== Test selection and review ==

Test selection should begin with the decision and its controlling mechanisms. Material-level ignition and heat release may be sufficient for a simple comparison, but an enclosure or assembly can introduce new feedback. The test should include those mechanisms without adding irrelevant complexity.<ref name="Janssens-3-39" /><ref name="Babrauskas-3-3" />

A test plan should specify the specimen, exposure, instrumentation and endpoint before testing. Mounting, backing, moisture, orientation and pilot location can all change the result. Recording these choices makes the resulting data reproducible and helps prevent an incorrect comparison with another method.<ref name="Janssens-3-56" /><ref name="Kanury-2-231">Kanury (2002), pp. 2-231–2-232.</ref>

The exposure should be characterised as a time history where relevant. A constant radiant panel, a furnace curve and a developing compartment fire produce different boundary conditions. Using the first two as though they were interchangeable with the third would hide important transient behaviour.<ref name="Lie-4-201">Lie (2002), pp. 4-201–4-203.</ref><ref name="VR-5.1">Van Rossum (2027), §5.1.</ref>

Instrumentation should match the quantity required. Load cells measure mass loss, gas analysers measure species, exhaust measurements support oxygen-consumption calculations, and temperature and heat-flux instruments describe exposure. No one instrument supplies all of those outputs reliably without supporting measurements.<ref name="Janssens-3-56" /><ref name="Babrauskas-3-33" />

A test series can examine sensitivity rather than produce only one result. Changing heat flux, orientation, backing or ventilation reveals whether a conclusion remains stable. Those variations also identify the conditions under which extrapolation to the intended installation becomes uncertain.<ref name="Quintiere-2-247">Quintiere (2002), p. 2-247.</ref><ref name="Babrauskas-3-3" />

Interlaboratory comparison adds another check. It can reveal apparatus, operator and analysis differences that a single-laboratory procedure would miss. Confidence intervals should be reported alongside the measured curve so that small differences between products are not overinterpreted.<ref name="Babrauskas-3-33" />

Validation should compare like with like. A bench-scale heat-release curve should not be compared directly with a room-fire curve without accounting for enclosure feedback, and a layer-average temperature should not be compared directly with a near-ceiling reading. Definitions must match before agreement can be assessed.<ref name="Babrauskas-3-1" /><ref name="Cadorin-Franssen-412">Cadorin and Franssen (2003), p. 412.</ref>

A final report should separate measurement, calculation and acceptance. It states what was observed, which conversions were applied and which criterion was used to judge performance. This keeps the test result traceable when it is later used for classification, modelling or a design decision.<ref name="Janssens-3-39" /><ref name="CVM2-64" />

The [[Euroclass system]] illustrates why a test must be read through its regulatory method. A result becomes a classification only after the applicable procedures and criteria are applied, and another framework can use different evidence. The underlying measurement should not be assigned a class from an unrelated system without an equivalence assessment.<ref name="Janssens-3-38" /><ref name="CVM2-52" />

Acceptance criteria should be checked against the test's actual output. A furnace endpoint may be a temperature, a heat-release threshold, a spread observation or a retained structural function. Using the wrong endpoint can make a successful measurement answer an unsuccessful design question.<ref name="CVM2-64" /><ref name="Milke-4-210" />

For product comparison, uncertainty should be included when differences are small. Calibration and specimen variation can create differences of the same order as the apparent product effect. Repeating the exposure or comparing independent laboratories can show whether the ranking persists.<ref name="Babrauskas-3-33" /><ref name="Janssens-3-56" />

For design, the complete evidence chain should be documented. It links the tested specimen and exposure to the conversion, model and acceptance criterion used in the building. Any weak link can change the conclusion even when the original measurement is sound.<ref name="Janssens-3-39" /><ref name="Babrauskas-3-3" />

A final review should also state which hazards were outside the test. Limited smoke, toxicity, ageing, installation damage and altered ventilation may not be represented. A fire-test result should therefore be used for the properties it measures, not as a guarantee of complete fire safety.<ref name="Purser-2-96" /><ref name="Kodur-Harmathy-1-156" />

The test's role in the wider evidence chain should also be explicit. A result can support a classification, supply a model input or validate a predicted response, but those uses have different evidence requirements. A measurement that is adequate for one role may be incomplete for another.<ref name="Janssens-3-39" /><ref name="Babrauskas-3-3" />

== See also ==

* [[Froude scaling]]
* [[Heat release rate]]
* [[Combustibility]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Cadorin, J.-F., & Franssen, J.-M. (2003). A tool to design steel elements submitted to compartment fires: OZone V2. Part 1: Pre- and post-flashover compartment fire model. ''Fire Safety Journal, 38'', 395–427.
* Drysdale, D. D. (2002). Thermochemistry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Kanury, A. M. (2002). Flaming ignition of solid fuels. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Lie, T. T. (2002). Fire temperature-time relations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.). New Zealand Government.
* Mulholland, G. W. (2002). Smoke production and properties. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Quintiere, J. G. (2002). Surface flame spread. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Materials & Fire Testing]]

Flame spread

2026-11-02T21:32:51Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Flame spread''' is the movement of a flame across or adjacent to a condensed fuel whose evaporation or pyrolysis supplies the flame with gaseous fuel. It involves two advancing regions: the visible gas-phase flame and the evaporation or decomposition front in the solid or liquid. The rate of the condensed-phase front defines surface flame-spread velocity.<ref name="Quintiere-2-246">Quintiere (2002), p. 2-246.</ref>

The process differs from flame propagation through a premixed gas. In surface flame spread, fuel and oxygen are not already distributed uniformly throughout the gas. Heat from the advancing flame must first produce new vapour ahead of the reaction region.<ref name="Quintiere-2-246" />

Flame spread influences how rapidly a small ignition develops into a larger fire. It can accelerate as more fuel and stronger heat feedback become involved, or stop when forward heating, fuel continuity or combustion conditions become inadequate.<ref name="Quintiere-2-246" /><ref name="Drysdale-1-97">Drysdale (2002), p. 1-97.</ref>

== Flame and decomposition fronts ==

The visible flame occupies the gas phase, while the condensed fuel remains beneath or beside it. Heat transferred from the flame evaporates liquid or decomposes solid ahead of the current burning area. The new vapour mixes with air and allows the flame to advance.<ref name="Quintiere-2-246" />
[[File:fse-flame-spread-v1.svg|thumb|upright=1.5|alt=Gas-phase flame above a solid with a separate advancing pyrolysis front.|Surface flame spread involves two advancing fronts. Based on Quintiere (2002), p. 2-246.]]

The evaporation or pyrolysis front is harder to observe than the flame, but it marks the region being converted into gaseous fuel. Its position and movement connect the visible flame with fuel consumption. A flame can appear substantial while the underlying front moves comparatively slowly.<ref name="Quintiere-2-246" />

This mechanism can be viewed as successive [[Ignition]] of new material. Each newly heated region must reach a condition supporting piloted reaction and continued vapour supply. Flame spread therefore depends on the target's initial temperature and ignition response as well as on the existing flame.<ref name="Kanury-2-229">Kanury (2002), p. 2-229.</ref>

A premixed gas flame follows a different mechanism. Fuel and oxidiser are already present in the gas, so propagation can be much faster and does not require an advancing solid-decomposition front. The two processes should not share an unqualified spread-rate value.<ref name="Quintiere-2-246" />

== Heat transfer ahead of the flame ==

Forward heat transfer raises fuel from its initial temperature towards its ignition condition. Conduction through gas and solid, convection from hot gases and radiation from the flame can all contribute. Their relative importance depends on flow, orientation, scale and material properties.<ref name="Quintiere-2-247">Quintiere (2002), p. 2-247.</ref>

Quintiere's conceptual energy balance compares heat delivered ahead of the front with the energy needed to prepare new fuel. Lower initial temperature requires more heating, while preheating by the wider fire reduces the additional energy needed. Spread can therefore accelerate as the surroundings become hotter.<ref name="Quintiere-2-247" />

Heat losses can prevent the front from sustaining itself. Energy entering a thick solid can drain into its interior, and convection can cool the reaction region. Stronger opposed flow may enhance some heat-transfer paths while reducing the time available for chemical reaction, so its effect is not universally positive or negative.<ref name="Quintiere-2-248">Quintiere (2002), pp. 2-248–2-250.</ref>

Flame temperature and heat flux are also coupled with oxygen and chemistry. Reduced oxygen can lower reaction and heat release, while excessive flow can quench the reaction region. Material data alone cannot predict spread without these fire conditions.<ref name="Quintiere-2-248" />

== Direction and airflow ==

[[Upward flame spread]] benefits from buoyant hot gases and flame contact preheating fuel above the front. This can produce a large heated region and rapid acceleration on vertical surfaces. Van Rossum identifies this mechanism as an important reason for faster upward spread.<ref name="VR-4.3">Van Rossum (2027), §4.3.</ref><ref name="Quintiere-2-247" />
[[File:fse-flame-spread-v2.svg|thumb|upright=1.5|alt=Upward flame preheating fuel above and a front advancing against airflow.|Flow direction changes flame-spread heat transfer. Based on Van Rossum (2027), §4.3 and Quintiere (2002), p. 2-247.]]

[[Opposed-flow flame spread]] occurs when the front advances against the surrounding gas flow. Forward heat must reach fuel despite that opposing transport. Quintiere distinguishes this from wind-aided spread, where the surrounding flow supports movement in the same direction.<ref name="Quintiere-2-247" />

Lateral and downward configurations have different heat-transfer paths and generally different rates from upward spread. The direction of gravity changes buoyancy, flame shape and which fuel is preheated. Material orientation must therefore accompany any reported rate.<ref name="Quintiere-2-247" />

External wind and fire-induced natural convection can both create the relevant flow. A value measured in still air cannot be transferred automatically to a ventilated shaft, open facade or compartment with strong fire-driven circulation.<ref name="Quintiere-2-247" /><ref name="IFEG-2.6-12">Australian Building Codes Board et al. (2005), p. 2.6-12.</ref>

The distance heated ahead of the front helps explain the difference between the flow arrangements. Quintiere gives illustrative heating lengths of about 1–3 mm for opposed spread and 0.1–10 m for wind-aided spread. The latter can extend over much of the adjacent flame and hot-gas region. These lengths belong to the simplified configurations and do not replace a heat-flux calculation.<ref name="Quintiere-2-251">Quintiere (2002), p. 2-251.</ref>

== Material thickness and thermal response ==

Thermally thin materials have relatively little temperature variation through their thickness in the simplified model. Paper, garments and draperies can sometimes approach this behaviour. Thermally thick materials retain important internal gradients, and heat conducted into them is unavailable at the surface.<ref name="Quintiere-2-248" />

Geometric thickness alone does not define the thermal class. Conductivity, density, specific heat, exposure time and backing conditions all influence the response. Quintiere gives approximate material-specific examples, but these should not be converted into universal thickness thresholds.<ref name="Quintiere-2-249">Quintiere (2002), p. 2-249.</ref>

Low density can favour rapid response because less energy is required to prepare a given volume for ignition. Substrates can add further heat storage or loss. A thin combustible finish on a massive backing can consequently behave differently from the same finish without that backing.<ref name="Quintiere-2-247" /><ref name="Quintiere-2-249" />

Moisture, melting and char formation change the response during heating. They alter heat consumption, surface integrity and volatile release. Treating the material as homogeneous and unchanged is a modelling simplification whose limits must be stated.<ref name="Kanury-2-232">Kanury (2002), p. 2-232.</ref><ref name="Beyler-Hirschler-1-112">Beyler and Hirschler (2002), pp. 1-112–1-113.</ref>

== Spread rate and fire growth ==

Quintiere illustrates growth with an upholstered-chair ignition region 6 cm in diameter and an unenhanced spread rate of about 1 mm/s. After one minute in the example, the pyrolysing region reaches 18 cm in diameter as the front advances 6 cm. The larger fuel area can then strengthen heat feedback.<ref name="Quintiere-2-246" />

For an ideal circular region, increasing the diameter from 6 cm to 18 cm multiplies the area by nine. The initial area is about 0.0028 m² and the later area about 0.025 m². This calculation assumes that the entire enclosed region remains involved. It illustrates how even a constant front speed can produce increasing burning area.<ref name="Quintiere-2-246" />

The example demonstrates area growth rather than a universal chair-fire rate. Spread rate can change as heat release increases, and fuel burnout can limit later development. Early spread and long-term fire growth therefore require a time-dependent description.<ref name="Quintiere-2-246" />

The handbook's order-of-magnitude table lists smouldering at 0.001 to 0.01 cm/s, lateral or downward spread on thick solids around 0.1 cm/s, and upward spread on thick solids from 1 to 100 cm/s. Premixed laminar deflagration is listed from 10 to 100 cm/s. These ranges show different mechanisms and scales, not values for direct substitution into another scenario.<ref name="Quintiere-2-247" />
[[File:fse-flame-spread-v3.svg|thumb|upright=1.5|alt=Log-scale ranges for smouldering, lateral spread, upward spread and premixed flame.|Order-of-magnitude flame-spread rates from the SFPE Handbook. Based on Quintiere (2002), p. 2-247.]]

[[Fire spread]] beyond the first object adds further pathways, including radiation across gaps, direct flame contact and burning debris. Surface flame spread is one mechanism within this wider process. A room or building fire should not be modelled as one continuous sheet of fuel unless that geometry actually applies.<ref name="IFEG-1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

== Materials and fire performance ==

[[Combustibility]] describes whether and how a material can burn under relevant conditions, but it does not specify a flame-spread rate by itself. Ignition response, heat capacity, decomposition and geometry all affect movement across the material. Two combustible products can therefore spread fire very differently.<ref name="Quintiere-2-247" /><ref name="Beyler-Hirschler-1-112" />

[[Reaction to fire]] testing examines product behaviour under a specified fire exposure. For flame spread, relevant observations include ignition, front movement and heat release. These describe the product in its tested configuration, whereas a spread model additionally needs the heat-transfer conditions around the advancing front.<ref name="Quintiere-2-247" /><ref name="Babrauskas-3-32">Babrauskas (2002), p. 3-32.</ref>

Surface orientation and installation affect measured performance. A product tested horizontally may not behave identically on a wall or ceiling, and joints or substrates can alter heat transfer. The tested specimen and the installed product must be compared explicitly.<ref name="Quintiere-2-247" />

A material can resist initial ignition yet still spread flame under a larger exposure. The threshold crossed in one test does not prove performance in every fire. Scenario severity and duration remain part of the assessment.<ref name="Kanury-2-231">Kanury (2002), pp. 2-231–2-232.</ref>

== Testing and measurement ==

The Single Burning Item test is described in the 2002 handbook as a European regulatory heat-release-rate test for building products. Two panels form a corner without a ceiling. This geometry differs from a complete room, so its result does not directly represent every installed exposure.<ref name="Babrauskas-3-32" />

Quintiere discusses cone-calorimeter and lateral ignition and flame-spread tests as sources of material data. These methods helped replace less meaningful flammability indices with measurements linked to ignition and spread models. They do not remove all uncertainty in heat-transfer and material-property inputs.<ref name="Quintiere-2-247" />

A spread-rate measurement needs an identifiable front, direction and exposure condition. Visible flame length alone does not establish how quickly the pyrolysis region moves. Measurement definitions can therefore change the reported result.<ref name="Quintiere-2-246" />

A room-corner test provides another configuration for interior finishes. Quintiere describes studies combining cone-calorimeter data with flame-spread models to reproduce its fire growth. The calculation still needs relationships for flame length and heat transfer in that particular geometry. Obtaining a material property in one apparatus therefore supplies part of the prediction, rather than the whole installed-product response.<ref name="Quintiere-2-254-test">Quintiere (2002), p. 2-254.</ref>

Tests at reduced scale can underrepresent radiation and room feedback. As the fire grows, upper-layer radiation and heated boundaries can preheat new regions beyond the local test arrangement. Applying small-scale rates to a developed enclosure fire requires an appropriate model.<ref name="Tien-1-73">Tien, Lee, and Stretton (2002), p. 1-73.</ref><ref name="IFEG-2.4-4">Australian Building Codes Board et al. (2005), p. 2.4-4.</ref>

== Calculating spread and recognising its limits ==

The basic energy balance equates forward heating with the energy needed to prepare fresh material for burning. In a simplified steady model, spread speed increases when more energy reaches the fuel ahead of the front. It decreases when that fuel needs a larger temperature rise. Density and heat capacity determine how much energy the heating requires.<ref name="Quintiere-2-247" />

<math display="block">\rho V c(T_{ig}-T_s)=\dot q''</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\rho</math> || Fuel density || kg/m³
|-
| <math>V</math> || Spread speed || m/s
|-
| <math>c</math> || Specific heat capacity || kJ/(kg·K)
|-
| <math>T_{ig}</math> || Effective surface ignition temperature || °C
|-
| <math>T_s</math> || Fuel temperature ahead of the front || °C
|-
| <math>\dot q''</math> || Net heat flux preparing fresh fuel in the conceptual balance || kW/m²
|}

The temperature difference has the same numerical value in kelvin and degrees Celsius. The heat flux in this balance is the effective forward heating, rather than the fire's total heat release rate. A detailed model must establish how much energy actually reaches the fresh fuel. It must also represent the distance over which that heat acts.<ref name="Quintiere-2-247" />

For opposed-flow spread over thermally thick materials, Quintiere gives a relation fitted using lateral-spread tests. The denominator combines the material's thermal inertia with the square of the required temperature rise. The fitted parameter represents the spread conditions and fuel response. It is not a universal constant for all flows or oxygen concentrations.<ref name="Quintiere-2-250">Quintiere (2002), pp. 2-250–2-251.</ref>

<math display="block">V=\frac{\Phi}{k\rho c(T_{ig}-T_s)^2}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>k\rho c</math> || Effective thermal inertia, conductivity × density × specific heat || kW²·s/(m⁴·K²)
|-
| <math>\Phi</math> || Empirical flame-spread parameter for the material and exposure || kW²/m³
|-
| <math>V,T_{ig},T_s</math> || Spread speed and temperatures as defined above || m/s, °C, °C
|}

The test method preheats a vertical specimen by external radiation before lateral spread begins. The surface is allowed to approach a steady temperature for each exposure. The fitted properties describe that arrangement under natural convection in air. The spread relation does not calculate the preceding time needed to establish the preheated state. Downward-spread results were similar for the materials examined, except where excessive melting and dripping changed the behaviour.<ref name="Quintiere-2-250" />

For 1.27 cm Douglas fir particleboard, the handbook lists an effective ignition temperature of 382 °C. Its thermal inertia is 0.94 kW²·s/(m⁴·K²), and its spread parameter is 12.7 kW²/m³. The listed minimum surface temperature supporting continued spread is 210 °C. These are effective properties from the reported experiments, rather than universal values for all timber.<ref name="Quintiere-2-250" />

As an illustration, choose a preheated surface temperature of 250 °C, above that measured minimum. The resulting calculated spread speed is approximately 0.78 mm/s. Choosing 300 °C with the same fitted properties gives approximately 2.0 mm/s. These two chosen temperatures demonstrate the effect of preheating; they are not separate measured test results.<ref name="Quintiere-2-250" />

<math display="block">V_{250}=\frac{12.7}{0.94(382-250)^2}=0.000775\ldots\;\mathrm{m/s}\approx0.78\;\mathrm{mm/s}</math>
<math display="block">V_{300}=\frac{12.7}{0.94(382-300)^2}=0.002009\ldots\;\mathrm{m/s}\approx2.0\;\mathrm{mm/s}</math>

The relation cannot be continued without limit towards the ignition temperature. Its assumptions describe a particular spread process with fitted properties and established heating conditions. Widespread ignition, changing heat flux or a different airflow requires another treatment. Below the measured minimum temperature, continuing spread was not sustained, despite the algebraic formula still returning a positive number.<ref name="Quintiere-2-250" />

Burnout introduces a separate limitation. Fuel behind the front can finish burning while fresh material is still being heated. If spread is fast relative to burning time, the active burning area can grow; if it is slow, growth can decelerate or stop. A calculation of front speed alone therefore does not determine the complete fire's heat release.<ref name="Quintiere-2-246" />

Liquid fuels introduce an additional mechanism that the solid-material relation does not include. Surface-tension differences and circulation can transport heat within the liquid ahead of the flame. Quintiere distinguishes spread governed by this liquid motion from faster propagation through an existing flammable vapour layer. The liquid's initial temperature relative to its flash point helps distinguish these regimes.<ref name="Quintiere-2-254">Quintiere (2002), pp. 2-254–2-255.</ref>

== See also ==

* [[Euroclass system]]
* [[Travelling fire]]
* [[Trench effect]]
* [[Wildfire]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association.
* Beyler, C. L., & Hirschler, M. M. (2002). Thermal decomposition of polymers. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-110–1-131). National Fire Protection Association.
* Drysdale, D. D. (2002). Thermochemistry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-90–1-98). National Fire Protection Association.
* Kanury, A. M. (2002). Flaming ignition of solid fuels. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-229–2-245). National Fire Protection Association.
* Quintiere, J. G. (2002). Surface flame spread. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-246–2-257). National Fire Protection Association.
* Tien, C. L., Lee, K. Y., & Stretton, A. J. (2002). Radiation heat transfer. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-73–1-89). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Ignition & Flame Spread]]

Flammability limits

2026-11-02T21:32:51Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

'''Flammability limits''' are the lowest and the highest concentrations of a fuel gas or vapour in air, or in another oxidant mixture, between which a flame can propagate through the mixture.<ref name="BE-2-172">Beyler (2002b), p. 2-172.</ref> The lower limit is called the lower flammable limit (LFL) and the upper limit the upper flammable limit (UFL).<ref name="BE-2-172" /> Methane in air, for example, can only carry a flame at concentrations between 5 and 15 % by volume.<ref name="BE-2-172" /> A mixture below the lower limit contains too little fuel, and a mixture above the upper limit too little oxygen.<ref name="BE-2-174">Beyler (2002b), p. 2-174.</ref> The same boundaries are often called the lower and upper explosion limits (LEL and UEL).<ref name="IS-15-4">Iqbal and Salley (2004), p. 15-4.</ref>

The limits describe [[premixed flame|premixed flames]], in which fuel and oxidant are mixed before ignition.<ref name="BE-2-172" /> They are therefore basic data for assessing the fire and explosion risk of gases and vapours, including smoke gas explosions in fires.<ref name="SI-1-146">Simmons (2002), p. 1-146.</ref><ref name="VR-4.10">Van Rossum (2027), §4.10.</ref> Their values depend on temperature, pressure, the direction of flame travel and the test apparatus, so a tabulated limit is a measured property rather than an exact physical constant.<ref name="BE-2-173">Beyler (2002b), p. 2-173.</ref><ref name="BE-2-174" /> Safety strategies for gases usually aim to keep concentrations well below the lower limit, or to remove enough oxygen to make every mixture non-flammable.<ref name="IFEG-3.3-2">National Research Council of Canada et al. (2005), p. 3.3-2.</ref><ref name="BE-2-179">Beyler (2002b), p. 2-179.</ref>

== Definition ==
Not every mixture of fuel, oxidant and inert gas can carry a flame. There are limits of composition outside which normal flame-type combustion cannot be sustained.<ref name="BE-2-172" /> Flammability limits are expressed as concentrations of the fuel in a specified oxidant and diluent mixture, at a specified temperature and pressure.<ref name="BE-2-172" /> For gases and vapours in air, they are normally given in percent by volume at normal temperature and pressure.<ref name="IS-B-25">Iqbal and Salley (2004), p. B-25.</ref> NUREG-1805 defines the lower limit as the lowest concentration of fuel in air that can support flame propagation, and the upper limit as the highest.<ref name="IS-B-25" />

The terms flammable limits and explosive limits are used interchangeably in the technical literature.<ref name="IS-B-25" /> The word explosive refers to the overpressure that results when a flame passes through a closed vessel.<ref name="IS-B-25" /> Zalosh draws a finer distinction. Limits measured in pressure vessels, where a pressure rise shows that a flame has spread, are strictly explosion limits. For some fuels the two kinds of limit are virtually the same, but for others they differ substantially.<ref name="ZA-3-402">Zalosh (2002), p. 3-402.</ref> ''Introduction to Fire Safety Engineering'' uses the explosion terms LEL and UEL.<ref name="VR-4.10" />

Between the limits, the speed of the flame varies with the composition. At the lower or upper limit, an ignited mixture burns with only an insignificant spread of flame. Between the two limits lies a point at which flame propagation is fastest.<ref name="IS-15-4" /> The most flammable mixture is the stoichiometric one, in which fuel and oxygen are present in exactly the proportions needed for complete oxidation.<ref name="IS-B-25" /> For most simple hydrocarbons, the lower and upper limits correspond to about half and three times the stoichiometric fuel-to-air ratio. Their lower limit corresponds to about 48 g of fuel per cubic metre.<ref name="BE-2-172" />

[[File:fse-flammability-limits-v1.svg|thumb|upright=1.5|alt=Scale of methane in air from 0 to 20 %: too lean below 5 %, flammable from 5 to 15 %, too rich above 15 %, stoichiometric at 9.5 %.|Methane in air: too lean below the lower flammable limit (5 %), too rich above the upper flammable limit (15 %); the stoichiometric mixture (about 9.5 %) lies in between. Based on Beyler (2002b), p. 2-172, and Zalosh (2002), p. 3-403.]]

== Why flames have limits ==
[[Stoichiometry]] describes the ratios in which substances are consumed and formed in a chemical reaction. The stoichiometric ratio is the ideal mixing ratio, at which all of the fuel and all of the oxygen take part in the reaction.<ref name="VR-3.3">Van Rossum (2027), §3.3.</ref> The further a mixture departs from this ratio, the slower the combustion becomes. Substances that do not take part in the reaction are still heated by it.<ref name="VR-3.3" /> Drysdale interprets the lower limit as the point where the heat losses from the flame, mainly by radiation, exceed the rate of heat production within it. The flame then cannot sustain itself.<ref name="DR-1-97">Drysdale (2002), p. 1-97.</ref>

This idea can be made quantitative with the adiabatic flame temperature, the temperature that the products would reach if no heat were lost. For most flammable gases in air, this temperature is about 2,300 K for a stoichiometric mixture. It falls to about 1,600 K for a mixture at the lower limit.<ref name="IS-B-25" /> As early as 1911, Burgess and Wheeler noted that lower-limit mixtures of alkanes and air release almost the same heat per unit volume.<ref name="BE-2-177">Beyler (2002b), p. 2-177.</ref> For a wide range of fuels containing only carbon, hydrogen and oxygen, the calculated flame temperature at the lower limit is about 1,600 K, with a spread of about 150 K.<ref name="BE-2-177" /> Hydrogen (980 K), carbon monoxide (1,300 K) and acetylene (1,280 K) are notable exceptions, and a lower value indicates a more reactive fuel.<ref name="BE-2-177" />

The limit temperature changes little with the diluent or with the initial temperature of the mixture.<ref name="BE-2-177" /> It therefore allows engineers to predict how the limits shift with temperature and with added inert gases.<ref name="BE-2-177" /> Even so, Beyler stresses that the mechanism responsible for flammable limits is not yet understood, although much has been learned that has practical value.<ref name="BE-2-172" />

Mixtures outside the limits can still react if energy is supplied throughout their volume. In one experiment, a small hydrogen pilot flame burned in a stream of lean methane and air. Below 5 % methane, combustion occurred only in the wake of the pilot flame. Above 5 %, the flame could travel away from the pilot.<ref name="BE-2-173" /> The limits therefore describe self-sustaining propagation away from an ignition source, not whether any reaction at all can take place.<ref name="SI-1-146" />

== Measurement ==
The most widely used method was developed by the United States Bureau of Mines. A vertical tube 1.5 m long and 0.05 m in diameter is filled with the test mixture and ignited by a spark or a small pilot flame at its open lower end.<ref name="BE-2-172" /> The mixture counts as flammable if the flame travels at least halfway up the tube. The tube diameter is the smallest at which heat losses to the wall have little effect on the result.<ref name="BE-2-172" /><ref name="BE-2-173" /> Limits are normally measured for upward propagation, because this gives the widest range.<ref name="SI-1-146" />

The direction of flame travel matters. Limits for downward propagation are narrower than those for upward propagation.<ref name="BE-2-173" /> Other methods use a flask of 5 litres with a central spark, or a closed pressure vessel in which a pressure rise shows that the flame has spread.<ref name="ZA-3-402" /> A spherical vessel is more representative of a real tank than the tube method.<ref name="IS-B-25" /> The lower limit is reported as the average of the lowest concentration that propagates a flame and the highest one that does not.<ref name="ZA-3-402" /> Different national methods give broadly similar results, but some variation remains.<ref name="BE-2-173" />

Hydrogen shows how large the effect of direction can be. In air at room temperature its lower limit is 4.1 % for upward propagation, 6.0 % for horizontal propagation and 9.0 % for downward propagation.<ref name="IS-16-2">Iqbal and Salley (2004), p. 16-2.</ref> In spherical vessel tests, overpressures were only measured above about 8 % hydrogen. The pressures matched theoretical values only from about 10 % hydrogen upwards.<ref name="IS-B-26">Iqbal and Salley (2004), p. B-26.</ref> NUREG-1805 therefore notes that standards based on the 4 % value contain an implicit additional safety factor for hydrogen.<ref name="IS-B-26" />

== Typical values ==
Tabulated limits refer to a given temperature and pressure, usually mixtures with air at normal conditions.<ref name="BE-2-172" /> The selection below is taken from the International Fire Engineering Guidelines (2005), which draw on published tabulations.<ref name="IFEG-3.3-2" /> Hydrogen, carbon monoxide and acetylene have very wide ranges. The hydrocarbons in the table have much narrower ranges, with lower limits of about 1 to 5 % and upper limits of about 7 to 15 %.<ref name="IFEG-3.3-3">National Research Council of Canada et al. (2005), p. 3.3-3.</ref>

[[File:fse-flammability-limits-v2.svg|thumb|upright=1.5|alt=Horizontal bars from lower to upper flammability limit for ten gases; hydrogen, carbon monoxide and acetylene have very wide ranges.|Flammable ranges in air of selected gases and vapours, from the lower to the upper flammable limit. Based on National Research Council of Canada et al. (2005), pp. 3.3-2 to 3.3-3.]]

{| class="wikitable"
|+ Flammability limits of selected gases and vapours in air<ref name="IFEG-3.3-2" /><ref name="IFEG-3.3-3" />
! Substance !! LFL (vol %) !! UFL (vol %)
|-
| Methane || 5.0 || 15
|-
| Propane || 2.1 || 9.5
|-
| Butane || 1.8 || 8.4
|-
| Heptane || 1.05 || 6.7
|-
| Toluene || 1.2 || 7.1
|-
| Methanol || 6.7 || 36
|-
| Ethanol || 3.3 || 19
|-
| Hydrogen || 4.0 || 75
|-
| Carbon monoxide || 12.5 || 74
|-
| Acetylene || 2.5 || 100
|}

Dusts behave differently from gases. For very fine particles, the lower limit no longer depends on the particle size. For coal dust, however, it lies well above the 48 g/m³ that is typical of gaseous hydrocarbons, because not all of the dust turns into vapour.<ref name="BE-2-182">Beyler (2002b), p. 2-182.</ref> The lower limit of such coal dust is not expected to fall below about 50 g/m³, even in pure oxygen.<ref name="BE-2-182" />

== Effect of conditions ==
Oxygen affects the two limits differently. When the oxygen concentration rises and the inert gas content falls, the upper limit increases while the lower limit hardly changes.<ref name="BE-2-174" /> At the lower limit, there is always more oxygen than needed for complete combustion, so extra oxygen simply replaces inert gas. At the upper limit, oxygen is short, so extra oxygen takes part in the combustion.<ref name="BE-2-174" />

Pressure also affects the limits. The lower limit is insensitive to pressure, except well below atmospheric pressure. The upper limit rises when the pressure increases above atmospheric.<ref name="BE-2-174" /> Below about one tenth of an atmosphere, the two limits suddenly narrow and the gas becomes non-flammable.<ref name="ZA-3-402" />

The limits widen as the mixture temperature rises.<ref name="BE-2-174" /> Beyler's example uses the constant limit flame temperature of 1,600 K. Propane has a lower limit of 2.1 % at 20 °C, which falls to about 1.8 % at 200 °C.<ref name="BE-2-178">Beyler (2002b), p. 2-178.</ref> This rule only holds as long as no significant reactions take place before the flame arrives. For mixtures held near their autoignition temperature, the limit temperature is not expected to stay constant.<ref name="BE-2-177" />

For liquids, the limits are linked to the vapour pressure. The [[flash point]] is the liquid temperature at which the vapour pressure is just enough to give a lower-limit mixture of vapour and air.<ref name="SI-1-147">Simmons (2002), p. 1-147.</ref> In a closed container held above a corresponding upper limit temperature, the vapour is too rich to burn, as typically happens in a car fuel tank.<ref name="BE-2-174" /> In an open container, however, the vapour is diluted somewhere above the surface into the flammable range. It will then ignite if an ignition source is present.<ref name="BE-2-174" />

[[File:fse-flammability-limits-v4.svg|thumb|upright=1.5|alt=Schematic chart: lower and upper limit lines widening with temperature, crossed by a rising vapour pressure curve that marks the flash point.|Effect of temperature on the flammable range of a liquid's vapour in air; the flash point is where the saturated vapour reaches the lower limit. Based on Beyler (2002b), p. 2-174 (Figure 2-7.5, redraw, do not copy), and Simmons (2002), p. 1-147.]]

Inert gases narrow the flammable range. Flammability diagrams for methane and n-hexane show this effect for several diluents, including nitrogen and carbon dioxide. The lower limit rises in proportion to the heat capacity of the added diluent.<ref name="BE-2-180">Beyler (2002b), p. 2-180.</ref>

Beyond a certain amount of inert gas, no mixture of fuel and air can carry a flame. The oxygen concentration at this point is the limiting oxygen concentration (LOC).<ref name="BE-2-179" /> With nitrogen as the diluent, the LOC of most fuels lies between 10 and 12 %. With carbon dioxide, it is generally 2 to 3 percentage points higher, because carbon dioxide has a higher molar heat capacity.<ref name="BE-2-179" /> For propane, the oxygen content of an air and nitrogen mixture must fall below about 12 % before no mixture can burn.<ref name="SI-1-150">Simmons (2002), p. 1-150.</ref>

[[File:fse-flammability-limits-v3.svg|thumb|upright=1.5|alt=Triangle-shaped chart of methane against nitrogen with a closed flammable region, the air line and the limit line touching its tip.|Flammability diagram for methane, oxygen and nitrogen: the limit line touching the flammable region defines the limiting oxygen concentration. Based on Beyler (2002b), pp. 2-178 to 2-179 (Figure 2-7.7b, redraw, do not copy).]]

== Mixtures of fuel gases ==
Real releases often contain several fuel gases, for example the pyrolysis gases of a fire. Le Chatelier's rule, an empirical rule from the late nineteenth century, estimates the lower limit of such a mixture in air from the lower limits of its components.<ref name="BE-2-174" /> Each gas contributes in proportion to its share of the fuel mixture, divided by its own lower limit.<ref name="BE-2-174" />

<math display="block">\mathrm{LFL}_m = \frac{100}{\sum_{i=1}^{n} C_{f,i} / \mathrm{LFL}_i}</math>

{| class="wikitable"
|+ Symbols in Le Chatelier's rule
! Symbol !! Description !! Unit
|-
| <math>\mathrm{LFL}_m</math> || lower flammable limit of the fuel mixture in air || vol %
|-
| <math>C_{f,i}</math> || share of fuel gas ''i'' in the fuel gas mixture (without air) || vol %
|-
| <math>\mathrm{LFL}_i</math> || lower flammable limit of fuel gas ''i'' alone in air || vol %
|-
| <math>n</math> || number of fuel gases in the mixture || –
|}

Beyler gives a worked example for a fuel gas of 50 % methane, 25 % carbon monoxide and 25 % hydrogen. Their lower limits in air are 5.0, 12.5 and 4.0 %.<ref name="BE-2-174" /> The sum of the shares divided by the limits is 10 + 2 + 6.25 = 18.25. The lower limit of the mixture is therefore 100 / 18.25 = 5.48 %.<ref name="BE-2-174" /> At this limit the mixture contains 2.74 % methane, 1.37 % carbon monoxide, 1.37 % hydrogen and 94.5 % air.<ref name="BE-2-177" />

The rule is empirical. In the form shown here, it applies to the lower limit of a mixture of flammable gases in air.<ref name="BE-2-174" /> Beyler uses the same rule at the stoichiometric limit to judge whether a hot smoke layer containing several fuel gases can burn.<ref name="BE-2-183">Beyler (2002b), p. 2-183.</ref> In his example, a layer at 700 K contains 10 % hydrocarbons, 2 % carbon monoxide and 1 % hydrogen. The weighted sum comes to 1.07, which is above one, so the layer can ignite and burn when it mixes with air.<ref name="BE-2-184">Beyler (2002b), p. 2-184.</ref><ref name="BE-2-185">Beyler (2002b), p. 2-185.</ref>

== Use in fire safety engineering ==
Flammability limits are the starting point of every gas or vapour [[explosion]] assessment. Combustible gases, vapours and dusts present an explosion hazard when they are mixed with air in proportions between the lower and upper limits.<ref name="ZA-3-402" /> The hazard arises when fuel and oxidant are premixed in a confined space before an ignition source appears. On ignition, the confinement prevents free expansion and the pressure rises rapidly.<ref name="ZA-3-402" /> Protection either prevents a flammable mixture from forming, removes ignition sources or limits the pressure rise.<ref name="ZA-3-402" />

The International Fire Engineering Guidelines (2005) state that the normal safety strategy for gaseous fuels is to avoid concentrations within the flammable range. In practice this means keeping the concentration well below the lower limit. It is hard to make sure that a mixture above the upper limit will never be diluted into the flammable range.<ref name="IFEG-3.3-2" /> Within the flammable range, ignition sources of only a few millijoules can be enough.<ref name="IFEG-3.3-2" /> The ignition energy is lowest near the stoichiometric mixture and rises sharply as either limit is approached.<ref name="BE-2-181">Beyler (2002b), p. 2-181.</ref>

[[Inerting]] is the alternative when the fuel cannot be kept out. If the oxygen concentration stays below the LOC, premixed burning is prevented.<ref name="BE-2-179" /> In one of Beyler's examples, a 200 m³ room contains 30 % methane after a leak. About 167 m³ of nitrogen must be added before air can safely enter, assuming good mixing during the injection.<ref name="BE-2-181" /> For tanks at United States nuclear facilities, NUREG-1805 refers to NFPA 69. That standard requires the oxygen to stay at 60 % of the LOC when the LOC is above 5 %, or the fuel gas to stay below 25 % of the LEL.<ref name="IS-B-27">Iqbal and Salley (2004), p. B-27.</ref>

In fires, flammable mixtures can form from the products of the fire itself. ''Introduction to Fire Safety Engineering'' describes a [[smoke explosion]] as the very rapid burning of flammable gases from decomposing fuel or incomplete combustion. A typical condition is that air and pyrolysis gases are reasonably premixed and lie between the LEL and UEL.<ref name="VR-4.10" /> The mixture can then be ignited by autoignition, by a spark from electrical equipment or by glowing particles from the fire.<ref name="VR-4.10" /> NUREG-1805 adds that smouldering fires, for example in polyurethane foam, can produce enough unburnt fuel and carbon monoxide for such an explosion.<ref name="IS-15-4" />

The same principle applies to new hazards. In a Dutch study of car parks, gases released from electric vehicle batteries can build up in confined or poorly ventilated spaces. If their lower explosion limit is reached and the mixture is ignited, a fire gas explosion can occur.<ref name="VdG-27">Van der Graaf et al. (2021/2023), p. 27.</ref> Outdoors, a cloud of vapour from a spill burns only if it meets an ignition source while part of the cloud lies within the flammable range.<ref name="BE2A-3-303">Beyler (2002a), p. 3-303.</ref> The regions within the limits then burn as premixed flames, followed by diffusion burning of the richer parts.<ref name="BE2A-3-303" /> NUREG-1805 describes an unconfined [[vapour cloud explosion]] as the case in which an ignition source sets off a deflagration in such a cloud, seen as a fireball.<ref name="IS-F-67">Iqbal and Salley (2004), p. F-67.</ref>

The limits also have known weaknesses as design data. Because concentrations within a real cloud vary, fire risk analyses for United States nuclear plants commonly use half the lower limit for hydrogen clouds.<ref name="NO-N-8">Nowlen et al. (2005b), p. N-8.</ref> Published values for the same gas also differ slightly between sources, as for the upper limit of hydrogen, given as 74 % and 75 %.<ref name="IS-16-2" /><ref name="IFEG-3.3-3" />

== See also ==
* [[Fire triangle]]
* [[Deflagration]]
* Hazardous area classification
* [[Hydrogen safety]]
* [[Minimum ignition energy]]
* [[Equivalence ratio]]

== Notes ==
<references />

== References ==
* Beyler, C. L. (2002a). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-268–3-314). National Fire Protection Association; Society of Fire Protection Engineers.
* Beyler, C. L. (2002b). Flammability limits of premixed and diffusion flames. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-172–2-187). National Fire Protection Association; Society of Fire Protection Engineers.
* Drysdale, D. D. (2002). Thermochemistry. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-90–1-98). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Nowlen, S. P., Najafi, B., Wyant, F. J., Forester, J., Kazarians, M., Kolaczkowski, A., Joglar, F., Funk, D., Hannaman, G., & Anoba, R. (2005b). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Vol. 2. Detailed methodology'' (NUREG/CR-6850; EPRI 1011989). Electric Power Research Institute; U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research.
* Simmons, R. F. (2002). Premixed burning. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-144–1-154). National Fire Protection Association; Society of Fire Protection Engineers.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-402–3-421). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Combustion]]

Fire scenario

2026-11-02T21:32:50Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''fire scenario''' is a description of how one particular fire could start and develop in a building, from ignition through growth, spread and decay to burnout, as modified by the building's fire safety system.<ref name="IFEG-053">National Research Council of Canada et al. (2005), p. 0.5-3 (Part 0, Australia).</ref> It is described by the times at which its key events occur, such as detection, sprinkler operation, flashover or the failure of a barrier.<ref name="IFEG-053" /> A fire scenario is broader than the fire alone. It includes the ignition source and the first item ignited, the arrangement of fuel and enclosures, the status of fire protection measures, the occupants and, where relevant, external conditions such as wind.<ref name="BU-231">Bukowski (2002), p. 5-231.</ref><ref name="IFEG-222">National Research Council of Canada et al. (2005), pp. 2.2-2–2.2-3.</ref>

Fire scenarios are the starting point of almost every fire safety analysis. Watts and Hall describe fire risk analysis as answering three questions, the first being what could happen. A sequence of events ending in a fire loss is called a scenario.<ref name="WH-2">Watts and Hall (2002), p. 5-2.</ref> Because a building can burn in countless ways, engineers analyse only a limited set of design fire scenarios.<ref name="IFEG-1227">National Research Council of Canada et al. (2005), p. 1.2-27.</ref> These are chosen to be severe but credible, and each is turned into a design fire for calculation.<ref name="IFEG-1227" /> Several regulations now prescribe a minimum set of design scenarios, such as the ten scenarios of New Zealand's Verification Method C/VM2.<ref name="CVM2-7">Ministry of Business, Innovation and Employment (2025b), p. 7.</ref>

== Definitions ==
The International Fire Engineering Guidelines (IFEG, 2005) define a fire scenario as the ignition, growth, spread, decay and burnout of a fire in a building as modified by its fire safety system.<ref name="IFEG-053" /> The glossary of NUREG-1805, a report of the U.S. Nuclear Regulatory Commission, gives a similar definition. There a fire scenario is a set of conditions that defines the development of fire and the spread of combustion products through a building or part of a building.<ref name="IS-F28">Iqbal and Salley (2004), p. F-28.</ref> Bukowski, writing about fire hazards in passenger rail, describes a fire scenario as the sequence of events that must occur to result in an uncontrolled fire.<ref name="BU-231" />

Three related terms are easily confused. A fire scenario is any possible course of a fire, whereas a design fire scenario is the subset selected for design purposes.<ref name="ME-162">Meacham (2002), p. 5-162.</ref> The IFEG define a design fire scenario as a fire scenario that is used as the basis for a [[design fire]].<ref name="IFEG-052">National Research Council of Canada et al. (2005), p. 0.5-2 (Part 0, Australia).</ref> A design fire in turn is a representation of a fire by the variation of its heat output with time.<ref name="IFEG-052" /> The scenario is therefore the story, and the design fire is the quantified heat release curve used to tell it in a calculation.

The NUREG-1805 glossary stresses the purpose of a design fire scenario. It is a set of conditions that describes the critical factors for determining the outcomes of trial designs.<ref name="IS-F21">Iqbal and Salley (2004), p. F-21.</ref> New Zealand's C/VM2 uses the shorter term design scenario. The first edition defined it as a specific scenario on which a deterministic fire safety engineering analysis is conducted.<ref name="MBIE13-9">Ministry of Business, Innovation and Employment (2013), p. 9.</ref>

== What a scenario describes ==
A fire scenario combines the fire with the building and the people in it. The IFEG list the factors that a scenario takes into account. These are the nature, quantity, arrangement and burning behaviour of combustibles, the geometry of the enclosure, and the number of enclosures and the connections between them.<ref name="IFEG-1227" /> The fire protection measures in the building and their effect on the fire complete the list.<ref name="IFEG-1227" />

A scenario represents one particular combination of outcomes for the types of fire, its development and the external environment.<ref name="IFEG-222" /> The fire may be smouldering, flaming without flashover, or flashover.<ref name="IFEG-222" /> Its development is influenced by the size and type of ignition source, the distribution and type of fuel, the fire load density, the location of the fire, ventilation, construction materials and air handling equipment.<ref name="IFEG-222" /> External conditions include the season, wind speed and direction, and the stack effect.<ref name="IFEG-222" />

The IFEG also define a scenario by the outcome of each of the six sub-systems of a fire safety system.<ref name="IFEG-223">National Research Council of Canada et al. (2005), p. 2.2-3.</ref> Typical alternatives are whether smoke management operates, whether doors are open or closed, and whether detectors and sprinklers succeed. Others are whether occupants are awake or asleep, and whether the fire service rescues and extinguishes successfully.<ref name="IFEG-223" /> A simple example with sprinklers and barriers gives three scenarios. In the first, sprinklers control the fire; in the second, sprinklers fail but the barriers contain the fire; in the third, both fail and the fire spreads to adjoining enclosures.<ref name="IFEG-223" />

[[File:fse-fire-scenario-v1.svg|thumb|upright=1.5|alt=Event tree: ignition, sprinklers succeed (scenario I) or fail; if they fail, barriers hold (scenario II) or fail (scenario III).|Event tree for a fire with sprinklers and barriers: each path from ignition to an outcome is one fire scenario. Based on National Research Council of Canada et al. (2005), pp. 2.2-3–2.2-4.]]

The people form part of the scenario as well. The IFEG describe occupant response scenarios in which people notice the fire directly, respond to an alarm, or respond later to new cues or to warnings from others.<ref name="IFEG-225">National Research Council of Canada et al. (2005), p. 2.2-5.</ref> Each occupant response scenario is combined separately with each fire scenario.<ref name="IFEG-226">National Research Council of Canada et al. (2005), p. 2.2-6.</ref> For escape analysis, ''Introduction to Fire Safety Engineering'' lists the possible or expected fire scenario among the aspects that determine whether people can escape safely.<ref name="VR-7">Van Rossum (2027), §7.</ref>

== Identifying potential scenarios ==
The first task is to find the potential fire scenarios. The IFEG suggest reviewing the information assembled for the fire engineering brief, especially the hazard analysis.<ref name="IFEG-1227" /> Other sources are the published literature, fire statistics, and the experience and knowledge of the team.<ref name="IFEG-1227" /> The Australian handbook for the Fire Safety Verification Method (FSVM) names several hazard identification techniques. These are checklists, what-if analysis, hazard identification (HAZID), hazard and operability analysis (HAZOP), failure mode and effects analysis, and reviews of the literature and of historic records.<ref name="HB-59">Australian Building Codes Board (2020b), p. 59.</ref> The handbook recommends a mix of structured and informal methods, so that free thinking can reveal significant events of low probability and high consequence.<ref name="HB-59" />

For a systematic search, the IFEG recommend [[event tree analysis]]. An event tree starts with an initiating event, such as ignition, and branches at each system or event into success or failure.<ref name="IFEG-224">National Research Council of Canada et al. (2005), p. 2.2-4.</ref> Each path through the tree, from the initiating event to a final event, defines one fire scenario.<ref name="IFEG-224" /> Where the probability of an event is not known, fault trees can be used to calculate it from the failure mechanisms of the system.<ref name="IFEG-224" />

The number of scenarios grows quickly. Meacham gives the example of a building with three compartmented rooms.<ref name="ME-162" /> If only the room of origin and the order of spread are considered, there are 15 possible paths of fire propagation. Adding simultaneous spread to the second and third rooms gives 18 scenarios.<ref name="ME-162" /> That count is reached before open or closed doors, the characteristics of the people present, or whether they are asleep are even considered.<ref name="ME-162" />

[[File:fse-fire-scenario-v4.svg|thumb|upright=1.5|alt=Plan of three rooms in a row with a list of the five spread paths for a fire starting in room 1; 15 paths in total.|A building of three rooms already has 15 possible paths of fire spread, or 18 with simultaneous spread. Based on Meacham (2002), p. 5-162.]]

== Selecting design fire scenarios ==
A fire engineering analysis can consider only a limited number of the potential scenarios.<ref name="IFEG-1227" /> The IFEG describe a three-step approach. The team first determines the potential fire scenarios, then selects the design fire scenarios, and finally specifies a schematic design fire for each.<ref name="IFEG-1227" /> Usually, the selected scenarios are severe, have a reasonable probability of occurrence and have a significant potential for loss.<ref name="IFEG-1227" /> Events with a very low probability should not be analysed unnecessarily. If their consequences could be very high, however, they deserve consideration at least in the sensitivity studies.<ref name="IFEG-1227" />

[[File:fse-fire-scenario-v2.svg|thumb|upright=1.5|alt=Funnel: many potential fire scenarios narrow to a few design fire scenarios, each turned into a design fire curve.|From potential fire scenarios to design fires in three steps. Based on National Research Council of Canada et al. (2005), p. 1.2-27.]]

Deliberately started fires are treated in the same way as accidental ones when design scenarios are chosen.<ref name="IFEG-1227" /> The IFEG recognise, however, that some large arson attacks and terrorist events may be beyond the capacity of the fire safety system and need other measures.<ref name="IFEG-1228">National Research Council of Canada et al. (2005), p. 1.2-28.</ref> The selection is made by the stakeholders in the fire engineering brief.<ref name="IFEG-1227" /> At that stage, the design fires are defined and described as far as possible without calculation, in a largely qualitative review of the design.<ref name="IFEG-1229">National Research Council of Canada et al. (2005), p. 1.2-29.</ref>

Some regulations prescribe a minimum set of design scenarios. In New Zealand, Verification Method C/VM2 (second edition, 2025) contains ten design scenarios that must each be satisfied separately.<ref name="CVM2-7" /> They range from a fire that blocks an exit and a smouldering fire to horizontal and vertical fire spread, firefighting operations and a challenging fire.<ref name="CVM2-8">Ministry of Business, Innovation and Employment (2025b), p. 8.</ref> The scenarios are intended to give a diverse range of fire events that will challenge the design and its fire safety systems.<ref name="CVM2-7" /> Many can be satisfied by inspection or by providing features such as fire separations or automatic alarms.<ref name="CVM2-7" /> Only a few need a comparison of the available safe egress time (ASET) with the required safe egress time (RSET), or other computational modelling.<ref name="CVM2-7" />

The challenging fire scenario of C/VM2 represents credible worst cases in normally occupied spaces. Design fires are placed in various locations in the building, using a single fire source for each location.<ref name="CVM2-56">Ministry of Business, Innovation and Employment (2025b), p. 56.</ref> In this scenario, active and passive fire safety systems are assumed to perform as designed.<ref name="CVM2-57">Ministry of Business, Innovation and Employment (2025b), p. 57.</ref> A separate scenario then assumes the failure of each key fire safety system in turn.<ref name="CVM2-58">Ministry of Business, Innovation and Employment (2025b), p. 58.</ref> The commentary to the first edition explains that the framework was modelled on structural design, which also specifies design events such as wind, earthquake and snow.<ref name="MBIE13-11">Ministry of Business, Innovation and Employment (2013), p. 11.</ref>

In Australia, the FSVM specifies a minimum of twelve design scenarios. Each is considered in one or more locations to compare the proposed design with a reference building that fully complies with the deemed-to-satisfy provisions.<ref name="HB-7">Australian Building Codes Board (2020b), p. 7.</ref> The handbook explains that prescribing scenarios reduces the risk that critical design scenarios are missed. It notes similar approaches in C/VM2, in NFPA 5000 in the United States and in ISO 16733-1.<ref name="HB-8">Australian Building Codes Board (2020b), p. 8.</ref>

Hazard identification may show that some prescribed scenarios do not apply. For example, the smouldering fire scenario near sleeping areas is not needed in an office without sleeping accommodation.<ref name="HB-60">Australian Building Codes Board (2020b), p. 60.</ref> Buildings with innovative or unusual features may need additional scenarios.<ref name="HB-60" />

== From scenario to design fire ==
Once a design fire scenario has been chosen, it must be quantified. The Australian handbook lists what is needed: a design fire, the status of active and passive fire protection, occupant characteristics where required, and acceptance criteria.<ref name="HB-59" /> The IFEG compare this step with structural engineering, where the loads must be specified before safety can be evaluated.<ref name="IFEG-1227" /> The validity of the whole fire engineering evaluation rests on the validity of the design fires.<ref name="IFEG-1227" />

The IFEG first sketch each design fire as a schematic heat release rate curve. A smouldering fire that does not become flaming typically has a maximum heat release rate below 5 kW.<ref name="IFEG-1229" /> For flaming fires, the heat release rate is generally assumed to grow with the square of time, reach a steady value limited by fuel or ventilation, and then decay.<ref name="IFEG-1230">National Research Council of Canada et al. (2005), p. 1.2-30.</ref> For a flashover fire, flashover is drawn as an instantaneous jump in heat release rate.<ref name="IFEG-1230" /> The curve is then adjusted for events such as windows breaking, smoke management operating, doors burning through, and suppression by sprinklers, occupants or the fire service.<ref name="IFEG-1230" />

[[File:fse-fire-scenario-v3.svg|thumb|upright=1.5|alt=Three heat release rate curves: a low smouldering curve, a non-flashover curve with growth, plateau and decay, and a flashover curve with a vertical jump.|Schematic design fires for smouldering, non-flashover and flashover fire scenarios. Based on National Research Council of Canada et al. (2005), pp. 1.2-29–1.2-30.]]

''Introduction to Fire Safety Engineering'' describes the t-squared growth curve as a widely used starting point in a fire scenario. Its four standard growth rates reach 1 MW after 75 s (ultra-fast), 150 s (fast), 300 s (medium) and 600 s (slow).<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> The book stresses that a temperature-time curve is not suitable for representing a fire in a room. The temperature is a result of a fire scenario, not an input to it.<ref name="VR-8.6" /> A study of fires in indoor car parks makes the same point, representing the car park fire scenario by a heat release rate curve rather than a temperature curve.<ref name="VG-24">DGMR (2015), as cited in Van der Graaf et al. (2021/2023), p. 24.</ref>

Fire models do not choose the scenario themselves. The book points out that a computational fluid dynamics model does not predict how a fire develops. The modeller must prescribe the fire scenario and the growth of the heat release rate.<ref name="VR-11.4">Van Rossum (2027), §11.4.</ref> Before any model is used, it must also be established that the scenario lies within the model's field of application.<ref name="VR-8.1">Van Rossum (2027), §8.1.</ref>

== Scenarios in risk analysis ==
A deterministic analysis calculates the outcome of each design fire scenario, but it does not indicate the probability of that outcome. A probabilistic analysis also assigns a probability to each scenario and combines the results.<ref name="IFEG-1222">National Research Council of Canada et al. (2005), p. 1.2-22.</ref> The IFEG note that the use of multiple scenarios combined by probabilistic techniques is the key feature of some risk methods.<ref name="IFEG-1222" /> Such methods need the [[reliability of fire protection systems]], because each branch of the event tree depends on whether a system works.<ref name="ME-162" /> Meacham distinguishes availability, meaning a system is ready to perform, from reliability, meaning that an available system actually functions.<ref name="ME-162" />

The risk-cost assessment model described by Meacham shows how scenarios are built up in practice. It uses six design fires in the room of origin: smouldering, flaming without flashover, and flashover, each with the room door open or closed.<ref name="ME-163">Meacham (2002), p. 5-163.</ref> The probability of each design fire is based on statistics. In Canada, 18% of apartment fires reach flashover, 63% are flaming fires without flashover, and 19% are smouldering fires.<ref name="ME-163" /> The number of fire scenarios is the product of the number of design fires, the number of apartment units, and whether the occupants are awake or asleep.<ref name="ME-163" /> For an illustrative building of 20 apartments, this already gives 6 × 20 × 2 = 240 scenarios.

[[File:fse-fire-scenario-v5.svg|thumb|upright=1.5|alt=Bar chart of Canadian apartment fires: flashover 18%, flaming without flashover 63%, smouldering 19%.|Share of apartment fires in Canada by type, used to give each design fire a probability. Based on Meacham (2002), p. 5-163.]]

Frequencies must be handled with care. Meacham warns that a single scenario with a frequency of 10<sup>−7</sup> per year may suggest that fire is not a concern.<ref name="ME-166">Meacham (2002), p. 5-166.</ref> If 30 such scenarios are developed, however, their combined frequency is 3 × 10<sup>−6</sup> fires per year.<ref name="ME-166" /> In a [[fire risk assessment]], the consequences of each scenario are therefore weighted by its likelihood and summed over all scenarios.<ref name="BU-231" /><ref name="ME-161">Meacham (2002), p. 5-161.</ref>

In fire probabilistic risk assessment of US nuclear power plants, a fire scenario is defined by the location and burning characteristics of the initiating fire.<ref name="SI-216">Siu (2002), p. 5-216.</ref> Scenarios can be defined broadly, for example as a fire anywhere in an area, or in detail with a precise location and initial size.<ref name="SI-217">Siu (2002), p. 5-217.</ref> Broad definitions are used where a conservative analysis is enough, and detailed ones where the area is risk-significant.<ref name="SI-217" />

== Limits and misconceptions ==
A design fire scenario is not a prediction of the fire that will occur. It is a deliberately chosen case for testing a design, and design fires are normally intended to be conservative simplifications.<ref name="IFEG-1229" /> The IFEG warn that fire and its effects are complex and variable, so a fire safety system may not cope with every possible scenario.<ref name="IFEG-014">National Research Council of Canada et al. (2005), p. 0.1-4 (Part 0, Australia).</ref> Owners, occupiers and approving authorities need to understand this limit when they assess a fire engineered solution.<ref name="IFEG-014" />

"Worst credible" is not the same as "worst possible". Selection balances severity against probability, and very unlikely events are usually examined only in sensitivity studies.<ref name="IFEG-1227" /> For the same reason, a scenario set chosen for one building cannot be transferred to another without checking. The Australian handbook stresses that practitioners must consider each project case by case and not rely only on tables of scenarios.<ref name="HB-55">Australian Building Codes Board (2020b), p. 55.</ref>

Scenarios can also be used without any probability. A Dutch study on indoor car parks with electric vehicles defined three realistic scenarios. These were a long-lasting battery fire in one car, an electric car exposed to radiation from a burning neighbour, and several burning battery packs, for example in a travelling fire.<ref name="VG-32">Van der Graaf et al. (2021/2023), pp. 32–33.</ref> The authors state that no statements can be made about the probability of these scenarios. They served only as a conceptual framework for choosing prevention and firefighting measures.<ref name="VG-32" /> Such qualitative scenarios support decisions in [[performance-based design]], but they do not by themselves quantify risk.

== See also ==
* [[Fire safety strategy]]
* [[Prescriptive design]]
* [[Fire safety objectives]]
* [[Acceptance criteria]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (Print version 1.1).
* Bukowski, R. W. (2002). Fire hazard assessment for transportation vehicles. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-227–5-233). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Meacham, B. J. (2002). Building fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-153–5-175). National Fire Protection Association; Society of Fire Protection Engineers.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Siu, N. (2002). Fire risk assessment for nuclear power plants. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-214–5-226). National Fire Protection Association; Society of Fire Protection Engineers.
* Van der Graaf, J., Hessels, T., & Rosmuller, N. (2023). ''Fire safety of indoor car parks accommodating electrically powered vehicles''. Nederlands Instituut Publieke Veiligheid. (Original work published 2021)
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Watts, J. M., Jr., & Hall, J. R., Jr. (2002). Introduction to fire risk analysis. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-1–5-7). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Safety Design & Regulation]]

Flame detector

2026-11-02T21:32:50Z

Jan: Remove links to pages that do not exist; retain displayed text (wiki-wide link audit).

A '''flame detector''' is a fire detector that is activated by the electromagnetic radiation emitted by flames.<ref name="IS-F-30">Iqbal and Salley (2004), p. F-30.</ref> The common types sense ultraviolet (UV) or infrared (IR) radiation, and some units combine both.<ref name="IFEG-2.7-2">National Research Council of Canada et al. (2005), p. 2.7-2.</ref><ref name="Stroup-3-23">Stroup et al. (2016), p. 3-23.</ref> Unlike a [[smoke detector]] or a [[heat detector]], a flame detector does not wait for combustion products or hot gases to reach it.<ref name="SMC-4-4">Schifiliti et al. (2002), p. 4-4.</ref> It responds to radiation that travels in a straight line from the flame, so it must have a clear view of the fire.<ref name="SMC-4-30">Schifiliti et al. (2002), p. 4-30.</ref>

Flame detectors often start fast-response extinguishing or explosion suppression systems, which makes a reliable response within the required time essential.<ref name="SMC-4-30" /> The SFPE Handbook gives the example of infrared detectors that must find a 1 m² pool fire of jet fuel in a 20 m high aircraft hangar.<ref name="SMC-4-31">Schifiliti et al. (2002), p. 4-31.</ref> UV detectors give the fastest response of the detectors used to trigger suppression of gas explosions.<ref name="Zalosh-3-417">Zalosh (2002), p. 3-417.</ref> The range of a flame detector depends on the size of the fire, the distance, the angle to the detector's axis and the absorption of radiation by the air.<ref name="SMC-4-31" /> Designers therefore work with manufacturer curves of fire size against distance, which are based on the inverse square law.<ref name="SMC-4-30" /><ref name="SMC-4-31" /> For analysis and design, the International Fire Engineering Guidelines (2005) refer designers to the relevant standards, handbooks and manufacturer data.<ref name="IFEG-2.7-6">National Research Council of Canada et al. (2005), p. 2.7-6.</ref>

== How flame detectors work ==
Every fire detector senses one or more fire signatures. The SFPE Handbook lists these signatures as radiation, invisible and visible products of combustion, a rapid change in temperature and a high temperature.<ref name="SMC-4-4" /> Smoke detectors respond to the products of combustion and heat detectors respond to temperature.<ref name="SMC-4-4" /> Ultraviolet and infrared detectors are the only types in that list that respond to radiation.<ref name="SMC-4-4" /> A flame detector is therefore one part of a [[fire alarm system]] that can sense a fire at a distance, before any heat or smoke reaches the ceiling.<ref name="SMC-4-4" /><ref name="SMC-4-30" />

The radiation that a flame detector senses is the same [[thermal radiation]] that transfers heat from a fire. Radiation is emitted by the surface of a hot body, which can be a solid, a liquid or a gas body such as a flame or a smoke layer.<ref name="VR-5.4">Van Rossum (2027), §5.4.</ref> At the temperatures that matter in fires, most of this radiation lies in the infrared and part of it in the visible range; ultraviolet usually plays a small role in heat transfer.<ref name="VR-5.4" /> Gases between the fire and a receiving surface can absorb part of the radiation.<ref name="VR-5.4" />

Fire detection devices operate in only one of three bands of the spectrum.<ref name="SMC-4-30" /> The SFPE Handbook gives ultraviolet as 0.1 to 0.35 micrometres, visible light as 0.35 to 0.75 micrometres and infrared as 0.75 to 220 micrometres.<ref name="SMC-4-30" /> Its table of fire signatures assigns the ultraviolet detector to radiation with a wavelength of 1700 to 2900 ångström, that is 0.17 to 0.29 micrometres.<ref name="SMC-4-4" /> A sensor reacts only to specific wavelengths, so the fuel must emit radiation within the sensor's band.<ref name="SMC-4-30" /> An infrared detector with a single sensor tuned to 4.3 micrometres, the emission peak of carbon dioxide, cannot be expected to detect a fire of a fuel that contains no carbon.<ref name="SMC-4-30" />

[[File:fse-flame-detector-v1.svg|thumb|upright=1.5|alt=Horizontal wavelength bar divided into ultraviolet, visible and infrared bands, with the UV detector band and the 4.3 micrometre carbon dioxide peak marked.|The three bands used by flame detectors, with the ultraviolet detector band and the 4.3 µm carbon dioxide emission peak. Based on Schifiliti et al. (2002), pp. 4-4 and 4-30.]]

== Types and selection ==
The International Fire Engineering Guidelines name ultraviolet and infrared flame detectors as the two main examples.<ref name="IFEG-2.7-2" /> Combination ultraviolet/infrared optical flame detectors also exist; they were among the devices tested in large US Navy aircraft hangars, 15 m and 22 m high.<ref name="Stroup-3-23" /> Fires of jet fuel in those tests ranged from 100 kW to about 33 MW.<ref name="Stroup-3-23" />

Selecting a sensor depends on the fuel, the growth rate of the fire, the ambient conditions and the control or extinguishing function that the detector must start.<ref name="SMC-4-30" /> The designer must also consider absorption of radiation by the air, other sources of radiation in the area, the size of the spark, ember or fire to be detected, and the distance to the sensor.<ref name="SMC-4-30" /> In the hangar example of the SFPE Handbook, infrared detection at 4.3 micrometres suits the carbon-based jet fuel.<ref name="SMC-4-31" /> Infrared detectors were also expected to cover a larger area per device than ultraviolet detectors and so to cost less in that case.<ref name="SMC-4-31" />

Sources of radiation that are not fires can cause false alarms. Resistance to such false responses can be obtained by filtering, by using several sensors in one unit, such as a two- or three-channel detector, or by both.<ref name="SMC-4-31" /> A system can also use coincident detection, in which two or more detectors must operate before an alarm is accepted.<ref name="IFEG-2.7-2" /> In explosion suppression, the choice between pressure sensors and ultraviolet detectors depends on the required response time and on concerns about spurious activation and about the detectors' view being blocked.<ref name="Zalosh-3-417" />

== Detection distance and the inverse square law ==
The radiant power that reaches a sensor falls quickly as the distance to the fire grows. Standard practice for the design of radiant energy detection is based on curves of fire size against distance, which are derived from the inverse square law.<ref name="SMC-4-30" /> The SFPE Handbook gives the relation as:<ref name="SMC-4-31" />

<math display="block">S = \frac{k\,P\,e^{-\zeta d}}{d^{2}}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>S</math> || radiant power reaching the detector || W
|-
| <math>k</math> || proportionality constant for the detector || –
|-
| <math>P</math> || radiant power emitted by the fire || W
|-
| <math>\zeta</math> || extinction coefficient of air || m<sup>−1</sup>
|-
| <math>d</math> || distance between the fire and the detector || m
|}

The handbook prints the exponential term without its minus sign.<ref name="SMC-4-31" /> The minus sign used here follows from the handbook's own statement that humidity and dust absorb radiation and so limit the radiation that reaches the sensor.<ref name="SMC-4-31" /> Manufacturers test a sensor with several fuels and plot the normalised fire size against the normalised distance.<ref name="SMC-4-31" /> The resulting curve gives the largest distance at which the sensor consistently detects a fire of a given size, usually stated in square metres of burning area.<ref name="SMC-4-31" />

As a worked example, the hangar case in the SFPE Handbook uses a detector that sees a 1.0 m² fire at 40 m on its axis.<ref name="SMC-4-32">Schifiliti et al. (2002), p. 4-32.</ref> In clear air, with the absorption term equal to one, halving the distance to 20 m makes the received power four times larger, because it scales with one over the distance squared. The other way round, a fire that emits only half the radiant power reaches the same signal only at 40/√2, about 28 m. Real air absorbs part of the radiation, so these clear-air values are upper limits for the reach of the detector.<ref name="SMC-4-31" />

[[File:fse-flame-detector-v2.svg|thumb|upright=1.5|alt=Falling curve of relative radiant power against distance from 10 to 60 m, equal to 1 at 40 m and 4 at 20 m.|Relative radiant power at the detector against distance in clear air, set to 1 at 40 m. Halving the distance gives four times the power. Based on Schifiliti et al. (2002), pp. 4-31 to 4-32.]]

The handbook then applies typical reductions to the detection distance of the hangar detectors, which have a field of view of 45 degrees.<ref name="SMC-4-32" /> A 30% loss of sensitivity at the edge of the field of view reduces the distance for the 1.0 m² fire from 40 m to 28 m.<ref name="SMC-4-32" /> A further loss of 3% at an ambient temperature of 50 °C gives about 26.8 m, and another 3% at 90% relative humidity gives about 25.6 m.<ref name="SMC-4-32" /> The largest viewing distance in the layout at 45 degrees is 20 m, so the design is considered valid.<ref name="SMC-4-32" /> Had the distance dropped below 20 m, a different layout or different devices would have been needed.<ref name="SMC-4-32" />

[[File:fse-flame-detector-v3.svg|thumb|upright=1.5|alt=Hangar cross-section with flame detectors in the upper corners, their 45 degree fields of view and a 1 square metre pool fire on the floor.|Infrared flame detectors in an aircraft hangar: the detection distance for a 1.0 m² fire falls from 40 m on axis to about 25.6 m at the edge of the view, still above the 20 m needed. Based on Schifiliti et al. (2002), pp. 4-31 to 4-32.]]

== Design of a flame detection system ==
Fire detection systems serve goals of life safety, property protection, business protection and environmental protection.<ref name="SMC-4-1">Schifiliti et al. (2002), p. 4-1.</ref> Detectors may also start other fire protection systems, such as special extinguishing systems and smoke control systems.<ref name="SMC-4-2">Schifiliti et al. (2002), p. 4-2.</ref> When a flame detector activates a fast extinguishing or control system, such as an explosion suppression system, it must respond reliably within the required time.<ref name="SMC-4-30" />

The SFPE Handbook describes the design in a fixed order.<ref name="SMC-4-31" /> First a detector type is chosen that matches the fuel. Then the possible sources of interfering radiation are identified and a device is selected that resists them.<ref name="SMC-4-31" /> Next, the manufacturer's data give the mounting height and lateral distance limits for the critical fire size.<ref name="SMC-4-31" /> The layout must then account for all obstructions so that every part of the space is watched.<ref name="SMC-4-31" /> Finally, the reductions in sensitivity due to viewing angle, temperature and humidity are checked against the actual viewing distances.<ref name="SMC-4-31" /><ref name="SMC-4-32" />

The International Fire Engineering Guidelines describe a flame detector as a point that receives radiation from a flame with a specific flame temperature and emissivity.<ref name="IFEG-2.7-6" /> The intensity of the radiation it receives can be calculated with the methods for radiation from fires in the same guidelines.<ref name="IFEG-2.7-6" /> The sensitivity varies with the direction of the incoming radiation, and this off-axis sensitivity must be considered in design.<ref name="IFEG-2.7-6" /> A method for estimating flame height is also needed for the operation of flame detectors.<ref name="IFEG-2.4-6">National Research Council of Canada et al. (2005), p. 2.4-6.</ref> In New Zealand, the fixed detector criteria of C/VM2 (second edition, 2025) do not cover flame detectors.<ref name="MBIE25-27">Ministry of Business, Innovation and Employment (2025b), p. 27.</ref> Its table gives activation criteria only for heat detectors, smoke detectors and sprinklers.<ref name="MBIE25-27" />

== Applications ==
The sources describe flame detectors in large hangars, in process plants and in explosion suppression systems. The SFPE Handbook uses an aircraft hangar of 50 m by 80 m with a 20 m ceiling, where a fuel spill fire must activate a fixed suppression system.<ref name="SMC-4-31" /> In the chemical process industries, smaller leaks may be detected by gas or flame detectors, if these are installed.<ref name="Barry-5-184">Barry (2002), p. 5-184.</ref> A quantitative risk assessment should then establish the position, effectiveness and reliability of these detectors.<ref name="Barry-5-184" /> It should also describe in detail how gas and flame detection start the emergency shutdown system.<ref name="Barry-5-182">Barry (2002), p. 5-182.</ref>

In explosion suppression systems, detectors, a power supply and control system and fast extinguishing units work together.<ref name="Zalosh-3-417" /> Dust explosion applications usually use pressure sensors, while gas explosion applications can use pressure sensors or ultraviolet detectors.<ref name="Zalosh-3-417" /> Of these, ultraviolet detectors give the fastest response.<ref name="Zalosh-3-417" /> The control system includes interlocks that monitor the system itself, shut down processes and trigger alarms when the system activates.<ref name="Zalosh-3-417" />

Detectors in such plants may be installed where a flammable gas atmosphere can form, and one way to prevent an explosion there is to exclude ignition sources.<ref name="Beyler-2-181">Beyler (2002b), p. 2-181.</ref> Low-power equipment can be designed so that even its worst fault cannot release the minimum ignition energy of a given gas; such equipment is called intrinsically safe.<ref name="Beyler-2-181" /> Where this is not possible, the equipment can be housed in an explosion-proof enclosure that stops a flame from spreading out of it.<ref name="Beyler-2-181" /> The fuel oil tank room of World Trade Center 7 is an example. All its electrical devices were explosion proof, suitable for Class 1, Division 1, Group C in the hazardous area classification of the New York City building code.<ref name="GJ-27">Grill and Johnson (2005a), p. 27.</ref>

== Limits ==
A flame detector is mainly a line-of-sight device.<ref name="SMC-4-30" /> A fire hidden behind equipment, stored goods or structure may not be seen, which is why the layout must consider all obstructions.<ref name="SMC-4-31" /> Sensitivity decreases as the fire moves away from the optical axis: a fire detectable at a given distance on the axis may not be detectable at the same distance 30 degrees off the axis.<ref name="SMC-4-31" />

The surroundings also matter. Humidity and dust absorb radiation, and a higher ambient temperature can lower the relative sensitivity of the sensor.<ref name="SMC-4-31" /> Even a small decrease can affect the response to the expected fire.<ref name="SMC-4-31" /> Other radiation sources in the area, or air that absorbs a large fraction of the radiation, may change the type, location and spacing of the sensors.<ref name="SMC-4-30" />

The detector also has to match the fuel. A sensor that reacts only to a narrow band, such as the carbon dioxide peak at 4.3 micrometres, will not detect fuels that do not emit in that band.<ref name="SMC-4-30" /> Finally, the performance data of flame detectors come largely from manufacturers.<ref name="SMC-4-31" /> The International Fire Engineering Guidelines therefore advise taking relevant standards, handbooks and manufacturer data into account in analysis and design.<ref name="IFEG-2.7-6" />

== See also ==
* [[Deluge system]]
* [[Beam smoke detector]]
* [[Multi-sensor detector]]
* [[Detector activation time]]
* [[Aspirating smoke detection]]

== Notes ==
<references />

== References ==
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-176–5-213). National Fire Protection Association; Society of Fire Protection Engineers.
* Beyler, C. L. (2002b). Flammability limits of premixed and diffusion flames. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-172–2-187). National Fire Protection Association; Society of Fire Protection Engineers.
* Grill, R. A., & Johnson, D. A. (2005a). ''Documentation of the fuel system for emergency power in World Trade Center 7'' (NIST NCSTAR 1-1J). National Institute of Standards and Technology.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association; Society of Fire Protection Engineers.
* Stroup, D., Lindeman, A., McGrattan, K., Peacock, R., Overholt, K., Joglar, F., LeStrange, S., & Montanez, S. (2016). ''Verification and validation of selected fire models for nuclear power plant applications: Supplement 1'' (NUREG-1824, Supplement 1; EPRI 3002002182). U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research; Electric Power Research Institute.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-402–3-421). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Detection & Alarm]]