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Hydrocyanic acid

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Daan: Redirect to Hydrogen cyanide (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Hydrogen cyanide]]

HCN

2026-11-01T23:00:20Z

Daan: Redirect to Hydrogen cyanide (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Hydrogen cyanide]]

Hydrogen cyanide

2026-11-01T23:00:14Z

Daan: New FSE wiki article: Hydrogen cyanide (written by Claude Opus 5.5)

'''Hydrogen cyanide''' (HCN) is a highly toxic gas that is released when materials containing nitrogen burn or decompose. Together with [[carbon monoxide]], it is one of the two major asphyxiant gases in fires.<ref name="P-100">Purser (2002), p. 2-100.</ref> It is always present to some extent when nitrogen-containing materials such as acrylics, polyurethane foams, melamine, nylon and wool are involved in a fire, and these materials occur in most buildings.<ref name="P-100" /> Its concentrations are likely to be high in large post-flashover fires.<ref name="P-100" /> The gas is also called hydrocyanic acid.<ref name="IS-F54">Iqbal and Salley (2004), p. F-54.</ref>

In fires, hydrogen cyanide is about 20 to 40 times more potent than carbon monoxide.<ref name="P-91">Purser (2002), p. 2-91.</ref> While carbon monoxide poisoning sets in slowly and insidiously, hydrogen cyanide poisoning tends to be rapid and dramatic.<ref name="P-103">Purser (2002), p. 2-103.</ref> Concentrations of 100 to 200 ppm can make fire victims lose consciousness quickly, after which they may die from carbon monoxide or other causes.<ref name="P-105">Purser (2002), p. 2-105.</ref> Its contribution to deaths in fires is hard to establish, because blood cyanide is often not measured and decomposes after death.<ref name="P-100" /><ref name="P-106">Purser (2002), p. 2-106.</ref> Hydrogen cyanide is therefore an important but often uncertain part of [[fire toxicity]].<ref name="P-103" />

== Sources in fires ==
Hydrogen cyanide forms from materials whose molecules contain both nitrogen and hydrogen. A US Nuclear Regulatory Commission guide lists polyacrylonitrile, nylon, wool, polyurethane, urea-formaldehyde and acrylonitrile-butadiene-styrene (ABS) as examples.<ref name="IS-B68">Iqbal and Salley (2004), p. B-68.</ref> Several of them, such as polyurethane, nylon and ABS, are plastics, which makes hydrogen cyanide an important product of [[plastics in fire]].<ref name="IS-B68" /> In flames, hydrogen cyanide is formed in the oxygen-poor reduction zone, while nitrogen dioxide forms from the oxidation of hydrogen cyanide where oxygen is available.<ref name="T-128">Tewarson (2002), p. 3-128.</ref>

The temperature at which materials decompose affects the yield. Polyacrylonitrile starts to decompose between 525 and 625 K and then releases small amounts of ammonia and hydrogen cyanide.<ref name="BH-125">Beyler and Hirschler (2002), p. 1-125.</ref> Wool heated to 873 to 1198 K yields large amounts of hydrogen cyanide. For polyurethanes, the production of hydrogen cyanide and carbon monoxide increases with the decomposition temperature.<ref name="BH-128">Beyler and Hirschler (2002), p. 1-128.</ref> In tests at 900 °C, flexible polyurethane foam gave a clear atmosphere consisting mainly of hydrogen cyanide and carbon monoxide. At lower temperatures the same foam produced a dense yellow isocyanate smoke with low yields of both gases.<ref name="P-124">Purser (2002), p. 2-124.</ref>

The supply of oxygen matters as much as temperature. In early, well-ventilated flaming fires, most of the nitrogen in materials is oxidised to nitrogen oxides and nitrogen, and the yield of hydrogen cyanide is generally low. Acrylic materials, and to some extent rigid polyurethanes, are the exceptions.<ref name="P-153">Purser (2002), p. 2-153.</ref> Under hot, oxygen-starved conditions, the yield of hydrogen cyanide from all nitrogen-containing materials increases dramatically.<ref name="P-156">Purser (2002), p. 2-156.</ref> The generation efficiency of hydrogen cyanide from nylon increases with the [[equivalence ratio]], that is, as the fire becomes shorter of air.<ref name="T-128" />

Large-scale tests show the resulting pattern. In post-flashover fires, with the victim in a location remote from the fire, the atmosphere can contain 0 to 500 ppm of hydrogen cyanide together with up to 3 per cent carbon monoxide.<ref name="P-123">Purser (2002), p. 2-123.</ref> Above 800 °C with little oxygen, the main decomposition products break down into small molecules, including high concentrations of carbon monoxide and hydrogen cyanide.<ref name="P-123" /> The International Fire Engineering Guidelines (2005) note that smouldering polyurethane foam can also yield significant hydrogen cyanide.<ref name="IFEG-12">National Research Council of Canada et al. (2005), p. 2.4-12.</ref>

== Effects on the body ==
Hydrogen cyanide acts by blocking the use of oxygen in the body. The cyanides combine in the tissues with enzymes involved in cellular oxidation. Oxygen is then unavailable to the tissues, and death follows through asphyxia.<ref name="IS-F54" /> The toxic agent is the cyanide ion. Unlike carbon monoxide, which stays mainly in the blood, the cyanide ion spreads through the body fluids and reaches the cells of vital organs.<ref name="IS-B68" /> Hydrogen cyanide is carried rapidly to the brain, which explains why its effects appear faster than those of carbon monoxide.<ref name="P-104">Purser (2002), p. 2-104.</ref>

Experiments with monkeys show the typical course of poisoning. At 147 ppm the first effects were minor, but at some time during a 30-minute exposure breathing increased sharply, up to four times the normal volume. Within one to five minutes of the start of this hyperventilation the animals lost consciousness.<ref name="P-103" /> The increased breathing drew in more gas and stimulated breathing further, a positive feedback.<ref name="P-104" /> Once exposure ended, recovery was rapid and almost complete within five to ten minutes.<ref name="P-104" />

The response depends strongly on the concentration. Below about 80 ppm, effects in the animal experiments were minor for up to one hour. Between 80 and about 180 ppm, unconsciousness occurred at some time within 30 minutes. Above 180 ppm it followed within a few minutes.<ref name="P-104" />

Limited human data show a similar pattern. Incapacitation occurred after 20 to 30 minutes at 100 ppm and after 2 minutes at 200 ppm, with rapid death above about 300 ppm.<ref name="P-104" /> Body size also plays a part. Children take up the gas faster because of their smaller size, and physical activity speeds up uptake in adults.<ref name="P-104" />

A US Nuclear Regulatory Commission guide quotes the following effects from a 1971 source. The threshold limit value for workers is 10 ppm, and 20 to 40 ppm can be inhaled for several hours without appreciable effect. Concentrations of 120 to 150 ppm are dangerous within 30 to 60 minutes, and 3000 ppm or more is rapidly fatal.<ref name="IS-B68" /> The same guide notes that more than 180 ppm leads to unconsciousness within minutes, and that the fatal effect would normally come from carbon monoxide after hydrogen cyanide has made the victim unconscious.<ref name="IS-F54" />

== Time to incapacitation ==
Unlike carbon monoxide, hydrogen cyanide does not follow Haber's rule of a constant dose. For carbon monoxide, incapacitation occurs at about 27,000 ppm·min whatever the concentration. For hydrogen cyanide, the dose was about 2000 ppm·min at 100 ppm but only 400 ppm·min at 200 ppm.<ref name="P-104" /> Haber himself recognised this deviation in 1924.<ref name="P-104" /> The most important factor appears to be the rate of uptake, which depends on the concentration in the smoke and on breathing.<ref name="P-104" /> Concentrations above about 150 ppm are therefore more toxic than longer exposures to lower concentrations would suggest.<ref name="P-104" />

From primate and human data, the SFPE Handbook derives an exponential expression for the time to incapacitation at a constant concentration. A simpler linear expression fits the data between 80 and 180 ppm, but the exponential form also covers higher and lower concentrations.<ref name="P-105" /> It fits the data with a regression coefficient of 0.984:<ref name="P-105" />

<math display="block">t_{I,CN} = \exp\left(5.396 - 0.023\, C_{HCN}\right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_{I,CN}</math> || time to incapacitation (loss of consciousness) at a constant concentration || min
|-
| <math>C_{HCN}</math> || concentration of hydrogen cyanide in the inhaled air || ppm
|}

The expression is based mainly on data between about 80 and 180 ppm, where the time to incapacitation lies between about 2 and 30 minutes.<ref name="P-105" /> At 100 ppm it gives about 22 minutes and at 200 ppm about 2.2 minutes, which reflects the tenfold drop when the concentration doubles.<ref name="P-105" /> Real fires involve changing concentrations, and averaging the concentration over the exposure tends to overestimate the time to incapacitation.<ref name="P-105" /> The handbook therefore divides each minute of exposure by the time to incapacitation at that minute's concentration, and adds these fractions. Incapacitation is predicted when the sum reaches 1.<ref name="P-105" />

As a worked example, the handbook considers a person exposed to 90 ppm of hydrogen cyanide for 15 minutes and then to 180 ppm for 2 minutes.<ref name="P-105" /> Both concentrations lie in the range where the expression was fitted.<ref name="P-105" /> The fraction for each period is its duration divided by the time to incapacitation at its concentration:

<math display="block">\begin{aligned} t_{I,CN}(90) &= \exp(5.396 - 0.023 \times 90) = 27.83\ \mathrm{min} \\ t_{I,CN}(180) &= \exp(5.396 - 0.023 \times 180) = 3.51\ \mathrm{min} \\ F &= \tfrac{15}{27.83} + \tfrac{2}{3.51} = 0.54 + 0.57 = 1.11 \end{aligned}</math>

The fraction exceeds 1, so the person is predicted to be incapacitated. After 15 minutes at 90 ppm the fraction is only 0.54, but the two minutes at 180 ppm add more than the whole first period. The handbook places incapacitation between 17 and 18 minutes.<ref name="P-105" /> Interpolating within the second minute at 180 ppm gives about 16.6 minutes, so the short peak is decisive in either case. The same approach is used in the [[fractional effective dose]] for the asphyxiant gases, in which a simplified form of the cyanide fraction also corrects for other nitriles and for nitrogen dioxide.<ref name="P-105" />

== Combined effects with other gases ==
In a fire, hydrogen cyanide is never inhaled alone. Carbon monoxide reduces the transport of oxygen in the blood, while hydrogen cyanide reduces the ability of the tissues to use the oxygen delivered.<ref name="P-109">Purser (2002), p. 2-109.</ref> On theoretical grounds little interaction would therefore be expected. The consensus view is nevertheless that the two gases have at least some additive effect. In primate experiments, near-toxic levels of carbon monoxide slightly shortened the time to incapacitation by hydrogen cyanide.<ref name="P-109" />

For hazard calculations, the handbook proposes to treat carbon monoxide and hydrogen cyanide as directly additive on a fractional dose basis.<ref name="P-110">Purser (2002), p. 2-110.</ref> The uptake of both gases is assumed to increase in proportion to the faster breathing caused by carbon dioxide.<ref name="P-110" /> For most practical fires, carbon monoxide remains the most important asphyxiant. Hydrogen cyanide and low oxygen add to its effects and may shorten the time to incapacitation considerably in some situations.<ref name="P-110" />

The combination also shapes how fire victims die. In the Strathclyde study of fire deaths in Scotland, high blood cyanide levels were usually found together with lethal carboxyhaemoglobin levels, so the separate role of cyanide could not be established.<ref name="P-103" /> Because of its rapid "knockdown" effect, hydrogen cyanide at 100 to 200 ppm can cause a quick loss of consciousness, after which the victim dies from accumulating carbon monoxide.<ref name="P-105" /> Hydrogen cyanide is thus one of the narcotic gases in [[smoke inhalation]], together with carbon monoxide, carbon dioxide and low oxygen.<ref name="IS-F54" />

== Toxic potency of materials ==
The release of hydrogen cyanide makes nitrogen-containing materials more toxic than other materials in some fire conditions. Under nonflaming conditions, materials that release hydrogen cyanide at low temperatures, such as polyacrylonitrile, modacrylic and rigid polyurethane foam, have toxic potency factors of 3 to 8 relative to a normal material.<ref name="P-98">Purser (2002), p. 2-98.</ref> Under post-flashover conditions, the potency of all materials rises because of higher yields of hydrogen cyanide and carbon monoxide. For nitrogen-containing materials it then ranges from about 2.5 for flexible polyurethane foam to about 11 for modacrylic and polyacrylonitrile.<ref name="P-98" />

Even below post-flashover temperatures, hydrogen cyanide can dominate. For wool decomposed at 700 °C, the toxicity is likely to be dominated by the high hydrogen cyanide yield, and the same is considered true for most other nitrogen-containing materials.<ref name="P-157">Purser (2002), p. 2-157.</ref> The handbook stresses that data for this type of fire are scarce.<ref name="P-157" /> Hydrogen cyanide is also flammable, with flammability limits of 5.6 to 40 per cent in air, far above toxic concentrations.<ref name="B-176">Beyler (2002b), p. 2-176.</ref>

== Treatment in design and regulation ==
Fire engineering guidance often lists hydrogen cyanide among the toxic species to consider. The International Fire Engineering Guidelines (2005) name carbon monoxide, carbon dioxide, hydrogen cyanide and low oxygen as the toxic species often considered for life safety.<ref name="IFEG-1.5">National Research Council of Canada et al. (2005), p. 1.5-4.</ref> In practice, however, the same guidelines state that the analysis can generally be restricted to carbon monoxide unless the materials are atypical.<ref name="IFEG-12" />

In New Zealand, the first edition of Verification Method C/VM2 specified design yields for carbon monoxide, carbon dioxide and soot, and stated that hydrogen cyanide production need not be considered.<ref name="NZC-154">Ministry of Business, Innovation and Employment (2013), p. 154.</ref> The commentary explains that only carbon monoxide, carbon dioxide and oxygen were included because of a lack of confidence in the data for other species. Carbon monoxide was also found to reach toxic levels before other species.<ref name="NZC-43">Ministry of Business, Innovation and Employment (2013), p. 43.</ref> The second edition (2025) keeps a fractional effective dose of carbon monoxide that includes only carbon monoxide, carbon dioxide and oxygen.<ref name="NZ-17">Ministry of Business, Innovation and Employment (2025b), p. 17.</ref> In Australia, the Fire Safety Verification Method handbook (2020) notes that the production of carbon monoxide and hydrogen cyanide is sensitive to the materials and the combustion regime.<ref name="ABCB-111">Australian Building Codes Board (2020b), p. 111.</ref>

Fire models can track hydrogen cyanide where the user supplies the data. In the zone model CFAST, the fuel molecule may contain nitrogen, and the yield of hydrogen cyanide is limited by the nitrogen in the fuel.<ref name="CF-12">Peacock et al. (2026), p. 12.</ref> Any nitrogen not converted to hydrogen cyanide is released as nitrogen gas.<ref name="CF-12" /> The result therefore depends entirely on the yield chosen by the user.<ref name="CF-11">Peacock et al. (2026), p. 11.</ref>

== Limits of knowledge ==
The importance of hydrogen cyanide in fire deaths can be underestimated. The dynamics of its uptake, distribution and breakdown in the body are poorly understood, and few blood measurements exist for injured and dead fire victims.<ref name="P-105" /> Carboxyhaemoglobin is routinely measured in fire victims, but blood cyanide is measured less often and usually a day or more after exposure.<ref name="P-106" /> Cyanide decomposes by about 50 per cent within one to two days in a body. Blood levels of 2.0 to 2.5 µg/ml in fresh samples are considered capable of causing incapacitation and 3.0 µg/ml lethal, with lower thresholds for stored samples.<ref name="P-106" />

The toxicity data also have limits. Human exposure data are limited, and some reports suggest that people may survive higher concentrations for short periods. One person survived an accidental exposure to 444 ppm, and a 10-minute lethal concentration of 539 ppm has been suggested for humans.<ref name="P-104" /> The handbook considers the primate data a reasonable model for humans that probably errs slightly on the side of safety.<ref name="P-104" /> The fractional dose method is expected to give reasonable predictions only while the concentration is stable or increasing.<ref name="P-105" />

== See also ==
* [[Haber's rule]]
* [[Oxygen depletion]]
* [[Carbon dioxide]]
* [[Tenability criteria]]
* [[Smoke]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020b). ''Handbook: Fire Safety Verification Method'' (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.
* 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.
* 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.
* 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.

[[Category:Smoke, Toxicity & Tenability]]

Total flooding system

2026-11-01T22:59:23Z

Daan: Redirect to Gaseous extinguishing system (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Gaseous extinguishing system]]

Clean agent system

2026-11-01T22:59:17Z

Daan: Redirect to Gaseous extinguishing system (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Gaseous extinguishing system]]

Gaseous suppression system

2026-11-01T22:59:10Z

Daan: Redirect to Gaseous extinguishing system (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Gaseous extinguishing system]]

Gaseous fire extinguishing system

2026-11-01T22:59:04Z

Daan: Redirect to Gaseous extinguishing system (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Gaseous extinguishing system]]

Gaseous extinguishing system

2026-11-01T22:58:58Z

Daan: New FSE wiki article: Gaseous extinguishing system (written by Claude Opus 5.5)

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>

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" />

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" />

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]].

== 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]]

Fire water supply

2026-11-01T22:58:52Z

Daan: FSE wiki: Write out abbreviations at first use (NFPA, NIST, NRC, WTC, AFFF, PMMA) (written by Claude Opus 5.5)

A '''fire water supply''' is the source, storage and distribution of the water that sprinkler systems, hydrants, risers and hoses need to fight a fire. It can come from a public water main, from tanks on site, or from pumps that draw on either of them.<ref name="HO-21">Hopkins et al. (2005), p. 21.</ref><ref name="FL-83">Fleming (2002), p. 4-83.</ref> Its strength is described by how much water it can deliver, at what pressure, and for how long. Fleming calls the strength of the water supply the key to whether it will adequately serve a [[sprinkler system]].<ref name="FL-81">Fleming (2002), p. 4-81.</ref>

The supply serves two groups of users. Automatic systems such as sprinklers need water at once and without human action.<ref name="HO-21" /> The fire service needs water at the building for its hoses, from a [[fire hydrant]], from a riser inside the building or from its own pumping appliances.<ref name="EV-18">Evans et al. (2005), p. 18.</ref><ref name="MBIE-54">Ministry of Business, Innovation and Employment (2025b), p. 54.</ref>

In New Zealand, Building Code clause C5.5, as reproduced in C/VM2 (second edition, 2025), requires buildings to be provided with the means to deliver water for firefighting to all parts of the building.<ref name="MBIE-53">Ministry of Business, Innovation and Employment (2025b), p. 53.</ref> A water supply can also be a single point of failure. A closed valve, an empty tank or a pump that does not start can disable every system that depends on it.<ref name="IS-10-2">Iqbal and Salley (2004), p. 10-2.</ref> Redundant supply paths and independent sources are used to reduce this dependence.<ref name="EV-32">Evans et al. (2005), p. 32.</ref><ref name="MBIE-44">Ministry of Business, Innovation and Employment (2025b), p. 44.</ref>

== Sources of water ==
Water can come from several kinds of source. In the United States, a wet standpipe system needs a direct connection to an automatic water supply. Examples are a city water distribution system, a tank and pump, an elevated tank or a pressure tank.<ref name="HO-21" /> Sprinkler systems draw on the same kinds of source. NFPA 13, the US sprinkler standard of the National Fire Protection Association (NFPA), refers to separate standards for the supply components. These are NFPA 14 for standpipes, NFPA 20 for fire pumps, NFPA 22 for water tanks and NFPA 24 for private fire service mains.<ref name="FL-73">Fleming (2002), p. 4-73.</ref>

If not enough water is available at a suitable pressure, a stored water supply becomes necessary.<ref name="FL-82" /> The basic choice is between an elevated (gravity) tank, a pressure tank, or a suction tank combined with a pump.<ref name="FL-83" /> Without a pump, the energy for the system must come from the height of a gravity tank or from the air pressure in a pressure tank.<ref name="FL-83" />

Elevation adds or removes pressure at 0.433 psi per foot, or 0.099 bar per metre.<ref name="FL-80">Fleming (2002), p. 4-80.</ref> The pressure of a gravity tank must therefore be calculated from the lowest expected water level, which is normally the level at which the tank counts as empty.<ref name="FL-83" /> A pressure tank must contain enough air to push out the last water at an adequate pressure. A common rule of thumb has been one-third air at a minimum pressure of 75 psi (5.17 bar), but this rule does not hold for systems with high pressures.<ref name="FL-83" />

Fire pumps make up for a lack of pressure where enough water is available at a suitable suction pressure.<ref name="FL-82">Fleming (2002), p. 4-82.</ref> Plumbing codes sometimes set a minimum suction pressure of 10 to 20 psi (0.69 to 1.38 bar).<ref name="FL-82" /> Listed fire pumps have diesel or electric drivers and capacities from 25 to 5,000 gpm (95 to 18,927 L/min). The most common sizes lie between 250 and 2,500 gpm (946 to 9,463 L/min).<ref name="FL-82" /> NFPA 20 requires each horizontal fire pump to deliver at least 100 % of its rated pressure at its rated flow and at least 65 % of that pressure at 150 % of the flow. With no flow, the pressure must not exceed 140 % of the rated pressure.<ref name="FL-82" />

The World Trade Center complex in New York shows how these elements are combined in a large building. Its primary supply was a 12 in. fire main that looped the complex and was fed from the municipal supply by two redundant 16 in. connections.<ref name="EV-14">Evans et al. (2005), p. 14.</ref> Each tower had reserve tanks of 5,000 gal (about 19 m³) on several mechanical floors, and the tanks on the 41st floor had automatic fill lines from the domestic water system. Twelve fire pumps moved the water up the building.<ref name="EV-18" /> Fire department engines could also pump water from street hydrants into the buildings through 32 fire department connections at 14 locations.<ref name="EV-18" />

== Flow, pressure and duration ==
A water supply is assessed by testing it. Each test gives at least two values: the static pressure without flow and the residual pressure while a known flow is taken.<ref name="FL-81" /> The static pressure is read from a gauge on a hydrant. The residual pressure is read on the same gauge while water flows from another hydrant, preferably downstream.<ref name="FL-81" />

The static pressure reflects elevated tanks and running pumps, while the drop to the residual pressure reflects friction losses in the pipes.<ref name="FL-81" /> Because friction loss grows with the flow to the power 1.85, the two points can be drawn as a straight line on special graph paper. This line, the water supply curve, gives the available pressure at any flow.<ref name="FL-81" />

The required flow and pressure come from a [[hydraulic calculation]] of the system. For an adequate design, the system demand point, including the allowance for fire service hoses, must lie below the water supply curve.<ref name="FL-81" /> Outside the design area of a sprinkler system, no flow is added other than the hose stream allowances.<ref name="FL-75">Fleming (2002), p. 4-75.</ref> For standpipes, US practice based on NFPA 14 (2000) requires 500 gpm (1,893 L/min) at 100 psi (6.9 bar) at the hydraulically most remote standpipe. Each additional standpipe adds 250 gpm (946 L/min), up to a maximum of 1,250 gpm (4,732 L/min).<ref name="HO-20">Hopkins et al. (2005), p. 20.</ref>

Duration is the third requirement. Tanks must be sized to provide the minimum durations set by NFPA 13 or another applicable standard, and the required pressure must still be available when the tank is nearly empty.<ref name="FL-83" /> The stored volume follows from the flow and the duration:

<math display="block">V = Q \times t</math>

{| class="wikitable"
|+ Symbols
! Symbol !! Description !! Unit
|-
| <math>V</math> || usable stored water volume || m³ (or L)
|-
| <math>Q</math> || water demand (flow) of the systems supplied || m³/min (or L/min)
|-
| <math>t</math> || required duration of supply || min
|}

The relation assumes a constant demand and no refill during the fire. Any automatic refill, for example from the public main, lengthens the actual duration. The volume is the usable volume above the level at which the tank counts as empty.<ref name="FL-83" /><ref name="EV-18" />

=== Worked example ===
Two 5,000 gal tanks and a 5,000 gal standpipe reserve tank on the 110th floor of each World Trade Center tower supplied the booster pump for the highest sprinkler zone. Their combined capacity was 15,000 gal (56.8 m³).<ref name="EV-18" /><ref name="EV-19">Evans et al. (2005), p. 19.</ref> The fire pump was rated at 500 gpm (1,893 L/min), and the maximum permissible flow was 150 % of that, 750 gpm (2,839 L/min).<ref name="EV-19" /> Rearranging the relation gives the duration of supply:

<math display="block">t = \frac{V}{Q} = \frac{56.8\ \mathrm{m^3}}{1.893\ \mathrm{m^3/min}} = 30\ \mathrm{min}</math>

At the maximum flow of 2.839 m³/min, the same tanks last 20 minutes. The National Institute of Standards and Technology (NIST) gives the same values: a minimum of 30 minutes at 500 gpm, without any supplemental water from the domestic system, and 20 minutes at 750 gpm.<ref name="EV-19" /> Fleming's example for a pressure tank shows the same logic. A 30-minute supply for a demand of 140 gpm (530 L/min) requires at least 4,200 gal (15.9 m³) of water, plus the air needed to keep the pressure up.<ref name="FL-83" />

Hydraulic calculations by NIST for the light hazard sprinkler systems of the towers gave delivered densities of 0.10 to 0.27 gpm/ft² with up to 16 open sprinklers. The primary water supply could maintain these flows for about 10 to 89 minutes, depending on the location and number of open sprinklers.<ref name="EV-32" /> NIST concluded that the storage tanks gave enough duration for normally expected fires to allow the fire department to respond and supplement the supply.<ref name="EV-40">Evans et al. (2005), p. 40.</ref>

== Water for the fire service ==
The fire service draws its water from hydrants, from risers and from its own vehicles. In a fire engineering analysis, the time to set up a water supply is one of the steps in the fire brigade intervention model of the International Fire Engineering Guidelines.<ref name="IFEG-2.9-5">National Research Council of Canada et al. (2005), p. 2.9-5.</ref> The amount of firefighting water available at the scene is one of the resources to be assessed.<ref name="IFEG-1.9-5">National Research Council of Canada et al. (2005), p. 1.9-5.</ref> If the water supply or the number of firefighters is insufficient for interior firefighting, the strategy may change from offensive, fighting the fire, to defensive, stopping its spread to neighbouring buildings.<ref name="IFEG-2.9-4">National Research Council of Canada et al. (2005), p. 2.9-4.</ref>

National rules set the facilities. In Australia, Table 2.8 of the Fire Safety Verification Method Standard 2022 requires external fire hydrants for all buildings in the fire brigade intervention scenario. Internal hydrants are required in sprinklered buildings if any point is more than 100 m away or the building has more than three levels, and in unsprinklered buildings from 70 m.<ref name="ABCB-16">Australian Building Codes Board (2022), p. 16.</ref> The scenario applies only to buildings within 50 km road travel of a fire station.<ref name="ABCB-15">Australian Building Codes Board (2022), p. 15.</ref> In New Zealand, C/VM2 (second edition, 2025) accepts water from a pumping appliance parked so that any point in the building lies within 75 m, about three hose lengths. Otherwise an internal hydrant to NZS 4510 is needed.<ref name="MBIE-54" />

Inside tall buildings, risers bring the water to the floors. Standpipe systems are classed as wet, damp or dry by their water supply. Wet systems are filled with water at all times, while manual [[Dry and wet risers|dry standpipes]] have only fire department connections and no automatic supply.<ref name="HO-21" /> Removing the need for long hose lays from the fire engine to an upper floor improves the initial attack.<ref name="HO-21" /> For Dutch indoor car parks, NIPV notes that a dry riser can shorten the attack time, because less hose has to be rolled out.<ref name="NIPV-66">Van der Graaf et al. (2021/2023), p. 66.</ref>

Occupants can use the same water. The International Fire Engineering Guidelines mention suppression by building occupants with extinguishers and a [[hose reel]].<ref name="IFEG-1.7-1">National Research Council of Canada et al. (2005), p. 1.7-1.</ref> The New York City building code had no requirement for fire extinguishers, because it required occupant hose reels.<ref name="LE-151">Lew et al. (2005), p. 151.</ref> In World Trade Center Building 7 (WTC 7), hose reels were located in the stair enclosures, with hose cabinets throughout the floors.<ref name="HO-128">Hopkins et al. (2005), p. 128.</ref>

== Reliability and redundancy ==
Several common causes of sprinkler failure lie in the water supply. The US Nuclear Regulatory Commission (NRC) lists a closed water supply valve, a broken supply header, an empty water tank and a fire pump that fails to start among the causes.<ref name="IS-10-2" /> An electric pump can fail through a power failure, and a diesel pump through poor maintenance, dead batteries or lack of fuel.<ref name="IS-10-2" /> The Australian data sheets summarise US statistics by Ahrens. A system that was shut off accounted for 59 % of the cases in which a sprinkler system failed to operate. When systems did operate but were ineffective, 30 % of the cases involved not enough water being discharged.<ref name="AH-79">Ahrens (2017), as cited in Australian Building Codes Board (2020a), Data Sheet C2, p. 79.</ref>

The [[reliability of fire protection systems]] therefore depends strongly on valves and their management. An Australian fault tree study of sprinkler systems in high-rise offices found reliabilities between 86.6 % and 97.9 %. Shutting off sprinkler zones during tenancy changes was one of the main factors in failure.<ref name="MT-81">Moinuddin and Thomas, as cited in Australian Building Codes Board (2020a), Data Sheet C2, p. 81.</ref> According to the fault tree analysis, a zone isolation valve for each floor could reduce the failure probability by 10 % to 63 % of its original value.<ref name="MT-81" />

Redundancy reduces the dependence on a single source. In New Zealand, C/VM2 (second edition, 2025) states that a sprinkler system with two independent supplies, of which only one may depend on a town's main, has a very high degree of reliability. Such a system, with a Class A or Class B2 water supply to NZS 4541, can alone satisfy clause C3.6, which limits the radiation received at the relevant boundary.<ref name="MBIE-43">Ministry of Business, Innovation and Employment (2025b), p. 43.</ref><ref name="MBIE-44" /> The World Trade Center towers were supplied from loops at two remote locations, with isolation valves that allowed either main to operate independently.<ref name="EV-30">Evans et al. (2005), p. 30.</ref> WTC 7, by contrast, was fed by two mains within 12 ft (3.7 m) of each other from the same city main.<ref name="EV-30" />

Redundant sources can still share a weak point, which then becomes a [[common cause failure]]. NIST found that the risers of WTC 1, 2 and 7 provided redundant supply. Each floor's sprinkler system, however, had a single connection to the riser, a single point of failure for the sprinklers on that floor.<ref name="EV-41">Evans et al. (2005), p. 41.</ref> The emergency fire pumps lacked remote redundancy in their power lines, which could have affected the sprinklers and standpipes once power was lost.<ref name="EV-42">Evans et al. (2005), p. 42.</ref>

At one chemical plant, the fire pump house flooded three times in five years, and the pump controllers were shut off each time. The pumps thus formed a common cause failure for numerous deluge systems. Barry gives target availabilities for such systems of 0.98 to 0.999.<ref name="BA-203">Barry (2002), p. 5-203.</ref>

== Limits and practical issues ==
A design water supply covers the expected fire, not every fire. In the World Trade Center, the secondary water supply for the high and mid-level zones depended on manually started fire pumps. NIST notes that an automatic supplemental supply is required by NFPA 14 and represents current best practice.<ref name="EV-41" /> The lower floors of WTC 7 were supplied directly from the city system, so there was no secondary source if that system failed.<ref name="EV-40" /><ref name="EV-41" /> A long run of 4 in. pipe from the 110th floor tanks restricted the flow to several floors, although it was sufficient for the design.<ref name="EV-41" />

New hazards can change the demand. NIPV reports that fires in electric vehicles in car parks need large amounts of water for a long time to cool effectively. The extinguishing water supply and water drainage should be designed for this, and contaminated cooling water needs attention.<ref name="NIPV-6">Van der Graaf et al. (2021/2023), p. 6.</ref> The operating time of a sprinkler system, typically 30 to 120 minutes depending on the standard, limits how long it can support the fire service.<ref name="NIPV-47">Van der Graaf et al. (2021/2023), p. 47.</ref> Firefighting water can also harm the environment. The International Fire Engineering Guidelines name run-off of firefighting water from a chemical warehouse as an example.<ref name="IFEG-2.9-3">National Research Council of Canada et al. (2005), p. 2.9-3.</ref>

Statistics on sprinkler performance can hide supply problems. Australian and New Zealand data in the International Fire Engineering Guidelines show that 65 % of fires were controlled by one sprinkler head. These data exclude fires in which sprinklers failed to operate or water supplies were not available, so they may not reflect the overall reliability of sprinkler systems.<ref name="IFEG-3.7-3">National Research Council of Canada et al. (2005), p. 3.7-3.</ref>

== See also ==
* [[Wet pipe sprinkler system]]
* [[Dry pipe sprinkler system]]
* [[Deluge system]]
* [[Sprinkler design density]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, 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.
* 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.
* 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 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)

[[Category:Fire Suppression]]

Schematic design fire

2026-11-01T22:58:46Z

Daan: Redirect to Design fire (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Design fire]]

Extinguishing mechanisms

2026-11-01T22:58:40Z

Daan: FSE wiki: Write out abbreviations at first use (NFPA, NIST, NRC, WTC, AFFF, PMMA) (written by Claude Opus 5.5)

'''Extinguishing mechanisms''' are the physical and chemical ways in which a fire is put out or suppressed. Four mechanisms are distinguished, and usually several act at the same time. They are physically separating the fuel from the flame, removing or diluting the oxygen, lowering the temperature of the fuel or the flame, and adding chemicals that change the combustion chemistry.<ref name="IS-B15">Iqbal and Salley (2004), p. B-15.</ref> A glossary of the US Nuclear Regulatory Commission (NRC) lists the matching methods as cooling, oxygen depletion or removal, inhibition of the chemical reaction and flame removal, or blowout.<ref name="IS-F23">Iqbal and Salley (2004), p. F-23.</ref>

The mechanisms follow from the conditions that a fire needs. The [[fire triangle]] shows fuel, oxygen and heat; taking away any one of them stops the combustion.<ref name="IS-1-5">Iqbal and Salley (2004), p. 1-5.</ref> The [[fire tetrahedron]] adds a fourth element, the chain reaction of combustion, which explains why some agents work without cooling or smothering.<ref name="GR-152">Grant (2002), p. 4-152.</ref> Each [[extinguishing agent]] uses a mix of mechanisms. Water cools, foam excludes air from the fuel surface, inert gases act primarily by depleting the oxygen, and halons interrupt the chain reaction.<ref name="IS-10-1" /><ref name="SC-88">Scheffey (2002), p. 4-88.</ref><ref name="IS-B41" /><ref name="GR-153" /> The relative importance of each contribution varies with the circumstances.<ref name="IS-B16">Iqbal and Salley (2004), p. B-16.</ref>

== The fire triangle and the fire tetrahedron ==
''Introduction to Fire Safety Engineering'' describes combustion with three factors: oxygen, fuel and temperature.<ref name="VR-4.2">Van Rossum (2027), §4.2.</ref> Air contains 78 % nitrogen, 21 % oxygen and 1 % other gases by volume. If the oxygen level falls, a fire stops spreading and may eventually go out, depending on the exact oxygen concentration.<ref name="VR-4.2" /> A fuel mixed with oxygen cannot ignite unless enough heat is added, and the amount depends on the fuel.<ref name="VR-4.2" /> In the NRC guidance, the fire triangle requires fuel, an oxidising agent and a heat source in the same place at the same time. If any leg of the triangle is removed, the combustion is not sustained.<ref name="IS-1-5" />

The triangle leads directly to three classic mechanisms. Typical extinguishment removes the fuel from the fire, limits the oxygen (smothering), or removes the heat (quenching).<ref name="GR-152" /> The NRC adds that the triangle fits most scenarios, with the exception of extinguishment by dry chemicals and halons.<ref name="IS-1-5" />

Grant explains that the theory had to be modified as halons became better understood. Halons do not work in any of the three classic ways, but break up the uninhibited chain reaction of the combustion process.<ref name="GR-152" /> The resulting model is called the tetrahedron of fire, with temperature, oxygen, fuel and the chain reaction as its four faces.<ref name="GR-153">Grant (2002), p. 4-153.</ref> The NRC glossary defines it as a representation of fire in which fuel, oxidant, heat and chain reactions are the four corners of a tetrahedron.<ref name="IS-F29">Iqbal and Salley (2004), p. F-29.</ref>

The tetrahedron is also used in firefighting practice. The Netherlands Institute for Public Safety (NIPV) published guidance on fires in Dutch indoor car parks. For an interior attack, it advises crews to think in terms of the fuel, heat, oxygen and chemical chain reaction tetrahedron.<ref name="NIPV-63">Van der Graaf et al. (2021/2023), p. 63.</ref> The same guidance asks whether enough cooling capacity is available before an attack from inside or outside is chosen.<ref name="NIPV-63" />

== Cooling ==
Cooling removes heat from the fuel or the flame. Water is by far the most common cooling agent, mainly because it is widely available and inexpensive.<ref name="FL-72">Fleming (2002), p. 4-72.</ref> It also has a high [[specific heat capacity]] and a high latent heat of vaporisation.<ref name="FL-72" /> The specific heat of water at room temperature is 4,186 J/(kg·K), about four times that of air at 1,005 J/(kg·K).<ref name="VR-3.4">Van Rossum (2027), §3.4.</ref> When water evaporates, it takes extra energy from its surroundings, because every change from liquid to gas absorbs energy.<ref name="VR-3.5">Van Rossum (2027), §3.5.</ref>

The heat that a mass of water can absorb follows from the energy needed to heat it to its boiling point plus the energy needed to evaporate it. ''Introduction to Fire Safety Engineering'' gives the sensible part as mass times specific heat times temperature rise, and notes that the energy of a phase change must be added.<ref name="VR-3.4" /> Combined, the heat absorbed is:

<math display="block">E = m \left( c_p \, \Delta T + h_v \right)</math>

{| class="wikitable"
|+ Symbols
! Symbol !! Description !! Unit
|-
| <math>E</math> || heat absorbed by the water || kJ
|-
| <math>m</math> || mass of water || kg
|-
| <math>c_p</math> || specific heat of liquid water || kJ/(kg·K)
|-
| <math>\Delta T</math> || temperature rise from the initial temperature to the boiling point || K
|-
| <math>h_v</math> || heat of vaporisation of water at the boiling point || kJ/kg
|}

The relation assumes a constant specific heat and that all of the water evaporates. Water that runs off or drains away absorbs only the sensible part, or less.<ref name="VR-3.4" /> Tewarson gives the property values: a specific heat of 0.0042 kJ/(g·K) and a heat of vaporisation of 2.26 kJ/g at 373 K.<ref name="TE-100">Tewarson (2002), p. 3-100.</ref>

=== Worked example ===
Tewarson calculates the heat needed to gasify water that starts at 298 K (25 °C). Heating the water to 373 K takes 0.0042 × 75 = 0.32 kJ/g, and evaporating it takes 2.26 kJ/g, so the total is 2.58 kJ/g.<ref name="TE-100" /> One kilogram of water, about one litre, therefore absorbs about 2.58 MJ. Almost 88 % of this is absorbed by evaporation rather than by heating. Fleming gives 9,280 Btu for one US gallon of water heated from 21 °C to steam at 100 °C, which is equivalent to about 2.59 MJ per litre.<ref name="FL-72" />

An average living room sofa can burn at about 2.5 MW.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref> To absorb all of that heat, water would have to evaporate at 2,500 / 2,580 ≈ 0.98 kg/s, or about 59 L/min. If the water were only heated to 100 °C without evaporating, the same task would need about eight times as much water. In practice, much less than the full heat release has to be absorbed, as the section on flame cooling below explains. The calculation does show why evaporation, not heating, gives water most of its cooling power. In ''Introduction to Fire Safety Engineering'', the heat release rate of such an object is set against the cooling capacity that a fire service can deliver at a given flow rate.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref>

=== Cooling the fuel ===
Cooling the fuel surface slows down the pyrolysis that feeds the flame with gaseous fuel. When water is applied to a burning solid in air, the solid is cooled by contact with the water, so its rate of pyrolysis falls.<ref name="IS-B15" /> For fuels that give no flammable vapour at room temperature, such as solids and liquids with a high flash point, wetting and cooling of the surface is in many cases the dominant mechanism.<ref name="MB-314">Mawhinney and Back (2002), p. 4-314.</ref> If the vapour and air mixture above the surface falls below the lower flammability limit, the flame goes out.<ref name="MB-314" /> The NRC describes sprinklers in the same terms. The water vaporises and cools the burning materials below their ignition temperature, and nearby materials can no longer heat up to it.<ref name="IS-10-1">Iqbal and Salley (2004), p. 10-1.</ref>

Tewarson links this mechanism to the fire properties of the fuel. He calculates a [[critical water application rate]] for [[flame extinction]], expressed in grams of water per square metre of burning surface per second.<ref name="TE-148">Tewarson (2002), p. 3-148.</ref> The calculated values assume no water puddle on the surface and perfect efficiency. They are 2.1 to 2.5 g/(m²·s) for polyoxymethylene, polymethyl methacrylate (PMMA) and polyethylene with 25 % chlorine. Polyethylene and polypropylene need 3.5 to 4.1 g/(m²·s), and polystyrene 5.1 g/(m²·s).<ref name="TE-148" /> Materials that do not burn in normal air without an external heat flux have a critical rate of zero.<ref name="TE-148" />

=== Cooling the flame ===
Water can also act in the gas phase. Gas phase cooling is the removal of heat from the flame and hot gases by evaporating water, and fine droplets evaporate faster.<ref name="MB-313">Mawhinney and Back (2002), p. 4-313.</ref> If the flame temperature falls below the limiting adiabatic flame temperature, about 1,600 K (1,326 °C) for diffusion flames, the flame goes out.<ref name="MB-313" /> Only enough heat has to be removed to bring the flame down to this limit, not to ambient temperature.<ref name="MB-313" /> In Wighus's experiments, the heat absorbed by evaporating water needed to be only 0.3 times the heat release rate for an unconfined propane flame under optimum conditions. For more realistic machinery spaces, ratios of about 0.6 were noted.<ref name="MB-313" />

A cooler flame also radiates less heat back to the fuel, which further reduces the pyrolysis rate.<ref name="MB-313" /><ref name="IS-B15" /> In laboratory counterflow methane flames, water mist and vapour were more effective on a mass basis than Halon 1301, provided they were delivered with nearly 100 % efficiency. In full-scale compartment fires the efficiency is much lower.<ref name="MB-313" />

== Removing or diluting the oxygen ==
A flame needs a minimum oxygen concentration. For most hydrocarbon fuels, this limiting oxygen concentration is about 13 %.<ref name="MB-314" /> Smothering means limiting the oxygen supply to the fire.<ref name="GR-152" /> In an interior attack on a building fire, NIPV advises anti-ventilation, keeping the structure closed where possible.<ref name="NIPV-63" /> ''Introduction to Fire Safety Engineering'' notes that a fire stops spreading and may go out as the oxygen level falls.<ref name="VR-4.2" />

Water can dilute the oxygen as steam. When water droplets evaporate, the volume of the water increases by more than three orders of magnitude.<ref name="MB-314" /> In the flame, this expansion can disrupt the entrainment of air. In a compartment, steam from water hitting the flame, hot gases or hot surfaces can significantly reduce the oxygen concentration.<ref name="MB-314" /> The NRC notes that steam may keep oxygen away from the fire under some confined conditions.<ref name="IS-B15" />

Inert gases work in the same way, but they also act thermally. They lower the flame temperature below the threshold for the combustion reactions, both 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 reduce the oxygen concentration below 12 % extinguishes flaming fires.<ref name="DN-174" /> Carbon dioxide displaces the normal atmosphere and reduces the oxygen below the 15 % that the NRC report gives as necessary for a diffusion flame.<ref name="IS-B46">Iqbal and Salley (2004), p. B-46.</ref>

The NRC report describes the action of carbon dioxide as mainly thermophysical. The reacting gases are kept below the temperature needed to maintain the free radicals that sustain the flame chemistry.<ref name="IS-B46" /> For inert gases, the extinguishing concentration is linearly related to the heat capacity of the agent and air mixture.<ref name="IS-B46" />

== Separating the fuel from the flame ==
The third route breaks the contact between fuel, heat and air. Physically separating the combustible substance from the flame is one of the four mechanisms in the NRC list.<ref name="IS-B15" /> The simplest form is removing the fuel from the fire.<ref name="GR-152" /> Flame removal, or blowout, is listed in the NRC glossary as a further method of extinguishment.<ref name="IS-F23" />

Firefighting foam is the best known separating agent. It consists of air-filled bubbles formed from a solution of foam concentrate in water, typically 1, 3 or 6 % concentrate.<ref name="SC-88" /> The foam floats on the fuel and forms an air-excluding layer that halts the vaporisation of fuel at the surface. If the entire surface is covered, the fuel vapour is completely suppressed and the fire goes out.<ref name="SC-88" /> Film-forming foams can also produce a vapour-sealing film of surface-active water solution on most hydrocarbon fuels.<ref name="SC-88" /> Low-expansion foams are effective on flat pool fires, but not on three-dimensional fires such as running fuel or pressurised sprays.<ref name="SC-88" />

Foam combines several mechanisms on a burning pool. It stops radiant heat from the fire reaching the liquid surface and supplying the heat of vaporisation. If the fire point of the liquid is above the foam temperature, the liquid is cooled and its vapour pressure falls.<ref name="IS-B15" /> A water-soluble fuel such as alcohol is also diluted by water from the foam.<ref name="IS-B15" /> Water alone cannot separate a hydrocarbon fuel from the air. It is denser than most hydrocarbon fuels and does not mix with them, so the fuel floats on the water and may continue to burn and spread.<ref name="FL-72" />

== Chemical inhibition ==
Chemical inhibition interrupts the chain reaction in the flame rather than removing a leg of the triangle. Halogenated agents act in this way, although the mechanism is not completely understood.<ref name="GR-153" /> The halogen atoms remove the active chemical species that carry the flame chain reaction.<ref name="GR-153" />

Bromine is much more effective than chlorine or fluorine.<ref name="GR-153" /> In Halon 1301, which is 54 % bromine by weight, it is the bromine radical that acts as the inhibitor.<ref name="GR-153" /> The NRC report states that Halon 1301 suppresses a fire chemically and very quickly, unlike agents that work by removing heat or oxygen.<ref name="IS-B42">Iqbal and Salley (2004), p. B-42.</ref>

The replacements for halon show that the boundary between chemical and physical action is not sharp. Halocarbon clean agents extinguish fires by a combination of chemical and physical mechanisms, depending on the compound.<ref name="DN-174" /> Compounds with bromine or iodine scavenge flame radicals in the same way as Halon 1301. Other compounds work mainly by extracting heat from the flame zone, through their heat of vaporisation, their heat capacity and the energy absorbed when they decompose.<ref name="DN-174" /> Because these compounds have little chemical inhibition, they need higher extinguishing concentrations than Halon 1301.<ref name="DN-174" /> The NRC report likewise describes halocarbon agents as acting largely by absorbing heat, with some chemical effect on the flame reactions.<ref name="IS-B41">Iqbal and Salley (2004), p. B-41.</ref>

Dry chemical agents also combine mechanisms. They can interact chemically with the flame, coat the fuel surface, cool the flame and block the transfer of radiant heat.<ref name="IS-B15" /> The NRC also treats extinguishment by dry chemicals, like that by halons, as an exception to the simple fire triangle.<ref name="IS-1-5" />

== Combined action of common agents ==
In practice, no agent relies on a single mechanism, and the relative importance of each mechanism varies with the circumstances.<ref name="IS-B16" /> The table summarises the mechanisms that the sources describe for the most common agents. It is based on the descriptions of the individual agents.<ref name="IS-B15" /><ref name="IS-B41" /><ref name="IS-B46" /><ref name="MB-313" /><ref name="MB-314" /><ref name="SC-88" /><ref name="DN-174" /><ref name="GR-153" />

{| class="wikitable"
|+ Main extinguishing mechanisms of common agents
! Agent !! Cooling !! Oxygen removal or dilution !! Separation of fuel and flame !! Chemical inhibition
|-
| Water spray || fuel and flame || steam, in confined conditions || – || –
|-
| Water mist || flame and fuel || steam, locally and in the compartment || – || –
|-
| Foam || cools the liquid || – || floating, air-excluding layer || –
|-
| Dry chemical || flame || – || coats the surface || yes
|-
| Inert gases, carbon dioxide || raised heat capacity || primary action || – || –
|-
| Halon 1301 and bromine or iodine clean agents || – || – || – || primary action
|-
| Other halocarbon clean agents || heat extraction (primary) || important role || – || minor
|}

Water mist shows how mechanisms interact. Mawhinney and Back name gas phase cooling, oxygen depletion with dilution of the fuel vapour, and wetting and cooling of the fuel surface as primary mechanisms. Radiation attenuation and kinetic effects are secondary.<ref name="MB-313" /> All of these act to some degree, with different weights for liquid and solid fuels.<ref name="MB-313" /> Water vapour between the fuel and the flame absorbs radiant energy, which helps to prevent fire spread to unburnt fuel.<ref name="MB-314" />

The choice of agent also depends on the class of fire. The NRC table matches agents to fire classes. Water, dry chemicals, foam and some halons are listed for ordinary combustibles (Class A), and carbon dioxide, dry chemicals, halons and foam for flammable liquids and gases (Class B).<ref name="IS-B16" /> Water and water-based extinguishers must never be used on burning metals (Class D).<ref name="IS-B16" />

== Limits and misconceptions ==
A common misconception is that the fire triangle explains every extinguishment. The NRC notes that it does not apply to dry chemicals and halons, which act on the chain reaction.<ref name="IS-1-5" /> Another is that a flame that has gone out means the fire is extinguished. Halon 1301 at normal concentrations of 5 to 6 % instantly extinguishes visible flames on Class A materials. Glowing combustion inside the material may continue and reignite when the enclosure is ventilated.<ref name="IS-B43">Iqbal and Salley (2004), p. B-43.</ref>

Some fuels resist the usual mechanisms. Reactive metals such as magnesium, sodium and titanium burn so intensely that they overpower halon.<ref name="GR-152" /> Fuels that contain their own oxidiser, such as gunpowder and cellulose nitrate, also burn freely in a halon atmosphere.<ref name="GR-152" /> Water can be inappropriate for water-reactive materials, because it may produce heat, flammable or toxic gases, or explosions.<ref name="FL-72" />

Water can even make a flame worse at first. Flare-up of a flame on first contact with water mist has been measured, possibly because the rapid evaporation adds turbulence and speeds up burning.<ref name="MB-314" /> Finally, the mechanisms are understood far better than they can be calculated. The ways in which water suppresses fire have not been characterised well enough for mathematical modelling, so sprinkler design remains empirical.<ref name="FL-73">Fleming (2002), p. 4-73.</ref> No fundamental explanation of foam performance based on first principles has been developed either.<ref name="SC-88" /> Even where water cannot suppress a fire, its cooling can still protect the structure by containing the fire until other means put it out.<ref name="FL-72" />

== See also ==
* [[Firefighting foam]]
* [[Firefighting]]
* [[Water mist 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.
* 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.
* Grant, C. C. (2002). Halon design 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. 4-149–4-172). 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.
* 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.
* 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]]

Design fire

2026-11-01T22:58:34Z

Daan: New FSE wiki article: Design fire (written by Claude Opus 5.5)

A '''design fire''' is a quantified, idealised description of a fire that is used as input for the fire safety design of a building.<ref name="ABCB-B1-5">Australian Building Codes Board (2020a), Data Sheet B1, p. 5.</ref> It is usually expressed as a curve of [[heat release rate]] against time, often supplemented by the production of smoke and toxic gases.<ref name="IFEG-1.2-29">National Research Council of Canada et al. (2005), p. 1.2-29.</ref> A typical design fire has a growth phase, a peak or fully developed phase and a decay phase.<ref name="IFEG-1.2-30">National Research Council of Canada et al. (2005), p. 1.2-30.</ref> The growth phase is commonly described as a [[t-squared fire]], in which the heat release rate rises with the square of time.<ref name="ABCB-B1-10">Australian Building Codes Board (2020a), Data Sheet B1, p. 10.</ref>

Design fires are a central input of [[performance-based design]]. They turn a [[fire scenario]], a description of how a fire might start and develop in a particular building, into numbers that hand calculations and computer models can use.<ref name="IFEG-1.2-29" /><ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> They are normally meant to be conservative.<ref name="IFEG-1.2-29" /> New Zealand's verification method C/VM2 (second edition, 2025) describes them as representing the worst credible scenarios that will challenge the fire safety design.<ref name="CVM2-19">Ministry of Business, Innovation and Employment (2025b), p. 19.</ref> The choice of design fire can critically affect the outcome of a fire safety engineering analysis.<ref name="ABCB-B1-5" />

== Purpose and use ==
In a fire engineering analysis, the design fire defines the heat and smoke that the building and its occupants must cope with. The [[fire modelling|fire models]] used in engineering, such as zone models and computational fluid dynamics (CFD) models, usually need a heat release rate curve as input.<ref name="VR-8.6" /> ''Introduction to Fire Safety Engineering'' lists the inputs that a fire model needs: data on the fire itself, on the building and its openings, and on the heat release rate and energy.<ref name="VR-8.4">Van Rossum (2027), §8.4.</ref> The design fire provides the last group. It sets how fast the fire grows, how large it becomes and how long it lasts.<ref name="VR-8.4" />

The International Fire Engineering Guidelines (IFEG, 2005) place the selection of design fires early in the design process, in the fire engineering brief agreed between the parties involved.<ref name="IFEG-1.2-29" /> At that stage, each fire scenario is formalised as a design fire and drawn as a simple graph called a schematic design fire. The numbers are then quantified during the analysis.<ref name="IFEG-1.2-29" /> In the SFPE Handbook, Notarianni describes design fires as descriptions of fire events, such as a grease fire on a stove or a smouldering cigarette fire on a sofa.<ref name="Notarianni-5-43">Notarianni (2002), p. 5-43.</ref>

A design fire must suit the problem it is used for. The Australian data sheets for the Fire Safety Verification Method list the factors that matter. These are the geometry and materials of the room, the location and character of the fire, the building use and the ventilation.<ref name="ABCB-B1-5" /> The fire safety question and the method of analysis matter as well.<ref name="ABCB-B1-5" /> A design fire for checking escape routes therefore focuses on the early growth of the fire. A design fire for checking the structure focuses on the fully developed fire and its duration.<ref name="VR-8.5">Van Rossum (2027), §8.5.</ref>

== Parameters of a design fire ==
Design fires are usually characterised by one or more of the following parameters: the heat release rate over time, the peak heat release rate and the production of smoke and toxic gases. Temperature or heat flux over time, the duration of the fire and its position can also be part of the definition.<ref name="ABCB-B1-6">Australian Building Codes Board (2020a), Data Sheet B1, p. 6.</ref> C/VM2 (second edition, 2025) uses a similar list, which adds the [[fire load density|fire load energy density]] and the heat of combustion.<ref name="CVM2-19" />

C/VM2 gives fixed values for many of these parameters. For most buildings, it prescribes a soot yield of 0.07 kg/kg, a carbon monoxide yield of 0.04 kg/kg and a heat of combustion of 20 MJ/kg before flashover. The radiative fraction is 0.35.<ref name="CVM2-20">Ministry of Business, Innovation and Employment (2025b), p. 20.</ref> After flashover, or once the fire becomes limited by ventilation, the yields rise to 0.14 kg/kg for soot and 0.40 kg/kg for carbon monoxide.<ref name="CVM2-21">Ministry of Business, Innovation and Employment (2025b), p. 21.</ref>

The size of a fire is often linked to its area through the [[heat release rate per unit area]]. ''Introduction to Fire Safety Engineering'' gives about 250 kW/m² for a developed fire in an average building other than storage.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref> The Dutch national annex to Eurocode 1 uses 250 kW/m² for dwellings, offices and many other uses, and 500 kW/m² for theatres, cinemas, libraries and larger shops such as supermarkets.<ref name="VR-8.5" /> In a CFD model under C/VM2, the fire is modelled as an area sized from 500 to 1000 kW/m² for most buildings. In a zone model, 250 kW/m² is used.<ref name="CVM2-20" />

== Stages of a design fire ==
A design fire for a room is commonly divided into four stages: incipient, growth, fully developed and decay. A cooling stage may be added when the behaviour of the structure after the fire matters.<ref name="ABCB-B1-7">Australian Building Codes Board (2020a), Data Sheet B1, p. 7.</ref> The IFEG distinguishes three basic types of schematic design fire. A smouldering fire has a maximum heat release rate typically below 5 kW. The other two types are a flaming fire that does not reach flashover and a flaming fire that does.<ref name="IFEG-1.2-29" />

For flaming fires, the IFEG generally assumes that the heat release rate grows with the square of time after ignition. It then reaches a steady value limited either by the fuel or by the ventilation, and finally decreases when the fuel runs out.<ref name="IFEG-1.2-30" /> In a fire that reaches flashover, the jump in heat release rate is assumed to be instantaneous and is drawn as a vertical line.<ref name="IFEG-1.2-30" /> C/VM2 assumes that flashover occurs when the average upper layer temperature first reaches 500 °C.<ref name="CVM2-21" /> The Australian data sheets mention an SFPE engineering standard that uses an upper layer temperature above 600 °C or a heat flux to the floor above 20 kW/m².<ref name="ABCB-B1-12">Australian Building Codes Board (2020a), Data Sheet B1, p. 12.</ref>

The incipient stage before flaming is usually left out. C/VM2 regards it as too unpredictable to include in design.<ref name="CVM2-19" /> The Australian data sheets use it mainly for smouldering fires in sleeping areas.<ref name="ABCB-B1-7" />

== The growth phase ==
Growing fires are commonly described as a t-squared fire, or as a series of such fires that cover the range of credible fires in a room.<ref name="ABCB-B1-10" /> A single growth coefficient then describes how quickly the fire develops. The heat release rate then increases with the square of the time since the start of flaming:<ref name="ABCB-B1-10" />
<math display="block">\dot{Q} = \alpha \, t^2</math>

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

Four standard growth categories are in common use. They are named after the time the fire needs to reach about 1 MW: slow (600 s), medium (300 s), fast (150 s) and ultrafast (75 s).<ref name="ABCB-B1-11">Australian Building Codes Board (2020a), Data Sheet B1, p. 11.</ref> The matching growth coefficients are 0.00293, 0.0117, 0.047 and 0.188 kW/s².<ref name="ABCB-B1-11" /> The Australian data sheets define the reference size as 1055 kW, while ''Introduction to Fire Safety Engineering'' uses exactly 1 MW.<ref name="ABCB-B1-10" /><ref name="VR-8.6" /> The difference is about 5% and rarely matters in practice.

The growth rate is chosen mainly on the basis of the contents of the space. ''Introduction to Fire Safety Engineering'' lists values from the Dutch national annex to Eurocode 1. Dwellings, hotels and classrooms are given a medium growth rate, theatres and cinemas a fast one, and museums a slow one.<ref name="VR-8.6" />

Storage of alcohol or upholstered furniture and chemical plants are given ultrafast growth.<ref name="VR-8.6" /> These values are meant as a safe estimate, because many real fires grow more slowly.<ref name="VR-8.6" /> The t-squared curves assume that the fire spreads horizontally in all directions. They are therefore not suitable for fires that also spread vertically, as in high-rack storage.<ref name="VR-8.6" />

As a worked example, consider a fire in a dwelling with medium growth, so that α = 0.0117 kW/s². After 300 s, the heat release rate is 0.0117 × 300², or about 1.05 MW. The fire reaches 2.5 MW, the size of a burning sofa, after about 460 s, or just under 8 minutes.<ref name="VR-4.5" /> After 600 s, it has grown to about 4.2 MW. With a heat release rate per unit area of 250 kW/m², the burning area is then about 17 m².<ref name="VR-8.5" />

C/VM2 sets its own growth rates. For most buildings, including storage below 3.0 m, the fire grows as 0.0469 t² up to a peak of 20 MW.<ref name="CVM2-20" /> This is close to the fast category: the fire reaches 1 MW after about 146 s and 20 MW after about 650 s. Car parks without stacking systems use 0.0117 t², and storage between 3.0 and 5.0 m high uses 0.188 t² up to 50 MW. Higher storage uses a growth with the cube of time.<ref name="CVM2-20" />

== Peak, fully developed fire and duration ==
A growing fire cannot grow forever. In C/VM2, the growth phase ends when the fire reaches flashover, its peak heat release rate or the ventilation limit. In sprinklered buildings, it can also end when the sprinklers activate.<ref name="CVM2-20" /> The ventilation limit is the heat release rate at which the modelled energy release first falls below the design fire because there is not enough oxygen.<ref name="CVM2-21" /> After flashover or once the ventilation limit is reached, C/VM2 raises the input heat release rate within 15 seconds. It goes either to the peak value or to 1.5 times the ventilation limit, depending on the case.<ref name="CVM2-21" />

Ventilation-limited fires are difficult to model. ''Introduction to Fire Safety Engineering'' notes that most models handle a ventilation-controlled fire poorly, if at all.<ref name="VR-8.4" /> The user must therefore tell the model what happens when oxygen runs short. The options are that all gases still burn in the room, that the excess burns outside as flames from the openings, or that combustion stops.<ref name="VR-8.4" />

The total energy available sets the duration of the fire. In fire models, the fire load is mainly important for determining how long the fire lasts, because the fire stops when the fuel is used up.<ref name="VR-8.5" /> For escape analyses this is often less important, since the first phase of the fire matters most. For the thermal load on structures and fire-separating elements, it is essential.<ref name="VR-8.5" /> The Dutch national annex to Eurocode 1 gives average fire load densities of 780 MJ/m² for dwellings and 420 MJ/m² for offices.<ref name="VR-8.5" /> At 250 kW/m², each square metre of a dwelling fire could therefore burn for roughly 50 minutes at full intensity.

C/VM2 prescribes design fire load energy densities of 400, 800 or 1200 MJ/m², depending on the activities in the space. For high-hazard storage above 3.0 m, it prescribes 800 MJ/m² per metre of storage height, with a minimum of 2400 MJ/m².<ref name="CVM2-22">Ministry of Business, Innovation and Employment (2025b), p. 22.</ref> For sprinklered firecells, the fire load used to calculate the fire duration may be halved.<ref name="CVM2-23">Ministry of Business, Innovation and Employment (2025b), p. 23.</ref>

Temperature-time curves such as the standard fire curve are not design fires in this sense. They are agreed temperature histories for testing the fire resistance of building elements.<ref name="VR-8.6" /> ''Introduction to Fire Safety Engineering'' stresses that the temperature in a room is a result of the fire scenario, not a starting point for it. Such curves are therefore unsuitable for representing a fire in a room.<ref name="VR-8.6" />

== Interventions and object fires ==
A design fire is modified by events during the fire. The IFEG names changes in ventilation, such as breaking windows or the operation of smoke control, and the start of suppression. Suppression can come from automatic systems, from occupants or from the fire service.<ref name="IFEG-1.2-30" /> In C/VM2 life safety analyses of sprinklered buildings, the fire is assumed to be controlled at a constant heat release rate after the sprinklers activate.<ref name="CVM2-20" />

Some design fires describe single objects rather than rooms. ''Introduction to Fire Safety Engineering'' presents a heat release rate curve for a burning sofa measured by the Netherlands Institute for Public Safety (NIPV). It stresses that this curve applies only to the tested sofa, and that in a building the ignition of nearby objects must be modelled as well.<ref name="VR-8.6" /> The book also presents the car fire curve of the Dutch standard NEN 6098 for car parks, based on tests by TNO in 1999. In that curve, the fire spreads to the neighbouring cars after 10 to 15 minutes, so that three cars are burning after 15 minutes.<ref name="VR-8.6" />

The book warns that such curves can become less conservative as cars contain more plastics.<ref name="VR-8.6" /> A report on car parks with electric vehicles by the NIPV states that fire scenarios for indoor car parks are represented by a heat release rate curve rather than a temperature curve.<ref name="NIPV-24">Van der Graaf et al. (2021/2023), p. 24.</ref> It concludes that electric and conventional cars reach similar peak heat release rates, on average about 6 MW. Electric cars with larger battery packs of 100 kWh or more may reach about 8 MW.<ref name="NIPV-25">Van der Graaf et al. (2021/2023), p. 25.</ref>

== Limits and uncertainty ==
A design fire is a simplification of a process that varies from fire to fire. Notarianni points out that it is impossible to evaluate the performance of a building for every fire that might occur. Designers therefore usually choose worst-case or reasonable worst-case scenarios.<ref name="Notarianni-5-43" /> It is not always obvious which scenario is the worst, nor how likely it is. The usual selection process does not take the likelihood of the design fire into account.<ref name="Notarianni-5-43" />

The outcome of an analysis can depend strongly on the chosen growth rate. In an absolute approach, choosing a faster growth rate can turn an acceptable result into an unacceptable one.<ref name="ABCB-B1-6" /><ref name="ABCB-B1-7" /> The Australian Fire Safety Verification Method therefore compares a design with a reference building that meets the deemed-to-satisfy provisions. The comparison is less sensitive to the assumed growth rate, as long as the growth rate is the same in both buildings.<ref name="ABCB-B1-7" /> The data sheets recommend considering a range of growth rates to check that the design is not overly sensitive to this choice.<ref name="ABCB-B1-11" />

Tabulated values also carry their own uncertainty. The fire load densities from the Dutch national annex are average values, and other sources give different numbers. The national annex also gives 80% fractile values for a more conservative approach.<ref name="VR-8.5" /> ''Introduction to Fire Safety Engineering'' notes that the heat release rate densities of the annex are intended for structural assessment. For escape analyses, additional calculations with higher values may be needed.<ref name="VR-8.5" />

== See also ==
* [[Fire dynamics]]
* [[Fire load]]
* [[Fuel-controlled fire]]
* [[Fire Dynamics Simulator]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* 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 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 Dynamics]]

Dry pipe sprinkler system

2026-11-01T22:58:27Z

Daan: FSE wiki: Write out abbreviations at first use (NFPA, NIST, NRC, WTC, AFFF, PMMA) (written by Claude Opus 5.5)

A '''dry pipe sprinkler system''' is an automatic [[sprinkler system]] whose pipes contain compressed air or nitrogen instead of water, so that it can be installed where water in the pipes would freeze.<ref name="FL-72">Fleming (2002), p. 4-72.</ref> A special dry pipe valve holds the water back. The gas pressure in the pipes keeps this valve closed until a sprinkler opens in a fire.<ref name="FL-72" /> The escaping gas lowers the pressure, the valve opens, and water flows through the pipes to the sprinklers that have operated.<ref name="FL-72" /><ref name="IS-10-2">Iqbal and Salley (2004), p. 10-2.</ref>

The dry pipe system is one of the four basic types of sprinkler system, next to the [[Wet pipe sprinkler system|wet pipe system]], the preaction system and the [[deluge system]].<ref name="FL-72" /> Like a wet pipe system, it uses closed automatic sprinklers that open one by one in response to heat.<ref name="FL-72" /> The price for frost protection is a delay. Before water reaches a fire, the gas must first escape and the water must travel through empty pipes, a process that may take up to 60 seconds at the most remote point of the system.<ref name="HO-15">Hopkins et al. (2005), p. 15.</ref> In the United States, NFPA 13, the sprinkler standard of the National Fire Protection Association (NFPA), compensates for this delay by requiring a design area 30 % larger than for a wet pipe system.<ref name="HO-15" /> Dry pipe systems are also more expensive to install and maintain, and they are therefore used only where they are really needed, such as in unheated loading docks, cold stores and attics.<ref name="NO-F59">Nolan (2000), as cited in Iqbal and Salley (2004), p. F-59.</ref><ref name="HO-14">Hopkins et al. (2005), p. 14.</ref>

== How it works ==
The overhead pipes of a dry pipe system are normally filled with pressurised air, or sometimes nitrogen.<ref name="HO-15" /><ref name="IS-10-2" /> The system uses the same closed automatic sprinklers as a wet pipe system. In the description of the US Nuclear Regulatory Commission (NRC), compressed air replaces the water of a wet pipe system. A dry pipe valve replaces its alarm check valve.<ref name="IS-10-2" /> The compressed air holds the dry pipe valve shut and so keeps water out of the system.<ref name="IS-10-2" />

When the heat of a fire opens a [[sprinkler head]], the air escapes through the open sprinkler and the pressure in the pipes falls.<ref name="HO-15" /> At a certain point the air pressure no longer outweighs the water pressure below the valve. This point is called the trip pressure, and it is typically 20 psi (138 kPa).<ref name="HO-15" /> The valve then opens, and the pressure of the water supply drives water into the pipes and out of the sprinklers that have opened.<ref name="HO-15" /><ref name="IS-10-2" /> Sprinklers that the fire has not heated stay closed, just as in a wet pipe system.<ref name="NO-F59" />

A dry pipe valve can hold back water at a higher pressure with air at a lower pressure. The National Institute of Standards and Technology (NIST) describes the principle of the dry pipe valve used in automatic dry standpipes. The valve contains a differential clapper. The lower air pressure on the system side acts on a larger surface than the higher water pressure on the supply side.<ref name="HO-21">Hopkins et al. (2005), p. 21.</ref> When air is released, the force of the air falls until the water pressure can overcome it, and water then fills the system.<ref name="HO-21" />

Each automatic sprinkler acts both as a heat detector and as a water distribution nozzle.<ref name="FL-85">Fleming (2002), p. 4-85.</ref> The most common sprinklers open when a soldered metal element melts or a liquid-filled glass bulb breaks at a set temperature.<ref name="IS-10-3">Iqbal and Salley (2004), p. 10-3.</ref> In a dry pipe system the sprinkler therefore still decides where water is discharged; the dry pipe valve only decides when water enters the pipes.<ref name="FL-72" />

== Where dry pipe systems are used ==
A wet pipe system needs enough heat to keep the water in its pipes from freezing.<ref name="HO-14" /> In the United States, NFPA 13 requires a minimum temperature of 40 °F (4.4 °C) at all times and in all places where wet pipe systems are installed.<ref name="HO-14" /> The NRC guidance therefore calls wet pipe systems unsuitable for automatic fire protection in unheated buildings.<ref name="IS-10-1">Iqbal and Salley (2004), p. 10-1.</ref> Dry pipe systems were developed for parts of buildings where water-filled pipes could freeze. They are usually installed where heating the building, or part of it, is impractical or undesirable.<ref name="HO-14" />

Typical locations named by NIST are loading docks, cold storage warehouses and attics.<ref name="HO-14" /> Building codes can offer the dry pipe system as one of several options. The New York City building code applied to the World Trade Center required wet pipe systems in all sprinklered areas. In areas subject to freezing, the system had to be protected by insulation, heat tracing or an antifreeze solution, or a dry pipe system had to be provided.<ref name="GJ-29">Grill and Johnson (2005b), p. 29.</ref>

Car parks that are open to the outside air face the same climatic problem. A report by the Netherlands Institute for Public Safety (NIPV) defines an open indoor car park as a naturally ventilated car park whose sides are all open to the outside air.<ref name="NIPV-48">Van der Graaf et al. (2021/2023), p. 48.</ref> It notes that weather influences make sprinkler systems less suitable for such car parks. Sprinklers nevertheless remain the most obvious way to contain a [[car park fire]] and to stop it spreading from one car to the next.<ref name="NIPV-49">Van der Graaf et al. (2021/2023), p. 49.</ref> In the Netherlands, a consultation on making sprinkler systems mandatory for certain indoor car parks started on 10 July 2021.<ref name="NIPV-6">Van der Graaf et al. (2021/2023), p. 6.</ref>

== Delay in water delivery ==
The main drawback of a dry pipe system is the delay between the operation of a sprinkler and the discharge of water.<ref name="HO-15" /> Fleming splits the total water delivery time into two parts. The trip time is the time needed for the air pressure to bleed down until the dry valve opens. The transit time is the time the water then needs to flow from the valve to the open sprinkler.<ref name="FL-85" /> The water delivery time starts when the first sprinkler opens.<ref name="FL-85" />

NFPA 13 limits this delay by limiting the size of the system. As described in 2002, the standard contained no maximum water delivery time if the system volume was no more than 750 US gallons (2,839 L).<ref name="FL-85" /> Larger systems were permitted only if water reached the test point within 60 seconds.<ref name="FL-85" /> The rule of thumb is that no more than 60 seconds should be tolerated, and that systems should be divided into smaller systems where necessary.<ref name="FL-85" /> NIST describes the 60-second limit as a performance-based alternative to the volume limit.<ref name="HO-15" />

The delivery time is checked in the field with an inspector's test connection. This connection sits at the most remote point of the system from the dry valve and has an orifice that simulates a single sprinkler.<ref name="FL-85" /> The time measured in this test is not a realistic indication of the delay in a real fire, for two reasons. The first sprinkler to open is likely to be closer to the dry valve, which shortens the transit time. If more sprinklers open, the air escapes faster, so that both the trip time and the transit time become shorter.<ref name="FL-85" />

Researchers at Factory Mutual Research Corporation derived a relation for the trip time. It grows with the dry volume of the system and with the ratio between the initial air pressure and the trip pressure. It falls with a larger flow area of open sprinklers.<ref name="FL-85" /> The relation also contains the air temperature. Transit time is harder to calculate and requires a numerical model in which the system is divided into sections.<ref name="FL-85" />

The delay adds to the time that the sprinkler itself needs to respond. The International Fire Engineering Guidelines allow suppression to be assumed to start at sprinkler activation only in limited cases. Examples are a low, small enclosure with a relatively small fire that one or a few sprinklers can extinguish.<ref name="IFEG-7">National Research Council of Canada et al. (2005), p. 2.7-7.</ref>

== Design area and water demand ==
A dry pipe system is expected to open more sprinklers than a wet pipe system, which discharges water immediately after the first sprinkler responds.<ref name="HO-15" /> In a sprinkler design, water is supplied for the sprinklers in a design area, which is chosen together with a design density (the depth of water applied per minute) from the hazard of the occupancy.<ref name="FL-74">Fleming (2002), p. 4-74.</ref> NFPA 13 contains special changes to the design area for dry systems.<ref name="FL-74" /> According to NIST, it requires the design area of a dry pipe system to be 30 % larger than that of a wet pipe system, with the same density:<ref name="HO-15" />

<math display="block">A_\mathrm{dry} = 1.3 \times A_\mathrm{wet}</math>

{| class="wikitable"
|+ Symbols
! Symbol !! Description !! Unit
|-
| <math>A_\mathrm{dry}</math> || design area of the dry pipe system || m²
|-
| <math>A_\mathrm{wet}</math> || design area required for a wet pipe system with the same hazard and density || m²
|}

The factor applies to the design area only. The density stays the same, so the required water flow rises in proportion to the area. The minimum flow of each sprinkler is still its area of coverage multiplied by the density.<ref name="FL-75">Fleming (2002), p. 4-75.</ref> The factor is a design rule of NFPA 13 in the United States; it is not derived from a calculation of the actual delay.<ref name="HO-15" />

=== Worked example ===
The design criteria for World Trade Center Building 7 (WTC 7), designed in the mid-1980s, show the rule in practice.<ref name="HO-64">Hopkins et al. (2005), p. 64.</ref> For Ordinary Hazard Group 1 areas with wet pipe systems, the criteria gave a density of 0.16 gpm/ft² (6.5 mm/min) over 1,500 ft² (139 m²).<ref name="HO-64" /> The loading berth had a dry pipe system with the same hazard and density, designed over 1,950 ft² (181 m²).<ref name="HO-65">Hopkins et al. (2005), p. 65.</ref> The rule reproduces this value:

<math display="block">A_\mathrm{dry} = 1.3 \times 139\ \mathrm{m^2} \approx 181\ \mathrm{m^2}</math>

At 6.5 mm/min, the minimum flow over the design area rises from about 910 L/min for the wet system to about 1,190 L/min for the dry system. The loading dock had a layout with about 12 m² (126 ft²) per sprinkler.<ref name="MA-76">McAllister et al. (2008), p. 76.</ref> At that spacing, the design area grows from 12 to 16 sprinklers.

The dry system also loses more pressure in its pipes. For friction loss calculations with the Hazen–Williams formula, steel pipe in dry and preaction systems is given a coefficient C of 100, against 120 for wet and deluge systems.<ref name="FL-76">Fleming (2002), p. 4-76.</ref> A lower C means a larger friction loss for the same flow. The values are chosen to simulate the expected interior roughness of aged pipe.<ref name="FL-76" />

== Related system types ==
{| class="wikitable"
|+ Comparison of sprinkler system types<ref name="FL-72" /><ref name="NO-F59" />
! Type !! Contents of the pipes !! What starts the water flow !! Main reason for use
|-
| Wet pipe || water under pressure || heat opens a sprinkler || most common type; heated buildings
|-
| Dry pipe || air or nitrogen under pressure || an opened sprinkler releases the air, the dry pipe valve trips || risk of freezing
|-
| Preaction || air, under pressure or not || detection opens the valve; heat opens sprinklers || concern for accidental discharge
|-
| Deluge || no water; open nozzles || detection opens the deluge valve || rapidly spreading, high hazard fires
|}

The preaction system was designed in part to overcome the weaknesses of the dry pipe system. It uses automatic sprinklers in pipes containing air, which may or may not be under pressure, together with a separate detection system in the same area.<ref name="NO-F59" /> The detectors open the valve, so that the pipes fill with water before a sprinkler opens. Preaction systems are meant to counteract the delay of dry pipe systems and to prevent damage from a broken pipe or sprinkler head.<ref name="NO-F59" />

A combined dry pipe and preaction system joins both principles. Its pipes contain air under pressure, and a detection system opens the dry pipe valves without a loss of air pressure. At the same time it opens air exhaust valves at the end of the feed main, so that the system normally fills with water before any sprinkler opens.<ref name="NO-F59" /> In a fire risk analysis for United States nuclear power plants, the detection-suppression event tree of NUREG/CR-6850 treats a preaction or dry pipe system in one example case. It notes that a preaction system needs two signals to succeed: an automatic detection signal and the opening of the sprinkler itself.<ref name="NW-P5">Nowlen et al. (2005b), p. P-5.</ref>

== Limitations ==
Dry pipe systems operate more slowly than wet pipe systems and are more expensive to install and maintain.<ref name="NO-F59" /> They are therefore used only where there is an absolute necessity, such as a risk of freezing.<ref name="NO-F59" /> The NRC report names two reasons to restrict them to low-temperature areas. The first is the delay between the release of the compressed air and the arrival of water. The second is internal corrosion and tuberculation of the pipes caused by alternating wet and dry periods.<ref name="IS-10-2" /> Corrosion or tuberculation in the sprinkler piping is also listed among the general causes of sprinkler failure.<ref name="IS-10-2" />

Sprinkler systems in general fail for reasons that also apply to dry pipe systems. The NRC report lists a closed water supply valve, an empty water tank, a fire pump that does not start, corroded or painted sprinkler heads and an inadequate water supply.<ref name="IS-10-2" /> Most sprinkler systems in office buildings are designed to control a fire, and full extinguishment may require the fire service.<ref name="HO-15" /><ref name="HO-16">Hopkins et al. (2005), p. 16.</ref> In a dry pipe system, the delay means that more sprinklers are expected to open before control is reached.<ref name="HO-15" />

== Examples ==
In the World Trade Center towers and WTC 7, wet pipe systems protected the main office and support spaces. Dry pipe and preaction systems were used on a limited basis for computer rooms and other special hazards, in less than 10 % of the floor area.<ref name="HO-14" /> In WTC 7, a dry pipe system protected two 12,000 gal (about 45,000 L) fuel oil storage tanks beneath the loading berths.<ref name="HO-128">Hopkins et al. (2005), p. 128.</ref> The fuel oil pump rooms also had dry pipe systems, designed as Ordinary Hazard Group 3 with 0.21 gpm/ft² (8.6 mm/min) over the entire pump room.<ref name="HO-65" />

A worked example in the SFPE Handbook shows a dry pipe system combined with another agent. A warehouse with crude rubber in piles has a dry pipe system with a maximum discharge of 0.2 gpm/ft² (8.1 mm/min) over 2,000 ft² (186 m²).<ref name="SH-141">Scheffey and Hickey (2002), p. 4-141.</ref> This density is not considered adequate for the hazard, so a fixed high-expansion foam system supplements the sprinklers.<ref name="SH-141" /> The foam system is arranged to start when the dry pipe valve trips because a sprinkler head has operated.<ref name="SH-143">Scheffey and Hickey (2002), p. 4-143.</ref>

== See also ==
* [[Fire water supply]]
* [[Hydraulic calculation]]
* [[Sprinkler design density]]
* [[Response time index]]

== Notes ==
<references />

== References ==
* 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.
* Grill, R. A., & Johnson, D. A. (2005b). ''Fire protection and life safety provisions applied to the design and construction of WTC 1, 2, and 7 and post-construction provisions applied after occupancy'' (NIST NCSTAR 1-1D). National Institute of Standards and Technology.
* 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.
* Scheffey, J. L., & Hickey, H. E. (2002). Foam 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. 4-123–4-148). 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)

[[Category:Fire Suppression]]

Deluge system

2026-11-01T22:58:21Z

Daan: FSE wiki: Write out abbreviations at first use (NFPA, NIST, NRC, WTC, AFFF, PMMA) (written by Claude Opus 5.5)

A '''deluge system''' is a water-based fire suppression system in which every nozzle or sprinkler is permanently open, so that water discharges from all of them at once when a valve in the supply opens.<ref name="FL-72">Fleming (2002), p. 4-72.</ref> The valve, called a deluge valve, is opened by a separate fire detection system rather than by heat at the nozzles.<ref name="FL-72" /> The deluge system is one of the four basic types of [[sprinkler system]], next to the wet pipe, [[Dry pipe sprinkler system|dry pipe]] and preaction systems.<ref name="FL-72" /><ref name="IS-10-1">Iqbal and Salley (2004), p. 10-1.</ref>

Its purpose is to deliver the largest amount of water in the shortest time.<ref name="NO-F59">Nolan (2000), as cited in Iqbal and Salley (2004), p. F-59.</ref> Deluge systems are used against rapidly spreading, high hazard fires, such as fires in highly flammable fuels that develop quickly and reach very high temperatures.<ref name="FL-72" /><ref name="NO-F59" /> Typical applications in the sources include aircraft hangars, transformers, turbine-generator bearings, fan units and water curtains at openings.<ref name="SC-106">Scheffey (2002), p. 4-106.</ref><ref name="IS-H11">Iqbal and Salley (2004), p. H-11.</ref><ref name="IS-H20" /><ref name="HO-132">Hopkins et al. (2005), p. 132.</ref><ref name="IS-F69" /> The price of this speed is a large water demand and extensive water damage, both when the system is needed and when it operates by mistake.<ref name="IS-10-2">Iqbal and Salley (2004), p. 10-2.</ref><ref name="IS-H5">Iqbal and Salley (2004), p. H-5.</ref> In nuclear power plant risk studies, a deluge system is assumed to fail on demand about five times in a hundred.<ref name="NS-P6">Parkinson et al. (1994), as cited in Nowlen et al. (2005b), p. P-6.</ref>

== How a deluge system works ==
A deluge system consists of a network of pipes with open sprinklers or spray nozzles, connected to a water supply through a deluge valve.<ref name="FL-72" /> The open nozzles contain no fusible elements that could hold back the water.<ref name="IS-10-2" /> Instead, the deluge valve holds the water back from the piping until it is activated.<ref name="FL-72" /> The deluge valve sits on the water supply side of the system and opens automatically when the detection system calls for water.<ref name="IS-10-2" /> Once it has opened, water flows into the pipes and discharges from every outlet on the system at the same time.<ref name="NO-F59" /> In the words of the definition, there are no closed sprinklers in a deluge system.<ref name="NO-F59" />

The detection devices are installed in the same area as the nozzles.<ref name="NO-F59" /> In the nuclear guidance of the United States Nuclear Regulatory Commission (NRC), the system is described as typically actuated by heat detectors mounted above the open sprinklers.<ref name="IS-10-2" /> Most deluge systems can also be started by hand.<ref name="IS-10-2" /> A glossary in the same report defines the deluge sprinkler system simply as a system with open sprinklers or nozzles, in which all water flows out when the deluge valve actuates.<ref name="IS-F21">Iqbal and Salley (2004), p. F-21.</ref> The single word "deluge" is defined there as the immediate release of a commodity, usually a water spray released for fire suppression.<ref name="NO-F20">Nolan (2000), as cited in Iqbal and Salley (2004), p. F-20.</ref>

A water spray system works on the same principle. It is a fixed pipe system with spray nozzles chosen for a specific discharge and distribution over the surface or area to be protected.<ref name="NO-F59" /> Its control valve is opened automatically by fire detectors in the same area, or by hand.<ref name="NO-F59" /> In the United States, the National Fire Protection Association (NFPA) covers water spray systems in NFPA 15, ''Standard for Water Spray Fixed Systems for Fire Protection''. Foam-water sprinkler and spray systems fall under NFPA 16.<ref name="FL-73">Fleming (2002), p. 4-73.</ref> The same open-nozzle principle is used in total compartment application water mist systems, where water is discharged from all nozzles as soon as a control valve opens.<ref name="MB-327">Mawhinney and Back (2002), p. 4-327.</ref>

== Comparison with other sprinkler systems ==
All sprinkler systems can be placed in one of four basic types, which differ in how the water reaches the area of the fire.<ref name="FL-73" /> In a wet pipe system, the pipes are filled with water under pressure. Heat opens a single sprinkler, which then discharges water over its own area.<ref name="FL-72" /> In a dry pipe system, the pipes contain air or nitrogen under pressure, and water enters only after a sprinkler has opened and the air pressure has dropped.<ref name="FL-72" />

These two types use automatic sprinklers, which open one by one in response to heat. Only the sprinklers exposed to enough heat operate; the idea that all sprinklers open in a fire is a common misconception.<ref name="HO-14">Hopkins et al. (2005), p. 14.</ref> For a deluge system that idea is correct, because the whole system discharges together.<ref name="NO-F59" />

The preaction system is the closest relative. It is similar to a deluge system, but it uses automatic sprinklers instead of open ones.<ref name="FL-72" /> A separate detection system opens a deluge valve and fills the pipes, yet water flows only where heat has also opened a sprinkler.<ref name="FL-72" /> The NRC report describes it as a deluge system with closed heads, in which two conditions must be met before water is released.<ref name="IS-10-2" /> Preaction systems are used where accidental discharge of water is a special concern, as in valuable computer rooms.<ref name="FL-73" /> In the World Trade Center towers, the preaction systems used hydraulically operated differential diaphragm deluge valves with manual and electric detectors.<ref name="HO-50">Hopkins et al. (2005), p. 50.</ref>

{| class="wikitable"
|+ The four basic types of sprinkler system<ref name="FL-72" /><ref name="IS-10-2" />
! Type !! Sprinklers !! Pipes before operation !! What releases the water
|-
| Wet pipe || automatic (closed) || water under pressure || heat opens individual sprinklers
|-
| Dry pipe || automatic (closed) || air or nitrogen under pressure || an opened sprinkler lets the air escape, then the dry pipe valve opens
|-
| Preaction || automatic (closed) || usually air at a small pressure || detection opens the valve, heat opens individual sprinklers
|-
| Deluge || open || no water (held back by the deluge valve) || detection or manual action opens the deluge valve; all outlets discharge
|}

The difference also shows up in the hydraulic design. For pressure losses in steel pipe, the [[Hydraulic calculation|Hazen–Williams method]] assigns a roughness coefficient C of 120 to wet and deluge systems, but only 100 to dry and preaction systems.<ref name="FL-76">Fleming (2002), p. 4-76.</ref> A lower value means a rougher pipe and a larger friction loss for the same flow. The values are intended to simulate the expected interior roughness of aged pipe.<ref name="FL-76" />

== Detection and actuation ==
The nozzles of a deluge system cannot sense a fire, so the system relies on a separate detection system.<ref name="FL-72" /> The NRC report names heat detectors above the open sprinklers as the typical choice.<ref name="IS-10-2" /> In aircraft hangars, the systems were historically activated by rapid-response detection systems.<ref name="SC-106" /> The International Fire Engineering Guidelines list heat, smoke, gas sensing and flame detectors as the main detector types.<ref name="IFEG-2">National Research Council of Canada et al. (2005), p. 2.7-2.</ref> A [[flame detector]] is activated by electromagnetic radiation emitted by flames.<ref name="IS-F30">Iqbal and Salley (2004), p. F-30.</ref> It can be treated as a point that receives radiation from the flame, and its sensitivity can vary with the direction of the incoming radiation.<ref name="IFEG-6">National Research Council of Canada et al. (2005), p. 2.7-6.</ref>

A deluge valve can also be tied to more than one detector. In a coincident detection system, two or more detectors must operate before an alarm is recognised. These can be two similar detectors at different locations or two different types of detector.<ref name="IFEG-2" /> The air handling units of the World Trade Center towers used this approach. The first smoke detector to operate shut down the unit, and a second detector within the unit then activated its dedicated deluge system for a filter fire.<ref name="KG-39">Keough and Grill (2005), p. 39.</ref><ref name="KG-86">Keough and Grill (2005), p. 86.</ref>

False activation has been a serious problem in practice. All military service branches in North America experienced false activation of foam-water deluge systems over aircraft with open cockpits.<ref name="SC-110">Scheffey (2002), p. 4-110.</ref> The causes included lightning strikes, water hammer in aging underground mains, accidental releases by maintenance staff and vandalism. Accidental use of manual pull stations, failed pressure relief valves, roof leakage into overhead heat detection and false detector signals also played a part.<ref name="SC-110" />

Optical fire detectors were found to be prone to false alarms and were tested with fuels not typical of aviation.<ref name="SC-110" /> The concept that the U.S. Navy developed in response used low-level deluge nozzles for aqueous film-forming foam (AFFF), operated by improved optical detectors. These detectors were designed to be highly immune to false alarms and to detect fuel spill fires rapidly.<ref name="SC-111">Scheffey (2002), p. 4-111.</ref>

== Water demand ==
In a wet pipe system, water is supplied only for the sprinklers in a design area, since the others are not expected to open.<ref name="FL-74">Fleming (2002), p. 4-74.</ref> In a deluge system all outlets discharge together.<ref name="FL-72" /> The water supply must therefore feed the whole system at once. The minimum flow from one sprinkler is its area of coverage multiplied by the required density, the depth of water applied per minute.<ref name="FL-75">Fleming (2002), p. 4-75.</ref> Applied to a deluge system, the same product over the whole protected area gives the flow that the deluge valve must pass:

<math display="block">Q = D \times A</math>

{| class="wikitable"
|+ Symbols
! Symbol !! Description !! Unit
|-
| <math>Q</math> || total water flow through the deluge valve || L/min
|-
| <math>D</math> || design density (application rate) || L/(min·m²)
|-
| <math>A</math> || total floor area covered by all open nozzles of the system || m²
|}

The relation assumes an even discharge over the area. In reality, each outlet flows in proportion to the square root of the pressure at that outlet, so nozzles near the supply discharge more than the most remote one.<ref name="FL-75" /> The result is therefore a lower bound on the flow, before any pipe friction is taken into account. The density itself is not derived from theory; sprinkler design criteria are empirical, because the mechanisms by which water suppresses fire have not been characterised well enough for calculation.<ref name="FL-73" />

=== Worked example ===
Factory Mutual Research Corporation tested deluge arrangements for aircraft hangars. One arrangement used standard sprinklers at a spacing of 12.1 m² per head, discharging 6.6 L/(min·m²) of AFFF solution at an end head pressure of 97 kPa.<ref name="SC-107">Scheffey (2002), p. 4-107.</ref> Each head therefore delivers at least 6.6 × 12.1 = 79.9 L/min. Assume a deluge zone of 40 such heads, covering 484 m². The deluge valve must then pass at least:

<math display="block">Q = 6.6\ \mathrm{L/(min \cdot m^2)} \times 484\ \mathrm{m^2} \approx 3{,}200\ \mathrm{L/min}</math>

This is about 53 L/s for the zone, before any friction losses are added. In the same test series, this arrangement extinguished an 83.6 m² JP-4 pool fire in 1 minute 45 seconds.<ref name="SC-107" /> A wet pipe system, by contrast, needs water only for the sprinklers in its design area, because the other sprinklers are not expected to open.<ref name="FL-74" />

== Applications ==
Aircraft hangars are the best documented application in the sources. Hangar protection aims to protect the aircraft and to prevent collapse of the roof, which is usually unprotected steel.<ref name="SC-106" /> Before foam was developed, hangars were protected by water deluge systems discharging about 10.4 L/(min·m²) (0.25 gpm/ft²), together with sloped floors and drains.<ref name="SC-107" /> Even then, protection of aircraft fuselages against burnthrough within about 1 minute could not be ensured.<ref name="SC-107" /> In one 121 m² JP-4 fuel fire, ceiling temperatures of 927 °C were recorded within 30 seconds of ignition, before the deluge system discharged.<ref name="SC-107" />

The introduction of [[firefighting foam]] changed this design. Protein foam systems discharging 8.2 L/(min·m²) were an improvement on water alone.<ref name="SC-107" /> With AFFF through standard sprinklers, the NFPA 409 rate for overhead deluge systems may be reduced from 8.2 to 6.6 L/(min·m²), which is 20 % less foam.<ref name="SC-108">Scheffey (2002), p. 4-108.</ref> NFPA 16 requires a minimum of 6.6 L/(min·m²) for deluge and closed-head AFFF systems. This gives a safety factor over the 4.1 L/(min·m²) at which AFFF from sprinklers is effective on pool fires.<ref name="SC-112">Scheffey (2002), p. 4-112.</ref>

Tests with closed-head sprinklers instead of open heads showed that a large number of sprinklers opened during the fire tests, so that this alternative was not feasible for the hangar scenario.<ref name="SC-108" /> The later U.S. Navy concept combined a quick-response, closed-head wet pipe system in the hangar ceiling with low-level AFFF deluge nozzles for fuel spill fires.<ref name="SC-111" /> More generally, the foam-water deluge system is one type of fixed low-expansion foam system, used in bunds and on spills.<ref name="IS-B60">Iqbal and Salley (2004), p. B-60.</ref>

In nuclear power plants, deluge systems protect equipment such as transformers and turbine-generator bearings.<ref name="IS-H11" /><ref name="IS-H20" /> At North Anna Unit 2 in 1981, a main transformer failed and its oil burned. The deluge systems on two transformers activated, but the fire was too severe for the system and took the fire brigades about one hour to control.<ref name="IS-H11" /> The NRC drew the lesson that a fixed suppression system can be overwhelmed even when the fire starts in the equipment it protects.<ref name="IS-H11" /> At Salem Unit 2 in 1991, deluge systems on two generator bearing housings actuated as designed during a turbine failure. Together with other automatic systems, they extinguished some of the fires.<ref name="IS-H20">Iqbal and Salley (2004), p. H-20.</ref>

In buildings, deluge systems are used for local protection and for water curtains. A water curtain is a screen or wide-angle spray of water that protects exposures from radiated heat, smoke and flames, and may also be called a water screen.<ref name="IS-F69">Iqbal and Salley (2004), p. F-69.</ref> The New York City building code applied to the World Trade Center covered exit ramps in public garages. Their vehicle openings had to be protected by a deluge-type sprinkler water curtain of 3 gpm per linear foot (about 37 L/min per metre).<ref name="GJ-39">Grill and Johnson (2005b), p. 39.</ref> In the towers themselves, local application deluge systems protected the fan filters in the air handling units.<ref name="HO-59">Hopkins et al. (2005), p. 59.</ref><ref name="HO-132" />

Offshore platforms also use deluge nozzles. Their spray is much coarser than water mist, and in British Gas explosion tests such large-drop sprays increased turbulence and could make a gas deflagration worse.<ref name="MB-316">Mawhinney and Back (2002), p. 4-316.</ref> The editors of the industry report concluded that more work was needed with sprays of finer drop sizes.<ref name="MB-316" />

Deluge systems are specified where highly flammable fuels can produce a fast, very hot fire.<ref name="NO-F59" /> In industrial processes, many substances that are gases at ambient conditions are stored under pressure as a liquid with vapour above it.<ref name="IS-5-15">Iqbal and Salley (2004), p. 5-15.</ref> The failure of such a container while its liquid is above its normal boiling point is called a [[BLEVE]], a boiling liquid expanding vapour explosion. A BLEVE typically occurs in a metal container that has been overheated above 538 °C. The liquid absorbs heat, so the wetted part of the shell is usually not at risk; the danger lies in the surfaces of the vapour space.<ref name="IS-5-15" />

== Reliability and limitations ==
Unlike a wet pipe system, a deluge system needs both a detection signal and a deluge valve that opens before any water flows.<ref name="FL-72" /> Unreliability values from a 1994 data report by Parkinson and co-workers are recommended in the fire risk method for United States nuclear power plants. They are 0.05 for deluge or preaction sprinkler systems, compared with 0.02 for wet pipe systems.<ref name="NS-P6" /> These values do not include unavailability during maintenance, credit for manual actuation, dependent failures or plant-specific data.<ref name="NS-P6" /> Earthquakes add a further failure mode, because deluge trip valves may not withstand an earthquake and may open spuriously or jam shut.<ref name="NO-13-3">Nowlen et al. (2005b), p. 13-3.</ref>

The main disadvantage named in the NRC report is extensive water damage, because all of the open sprinklers discharge.<ref name="IS-10-2" /> Unwanted operation makes this worse. At Fort Calhoun in 2001, smoke from a fire in another area actuated a deluge water curtain in a stairwell. The water sprayed onto safety-related motor control centres and caused short circuits in safety-related circuits.<ref name="IS-H5" /> The curtain had been installed because there was no fixed fire barrier between the two fire areas.<ref name="IS-H5" />

A deluge system also depends on its water supply, which can be a shared weak point. At one chemical plant, the fire pump house was flooded three times in five years, and the pump controllers were shut off each time. The pumps thus formed a [[common cause failure]] for numerous deluge water spray systems.<ref name="BA-203">Barry (2002), p. 5-203.</ref> Finally, a deluge system may control a fire rather than extinguish it. The International Fire Engineering Guidelines distinguish three possible effects of suppression on a design fire: no effect, control and extinguishment.<ref name="IFEG-7">National Research Council of Canada et al. (2005), p. 2.7-7.</ref> The North Anna transformer fire shows that a system which operates can still be overwhelmed by the fire it is meant to protect against.<ref name="IS-H11" />

== See also ==
* [[Jet fire]]
* [[Wet pipe sprinkler system]]
* [[Water mist system]]
* [[Fire water supply]]

== 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.
* 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.
* Grill, R. A., & Johnson, D. A. (2005b). ''Fire protection and life safety provisions applied to the design and construction of WTC 1, 2, and 7 and post-construction provisions applied after occupancy'' (NIST NCSTAR 1-1D). National Institute of Standards and Technology.
* 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.
* Keough, R. J., & Grill, R. A. (2005). ''Fire alarm systems'' (NIST NCSTAR 1-4C). National Institute of Standards and Technology.
* 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.
* 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.

[[Category:Fire Suppression]]

ASD

2026-11-01T22:58:14Z

Daan: Redirect to Aspirating smoke detection (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Aspirating smoke detection]]

Wildland urban interface

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Daan: Redirect to Wildland-urban interface (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Wildland-urban interface]]

Plastic in fire

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Daan: Redirect to Plastics in fire (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Plastics in fire]]

Aspirating smoke detector

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Daan: Redirect to Aspirating smoke detection (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Aspirating smoke detection]]

WUI

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Daan: Redirect to Wildland-urban interface (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Wildland-urban interface]]

Polymers in fire

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Daan: Redirect to Plastics in fire (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Plastics in fire]]

Required safe evacuation time

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#REDIRECT [[Required safe egress time]]

Air sampling smoke detection

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#REDIRECT [[Aspirating smoke detection]]

Wildland-urban interface

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Daan: New FSE wiki article: Wildland-urban interface (written by Claude Opus 5.5)

The '''wildland-urban interface''' ('''WUI''') is the term used for areas where buildings are exposed to fires in natural vegetation. In such areas a [[wildfire]] can spread from the vegetation to buildings and from one building to the next.<ref name="McG-ix">McGrattan et al. (2026), p. ix.</ref><ref name="IFEG-1.6-5">National Research Council of Canada et al. (2005), p. 1.6-5.</ref> Fire engineering guidance notes that flying brands and embers may need to be considered to limit fire spread to adjoining property, and that this can have design implications in areas prone to bushfires and wildfires.<ref name="IFEG-1.6-5" />

Fire can reach a building in three ways: through burning embers and other debris, through radiation and through direct flame contact.<ref name="IFEG-1.6-7">National Research Council of Canada et al. (2005), p. 1.6-7.</ref> Wind can carry embers, also called [[firebrands]], over great distances and start spot fires at other locations.<ref name="Qui-255">Quintiere (2002b), p. 2-255.</ref> The United States Forest Service supported the development of sub-models in the Fire Dynamics Simulator for fire spread in the wildland-urban interface.<ref name="McG-ix" /> Once buildings are alight, the methods for [[fire spread between buildings]] apply, and these rest on the same processes of radiant ignition and brand transport.<ref name="Kan-229">Kanury (2002a), p. 2-229.</ref><ref name="AR-396">Albini and Rand, as cited in Ramachandran (2002c), p. 3-396.</ref>

== Wildfire behaviour ==
Flame spread in a forest depends on the type and arrangement of the fuel, the terrain, the wind and the humidity. It is driven by radiant heat transfer and by convective heating caused by wind or by the slope of the terrain.<ref name="Qui-255" /> In most fires the porous brush on the forest floor burns. In severe fires the crowns of the trees also burn, or only the crowns.<ref name="Qui-255" /> Forest fires accelerate up slopes because the flames lean, an effect that was also seen in the escalator trench in the fire at King's Cross underground station.<ref name="CK-207">Cox and Kumar (2002), p. 3-207.</ref>

Thomas proposed an approximate relation for the rate of spread of wildland fires, wood cribs and urban conflagrations. In it, the spread rate times the bulk density of the fuel is proportional to one plus the wind speed, with a constant of 0.07 for wildland fires.<ref name="Tho-255">Thomas (1971), as cited in Quintiere (2002b), p. 2-255.</ref> The relation shows two trends: the spread rate rises with the wind speed, and it falls as the fuel is packed more densely. Quintiere also compares spread rates for cribs, gorse and heather and urban fires in Japan at wind speeds of up to 30 m/s.<ref name="Qui-255" /> He lists the spread rate of forest and urban fires as of the order of 1 to 100 cm/s.<ref name="Qui-247">Quintiere (2002b), p. 2-247.</ref> A glossary in NUREG-1805 gives 1 to 30 cm/s for wind-driven spread through forest debris.<ref name="Nol-F31">Nolan (2000), as cited in Iqbal and Salley (2004), p. F-31.</ref>

The United States Department of Agriculture Forest Service has developed practical methods for estimating flame spread in forests under a range of field conditions. Rothermel reviewed the theory and models for fire danger rating and fire behaviour prediction, including the computer model BEHAVE.<ref name="Qui-255" /> Breaks in the fuel can stop the spread, but the width needed depends on the size of the fire and its heat transfer.<ref name="Qui-255" /> When a forest fire jumps across a firebreak, this is generally regarded as ignition by radiation.<ref name="Kan-229" />

The advancing front of a forest fire is an example of a line fire, like a row of burning townhouses, and like other natural fires it burns as a diffusion flame.<ref name="IS-9-2">Iqbal and Salley (2004), p. 9-2.</ref><ref name="IS-3-12">Iqbal and Salley (2004), p. 3-12.</ref> Behind the front, the passage of a forest fire often ignites the duff layer, the porous layer of decaying organic material on the forest floor, to smouldering. This smouldering is very irregular in extent and can reignite a flaming fire.<ref name="Ohl-206">Ohlemiller (2002), p. 2-206.</ref>

== How fire reaches buildings ==
The International Fire Engineering Guidelines name three routes by which fire spreads to an adjacent enclosure, building or property boundary: burning embers and other debris, radiation, and direct flame contact.<ref name="IFEG-1.6-7" /> Wind speed and direction influence how far flames project from the windows of a burning building, and openings on both the windward and the leeward side make the effect of wind more significant.<ref name="IFEG-1.6-5" /> A firebrand is a flaming or smouldering airborne object that emerges from a fire and can sometimes ignite remote combustibles. An ember is a particle of solid material that emits radiant energy because of its temperature or because of combustion at its surface.<ref name="IS-F-24">Iqbal and Salley (2004), p. F-24.</ref><ref name="IS-F-22">Iqbal and Salley (2004), p. F-22.</ref> Burning brands that are lifted by the convective flow of a fire and fall onto combustible materials are a common mechanism of fire spread, observed in wildland fires and in warehouse fires.<ref name="Ham-30">Hamins, Maranghides, McGrattan, Ohlemiller, and Anleitner (2005), p. 30.</ref> How far a burning brand rising in the plume may be carried by the wind is often difficult to establish with any certainty.<ref name="IFEG-2.6-12">National Research Council of Canada et al. (2005), p. 2.6-12.</ref>

Radiation from the flames heats building surfaces until they ignite. For fire growth over separate items, such as buildings in a city, radiant heating to ignition is the main process.<ref name="Kan-229" /> Kanury distinguishes piloted ignition, caused by a small flame, a heated wire or a spark, from spontaneous ignition without such a pilot.<ref name="Kan-230">Kanury (2002a), p. 2-230.</ref> Wood heated for less than 30 min needs a minimum heat flux of about 12 kW/m² for piloted ignition and 20 kW/m² for autoignition. For exposures lasting hours or days, a value of 4.3 kW/m² should be used.<ref name="Bab-3.3-4">Babrauskas (2003), as cited in National Research Council of Canada et al. (2005), p. 3.3-4.</ref> Tewarson's critical heat flux for ignition of wood is 10 kW/m²; below this level, ignition and flame spread are not possible.<ref name="Tew-6-4">Tewarson (1995), as cited in Iqbal and Salley (2004), p. 6-4.</ref>

The [[combustibility]] of the materials on and around a building therefore matters. Embers that land on combustible surfaces may ignite them, and a radiant flux of 10 to 20 kW/m² may cause objects to ignite.<ref name="Ham-30" /><ref name="Nol-F35">Nolan (2000), as cited in Iqbal and Salley (2004), p. F-35.</ref> The heat flux that a surface receives from a fire depends on the [[flame radiation]] and on the geometry between flame and surface, which engineers express with a view factor.<ref name="IFEG-2.6-12" /><ref name="VR-5.4">Van Rossum (2027), §5.4.</ref>

== Building protection ==
Roofs are exposed to both embers and radiation. British Standard BS 476: Part 3 describes a test of the ignitability and fire spread of external roof surfaces under radiation from a fire in an adjacent building and piloted ignition from flying brands.<ref name="IFEG-2.6-12" /> In the United States, roof coverings are rated in the test of ASTM E108, UL 790 and NFPA 256, which measures the spread of flame, intermittent flame, burning brands and flying brands. Class A roof coverings must limit flame spread to less than 1.82 m, Class B to less than 2.44 m and Class C to less than 3.96 m.<ref name="IS-C-11">Iqbal and Salley (2004), p. C-11.</ref><ref name="IS-C-12">Iqbal and Salley (2004), p. C-12.</ref> For all classes, no flying brands or particles may continue to flame or glow after reaching the floor.<ref name="IS-C-11" />

Separation distance limits the radiation that reaches a building. The International Fire Engineering Guidelines prefer a first-principles approach for each case to methods derived from codes. They refer to an SFPE guide for the time to piloted ignition under flame radiation and for safe separation distances, which often require view factor calculations.<ref name="IFEG-2.6-11">National Research Council of Canada et al. (2005), p. 2.6-11.</ref><ref name="IFEG-2.6-12" />

These methods were developed for fires in buildings. In New Zealand, for example, the Building Code limits the radiation from a building fire to 30 kW/m² at the relevant boundary and 16 kW/m² at 1 m beyond it. External walls closer than 1 m to the boundary must be non-combustible, or must not ignite within 15 or 30 min under a radiant flux of 30 kW/m². The required time depends on the importance level of the building.<ref name="MBIE-43">Ministry of Business, Innovation and Employment (2025b), p. 43.</ref>

Firefighting foams can protect exposed buildings. Class A foams have been used extensively to suppress wildland fires. In tests, Class A foam lengthened the time to ignition of a combustible surface compared with the same rate and duration of water.<ref name="SH-144">Scheffey and Hickey (2002), p. 4-144.</ref> In portable equipment, foam is mainly used against wildland fires in Class A fuels, mixed with water at 0.1 to 1.0 %.<ref name="IS-B-60">Iqbal and Salley (2004), p. B-60.</ref>

== Spread between buildings and conflagration ==
Once buildings burn, the fire can spread through a built-up area as it does through a forest. Ramachandran describes models in which buildings are linked by ''bonds'' whose chance of transmitting fire depends on the building and its contents, the wind and the distance between buildings. He notes that the same problem arises when predicting fire spread in a forest or from building to building in an urban area.<ref name="Ram-395">Ramachandran (2002c), p. 3-395.</ref>

Data from fires in Tokyo were used to express the probability of fire spread between two buildings as an exponential function that decreases with the distance between them. The analysis showed that the construction of the buildings was the main factor in fire spread.<ref name="SJ-396">Sasaki and Jin, as cited in Ramachandran (2002c), p. 3-396.</ref> In a forest model with randomly placed combustible and non-combustible blocks, fire stopped spreading without wind when about 39 % of the blocks were non-combustible. With wind, up to 65 % non-combustible blocks were needed to stop it.<ref name="Nah-396">Nahmias et al., as cited in Ramachandran (2002c), p. 3-396.</ref>

Albini and Rand modelled urban fire spread as depending on whether a burning building is closer to its unburnt neighbours than a safe distance for radiation or brand transfer.<ref name="AR-396" /> Thomas's spread relation was also applied to the Great Fire of London, with a constant of 0.046 at a wind speed of 4.5 m/s, close to the value of 0.07 for wildland fires.<ref name="Tho-255" /> Wildland fires are also listed among the natural catastrophes, such as lightning, earthquakes and wind storms, that make a fire risk of zero unachievable.<ref name="WH-4">Watts and Hall (2002), p. 5-4.</ref>

== Modelling ==
The Fire Dynamics Simulator offers two ways to model fire spread through vegetation. In the particle model, vegetation such as grass, leaves or airborne burning brands is represented by Lagrangian particles that exchange heat and mass with the gas.<ref name="McG-96">McGrattan et al. (2026), p. 96.</ref><ref name="McG-135">McGrattan et al. (2026), p. 135.</ref> For radiation, vegetation is treated as a collection of large, opaque particles that do not scatter.<ref name="McG-76">McGrattan et al. (2026), p. 76.</ref>

The level set model replaces the details of heat transfer and decomposition by an empirical spread rate, which greatly reduces the complexity of the model.<ref name="McG-135" /> By default each point of the fire front spreads as an ellipse, whose length-to-breadth ratio depends on the combined effect of wind and slope.<ref name="McG-135" /><ref name="McG-136">McGrattan et al. (2026), p. 136.</ref> The spread rate of the head of the fire follows Rothermel's model: a rate without wind and slope, increased by factors for wind and slope. The model treats the spread rate as the ratio of the energy received by unburnt fuel to the energy needed for its ignition.<ref name="McG-137">McGrattan et al. (2026), p. 137.</ref> The wind is taken from a reference height of 6.1 m, equivalent to a standard 20 ft weather station.<ref name="McG-138">McGrattan et al. (2026), p. 138.</ref>

== Limitations ==
Estimates of flame spread require complex analysis and specific data on the fuel, its arrangement and the ambient conditions, and the available formulas are limited.<ref name="Qui-256">Quintiere (2002b), p. 2-256.</ref> The distance over which brands are carried is difficult to establish.<ref name="IFEG-2.6-12" /> The ignition fluxes and radiation limits above come from studies of materials and building fires, not from wildfires, and Thomas's relation is an approximation.<ref name="Bab-3.3-4" /><ref name="MBIE-43" /><ref name="Tho-255" /> A common misconception is that a wildfire only threatens buildings that the flame front touches. Embers carried by the wind can start fires at a distance, and smouldering duff can reignite the fire after the front has passed.<ref name="Qui-255" /><ref name="Ohl-206" />

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

== Notes ==
<references />

== References ==
* 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.
* Hamins, A., Maranghides, A., McGrattan, K. B., Ohlemiller, T. J., & Anleitner, R. L. (2005). ''Experiments and modeling of multiple workstations burning in a compartment'' (NIST NCSTAR 1-5E). 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.
* Kanury, A. M. (2002a). Flaming ignition of solid 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. 2-229–2-245). 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.
* Ohlemiller, T. J. (2002). Smoldering combustion. 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. 2-200–2-210). National Fire Protection Association; Society of Fire Protection Engineers.
* Quintiere, J. G. (2002b). Surface flame spread. 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. 2-246–2-257). National Fire Protection Association; Society of Fire Protection Engineers.
* 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.
* Scheffey, J. L., & Hickey, H. E. (2002). Foam 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. 4-123–4-148). 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:Special Hazards & Building Types]]

Standpipe system

2026-11-01T22:57:19Z

Daan: Redirect to Dry and wet risers (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Dry and wet risers]]

Required safe egress time (RSET)

2026-11-01T22:57:12Z

Daan: Redirect to Required safe egress time (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Required safe egress time]]

Plastics in fire

2026-11-01T22:57:06Z

Daan: FSE wiki: Split an over-long sentence (style check) (written by Claude Opus 5.5)

'''Plastics in fire''' describes how synthetic polymer materials, such as polyethylene, polystyrene, polyurethane foam and PVC, behave when they are heated and burn. In the classification of the SFPE Handbook, plastics are polymers that can be deformed only partly reversibly. Thermoplastics soften and may melt when heated, while thermosets change irreversibly and do not melt.<ref name="BH-111">Beyler and Hirschler (2002), p. 1-111.</ref><ref name="BH-112">Beyler and Hirschler (2002), p. 1-112.</ref> Like wood, a plastic burns only after heat has broken it down into combustible gases.<ref name="VR-3.1">Van Rossum (2027), §3.1.</ref><ref name="BH-124">Beyler and Hirschler (2002), p. 1-124.</ref>

Plastics matter in fire safety because they are everywhere in buildings and vehicles and because many of them burn intensely. Polyethylene and polypropylene release more than 43 kJ of heat per gram when burnt completely, about two and a half times as much as wood.<ref name="T-108">Tewarson (2002), p. 3-108.</ref> Many plastics also produce much more soot than wood and so reduce visibility faster.<ref name="VR-6.2">Van Rossum (2027), §6.2.</ref> Plastics that contain nitrogen release hydrogen cyanide, and PVC releases hydrogen chloride.<ref name="P-100">Purser (2002), p. 2-100.</ref><ref name="BH-126">Beyler and Hirschler (2002), p. 1-126.</ref> Their behaviour varies widely, however: some plastics burn fiercely, while others such as PVC and PTFE have a very low peak heat release rate in standard tests.<ref name="BH-124" />

== Types of plastics ==
Polymers are large molecules built from repeating units. The SFPE Handbook classifies them by their physical properties into elastomers, plastics and fibres. Elastomers, or rubbers, can be stretched to several times their length and recover almost completely. Plastics can be stretched by 100 to 200 per cent before they break, and their deformation is only partly reversible.<ref name="BH-111" /> Plastics are further divided into thermoplastics, which soften on heating without permanent change, and thermosets, which undergo irreversible changes when heated.<ref name="BH-111" />

The chemical composition gives a better indication of how a plastic behaves in fire. The main polymers containing only carbon and hydrogen are the polyolefins polyethylene (PE) and polypropylene (PP), and the styrenics such as polystyrene (PS). Polystyrene is widely used as a foam and for injection-moulded products.<ref name="BH-111" />

Oxygen-containing plastics include poly(methyl methacrylate) (PMMA), used for its transparency, and polyesters such as polyethylene terephthalate (PET) and polycarbonate.<ref name="BH-111" /> Nitrogen-containing polymers include nylons, polyurethanes (PU) and polyacrylonitrile; polyurethanes are mainly used as flexible and rigid foams and as thermal insulation.<ref name="BH-111" /> Poly(vinyl chloride) (PVC) contains chlorine. Together with polyethylene and polypropylene it is one of the three most widely used synthetic polymers, both as a rigid and as a flexible, plasticised material.<ref name="BH-112" /> Fluorine-containing polymers such as polytetrafluoroethylene (PTFE) are very inert to heat and chemicals.<ref name="BH-112" />

== How plastics burn ==
Solid plastics do not burn directly. When heated, they undergo [[pyrolysis]]: the large molecules break down into smaller ones, which escape as combustible gases. Pyrolysis needs no oxygen, but the burning of the gases does.<ref name="VR-3.1" /> Burning becomes self-sustaining when the flame feeds enough heat back to the surface to keep producing these gases, a loop of heat, gas release and flame.<ref name="BH-110">Beyler and Hirschler (2002), p. 1-110.</ref> The SFPE Handbook sums this up in one phrase: polymers cannot burn if they do not break down.<ref name="BH-124" />

The products of decomposition depend on the polymer. Polyethylene and polypropylene form very little of their original building block, the monomer, and instead release up to about 70 different small molecules, mostly hydrocarbons.<ref name="BH-124" /> PMMA decomposes almost entirely back to its monomer and burns at a very steady rate. For this reason it is a favourite material in fire research.<ref name="BH-125">Beyler and Hirschler (2002), p. 1-125.</ref> PVC first loses its chlorine as hydrogen chloride gas, nearly completely, between about 500 and 550 K by a process called chain stripping. In commercial PVC compounds the stabilisers delay this, so that hydrogen chloride is not released until above 520 K and the main stage starts at about 600 K.<ref name="BH-126" />

Thermoplastics may melt and flow before they decompose. This can improve or worsen fire safety. A plastic that flows away from the heat source may avoid ignition or further fire growth, but plastic that flows towards the heat source can make the fire worse.<ref name="BH-123">Beyler and Hirschler (2002), p. 1-123.</ref> Polyethylene melts and flows readily, while high-quality cast PMMA flows only slightly.<ref name="BH-123" /> Many standard fire tests let a melting material flow away from the heat source and are therefore unsuitable for assessing the hazard of materials that drip or flow.<ref name="BH-123" /> Thermosets cannot melt, so they undergo no notable physical change before they decompose.<ref name="BH-112" />

Some plastics form a char, a carbon-rich solid residue. A char layer reduces the amount of combustible gas and protects the material below from heat, so it slows down burning.<ref name="BH-123" /> Char is not always an advantage, however: the char itself can keep burning as sustained smouldering combustion.<ref name="BH-123" />

== Heat release ==
The energy content of plastics varies widely. It depends mainly on the elements in the polymer: plastics made of carbon and hydrogen only release the most heat, while oxygen, chlorine and fluorine lower the value. The SFPE Handbook gives the following net heats of complete combustion, measured in an oxygen bomb calorimeter:<ref name="T-108" />

{| class="wikitable"
! Material !! Net heat of complete combustion (kJ/g)
|-
| Polyethylene || 43.6
|-
| Polypropylene || 43.4
|-
| Polystyrene || 39.2
|-
| Expanded polystyrene || 35.6 to 38.1
|-
| Nylon || 30.8
|-
| Rigid polyurethane foams || 25.0 to 28.0
|-
| Flexible polyurethane foams || 23.2 to 27.2
|-
| Poly(methyl methacrylate) || 25.2
|-
| Poly(vinyl chloride) || 16.4
|-
| Polytetrafluoroethylene || 6.2
|-
| Red oak (for comparison) || 17.1
|}

The [[heat of combustion]] of the hydrocarbon plastics is thus about two and a half times that of wood, while chlorine and fluorine lower it. PVC releases about as much heat per kilogram as oak, and PTFE much less.<ref name="T-108" /> ''Introduction to Fire Safety Engineering'' lists a net heat of combustion of 18 MJ/kg for PVC roofing, the same as for beech wood.<ref name="VR-4.4">Van Rossum (2027), §4.4.</ref> In a real fire, combustion is not complete, so the heat actually released is lower than these values.<ref name="VR-4.4" />

The rate at which a plastic releases heat matters even more than its energy content. The heat release rate is the main variable that determines how much a material adds to the hazard of a fire in a room.<ref name="J-38" /> In the cone calorimeter, at an irradiance of 40 kW/m² and a thickness of 6 mm, polypropylene reached a peak heat release rate of 1500 kW/m², high-density polyethylene 1400 kW/m² and polystyrene 1100 kW/m².<ref name="BH-124" /> PMMA reached 670 kW/m², PVC 180 kW/m² and PTFE only 13 kW/m². For comparison, values from other sources quoted in the same table are 450 kW/m² for cotton and 310 kW/m² for wool.<ref name="BH-124" /> The handbook warns that the temperature at which a polymer starts to decompose does not on its own predict its fire performance.<ref name="BH-124" />

In large fires, the heat released per square metre of burning surface can be estimated from two material properties. The first is the mass loss rate per unit area. The second is the chemical heat of combustion, the heat actually released per gram of material lost in a real fire. The chemical heat release rate is the product of the two:<ref name="T-110">Tewarson (2002), p. 3-110.</ref>
<math display="block">\dot{Q}''_\mathrm{ch} = \dot{m}'' \, \Delta H_\mathrm{ch}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot{Q}''_\mathrm{ch}</math> || chemical heat release rate per unit area of burning surface || kW/m²
|-
| <math>\dot{m}''</math> || mass loss rate per unit area || g/(m²·s)
|-
| <math>\Delta H_\mathrm{ch}</math> || chemical heat of combustion || kJ/g
|}

The SFPE Handbook applies this relation to the steady mass loss rates expected in large, well-ventilated fires.<ref name="T-110" /> For polyethylene, the expected mass loss rate is 26 g/(m²·s) and the chemical heat of combustion 38.4 kJ/g, so the heat release rate is 26 × 38.4 = 998 kW/m². Polystyrene gives 36 × 27.0 = 972 kW/m².<ref name="T-110" /> PVC, by contrast, gives only 16 × 5.7 = 91 kW/m², and FEP Teflon 7 × 4.1 = 28 kW/m².<ref name="T-110" /> For PVC, the chemical heat of combustion is only about a third of its heat of complete combustion, while for polyethylene it is close to 90 per cent (calculated).<ref name="T-108" /><ref name="T-110" /> The relation describes a fire that is not limited by its air supply; in a ventilation-controlled fire, combustion is less complete.<ref name="T-110" />

Plastics have changed the fire load of everyday objects. A study for the Netherlands Institute for Public Safety notes that modern cars, with their high plastic content, have a greater fire load and a higher heat release rate than older steel models. In indoor car parks this leads to very high temperatures and dense black smoke.<ref name="NIPV-11">Van der Graaf et al. (2021/2023), p. 11.</ref> ''Introduction to Fire Safety Engineering'' notes for the same reason that the design fire curves for cars in Dutch car park standards may be less conservative in some situations.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref>

== Smoke and soot ==
Plastics are major producers of smoke. The production of [[soot]] depends on the fuel and on the combustion conditions: plastics produce relatively much soot, wood much less, and ethanol very little.<ref name="VR-6.2" /> The soot yield is the mass of soot produced per mass of fuel burnt. Two sources give the following values for well-ventilated flaming combustion:

{| class="wikitable"
! Material !! Soot yield, ''Introduction to Fire Safety Engineering'' (kg/kg) !! Particulate yield, NUREG-1805 (kg/kg)
|-
| Wood || 0.015 || 0.015 (red oak)
|-
| Poly(methyl methacrylate) || – || 0.022
|-
| Polypropylene || – || 0.059
|-
| Acrylonitrile-butadiene-styrene (ABS) || – || 0.105
|-
| Poly(vinyl chloride) || 0.14 || –
|-
| Polystyrene || 0.16 || 0.164
|-
| Expanded polystyrene || 0.195 || –
|-
| Polyurethane || 0.23 || 0.188 (flexible foam), 0.118 (rigid foam)
|}

The values in ''Introduction to Fire Safety Engineering'' are pre-flashover values, for burning with excess oxygen.<ref name="VR-6.2" /> The NUREG-1805 values come from small-scale tests of turbulent flaming combustion compiled by Klote and Milke.<ref name="KM">Klote and Milke (2002), as cited in Iqbal and Salley (2004), p. 18-4.</ref> In both sources, polystyrene and polyurethane produce roughly 8 to 15 times as much soot per kilogram as wood (calculated). A fire that is smothered, for example by a sprinkler, burns less completely and produces even more soot per kilogram of fuel.<ref name="VR-6.2" />

== Toxic gases ==
All fires produce carbon monoxide, but some plastics add specific toxic gases. [[Hydrogen cyanide]] is always present to some extent when nitrogen-containing materials burn, such as acrylics, polyurethane foams, melamine, nylon and wool. High concentrations are likely in large post-flashover fires.<ref name="P-100" /> PVC releases hydrogen chloride as it decomposes, and acid gases such as hydrogen chloride are among the most important irritants in smoke.<ref name="BH-126" /><ref name="P-91">Purser (2002), p. 2-91.</ref> PTFE produces carbonyl fluoride, a highly toxic lung irritant.<ref name="P-87">Purser (2002), p. 2-87.</ref> In vehicle fires, the burning plastic parts already create severely toxic smoke, which seriously limits the possibilities for escape.<ref name="RISE">RISE (2020), as cited in Van der Graaf et al. (2021/2023), p. 30.</ref>

The SFPE Handbook compares the toxicity of the smoke of material classes with a potency factor, where 1 corresponds to a typical lethal exposure dose of about 500 g·m−3·min.<ref name="P-98">Purser (2002), p. 2-98.</ref> In non-flaming decomposition, most materials have a factor close to 1. Nitrogen-containing materials that release much hydrogen cyanide at low temperatures, such as polyacrylonitrile and rigid polyurethane foam, reach 3 to 8.<ref name="P-98" />

In early, well-ventilated flaming fires, wood and cotton are the least toxic, with a factor of 0.2. Plastics containing only carbon, hydrogen and oxygen have a factor of about 0.4, and PVC and fire-retarded materials about 1.<ref name="P-98" /> After flashover, the potency of all materials rises. For nitrogen-containing materials it ranges from about 2.5 for flexible polyurethane foam to about 11 for polyacrylonitrile, and PVC is suggested to reach about 2.5.<ref name="P-98" />

== Flame retardants ==
A [[flame retardant]] is added to a plastic to change the way it decomposes and burns, and its effect depends on chemistry and timing. In thermal analysis, the overlap between the decomposition stages of the polymer and of the additive indicates how effective an additive is.<ref name="BH-115">Beyler and Hirschler (2002), p. 1-115.</ref> The mechanisms and likely effectiveness of flame retardants can therefore be predicted well from thermal decomposition data.<ref name="BH-124" /> In one example from the SFPE Handbook, a bromine compound in ABS worked together with antimony oxide, because the antimony bromide formed could evaporate. The same compound was ineffective with iron oxide, whose bromide does not evaporate, and with zinc oxide, whose bromide evaporates before the polymer starts to break down.<ref name="BH-124" />

Flame retardants involve a trade-off. Many treatments increase the yield of toxic gases per gram of material but greatly reduce the rate at which the material burns, so that the overall fire hazard falls.<ref name="J-38">Janssens (2002), p. 3-38.</ref> In full-scale tests with upholstered chairs, fire-retarded covers increased the time before conditions became untenable through asphyxiant gases by about 1.5 minutes.<ref name="P-140">Purser (2002), p. 2-140.</ref> The handbook concludes that some modern materials and fire retardant systems may present toxic or environmental problems, but give considerable overall benefits if they reduce the number of fires and slow fire development.<ref name="P-140" />

== Plastics in buildings and regulation ==
[[Building regulations]] can limit the use of combustible linings through reaction-to-fire classes. In New Zealand, lining materials are classified by the time to flashover in a full-scale room test. Exposed polyurethane foams reach flashover within two minutes and fall into the worst class, Group Number 4, which is not acceptable in occupied spaces.<ref name="CVM2C-141">Ministry of Business, Innovation and Employment (2013), p. 141.</ref> Some plastic-containing products cannot be judged with small-scale tests. The New Zealand commentary names metal-faced [[sandwich panel]]s and foil-faced combustible insulation as products for which the small-scale correlation does not work.<ref name="CVM2C-141" />

== Limits and common misconceptions ==
A common misconception is that all plastics behave alike in a fire. The data above show that peak heat release rates in the cone calorimeter range from 13 to 1500 kW/m², and heats of combustion from 6.2 to 43.6 kJ/g.<ref name="BH-124" /><ref name="T-108" /> PVC is an example of a plastic with a low heat release rate but an important release of hydrogen chloride.<ref name="BH-124" /><ref name="BH-126" />

A second misconception is that a single property, such as the limiting oxygen index or the decomposition temperature, describes fire performance. The SFPE Handbook notes that the oxygen index technique has fallen into disrepute and that thermal decomposition data alone cannot predict fire performance.<ref name="BH-124" /> Toxicity data are also limited: the handbook calls the database of toxic potency tests very poor, especially for post-flashover conditions.<ref name="P-98" /> Values for soot yield and toxicity depend strongly on the fire conditions, and the same material gives different results in well-ventilated and in smothered fires.<ref name="VR-6.2" /><ref name="P-98" />

== See also ==
* [[Euroclass system]]
* [[Fire resistance test]]
* [[Combustibility]]
* [[Cone calorimeter]]

== Notes ==
<references />

== References ==
* 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.
* 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.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* 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.
* 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:Materials & Fire Testing]]

Premixed combustion

2026-11-01T22:57:00Z

Daan: Redirect to Premixed flame (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Premixed flame]]

Aspirating smoke detection

2026-11-01T22:56:54Z

Daan: New FSE wiki article: Aspirating smoke detection (written by Claude Opus 5.5)

'''Aspirating smoke detection''' is a method of fire detection in which a fan draws air from the protected space through pipes with sampling holes. A central detector then analyses the air for products of combustion.<ref name="IFEG-2.7-6">National Research Council of Canada et al. (2005), p. 2.7-6.</ref><ref name="IS-F-3">Iqbal and Salley (2004), p. F-3.</ref> The system is also called air sampling smoke detection.<ref name="IFEG-2.7-6" /> The central unit is usually a sensitive light scattering detector.<ref name="IFEG-2.7-6" /> Because its alarm threshold can be set for each installation, an aspirating system is often up to ten times as sensitive as a point-type [[smoke detector]].<ref name="IFEG-2.7-6" />

Aspirating systems are used where very early warning matters. Very early warning fire detection systems are used extensively in telecommunications facilities.<ref name="Hyslop-13-1">Hyslop et al. (2010), p. 13-1.</ref> In nuclear power plants, aspirating detectors of this type can detect slowly degrading electrical components in cabinets before open flaming starts.<ref name="Hyslop-13-2">Hyslop et al. (2010), p. 13-2.</ref> The price of this sensitivity is a delay: smoke is diluted in the pipes and needs time to travel to the detector.<ref name="IFEG-2.7-6" /> Fire engineering design methods therefore treat the system with care. New Zealand's Verification Method C/VM2 (second edition, 2025) states that such detectors require specialised design.<ref name="MBIE25-27">Ministry of Business, Innovation and Employment (2025b), p. 27.</ref>

== How the system works ==
An aspirating detector consists of a piping or tubing network that runs from the detector unit to the areas to be protected.<ref name="IS-F-3" /> A fan in the detector housing draws air from the protected area back to the detector through sampling ports in the pipes.<ref name="IS-F-3" /> At the detector, the air is analysed for products of combustion.<ref name="IS-F-3" /> The International Fire Engineering Guidelines list aspirating detectors among the smoke detectors, next to ionisation, optical scatter and beam detectors.<ref name="IFEG-2.7-2">National Research Council of Canada et al. (2005), p. 2.7-2.</ref>

The active suction is the main difference from point detectors. A point detector only responds once smoke has entered its sensing chamber, and experiments show that this requires a gas velocity of about 0.15 m/s for the detectors tested.<ref name="SMC-4-27">Schifiliti et al. (2002), p. 4-27.</ref> Insect screens, the chamber design and the distance to the ceiling all affect smoke entry.<ref name="SMC-4-27" /> In an aspirating system, the fan transports the air from each sampling hole to the detector.<ref name="IS-F-3" /> Each sampling hole can therefore be thought of as a separate point detector, which is how the International Fire Engineering Guidelines recommend modelling it.<ref name="IFEG-2.7-6" />

Most systems of this kind give two or more warning levels. Thresholds set to trigger before the flaming stage are usually called alerts, and thresholds set for the flaming or true fire stage are called alarms.<ref name="Hyslop-13-6">Hyslop et al. (2010), p. 13-6.</ref> An alert gives staff time to investigate the source of the signal.<ref name="Hyslop-13-6" /> In New Zealand, C/VM2 treats air sampling detectors as one of the detector types of the [[fire alarm system]], which must be installed to NZS 4512.<ref name="MBIE25-26">Ministry of Business, Innovation and Employment (2025b), p. 26.</ref><ref name="MBIE25-27" />

== Sensitivity and obscuration ==
The sensitivity of smoke detectors is expressed as the amount of light that smoke removes over a given distance. Schifiliti, Meacham and Custer define the percent obscuration as 100 times one minus the fraction of light that is transmitted.<ref name="SMC-4-22">Schifiliti et al. (2002), p. 4-22.</ref> Many fire models calculate the optical density per unit distance, which follows from the same measurement:<ref name="SMC-4-22" /><ref name="Peacock-36">Peacock et al. (2026), p. 36.</ref>

<math display="block">D_u = \frac{1}{l}\,\log_{10}\!\left(\frac{I_0}{I}\right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>D_u</math> || optical density per unit distance || m⁻¹
|-
| <math>l</math> || path length of the light beam || m
|-
| <math>I_0</math> || light intensity at the receiver without smoke || W/m²
|-
| <math>I</math> || light intensity at the receiver with smoke present || W/m²
|}

Detector thresholds are often quoted as percent obscuration per foot or per metre, so that the path length is 0.3048 m or 1 m.<ref name="McG-109">McGrattan et al. (2026), p. 109.</ref> The relation assumes that the smoke is evenly spread along the light path.<ref name="SMC-4-23">Schifiliti et al. (2002), p. 4-23.</ref> It describes how much light the smoke blocks, not how much light it scatters.<ref name="SMC-4-22" /> A scattering detector therefore responds at different optical densities for different types of smoke.<ref name="SMC-4-23" /> One scattering detector that alarms at 0.029 m⁻¹ (2.0 %/ft) for smoke from a smouldering cotton lamp wick may need 0.15 m⁻¹ (10 %/ft) for smoke from a kerosene fire.<ref name="SMC-4-23" />

A worked example compares the thresholds. The US standard NFPA 76 requires very early warning systems to reach an alert sensitivity of at least 0.2 % per foot. The alarm sensitivity must be at least 1 % per foot, both measured at each sampling port.<ref name="Hyslop-13-2" /> An obscuration of 1 % per foot means that 99 % of the light passes 0.3048 m of smoke, so <math>D_u</math> = log10(1/0.99) / 0.3048 ≈ 0.0143 m⁻¹. In the same way, 0.2 % per foot gives about 0.0029 m⁻¹.

C/VM2 (second edition, 2025) uses an optical density at alarm of 0.097 m⁻¹ for smoke detectors in design calculations, which equals an obscuration of about 20 % per metre.<ref name="MBIE25-27" /> The NFPA 76 alarm level is thus about 6.8 times as sensitive as the C/VM2 design value, and the alert level about 34 times. This is of the same order as the statement in the International Fire Engineering Guidelines that aspirating detectors are often up to ten times as sensitive as point detectors.<ref name="IFEG-2.7-6" />

The same relation checks values from other sources. The smoke detector test standard UL 268 limits the response threshold of point detectors to 0.0581 m⁻¹, which Schifiliti and colleagues give as 4.0 % per foot.<ref name="SMC-4-25">Schifiliti et al. (2002), p. 4-25.</ref> The fire model CFAST uses a default activation value of 24 % per metre, equal to 8 % per foot, for point smoke detectors.<ref name="Peacock-36" />

== Transport delay and dilution ==
High sensitivity at the detector does not mean early detection at the fire. The International Fire Engineering Guidelines point out that smoke is diluted and travels at a finite speed along the pipework, so there is usually a considerable delay before the system activates.<ref name="IFEG-2.7-6" /> Smoke drawn in at one hole is mixed with the air drawn in at all the other holes.<ref name="McG-109" /> In a large pipework system, the location of the fire may also be hard to identify.<ref name="IFEG-2.7-6" /> To predict the activation time, the guidelines recommend using the manufacturer's specification together with the smoke conditions calculated for the design fire.<ref name="IFEG-2.7-6" />

C/VM2 (second edition, 2025) lists the main factors that determine the response: the air flow rates, the length of the sampling tubes and the alarm threshold levels.<ref name="MBIE25-27" /> For design calculations under this method, air sampling detectors are nevertheless modelled with the same criteria as point smoke detectors. These are an optical density at alarm of 0.097 m⁻¹, a radial distance of 7.0 m and a position at least 25 mm below the ceiling.<ref name="MBIE25-27" /> The detection time found this way is the first term of the required safe egress time in C/VM2.<ref name="MBIE25-26" />

Computational models can represent the system in more detail. In the Fire Dynamics Simulator, the user specifies the sampling locations, the flow rate at each, and the transport time from each point to the detector. Any bypass flow and the obscuration at which the detector alarms are also entered.<ref name="McG-109" /> The model then weights the smoke concentrations at the sampling points by their flow rates, after applying the time delay of each point.<ref name="McG-109" /> The zone model CFAST, by contrast, does not account for transport delays from the fire to a detector.<ref name="Peacock-36" />

== Stratification and air movement ==
Smoke from a small fire does not always reach the ceiling. [[Smoke stratification]] occurs when the plume temperature falls to that of the surrounding air, so that the smoke stops rising and stays at that height.<ref name="SMC-4-27" /> A worked example in the SFPE Handbook concerns overheated cable insulation with a critical fire of 1,000 W. It must be detected in a 7 m high, air-conditioned room with a temperature difference of 10 °C.<ref name="SMC-4-27" /> The smoke is estimated to rise no higher than 6 m, so ceiling-mounted detectors may not meet the design objective.<ref name="SMC-4-27" />

Atria and other tall spaces are prone to this effect. Milke reports floor-to-ceiling temperature differences of about 50 °C in some atria with glazed ceilings, where the sun heats the air below the roof.<ref name="Milke-4-304">Milke (2002b), p. 4-304.</ref> Smoke then stratifies below the warm layer, and ceiling-mounted devices may respond late.<ref name="Milke-4-304" /> Such delays matter for [[atrium smoke control]], which relies on detection to start. Because each sampling hole acts as a separate detection point, the position of the holes determines whether the system sees smoke that has stratified below the ceiling.<ref name="IFEG-2.7-6" />

Ventilation is a second source of dilution. Schifiliti, Meacham and Custer explain that heating and ventilation systems with high exchange rates can draw smoke away from detectors in the early stage of a fire, when the plume is weak.<ref name="SMC-4-26">Schifiliti et al. (2002), p. 4-26.</ref> There are no quantitative methods for these effects, which become larger as the fire to be detected becomes smaller.<ref name="SMC-4-26" /> The ''Introduction to Fire Safety Engineering'' notes that ordinary ventilation systems can strongly influence smoke spread, so it can be hard to decide what they should do when a fire is detected.<ref name="VR-6.6">Van Rossum (2027), §6.6.</ref>

== Very early warning in electrical equipment ==
The most detailed treatment in the sources comes from the US nuclear industry. Very early warning fire detection systems have been used extensively in telecommunications, and the standard NFPA 76 essentially requires them in high-value areas such as main distribution frames.<ref name="Hyslop-13-1" /> In 2010, the US Nuclear Regulatory Commission published an interim position on crediting aspirating smoke detectors in fire risk assessments of nuclear plants.<ref name="Hyslop-13-2" /> The position covers detectors that monitor low-voltage electrical cabinets of 250 V or less.<ref name="Hyslop-13-5">Hyslop et al. (2010), p. 13-5.</ref>

The idea is that many low-voltage components degrade slowly, with signs that a sensitive detector can pick up long before a fire starts. Examples include terminal strips, cables, relays, transformers and power supplies.<ref name="Hyslop-13-2" /> Some components, such as circuit boards with electrolytic capacitors or cooling fan motors, can fail quickly and leave no time for this.<ref name="Hyslop-13-3">Hyslop et al. (2010), p. 13-3.</ref> For a cabinet with 25 slowly degrading relays, a cooling fan and a motor-driven timer, the NRC example gives a fraction of 2/27, or about 0.074, of components without a detectable incipient phase.<ref name="Hyslop-13-5" /> Aspirating systems would also not work properly in a tightly sealed cabinet.<ref name="Hyslop-13-5" /> Data on how long the incipient stage lasts are limited, which makes the benefit uncertain.<ref name="Hyslop-13-3" />

The credit depends on a chain of events. The detection system must issue an alert, for which a failure probability of 0.01 may be used if the system is similar to the cloud chamber and laser aspirating systems evaluated by EPRI.<ref name="Hyslop-13-5" /> Operators must then find the cabinet and post a trained fire watch, with failure probabilities of 0.01 or 0.005, assuming at least one hour of warning before open flaming.<ref name="Hyslop-13-6" /> The posted responder then fails to suppress a fire in time with a probability of 0.001.<ref name="Hyslop-13-8">Hyslop et al. (2010), p. 13-8.</ref> The chance that a technician removes power from the failing part in time is not credited at all, because it is hard to assess.<ref name="Hyslop-13-7">Hyslop et al. (2010), p. 13-7.</ref> These values are examples of the inputs to an [[Event tree analysis|event tree]] rather than general properties of the technology.

== Reliability, maintenance and unwanted alarms ==
High sensitivity makes setting and maintenance important. The NRC position requires systems to be designed and installed to NFPA 76 by trained technicians, to pass the vendor's acceptance and sensitivity tests, and to be tested and calibrated under NFPA 72.<ref name="Hyslop-13-5" /><ref name="Hyslop-13-6" /> Alert and alarm levels should be under formal setpoint control.<ref name="Hyslop-13-6" /> Any recalibration that reduces the sensitivity, such as rebaselining the levels, must be evaluated so that the early warning function is not lost.<ref name="Hyslop-13-6" />

High sensitivity also raises the question of [[unwanted fire alarms]]. Schifiliti, Meacham and Custer note that smoke detectors in general often use complex response algorithms to reduce false and nuisance alarms, and that manufacturers generally do not publish these algorithms.<ref name="SMC-4-22" /> The same algorithms make it harder to predict the actual response of a detector from smoke measurements.<ref name="SMC-4-22" /> In the NRC approach, an alert leads to an investigation of the cabinet and a posted fire watch, so that a small signal is checked before it becomes a fire.<ref name="Hyslop-13-6" />

Availability has a strong effect on the benefit. The NRC estimates that an out-of-service period of four days would reduce the effectiveness of a very early warning system by an order of magnitude, and a single day by a factor of about three.<ref name="Hyslop-13-9">Hyslop et al. (2010), p. 13-9.</ref> Compensatory measures such as a continuous fire watch or a portable detector are therefore expected during outages.<ref name="Hyslop-13-9" /> Even with such a system installed, the other layers of defence in depth remain required.<ref name="Hyslop-13-9" /> In general building design, the first warning to occupants comes from detection and alarm by installed systems or by people, as the ''Introduction to Fire Safety Engineering'' explains.<ref name="VR-7.3">Van Rossum (2027), §7.3.</ref>

== See also ==
* [[Beam smoke detector]]
* [[Multi-sensor detector]]
* [[Heat detector]]
* [[Detector activation time]]

== Notes ==
<references />

== References ==
* Hyslop, J. S., Kratchman, J., Siu, N., Afshar, C., Najafi, B., Joglar, F., Li, Y., Henneke, D., & Warner, M. (2010). ''Fire probabilistic risk assessment methods enhancements: Supplement 1 to NUREG/CR-6850 and EPRI 1011989'' (NUREG/CR-6850, Supplement 1; EPRI 1019259). Electric Power Research Institute; U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research.
* 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
* Milke, J. A. (2002b). Smoke management in covered malls and atria. 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. 4-292–4-310). 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.
* 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
* 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.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Detection & Alarm]]

Standpipe

2026-11-01T22:56:48Z

Daan: Redirect to Dry and wet risers (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Dry and wet risers]]

RSET

2026-11-01T22:56:42Z

Daan: Redirect to Required safe egress time (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Required safe egress time]]

Premixed burning

2026-11-01T22:56:36Z

Daan: Redirect to Premixed flame (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Premixed flame]]

Plastics in fire

2026-11-01T22:56:30Z

Daan: New FSE wiki article: Plastics in fire (written by Claude Opus 5.5)

'''Plastics in fire''' describes how synthetic polymer materials, such as polyethylene, polystyrene, polyurethane foam and PVC, behave when they are heated and burn. In the classification of the SFPE Handbook, plastics are polymers that can be deformed only partly reversibly. Thermoplastics soften and may melt when heated, while thermosets change irreversibly and do not melt.<ref name="BH-111">Beyler and Hirschler (2002), p. 1-111.</ref><ref name="BH-112">Beyler and Hirschler (2002), p. 1-112.</ref> Like wood, a plastic burns only after heat has broken it down into combustible gases.<ref name="VR-3.1">Van Rossum (2027), §3.1.</ref><ref name="BH-124">Beyler and Hirschler (2002), p. 1-124.</ref>

Plastics matter in fire safety because they are everywhere in buildings and vehicles and because many of them burn intensely. Polyethylene and polypropylene release more than 43 kJ of heat per gram when burnt completely, about two and a half times as much as wood.<ref name="T-108">Tewarson (2002), p. 3-108.</ref> Many plastics also produce much more soot than wood and so reduce visibility faster.<ref name="VR-6.2">Van Rossum (2027), §6.2.</ref> Plastics that contain nitrogen release hydrogen cyanide, and PVC releases hydrogen chloride.<ref name="P-100">Purser (2002), p. 2-100.</ref><ref name="BH-126">Beyler and Hirschler (2002), p. 1-126.</ref> Their behaviour varies widely, however: some plastics burn fiercely, while others such as PVC and PTFE have a very low peak heat release rate in standard tests.<ref name="BH-124" />

== Types of plastics ==
Polymers are large molecules built from repeating units. The SFPE Handbook classifies them by their physical properties into elastomers, plastics and fibres. Elastomers, or rubbers, can be stretched to several times their length and recover almost completely. Plastics can be stretched by 100 to 200 per cent before they break, and their deformation is only partly reversible.<ref name="BH-111" /> Plastics are further divided into thermoplastics, which soften on heating without permanent change, and thermosets, which undergo irreversible changes when heated.<ref name="BH-111" />

The chemical composition gives a better indication of how a plastic behaves in fire. The main polymers containing only carbon and hydrogen are the polyolefins polyethylene (PE) and polypropylene (PP), and the styrenics such as polystyrene (PS). Polystyrene is widely used as a foam and for injection-moulded products.<ref name="BH-111" />

Oxygen-containing plastics include poly(methyl methacrylate) (PMMA), used for its transparency, and polyesters such as polyethylene terephthalate (PET) and polycarbonate.<ref name="BH-111" /> Nitrogen-containing polymers include nylons, polyurethanes (PU) and polyacrylonitrile; polyurethanes are mainly used as flexible and rigid foams and as thermal insulation.<ref name="BH-111" /> Poly(vinyl chloride) (PVC) contains chlorine. Together with polyethylene and polypropylene it is one of the three most widely used synthetic polymers, both as a rigid and as a flexible, plasticised material.<ref name="BH-112" /> Fluorine-containing polymers such as polytetrafluoroethylene (PTFE) are very inert to heat and chemicals.<ref name="BH-112" />

== How plastics burn ==
Solid plastics do not burn directly. When heated, they undergo [[pyrolysis]]: the large molecules break down into smaller ones, which escape as combustible gases. Pyrolysis needs no oxygen, but the burning of the gases does.<ref name="VR-3.1" /> Burning becomes self-sustaining when the flame feeds enough heat back to the surface to keep producing these gases, a loop of heat, gas release and flame.<ref name="BH-110">Beyler and Hirschler (2002), p. 1-110.</ref> The SFPE Handbook sums this up in one phrase: polymers cannot burn if they do not break down.<ref name="BH-124" />

The products of decomposition depend on the polymer. Polyethylene and polypropylene form very little of their original building block, the monomer, and instead release up to about 70 different small molecules, mostly hydrocarbons.<ref name="BH-124" /> PMMA decomposes almost entirely back to its monomer and burns at a very steady rate. For this reason it is a favourite material in fire research.<ref name="BH-125">Beyler and Hirschler (2002), p. 1-125.</ref> PVC first loses its chlorine as hydrogen chloride gas, nearly completely, between about 500 and 550 K by a process called chain stripping. In commercial PVC compounds the stabilisers delay this, so that hydrogen chloride is not released until above 520 K and the main stage starts at about 600 K.<ref name="BH-126" />

Thermoplastics may melt and flow before they decompose. This can improve or worsen fire safety. A plastic that flows away from the heat source may avoid ignition or further fire growth, but plastic that flows towards the heat source can make the fire worse.<ref name="BH-123">Beyler and Hirschler (2002), p. 1-123.</ref> Polyethylene melts and flows readily, while high-quality cast PMMA flows only slightly.<ref name="BH-123" /> Many standard fire tests let a melting material flow away from the heat source and are therefore unsuitable for assessing the hazard of materials that drip or flow.<ref name="BH-123" /> Thermosets cannot melt, so they undergo no notable physical change before they decompose.<ref name="BH-112" />

Some plastics form a char, a carbon-rich solid residue. A char layer reduces the amount of combustible gas and protects the material below from heat, so it slows down burning.<ref name="BH-123" /> Char is not always an advantage, however: the char itself can keep burning as sustained smouldering combustion.<ref name="BH-123" />

== Heat release ==
The energy content of plastics varies widely. It depends mainly on the elements in the polymer: plastics made of carbon and hydrogen only release the most heat, while oxygen, chlorine and fluorine lower the value. The SFPE Handbook gives the following net heats of complete combustion, measured in an oxygen bomb calorimeter:<ref name="T-108" />

{| class="wikitable"
! Material !! Net heat of complete combustion (kJ/g)
|-
| Polyethylene || 43.6
|-
| Polypropylene || 43.4
|-
| Polystyrene || 39.2
|-
| Expanded polystyrene || 35.6 to 38.1
|-
| Nylon || 30.8
|-
| Rigid polyurethane foams || 25.0 to 28.0
|-
| Flexible polyurethane foams || 23.2 to 27.2
|-
| Poly(methyl methacrylate) || 25.2
|-
| Poly(vinyl chloride) || 16.4
|-
| Polytetrafluoroethylene || 6.2
|-
| Red oak (for comparison) || 17.1
|}

The [[heat of combustion]] of the hydrocarbon plastics is thus about two and a half times that of wood, while chlorine and fluorine lower it. PVC releases about as much heat per kilogram as oak, and PTFE much less.<ref name="T-108" /> ''Introduction to Fire Safety Engineering'' lists a net heat of combustion of 18 MJ/kg for PVC roofing, the same as for beech wood.<ref name="VR-4.4">Van Rossum (2027), §4.4.</ref> In a real fire, combustion is not complete, so the heat actually released is lower than these values.<ref name="VR-4.4" />

The rate at which a plastic releases heat matters even more than its energy content, because the heat release rate is the main variable that determines how much a material adds to the hazard of a fire in a room.<ref name="J-38" /> In the cone calorimeter, at an irradiance of 40 kW/m² and a thickness of 6 mm, polypropylene reached a peak heat release rate of 1500 kW/m², high-density polyethylene 1400 kW/m² and polystyrene 1100 kW/m².<ref name="BH-124" /> PMMA reached 670 kW/m², PVC 180 kW/m² and PTFE only 13 kW/m². For comparison, values from other sources quoted in the same table are 450 kW/m² for cotton and 310 kW/m² for wool.<ref name="BH-124" /> The handbook warns that the temperature at which a polymer starts to decompose does not on its own predict its fire performance.<ref name="BH-124" />

In large fires, the heat released per square metre of burning surface can be estimated from two material properties. The first is the mass loss rate per unit area. The second is the chemical heat of combustion, the heat actually released per gram of material lost in a real fire. The chemical heat release rate is the product of the two:<ref name="T-110">Tewarson (2002), p. 3-110.</ref>
<math display="block">\dot{Q}''_\mathrm{ch} = \dot{m}'' \, \Delta H_\mathrm{ch}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot{Q}''_\mathrm{ch}</math> || chemical heat release rate per unit area of burning surface || kW/m²
|-
| <math>\dot{m}''</math> || mass loss rate per unit area || g/(m²·s)
|-
| <math>\Delta H_\mathrm{ch}</math> || chemical heat of combustion || kJ/g
|}

The SFPE Handbook applies this relation to the steady mass loss rates expected in large, well-ventilated fires.<ref name="T-110" /> For polyethylene, the expected mass loss rate is 26 g/(m²·s) and the chemical heat of combustion 38.4 kJ/g, so the heat release rate is 26 × 38.4 = 998 kW/m². Polystyrene gives 36 × 27.0 = 972 kW/m².<ref name="T-110" /> PVC, by contrast, gives only 16 × 5.7 = 91 kW/m², and FEP Teflon 7 × 4.1 = 28 kW/m².<ref name="T-110" /> For PVC, the chemical heat of combustion is only about a third of its heat of complete combustion, while for polyethylene it is close to 90 per cent (calculated).<ref name="T-108" /><ref name="T-110" /> The relation describes a fire that is not limited by its air supply; in a ventilation-controlled fire, combustion is less complete.<ref name="T-110" />

Plastics have changed the fire load of everyday objects. A study for the Netherlands Institute for Public Safety notes that modern cars, with their high plastic content, have a greater fire load and a higher heat release rate than older steel models. In indoor car parks this leads to very high temperatures and dense black smoke.<ref name="NIPV-11">Van der Graaf et al. (2021/2023), p. 11.</ref> ''Introduction to Fire Safety Engineering'' notes for the same reason that the design fire curves for cars in Dutch car park standards may be less conservative in some situations.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref>

== Smoke and soot ==
Plastics are major producers of smoke. The production of [[soot]] depends on the fuel and on the combustion conditions: plastics produce relatively much soot, wood much less, and ethanol very little.<ref name="VR-6.2" /> The soot yield is the mass of soot produced per mass of fuel burnt. Two sources give the following values for well-ventilated flaming combustion:

{| class="wikitable"
! Material !! Soot yield, ''Introduction to Fire Safety Engineering'' (kg/kg) !! Particulate yield, NUREG-1805 (kg/kg)
|-
| Wood || 0.015 || 0.015 (red oak)
|-
| Poly(methyl methacrylate) || – || 0.022
|-
| Polypropylene || – || 0.059
|-
| Acrylonitrile-butadiene-styrene (ABS) || – || 0.105
|-
| Poly(vinyl chloride) || 0.14 || –
|-
| Polystyrene || 0.16 || 0.164
|-
| Expanded polystyrene || 0.195 || –
|-
| Polyurethane || 0.23 || 0.188 (flexible foam), 0.118 (rigid foam)
|}

The values in ''Introduction to Fire Safety Engineering'' are pre-flashover values, for burning with excess oxygen.<ref name="VR-6.2" /> The NUREG-1805 values come from small-scale tests of turbulent flaming combustion compiled by Klote and Milke.<ref name="KM">Klote and Milke (2002), as cited in Iqbal and Salley (2004), p. 18-4.</ref> In both sources, polystyrene and polyurethane produce roughly 8 to 15 times as much soot per kilogram as wood (calculated). A fire that is smothered, for example by a sprinkler, burns less completely and produces even more soot per kilogram of fuel.<ref name="VR-6.2" />

== Toxic gases ==
All fires produce carbon monoxide, but some plastics add specific toxic gases. [[Hydrogen cyanide]] is always present to some extent when nitrogen-containing materials burn, such as acrylics, polyurethane foams, melamine, nylon and wool. High concentrations are likely in large post-flashover fires.<ref name="P-100" /> PVC releases hydrogen chloride as it decomposes, and acid gases such as hydrogen chloride are among the most important irritants in smoke.<ref name="BH-126" /><ref name="P-91">Purser (2002), p. 2-91.</ref> PTFE produces carbonyl fluoride, a highly toxic lung irritant.<ref name="P-87">Purser (2002), p. 2-87.</ref> In vehicle fires, the burning plastic parts already create severely toxic smoke, which seriously limits the possibilities for escape.<ref name="RISE">RISE (2020), as cited in Van der Graaf et al. (2021/2023), p. 30.</ref>

The SFPE Handbook compares the toxicity of the smoke of material classes with a potency factor, where 1 corresponds to a typical lethal exposure dose of about 500 g·m−3·min.<ref name="P-98">Purser (2002), p. 2-98.</ref> In non-flaming decomposition, most materials have a factor close to 1. Nitrogen-containing materials that release much hydrogen cyanide at low temperatures, such as polyacrylonitrile and rigid polyurethane foam, reach 3 to 8.<ref name="P-98" />

In early, well-ventilated flaming fires, wood and cotton are the least toxic, with a factor of 0.2. Plastics containing only carbon, hydrogen and oxygen have a factor of about 0.4, and PVC and fire-retarded materials about 1.<ref name="P-98" /> After flashover, the potency of all materials rises. For nitrogen-containing materials it ranges from about 2.5 for flexible polyurethane foam to about 11 for polyacrylonitrile, and PVC is suggested to reach about 2.5.<ref name="P-98" />

== Flame retardants ==
A [[flame retardant]] is added to a plastic to change the way it decomposes and burns, and its effect depends on chemistry and timing. In thermal analysis, the overlap between the decomposition stages of the polymer and of the additive indicates how effective an additive is.<ref name="BH-115">Beyler and Hirschler (2002), p. 1-115.</ref> The mechanisms and likely effectiveness of flame retardants can therefore be predicted well from thermal decomposition data.<ref name="BH-124" /> In one example from the SFPE Handbook, a bromine compound in ABS worked together with antimony oxide, because the antimony bromide formed could evaporate. The same compound was ineffective with iron oxide, whose bromide does not evaporate, and with zinc oxide, whose bromide evaporates before the polymer starts to break down.<ref name="BH-124" />

Flame retardants involve a trade-off. Many treatments increase the yield of toxic gases per gram of material but greatly reduce the rate at which the material burns, so that the overall fire hazard falls.<ref name="J-38">Janssens (2002), p. 3-38.</ref> In full-scale tests with upholstered chairs, fire-retarded covers increased the time before conditions became untenable through asphyxiant gases by about 1.5 minutes.<ref name="P-140">Purser (2002), p. 2-140.</ref> The handbook concludes that some modern materials and fire retardant systems may present toxic or environmental problems, but give considerable overall benefits if they reduce the number of fires and slow fire development.<ref name="P-140" />

== Plastics in buildings and regulation ==
[[Building regulations]] can limit the use of combustible linings through reaction-to-fire classes. In New Zealand, lining materials are classified by the time to flashover in a full-scale room test. Exposed polyurethane foams reach flashover within two minutes and fall into the worst class, Group Number 4, which is not acceptable in occupied spaces.<ref name="CVM2C-141">Ministry of Business, Innovation and Employment (2013), p. 141.</ref> Some plastic-containing products cannot be judged with small-scale tests. The New Zealand commentary names metal-faced [[sandwich panel]]s and foil-faced combustible insulation as products for which the small-scale correlation does not work.<ref name="CVM2C-141" />

== Limits and common misconceptions ==
A common misconception is that all plastics behave alike in a fire. The data above show that peak heat release rates in the cone calorimeter range from 13 to 1500 kW/m², and heats of combustion from 6.2 to 43.6 kJ/g.<ref name="BH-124" /><ref name="T-108" /> PVC is an example of a plastic with a low heat release rate but an important release of hydrogen chloride.<ref name="BH-124" /><ref name="BH-126" />

A second misconception is that a single property, such as the limiting oxygen index or the decomposition temperature, describes fire performance. The SFPE Handbook notes that the oxygen index technique has fallen into disrepute and that thermal decomposition data alone cannot predict fire performance.<ref name="BH-124" /> Toxicity data are also limited: the handbook calls the database of toxic potency tests very poor, especially for post-flashover conditions.<ref name="P-98" /> Values for soot yield and toxicity depend strongly on the fire conditions, and the same material gives different results in well-ventilated and in smothered fires.<ref name="VR-6.2" /><ref name="P-98" />

== See also ==
* [[Euroclass system]]
* [[Fire resistance test]]
* [[Combustibility]]
* [[Cone calorimeter]]

== Notes ==
<references />

== References ==
* 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.
* 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.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* 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.
* 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:Materials & Fire Testing]]

Structural fire design

2026-11-01T22:56:23Z

Daan: Redirect to Structural fire engineering (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Structural fire engineering]]

Embers

2026-11-01T22:56:17Z

Daan: Redirect to Firebrands (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Firebrands]]

Aqueous film forming foam

2026-11-01T22:56:11Z

Daan: Redirect to Aqueous film-forming foam (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Aqueous film-forming foam]]

Wet riser

2026-11-01T22:56:05Z

Daan: Redirect to Dry and wet risers (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Dry and wet risers]]

Required safe egress time

2026-11-01T22:55:59Z

Daan: New FSE wiki article: Required safe egress time (written by Claude Opus 5.5)

The '''required safe egress time''' ('''RSET''') is the time occupants need to leave a room or building in a fire. It is counted from ignition until all of them have left that space or reached a place of safety.<ref name="MBIE25-26">Ministry of Business, Innovation and Employment (2025b), p. 26.</ref><ref name="VR-7.1">Van Rossum (2027), §7.1.</ref> It includes not only the walking time but also everything that happens before people start to move, such as detection, the alarm and the time occupants take to respond.<ref name="VR-7.1" /> RSET is one half of the comparison at the centre of performance-based life safety design. The other half is the [[available safe egress time]] (ASET), the time until conditions in the space become untenable.<ref name="NM-367">Nelson and Mowrer (2002), p. 3-367.</ref>

A design is acceptable for life safety when ASET is longer than RSET, usually with a safety margin or safety factor.<ref name="VR-7.1" /> The RSET is calculated by adding the detection time, the notification time, the [[pre-movement time]] and the movement time.<ref name="MBIE25-26" /> The movement time in turn depends on the [[walking speed]] of the occupants and on the flow capacity of doors and stairs.<ref name="VR-7.4">Van Rossum (2027), §7.4.</ref> Because human behaviour before movement is hard to predict, and simple models assume ideal movement, a calculated RSET is best seen as a minimum time rather than a prediction of the real evacuation.<ref name="Proulx-364">Proulx (2002), p. 3-364.</ref>

== Definition and terminology ==
In New Zealand, C/VM2 (second edition, 2025) defines the RSET as the calculated time between ignition of the design fire and the moment when all occupants of a specified room or location have left it.<ref name="MBIE25-26" /> The commentary to the first edition adds that RSET is generally the time for all occupants to reach a place of safety. It can also be defined for one space, such as the room of fire origin.<ref name="MBIE13-198">Ministry of Business, Innovation and Employment (2013), p. 198.</ref> The ''Introduction to Fire Safety Engineering'' describes RSET as the time needed to leave the room or building, and stresses that its calculation rests on assumptions about how people will react.<ref name="VR-7.1" />

The International Fire Engineering Guidelines (2005) use the expansion "Required Safe Evacuation Time" for the same abbreviation.<ref name="IFEG-1.8-1">National Research Council of Canada et al. (2005), p. 1.8-1.</ref> They define it as the time from fire initiation needed for occupants to reach a place of safety, which is then compared with ASET.<ref name="IFEG-1.8-1" /><ref name="IFEG-1.8-3">National Research Council of Canada et al. (2005), p. 1.8-3.</ref> The guidelines note that the times may vary with the location of the occupants relative to the fire.<ref name="IFEG-1.8-1" />

== Components ==
Most sources split the RSET into four or five consecutive periods. C/VM2 uses a detection time, a notification time, a pre-travel activity time and a travel or flow time.<ref name="MBIE25-26" /> The Australian data sheets for the Fire Safety Verification Method use the same four parts.<ref name="ABCB-242">Australian Building Codes Board (2020a), Data Sheet D1, p. 242.</ref> Nelson and Mowrer split the time before movement into two parts: until occupants decide to act, and from that decision until evacuation starts.<ref name="NM-367" /> The International Fire Engineering Guidelines speak of a cue period, a response period, a delay period and a movement period.<ref name="IFEG-1.8-2">National Research Council of Canada et al. (2005), p. 1.8-2.</ref>

The detection time runs from ignition until an automatic system or a person detects the fire. C/VM2 requires it to be found from deterministic modelling of the detectors or sprinklers, using fixed detector properties regardless of the products to be installed.<ref name="MBIE25-26" /><ref name="MBIE25-27">Ministry of Business, Innovation and Employment (2025b), p. 27.</ref> Methods to calculate it are described under [[detector activation time]]. The notification time covers the delay between detection and the alarm reaching the occupants. C/VM2 takes it as 30 s for standard evacuation strategies, and longer where the alarm is first investigated by staff.<ref name="MBIE25-29">Ministry of Business, Innovation and Employment (2025b), p. 29.</ref>

The pre-movement time follows: the time between the alarm or a cue and the moment occupants begin to move.<ref name="VR-7.3">Van Rossum (2027), §7.3.</ref> In residential drills studied by Proulx, three-quarters of the evacuation time was spent before moving.<ref name="Proulx-348">Proulx (2002), p. 3-348.</ref> The last component is the movement time. Proulx distinguishes the time needed to go from a starting point to a destination such as a place of safety from the flow time. The flow time is the time a crowd needs to pass one element of the route, such as a door or stair.<ref name="Proulx-347">Proulx (2002), p. 3-347.</ref> The flow time follows from the number of people and the [[exit capacity]] of the usable width.<ref name="Proulx-347" />

== Calculation ==
C/VM2 (second edition, 2025) calls its standard method the simple hydraulic model for RSET.<ref name="MBIE25-26" /> The time before movement is the sum of the detection, notification and pre-travel times. The movement time is either the travel time to the exit or the flow time through the exit, whichever is greater.<ref name="MBIE25-26" />
<math display="block">\mathrm{RSET} = t_\mathrm{d} + t_\mathrm{n} + t_\mathrm{pre} + \max\left(t_\mathrm{trav},\, t_\mathrm{flow}\right)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\mathrm{RSET}</math> || required safe egress time || s
|-
| <math>t_\mathrm{d}</math> || detection time, from ignition until detection || s
|-
| <math>t_\mathrm{n}</math> || notification time, from detection until the occupants are alerted || s
|-
| <math>t_\mathrm{pre}</math> || pre-travel activity time, from notification until evacuation begins || s
|-
| <math>t_\mathrm{trav}</math> || travel time to the exit || s
|-
| <math>t_\mathrm{flow}</math> || time spent in queues, controlled by the flow capacity of the exit || s
|}

The relation applies to the occupants of one room or location. For the room of fire origin, C/VM2 assumes that the occupants are spread evenly, so that the larger of the travel and flow times governs.<ref name="MBIE25-26" /> For routes through several spaces, the analysis must cover the whole route, so that a restriction closer to the final exit is not missed.<ref name="MBIE25-33">Ministry of Business, Innovation and Employment (2025b), p. 33.</ref> The travel speed falls with crowd density and is capped at 1.2 m/s on level routes.<ref name="MBIE25-32">Ministry of Business, Innovation and Employment (2025b), p. 32.</ref> The flow through a door is calculated from its effective width and a density of 1.9 persons/m², and is limited to 50 people per minute for each self-closing door leaf.<ref name="MBIE25-33" /><ref name="MBIE25-34">Ministry of Business, Innovation and Employment (2025b), p. 34.</ref>

Like other hydraulic methods, this calculation assumes that all occupants start at the same moment and move without interruptions, and that most are free of disabilities that would slow the group.<ref name="NM-367" /> The ''Introduction to Fire Safety Engineering'' adds that a hand calculation requires a homogeneous group of people and a simple geometry.<ref name="VR-7.5">Van Rossum (2027), §7.5.</ref> Its eight-step method determines the people per space, the flow capacity of each exit, the distribution of people over the exits and the governing exit. It then adds the walking time of the first person, the flow time of the governing exit and the walking time of the last person to safety.<ref name="VR-7.5" />

== Worked example ==
The commentary to the first edition of C/VM2 calculates the RSET for a ballroom of 50 m by 20 m holding 1,000 people.<ref name="MBIE13-190">Ministry of Business, Innovation and Employment (2013), p. 190.</ref> In the sprinklered building, the design fire grows as a fast t-squared fire and is controlled by the sprinklers at a peak of 2,700 kW.<ref name="MBIE13-202">Ministry of Business, Innovation and Employment (2013), p. 202.</ref> Fire modelling shows that the smoke detectors respond after 66 s. The notification time is 30 s. Because the occupants are awake, unfamiliar with the building and alerted by a voice alarm, the pre-travel activity time is 30 s.<ref name="MBIE13-203">Ministry of Business, Innovation and Employment (2013), p. 203.</ref>

The travel time is checked first. At a density of 1 person/m², the travel speed is 1.03 m/s, and the longest route, taken as length plus width of the room, is 70 m. The travel time is therefore 68 s.<ref name="MBIE13-204">Ministry of Business, Innovation and Employment (2013), p. 204.</ref>

For the flow, each of four exit routes takes a quarter of the occupants, or 250 people.<ref name="MBIE13-204" /> A door leaf of 0.95 m has an effective width of 0.65 m. The flow equation gives about 51 people per minute, which is capped at 50, so a pair of doors passes 100 people per minute.<ref name="MBIE13-205">Ministry of Business, Innovation and Employment (2013), p. 205.</ref> The flow time of 150 s is longer than the travel time and governs:
<math display="block">\mathrm{RSET} = 66 + 30 + 30 + \max(68,\ 150) = 276\ \mathrm{s}</math>
For the people who leave through the foyer, the commentary adds another 150 s of flow time, giving 426 s.<ref name="MBIE13-206">Ministry of Business, Innovation and Employment (2013), p. 206.</ref> The modelled tenability limit for carbon monoxide was not reached within the 1,200 s simulated, so ASET exceeds RSET by more than 924 s in the ballroom.<ref name="MBIE13-206" /> The commentary notes that, strictly, the dose must be calculated at the locations of the moving occupants, which may mean using data from different rooms for different periods.<ref name="MBIE13-206" />

The ''Introduction to Fire Safety Engineering'' gives a simpler example of the movement part alone. Three hundred people are divided equally over four stairs, and the two narrowest stairs of 1.6 m govern. Each passes 1.2 persons per second, so 75 people need about 63 s.<ref name="VR-7.5" /> Adding 5 s for the first person to reach the stair and 10 s for the last person to reach safety gives a movement time of 78 s.<ref name="VR-7.5" />

== Methods ==
Escape safety can be assessed with methods of increasing complexity. The ''Introduction to Fire Safety Engineering'' lists the rules of the Dutch building regulations, a capacity model, hand calculations and evacuation simulations with programs such as Simulex, buildingEXODUS and Pathfinder.<ref name="VR-7.5" /> The more complex the building, the more detailed the model needs to be, and a simple method can check a complex one.<ref name="VR-7.5" />

[[Evacuation modelling]] with computer software rebuilds the geometry in three dimensions and fills it with people, often with several occupant profiles.<ref name="VR-10.1">Van Rossum (2027), §10.1.</ref> Its output includes the total evacuation time, queues, densities and bottlenecks, which can be used directly in an ASET/RSET comparison.<ref name="VR-10.1" /> Its main limitation is human behaviour. However convincing the output looks, it reflects the choices made by the modeller, such as which exit people use.<ref name="VR-10.2">Van Rossum (2027), §10.2.</ref> The International Fire Engineering Guidelines likewise warn that hydraulic and network models may give shorter times than real evacuations, because they leave out occupant behaviour.<ref name="IFEG-2.8-3">National Research Council of Canada et al. (2005), p. 2.8-3.</ref><ref name="IFEG-2.8-4">National Research Council of Canada et al. (2005), p. 2.8-4.</ref>

Nelson and Mowrer call the result of a hydraulic calculation the modelled evacuation time. The actual time will generally be longer.<ref name="NM-368">Nelson and Mowrer (2002), p. 3-368.</ref> They express the difference as an apparent evacuation efficiency. It covers delays caused by wardens, stops and restarts where flows merge, individual delays and unbalanced use of exits.<ref name="NM-368" /> Proulx therefore stresses that such calculations give only minimum evacuation times. Some consultants have wrongly presented them as maximum times.<ref name="Proulx-363">Proulx (2002), p. 3-363.</ref><ref name="Proulx-364" />

== RSET for different locations ==
An RSET is not a single number for a whole building. The International Fire Engineering Guidelines recommend carrying out the analysis for each enclosure, such as a room or a mall, or for groups of enclosures such as a floor or the whole building.<ref name="IFEG-1.8-7">National Research Council of Canada et al. (2005), p. 1.8-7.</ref> The analysis is repeated for each design occupant group defined in the fire engineering brief.<ref name="IFEG-1.8-4">National Research Council of Canada et al. (2005), p. 1.8-4.</ref> Occupants far from the fire usually receive fewer cues and therefore get longer pre-movement times than those in the room of fire origin.<ref name="MBIE25-31" />

In New Zealand, the challenging fire scenario of C/VM2 (second edition, 2025) places design fires in various locations and requires ASET to exceed RSET for each of them.<ref name="MBIE25-56">Ministry of Business, Innovation and Employment (2025b), p. 56.</ref> For some smaller rooms, tenability need not be shown for the occupants of the room of fire origin. This applies, for example, to rooms under 500 m² with fewer than 150 occupants and more than one direction of travel.<ref name="MBIE25-56" /> It must still be shown that a fire in such a room does not threaten the occupants in the rest of the building.<ref name="MBIE25-56" /> Tenability is then assessed in the escape routes over the time occupants need to escape, and at the locations of the occupants throughout the evacuation.<ref name="MBIE25-57">Ministry of Business, Innovation and Employment (2025b), p. 57.</ref>

Evacuation strategies also change the RSET from place to place. Where a building uses a phased evacuation, the alarm may sound later in some areas. The Australian data sheets require such delays to be included in the notification time for those areas.<ref name="ABCB-243">Australian Building Codes Board (2020a), Data Sheet D1, p. 243.</ref> In the commentary example above, the occupants who leave the ballroom through the foyer have a longer RSET than those who leave directly outside, because they pass two sets of doors.<ref name="MBIE13-205" /><ref name="MBIE13-206" />

== Comparison with ASET and safety margins ==
Because many inputs for both ASET and RSET are uncertain, a safety margin is important.<ref name="VR-7.1" /> The ''Introduction to Fire Safety Engineering'' gives two common forms: ASET at least equal to a safety factor times RSET, or ASET minus RSET at least equal to a margin.<ref name="VR-7.1" /> The more reliable the inputs, the smaller the margin needed, and a sensitivity analysis can show whether the margin is sufficient.<ref name="VR-7.1" />

In the Netherlands, the standards for large fire compartments, NEN 6060 and NEN 6079, include an ASET/RSET comparison with safety factors.<ref name="VR-7.1" /> For new buildings assessed with the rule-of-thumb method and conservative inputs, the factor is 1.5 when RSET is up to 3 minutes and 2.0 when it is longer.<ref name="VR-7.1" /> With nominal inputs, the factors are 2.0 and 2.5. Existing buildings have lower factors, between 1.0 and 1.5.<ref name="VR-7.1" /> Proulx suggests that, in a conservative approach, the time available should be at least twice the time required.<ref name="Proulx-363" />

Other frameworks compare designs rather than set a fixed factor. In Australia, the Fire Safety Verification Method expects the margin of safety, ASET minus RSET, of a proposed performance solution to be at least that of a reference building.<ref name="ABCB-241">Australian Building Codes Board (2020a), Data Sheet D1, p. 241.</ref> In New Zealand, C/VM2 (second edition, 2025) notes that its design fires leave out the incipient phase of a fire, which provides an inherent safety factor for its pre-travel activity times.<ref name="MBIE25-31">Ministry of Business, Innovation and Employment (2025b), p. 31.</ref>

== Limits and uncertainty ==
The largest uncertainty usually lies in the time before movement. Human behaviour is one of the least predictable aspects of fire safety, and the data available have not led to generally valid models for pre-evacuation times.<ref name="VR-7.3" /> The movement part can also be slower than design values suggest. In the first World Trade Center tower in 2001, the median occupant moved down the stairs at about 0.2 m/s, including all interruptions. This is at the slow end of the published values.<ref name="Averill-129">Averill et al. (2005), p. 129.</ref> The flow from the stairs was about 0.5 people per second per door, roughly half the common rule of thumb.<ref name="Averill-130">Averill et al. (2005), p. 130.</ref>

A single RSET also hides the spread between occupants. The Australian data sheets recommend evaluating several scenarios to reflect the different responses of occupant groups and individuals.<ref name="ABCB-241" /> The International Fire Engineering Guidelines list ways to shorten RSET. These include additional and less ambiguous cues, trained personnel, better signage and improved design of escape routes.<ref name="IFEG-1.8-13">National Research Council of Canada et al. (2005), p. 1.8-13.</ref>

== See also ==
* [[Evacuation]]
* [[Occupant load]]
* [[Hydraulic evacuation model]]

== 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.
* 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.
* Nelson, H. E., & Mowrer, F. W. (2002). Emergency movement. 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. 3-367–3-380). 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.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Human Behaviour & Evacuation]]

Premixed flame

2026-11-01T22:55:53Z

Daan: New FSE wiki article: Premixed flame (written by Claude Opus 5.5)

A '''premixed flame''' is a [[flame]] in which the fuel gas and the air, or another oxidant, are mixed before the mixture reaches the flame and is ignited.<ref name="VR-4.3">Van Rossum (2027), §4.3.</ref><ref name="TI-1-86">Tien et al. (2002), p. 1-86.</ref> A gas cooker, a Bunsen burner and the cylinder of a petrol engine burn premixed flames.<ref name="VR-4.3" /><ref name="IS-3-12">Iqbal and Salley (2004), p. 3-12.</ref> Because fuel and oxygen are already mixed, the flame does not have to wait for them to meet.<ref name="TI-1-86" /> It moves into the unburnt mixture at a characteristic speed, the burning velocity.<ref name="SI-1-144">Simmons (2002), p. 1-144.</ref>

Most unwanted fires burn as [[diffusion flame|diffusion flames]], in which fuel and air only mix at the flame.<ref name="IS-3-12" /> Premixed flames still matter in fire safety engineering. They govern the ignition of flammable vapours above a liquid or a heated solid, gas and dust explosions, backdrafts and smoke gas explosions.<ref name="SI-1-147">Simmons (2002), p. 1-147.</ref><ref name="IS-15-4">Iqbal and Salley (2004), p. 15-4.</ref><ref name="VR-4.10">Van Rossum (2027), §4.10.</ref> A premixed flame can only exist between the [[flammability limits]] of the mixture.<ref name="BE-2-172">Beyler (2002b), p. 2-172.</ref> In a closed space, it can raise the pressure to about seven to nine times the initial value.<ref name="SI-1-147" /><ref name="ZA-3-407">Zalosh (2002), p. 3-407.</ref>

== Definition and comparison with diffusion flames ==
Flames are the visible part of a combustion process, in which gaseous fuel reacts with oxygen. The fuel gas is either premixed with air at the source, or it mixes with air at the flame by diffusion or turbulence.<ref name="VR-4.3" /> ''Introduction to Fire Safety Engineering'' defines the premixed flame as a flame whose air and fuel mixture is already mixed before it is ignited.<ref name="VR-4.3" /> NUREG-1805 describes a flame in which oxygen is mixed with the combustible gas by a mechanical device before combustion.<ref name="IS-3-10">Iqbal and Salley (2004), p. 3-10.</ref>

The difference from a diffusion flame can be expressed in time scales. In a premixed flame, fuel and oxygen are mixed before they reach the combustion zone, so the times for transport and for reaction are of similar size.<ref name="TI-1-86" /> In a diffusion flame, transporting fuel and oxygen to the reaction zone takes much longer than the chemical reaction itself.<ref name="TI-1-86" /> A premixed flame can therefore travel through a flammable mixture on its own.<ref name="SI-1-146" /> A diffusion flame, by contrast, stays in the zone where fuel and oxygen meet from opposite sides.<ref name="IS-3-10" />

Turbulent premixed flames occur mostly in engineered combustion systems. Examples are boilers, furnaces, process heaters, gas burners, oxyacetylene torches, petrol engines and domestic gas cookers.<ref name="IS-3-12" /> In such a burner, air or pure oxygen is mixed with the gas at the base, so that the fuel is consumed almost instantly at the mouth of the burner.<ref name="IS-3-9">Iqbal and Salley (2004), p. 3-9.</ref> The hottest part of a Bunsen burner flame reaches about 1,600 °C. An oxyacetylene cutting torch reaches about 3,500 °C, because of its higher oxygen content.<ref name="IS-3-9" />

The two flame types also occur together. If the gas mixture in a Bunsen burner contains too little oxygen to burn all of the fuel, the outer sheath of the flame is essentially a diffusion flame.<ref name="SI-1-144" /> Conversely, a jet of fuel gas burning as a diffusion flame is anchored by a small pocket of premixed gas just above the burner rim.<ref name="SI-1-151">Simmons (2002), p. 1-151.</ref>

== Structure of a premixed flame ==
A Bunsen burner flame has a luminous inner cone, surrounded by an outer sheath of hot combustion gases.<ref name="SI-1-144" /> The inner cone marks the end of the primary reaction zone, where a fast oxidation reaction takes place and the temperature rises very rapidly.<ref name="SI-1-144" /> In a lean mixture, the outer sheath is indistinct, because the mixture already contains enough oxygen to burn the fuel completely.<ref name="SI-1-144" />

Measurements through a flat laminar flame show several distinct zones. In the preheating zone, the gas is heated by conduction from the hotter parts of the flame. Chemical reaction does not start until the temperature reaches about 700 K.<ref name="SI-1-148">Simmons (2002), p. 1-148.</ref> In the primary reaction zone, free radicals diffusing back from the hot gas attack the fuel molecules. A rapid build-up of radicals then produces the luminous flame front.<ref name="SI-1-148" /><ref name="SI-1-150">Simmons (2002), p. 1-150.</ref> In the secondary reaction zone, most of the carbon monoxide is converted to carbon dioxide and the temperature rises further, more slowly, to its final value.<ref name="SI-1-150" />

The highest temperature is usually reached a little downstream of the inner cone. In a large flame, the calculated adiabatic flame temperature is nearly reached in the middle of the gas stream.<ref name="SI-1-144" /> In a burner flame of 7.5 % natural gas in air, the highest measured temperature contour is 1,755 °C.<ref name="SI-1-145">Simmons (2002), p. 1-145.</ref> Small premixed flames and turbulent flames of all kinds normally fall short of the adiabatic value, because they lose appreciable heat.<ref name="SI-1-145" />

The chemistry is complex. Detailed calculations of a one-dimensional laminar flame typically involve more than 120 elementary reaction steps, even for simple hydrocarbon fuels.<ref name="SI-1-150" /> For engineering use, such schemes are reduced to a few global steps. A three-step mechanism, for example, represents a stoichiometric methane and air flame well.<ref name="SI-1-150" />

== Burning velocity ==
The key property of a premixed flame is its burning velocity. Simmons defines it as the velocity with which a premixed flame moves, normal to its surface, through the adjacent unburnt mixture.<ref name="SI-1-144" /> A flat flame on a burner is only stable when the flow velocity of the incoming mixture equals the burning velocity. If the flow is too fast, the flame is blown off; if it is too slow, the flame flashes back into the burner.<ref name="SI-1-144" /> A conical flame, like that of a Bunsen burner, is stable over a much wider range of flows. The area of its cone adjusts to keep the burning velocity and the flow velocity normal to the flame front in balance.<ref name="SI-1-144" />

The burning velocity depends on the fuel, the oxidant and the composition of the mixture. All saturated hydrocarbons have about the same maximum burning velocity in air.<ref name="SI-1-146">Simmons (2002), p. 1-146.</ref> For propane and air, most measured maximum values lie at 41 ± 2 cm/s.<ref name="SI-1-146" /> Hydrogen and acetylene burn much faster. Burning in pure oxygen is faster still, for example 360 cm/s for propane instead of 41 cm/s in air.<ref name="SI-1-146" />

{| class="wikitable"
|+ Maximum laminar burning velocities at room temperature and atmospheric pressure<ref name="SI-1-146" />
! Mixture !! Maximum burning velocity (cm/s)
|-
| Propane and air || 41
|-
| Ethene and air || 68
|-
| Acetylene and air || 175
|-
| Hydrogen and air || 320
|-
| Propane and oxygen || 360
|-
| Acetylene and oxygen || 1,120
|-
| Hydrogen and oxygen || 1,180
|}

Zalosh lists slightly different laminar burning velocities in air, for example 40 cm/s for methane, 46 cm/s for propane, 166 cm/s for acetylene and 312 cm/s for hydrogen.<ref name="ZA-3-407" /> Hotter flames burn faster. Raising the initial temperature of a propane and air mixture from 300 to 480 K doubles its maximum burning velocity.<ref name="SI-1-146" /> Inert gases such as nitrogen, argon and carbon dioxide lower the flame temperature. If the burning velocity falls far enough, the flame is extinguished.<ref name="SI-1-150" />

Turbulence increases the speed of a premixed flame. In laminar flow, the flame front is sharply defined. At higher Reynolds numbers it becomes a blurred "brush", because local velocity fluctuations wrinkle the front and increase its area.<ref name="SI-1-146" /> Flow in a tube is always laminar below a Reynolds number of 2,300 and usually turbulent above 3,200. For propane, ethene and acetylene flames, the burning velocity roughly doubles at a Reynolds number of 40,000. Theory suggests an increase of up to five times in very intense turbulence.<ref name="SI-1-146" />

== Flame propagation in ducts and enclosures ==
When the flow is too slow to hold a stationary flame, a premixed flame travels through the mixture, provided that its composition lies within the limits of flammability.<ref name="SI-1-146" /> In a duct, the area of the flame front is larger than the cross-section of the duct. The visible flame therefore moves faster than the burning velocity.<ref name="SI-1-147" /> Simmons relates the two through the ratio of the areas:<ref name="SI-1-147" />

<math display="block">V = \frac{S_u \, A_f}{A_d}</math>

{| class="wikitable"
|+ Symbols in the flame speed relation
! Symbol !! Description !! Unit
|-
| <math>V</math> || linear speed of the flame along the duct || m/s
|-
| <math>S_u</math> || burning velocity of the mixture || m/s
|-
| <math>A_f</math> || area of the flame front || m²
|-
| <math>A_d</math> || cross-sectional area of the duct || m²
|}

The relation applies to a flame that moves along a duct away from an open end at a fairly uniform speed. The flame front area is always larger than the duct section, typically by a factor of two or three.<ref name="SI-1-147" /> For a propane and air mixture with a burning velocity of 0.41 m/s, the flame therefore moves along the duct at about 0.41 × 2 = 0.82 m/s to 0.41 × 3 = 1.2 m/s.<ref name="SI-1-146" /><ref name="SI-1-147" /> For hydrogen and air, at 3.2 m/s, the same factors give about 6.4 to 9.6 m/s. Simmons stresses that this difference between flame speed and burning velocity matters in the design of automatic protection.<ref name="SI-1-147" />

If the hot products cannot escape, they push the flame and the unburnt gas forward with increasing speed. This creates turbulence ahead of the flame, which increases the burning velocity further.<ref name="SI-1-147" /> In a long duct the flame front can then act as an accelerating piston. A shock wave forms, and the flame becomes a detonation that travels at 1,500 to 3,000 m/s.<ref name="SI-1-147" /> Behind a detonation, the pressure can reach 20 bar for gases initially at atmospheric pressure, and up to 100 bar where it is reflected from the end of the duct.<ref name="SI-1-147" />

A premixed flame that propagates more slowly than sound is called a [[deflagration]]. NUREG-1805 gives the speed of sound in air at 20 °C, about 330 m/s, as the upper bound for a deflagration and about 2,000 m/s for a detonation.<ref name="IS-15-3">Iqbal and Salley (2004), p. 15-3.</ref> A flame can also be quenched. If it tries to pass through a gap that is too small, heat loss to the walls and the removal of free radicals stop it. Flame traps use this effect.<ref name="SI-1-147" />

== Premixed flames in fires and explosions ==
Even fires that later burn as diffusion flames usually begin with a premixed flame. Simmons notes that the initial ignition of a liquid or solid fuel involves a mixture of fuel vapour and air in the boundary layer above its surface.<ref name="SI-1-147" /> The flash point of a liquid is the temperature at which its vapour pressure just gives a lean limit mixture with air. A somewhat higher temperature, the fire point, is needed before the fuel keeps burning.<ref name="SI-1-147" />

Premixed burning is the mechanism behind gas and vapour [[explosion|explosions]]. Combustible gases, vapours and dusts present an explosion hazard when they are mixed with air in proportions between the lower and upper flammable limits.<ref name="ZA-3-402">Zalosh (2002), p. 3-402.</ref> The hazard lies in the premixing of fuel and oxidant in a confined space before an ignition source appears. On ignition, the flame spreads through the mixture, and the confinement prevents the free expansion of the hot products.<ref name="ZA-3-402" /> NUREG-1805 names three conditions that must exist together: a flammable mixture, a means of ignition and an enclosure.<ref name="IS-15-3" />

The resulting pressure follows from the temperature rise of the gas. A stoichiometric hydrocarbon and air mixture at 300 K has an adiabatic flame temperature of about 2,200 K. In a closed vessel, the pressure can therefore reach a little over 7 bar.<ref name="SI-1-147" /> Heat losses to the walls make the real maximum somewhat lower, but a vessel that was not designed for such pressures will rupture. Connected vessels are worse, because burning in the first vessel raises the pressure in the second before the flame arrives there.<ref name="SI-1-147" />

Zalosh obtains the pressure rise from the ideal gas law. The ratio of final to initial pressure equals the ratio of the number of moles times the absolute temperature after and before the deflagration.<ref name="ZA-3-406">Zalosh (2002), p. 3-406.</ref> The [[stoichiometry]] of the mixture matters, but the worst case lies slightly on the rich side. Calculated maximum pressures occur at equivalence ratios of 1.1 to 1.2 and reach 8 to 9.6 atm.<ref name="ZA-3-406" />

Near the flammability limits, measured pressures are much lower than calculated ones.<ref name="ZA-3-406" /> The flame may burn only part of the mixture, and slow flames lose heat to the walls.<ref name="ZA-3-407" /> In lean hydrogen and air mixtures, for example, the burnt fraction of the hydrogen rises from zero at 4 % to almost one at 8 % hydrogen.<ref name="ZA-3-407" /> Measured maximum explosion pressures of most gases and vapours lie between 6.8 and 8.1 bar above atmospheric pressure. Acetylene, at 10.6 bar, and ammonia, at 5.4 bar, are the exceptions.<ref name="ZA-3-407" />

{| class="wikitable"
|+ Deflagration data for selected gases in air<ref name="ZA-3-407" />
! Gas !! Maximum pressure (bar g) !! Laminar burning velocity (cm/s)
|-
| Methane || 7.1 || 40
|-
| Propane || 7.9 || 46
|-
| n-Butane || 8.0 || 45
|-
| Hydrogen || 6.8 || 312
|-
| Acetylene || 10.6 || 166
|}

Fires can create premixed mixtures of their own. A backdraft occurs when fresh air enters a closed, oxygen-starved fire room and mixes with the accumulated fuel-rich smoke. NUREG-1805 notes that it has the characteristics of a premixed fuel and air deflagration.<ref name="IS-15-4" /> ''Introduction to Fire Safety Engineering'' describes the smoke gas explosion in the same way. A typical condition is that air and pyrolysis gases are reasonably premixed and lie between the lower and upper explosion limits.<ref name="VR-4.10" />

== Limits of flammability and stability ==
A stable premixed flame can only be obtained over a limited range of mixture compositions and flow rates.<ref name="SI-1-144" /> The composition limits are the lower and upper flammable limits. Methane in air, for example, can carry a flame between 5 and 15 % by volume at normal temperature and pressure.<ref name="BE-2-172" /> At the lower limit, the calculated adiabatic flame temperature of most fuels containing only carbon, hydrogen and oxygen is about 1,600 K.<ref name="BE-2-177">Beyler (2002b), p. 2-177.</ref> The limits are measured for upward flame propagation in a tube about 1 m long and 5 cm wide, because this gives the widest range.<ref name="SI-1-146" />

The limits widen as the temperature of the mixture rises.<ref name="SI-1-147" /> Adding inert gas narrows them. For propane, the oxygen content of an air and nitrogen mixture must fall below 12 % before no mixture with propane can burn.<ref name="SI-1-150" /> Bromine compounds act differently: they are chemical inhibitors, and even traces markedly reduce the burning velocity of a premixed flame.<ref name="SI-1-151" /> Very rich premixed flames, like diffusion flames, can also form soot.<ref name="IS-F-55">Iqbal and Salley (2004), p. F-55.</ref>

== See also ==
* [[Smoke explosion]]
* [[Adiabatic flame temperature]]
* [[Equivalence ratio]]
* [[Flame extinction]]

== Notes ==
<references />

== References ==
* 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.
* 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.
* 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.
* Tien, C. L., Lee, K. Y., & Stretton, A. J. (2002). Radiation heat transfer. 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. 1-73–1-89). National Fire Protection Association; Society of Fire Protection Engineers.
* 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]]

Structural design for fire

2026-11-01T22:55:47Z

Daan: Redirect to Structural fire engineering (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Structural fire engineering]]

Post-flashover

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Daan: Redirect to Post-flashover fire (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Post-flashover fire]]

Burning brands

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Daan: Redirect to Firebrands (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Firebrands]]

Aqueous film-forming foam (AFFF)

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Daan: Redirect to Aqueous film-forming foam (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Aqueous film-forming foam]]

Toxicity of combustion products

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#REDIRECT [[Fire toxicity]]

Dry riser

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#REDIRECT [[Dry and wet risers]]

Ethics in fire safety engineering

2026-11-01T22:55:10Z

Daan: FSE wiki: Split one sentence in the lead that exceeded the style limit of 35 words (written by Claude Opus 5.5)

'''Ethics in fire safety engineering''' concerns the right conduct of engineers who design and assess fire safety: acting with integrity, working within their competence and being open about assumptions and uncertainty. Ethics is the branch of philosophy that reflects critically on right action. It seeks criteria for judging whether an action is good or wrong and for weighing its motives and consequences.<ref name="VR2">Van Rossum (2027), §2.</ref> In fire safety, integrity matters because a wrong decision can cost lives, while clients and employers may create incentives that tempt an engineer to act otherwise.<ref name="VR2" />

The issue is sharper in [[fire safety engineering]] than in rule-based design. A performance-based justification can be so complex that the authority reviewing it cannot check it, and must then rely on the integrity of the engineer.<ref name="VR2.1">Van Rossum (2027), §2.1.</ref> Guidance in several countries responds by setting requirements for competence and by providing for independent review. The Australian Fire Safety Verification Method, for example, may only be used by fire safety engineers with demonstrated competency. The need for a peer review must be considered at the design brief stage of each project.<ref name="FSVM5">Australian Building Codes Board (2022), p. 5.</ref><ref name="FSVM6">Australian Building Codes Board (2022), p. 6.</ref>

== Why ethics matters in fire safety engineering ==
In a prescriptive approach, the reviewing authority checks a design against fixed rules, which is relatively easy. In a scientific approach such as fire safety engineering, the justification provided by the applicant may be so complex that the authority cannot verify it, or can do so only with difficulty.<ref name="VR2.1" /> ''Introduction to Fire Safety Engineering'' gives computational fluid dynamics (CFD) as an example. Understanding how CFD works requires long scientific training and frequent use, and a reviewing authority seldom employs a CFD specialist.<ref name="VR2.1" /> The boundary conditions and assumptions of a simulation are then often unknown to the reviewer, although checking exactly these is important.<ref name="VR2.1" />

Where a design cannot be checked, the authority has to rely on the integrity of the fire safety engineer. A counter-expertise by a second engineer is possible, but it is not economically feasible for every project.<ref name="VR2.1" /> The book recommends one where there are good reasons, for example when results are unexpected or when the engineer is new and has no reputation yet.<ref name="VR2.1" />

The same point is made by the developers of fire models. The technical guides of CFAST and the Fire Dynamics Simulator (FDS) state that users bear sole responsibility for judging whether the model suits an application and for the conclusions they draw. The models are intended only for people competent in fluid dynamics, thermodynamics, heat transfer, combustion and fire science.<ref name="CFASTix">Peacock et al. (2026), p. ix.</ref><ref name="FDSvii">McGrattan et al. (2026), p. vii.</ref> A model "may or may not have predictive capability" in a particular case, and all results should be evaluated by an informed user.<ref name="CFASTix" />

== Interests and incentives ==
Almost every party in a building project has an economic interest in the outcome of a fire safety analysis. ''Introduction to Fire Safety Engineering'' lists what a client may gain: a permit, and savings on construction through cheaper building methods or materials, a lower level of fire protection installations or dropping costly measures.<ref name="VR2.2">Van Rossum (2027), §2.2.</ref> In a tender, the contractor bidding for the work also has an interest. An engineer employed by a firm may find that the employer favours certain outcomes for the same reasons, and in a government body the pressure may be political.<ref name="VR2.2" />

Giving in to these interests can bring short-term advantages, such as a follow-up commission, a bribe or faster promotion. Resisting them can mean that a career stalls or, in the worst case, that the engineer is pushed out or dismissed.<ref name="VR2.2" /> The book therefore treats integrity as a responsibility that remains even when nobody else can see that advice has been bent.<ref name="VR2.5">Van Rossum (2027), §2.5.</ref>

Watts and Hall describe the same tension in terms of values. Accepting a level of risk requires a value judgement, and technical experts, ordinary citizens, enforcing authorities and managers judge differently.<ref name="WH5-1">Watts and Hall (2002), pp. 5-1–5-2.</ref> An engineer performing a fire risk analysis usually works for a client, but cannot base the analysis on the values of that client alone. The analysis must address both the client's values and the values of society.<ref name="WH5-2">Watts and Hall (2002), p. 5-2.</ref>

Enforcing authorities are often seen as the interpreters and guardians of those societal values.<ref name="WH5-2" /> Because they bear neither the costs nor the benefits of their decisions, they must also ask when it is acceptable to dictate safety choices to people. Examples are whether it is fair to require sprinklers in all homes, how costs should be shared and who is responsible for the reliability of the systems.<ref name="WH5-2" />

== Competence ==
Competence is the second pillar of professional ethics. ''Introduction to Fire Safety Engineering'' notes that in the Netherlands there are few mechanisms to assure the knowledge and skill of practitioners. There is no degree programme in fire safety in higher education and no established set of competences for the profession, so anyone can call themselves a fire safety adviser.<ref name="VR2.3">Van Rossum (2027), §2.3.</ref> It is therefore the engineer's own responsibility to be competent for the work.

Clients can help by asking for a CV with reference projects, which is usual on large, complex projects.<ref name="VR2.3" /> According to the book, an active role in fire safety engineering needs a higher technical education. People with secondary vocational training can still build the skills needed to check such analyses.<ref name="VR2.3" />

The book warns against overconfidence and names the Dunning–Kruger effect. People who are incompetent at a task tend to overestimate their performance, because their incompetence keeps them from seeing their own errors.<ref name="VR2.4">Van Rossum (2027), §2.4.</ref> The author, in the field since 2001, writes that further study has mainly shown him how much he does not yet know. He also reports meeting practitioners who gave themselves specialist titles after a course of three to five days.<ref name="VR2.4" /> For CFD in particular, the book advises a university background in physics or a related field and much practical experience. It refers back to its chapter on ethics for this point.<ref name="VR11.4">Van Rossum (2027), §11.4.</ref>

Other countries set formal requirements. In Australia, the Fire Safety Verification Method (FSVM) Standard 2022 states that the method may only be used by fire safety engineers who are suitably qualified and experienced. They must have demonstrated competency in fire safety engineering, be proficient in fire modelling methods and be familiar with fire testing and the validation of computational data.<ref name="FSVM5" /> In New Zealand, C/VM2 (second edition, 2025) is intended for professional fire engineers proficient in modelling methods, who are expected to apply appropriate judgement to model inputs and results.<ref name="VM2-7">Ministry of Business, Innovation and Employment (2025b), p. 7.</ref>

The FSVM handbook adds that some jurisdictions register fire safety engineers. National registers recognised in some jurisdictions serve as evidence of suitable qualification and experience.<ref name="HB6">Australian Building Codes Board (2020b), pp. 6–7.</ref> The Australian part of the ''International Fire Engineering Guidelines'' presupposes a level of competence and experience that would enable accreditation by an appropriate body.<ref name="IFEG013">National Research Council of Canada et al. (2005), p. 0.1-3 (Part 0, Australia).</ref>

== Honesty about assumptions and uncertainty ==
A fire safety engineering analysis rests on many assumptions, and ethical practice means making them visible. Notarianni writes that it is important to identify where value judgements enter a performance-based calculation. Assumptions about values, and their effect on the final design, should be made explicit.<ref name="No5-46">Notarianni (2002), p. 5-46.</ref> Decisions that would change if a value, attitude or risk perception changed must be explicit in the design, and agreement on them by all stakeholders is critical.<ref name="No5-46" /> This is a core requirement of [[performance-based design]].

Equivalence is a typical example. One person may consider non-combustible construction equivalent to a sprinkler system because both give enough time to leave the building. Another may disagree because the sprinkler system is less reliable.<ref name="No5-46" /> Designs may be equivalent for life safety but not for property protection or business interruption, so the assumptions behind an equivalence must be stated.<ref name="No5-46" />

In the Netherlands, the regulations do not say how safe is safe enough. Their limits apply to measures, such as travel distances, rather than to goals. Per hour of stay, for example, the risk of dying in a fire is much higher in a residential building than in an assembly building, yet detection requirements are stricter for assembly buildings. The acceptable residual risk must therefore be agreed in advance, for example by comparison with a reference design that meets the rules.<ref name="VR1.2">Van Rossum (2027), §1.2.</ref>

Uncertainty raises similar questions. Notarianni notes that [[uncertainty analysis]] is an uncomfortable topic for many stakeholders. One fear is that it would show that predictions of heat and toxic products are not accurate enough to judge a design with high confidence.<ref name="No5-44">Notarianni (2002), p. 5-44.</ref> She also warns that assumptions meant to be conservative may not be, for example when the reaction time of a resident is set equal to a travel time.<ref name="No5-44" /> ''Introduction to Fire Safety Engineering'' warns against false precision: an available escape time given as 187.4 s suggests an accuracy that the calculation cannot deliver. Two or at most three significant figures are realistic, and results compared with limits should be rounded to the safe side.<ref name="VR1.7">Van Rossum (2027), §1.7.</ref>

Models must also be fit for their use. Cox and Kumar note that the test cases supplied with commercial CFD software validate the technology in general terms only. The responsibility for ensuring validity for a fire application rests with the fire community.<ref name="CK3-203">Cox and Kumar (2002), p. 3-203.</ref> [[Verification and validation]] of models is one way to meet this responsibility. In the United States, the standard NFPA 805 for nuclear power plants requires that fire models are verified and validated and acceptable to the authority having jurisdiction.<ref name="NUREGxv">Najafi et al. (2007), p. xv.</ref>

== Review and independence ==
Independent review is the main safeguard against both error and undue influence. ''Introduction to Fire Safety Engineering'' advises engineers to have their work checked by colleagues.<ref name="VR2.5" /> In Australia, the FSVM Standard 2022 requires the design team to consider at the brief stage whether an independent fire safety engineer should review some or all of the proposed solutions. Where full agreement cannot be reached, dissenting views must be recorded and carried through the approval process.<ref name="FSVM6" />

Independence must be protected. The FSVM handbook states that the approving authority should not take part in design decisions for matters under its jurisdiction. Doing so creates a conflict, or a perceived conflict, of interest, because the authority must be independent and act in the public interest.<ref name="HB38">Australian Building Codes Board (2020b), p. 38.</ref> The same applies to a peer reviewer, who should not be involved in design decisions.<ref name="HB40">Australian Building Codes Board (2020b), p. 40.</ref>

The Australian part of the IFEG describes the attitude expected of a third party reviewer. The review should be constructive and help the authority approve a design, and it may help the engineer to justify expert judgement properly.<ref name="IFEG037">National Research Council of Canada et al. (2005), pp. 0.3-7–0.3-8 (Part 0, Australia).</ref> Professional detachment, flexibility and an open mind are essential. The reviewer must be independent of the project, keep the documents confidential and carry out check calculations where appropriate.<ref name="IFEG037" /> The conclusions of the review should be documented. Assertions and assumptions must be substantiated and referenced, and the remedial actions needed must be clearly identified.<ref name="IFEG037" />

The investigation of the World Trade Center disaster shows why a documented basis matters. NIST found no technical basis for the choice of the sprayed fire-resistive material used on the long-span floor trusses of the towers, or for its thickness.<ref name="NIST197">National Institute of Standards and Technology (2005), p. 197.</ref> The same report notes that, from 1993, new or modified fire safety systems in the towers required third-party review by a licensed architect or engineer.<ref name="NIST197" />

== Responsibilities of the engineer ==
''Introduction to Fire Safety Engineering'' sums up the responsibility of the fire safety engineer as giving advice that is both competent and honest. This applies despite the incentives and despite the fact that others cannot see whether advice has been compromised.<ref name="VR2.5" /> Dishonest advice may bring short-term gains but disastrous consequences if it leads to casualties. In the Netherlands, an adviser can be prosecuted if an investigation after a fire shows that the advice was demonstrably wrong by the standards of knowledge that could be expected at the time.<ref name="VR2.5" /> There is also the risk of damage to professional reputation.<ref name="VR2.5" />

The point is not limited to fire safety. Writing on structural engineering in the SFPE Handbook, Fitzgerald notes that safety is a major part of the professional responsibility.<ref name="Fi1-132">Fitzgerald (2002), p. 1-132.</ref> Because professionals do not know everything and mistakes remain human, the book recommends five habits. Engineers should dare to question their own knowledge and skill, and have their work checked by peers. They should also join professional associations to exchange knowledge, follow regular training and keep up with publications.<ref name="VR2.5" />

Professional societies such as the Society of Fire Protection Engineers ([[SFPE]]) publish engineering guidance. The Australian part of the IFEG, for example, lists the SFPE engineering guide to performance-based fire protection among its reference documents.<ref name="IFEG013" /> The SFPE Handbook is also one of the main sources of the calculation methods in the Fire Dynamics Tools of the US Nuclear Regulatory Commission.<ref name="IS-iii">Iqbal and Salley (2004), p. iii.</ref>

== See also ==
* [[Prescriptive design]]
* [[Building regulations]]
* [[Acceptance criteria]]
* [[Equivalency]]
* [[Qualitative design review]]

== 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''.
* 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.
* Fitzgerald, R. W. (2002). Structural mechanics. 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. 1-132–1-143). 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.
* 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.).
* Najafi, B., Joglar, F., & Dreisbach, J. (2007). ''Verification and validation of selected fire models for nuclear power plant applications: Vol. 1. Main report'' (NUREG-1824; EPRI 1011999). U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research; Electric Power Research Institute.
* 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.
* 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
* 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]]

Structural fire engineering

2026-11-01T22:55:04Z

Daan: New FSE wiki article: Structural fire engineering (written by Claude Opus 5.5)

'''Structural fire engineering''' is the part of fire safety engineering that predicts how a load-bearing structure behaves in a fire and designs it so that it does not collapse too early. The analysis has three parts: the fire exposure, the transfer of heat into the structural members, and the structural response of those members at high temperature.<ref name="Milke-4-209">Milke (2002a), p. 4-209.</ref><ref name="ABCB-B3-30">Australian Building Codes Board (2020a), Data Sheet B3, p. 30.</ref> Traditionally, the [[fire resistance]] of a member was found by testing it in a furnace for a set duration. Calculation methods were developed because tests are slow and expensive, and because old materials may no longer be available for testing.<ref name="Milke-4-209" />

Structural design for fire is conceptually similar to normal structural design, but with important differences. The applied loads are usually lower and the strength of materials is reduced. Cross-sections may become smaller through charring or spalling, and forces from thermal expansion must be considered.<ref name="IFEG-2.6-6">National Research Council of Canada et al. (2005), p. 2.6-6.</ref><ref name="IFEG-2.6-7">National Research Council of Canada et al. (2005), p. 2.6-7.</ref> Fire engineers usually predict the thermal effects of a fire, while structural engineers analyse how the structure responds.<ref name="IFEG-2.6-7" /> The collapse of World Trade Center 7 showed that thermal expansion can cause failure at temperatures well below those used to set conventional fire resistance ratings.<ref name="NCSTAR1A-xxxvi">National Institute of Standards and Technology (2008), p. xxxvi.</ref>

== Aims and scope ==
The basic aim is that building elements achieve the level of fire resistance that the design requires.<ref name="IFEG-2.6-6" /> ''Introduction to Fire Safety Engineering'' lists the preservation of the load-bearing structure as one of the sub-goals of the Dutch building regulations.<ref name="VR-1.2">Van Rossum (2027), §1.2.</ref> The limit state is reached when the load-bearing capacity of an element, frame or assembly falls below the dead load and other loads applied to it.<ref name="IFEG-2.6-6" />

How long the structure must survive depends on the building. In New Zealand, C/VM2 (second edition, 2025) requires that in buildings with an escape height above 10 m, the load-carrying structure and floors resist collapse and fire spread between floors until burnout. Lower buildings must resist collapse for at least 30 minutes.<ref name="CVM2-55">Ministry of Business, Innovation and Employment (2025b), p. 55.</ref> The 2013 commentary explains that taller buildings must not collapse catastrophically even after everyone has left, because people outside at ground level could be endangered.<ref name="MBIE13-151">Ministry of Business, Innovation and Employment (2013), p. 151.</ref>

The structure also matters for firefighting. ''Introduction to Fire Safety Engineering'' notes that the Dutch standard NEN 6093 sets limits for a fire service deployment in a space with a smoke and heat exhaust system. One of them is that the calculated maximum smoke layer temperature stays below the critical temperature of the load-bearing structure.<ref name="VR-9.3b">Van Rossum (2027), §9.3 (Results from zone models).</ref> The book stresses that a positive outcome of such an analysis does not mean that the fire service will actually attack the fire from inside. That decision always rests with the fire service present at the time.<ref name="VR-9.3b" />

Structural fire engineering is not limited to beams and columns. Non-loadbearing elements that provide compartmentation, and essential services such as power and communication cables, may also need to keep working during a fully developed fire.<ref name="ABCB-B3-30" /> C/VM2 calls the elements that provide the basic load-bearing capacity primary elements. If fire affects them, instability or premature collapse may follow.<ref name="CVM2-68">Ministry of Business, Innovation and Employment (2025b), p. 68.</ref>

== The three steps of an analysis ==
The first step describes the fire. Either a nominal curve such as the [[standard fire curve]] is assumed, or the expected real fire is modelled.<ref name="Milke-4-209" /> The Eurocodes give a choice between a temperature–time curve and a natural fire whose course follows from the fire and the room.<ref name="VR-8.6">Van Rossum (2027), §8.6.</ref> A [[parametric fire curve]] is a typical empirical way to derive the gas temperatures of the fully developed and decay phases.<ref name="ABCB-B3-32">Australian Building Codes Board (2020a), Data Sheet B3, p. 32.</ref> ''Introduction to Fire Safety Engineering'' adds that a zone model can provide the thermal load on load-bearing and separating elements.<ref name="VR-9.3b" />

The second step calculates how hot the members become. Heating within a member is treated mainly as conduction, with radiative and convective conditions at its surfaces. Radiation and convection inside the member may also matter if it contains voids or porous insulation.<ref name="Milke-4-209" /> For steel, a heat transfer analysis typically finds the time at which the member reaches a predetermined critical temperature. The temperature limits of the standard test are often accepted as these critical temperatures.<ref name="Milke-4-209" />

The third step checks the structural response. Many structural calculations resemble those for normal design, except that material properties are taken at high temperature and thermal expansion is included. The loading and end conditions must be known or assumed.<ref name="Milke-4-209" /> Deflections, strains and stresses are compared with set limits.<ref name="Milke-4-209" />

The three steps can be combined. [[Time equivalence]] merges them by relating the expected fire to a time of exposure to the standard heating regime, assuming all fire load is consumed. The fire resistance of the element is then compared with that equivalent time.<ref name="ABCB-B3-32" /> Fleischmann and Buchanan describe the full sequence as the rational design method. A design time–temperature curve is chosen, a heat transfer analysis gives the temperature profile, and a structural analysis gives the fire endurance.<ref name="FB-4-239">Fleischmann and Buchanan (2002), p. 4-239.</ref>

== Behaviour of the main materials ==
Each structural material responds differently, so the methods differ per material.<ref name="IFEG-2.6-6" /> [[Steel in fire]] heats rapidly when it is unprotected. The International Fire Engineering Guidelines (2005) note that unprotected steel structures therefore usually do not perform well, unless they are carefully detailed. Some unprotected structures survive if the fire is mild and the structure can redistribute thermal stresses.<ref name="IFEG-2.6-7" />

Protection systems include concrete encasement, boards of calcium silicate or gypsum, spray-applied materials and intumescent paints.<ref name="IFEG-2.6-7" /> Under ASTM E119, the average temperature of a steel column is limited to 538 °C and that of a loaded steel beam to 593 °C. At these temperatures steel loses much of its strength and stiffness.<ref name="Milke-4-211">Milke (2002a), p. 4-211.</ref><ref name="NCSTAR1A-21">National Institute of Standards and Technology (2008), p. 21.</ref>

[[Concrete in fire]] generally behaves well. Concrete is non-combustible and has a low thermal conductivity. It tends to stay in place, protecting the reinforcement, while the cool inner core continues to carry the load. Catastrophic failures of reinforced concrete structures are rare, but some occur.<ref name="FB-4-239" />

The main effects of fire are thermal bowing and the gradual heating of the reinforcement.<ref name="IFEG-2.6-8">National Research Council of Canada et al. (2005), p. 2.6-8.</ref> The critical temperature is about 593 °C for reinforcing steel and about 426 °C for prestressing steel.<ref name="KH-1-163">Kodur and Harmathy (2002), p. 1-163.</ref> Siliceous aggregate concrete keeps nearly its full compressive strength up to 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>

[[Timber in fire]] chars at its surface. The fire endurance of a timber member depends on its protective membrane, if any, on the depth of charring and on the load-carrying capacity of the uncharred wood.<ref name="White-4-257">White (2002), p. 4-257.</ref> The most widely used empirical model assumes a constant charring rate of 0.6 mm/min across the grain under standard fire exposure. Char has virtually no load-bearing capacity, and its base lies at about 300 °C.<ref name="White-4-260">White (2002), p. 4-260.</ref> After 60 minutes of standard exposure, about 36 mm of wood is therefore lost from each exposed face.<ref name="Calc-SFE">Calculated from White (2002), p. 4-260.</ref> Heavy timber construction uses members with a smallest dimension of at least 80 mm.<ref name="IFEG-2.6-9">National Research Council of Canada et al. (2005), p. 2.6-9.</ref>

== Calculation methods ==
Calculation methods range from simple to advanced. Milke distinguishes empirical correlations, heat transfer analyses and structural analyses.<ref name="Milke-4-209" /> Empirical correlations are fitted to many standard test results. They can only be applied to the fire exposure, loading and span of the standard test.<ref name="Milke-4-209" /> For concrete, national codes commonly give tables of minimum dimensions and minimum cover to the reinforcement.<ref name="IFEG-2.6-8" />

Many ratings still come directly from tests. For timber, White notes that listed ratings apply only to the assembly actually tested. They normally do not allow changes such as added insulation, other member sizes or wider spacing, although code interpretation sometimes accepts larger members or thicker protection.<ref name="White-4-257" /> In Europe, Eurocode 5 provides calculation methods for timber at three levels of complexity.<ref name="White-4-257" /> In New Zealand, C/VM2 (second edition, 2025) offers several routes to a rating. These include an equivalent time of exposure, a fire with the same destructive potential, and a thermal and structural calculation for the material concerned.<ref name="CVM2-18">Ministry of Business, Innovation and Employment (2025b), p. 18.</ref>

For steel, the guidelines describe two main approaches. Simple models for single elements use a lumped heat capacity analysis together with a limiting temperature that depends on the applied load. Because they follow the steel temperature over time, they can be used with any time–temperature regime.<ref name="IFEG-2.6-7" /> They are not suitable where large temperature gradients cross the section, such as in a beam supporting a concrete slab. In such cases [[finite element analysis]] is appropriate.<ref name="IFEG-2.6-7" /> For steel frames, a general method with specialist computer programs calculates the stresses, strains and internal forces in each member.<ref name="IFEG-2.6-7" />

For concrete, Buchanan's advice in the guidelines depends on the structure. Simply supported slabs and beams heated from below need only the reduced yield strength of the reinforcement, so hand calculations are possible. Continuous members also need the reduced compressive strength of the concrete. For moment-resisting frames or members with axial restraint, special-purpose computer programs are recommended.<ref name="IFEG-2.6-9" /> Finite element programs used widely for steel and concrete structures in fire include SAFIR and VULCAN.<ref name="IFEG-2.6-10">National Research Council of Canada et al. (2005), p. 2.6-10.</ref> ''Introduction to Fire Safety Engineering'' notes that such a model divides a structure into many small cells, much as a CFD model divides a room.<ref name="VR-11.2">Van Rossum (2027), §11.2.</ref>

The [[Eurocodes]] provide much of the design basis in Europe. ''Introduction to Fire Safety Engineering'' notes that they can be used to determine the fire resistance of load-bearing structures against collapse.<ref name="VR-9.3b" /> The zone model OZone, which follows EN 1993-1-2, calculates the temperature of a steel member under a natural or standard fire. The fire resistance of the member is then determined to that standard.<ref name="VR-9.5">Van Rossum (2027), §9.5.</ref> Its authors developed it as a practical tool for a performance-based analysis of simple steel elements in a compartment fire.<ref name="Ozone2-431">Cadorin et al. (2003), p. 431.</ref> Testing remains necessary, at least to validate calculation methods and to assess how members, insulation and other components interact.<ref name="Milke-4-210">Milke (2002a), p. 4-210.</ref>

== Behaviour of whole structures ==
Real structures behave differently from single tested members. When steel is heated it expands, and if columns or other members resist that expansion, forces develop that can buckle beams or break connections.<ref name="NCSTAR1A-21" /> In the collapse of World Trade Center 7, the columns reached only about 300 °C. Thermal expansion of floor beams, mainly at or below 400 °C, nevertheless damaged the floor framing on several floors.<ref name="NCSTAR1A-21" /> On the 13th floor the expanding beams pushed a girder so far that it walked off its seat at a column. Floor 13 then collapsed and started a cascade of floor failures.<ref name="NCSTAR1A-22">National Institute of Standards and Technology (2008), p. 22.</ref>

The investigators listed four contributing factors. Thermal expansion occurred at temperatures hundreds of degrees below those used to establish fire resistance ratings, and long-span floors magnified its effects. The connections were designed for gravity loads but not for thermally induced lateral loads, and the structural system was not designed to prevent fire-induced progressive collapse.<ref name="NCSTAR1A-xxxvi" /> NIST also noted that the standard test does not capture interactions between subsystems, elements and connections, because columns, girders and floor assemblies are tested separately.<ref name="NCSTAR1A-67">National Institute of Standards and Technology (2008), p. 67.</ref>

Protection also proved decisive in the World Trade Center towers. NIST concluded that the towers would likely not have collapsed if the thermal insulation had not been widely dislodged by the aircraft impacts.<ref name="NCSTAR1-xxxviii">National Institute of Standards and Technology (2005), p. xxxviii.</ref> Among its recommendations was a "structural frame" approach to fire resistance ratings, and better technical bases for ratings and test methods.<ref name="NCSTAR1-208">National Institute of Standards and Technology (2005), p. 208.</ref> A performance objective of burnout without collapse, NIST added, will require standard fire exposures different from those used today.<ref name="NCSTAR1-212">National Institute of Standards and Technology (2005), p. 212.</ref>

New hazards raise similar questions. For indoor car parks with electric vehicles, the Netherlands Institute for Public Safety suggests fire-resistant cladding or a sturdier construction near charging points. For a travelling car fire or a compartment fire, the entire structure may need greater fire resistance so that the car park survives a burnout.<ref name="NIPV-36">Van der Graaf et al. (2021/2023), p. 36.</ref> The report notes that car park structures are generally designed for a normative fire development, and that the effect of electric vehicle fires on them still needs research.<ref name="NIPV-36" />

== Limits and uncertainty ==
Structural fire engineering inherits the uncertainty of the fire itself. Variations in fire load of 50 % or more are common, which can change fire temperatures by hundreds of degrees and durations by 50 % or more.<ref name="Lie-4-202">Lie (2002), p. 4-202.</ref> Material properties at high temperature are a second source of uncertainty. For steel, all properties except density are strongly influenced by temperature.<ref name="Milke-4-211" /> The rational design method for concrete also relies on experimental strength data, which depend on the test method used.<ref name="FB-4-240" />

Simplified methods have clear limits. Methods for walls and columns may be less accurate because uneven heating can cause deformations that lead to instability.<ref name="IFEG-2.6-9" /> Calculation results for protected steel also assume that the protection stays in place, so its adhesion under full-scale deformations usually has to be confirmed by fire tests.<ref name="IFEG-2.6-8" /> The guidelines recommend structural engineers for structural analysis and limit the role of fire engineers, unless suitably trained, to predicting thermal effects.<ref name="IFEG-2.6-7" />

== See also ==
* [[Fire resistance criteria]]
* [[Travelling fire]]
* [[Progressive collapse]]
* [[Restrained thermal expansion]]
* [[Tensile membrane action]]

== 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
* 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.
* 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.
* 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 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.
* 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]]

Ceiling jet flow

2026-11-01T22:54:58Z

Daan: Redirect to Ceiling jet (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Ceiling jet]]

Reverse stack effect

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Daan: Redirect to Stack effect (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Stack effect]]

Protected exit

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Daan: Redirect to Protected escape route (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Protected escape route]]

Full room involvement

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Daan: Redirect to Post-flashover fire (FSE wiki, written by Claude Opus 5.5)

#REDIRECT [[Post-flashover fire]]