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Manual call point

2026-11-02T18:45:16Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''manual call point''' is a device that allows a person to initiate a fire alarm after recognising a possible fire. Its operation relies on human action rather than an automatic sensing element. Predicting the time to alarm therefore requires consideration of how the fire is noticed and when someone acts.<ref name="CVM_28_29">Ministry of Business, Innovation and Employment (2025), pp. 28–29.</ref>

Manual initiation can form part of a wider detection and warning arrangement, and it provides an input to the alarm system, which must then communicate the intended warning or protective command. Other occupants may still need time to understand the warning and prepare to leave. The person operating the device and the people receiving the alarm perform different roles.<ref name="SMC_4-3">Schifiliti, Meacham, and Custer (2002), p. 4-3.</ref><ref name="P_3-350_3-351">Proulx (2002), pp. 3-350–3-351.</ref>

Engineering methods may restrict the circumstances in which manual activation can replace an automatic detection assumption. New Zealand's C/VM2 (2025), for example, sets conditions for high-ceiling spaces with limited numbers of awake, familiar occupants. Its treatment of enclosed offices also depends on room size, floor level and the escape route.<ref name="CVM_28_29" />

== Human recognition and alarm initiation ==

A manual call point relies on a person to initiate a [[Fire alarm system]]. The initiating sequence begins before the device is operated. Someone must become aware of a possible fire, recognise the situation and act on that information. New Zealand's C/VM2, second edition (2025), explicitly identifies this human interaction as a difficulty when predicting manual alarm activation.<ref name="CVM_29">Ministry of Business, Innovation and Employment (2025), p. 29.</ref>

The International Fire Engineering Guidelines (IFEG, 2005) distinguish several ways people can receive fire cues: these include seeing smoke or flames, smelling smoke and hearing sounds associated with the fire. Someone who recognises such a cue may also warn other people. Cue occurrence, recognition and the resulting response are separate parts of its analysis.<ref name="IFEG_1.8-7_1.8-9">Australian Building Codes Board et al. (2005), pp. 1.8-7–1.8-9.</ref>

The physical act of operating the call point is therefore only one part of manual initiation. The time at which a person first notices the fire may dominate the earlier sequence. People in enclosed rooms may receive different information from those in an open warehouse. A credible assessment identifies who is expected to notice the fire and what information reaches them.<ref name="CVM_28_29" /><ref name="IFEG_1.8-7_1.8-9" />

[[File:fse-manual-call-point-v1.svg|thumb|upright=1.5|alt=Person sees fire, reaches and operates call point, and alarm notifies occupants.|Manual initiation depends on human recognition and action. Based on Ministry of Business, Innovation and Employment (2025), p. 29 and Australian Building Codes Board et al. (2005), p. 1.8-7.]]

== Relationship to automatic detection and warning ==

Automatic detection responds to a fire signature through a sensor rather than waiting for human operation of a call point. The SFPE Handbook describes detection, processing and signalling as separate alarm-system functions. Manual initiation changes the source of the input without removing the need for processing and a suitable output. The subsequent warning still has to reach the people expected to act.<ref name="SMC_4-3" /><ref name="CVM_29" />

An [[Evacuation alarm system]] supplies the warning that supports occupant response. Hearing a signal is not equivalent to immediately starting evacuation travel. Proulx describes information seeking, preparation and the influence of staff instructions on this response. Manual operation by one person therefore does not establish that everyone else has recognised the emergency.<ref name="P_3-349_3-351">Proulx (2002), pp. 3-349–3-351.</ref>

Manual and automatic initiation can provide alternative paths within a design. IFEG gives an example in which occupants, smoke detectors or sprinklers can identify a fire; its redundancy analysis asks what remains available if a component fails. The benefit of several inputs depends on the functioning of the complete paths to the required action.<ref name="IFEG_1.2-24">Australian Building Codes Board et al. (2005), p. 1.2-24.</ref>

A manually operated input cannot be credited merely because the device is present. The fire needs to become perceptible to someone who can recognise and respond to it. In a modelling method, those human and spatial conditions can restrict where manual initiation is accepted. C/VM2's warehouse provisions provide a specific example of such restrictions.<ref name="CVM_26__28_29">Ministry of Business, Innovation and Employment (2025), pp. 26, 28–29.</ref>

== A conditional New Zealand warehouse method ==

In New Zealand, C/VM2 (2025) permits its manual-activation approach only under stated conditions. The space must have an average ceiling height of at least 5 m. Occupants must be awake and familiar with their surroundings, and the occupant load must be fewer than 50 people. Other situations require automatic detection under that method.<ref name="CVM_28">Ministry of Business, Innovation and Employment (2025), p. 28.</ref>

The commentary explains the intended large-space application through warehouses. A high ceiling allows smoke to move beneath it before conditions threaten occupants below. The method assumes that occupants become aware of the fire when the ceiling jet has traversed the entire length of the space. It uses this smoke-transport period as a proxy for the delay before manual activation.<ref name="CVM_26__28_29" />

Within that particular approach, no additional notification or pre-travel activity period is added for the open warehouse population. The method expects the simple call-point system to activate immediately once operated, and this is a combined modelling assumption about recognition and action. It is not evidence that real occupants always operate a call point without delay.<ref name="CVM_28_29" />

The method also addresses intermediate floors: they must be open, with occupants fully aware of a fire located in the warehouse. An enclosed intermediate room would change the assumed access to fire cues. The permission therefore depends on both building geometry and the occupants' opportunity to recognise the event.<ref name="CVM_29" />

[[File:fse-manual-call-point-v2.svg|thumb|upright=1.5|alt=Open warehouse supports manual recognition; enclosed office needs automatic detection.|Layout determines whether manual initiation is credible. Based on Ministry of Business, Innovation and Employment (2025), pp. 28–29.]]

== Separated rooms and the means of escape ==

C/VM2 treats occupied rooms separated from the high-ceiling space as a distinct case. Under its 2025 provisions, the small room may have a maximum area of 500 m², and it must be on the ground floor and have an escape route directly outside. Occupants must not need to enter the high-ceiling warehouse to use that route.<ref name="CVM_29" />

The method assigns those room occupants 60 s of pre-travel activity after manual activation, and this additional period belongs to the separated-room provision. It differs from the open warehouse assumption that adds no further notification or pre-travel activity time. Mixing the two cases would remove a condition from the prescribed assessment.<ref name="CVM_29" />

The required [[Means of escape]] are therefore part of this permission to use manual initiation. The direct outside route matters alongside room size and floor level. If the separated-office conditions are not satisfied, C/VM2 requires automatic detection within the office. Its detection and notification periods then follow the relevant automatic-system provisions.<ref name="CVM_29" />

A further exception concerns very small isolated ground-floor spaces, such as washrooms or offices. Each must be no larger than 30 m², and their aggregate occupant load must not exceed ten people. C/VM2 assigns 60 s of pre-travel activity to escape from these spaces. These numerical limits belong to the specified New Zealand method and edition.<ref name="CVM_29" />

[[File:fse-manual-call-point-v3.svg|thumb|upright=1.5|alt=After activation, a 60-second pre-travel block precedes movement along a direct outside route.|Small-space method includes 60 seconds and a direct outside route. Based on Ministry of Business, Innovation and Employment (2025), p. 29.]]

== Occupants, staff and management assumptions ==

Recognition of a fire is affected by the information available to the person. Proulx describes the influence of familiarity, responsibility, alertness and commitment to the activity already underway. A visitor may wait for staff instructions while a familiar occupant interprets the situation differently. These factors help explain why human initiation cannot be reduced to one universal delay.<ref name="P_3-350_3-351" />

Staff training is connected to the actual building and its evacuation procedure. Proulx notes that people trained in one building may not behave the same way in another. Public occupants may have no training specific to the premises they are visiting. Where a strategy relies on staff recognition and response, their role needs to match the credited action.<ref name="P_3-350">Proulx (2002), p. 3-350.</ref>

[[Fire safety management]] therefore supports the human part of the alarm arrangement, and it concerns the procedures and staff behaviour assumed when interpreting and responding to a fire cue. IFEG requires the cue used in an analysis to be selected and justified. Assuming early manual initiation without identifying the relevant occupants would leave that part of the sequence unexplained.<ref name="P_3-350_3-351" /><ref name="IFEG_1.8-7_1.8-9" />

Warnings from other people can also matter. IFEG recognises them as an alternative cue, while Proulx reports the influence of direct staff instructions on movement. Such warnings may reinforce the alarm signal or precede it. Their usefulness depends on the people present and the information they can communicate.<ref name="IFEG_1.8-7_1.8-9" /><ref name="P_3-349_3-351" />

== Evidence and limits of the assessment ==

The C/VM2 example describes when manual initiation may be used in a particular engineering calculation. It does not supply a universal permission to omit automatic detection from warehouses. The specified ceiling, occupant and room conditions have to be considered together. A superficially similar building may fall outside that method's stated application.<ref name="CVM_26__28_29" />

IFEG identifies limitations in methods for predicting the period before people start moving. It accepts documented literature, field observations and simulated evacuations as potential evidence, with substantiated engineering judgement where necessary. The source of an assumed manual response time therefore matters. A precise input without a stated basis can conceal uncertainty in recognition and action.<ref name="IFEG_1.8-7">Australian Building Codes Board et al. (2005), p. 1.8-7.</ref>

Redundancy does not remove this uncertainty automatically. Multiple initiating routes may still rely on shared processing or signalling functions. IFEG's redundancy study examines single points of failure and available backup, including whether failures would be recognised. This functional analysis distinguishes an alternative means of initiation from an independently available warning.<ref name="IFEG_1.2-24" />

== See also ==

* [[Evacuation strategy]]
* [[Pre-movement time]]
* [[Smoke detector]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association.

[[Category:Detection & Alarm]]

Unwanted fire alarms

2026-11-02T18:42:55Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Unwanted fire alarms''' are fire-warning signals that occur without the fire condition the warning is intended to indicate. They can result from non-fire exposure, inappropriate operating conditions or signal interpretation. Tests and deliberate activations can also contribute to occupants repeatedly experiencing an alarm without a fire.<ref name="SMC_4-22">Schifiliti, Meacham, and Custer (2002), p. 4-22.</ref><ref name="N_12-1_12-4">Iqbal and Salley (2004), pp. 12-1–12-4.</ref><ref name="P_3-349_3-350">Proulx (2002), pp. 3-349–3-350.</ref>

The subject has both technical and human dimensions. A detector may respond to an environmental input, while occupants may become less willing to act after repeated false warnings. The cause of the signal and its effect on later evacuation behaviour therefore require separate consideration. A count of activations alone does not describe either mechanism completely.<ref name="N05_13-3">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. 13-3.</ref><ref name="P_3-350_3-351">Proulx (2002), pp. 3-350–3-351.</ref>

Measures that reject unwanted signals can also affect genuine-fire response. Verification delays and reductions in sensitivity must be considered against the required detection and intervention time. The engineering objective is to preserve the intended warning function while addressing the particular source of unwanted operation.<ref name="SMC_4-28_4-29">Schifiliti, Meacham, and Custer (2002), pp. 4-28–4-29.</ref><ref name="N10_13-6">U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), p. 13-6.</ref>

== What makes an alarm unwanted ==

An unwanted alarm occurs when a fire-warning signal is produced without the fire condition that the signal is intended to indicate. Different events can produce a similar warning to occupants. The SFPE Handbook discusses nuisance and false signals in detector processing, while Proulx distinguishes false, test and prank alarms in occupant experience. These causes have different implications for diagnosis and management.<ref name="SMC_4-22" /><ref name="P_3-349_3-350" />

A planned test is not evidence that a detector has malfunctioned. However, an occupant who cannot distinguish its purpose may experience another alarm without a fire. Proulx describes how this history can reduce the credibility of subsequent warnings. The technical cause of an activation and its effect on human interpretation are therefore separate questions.<ref name="P_3-349_3-350" />

The absence of visible flames does not by itself establish that a signal was unwanted. Very early warning systems can intentionally respond to conditions before open flaming develops. The 2010 supplement to NUREG/CR-6850 describes such alerts in specific United States nuclear applications. It links those alerts to investigation and a defined protective response.<ref name="N10_13-5_13-7">U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), pp. 13-5–13-7.</ref>

A [[Fire alarm system]] must therefore be assessed against the fire signatures and actions it is intended to recognise. An incipient-condition alert, an evacuation warning and a suppression-release command need not have the same operating criterion, and their purposes affect how an activation is interpreted. A simple count of signals without their context cannot describe all of these functions.<ref name="SMC_4-2_4-3">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3.</ref><ref name="N10_13-6" />

== Non-fire heat, particles and environmental exposure ==

Heat detectors respond to thermal conditions, including heat that may not come from a fire. NUREG-1805 discusses premature operation where the selected temperature rating is unsuitable for normal conditions near the ceiling, and it identifies high-temperature environments and non-fire heat sources as relevant to device selection. A correct operating mechanism can therefore produce an unwanted alarm when its exposure was not properly considered.<ref name="N_12-1_12-3">Iqbal and Salley (2004), pp. 12-1–12-3.</ref>

A pneumatic rate-of-rise detector illustrates how a device can accommodate ordinary changes: its small vent allows pressure to equalise during gradual heating, while rapid expansion can operate the contacts. This does not mean that every rapid temperature increase is a fire. The physical quantity sensed and the environment in which the device operates remain linked.<ref name="N_12-4">Iqbal and Salley (2004), p. 12-4.</ref>

A [[Smoke detector]] responds to particles through its particular sensing mechanism. The 2005 EPRI/NRC-RES methodology identifies dust and steam as possible causes of actuation in its seismic assessment for nuclear facilities. It notes that some incipient-detection arrangements are designed to reject such signals. This is evidence of mechanism-dependent environmental response, not a claim that every detector behaves identically.<ref name="N05_13-3" />

The relevant distinction is between the signal received by the device and the fire condition the designer wants it to identify. Schifiliti and colleagues explain that particle properties and signal processing affect this distinction. A calibration value measured with one smoke does not fully describe the response to other aerosols. Environmental suitability therefore cannot be reduced to one nominal sensitivity number.<ref name="SMC_4-21_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-21–4-24.</ref>

[[File:fse-unwanted-fire-alarms-v1.svg|thumb|upright=1.5|alt=Alarm triggered by ambient heat, aerosols, wrong rating, contamination and a test switch.|Unwanted alarms have several different causes. Based on Iqbal and Salley (2004), p. 12-3 and Schifiliti, Meacham, and Custer (2002), pp. 4-22–4-24; Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. 13-3; and Proulx (2002), p. 3-349.]]

== Confirmation and signal processing ==

The SFPE Handbook describes detector algorithms intended to reduce false and nuisance alarms while recognising fire signatures, and they can evaluate sensor information differently from a single instantaneous threshold. Their operation varies between products and may not be fully disclosed. These functions affect both unwanted-signal rejection and response to actual fires.<ref name="SMC_4-22_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-22–4-24.</ref>

A [[Multi-sensor detector]] requires evidence for the combined sensing and decision process. A favourable response from one sensing element does not establish the behaviour of the complete device. The same concern applies when signals are processed by a control system before an output is activated. Assessing performance requires the relevant sequence, not only an isolated sensor measurement.<ref name="SMC_4-22_4-24" />

The International Fire Engineering Guidelines (IFEG, 2005) describe coincident detection that requires two or more detectors before an alarm is recognised. The detectors may use similar or different sensing principles. NUREG-1805 describes cross-zoning as an example used to reduce unwanted suppression discharge. In that arrangement, confirmation requires signals from separate sensing circuits.<ref name="IFEG_2.7-2">Australian Building Codes Board et al. (2005), p. 2.7-2.</ref><ref name="N_F-18">Iqbal and Salley (2004), p. F-18.</ref>

Confirmation changes the activation condition and can therefore change response time; its effect must be assessed against the objective of the protected system. The presence of a second condition does not eliminate the need to check detection of the intended fire. A method intended to reduce unwanted operation can still be unsuitable if the required genuine-fire response becomes too slow.<ref name="SMC_4-2_4-3__4-28_4-29">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3, 4-28–4-29.</ref><ref name="IFEG_2.7-2" />

== Worked example of verification delay ==

Alarm verification can introduce a deliberate period between an initiating event and the subsequent response. The SFPE Handbook illustrates its timing effect in a hotel-ballroom example. The example assigns 10 s to system delay and 60 s to staff arrival after alarm indication. Verification can take between 15 s and 60 s.<ref name="SMC_4-28">Schifiliti, Meacham, and Custer (2002), p. 4-28.</ref>

The subtotal is calculated by adding the sequential delays after detector activation. The shorter verification setting gives 85 s, while the longer one gives 130 s. Smoke transport to the detector is excluded from both subtotals. These values describe the source example rather than prescribed verification settings for all buildings.<ref name="SMC_4-28_4-29" />

<math display="block">t_{\mathrm{post}}=t_{\mathrm{system}}+t_{\mathrm{verify}}+t_{\mathrm{staff}}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_{\mathrm{post}}</math> || Post-detection response subtotal in the example || s
|-
| <math>t_{\mathrm{system}}</math> || System delay before alarm initiation || s
|-
| <math>t_{\mathrm{verify}}</math> || Verification period || s
|-
| <math>t_{\mathrm{staff}}</math> || Time from alarm indication to staff arrival || s
|}

<math display="block">t_{\mathrm{post,short}}=10+15+60=85\ \mathrm{s}</math>
<math display="block">t_{\mathrm{post,long}}=10+60+60=130\ \mathrm{s}</math>

The longer verification period adds 45 s to this part of the response. During that interval, the fire may continue developing. The design question is whether the complete sequence still finishes before the limiting fire condition is reached. A reduction in unwanted alarms does not answer that timing question by itself.<ref name="SMC_4-2_4-3__4-28_4-29" />

The example also shows why a verification feature must be represented explicitly. Counting only detector activation would omit both processing and the time needed for the intended intervention. Counting the same delay twice would distort the result in the opposite direction. The sequence and its time boundaries need to be stated consistently.<ref name="SMC_4-28_4-29" />

== Alarm credibility and occupant response ==

Repeated alarms without a fire can affect how people interpret the next warning. Proulx describes an alarm tone as a cue that often prompts information seeking rather than immediate movement. Occupants may wait for staff, a spoken message or direct evidence of the fire. Their experience of previous false signals can influence that decision.<ref name="P_3-349_3-350" />

The resulting effect belongs to [[Pre-movement time]], the period before evacuation travel begins; it is not a reduction in walking speed after movement has started. Proulx explains that occupants' response depends on warning information, familiarity, responsibility and other characteristics. An alarm-history problem therefore interacts with the wider human and building context.<ref name="P_3-350_3-351" />

Proulx gives three or more false alarms over six months as an illustrative high frequency. The statement appears in a discussion of warning credibility and delayed response; it is not a statutory limit or a universal acceptable-alarm allowance. The source does not provide a fixed number of extra seconds to apply whenever that count is reached.<ref name="P_3-350">Proulx (2002), p. 3-350.</ref>

Informative live messages and trained staff can help occupants interpret a warning. Proulx reports cases where people responded to precise instructions after initially continuing their activities during an alarm tone. These observations support considering communication quality as well as signal generation. They do not establish that messages can compensate for every cause of repeated unwanted alarms.<ref name="P_3-349_3-351">Proulx (2002), pp. 3-349–3-351.</ref>

[[File:fse-unwanted-fire-alarms-v3.svg|thumb|upright=1.5|alt=Three alarms over six months followed by an occupant hesitating before moving.|Frequent false alarms can reduce credibility and response. Based on Proulx (2002), p. 3-350.]]

== Sensitivity changes in an early-warning application ==

A specialised example is provided by the 2010 supplement to NUREG/CR-6850, and it assesses very early warning detection used for defined electrical-cabinet applications in United States nuclear facilities. These systems can distinguish early alerts from later alarms associated with a developed fire. The credited response depends on personnel identifying the affected location and taking the required action.<ref name="N10_13-5_13-7" />

The report requires alert and alarm levels to be controlled through the plant's setpoint programme. A setpoint is the selected threshold at which the system issues its signal. Recalibration that reduces sensitivity must be evaluated for its effect on early warning. The risk assessment treats a reduction in sensitivity as a possible reduction in system effectiveness.<ref name="N10_13-6" />

The same application requires acceptance testing, functional testing, maintenance and calibration appropriate to the system. It also requires test and calibration records to be retained for the life of the plant; these are conditions of the specified nuclear assessment. They demonstrate why the performance credited to an early-warning system depends on controlled settings and documented operation.<ref name="N10_13-6" />

An alert can lead to investigation and deployment of trained personnel before open flaming occurs. The report links this response to procedures, equipment availability and training. Removing the early signal could therefore remove time that the protective strategy relies upon. An apparently quieter system is not necessarily equivalent to the system credited in the assessment.<ref name="N10_13-6_13-7">U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), pp. 13-6–13-7.</ref>

[[File:fse-unwanted-fire-alarms-v2.svg|thumb|upright=1.5|alt=Balance between fewer nuisance alarms and retaining early genuine detection.|Sensitivity changes must preserve genuine early detection. Based on U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), p. 13-6 and Schifiliti, Meacham, and Custer (2002), p. 4-22.]]

== Several unwanted signals can occur together ==

The 2005 EPRI/NRC-RES fire-risk methodology considers unwanted activation during an earthquake at a nuclear facility. Dust can be disturbed, steam lines can rupture and equipment can be damaged. The report identifies the possibility of several detector signals arising from these shared conditions. It also notes that genuine fires can occur during the same event.<ref name="N05_13-2_13-3">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. 13-2–13-3.</ref>

Multiple unwanted signals can complicate the task of distinguishing actual fires from spurious indications. The report specifically warns that they can mask valid signals; this example concerns a combined seismic and fire scenario, not the ordinary alarm rate of a typical building. Its significance is that the initiating environmental causes need not be independent.<ref name="N05_13-3" />

The same report notes that cross-zoned detection may receive spurious signals during such an event. Requiring more than one input does not guarantee that a shared disturbance affects only one detector. The assessed benefit of confirmation depends on the exposure and on the independence of the inputs. This is consistent with IFEG's requirement to examine single failures and remaining backup in redundant arrangements.<ref name="N05_13-3" /><ref name="IFEG_1.2-24">Australian Building Codes Board et al. (2005), p. 1.2-24.</ref>

The seismic assessment includes failures in control equipment as well as responses at detectors. Relay chatter in a control panel without suitable seismic qualification can initiate operation. Physical damage to piping or control components can also produce unintended release from suppression equipment. These mechanisms differ from a smoke sensor responding to airborne particles, even if the resulting event appears similar to the operator. The example demonstrates why identifying the initiating mechanism matters before interpreting several indications as evidence of several independent fires or independent detector faults.<ref name="N05_13-3" />

This case also distinguishes detection problems from unwanted operation of connected equipment. A false input may matter differently when it produces a warning than when it releases an extinguishing system. The complete functional sequence determines the consequence. The report therefore considers detection, control equipment and suppression actuation within the same event analysis.<ref name="N05_13-3" />

== Evidence for management and performance assessment ==

[[Fire safety management]] connects the technical signal with the procedures and people expected to respond. Proulx emphasises building-specific staff training and the influence of staff behaviour on occupant movement. The nuclear early-warning example likewise makes procedural response part of the credited protection. Equipment settings and human actions need to describe the same intended strategy.<ref name="P_3-350_3-351" /><ref name="N10_13-6_13-7" />

An assessment separates the cause of an unwanted signal from the remedy being considered. Normal thermal exposure, environmental particles, deliberate testing and signal-processing decisions do not represent the same mechanism. The cited sources address these through different physical and behavioural processes. Their distinction prevents a single adjustment from being assumed to resolve every source of unwanted activation.<ref name="N_12-1_12-4" /><ref name="N05_13-3" /><ref name="SMC_4-22" /><ref name="P_3-349">Proulx (2002), p. 3-349.</ref>

The evidence also needs to establish that the intended fire remains detectable within the required time. The SFPE Handbook describes limitations in smoke-response models and manufacturer algorithms. It identifies fire tests with detectors present and product performance tests as possible sources of relevant evidence. The fuel, exposure and response criterion define what those results can support.<ref name="SMC_4-22_4-24" />

The available sources do not provide one universal acceptable frequency or one numerical correction for alarm fatigue. Proulx's behavioural discussion and the nuclear application requirements have different purposes and scopes. A performance assessment identifies which evidence applies to the building, occupants and system concerned. The remaining uncertainty is then examined alongside the timing and reliability assumptions.<ref name="P_3-350_3-351" /><ref name="N10_13-6" /><ref name="IFEG_1.2-24" />

== See also ==

* [[Aspirating smoke detection]]
* [[Evacuation alarm system]]
* [[Human behaviour in fire]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Electric Power Research Institute, & U.S. Nuclear Regulatory Commission. (2005). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Volume 2: Detailed methodology'' (EPRI 1011989; NUREG/CR-6850).
* 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.
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association.
* U.S. Nuclear Regulatory Commission, & Electric Power Research Institute. (2010). ''Fire probabilistic risk assessment methods enhancements'' (NUREG/CR-6850, Supplement 1).

[[Category:Detection & Alarm]]

Smoke detector

2026-11-02T18:42:49Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''smoke detector''' is a device that responds to particles produced by combustion and supplies a signal when its alarm criterion is reached. Common sensing principles use changes in ion current, scattered light or transmitted light. The response depends on the particles reaching the sensing region and interacting with the particular sensor.<ref name="Mu_2-266_2-267">Mulholland (2002), pp. 2-266–2-267.</ref><ref name="SMC_4-21_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-21–4-24.</ref>

Smoke varies with the fuel, burning mode and conditions during transport. Two smokes with the same measured optical density can produce different responses in a scattering or ionisation detector. A calibration threshold therefore needs to be interpreted with the smoke and test conditions used to establish it.<ref name="SMC_4-21_4-24" />

Detection time also includes transport and, for enclosed sensing chambers, smoke-entry delay. Air sampling and projected-beam arrangements introduce different measurement paths. Engineering assessment combines those physical processes with the detector's response criterion and any later alarm processing, while recognising the limits of available input data.<ref name="SMC_4-22_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-22–4-24.</ref><ref name="CVM_27_28">Ministry of Business, Innovation and Employment (2025), pp. 27–28.</ref>

== How smoke becomes a detection signal ==

Smoke contains particles whose properties depend on the fuel and the way it burns. Detectors can respond through changes in electrical current or changes in light reaching a receiver. The SFPE Handbook distinguishes the response of the sensor from the transport of smoke to it. Both processes affect the time at which an alarm signal becomes available.<ref name="Mu_2-266_2-267" /><ref name="SMC_4-21_4-24" />

An ionisation detector uses an ion current within its sensing chamber. Smoke particles intercept ions and reduce the current until the alarm criterion is reached, while a light-scattering detector instead measures light redirected by particles within the chamber. The two mechanisms respond differently to particle size, concentration and other smoke characteristics.<ref name="Mu_2-266_2-267" />

A [[Beam smoke detector]] measures attenuation of a light beam across a space. Attenuation is the reduction of transmitted light caused by the smoke along its path. [[Aspirating smoke detection]] uses a sampling arrangement that draws air towards a sensing chamber. These arrangements introduce different measurement geometries and, for sampling systems, additional transport through the sampling network.<ref name="SMC_4-22_4-23">Schifiliti, Meacham, and Custer (2002), pp. 4-22–4-23.</ref><ref name="N_F-52">Iqbal and Salley (2004), p. F-52.</ref><ref name="CVM_27_28" />

A detector supplies an input to the [[Fire alarm system]], which processes the signal and produces its configured outputs. Detection and occupant notification are separate functions. The presence of smoke at the sensing location does not establish that the complete warning sequence is already finished. Processing and the intended human response remain part of the system assessment.<ref name="SMC_4-2_4-3">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3.</ref>

[[File:fse-smoke-detector-v1.svg|thumb|upright=1.5|alt=Ionisation chamber, scattering chamber, projected beam and aspirating sampler.|Smoke-detection principles measure different particle responses. Based on Mulholland (2002), pp. 2-266–2-267 and Schifiliti, Meacham, and Custer (2002), pp. 4-21–4-24 and Iqbal and Salley (2004), p. F-52.]]

== Particle size, fuel and burning mode ==

Smoke is not a uniform substance with one universal detector response. Schifiliti and colleagues identify particle size distribution, concentration, composition, colour and refractive index as relevant characteristics. Refractive index describes how the material interacts with light. Fuel composition, flaming or smouldering combustion and the supply of combustion air affect the particles produced.<ref name="SMC_4-21">Schifiliti, Meacham, and Custer (2002), p. 4-21.</ref>

Mulholland compares ionisation and scattering responses for particular detectors. In that comparison, ionisation response is stronger for particles smaller than about 0.3 µm. Light-scattering response is stronger for particles larger than about 0.3 µm. This is an approximate comparison from the reported detector response functions, not a sharp dividing line for every device.<ref name="Mu_2-266_2-267" />

The chapter associates relatively small particles with examples of flaming paper and wood fires. Larger droplets from smouldering combustion can favour the response of scattering detectors. These relationships explain why the same nominal optical obscuration does not imply the same electrical signal in every sensor. The burning mode and the detector principle must be considered together.<ref name="Mu_2-266_2-267" />

Particle properties also change during transport. Particles can settle or combine, changing the number and size distribution that reaches the detector. The SFPE detection chapter therefore distinguishes smoke characteristics at the fire from those at the sensing location. Using generation data alone can omit changes relevant to the eventual response.<ref name="SMC_4-21__4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-21, 4-24.</ref>

[[File:fse-smoke-detector-v2.svg|thumb|upright=1.5|alt=Ionisation sensitivity stronger below 0.3 µm and light-scattering sensitivity stronger above it.|Detector sensitivity varies with particle size. Based on Mulholland (2002), pp. 2-266–2-267.]]

== Getting smoke into the sensing region ==

A rising plume can carry smoke towards the ceiling, where a [[Ceiling jet]] distributes it away from the fire. Ceiling height, geometry and intervening barriers influence this route. Natural and mechanical air currents also affect the movement of smoke, particularly during early, low-energy fires. The transport time cannot be assumed identical for different detector locations.<ref name="SMC_4-21_4-22">Schifiliti, Meacham, and Custer (2002), pp. 4-21–4-22.</ref>

Smoke reaching the outside of a spot detector must still enter its sensing chamber. Screens, chamber geometry and the flow around the housing can resist entry. The SFPE Handbook calls this entry resistance. During an increasing external smoke concentration, the concentration within the chamber can lag behind the surrounding smoke.<ref name="SMC_4-24">Schifiliti, Meacham, and Custer (2002), p. 4-24.</ref>

This lag is conceptually separate from the detector's response threshold. A device may be sensitive to a particular smoke once it is inside the chamber but still receive that smoke slowly. The local gas velocity and the device's aerodynamic characteristics therefore matter. Treating external smoke concentration as instantaneously identical to chamber concentration can understate the response time.<ref name="SMC_4-22__4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-22, 4-24.</ref>

A weak fire beneath a high ceiling may also produce smoke that loses buoyancy before entering the assumed ceiling flow. The handbook discusses this possibility when examining low-energy fires and stratification. Stratification means that smoke can collect at a level determined by the surrounding temperature conditions. A detector near the ceiling may therefore receive a different exposure from the one assumed in a simple spreading-layer calculation.<ref name="SMC_4-28">Schifiliti, Meacham, and Custer (2002), p. 4-28.</ref>

Air sampling introduces a different transport arrangement. C/VM2 identifies airflow, sampling-tube length and alarm threshold as factors in the response of very high sensitivity sampling systems. The method treats these systems as requiring specialised design. A sensitive measuring chamber alone does not determine the time needed for a sample to arrive and initiate the intended output.<ref name="CVM_27">Ministry of Business, Innovation and Employment (2025), p. 27.</ref>

== Calibration does not define every fire response ==

[[Optical density]] describes how smoke attenuates a light beam over a specified distance, and it is useful for measuring smoke and for modelling projected-beam detectors. A scattering detector, however, measures redirected light rather than the same beam attenuation quantity. Its alarm threshold expressed as optical density therefore depends on the calibration smoke and the detector characteristics.<ref name="SMC_4-22_4-24" />

The SFPE Handbook gives an example of a scattering detector responding at 0.029 m<sup>−1</sup> to smoke from a smouldering grey cotton lamp wick. The same example describes a response at 0.15 m<sup>−1</sup> for kerosene-fire smoke. At those response points, the receiver detects the same scattered-light signal. The darker kerosene smoke scatters light differently from the lighter wick smoke.<ref name="SMC_4-23">Schifiliti, Meacham, and Custer (2002), p. 4-23.</ref>

These values are examples for the particular comparison, not universal detector sensitivities, and they show why a calibration value cannot be transferred indiscriminately between smoke types. Wavelength and scattering angle also affect the response. Appropriate input data need to represent both the smoke and the sensing mechanism being modelled.<ref name="SMC_4-23_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-23–4-24.</ref>

[[File:fse-smoke-detector-v3.svg|thumb|upright=1.5|alt=Grey cotton-wick smoke 0.029 and kerosene smoke 0.15 per metre as response examples.|Optical-density response depends on smoke type. Based on Schifiliti, Meacham, and Custer (2002), p. 4-23.]]

The handbook also discusses limits imposed by manufacturer algorithms: a product may process sensor readings over time rather than operate at one simple instantaneous threshold. Those algorithms can affect nuisance rejection and genuine-fire response. Without suitable product information, a concentration calculation may describe the exposure but not the complete activation decision.<ref name="SMC_4-22_4-24" />

== A beam calculation with a worked example ==

For uniform smoke along a beam, optical density per unit length is calculated from the fraction of light transmitted. The calculation uses the base-ten logarithm of the intensity ratio and divides by beam length. Greater attenuation gives a larger optical density. C/VM2 provides this relationship when describing projected-beam detector response.<ref name="CVM_28">Ministry of Business, Innovation and Employment (2025), p. 28.</ref>

<math display="block">D_u=-\frac{1}{L}\log_{10}\left(\frac{I}{I_0}\right),\qquad \frac{I}{I_0}=\frac{100-O}{100}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>D_u</math> || Optical density per unit beam length || m<sup>−1</sup>
|-
| <math>L</math> || Beam path length || m
|-
| <math>I</math> || Intensity at the receiver with smoke present || Same intensity unit as <math>I_0</math>
|-
| <math>I_0</math> || Intensity at the receiver without smoke || Same intensity unit as <math>I</math>
|-
| <math>O</math> || Total obscuration expressed as a percentage || %
|}

The worked example in New Zealand's C/VM2 (2025) uses a 10 m beam and an alarm setting of 50% total obscuration. Half of the original light intensity remains at the receiver. Substituting the source values gives approximately 0.030 m<sup>−1</sup>. This is the uniform optical density corresponding to the stated path and setting.<ref name="CVM_28" />

<math display="block">D_u=-\frac{1}{10}\log_{10}\left(\frac{100-50}{100}\right)=0.0301\ \mathrm{m}^{-1}\approx0.030\ \mathrm{m}^{-1}</math>

The calculation does not predict when the smoke will reach that value; a fire and smoke-transport analysis is still needed to estimate activation time. Nor is the result a universal point-detector threshold. It describes attenuation along the specified beam, using the detector's total-obscuration setting.<ref name="CVM_27_28" /><ref name="SMC_4-22_4-23" />

Smoke may occupy only part of the path, as when a plume crosses the beam. C/VM2 describes dividing a non-uniform path into segments and summing each segment's optical-density contribution. Schifiliti and colleagues describe the same distinction between uniform and segmented representations. Assuming a uniform layer when the actual exposure is local can misrepresent the beam measurement.<ref name="CVM_28" /><ref name="SMC_4-23" />

== Prescribed inputs in the New Zealand method ==

C/VM2, second edition (2025), specifies detector inputs for its verification calculations, and its smoke-detector representation includes ionisation, photoelectric spot and air sampling arrangements. The specified optical density at alarm is 0.097 m<sup>−1</sup>. The table also gives a radial distance of 7.0 m and a position at least 25 mm below the ceiling.<ref name="CVM_27" />

The document requires these analysis values regardless of the actual detector make or model, so they represent the method's prescribed simulation, rather than measured properties of every installed device. Projected-beam detectors are treated separately using beam length and total obscuration. The distinction prevents the spot-detector input from being applied as though it described every sensing arrangement.<ref name="CVM_27_28" />

C/VM2 permits the activation exposure to be obtained using a model with a ceiling-jet correlation or computational fluid dynamics. The latter approach calculates the gas flow and smoke or soot concentration directly. In either case, the response criterion and its application remain part of the method. A more detailed flow calculation does not by itself establish a different permitted detector threshold.<ref name="CVM_27" />

Prescribed regulatory inputs and experimental detector data answer different questions. The former provide consistency within a particular assessment route, while the latter describe response under the tested smoke and exposure conditions. A calculation identifies which type of evidence it uses so that its result can be interpreted within the correct scope.<ref name="CVM_27_28" /><ref name="SMC_4-22_4-24" />

== Signal processing and unwanted alarms ==

[[Unwanted fire alarms]] influence how a detector's signal is processed. The SFPE Handbook describes algorithms intended to distinguish fire signatures while reducing false and nuisance alarms; their details vary between products. These processing functions can change response relative to a calculation based solely on one smoke concentration.<ref name="SMC_4-22">Schifiliti, Meacham, and Custer (2002), p. 4-22.</ref>

A [[Multi-sensor detector]] combines sensing information, so the response of the combined device needs its own evidence. Knowing the calibration of one sensing element does not describe the complete processing decision, and the same principle applies when an alarm system requires confirmation from another detector. IFEG describes coincident systems that wait for two similar or dissimilar detectors before recognising an alarm.<ref name="SMC_4-22_4-24" /><ref name="IFEG_2.7-2">Australian Building Codes Board et al. (2005), p. 2.7-2.</ref>

A specialised nuclear-industry example illustrates the consequence of changing sensitivity. The 2010 supplement to NUREG/CR-6850 requires reduced sensitivity in very early warning systems to be assessed for loss of early detection benefit. It distinguishes early alerts from later fire alarms and controls their settings. Those provisions concern the defined United States nuclear application, not a universal classification of building alarms.<ref name="N10_13-6">U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), p. 13-6.</ref>

The nuclear report also limits the cabinet applications in which sampling can provide the credited warning. Smoke needs a path from the developing fault to the sampling location, but a tightly sealed cabinet can prevent the transport on which the arrangement depends. This application-specific limitation reinforces the distinction between a sensitive instrument and an effective detection path through the protected equipment.<ref name="N10_13-5">U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), p. 13-5.</ref>

The full response sequence includes the sensor, processing and the intended protective action. A lower number of nuisance signals alone does not demonstrate that the required fire is detected soon enough. Equally, a sensitive sensor can provide limited benefit if transport or subsequent action is delayed. The performance objective remains the basis for assessing the complete arrangement.<ref name="SMC_4-2_4-3__4-22">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3, 4-22.</ref><ref name="N10_13-6" />

== Evidence needed for a response prediction ==

Schifiliti and colleagues identify a gap between common smoke measurements and the information needed to predict individual detector response. Optical density is widely available, but it does not fully characterise ionisation or scattering behaviour. Manufacturer response algorithms and fuel-specific thresholds may also be unavailable. These limitations need to remain visible in the interpretation of a calculated activation time.<ref name="SMC_4-22_4-24" />

The handbook discusses experiments with detectors present as another source of response evidence. Product performance tests can provide limiting conditions even when detailed response traces are unpublished. The test fuel, smoke production, airflow and geometry still define the scope of that evidence. A result from one controlled exposure does not establish performance for every fire scenario.<ref name="SMC_4-23_4-24" />

Mulholland gives an illustrative calculation linking smoke production, detector response and deteriorating visibility. He explicitly notes that the example omits travel time to the detector and entry delay. He also identifies missing information on particle distributions and detector response to smoke agglomerates. The example therefore demonstrates a method and its data needs rather than establishing a complete real-fire warning time.<ref name="Mu_2-267_2-268">Mulholland (2002), pp. 2-267–2-268.</ref>

A sound comparison holds the fire and other relevant conditions consistent while examining changes in detector location or spacing. Schifiliti and colleagues caution against comparing uncertain smoke-response estimates directly with other predicted safety times without understanding their accuracy. The model, its inputs and its intended use must be compatible. Reported precision in seconds cannot remove uncertainty in the underlying smoke and sensor behaviour.<ref name="SMC_4-23" />

== See also ==

* [[Smouldering]]
* [[Heat detector]]
* [[Smoke stratification]]
* [[Smouldering-to-flaming transition]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Mulholland, G. W. (2002). Smoke production and properties. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-258–2-268). National Fire Protection Association.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association.
* U.S. Nuclear Regulatory Commission, & Electric Power Research Institute. (2010). ''Fire probabilistic risk assessment methods enhancements'' (NUREG/CR-6850, Supplement 1).

[[Category:Detection & Alarm]]

Manual call point

2026-11-02T18:42:44Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''manual call point''' is a device that allows a person to initiate a fire alarm after recognising a possible fire. Its operation relies on human action rather than an automatic sensing element. Predicting the time to alarm therefore requires consideration of how the fire is noticed and when someone acts.<ref name="CVM_28_29">Ministry of Business, Innovation and Employment (2025), pp. 28–29.</ref>

Manual initiation can form part of a wider detection and warning arrangement, and it provides an input to the alarm system, which must then communicate the intended warning or protective command. Other occupants may still need time to understand the warning and prepare to leave. The person operating the device and the people receiving the alarm perform different roles.<ref name="SMC_4-3">Schifiliti, Meacham, and Custer (2002), p. 4-3.</ref><ref name="P_3-350_3-351">Proulx (2002), pp. 3-350–3-351.</ref>

Engineering methods may restrict the circumstances in which manual activation can replace an automatic detection assumption. New Zealand's C/VM2 (2025), for example, sets conditions for high-ceiling spaces with limited numbers of awake, familiar occupants. Its treatment of enclosed offices also depends on room size, floor level and the escape route.<ref name="CVM_28_29" />

== Human recognition and alarm initiation ==

A manual call point relies on a person to initiate a [[Fire alarm system]]. The initiating sequence begins before the device is operated. Someone must become aware of a possible fire, recognise the situation and act on that information. New Zealand's C/VM2, second edition (2025), explicitly identifies this human interaction as a difficulty when predicting manual alarm activation.<ref name="CVM_29">Ministry of Business, Innovation and Employment (2025), p. 29.</ref>

The International Fire Engineering Guidelines (IFEG, 2005) distinguish several ways people can receive fire cues: these include seeing smoke or flames, smelling smoke and hearing sounds associated with the fire. Someone who recognises such a cue may also warn other people. Cue occurrence, recognition and the resulting response are separate parts of its analysis.<ref name="IFEG_1.8-7_1.8-9">Australian Building Codes Board et al. (2005), pp. 1.8-7–1.8-9.</ref>

The physical act of operating the call point is therefore only one part of manual initiation. The time at which a person first notices the fire may dominate the earlier sequence. People in enclosed rooms may receive different information from those in an open warehouse. A credible assessment identifies who is expected to notice the fire and what information reaches them.<ref name="CVM_28_29" /><ref name="IFEG_1.8-7_1.8-9" />

[[File:fse-manual-call-point-v1.svg|thumb|upright=1.5|alt=Person sees fire, reaches and operates call point, and alarm notifies occupants.|Manual initiation depends on human recognition and action. Based on Ministry of Business, Innovation and Employment (2025), p. 28 and Australian Building Codes Board et al. (2005), p. 1.8-7.]]

== Relationship to automatic detection and warning ==

Automatic detection responds to a fire signature through a sensor rather than waiting for human operation of a call point. The SFPE Handbook describes detection, processing and signalling as separate alarm-system functions. Manual initiation changes the source of the input without removing the need for processing and a suitable output. The subsequent warning still has to reach the people expected to act.<ref name="SMC_4-3" /><ref name="CVM_29" />

An [[Evacuation alarm system]] supplies the warning that supports occupant response. Hearing a signal is not equivalent to immediately starting evacuation travel. Proulx describes information seeking, preparation and the influence of staff instructions on this response. Manual operation by one person therefore does not establish that everyone else has recognised the emergency.<ref name="P_3-349_3-351">Proulx (2002), pp. 3-349–3-351.</ref>

Manual and automatic initiation can provide alternative paths within a design. IFEG gives an example in which occupants, smoke detectors or sprinklers can identify a fire; its redundancy analysis asks what remains available if a component fails. The benefit of several inputs depends on the functioning of the complete paths to the required action.<ref name="IFEG_1.2-24">Australian Building Codes Board et al. (2005), p. 1.2-24.</ref>

A manually operated input cannot be credited merely because the device is present. The fire needs to become perceptible to someone who can recognise and respond to it. In a modelling method, those human and spatial conditions can restrict where manual initiation is accepted. C/VM2's warehouse provisions provide a specific example of such restrictions.<ref name="CVM_26__28_29">Ministry of Business, Innovation and Employment (2025), pp. 26, 28–29.</ref>

== A conditional New Zealand warehouse method ==

In New Zealand, C/VM2 (2025) permits its manual-activation approach only under stated conditions. The space must have an average ceiling height of at least 5 m. Occupants must be awake and familiar with their surroundings, and the occupant load must be fewer than 50 people. Other situations require automatic detection under that method.<ref name="CVM_28">Ministry of Business, Innovation and Employment (2025), p. 28.</ref>

The commentary explains the intended large-space application through warehouses. A high ceiling allows smoke to move beneath it before conditions threaten occupants below. The method assumes that occupants become aware of the fire when the ceiling jet has traversed the entire length of the space. It uses this smoke-transport period as a proxy for the delay before manual activation.<ref name="CVM_26__28_29" />

Within that particular approach, no additional notification or pre-travel activity period is added for the open warehouse population. The method expects the simple call-point system to activate immediately once operated, and this is a combined modelling assumption about recognition and action. It is not evidence that real occupants always operate a call point without delay.<ref name="CVM_28_29" />

The method also addresses intermediate floors: they must be open, with occupants fully aware of a fire located in the warehouse. An enclosed intermediate room would change the assumed access to fire cues. The permission therefore depends on both building geometry and the occupants' opportunity to recognise the event.<ref name="CVM_29" />

[[File:fse-manual-call-point-v2.svg|thumb|upright=1.5|alt=Open warehouse supports manual recognition; enclosed office needs automatic detection.|Layout determines whether manual initiation is credible. Based on Ministry of Business, Innovation and Employment (2025), pp. 28–29.]]

== Separated rooms and the means of escape ==

C/VM2 treats occupied rooms separated from the high-ceiling space as a distinct case. Under its 2025 provisions, the small room may have a maximum area of 500 m², and it must be on the ground floor and have an escape route directly outside. Occupants must not need to enter the high-ceiling warehouse to use that route.<ref name="CVM_29" />

The method assigns those room occupants 60 s of pre-travel activity after manual activation, and this additional period belongs to the separated-room provision. It differs from the open warehouse assumption that adds no further notification or pre-travel activity time. Mixing the two cases would remove a condition from the prescribed assessment.<ref name="CVM_29" />

The required [[Means of escape]] are therefore part of this permission to use manual initiation. The direct outside route matters alongside room size and floor level. If the separated-office conditions are not satisfied, C/VM2 requires automatic detection within the office. Its detection and notification periods then follow the relevant automatic-system provisions.<ref name="CVM_29" />

A further exception concerns very small isolated ground-floor spaces, such as washrooms or offices. Each must be no larger than 30 m², and their aggregate occupant load must not exceed ten people. C/VM2 assigns 60 s of pre-travel activity to escape from these spaces. These numerical limits belong to the specified New Zealand method and edition.<ref name="CVM_29" />

[[File:fse-manual-call-point-v3.svg|thumb|upright=1.5|alt=After activation, a 60-second pre-travel block precedes movement along a direct outside route.|Small-space method includes 60 seconds and a direct outside route. Based on Ministry of Business, Innovation and Employment (2025), p. 29.]]

== Occupants, staff and management assumptions ==

Recognition of a fire is affected by the information available to the person. Proulx describes the influence of familiarity, responsibility, alertness and commitment to the activity already underway. A visitor may wait for staff instructions while a familiar occupant interprets the situation differently. These factors help explain why human initiation cannot be reduced to one universal delay.<ref name="P_3-350_3-351" />

Staff training is connected to the actual building and its evacuation procedure. Proulx notes that people trained in one building may not behave the same way in another. Public occupants may have no training specific to the premises they are visiting. Where a strategy relies on staff recognition and response, their role needs to match the credited action.<ref name="P_3-350">Proulx (2002), p. 3-350.</ref>

[[Fire safety management]] therefore supports the human part of the alarm arrangement, and it concerns the procedures and staff behaviour assumed when interpreting and responding to a fire cue. IFEG requires the cue used in an analysis to be selected and justified. Assuming early manual initiation without identifying the relevant occupants would leave that part of the sequence unexplained.<ref name="P_3-350_3-351" /><ref name="IFEG_1.8-7_1.8-9" />

Warnings from other people can also matter. IFEG recognises them as an alternative cue, while Proulx reports the influence of direct staff instructions on movement. Such warnings may reinforce the alarm signal or precede it. Their usefulness depends on the people present and the information they can communicate.<ref name="IFEG_1.8-7_1.8-9" /><ref name="P_3-349_3-351" />

== Evidence and limits of the assessment ==

The C/VM2 example describes when manual initiation may be used in a particular engineering calculation. It does not supply a universal permission to omit automatic detection from warehouses. The specified ceiling, occupant and room conditions have to be considered together. A superficially similar building may fall outside that method's stated application.<ref name="CVM_26__28_29" />

IFEG identifies limitations in methods for predicting the period before people start moving. It accepts documented literature, field observations and simulated evacuations as potential evidence, with substantiated engineering judgement where necessary. The source of an assumed manual response time therefore matters. A precise input without a stated basis can conceal uncertainty in recognition and action.<ref name="IFEG_1.8-7">Australian Building Codes Board et al. (2005), p. 1.8-7.</ref>

Redundancy does not remove this uncertainty automatically. Multiple initiating routes may still rely on shared processing or signalling functions. IFEG's redundancy study examines single points of failure and available backup, including whether failures would be recognised. This functional analysis distinguishes an alternative means of initiation from an independently available warning.<ref name="IFEG_1.2-24" />

== See also ==

* [[Evacuation strategy]]
* [[Pre-movement time]]
* [[Smoke detector]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association.

[[Category:Detection & Alarm]]

Heat detector

2026-11-02T18:42:39Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''heat detector''' is a fire-detection device that operates when its sensing element reaches a specified temperature or responds to a sufficiently rapid temperature rise. It detects thermal conditions rather than smoke particles. Its response depends on heat reaching the device and then changing the temperature or physical behaviour of the sensing element.<ref name="SMC_4-5_4-7">Schifiliti, Meacham, and Custer (2002), pp. 4-5–4-7.</ref><ref name="N_12-1_12-4">Iqbal and Salley (2004), pp. 12-1–12-4.</ref>

Hot gases moving beneath a ceiling commonly provide the exposure that heats the element. Gas temperature, gas velocity, detector position and thermal lag all affect when the device operates. The surrounding gas can therefore be hotter than the detector's nominal operating temperature before a fixed-temperature device responds.<ref name="IFEG_2.7-2">Australian Building Codes Board et al. (2005), p. 2.7-2.</ref><ref name="N_12-3">Iqbal and Salley (2004), p. 12-3.</ref>

Heat detectors include fixed-temperature, rate-of-rise, rate-compensated and combined arrangements. These mechanisms have different responses to fast and slow heating. Engineering assessment connects the selected mechanism to the expected fire, the normal environment and the time available for the intended protective action.<ref name="N_12-3_12-5">Iqbal and Salley (2004), pp. 12-3–12-5.</ref><ref name="SMC_4-19_4-20">Schifiliti, Meacham, and Custer (2002), pp. 4-19–4-20.</ref>

== What a heat detector senses ==

A heat detector responds to thermal conditions at its sensing element. Fixed-temperature devices operate when the element reaches a specified temperature. Rate-of-rise devices respond to a sufficiently rapid temperature increase. Iqbal and Salley describe both principles in NUREG-1805, a 2004 handbook prepared for United States nuclear fire protection inspections.<ref name="N_12-1_12-4" />

The detector forms an initiating input to a [[Fire alarm system]]; its operation does not itself mean that occupants have received a warning or that suppression has begun. The SFPE Handbook separates detection, processing and signalling when analysing the system. Those later functions can introduce additional time after the heat-sensitive element operates.<ref name="SMC_4-2_4-3">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3.</ref>

Heat detection requires sufficient energy to reach and heat the element, while a [[Smoke detector]] instead responds to combustion particles, which can provide an earlier indication in suitable fire conditions. A [[Flame detector]] senses emitted radiation and has different exposure requirements. The appropriate detection principle depends on the expected fire signature and the objective of the system.<ref name="N_12-1">Iqbal and Salley (2004), p. 12-1.</ref><ref name="SMC_4-3_4-4__4-30">Schifiliti, Meacham, and Custer (2002), pp. 4-3–4-4, 4-30.</ref>

Heat detection therefore cannot be described as universally interchangeable with smoke detection. NUREG-1805 associates it with situations such as confined spaces where rapidly developing fires are expected or environments unsuitable for other detection. The same source warns that thermal detection may be too slow for an early life-safety warning. These observations concern the relationship between the fire and the sensing mechanism.<ref name="N_12-1" />

== Fixed-temperature and rate-of-rise mechanisms ==

A fusible fixed-temperature element uses a material that melts at its operating temperature. Melting releases a mechanism or closes contacts to initiate the signal; the fusible element is not restored simply by cooling. NUREG-1805 distinguishes this arrangement from bimetallic devices that can return to their original condition after heating stops.<ref name="N_12-3" />

Bimetallic devices use metals with different thermal expansion behaviour: a strip can bend, or a shaped disc can reverse curvature when heated. This movement operates the electrical contacts. Electronic thermal detectors instead monitor a temperature-dependent electrical resistance and can apply a fixed-temperature or rate-of-rise criterion.<ref name="N_12-3__12-5">Iqbal and Salley (2004), pp. 12-3, 12-5.</ref>

A pneumatic rate-of-rise detector uses expanding air in a chamber or tube: a small vent accommodates gradual changes, while sufficiently rapid heating produces pressure faster than it can escape. That pressure operates a diaphragm and contacts. NUREG-1805 describes example operating rates around 7–8 °C per minute; this is not a universal threshold for every product.<ref name="N_12-4">Iqbal and Salley (2004), p. 12-4.</ref>

Heat detection can cover a compact point or extend along a line. NUREG-1805 describes a continuous cable in which heat-sensitive insulation separates two conductors until the operating condition is reached. Another arrangement uses temperature-dependent electrical conduction within the cable assembly. Pneumatic line detection instead responds to expansion within a length of tubing. The exposed length and the distribution of heating then affect the signal.<ref name="N_12-3__12-5" />

Combination devices can include both fixed-temperature and rate-of-rise functions: the rapid-rise element can respond during fast heating, while the fixed-temperature function remains relevant during slower heating. Rate-compensated devices use differential expansion to reduce the effect of thermal lag. Their internal mechanisms differ from a simple element represented by one uniform temperature.<ref name="N_12-4_12-5">Iqbal and Salley (2004), pp. 12-4–12-5.</ref><ref name="SMC_4-7">Schifiliti, Meacham, and Custer (2002), p. 4-7.</ref>

[[File:fse-heat-detector-v3.svg|thumb|upright=1.5|alt=Fixed-temperature alarm at a threshold and rate-of-rise alarm during rapid increase.|Fixed-temperature and rate-of-rise detection principles. Based on Iqbal and Salley (2004), pp. 12-3–12-4 and Schifiliti, Meacham, and Custer (2002), p. 4-19.]]

== Transport from the fire to the sensing element ==

Hot gases rise in a plume and spread beneath a ceiling as a [[Ceiling jet]]. A detector in this flow receives heat from the moving gases. Both gas temperature and gas velocity affect the transfer of energy to the element. The International Fire Engineering Guidelines (IFEG, 2005) also identify the element's distance below the ceiling as relevant.<ref name="IFEG_2.7-2" />

The temperature and velocity are not uniform throughout the flow, and their values change with location relative to the fire and with depth below the ceiling. A detector placed outside the relevant hot flow does not receive the exposure assumed for a detector within it. Geometry is therefore part of the response calculation rather than a separate installation detail.<ref name="IFEG_2.7-2" /><ref name="SMC_4-7" />

Thermal lag is the delay caused by the sensing element taking time to heat. During rising gas temperature, the element can remain cooler than the surrounding gases. Consequently, the gas temperature at operation can exceed the detector's nominal operating temperature. The rating applies to the element's response, not to instantaneous equality between gas and element temperatures.<ref name="N_12-3" />

The [[Detector activation time]] contains the effects of exposure and thermal response. A steady-exposure calculation begins when the assumed hot gases reach the element, so it does not automatically include the earlier transport of those gases from the fire. Schifiliti and colleagues explicitly identify this transport omission in the simplest steady ceiling-jet model.<ref name="SMC_4-7_4-8">Schifiliti, Meacham, and Custer (2002), pp. 4-7–4-8.</ref>

[[File:fse-heat-detector-v1.svg|thumb|upright=1.5|alt=Plume and ceiling jet transfer heat to a detector element, which responds after a lag.|Heat-detector response depends on ceiling-jet exposure and thermal lag. Based on Australian Building Codes Board et al. (2005), p. 2.7-2 and Schifiliti, Meacham, and Custer (2002), p. 4-7.]]

== Thermal response and response time index ==

A common model treats the sensing element as a single uniform thermal mass. This is called the lumped-mass approximation. It assumes that temperature differences within the element can be neglected. The temperature then increases according to the heat transferred from the gas and the element's thermal response.<ref name="SMC_4-5_4-6">Schifiliti, Meacham, and Custer (2002), pp. 4-5–4-6.</ref><ref name="N_12-6">Iqbal and Salley (2004), p. 12-6.</ref>

The [[Response time index]] (RTI) expresses thermal sensitivity in this model. For a given gas exposure, a smaller RTI gives faster heating of the element. The governing equation relates the rate of element heating to gas velocity and the temperature difference. As the element approaches the gas temperature, that driving temperature difference becomes smaller.<ref name="SMC_4-6">Schifiliti, Meacham, and Custer (2002), p. 4-6.</ref>

<math display="block">\frac{dT_d}{dt}=\frac{\sqrt{u}}{\mathrm{RTI}}(T_g-T_d)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>T_d</math> || Temperature of the detector's sensing element || °C
|-
| <math>T_g</math> || Gas temperature at the sensing element || °C
|-
| <math>t</math> || Time measured from the start of the assumed exposure || s
|-
| <math>u</math> || Gas velocity at the element || m/s
|-
| <math>\mathrm{RTI}</math> || Response time index || m<sup>1/2</sup>s<sup>1/2</sup>
|-
| <math>T_a</math> || Initial element temperature, equal to ambient in this model || °C
|-
| <math>T_r</math> || Element temperature required for operation || °C
|-
| <math>t_r</math> || Time to operation under the assumed constant exposure || s
|}

For constant gas temperature and velocity, the equation can be integrated to obtain the time to reach the operating temperature. The expression below uses the natural logarithm, and it applies when the element starts at ambient temperature and the gas temperature exceeds the operating threshold. It represents fixed-temperature response under the stated thermal assumptions.<ref name="SMC_4-8">Schifiliti, Meacham, and Custer (2002), p. 4-8.</ref><ref name="N_12-6" />

<math display="block">t_r=\frac{\mathrm{RTI}}{\sqrt{u}}\ln\left(\frac{T_g-T_a}{T_g-T_r}\right)</math>

The ratio inside the logarithm uses temperature differences, so consistent Celsius differences can be used. The response time becomes longer when the operating temperature approaches the imposed gas temperature. If the gas never becomes hot enough, this constant-exposure model does not predict threshold operation. A nominal temperature rating alone is therefore insufficient to calculate a response time.<ref name="SMC_4-6_4-8">Schifiliti, Meacham, and Custer (2002), pp. 4-6–4-8.</ref>

[[File:fse-heat-detector-v2.svg|thumb|upright=1.5|alt=Gas temperature rises quickly while element temperature follows more slowly past the rating.|Element temperature lags behind gas temperature. Based on Iqbal and Salley (2004), p. 12-3 and Schifiliti, Meacham, and Custer (2002), p. 4-7.]]

== Worked example under constant exposure ==

The SFPE Handbook's second example uses the gas conditions calculated for a 4 m² kerosene pool beneath a flat ceiling. The ceiling is 6 m above the fire and the detector is 6 m horizontally from the plume centre. The ambient temperature is 20 °C. Its calculated exposure is a gas temperature of 153 °C and a velocity of 2.4 m/s.<ref name="SMC_4-8" />

The example detector has an RTI of 55 m<sup>1/2</sup>s<sup>1/2</sup> and an operating temperature of 57 °C. Substituting those values gives an exposure response time of approximately 11.6 s. Rounded upwards to whole seconds, the required time is 12 s. This reproduces the response reported in the handbook example.<ref name="SMC_4-8" />

<math display="block">t_r=\frac{55}{\sqrt{2.4}}\ln\left(\frac{153-20}{153-57}\right)\ \mathrm{s}\approx12\ \mathrm{s}</math>

This is the time for the specified element to heat under the specified exposure. It is not a claim that a detector will alarm 12 s after every kerosene fire ignites. The example assumes the calculated gas conditions are already present and remain constant. Fire growth, transport to the detector and subsequent alarm-system delays require separate treatment.<ref name="SMC_4-2_4-3__4-8">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3, 4-8.</ref>

For growing fires, Schifiliti and colleagues divide the changing exposure into short time intervals. The updated element temperature is carried from one interval into the next. Gas temperature and velocity can then change as the fire grows. This approach preserves the element's heating history instead of restarting the calculation at ambient temperature each time.<ref name="SMC_4-8_4-9">Schifiliti, Meacham, and Custer (2002), pp. 4-8–4-9.</ref>

== What tests and prescribed inputs represent ==

A plunge test exposes the device to a gas flow with known, constant temperature and velocity. The measured operating time can be used to infer a thermal time constant and RTI. The SFPE Handbook explains that this is a simplified representation of heat transfer. Flow around the device and heat loss into its supporting body can limit the approximation.<ref name="SMC_4-6" />

Listed spacing is derived through defined test arrangements, but it does not directly state the time to respond to every fire in an actual building. Ceiling height, beams, airflow and detector exposure can differ from the test. Schifiliti and colleagues distinguish compliance with spacing rules from quantitative assessment against a specified fire-size or response objective.<ref name="SMC_4-3_4-4">Schifiliti, Meacham, and Custer (2002), pp. 4-3–4-4.</ref>

In New Zealand, C/VM2, second edition (2025), prescribes heat-detector modelling inputs regardless of the installed make or model. These include RTI 30 m<sup>1/2</sup>s<sup>1/2</sup>, an activation temperature of 57 °C and a radial distance of 4.2 m. The table also specifies a position at least 25 mm below the ceiling. These values belong to that verification method's analysis.<ref name="CVM_27">Ministry of Business, Innovation and Employment (2025), p. 27.</ref>

RTI describes the interaction between the sensing element and the moving gases; it is not a temperature rating or a direct statement of the time from ignition. The same RTI can give different response times when gas temperature or velocity changes. Likewise, two detectors with the same operating temperature can respond at different times because their thermal sensitivities differ. These distinctions explain why both temperature and sensitivity appear in the model.<ref name="SMC_4-6_4-8" />

The prescribed values must not be mistaken for a universal specification of actual detectors. A product can have measured characteristics different from those analysis inputs. The source distinguishes the required simulation from the device selected for installation. An engineering report therefore identifies whether its inputs are measured, assumed or prescribed by the chosen method.<ref name="CVM_27" /><ref name="SMC_4-6" />

== Choosing between thermal response principles ==

A fixed-temperature device and a rate-of-rise device respond to different features of the same exposure. A rapid temperature increase can activate the rate-of-rise function before the fixed-temperature element reaches its threshold. During slower heating, the rate-of-rise condition may be less favourable. Combination devices use both mechanisms to address these different conditions.<ref name="N_12-4_12-5" />

The handbook examines this distinction using several fire growth rates, and its examples show that detector spacing and response depend on the growth history as well as sensitivity. A device that responds earlier in one scenario need not do so in another. The result supports comparing detectors against the intended fire scenarios rather than ranking the mechanisms universally.<ref name="SMC_4-19_4-20" />

Rate-compensated and pneumatic rate-of-rise devices require particular care in modelling, and their internal heat transfer and mechanical response are more complex than one directly exposed element. The SFPE Handbook explains that a single lumped mass may not represent these mechanisms adequately. Applying the fixed-temperature equation unchanged would omit parts of the device's operating principle.<ref name="SMC_4-7" />

== Environmental effects and calculation limits ==

Normal non-fire temperatures influence the selection of a thermal operating rating. NUREG-1805 discusses higher-temperature devices for locations where ordinary ambient conditions would otherwise cause premature operation. The relevant exposure is the temperature near the detector, including expected non-fire heat sources. A rating chosen without those conditions can produce unwanted alarms.<ref name="N_12-1_12-3">Iqbal and Salley (2004), pp. 12-1–12-3.</ref>

The report's simple ceiling-jet method assumes an unconfined flat ceiling and a fire away from walls and corners. It excludes a developed hot layer beneath the jet during the period of interest. Obstructions and irregular ceilings can undermine the assumed flow. The method also does not explicitly include direct radiant heating of the sensing element.<ref name="N_12-10_12-11">Iqbal and Salley (2004), pp. 12-10–12-11.</ref>

The assumption of a constant RTI is itself an approximation. Schifiliti and colleagues discuss the complex gas flow around irregular detector shapes and the possibility of heat conduction into supporting parts. A plunge test may involve conditions in which those heat losses are relatively small, but their importance can differ during the slower flows of an actual fire. A thermal parameter obtained from one test condition therefore needs an appropriate range of application.<ref name="SMC_4-6" />

Modelled response after another protective device operates also requires care. The handbook notes that its basic calculations do not account for sprinkler cooling when predicting subsequent detector or sprinkler activation. The first operating device can change the environment experienced by other devices. Their later responses cannot automatically be inferred by continuing the original unsuppressed exposure unchanged.<ref name="SMC_4-7" />

The gas-flow calculation and the element-response calculation have separate limitations. Correctly integrating a thermal equation cannot compensate for an unsuitable gas temperature or velocity prediction. Conversely, suitable gas conditions do not establish the correct thermal model for every detector mechanism. The assessed geometry, fire development and device behaviour must all fit the chosen method.<ref name="SMC_4-7_4-9">Schifiliti, Meacham, and Custer (2002), pp. 4-7–4-9.</ref><ref name="N_12-10">Iqbal and Salley (2004), p. 12-10.</ref>

== See also ==

* [[Multi-sensor detector]]
* [[Thermal inertia]]
* [[Fire plume]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association.

[[Category:Detection & Alarm]]

Fire alarm system

2026-11-02T18:42:34Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''fire alarm system''' detects or receives an indication of fire, processes that information and produces the warning or control signals required by its design. The SFPE Handbook describes these functions as detection, processing and signalling. The system can warn occupants and initiate other protective actions, such as smoke control or door closing.<ref name="SMC_4-2_4-3">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3.</ref>

Its performance depends on the complete sequence from fire development to the intended response. Smoke or heat must reach an automatic detector before it can operate. Processing and verification may introduce further delay, followed by notification or intervention. A detector's activation time is therefore only one part of the system's response time.<ref name="SMC_4-2_4-3__4-21_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3, 4-21–4-24.</ref>

Engineering assessment starts with the safety objective and the fire scenarios against which it will be checked. Detector selection, location, warning arrangements and human response are then considered together. Testing and management support those assumptions, while analysis identifies delays, uncertain inputs and shared failures that could prevent the intended action.<ref name="SMC_4-1_4-3">Schifiliti, Meacham, and Custer (2002), pp. 4-1–4-3.</ref><ref name="IFEG_1.2-24">Australian Building Codes Board et al. (2005), p. 1.2-24.</ref>

== Detection, processing and signalling ==

Schifiliti, Meacham and Custer divide a fire alarm system into three functional elements: detection, processing and signalling. Detection senses a fire characteristic or receives an initiating input. Processing evaluates that input according to the system's configured functions. Signalling then communicates the warning or command required by the design.<ref name="SMC_4-3">Schifiliti, Meacham, and Custer (2002), p. 4-3.</ref>

An automatic initiating device responds to a physical fire signature: a [[Smoke detector]] responds to particles, while a [[Heat detector]] responds to thermal conditions. A [[Manual call point]] allows a person who recognises a fire to initiate the alarm. These inputs depend on different mechanisms and need not operate at the same time.<ref name="SMC_4-3_4-4">Schifiliti, Meacham, and Custer (2002), pp. 4-3–4-4.</ref><ref name="CVM_28_29">Ministry of Business, Innovation and Employment (2025), pp. 28–29.</ref>

The outputs can include an [[Evacuation alarm system]] and commands to other protective systems. The SFPE Handbook gives smoke control, lift recall, door closing and signalling to the fire service as examples. Which outputs operate depends on the intended function of the particular installation. An initiating signal and a completed protective action are therefore different events in the analysis.<ref name="SMC_4-2_4-3" />

This functional description does not prescribe a particular control-panel arrangement. The handbook treats panel selection and detailed auxiliary control design as outside its detection calculation chapter, and its method instead follows what each function needs to achieve and when. That distinction allows detector performance to be assessed without assuming that every alarm installation has identical hardware.<ref name="SMC_4-3" />

[[File:fse-fire-alarm-system-v1.svg|thumb|upright=1.5|alt=Smoke and heat detectors and call point feeding control, sounders, voice and linked systems.|Fire alarm components serve a shared safety goal. Based on Schifiliti, Meacham, and Custer (2002), pp. 4-1–4-3.]]

== Defining what the system must achieve ==

The system objective determines what counts as sufficiently early detection. For life safety, warning must leave enough time for the intended occupant response before conditions become untenable. Other objectives can concern damage to equipment, business interruption or environmental consequences. The SFPE Handbook begins its design process by identifying these goals.<ref name="SMC_4-1_4-2">Schifiliti, Meacham, and Custer (2002), pp. 4-1–4-2.</ref>

A performance objective becomes more useful when expressed through measurable conditions. Examples include limiting the fire's heat release rate or preventing damage beyond a specified item. Heat release rate describes how quickly the fire releases energy. The selected objective determines the latest acceptable point for detection and the subsequent response.<ref name="SMC_4-2_4-3" />

The fire may continue growing after the detector operates. Processing, warning, staff response or suppression initiation can consume additional time. Schifiliti and colleagues therefore distinguish the limiting design fire from the smaller fire that must trigger detection. The difference depends on fire growth during the remaining response period.<ref name="SMC_4-2_4-3" />

Several fire scenarios are considered because fuels, growth rates and locations can vary; the handbook describes testing a candidate design against alternative scenarios after establishing its detector type and spacing. A system that satisfies one scenario may fail its objective in another. This examination connects the detection arrangement to the hazards in the actual occupancy.<ref name="SMC_4-3" />

== Fire signatures and detector response ==

A fire signature is a measurable effect of combustion that can be sensed by a detector. Smoke particles, elevated temperature and emitted radiation are different signatures, and their strength and transport depend on the fuel and the fire's development. Selecting a detector therefore involves identifying the signature expected before the limiting fire condition occurs.<ref name="SMC_4-3_4-4" />

Heat detection depends on gases transferring energy to a sensing element, and the gas temperature and velocity at the device affect its rate of heating. Smoke detection depends on particle transport, entry into the sensing chamber and the sensor's response to those particles. Neither process is represented completely by a device's nominal alarm threshold alone.<ref name="SMC_4-5_4-8__4-21_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-5–4-8, 4-21–4-24.</ref>

Ceiling height, beams and other obstructions can change the route taken by fire products, and a higher plume can entrain more air before reaching the ceiling, reducing temperature and concentration. Air currents are particularly relevant to smoke transport during weak early fires. These effects explain why detector location is part of performance assessment.<ref name="SMC_4-4__4-21_4-22">Schifiliti, Meacham, and Custer (2002), pp. 4-4, 4-21–4-22.</ref>

Product testing supplies evidence about response under defined conditions; the handbook distinguishes this evidence from a calculation of the installed system's response to a particular fire. Test fuels, airflow and geometry may differ from those in the building. A stated installation spacing therefore needs to be interpreted alongside the conditions and objective of the assessment.<ref name="SMC_4-3_4-4__4-22_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-3–4-4, 4-22–4-24.</ref>

== Processing decisions and response delays ==

Processing can introduce a delay between an initial detector signal and the required output. Alarm verification is one example discussed in the SFPE Handbook, and it is intended to address nuisance signals, but its delay remains part of the response sequence. A timing calculation that omits it can overstate the time available for intervention.<ref name="SMC_4-2__4-28_4-29">Schifiliti, Meacham, and Custer (2002), pp. 4-2, 4-28–4-29.</ref>

The International Fire Engineering Guidelines (IFEG, 2005) describe coincident detection, which requires two or more detectors to operate before an alarm is recognised. The inputs may come from similar detectors at different locations or from different detector types. Such logic changes the condition required to initiate the output. It must therefore be represented when estimating activation rather than treating the first detector as sufficient.<ref name="IFEG_2.7-2">Australian Building Codes Board et al. (2005), p. 2.7-2.</ref>

[[Unwanted fire alarms]] and genuine fire response need to be considered together. Schifiliti and colleagues describe signal-processing algorithms intended to reduce nuisance alarms and identify fire signatures, and their operation can vary between products and may not be fully published. A simple threshold calculation may consequently omit part of the actual decision process.<ref name="SMC_4-22_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-22–4-24.</ref>

A warning or control output is useful only in relation to its intended recipient or equipment; the same initiating event may lead to several different actions in the building. The functional description therefore follows each output to the action relevant to the safety objective. This prevents a control-panel indication from being treated as if evacuation or suppression were already complete.<ref name="SMC_4-2_4-3" />

== Worked example of the response time budget ==

Example 20 in the SFPE detection chapter considers a hotel ballroom and an intended staff response to a chair fire. It assigns 10 s to the system delay between detector activation and alarm initiation. Alarm verification ranges from 15 s to 60 s in that example. Staff take a further 60 s from the indicated alarm to arrival.<ref name="SMC_4-28">Schifiliti, Meacham, and Custer (2002), p. 4-28.</ref>

The post-detection subtotal is found by adding these successive delays. Using the longer verification time gives 130 s. Using the shorter verification time gives 85 s. Both calculations exclude the time taken for smoke to reach the detector, which the source identifies separately.<ref name="SMC_4-28_4-29">Schifiliti, Meacham, and Custer (2002), pp. 4-28–4-29.</ref>

<math display="block">t_{\mathrm{post}}=t_{\mathrm{system}}+t_{\mathrm{verify}}+t_{\mathrm{staff}}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>t_{\mathrm{post}}</math> || Subtotal after detector activation, excluding smoke transport || s
|-
| <math>t_{\mathrm{system}}</math> || System delay used in the example || s
|-
| <math>t_{\mathrm{verify}}</math> || Alarm verification delay || s
|-
| <math>t_{\mathrm{staff}}</math> || Time from alarm indication to staff arrival || s
|}

<math display="block">t_{\mathrm{post,long}}=10+60+60=130\ \mathrm{s}</math>
<math display="block">t_{\mathrm{post,short}}=10+15+60=85\ \mathrm{s}</math>

These are source-specific example inputs, not standard delays for fire alarm systems. The difference illustrates why a processing feature can change the time available for the intended intervention. The complete assessment must still account for fire development and transport to the detector. It must also justify which verification and staff-response assumptions apply to the scenario.<ref name="SMC_4-28_4-29" />

[[File:fse-fire-alarm-system-v2.svg|thumb|upright=1.5|alt=Timeline split into detection, initiation, notification, pre-travel and movement.|A response-time budget separates each delay. Based on Ministry of Business, Innovation and Employment (2025), pp. 26–30.]]

== Connecting the alarm to occupant response ==

Notification is the point at which information reaches the occupants, not the moment at which an automatic detector first senses a fire. New Zealand's C/VM2, second edition (2025), separates detection time from notification time, and it also distinguishes pre-travel activity after notification from movement towards safety. These periods perform different roles in its required safe egress time calculation.<ref name="CVM_26">Ministry of Business, Innovation and Employment (2025), p. 26.</ref>

For standard evacuation strategies, C/VM2 assigns 30 s to notification. Where management investigates an activation before notifying occupants, the method requires the extended notification period to be considered. Its pre-travel activity values also vary with occupant group, location and warning type. These are provisions of the New Zealand method rather than universal properties of alarm equipment.<ref name="CVM_29_30">Ministry of Business, Innovation and Employment (2025), pp. 29–30.</ref>

A [[Voice alarm system]] can supply information that a tone alone does not convey. Proulx describes the influence of informative messages, staff instructions and familiarity on the decision to start moving. Audibility and intelligibility both affect whether a spoken warning can serve its purpose. The alarm's electrical operation and the occupant's response therefore require separate evidence.<ref name="P_3-349_3-351">Proulx (2002), pp. 3-349–3-351.</ref>

Occupants may also receive direct fire cues or warnings from other people. IFEG requires the cue used in an evacuation analysis to be identified and its selection justified. Different groups in different enclosures can receive different information. Treating every occupant as responding immediately to the first panel signal would bypass this part of the assessment.<ref name="IFEG_1.8-7_1.8-9">Australian Building Codes Board et al. (2005), pp. 1.8-7–1.8-9.</ref>

== Reliability and shared dependencies ==

Several initiating routes can support the same protective action. IFEG gives a shopping-centre example involving detection by people, smoke detectors or sprinklers. Smoke control can likewise receive automatic or manual activation signals. These alternatives provide useful redundancy only when the complete functional paths are considered.<ref name="IFEG_1.2-24" />

A redundancy study looks for single points of failure within apparently separate arrangements. If several paths depend on one component, failure of that component can remove their shared function. IFEG therefore asks what backup remains after an individual failure. Counting initiating devices alone does not establish the independence of the resulting warning or control actions.<ref name="IFEG_1.2-24" />

The same assessment distinguishes failure from reduced performance. A delayed response can matter even when the equipment eventually operates. IFEG describes sensitivity studies that vary important inputs and uncertainty studies that examine confidence in the outcome. These methods support an explicit treatment of the timing and reliability assumptions used in the design.<ref name="IFEG_1.2-24" />

The analysis also considers whether failure would be recognised by those responsible for the building. In IFEG's example, the objective includes avoiding unrecognised equipment failure and retaining a backup route, and this connects technical reliability to the arrangements for operating and managing the building. An alternative activation path cannot help if its availability is only assumed.<ref name="IFEG_1.2-24" />

[[File:fse-fire-alarm-system-v3.svg|thumb|upright=1.5|alt=Two detection and notification paths sharing one power and control dependency.|Redundant paths can share a single point of failure. Based on Australian Building Codes Board et al. (2005), p. 1.2-24.]]

== Testing, management and the limits of models ==

[[Fire safety management]] supports the response credited to the installed system. Staff who receive an indication need procedures consistent with the assumed action and timing. Proulx links training to the particular building and its evacuation arrangements. The modelled benefit of staff intervention therefore depends on more than the presence of an alarm output.<ref name="P_3-350_3-351">Proulx (2002), pp. 3-350–3-351.</ref>

A specialised example appears in the 2010 supplement to NUREG/CR-6850 for United States nuclear facilities, and its very early warning detection assessment depends on acceptance testing, maintenance, calibration and documented settings. It distinguishes an incipient alert from a later fire alarm. These conditions belong to that nuclear cabinet application and are not presented as general building rules.<ref name="N10_13-5_13-7">U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), pp. 13-5–13-7.</ref>

The same report requires reductions in sensitivity to be assessed for their effect on early detection. It also relates the credited benefit to personnel locating the source and taking the intended action. This example demonstrates how an engineering claim can depend on both equipment and operating procedures. Changing either can change the performance assumed in the assessment.<ref name="N10_13-6_13-7">U.S. Nuclear Regulatory Commission and Electric Power Research Institute (2010), pp. 13-6–13-7.</ref>

A verification method can prescribe analysis inputs that differ from the characteristics of the installed product. In New Zealand, C/VM2 (2025) requires its tabulated detector values to be used regardless of make or model. Its heat-detector representation uses an activation temperature of 57 °C and a response time index of 30 m<sup>1/2</sup>s<sup>1/2</sup>. The response time index characterises the thermal lag of the sensing element.<ref name="CVM_27">Ministry of Business, Innovation and Employment (2025), p. 27.</ref><ref name="SMC_4-6">Schifiliti, Meacham, and Custer (2002), p. 4-6.</ref>

The same table assigns an optical density of 0.097 m<sup>−1</sup> at alarm for its smoke-detector representation. Optical density describes attenuation of light by smoke along a specified distance. Projected-beam detectors are treated separately using the beam length and total obscuration setting. These distinctions concern the calculation required by that method, so they do not establish universal product sensitivities.<ref name="CVM_27_28">Ministry of Business, Innovation and Employment (2025), pp. 27–28.</ref>

A performance report therefore distinguishes prescribed analysis values, measured device characteristics and assumptions about system operation. Each answers a different question about the proposed arrangement. The handbook's detector calculations need suitable fire and sensor inputs, whereas the New Zealand method specifies some of those inputs directly. Reporting their origin makes the calculation reproducible and exposes where a different method could produce a different result.<ref name="SMC_4-21_4-24">Schifiliti, Meacham, and Custer (2002), pp. 4-21–4-24.</ref><ref name="CVM_27_28" />

Detector models also have limits independent of maintenance. Schifiliti and colleagues identify uncertainty in smoke properties, transport and manufacturer response algorithms. Simplified response estimates need to be interpreted within those limits. Where the required evidence is unavailable, a precise calculated time does not by itself establish precise system performance.<ref name="SMC_4-21_4-24" />

== See also ==

* [[Reliability of fire protection systems]]
* [[Flame detector]]
* [[Aspirating smoke detection]]
* [[Fire curtain]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association.
* U.S. Nuclear Regulatory Commission, & Electric Power Research Institute. (2010). ''Fire probabilistic risk assessment methods enhancements'' (NUREG/CR-6850, Supplement 1).

[[Category:Detection & Alarm]]

Evacuation alarm system

2026-11-02T18:42:29Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

An '''evacuation alarm system''' warns building occupants of a fire-related emergency so that they can begin the intended evacuation response. It communicates a cue through alarm signals or spoken information, often supported by staff instructions. Its effectiveness depends on people receiving, understanding and acting on that warning.<ref name="SMC_4-2_4-3">Schifiliti, Meacham, and Custer (2002), pp. 4-2–4-3.</ref><ref name="P_3-350_3-351">Proulx (2002), pp. 3-350–3-351.</ref>

Detection and evacuation are separate stages. A detector may identify a fire before occupants know about it, and people may take further time to interpret the warning. The notification period, preparation period and movement period therefore have different meanings in an evacuation calculation. Combining them into one unexplained delay can hide the assumptions that determine the result.<ref name="CVM_26">Ministry of Business, Innovation and Employment (2025), p. 26.</ref>

The appropriate warning depends on the occupants, the building and the planned evacuation strategy. Familiarity, sleep, assistance needs, staff behaviour and previous false alarms can affect the response. Engineering assessments connect these human factors to the warning equipment and identify the evidence behind the selected times.<ref name="P_3-350_3-351" /><ref name="IFEG_1.8-7_1.8-9">Australian Building Codes Board et al. (2005), pp. 1.8-7–1.8-9.</ref>

== From detection to a useful warning ==

An evacuation warning begins with information that a fire may be present; an automatic detector can respond to smoke, heat or another measurable fire characteristic. A [[Manual call point]] introduces a human decision into this chain. Someone must first perceive the fire, recognise its significance and operate the alarm.<ref name="IFEG_1.8-7_1.8-9" /><ref name="CVM_28_29">Ministry of Business, Innovation and Employment (2025), pp. 28–29.</ref>

The [[Fire alarm system]] processes the initiating signal and activates the required outputs, and its warning function is one part of a wider system that may also operate other protective equipment. Schifiliti, Meacham and Custer distinguish detection, processing and signalling when analysing this sequence. Separating these functions makes their individual delays and purposes easier to identify.<ref name="SMC_4-2_4-3" />

A warning is a cue: information that may prompt a person to interpret the situation as an emergency. The International Fire Engineering Guidelines (IFEG, 2005) distinguish the occurrence of a cue from its recognition. Seeing flames, smelling smoke or receiving a warning from another person can also provide cues. These alternatives depend on the fire scenario and the people who can perceive them.<ref name="IFEG_1.8-7_1.8-9" />

The analysis therefore identifies which cue is expected to reach each occupant group; a detector signal at a control panel is not automatically a warning received by every occupant. Equally, a person in the fire room may recognise smoke before the building warning operates. The selected cue and its timing need to be consistent throughout the evacuation calculation.<ref name="IFEG_1.8-7_1.8-9" />

[[File:fse-evacuation-alarm-system-v1.svg|thumb|upright=1.5|alt=Detection, alarm, notification, recognition, pre-travel activity and movement in sequence.|An evacuation alarm works through a complete response chain. Based on Australian Building Codes Board et al. (2005), p. 1.8-7 and Proulx (2002), pp. 3-350–3-351.]]

== Alarm tones and spoken information ==

An alarm tone attracts attention but may provide little information about the event. Occupants may seek confirmation, observe other people or wait for instructions before moving. Proulx describes warning effectiveness in terms of the information available and the response it produces. The assessment extends beyond whether a signalling device has operated.<ref name="P_3-349_3-351">Proulx (2002), pp. 3-349–3-351.</ref>

A [[Voice alarm system]] can communicate the nature and location of an incident and the action expected from occupants. Proulx reports that informative live messages can prompt a faster response than an unexplained tone; the same chapter distinguishes live instructions from general prerecorded messages. Their effectiveness depends on the message content and the conditions in which people receive it.<ref name="P_3-349_3-350">Proulx (2002), pp. 3-349–3-350.</ref>

Audibility means that occupants can hear the warning. Intelligibility means that they can understand spoken information. Proulx identifies both as matters to assess when evaluating a voice communication system. An audible message offers limited benefit if the recipient cannot understand its meaning.<ref name="P_3-350">Proulx (2002), p. 3-350.</ref>

The information may also need to differ between parts of a building. People near the fire and people on a remote floor do not necessarily face the same conditions. The SFPE Handbook describes the need for information about fire location and extent in partial evacuation or stay-in-place arrangements. Such strategies connect warning design to the planned protective action.<ref name="SMC_4-2">Schifiliti, Meacham, and Custer (2002), p. 4-2.</ref>

[[File:fse-evacuation-alarm-system-v3.svg|thumb|upright=1.5|alt=Occupant waits at a tone but moves after a precise live message or staff instruction.|Live voice and staff instructions can prompt faster response. Based on Proulx (2002), pp. 3-350–3-351.]]

== Why occupants do not all move immediately ==

[[Pre-movement time]] includes the period between receiving a warning and starting evacuation travel. During this period, people may interpret the warning, seek information or prepare to leave; it is distinct from the time spent walking towards an exit. Leaving it out can produce a misleadingly short estimate of the required escape time.<ref name="P_3-349_3-351" /><ref name="CVM_26" />

Familiarity affects how readily people understand the building and its evacuation arrangements. Office workers may know the alarm and exits, whereas visitors may depend on staff. Being awake and alert also differs from being asleep when the warning occurs. Proulx treats these as characteristics of the occupants and their situation, rather than a single universal response time.<ref name="P_3-350_3-351" />

People with family members or other close companions may try to gather them before leaving. Those committed to an activity may be reluctant to interrupt it without clearer information. Proulx gives examples involving restaurants, travel and entertainment. These activities affect the interpretation of the warning and the preparation needed before movement starts.<ref name="P_3-350_3-351" />

The surroundings influence this response as well: an open space can allow occupants to observe other people and notice smoke or staff instructions. Separate rooms may restrict access to that information. The warning system and the building layout therefore affect the same human decision process.<ref name="P_3-350" />

== Separating the time components ==

Required safe egress time is the calculated time needed for the specified occupants to leave the assessed location. In New Zealand, C/VM2, second edition (2025), separates detection, notification, pre-travel activity and movement. Notification begins after detection and ends when occupants are notified. Pre-travel activity then precedes the start of evacuation movement.<ref name="CVM_26" />

For its simple hydraulic calculation, C/VM2 uses the greater of travel time and flow time for evenly distributed occupants leaving the room of origin. Flow time represents congestion controlled by the capacity of the escape route; the expression below states that particular calculation, rather than a universal formula for every evacuation strategy. Additional provisions apply to delayed evacuation arrangements.<ref name="CVM_26" />

<math display="block">\mathrm{RSET}=t_d+t_n+t_{\mathrm{pre}}+\max(t_{\mathrm{trav}},t_{\mathrm{flow}})</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\mathrm{RSET}</math> || Required safe egress time for the assessed location || s
|-
| <math>t_d</math> || Detection time from ignition || s
|-
| <math>t_n</math> || Time from detection to occupant notification || s
|-
| <math>t_{\mathrm{pre}}</math> || Pre-travel activity time following notification || s
|-
| <math>t_{\mathrm{trav}}</math> || Travel time towards safety || s
|-
| <math>t_{\mathrm{flow}}</math> || Flow time associated with congestion || s
|}

For standard evacuation strategies, this New Zealand method assigns a notification time of 30 s. Non-standard arrangements must account for any extended notification time, and the document gives management investigation of a single activation as an example. The 30 s value is a modelling provision within this method, not a measured delay for every alarm installation.<ref name="CVM_29">Ministry of Business, Innovation and Employment (2025), p. 29.</ref>

[[File:fse-evacuation-alarm-system-v2.svg|thumb|upright=1.5|alt=Standard 30-second notification beside a longer non-standard period.|Notification time must match the evacuation strategy. Based on Ministry of Business, Innovation and Employment (2025), p. 29.]]

== Worked example of warning and preparation ==

C/VM2 assigns different pre-travel activity times according to occupant characteristics, location and warning type. Consider awake, alert occupants unfamiliar with the building, such as visitors in retail or exhibition spaces. For those remote from the enclosure of fire origin, the table assigns 120 s following a standard alarm signal. A voice alarm signal has an assigned pre-travel time of 60 s for the same group.<ref name="CVM_30">Ministry of Business, Innovation and Employment (2025), p. 30.</ref>

Using the method's standard notification allowance of 30 s, the notification and pre-travel subtotal becomes 150 s for the standard signal. For the voice signal, the corresponding subtotal is 90 s; the arithmetic uses the same group, location and notification assumption in both cases. Only the table's warning-dependent pre-travel value changes.<ref name="CVM_29_30">Ministry of Business, Innovation and Employment (2025), pp. 29–30.</ref>

<math display="block">(t_n+t_{\mathrm{pre}})_{\mathrm{standard}}=30+120=150\ \mathrm{s}</math>
<math display="block">(t_n+t_{\mathrm{pre}})_{\mathrm{voice}}=30+60=90\ \mathrm{s}</math>

The difference is 60 s within this calculation. Neither subtotal includes detection time or the movement component, so neither is a complete evacuation time. The result also does not establish that every real voice message saves exactly 60 s. It demonstrates the consequences of selecting the prescribed inputs for this particular New Zealand verification method.<ref name="CVM_26__29_30">Ministry of Business, Innovation and Employment (2025), pp. 26, 29–30.</ref>

Occupants in the enclosure of origin have different entries in the same table. For the awake, unfamiliar group, these are 60 s for a standard signal and 30 s for a voice signal. This distinction reflects the method's separate treatment of location. Applying the remote-room value to everyone would change the prescribed calculation.<ref name="CVM_30" />

== Matching the warning to the evacuation strategy ==

[[Evacuation]] may involve all occupants leaving or different groups receiving different instructions. The SFPE Handbook identifies partial evacuation and staying in place as strategies requiring information about the fire. Warning arrangements must support the intended response of each group. A common tone alone does not communicate the same detail as a location-specific instruction.<ref name="SMC_4-2" /><ref name="P_3-350" />

[[Phased evacuation]] makes the timing and recipient of each warning relevant to the analysis. People instructed to remain temporarily cannot be treated as if they were already travelling towards an exit. The calculation needs to represent the adopted sequence and any associated delay. IFEG requires the cue and response analysis to be applied to the relevant enclosure or group of enclosures.<ref name="IFEG_1.8-7_1.8-9" /><ref name="SMC_4-2" />

In New Zealand's C/VM2 (2025), delayed evacuation includes situations where occupants remain in place or move to safety inside the building. The spaces concerned must satisfy that document's place-of-safety provisions, and its commentary also identifies smoke detection and air handling as matters requiring particular attention in these environments. The warning assumption cannot be separated from the conditions in the place where occupants remain.<ref name="CVM_34">Ministry of Business, Innovation and Employment (2025), p. 34.</ref>

Occupants needing assistance introduce another dependence on staff response. C/VM2 distinguishes these populations from independently mobile, awake occupants when assigning pre-travel activity times. Proulx likewise identifies perceptual, physical and intellectual limitations as factors in starting evacuation. A suitable assessment describes the occupant group before selecting its timing assumptions.<ref name="CVM_30" /><ref name="P_3-351">Proulx (2002), p. 3-351.</ref>

== Staff behaviour, training and alarm credibility ==

Staff instructions can translate a warning into an understandable action. In public buildings, visitors may expect someone responsible for the premises to explain what is happening. Proulx describes responsibility and staff behaviour as influences on the time taken to start moving. The presence of an alarm therefore does not remove the human role in the warning process.<ref name="P_3-350_3-351" />

Training needs to relate to the actual building and its evacuation procedure. Proulx notes that familiarity with one building's response arrangements does not necessarily transfer to another location. Public occupants may have received no training for the premises they are visiting. In those circumstances, the competence and availability of staff affect how the warning is interpreted.<ref name="P_3-350" />

Repeated alarms without a fire can weaken the credibility of later warnings. Proulx discusses false alarms, tests and prank alarms as experiences that may encourage occupants to wait for confirmation. The chapter gives three or more false alarms in six months as an illustrative high frequency. This is a behavioural observation in a 2002 source, not a universal regulatory threshold.<ref name="P_3-349_3-350" />

The response to a tone and the response to an informative instruction may therefore differ substantially. Precise messages can identify the incident and the action expected, while staff can reinforce the warning. Proulx reports these effects through studies of drills and incidents. Those observations support consideration of communication quality without supplying one guaranteed delay for every building.<ref name="P_3-349_3-351" />

== Evidence and uncertainty in an assessment ==

IFEG recognises that validated methods for predicting pre-movement behaviour are limited, and it identifies documented literature, field studies and simulated evacuations as possible evidence. Where engineering judgement is used, its basis needs to be explained. A numerical input is more useful when its origin and applicability to the occupant group are clear.<ref name="IFEG_1.8-7">Australian Building Codes Board et al. (2005), p. 1.8-7.</ref>

Proulx reports an unannounced drill in a large retail store where staff quickly prompted customers to leave. Customers started moving after a mean of 25 s, with a reported maximum of 55 s. Staff closed cash counters and assisted people in changing rooms. These observations describe that exercise and its staff response, not an intrinsic property of the alarm signal.<ref name="P_3-349">Proulx (2002), p. 3-349.</ref>

The same chapter reports drills in three Canadian government office buildings involving more than a thousand recorded occupants. The mean time to start was 50 s despite occupant training and familiarity with the evacuation procedure. Some people completed tasks or gathered belongings before leaving their desks. Local wardens also prompted movement, showing why preparation and staff involvement remain relevant even among familiar occupants.<ref name="P_3-349" />

These examples illustrate the range of evidence that can inform an assessment; their interpretation requires attention to occupancy, training, observation method and the warning actually received. Transferring the reported mean alone would discard those conditions. The engineering task is to judge whether the underlying situation resembles the proposed scenario.<ref name="P_3-349_3-351" /><ref name="IFEG_1.8-7" />

Drill observations and accounts of actual incidents describe different conditions. Proulx discusses uncertainty in people's retrospective estimates of the time taken to leave. The chapter also notes that initial fire cues can be ambiguous. A real fire cannot automatically be assumed to produce a shorter response than an exercise.<ref name="P_3-349_3-351" />

Different groups may receive different cues at different times. Some occupants may hear a message, while others notice smoke or receive instructions from staff. IFEG requires the selected cue to be justified when more than one is possible. This avoids combining an early detection assumption with an unrelated, more favourable human response assumption.<ref name="IFEG_1.8-7_1.8-9" />

Sensitivity studies examine how the result changes when uncertain inputs vary. IFEG also distinguishes uncertainty studies and checks for failures affecting apparently redundant systems. Applied to warning arrangements, these checks expose dependence on a particular signal or human response. Their purpose is to understand the assessment's limits and the conditions under which the proposed sequence remains credible.<ref name="IFEG_1.2-24">Australian Building Codes Board et al. (2005), p. 1.2-24.</ref>

== See also ==

* [[Evacuation strategy]]
* [[Protective action decision model]]
* [[Required safe egress time]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association.
* Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-1–4-43). National Fire Protection Association.

[[Category:Detection & Alarm]]

Passive fire protection

2026-11-02T18:42:23Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Passive fire protection''' uses building construction and protective materials to restrict fire spread, delay heating and preserve specified structural or separating functions. Examples include fire-resisting barriers and insulation around structural members. The mechanisms depend on the physical and thermal behaviour of the installed construction.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="M_4-212_4-214">Milke (2002), pp. 4-212–4-214.</ref>

Passive does not mean that every component remains unchanged during fire. Materials can release moisture, char or swell as they heat; a broader compartmentation system can also contain doors or other closures that must operate. Static barriers, heat-responsive materials and movable protective features therefore have different dependencies.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Performance belongs to a defined assembly and exposure, rather than a material label alone. Thickness, continuity, attachment, supports and installation details can affect the result, and the protective function also needs to remain intact through later alterations and use. Testing, calculation and inspection provide different parts of the evidence for that continuing performance.<ref name="M_4-209_4-214">Milke (2002), pp. 4-209–4-214.</ref><ref name="IFEG_1.6-9" />

== Protective functions within a building ==

Passive protection uses the physical behaviour of construction to limit fire effects: a boundary can restrict passage between spaces, while an insulating layer can delay heating of a structural member. A material can also perform several functions together. Kodur and Harmathy distinguish load-bearing, insulating and combined roles when describing building materials.<ref name="KH_1-155" /><ref name="KH_1-157" />

[[Fire compartmentation]] applies the separating function to a volume within the building, and its boundary includes the walls and floors as well as their protected openings and supporting construction. The performance of one wall surface cannot describe the whole enclosure. The International Fire Engineering Guidelines identify several routes by which fire can pass beyond that boundary.<ref name="IFEG_1.6-6_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-8.</ref>

Thermal protection of a steel member addresses another function. Milke describes insulation, membranes, shielding and heat sinks as ways to reduce heating, and these measures affect the temperature history used in the structural assessment. Their purpose is not to make the steel immune to fire, but to change the rate and distribution of heat transfer.<ref name="M_4-212_4-214" />

[[File:fse-passive-fire-protection-v1.svg|thumb|upright=1.5|alt=Compartment, insulation and doors provide passive protection beside active alarm and sprinkler.|Passive measures and active systems have different roles. Based on Iqbal and Salley (2004), p. F-44.]]

A complete strategy can combine these functions with detection, warning and suppression. New Zealand's C/VM2 defines fire safety systems as the combination of active and passive measures serving evacuation, firefighting, spread control and structural stability. The category passive therefore describes how particular measures work. It does not mean that the entire building strategy has no operational dependencies.<ref name="CVM_65">Ministry of Business, Innovation and Employment (2025), p. 65.</ref><ref name="IFEG_1.6-9" />

== How thermal protection changes heating ==

An insulating layer alters the route by which heat reaches a protected member, and its thickness, conductivity and physical condition affect that route. The layer can also absorb energy as its own temperature rises. Milke distinguishes models that neglect this thermal storage from models that include it, particularly for materials such as concrete and gypsum.<ref name="M_4-223">Milke (2002), p. 4-223.</ref>

The initial temperature and exposure at the surface are also needed for a heat-transfer calculation. Rockett and Milke explain that the surface condition can be specified through temperature or heat flux. Those conditions can vary over the surface and with time. A material conductivity alone consequently cannot determine the temperature reached by a complete protected member.<ref name="RM_1-29">Rockett and Milke (2002), p. 1-29.</ref>

Protection can change chemically and physically during heating. Van Rossum describes evaporation, charring, loss of material and swelling as processes that alter thermal response. Gypsum also absorbs energy through release of chemically bound water. A model using fixed properties and unchanged geometry may omit part of the protection's behaviour.<ref name="VR_5.2" />

An [[Intumescent material]] expands under heating and develops an insulating structure, and this is a heat-induced response within a passive protective system. It differs from an electrically or mechanically commanded closure. Describing passive protection as completely unchanged during fire would therefore misrepresent one of its recognised mechanisms.<ref name="VR_5.2" /><ref name="M_4-214">Milke (2002), p. 4-214.</ref>

== Boundaries, doors and concealed spaces ==

A [[Fire door]] provides a closure where access interrupts a separation, and its rating concerns the specified doorset, while its closing function establishes the state credited during fire. The International Fire Engineering Guidelines distinguish operable barriers from static construction. A compartment containing an automatically closing door therefore includes an operating dependency as well as passive materials.<ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref><ref name="IFEG_1.6-9" />

[[Firestopping]] protects penetrations and narrow gaps that would otherwise interrupt the boundary. New Zealand's 2025 C/VM2 definition includes services and joints within or through fire separations, and its construction commentary links the product to the orientation and separating element. This connects the protective function to its installed arrangement.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref><ref name="CVM_65" />

A [[Cavity barrier]] addresses spread within a concealed space. C/VM2 distinguishes this function from sealing a penetration through a separation; the International Fire Engineering Guidelines identify ceiling voids, hollow construction and spaces behind cladding as possible spread routes. A continuous surface visible from an occupied room does not demonstrate that these concealed paths are interrupted.<ref name="CVM_62">Ministry of Business, Innovation and Employment (2025), p. 62.</ref><ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref>

The boundary also depends on its supports: a fire-resisting wall or floor can fail when the construction carrying it loses stability. The guidelines therefore connect supporting-member failure with the continued function of barriers. Treating every rated component independently can omit a shared physical dependency in the completed building.<ref name="IFEG_1.6-8">Australian Building Codes Board et al. (2005), p. 1.6-8.</ref>

== Fire-resistance evidence and failure modes ==

[[Fire resistance]] concerns specified functions maintained under a defined exposure. Structural adequacy addresses carrying loads, integrity addresses passage of flames or hot gases, and insulation addresses heat transmission. The applicable functions depend on the assembly and method. A quoted duration has meaning only alongside those conditions and endpoints.<ref name="KH_1-155" /><ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref><ref name="CVM_64" />

The International Fire Engineering Guidelines describe conduction, integrity loss and stability loss as separate barrier-failure mechanisms; an intact wall can transmit excessive heat without forming a hole. A crack or failed penetration treatment can permit passage while most of the wall remains sound. Collapse creates another form of loss, possibly involving the wall's supports.<ref name="IFEG_1.6-7_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-7–1.6-8.</ref>

A test establishes evidence for a particular assembly. Milke explains that standard furnace conditions include defined exposure, loading and restraint. Analytical methods can also be used, but their inputs and range of validity remain relevant. A test-based correlation does not automatically describe another exposure, span or loading condition.<ref name="M_4-209_4-211" />

Material combustibility is a separate question. Steel can remain unburned while its mechanical properties deteriorate, while timber can retain an uncharred load-bearing section during charring. Kodur and Harmathy distinguish these thermal, structural and fuel roles. A noncombustible label therefore cannot replace evidence for the claimed protective function of an assembly.<ref name="KH_1-157" /><ref name="W_4-257">White (2002), p. 4-257.</ref><ref name="W_4-260">White (2002), p. 4-260.</ref>

A fire-retardant treatment makes another, more limited claim. C/VM2 defines it as a substance or treatment that suppresses or delays combustion under specified conditions. White explains that treatment intended to limit surface flame spread does not automatically provide fire-resistive protection to a timber member. The outcome being claimed therefore determines the evidence required. An improved surface-burning result is not itself a structural endurance result.<ref name="CVM_64" /><ref name="W_4-259">White (2002), p. 4-259.</ref>

The assembly route can include calculation as well as testing. New Zealand's 2025 C/VM2 definition permits a specified calculation method verified against standard fire-resistance tests. Milke separates empirical correlations, heat-transfer analysis and structural analysis because they answer different questions: an empirical estimate inherits its test range, while a thermal result still needs a structural endpoint. The more detailed calculation does not eliminate the need to establish what performance is being demonstrated.<ref name="CVM_64" /><ref name="M_4-209">Milke (2002), p. 4-209.</ref>

Protection of a timber assembly further illustrates the interaction between layers and structure. White identifies the membrane's behaviour, the amount of charring and the capacity of the remaining wood as separate contributions. A change in the protective layer can affect the later condition of the load-bearing member. The overall rating consequently cannot be inferred from a favourable description of either component in isolation.<ref name="W_4-257" />

== Thickness, continuity and attachment ==

A thermal model represents a physical arrangement of protection around or in front of a member. Gaps and changes in thickness alter that arrangement. Carino and colleagues' investigation of World Trade Center protection specifically examined gaps and thickness variability. Their work connects the assumed insulation geometry to the thermal analysis.<ref name="WTC_iii">Carino et al. (2005), p. iii.</ref>

[[File:fse-passive-fire-protection-v2.svg|thumb|upright=1.5|alt=Uniform insulation beside a gap and thin region forming thermal bridges to a member.|Insulation gaps and thickness variation create thermal bridges. Based on Carino et al. (2005), p. iii and Rockett and Milke (2002), p. 1-29.]]

Attachment determines whether protective layers remain in their intended positions. Milke identifies the means of fixing board systems as a factor in assembly performance. He also includes bond strength, durability and resistance to damage among relevant properties of applied insulation. These characteristics concern retaining the thermal barrier, rather than conductivity alone.<ref name="M_4-212_4-214" />

The protection can be affected during construction or later modifications. Iqbal and Salley discuss sprayed mineral-fibre coatings being knocked from steel members during such work, and the report therefore distinguishes an effective applied layer from a damaged installation over time. The protective material's original test description does not establish its condition after alteration.<ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

Different protection forms also require different models. A board enclosure can surround a section without following its full contour, while an applied coating follows another thermal path. Some systems store appreciable heat within the protection itself. The calculation must represent the arrangement being credited, including its geometry and relevant material changes.<ref name="M_4-213_4-214">Milke (2002), pp. 4-213–4-214.</ref><ref name="M_4-223" />

== A World Trade Center specification example ==

NIST NCSTAR 1-6A investigates passive protection in the World Trade Center towers in connection with the 2001 disaster. Carino and colleagues review design decisions, construction records, material properties and available measurements of installed protection, and they also examine adhesion, gaps and variability in thickness. The report describes that historical investigation, not a general specification for other buildings.<ref name="WTC_iii" />

Its historical review identifies an issue in rewritten sprayed fire-resistive material specifications: a requirement linking finished thickness to particular ratings was apparently omitted during rewriting in 1969. The authors reproduce the relevant correspondence in their account. This is documentary evidence about the specification history, rather than a direct measurement of every installed member.<ref name="WTC_12_13">Carino et al. (2005), pp. 12–13.</ref>

The omitted wording linked the protection of specified support beams and steel deckwork to a three-hour rating, and it linked the specified pick-up girders and columns to four hours. These values belonged to that historic specification and its identified components. They are not general requirements for all beams and columns, nor proof of the actual endurance of every tower member.<ref name="WTC_13">Carino et al. (2005), p. 13.</ref>

[[File:fse-passive-fire-protection-v3.svg|thumb|upright=1.5|alt=Specification links finished insulation thickness to 3-hour and 4-hour member ratings.|WTC example links specification, thickness and fire rating. Based on Carino et al. (2005), p. 13.]]

The example separates intended performance, written specification and installed condition. The report treats construction records and in-place measurements as different forms of evidence, and its analysis of thickness and material properties then supports thermal-structural modelling. None of these steps can be replaced simply by stating that the building contained fireproofing.<ref name="WTC_iii" /><ref name="WTC_12_13" />

== Coordination with suppression and smoke control ==

A [[Fire suppression system]] acts on the developing fire, while passive measures restrict its effects on construction or adjacent spaces. The distinction does not make their credited performance independent. Iqbal and Salley describe a fire barrier used in conjunction with other protective measures. A design that relies on suppression consequently has different assumptions from one considering an uncontrolled fire.<ref name="N_F-29">Iqbal and Salley (2004), p. F-29.</ref><ref name="N_17-7">Iqbal and Salley (2004), p. 17-7.</ref>

Smoke separation also depends on the building's pressure conditions. Klote describes leakage through door gaps, penetrations and construction cracks. Mechanical smoke control can use pressure differences across barriers and airflow through openings. A physical boundary and an operating fan system can therefore contribute to the same protective objective.<ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref>

Opening a door changes that interaction during evacuation. The International Fire Engineering Guidelines obtain opening times from the occupant-movement analysis. New Zealand's 2025 C/VM2 similarly specifies different door-opening assumptions for intermittent passage and continuous queues. A strategy cannot infer the open-state performance solely from the rating of the closed doorset.<ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref><ref name="CVM_15">Ministry of Business, Innovation and Employment (2025), p. 15.</ref>

C/VM2's concealed-space scenario illustrates another form of coordination. For its stated scope, it permits separating elements, suppression or automatic detection as approaches to the specified concern. Those alternatives belong to the scenario's criteria and limitations. They do not establish unrestricted substitution between any passive measure and any active system elsewhere in a building.<ref name="CVM_41">Ministry of Business, Innovation and Employment (2025), p. 41.</ref>

== Construction, management and change ==

The International Fire Engineering Guidelines identify three physical checks during construction and commissioning: boundary integrity, conformity with specifications and operation of movable protective features. They also call for appropriate operation and maintenance information. These checks connect the design assumptions with the completed building. Each addresses a different part of the protective system.<ref name="IFEG_1.6-9" />

The guidelines note that passive features can be overlooked when a building is repaired or modified, and their continuing identification therefore forms part of preserving the strategy. A new service route or local construction change may affect a larger compartment boundary. The importance of that boundary may not be evident from the location of the work alone.<ref name="IFEG_1.6-9" />

Inspection and operational testing serve different purposes. The guidelines describe limited routine maintenance for static passive barriers while calling for operational tests of automatically closing features. Written maintenance requirements and recorded outcomes retain evidence of the resulting condition. The word passive therefore does not mean that the construction can be forgotten after installation.<ref name="IFEG_1.6-9" />

A maintained system preserves the arrangement supported by its evidence. Material data, assembly tests, calculation assumptions and construction records describe different parts of that arrangement. When geometry, exposure or operation changes, the relationship between those parts also changes. The technical assessment then concerns the revised system and the functions still supported by its evidence.<ref name="M_4-209_4-214" /><ref name="IFEG_1.6-9" />

== See also ==

* [[Fire safety strategy]]
* [[Structural fire engineering]]
* [[Fire wall]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Carino, N. J., Starnes, M. A., Gross, J. L., Yang, J. C., Kukuck, S. R., Prasad, K. R., & Bukowski, R. W. (2005). ''Passive fire protection'' (NIST NCSTAR 1-6A). 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Rockett, J. A., & Milke, J. A. (2002). Conduction of heat in solids. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-27–1-43). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* White, R. H. (2002). Analytical methods for determining fire resistance of timber members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-257–4-273). National Fire Protection Association.

[[Category:Passive Fire Protection]]

Firestopping

2026-11-02T18:42:18Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Firestopping''' is the use of materials or construction details to restrict fire spread through penetrations and gaps in separating construction. It preserves the boundary's intended function where services or joints would otherwise interrupt it. The function is part of assembly fire resistance, particularly the integrity of the separation.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="CVM_65">Ministry of Business, Innovation and Employment (2025), p. 65.</ref><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

A firestop is assessed in its installed context. The surrounding wall or floor, the penetrating service, the orientation and the relevant test evidence determine what performance is supported. A material described as fire resistant does not automatically establish the performance of every opening filled with it. New Zealand's 2025 C/VM2 explicitly links the product to the orientation and separating element.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref><ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref>

Related terms need careful distinction. A duct closure, a barrier within a concealed space and a feature limiting spread along a cable tray address different routes. The same broad firestopping terminology can otherwise obscure which physical function an installation is intended to perform.<ref name="N_F-19">Iqbal and Salley (2004), p. F-19.</ref><ref name="N_F-29">Iqbal and Salley (2004), p. F-29.</ref><ref name="CVM_62">Ministry of Business, Innovation and Employment (2025), p. 62.</ref>

== The route being sealed ==

Services often need to cross the walls or floors that form [[Fire compartmentation]]. Pipes, cables, cable trays and ventilation ducts can create openings through an otherwise continuous boundary, and a penetration seal addresses the route around those services. Its purpose is to preserve the intended separating function of the construction.<ref name="N_F-44" /><ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

New Zealand's C/VM2, second edition of 2025, defines a fire stop as a material or construction method restricting spread within or through a fire separation. Its definition includes sealing around penetrations and narrow gaps between building elements, and the stated fire resistance must be no less than that of the separation. This is a requirement within that New Zealand method.<ref name="CVM_65" />

[[File:fse-firestopping-v1.svg|thumb|upright=1.5|alt=Unsealed tray carrying flame and sealed penetration blocking it, with backing and contact shown.|Firestopping closes service paths through a fire separation. Based on Ministry of Business, Innovation and Employment (2025), p. 65.]]

A visible gap and heat transmission through intact construction are different paths; the International Fire Engineering Guidelines distinguish failed firestopping from excessive conduction through a barrier. Sealing an opening addresses the first mechanism but does not independently establish the thermal performance of the entire wall. The required functions remain those of the completed separation.<ref name="IFEG_1.6-7" /><ref name="KH_1-155" />

The surrounding construction matters to the seal's performance. C/VM2's construction commentary specifies proprietary products appropriate to the orientation and separating element. An installation in a floor and one in a wall are therefore not assumed interchangeable merely because their materials look similar. The evidence follows the application and construction in which the product is used.<ref name="CVM_13" />

== Materials and complete systems ==

A firestop is defined by the function of its installed arrangement: the opening, service and surrounding separation form part of that arrangement. Iqbal and Salley's penetration-seal definition expressly includes wiring, cables, pipes, ducts and building joints. The same material name does not establish performance across all those geometries and duties.<ref name="N_F-44" /><ref name="CVM_13" />

An [[Intumescent material]] expands when heated and can develop an insulating layer. Van Rossum identifies swelling as a process that changes thickness and heat transfer during fire, and this explains one possible protective-material mechanism. It does not establish a universal expansion factor, seal depth or application for an unspecified firestop product.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

Other aspects of an assembly can also change during exposure; the International Fire Engineering Guidelines include damaged service pipes and cable trays among conditions that can create openings. Integrity therefore depends on more than the initial appearance of the filled gap. The assessment concerns whether the intended boundary remains effective through the relevant event.<ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref>

Product evidence and installation details consequently answer different but connected questions. Testing supports a stated construction under defined conditions. Installation establishes whether that construction has been reproduced in the building. New Zealand's 2025 verification method explicitly connects construction detailing to the developed design.<ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref><ref name="CVM_13" />

== Distinction from dampers and cavity barriers ==

A [[Fire damper]] closes the passage inside a ventilation duct or opening, and a penetration seal addresses the path around that assembly where it crosses a wall or floor. Those paths can exist at the same location but require different protective functions. Closing one does not demonstrate that the other has been protected.<ref name="N_F-19" /><ref name="N_F-44" />

[[File:fse-firestopping-v2.svg|thumb|upright=1.5|alt=Damper stops airflow inside duct while firestop seals the gap between duct and wall.|Damper and firestop perform complementary functions. Based on Iqbal and Salley (2004), p. F-19 and p. F-44.]]

A [[Cavity barrier]] restricts spread within a concealed space or closes an opening within that space. C/VM2 defines it separately from the fire stop used at a separation, and the distinction concerns the route and location being protected. It prevents every concealed barrier or service seal from being treated as the same type of construction.<ref name="CVM_62" /><ref name="CVM_65" />

Building joints are another distinct application. Iqbal and Salley's list of standards separates through-penetration firestop tests from tests for building joint systems; a joint and a service penetration therefore have different evidential descriptions in that source. Their performance cannot be established by ignoring what the cited test actually evaluates.<ref name="N_C-15">Iqbal and Salley (2004), p. C-15.</ref>

Terminology can also vary between technical contexts, and the NUREG glossary uses fire stop for a feature restricting propagation along cables or towards nearby combustible material. It separately defines penetration seals at rated boundaries. A cable-tray fire stop described in an incident report is consequently not automatically a wall-penetration seal of the same design.<ref name="N_F-29" /><ref name="N_F-44" />

== Tests and the limits of a classification ==

A [[Fire resistance test]] evaluates specified functions under a defined exposure. The assembly, measurement criteria and duration belong together. A generic material description does not provide these details. The evidence therefore needs to identify the tested protective arrangement and the function claimed from it.<ref name="KH_1-155" /><ref name="M_4-209_4-210" />

The 2004 NUREG report identifies ASTM E814 and UL 1479 as through-penetration firestop test standards, and it separately lists UL 2079 for building joint systems. These references establish which test subjects the report distinguishes. The list is not a substitute for the full standards or a current classification of an installed product.<ref name="N_C-15" />

The source's regulatory setting also remains relevant. NUREG-1805 supports the United States nuclear fire-protection inspection programme, while C/VM2 provides a New Zealand verification method; their definitions and examples can explain physical functions without becoming universal installation rules. Any stated requirement retains the country, document and edition from which it comes.<ref name="N_F-44" /><ref name="CVM_13" /><ref name="CVM_65" />

Smoke performance requires its own interpretation. Klote explains that pressure differences can drive smoke through leakage paths around penetrations and construction joints. A fire-endurance description does not quantify that flow by itself. The credited smoke-separation function therefore needs evidence about the relevant path and operating conditions.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

== An incident showing the importance of configuration ==

NUREG-1805 includes an account of the Waterford 3 switchgear fire, drawing on United States regulatory reports issued in 1995. In that incident, propagation along a horizontal cable tray stopped at a raceway fire stop. In a vertical riser, the fire passed beyond a fire stop and continued. The account describes different outcomes within one event.<ref name="N_H-23">Iqbal and Salley (2004), p. H-23.</ref>

[[File:fse-firestopping-v3.svg|thumb|upright=1.5|alt=Horizontal stop holds fire while vertical tray fire jumps the stop and continues.|Waterford incident shows different firestop outcomes by orientation. Based on Iqbal and Salley (2004), p. H-23.]]

The authors state that it was unclear whether the vertical fire stop delayed propagation. That uncertainty matters: continued spread does not establish the size of any delay, and no delay should be invented from the account. The observed horizontal outcome likewise does not prove that every horizontal arrangement performs the same way. The evidence concerns the reported installation and incident.<ref name="N_H-23" />

The example also needs the correct object of comparison: these were cable-tray propagation features, not a controlled comparison of every wall and floor penetration system. The NUREG terminology distinguishes those uses. Treating the incident as a universal product test would extend the observation beyond what the report establishes.<ref name="N_H-23" /><ref name="N_F-29" /><ref name="N_F-44" />

Configuration nevertheless has direct relevance to construction evidence. C/VM2's separate requirement for appropriate orientation and separating element identifies the same need to retain application conditions. A result or observation becomes less informative when those conditions are removed. The evidence describes an arrangement, rather than the word firestop in isolation.<ref name="CVM_13" /><ref name="N_H-23" />

== Construction, alterations and inspection ==

The International Fire Engineering Guidelines identify barrier integrity and conformity with specifications as construction and commissioning concerns. Firestopping contributes to that integrity at services and joints. The completed boundary therefore includes the penetration treatment as well as the visible wall or floor. Missing treatment can create a spread route without any general failure of the main element.<ref name="IFEG_1.6-6" /><ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Later modifications can change the original arrangement. New services, altered openings or repairs can affect boundaries whose fire-safety role is not obvious locally. The guidelines note that passive components are liable to be overlooked during such work. Continued identification connects the alteration to the separation it crosses.<ref name="IFEG_1.6-9" />

Inspection and records preserve information about the resulting condition. The guidelines call for maintenance requirements to be documented and outcomes recorded, but they do not provide one universal seal recipe or inspection interval. The relevant product evidence and construction details remain necessary to assess the actual installed system.<ref name="IFEG_1.6-9" /><ref name="CVM_13" />

== See also ==

* [[Fire wall]]
* [[Passive fire protection]]
* [[Fire resistance]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire wall

2026-11-02T18:42:13Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''fire wall''' is a separating wall intended to restrict fire spread while maintaining the required resistance and structural stability. Its role combines the thermal and structural functions of building construction. In NUREG-1805's description of United States practice, a fire wall is distinguished from a barrier used alongside other protective measures.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="N_17-7">Iqbal and Salley (2004), p. 17-7.</ref>

The complete separation includes the wall's supports, ends, roof junction and protected openings. Fire can pass around an otherwise effective wall or through a damaged penetration. Some fire walls are designed to remain stable after construction collapses on either side, but that capability must be part of the stated design.<ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref><ref name="IFEG_1.6-6_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-8.</ref>

A fire-resistance duration alone does not describe all these conditions: the construction, exposure, support and required endpoints determine what the evidence demonstrates. Wall terminology and detailing provisions also differ between regulatory frameworks. Historical examples therefore need their document and jurisdictional context to remain explicit.<ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref><ref name="N_17-7" />

== Fire wall and fire barrier terminology ==

NUREG-1805 distinguishes two related forms of separating construction in its discussion of United States practice: a fire wall separates buildings or subdivides a building while providing resistance and structural stability. A fire barrier restricts spread and extends to the floor or roof deck above. The distinction follows the report's description of NFPA 221.<ref name="N_17-7" />

The same account differentiates the assumed fire conditions: the fire wall is intended to remain stable during an uncontrolled fire without effective sprinkler protection. The barrier is considered alongside other protective measures, such as sprinklers. This identifies the performance basis within that framework rather than making the terminology universal across countries.<ref name="N_17-7" />

[[File:fse-fire-wall-v1.svg|thumb|upright=1.5|alt=Fire wall stable during uncontrolled fire and fire barrier working with sprinklers.|Fire wall and fire barrier have different design roles. Based on Iqbal and Salley (2004), p. 17-7.]]

Both constructions can contribute to [[Fire compartmentation]], but their structural assumptions can differ; a wall's label does not independently explain whether surrounding construction may fail while the wall remains standing. That condition needs to be part of the design basis. Iqbal and Salley state that some fire walls are specifically designed to survive collapse on either side.<ref name="N_17-7_17-8">Iqbal and Salley (2004), pp. 17-7–17-8.</ref>

A time rating is also a different description from structural independence: the rating concerns specified performance under a defined exposure. Independence concerns the relationship between the wall and the structures around it. A design needs evidence for whichever combination of those functions it claims.<ref name="KH_1-155" /><ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref><ref name="N_17-8" />

== Heat transmission, openings and stability ==

[[Fire resistance criteria]] distinguish structural adequacy, integrity and insulation where those functions apply. Heat can pass through a wall even if the wall remains standing and has no opening. Cracks can permit gases or flames to pass before widespread collapse. These different mechanisms cannot be represented by observing only whether the wall is visibly upright.<ref name="KH_1-155" /><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

The insulation function depends on heat transfer through the construction, and a thick material can develop a hot exposed surface while its interior remains cooler. Conductivity, heat capacity and exposure duration affect this temperature distribution. A description of noncombustibility does not by itself establish how long the unexposed surface remains within a specified limit.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref>

Integrity concerns routes through the wall. Openings may be present initially or develop through damage, cracking or failed protection around services, and the International Fire Engineering Guidelines consider these routes separately from conduction through intact material. The neighbouring fuel and its exposure determine whether passage through a route develops into another fire.<ref name="IFEG_1.6-6_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-7.</ref>

Stability includes the wall and any structural support it relies on. The guidelines note that a barrier may fail when its supporting member fails, and they also require consideration of the effects on other barriers after structural failure. A separate wall rating cannot remove this dependency from the assembled building.<ref name="IFEG_1.6-8">Australian Building Codes Board et al. (2005), p. 1.6-8.</ref>

== Continuity at roofs, ends and penetrations ==

A wall can be bypassed at its edges even if the main surface performs as intended. Iqbal and Salley describe exterior wing walls at the ends of fire walls to restrict spread around them. They also describe a parapet continuing through and above the roof. These are examples of completing the separation in their United States technical context.<ref name="N_17-8" />

[[File:fse-fire-wall-v2.svg|thumb|upright=1.5|alt=Wing walls close the ends and a parapet carries the fire wall through and above the roof.|Wing walls and parapets close fire-wall bypass routes. Based on Iqbal and Salley (2004), p. 17-8.]]

The roof junction can otherwise connect the spaces on either side of the wall. The 2005 International Fire Engineering Guidelines identify concealed roof and ceiling spaces as possible routes between enclosures; a separating line in an occupied room does not automatically close those spaces. The boundary must be understood through its full extent and connections.<ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref><ref name="N_17-8" />

Service crossings require their own protection. [[Firestopping]] addresses the paths around pipes, conduits, cables and ducts where they pass through the boundary. Personnel or vehicle openings require suitable closures within the arrangement described by Iqbal and Salley. The wall, penetration protection and closures form complementary parts of the separating system.<ref name="N_17-8" /><ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref>

Service support can also influence the wall's condition during collapse. NUREG-1805 describes routing pipes, conduits and cables near floor level to reduce the risk of damaging the wall when construction collapses on one side. This is a specific detailing consideration in that report. It illustrates why the location of a penetration can matter beyond its initial seal.<ref name="N_17-8" />

== Historical resistance examples ==

[[Fire resistance]] is established for an assembly and stated conditions, rather than assigned from a generic material name. NUREG-1805 nevertheless provides a table of historical rules of thumb for common wall constructions. The report labels these as typical estimates. They are useful examples of the influence of construction, but they are not current approvals for unspecified walls.<ref name="N_17-7" /><ref name="M_4-209_4-210" />

The table associates a 12-inch brick wall with a ten-hour estimate, and it associates an 8-inch concrete-brick wall with six hours and a 16-inch nominal concrete-block wall with four hours. The corresponding nominal dimensions are approximately 305 mm, 203 mm and 406 mm. These conversions retain the original construction distinctions and do not create new tested specifications.<ref name="N_17-7" />

[[File:fse-fire-wall-v3.svg|thumb|upright=1.5|alt=Typical values: 12-inch brick 10 h, 8-inch concrete brick 6 h and 16-inch concrete block 4 h.|Typical wall fire-resistance examples from NUREG-1805. Based on Iqbal and Salley (2004), p. 17-7.]]

The concrete-block row also distinguishes nominal from actual thickness: its stated actual thickness is 15⅝ inches, approximately 397 mm, rather than the nominal 406 mm. That detail demonstrates why a rounded product description can differ from the tested or tabulated geometry. It also prevents the table from being read as a simple universal thickness-to-rating formula.<ref name="N_17-7" />

A contemporary application needs the evidence relevant to its actual wall and jurisdiction. Milke explains that test-based correlations remain limited by the conditions represented in their supporting tests. An old tabulated estimate does not independently resolve changes in loading, support or construction. The estimate and a verified rating are therefore different forms of evidence.<ref name="M_4-209_4-210" /><ref name="N_17-7" />

== Internal and external fire spread ==

A wall can address separation within one building and contribute to limiting [[Fire spread between buildings]]. The routes differ because external exposure can involve radiation, projecting flames and burning debris. The International Fire Engineering Guidelines treat these mechanisms explicitly. The adjacent building's openings and combustible surfaces are part of that assessment.<ref name="IFEG_1.6-5_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-7.</ref>

Radiation can expose material through glazing without the glass first falling out. A broken window can also change both the outgoing fire exposure and ventilation into the room. The guidelines therefore connect opening events to the fire-development analysis. A fire wall assessment cannot represent every external route solely through the temperature of the wall surface.<ref name="IFEG_1.6-7" />

The relative positions of boundaries and openings determine which routes require consideration. Vertical shafts and concealed spaces can connect different levels, while openings can connect neighbouring enclosures horizontally. The guidelines treat those connected spaces as enclosures within the analysis. The wall's function is therefore evaluated within a network of possible paths.<ref name="IFEG_1.6-6" />

Fire-separating and smoke-separating performance also differ. Klote describes smoke movement through construction cracks under pressure differences. An intact wall can consequently restrict flames while permitting some gas leakage. Where the strategy assigns a smoke-control function, the pressure and leakage conditions require attention alongside fire endurance.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

== Testing, installation and continued condition ==

A standard test represents a specified wall construction, load and support arrangement. Milke describes practical furnace and specimen constraints that limit direct reproduction of whole buildings. The result provides evidence for the assembly and permitted applications. Changes in the proposed wall therefore need to remain connected to the supporting test or calculation method.<ref name="M_4-209_4-211" />

New Zealand's C/VM2, second edition of 2025, gives one example of this connection in construction provisions. Details must match the developed design, while its commentary links penetration protection to the relevant orientation and separating element. These are requirements within that method. They do not convert a historical United States wall estimate into a New Zealand classification.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref>

The International Fire Engineering Guidelines identify barrier integrity and conformity with specifications as construction checks, and they also note that passive features may be overlooked during later repairs and modifications. Continued identification of the wall's fire-safety role connects such work to the original strategy. This is particularly relevant where new openings or services alter its continuity.<ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Inspection records concern the condition that exists, while the test or calculation describes the condition credited in the design. Both are needed to keep those descriptions aligned. The guidelines include documentation of maintenance requirements and recorded outcomes. They do not supply one universal inspection interval or wall detail for every application.<ref name="IFEG_1.6-9" />

== See also ==

* [[Passive fire protection]]
* [[Fire door]]
* [[Protected escape route]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire door

2026-11-02T18:42:08Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''fire door''' is a rated doorset that protects an opening in a fire separation. It allows access through the boundary while providing specified resistance when closed. The thermal and integrity functions concern the complete construction, while closing and latching establish the operating state on which that performance depends.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

A door is consequently more than its leaf material: its installation, associated components and evidence of assembly performance matter to the claimed rating. Smoke control may require additional performance beyond the fire-resistance function. New Zealand's C/VM2, second edition of 2025, distinguishes those requirements explicitly.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref><ref name="CVM_15">Ministry of Business, Innovation and Employment (2025), p. 15.</ref><ref name="CVM_64" />

A fire door also forms a changing part of [[Fire compartmentation]]. Occupants open it during evacuation, while pressure differences can move smoke through gaps or the open doorway. Understanding its role therefore requires both the closed-state evidence and the conditions under which it opens and closes during the event.<ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref><ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref>

== The complete doorset ==

A fire door belongs to the separating construction surrounding its opening. New Zealand's C/VM2, second edition of 2025, defines it as a single-leaf or multiple-leaf doorset with a specified rating. The definition includes automatic closing and self-latching during fire if the door is not already closed. Smoke-control capability is an additional feature in specified situations.<ref name="CVM_64" />

The word doorset keeps attention on the assembled opening protection. A door leaf operates within a frame and a surrounding separation, while the closing and latching functions establish its intended state. A claim about one material does not describe all these functions. The rating concerns the construction and conditions supported by the relevant test evidence.<ref name="CVM_13" /><ref name="CVM_64" /><ref name="N_C-10">Iqbal and Salley (2004), p. C-10.</ref>

[[File:fse-fire-door-v1.svg|thumb|upright=1.5|alt=Fire door with labelled leaf, frame, intumescent seal, closer and latch in a fire separation.|A fire door is a complete doorset, not only a leaf. Based on Ministry of Business, Innovation and Employment (2025), p. 64 and Iqbal and Salley (2004), p. C-10.]]

An [[Intumescent material]] swells during heating and can change the thermal path through an assembly. Van Rossum describes that general protective mechanism without defining the performance of a particular doorset; its presence does not replace evidence for the complete door. The construction, operation and claimed fire performance remain separate parts of the assessment.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="CVM_13" />

[[Fire-resistant glazing]] likewise concerns a complete assembly rather than glass alone. C/VM2's definition includes the glazing, frame, fixings and associated components, and the source therefore distinguishes a rated glazing arrangement from an unspecified glazed opening. A glazed door requires evidence relevant to the assembled construction in which that glazing is used.<ref name="CVM_64" /><ref name="CVM_13" />

== Fire resistance and smoke performance ==

[[Fire resistance criteria]] identify the functions evaluated under the prescribed exposure. Integrity addresses the passage of flames or hot gases, while insulation addresses heat transmission; a separating element may require different evidence for these outcomes. Neither can be inferred solely from the appearance or combustibility of the door material.<ref name="KH_1-155" /><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref>

[[Smoke movement]] introduces leakage paths and pressure differences. Klote identifies cracks around closed doors as paths through which gases can move, so a closed leaf does not imply an airtight boundary. The amount and direction of movement depend on both the available path and the forces acting across it.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

New Zealand's 2025 C/VM2 explicitly separates fire-door and smoke-control-door provisions. A fire door with smoke-control capability must satisfy both sets of provisions identified by that method; this distinction prevents a fire rating from being read as a complete smoke-leakage specification. It also identifies which function is being credited in the analysis.<ref name="CVM_15" />

A smoke separation need not have the same fire-resisting capability as a fire separation. C/VM2 applies different assumptions to their continued presence as conditions become more severe, and its discussion explains why a boundary credited early in a fire may not be credited after flashover. That is a modelling distinction, not a universal physical failure temperature for every door.<ref name="CVM_14_15">Ministry of Business, Innovation and Employment (2025), pp. 14–15.</ref>

== Testing and interpretation of ratings ==

A [[Fire resistance test]] places the doorset under a defined exposure and evaluates specified endpoints. The 2004 NUREG-1805 report summarises United States NFPA 252 door-assembly testing, and it describes tests continuing to the selected rating period or an earlier performance failure. The report is a historical technical summary, not the full standard or a current product approval.<ref name="N_C-10" />

The summary includes rated periods such as 20, 30, 45, 60, 90 and 180 minutes; these durations belong to the reported test framework. They do not establish a universal duration required for every door or every location. The required performance follows the building context and the applicable classification and design provisions.<ref name="N_C-10" /><ref name="CVM_13" />

The same summary describes a hose-stream exposure following the fire-endurance test, and its purpose is to apply impact, erosion and cooling to the heated assembly. The report identifies an exception in which the hose stream is optional for the stated 20-minute-rated assemblies. It is therefore inaccurate to describe this stage as mandatory for every door test worldwide.<ref name="N_C-10" />

[[File:fse-fire-door-v3.svg|thumb|upright=1.5|alt=Door in furnace followed by hose-stream impact, erosion and cooling.|Fire-door testing includes endurance and hose-stream response. Based on Iqbal and Salley (2004), p. C-10.]]

Test evidence also retains its construction context. New Zealand's 2025 verification method requires details during construction to match the developed design; its commentary connects rated closures to testing under an internationally recognised standard. This links the installed doorset to its evidence instead of assigning a rating from its thickness or material name alone.<ref name="CVM_13" />

== Door use during evacuation ==

A door protecting [[Means of escape]] must be considered in both its closed and open states. When occupants pass through, they temporarily change the separating boundary, and the International Fire Engineering Guidelines therefore obtain opening times from the evacuation analysis. A closed-door furnace result does not describe those periods of use.<ref name="IFEG_1.6-7" />

C/VM2, second edition of 2025, provides a specific modelling convention for this interaction. Fire and smoke-control doors with self-closers are assumed closed unless occupants are using them. For low occupant demand, the model allows three seconds of opening per occupant. The commentary connects that interval to opening the leaf, passing through and allowing it to close.<ref name="CVM_15" />

Where a queue keeps occupants passing continuously, the same document treats the door as open for the queuing period. This is a different physical state from isolated short openings. Applying the low-demand convention while a continuous queue holds the leaf open would misrepresent the intended assumption. The distinction belongs to the New Zealand method's movement and smoke analyses.<ref name="CVM_15" />

[[File:fse-fire-door-v2.svg|thumb|upright=1.5|alt=Door opens for three seconds per occupant and remains open during a queue before closing.|Fire-door state changes during evacuation. Based on Ministry of Business, Innovation and Employment (2025), p. 15.]]

For smoke-flow calculations during egress, C/VM2 represents the open door using half its width. The commentary explains that the moving leaf and occupants obstruct part of the opening; this is an effective opening assumption for that analysis. It does not redefine the constructed door width or the width available under separate escape provisions.<ref name="CVM_15_16">Ministry of Business, Innovation and Employment (2025), pp. 15–16.</ref>

== Pressure differences and open doorways ==

A closed door and an open doorway present different airflow problems. With a closed door, the paths may consist mainly of small gaps. With an open door, a much larger passage connects the spaces. Klote distinguishes pressure control across mostly closed barriers from airflow control through large openings.<ref name="Kl_4-278_4-279">Klote (2002), pp. 4-278–4-279.</ref>

Mechanical pressurisation can oppose smoke entry through leakage paths, and its intended airflow is from the protected side towards the smoke-exposed side. When a door opens, however, low air velocity may permit smoke to flow back through part of the opening. The closed-door pressure condition does not by itself establish the open-door performance.<ref name="Kl_4-278">Klote (2002), p. 4-278.</ref>

The forces moving smoke can also come from outside the mechanical system. Buoyancy, stack effect and wind affect the pressure field within a building. Klote explains that fan shutdown alone does not stop movement through all available paths. A door's leakage and operating state therefore interact with the surrounding building conditions.<ref name="Kl_4-274">Klote (2002), p. 4-274.</ref><ref name="Kl_4-277">Klote (2002), p. 4-277.</ref>

These interactions explain why fire separation and smoke control cannot be assessed as completely independent systems. The same opening can support evacuation, interrupt a smoke boundary and influence airflow. The analysis identifies which state is assumed during each part of the event. It then connects that state to the function attributed to the doorset.<ref name="Kl_4-278_4-279" /><ref name="IFEG_1.6-7" />

== Closing functions and commissioning ==

A rating establishes performance under its tested conditions; it does not prove that an installed door will reach the necessary closed state. Closing and latching are operating functions in C/VM2's definition. Their role is distinct from the material's thermal response. Both are needed where the strategy relies on an automatically closed opening.<ref name="CVM_64" /><ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

The International Fire Engineering Guidelines include operable systems among construction and commissioning checks. Components must match the specification, and automatically closing doors must perform their intended function. The guidelines also include operating and maintenance information. This creates an evidence chain from the design description to the completed and functioning installation.<ref name="IFEG_1.6-9" />

The state assumed in a model can depend on use and management. C/VM2 explains its short opening convention through a well-maintained self-closing door and intermittent occupant arrivals. That convention does not describe a door permanently held open. Its use therefore rests on the operational condition stated in the method.<ref name="CVM_15" />

== Inspection, alterations and continuing evidence ==

The 2005 International Fire Engineering Guidelines distinguish routine inspection of static barriers from operational testing of active closures. A fire door may combine both types of concern: the physical separation and the movement required to restore it. Inspection of the wall alone cannot demonstrate the closing function. An operating check alone cannot establish the wall's complete fire-resisting construction.<ref name="IFEG_1.6-9" />

Repairs and modifications can affect the original boundary. The guidelines note that passive components may be overlooked during building changes. Continued identification of the separation links local work to its wider fire-safety role. That includes the opening protection as well as the surrounding construction.<ref name="IFEG_1.6-9" />

Maintenance records identify the required functions and document observed outcomes. The guidelines do not prescribe one universal inspection interval or one component specification for every doorset. Those details require the applicable standard and product evidence. The general framework preserves the connection between the designed boundary, the installed assembly and its continuing operation.<ref name="IFEG_1.6-9" /><ref name="CVM_13" />

== See also ==

* [[Passive fire protection]]
* [[Stair pressurisation]]
* [[Protected escape route]]
* [[Fire-induced pressure]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire damper

2026-11-02T18:42:03Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''fire damper''' is an automatic closure in an air-distribution passage intended to resist the passage of heat and flame. It protects an opening that would otherwise interrupt a fire-separating wall or floor. The detailed definition in NUREG-1805 distinguishes its fire-resistance function from its ability to close under particular airflow conditions.<ref name="N_F-19">Iqbal and Salley (2004), p. F-19.</ref>

The device forms part of a complete boundary: its closed state addresses the path through the ventilation opening, while the surrounding penetration requires suitable treatment. Smoke can also move through a building under pressure differences caused by buoyancy, wind and ventilation. A closure specification therefore needs more information than a nominal fire duration.<ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref><ref name="Kl_4-274">Klote (2002), p. 4-274.</ref><ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

Fire dampers and smoke dampers have related but different functions. The evidence needed for resisting fire is not identical to the evidence needed for limiting leakage or operating against airflow. The selected arrangement must correspond to the functions assigned to the opening in the building's fire strategy.<ref name="N_F-19" /><ref name="N_C-11">Iqbal and Salley (2004), p. C-11.</ref>

== The opening that a damper protects ==

Ventilation ducts connect spaces that may otherwise be separated by walls or floors, and an open air passage can therefore bypass part of the intended [[Fire compartmentation]]. The damper supplies a closure within that passage. Its function is different from the wall's ability to resist heating through its solid material.<ref name="N_F-19" /><ref name="IFEG_1.6-6_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-7.</ref>

There can also be a separate path around the duct or damper assembly. [[Firestopping]] protects the surrounding penetration so that the crossing does not impair the barrier's intended performance. Closing the duct does not automatically seal this outside path. Both functions belong to the completed boundary.<ref name="N_F-19" /><ref name="N_F-44" />

[[File:fse-fire-damper-v1.svg|thumb|upright=1.5|alt=Open duct with airflow and closed damper blocking fire, with firestop around the frame.|A fire damper closes the duct; firestopping seals the surrounding penetration. Based on Iqbal and Salley (2004), p. F-19 and p. F-44.]]

The separating construction also provides the damper's installation context. New Zealand's C/VM2, second edition of 2025, links construction details to the approved design, and its commentary specifies firestopping appropriate to the orientation and separating element. This illustrates why evidence about an opening protection cannot be detached from the construction containing it.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref>

A damper is consequently assessed as part of an opening-protection arrangement; the duct, surrounding separation and penetration treatment perform complementary roles. The International Fire Engineering Guidelines identify both unprotected openings and failed firestopping as possible routes of spread. The presence of a closure alone does not describe every route through the boundary.<ref name="IFEG_1.6-6_1.6-7" />

== Closure and airflow conditions ==

The NUREG-1805 glossary describes assemblies of blades or louvers released by a fusible link or a remote activation signal. A fusible link responds to heat by melting and allowing closure, and a remote signal provides another means of initiating the movement. These are alternative arrangements in the source, rather than a description of every product.<ref name="N_F-19" />

The conditions during closure matter as well as the closed-state fire performance. Iqbal and Salley distinguish a fire-resistance rating from an airflow-closure rating, and the latter depends on whether the ventilation system is stopped when fire is detected. The design therefore needs to connect the assumed fan state to the damper's closing duty.<ref name="N_F-19" />

A static closure arrangement is associated with stopped airflow. A dynamic arrangement is intended to close under the relevant airflow conditions; these labels concern the operating condition against which closure is assessed. They do not, by themselves, describe smoke leakage, the surrounding wall or every subsequent control action.<ref name="N_F-19" />

[[File:fse-fire-damper-v2.svg|thumb|upright=1.5|alt=Static closure in stopped air and dynamic closure against fan pressure.|Static and dynamic fire-damper closure conditions. Based on Iqbal and Salley (2004), p. F-19.]]

Stopping a fan also does not remove every force moving gases through a building. Klote identifies stack effect, buoyancy and wind as additional drivers; these can continue moving smoke through ventilation passages even after mechanical supply stops. The intended closure function therefore remains distinct from the instruction to switch off a fan.<ref name="Kl_4-274" /><ref name="Kl_4-277">Klote (2002), p. 4-277.</ref>

== Fire dampers and smoke dampers ==

[[Smoke movement]] depends on available paths and the pressure differences driving flow through them. A smoke damper is intended to restrict that movement within a ventilation system, and its leakage performance is consequently relevant even when flames are not passing through the opening. Iqbal and Salley distinguish this role from resisting heat and flame.<ref name="Kl_4-277_4-278" /><ref name="N_F-19" />

Their account describes smoke dampers used in systems that stop airflow and in engineered systems that continue operating selected fans. The latter use controlled pressure differences to restrict smoke spread. Closure and fan operation therefore form part of a coordinated strategy. A universal instruction that every ventilation component must take the same state would omit these different functions.<ref name="N_F-19" /><ref name="Kl_4-278_4-279">Klote (2002), pp. 4-278–4-279.</ref>

The source states that a smoke damper need not meet every design function of a fire damper, and its smoke-damper test summary identifies leakage class, pressure, velocity, installation orientation and temperature. A fire-endurance claim therefore does not automatically demonstrate the separate leakage and operating characteristics. Evidence of one function cannot silently substitute for evidence of the other.<ref name="N_F-19" /><ref name="N_C-11" />

[[File:fse-fire-damper-v3.svg|thumb|upright=1.5|alt=Fire-damper flame rating beside smoke-damper leakage, pressure and velocity classes.|Fire dampers and smoke dampers have different evaluation criteria. Based on Iqbal and Salley (2004), p. F-19 and p. C-11.]]

The distinction also changes the question asked about an installed device. For fire separation, the question concerns the required resistance under the specified exposure. For smoke control, it also concerns the flow permitted under the relevant pressure and temperature conditions. The complete specification follows the functions assigned to that opening.<ref name="N_C-11" /><ref name="N_F-19" />

== Test evidence and material behaviour ==

[[Fire resistance criteria]] define the performance being claimed during a stated exposure. The 2004 NUREG report identifies UL 555 in its summary of fire-damper testing and UL 555S for smoke dampers. These references describe the report's historical United States context. The summary is not the complete text of either standard or a current product classification.<ref name="N_C-11" /><ref name="N_C-15">Iqbal and Salley (2004), p. C-15.</ref>

Test duration is only one part of that evidence; the smoke-damper summary expressly includes operating pressure, velocity and installation mode. Fire-damper application also includes the airflow condition during closure. Two products with a similar quoted duration can therefore represent different operating duties.<ref name="N_C-11" /><ref name="N_F-19" />

An [[Intumescent material]] changes through swelling when heated, which can alter the heat-conduction path. Van Rossum describes this as a general protective-material mechanism; it is distinct from the fusible-link and remote-signal closure mechanisms described for dampers. The general material behaviour alone does not establish the performance of a particular opening-protection assembly.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="N_F-19" />

The surrounding barrier has its own thermal, integrity and stability functions. The International Fire Engineering Guidelines show that barrier failure can arise through conduction, cracking or collapse. A damper assessment addresses an opening within that system. It does not independently establish the performance of the entire supporting wall or floor.<ref name="IFEG_1.6-7_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-7–1.6-8.</ref>

== Installation and operational dependencies ==

The installed arrangement joins building construction and ventilation control. Its assumed conditions include the protected boundary, the air passage and the state of the ventilation system during fire. The damper's closure duty must correspond to that operating state. Otherwise, the design would rely on a function different from the one described by the selected evidence.<ref name="N_F-19" /><ref name="CVM_13" />

The opening can be affected by changes elsewhere in the system. Klote explains that fan operation and other pressure drivers influence smoke movement. A revised ventilation arrangement can therefore change the physical conditions at the closure. This relationship follows from the system behaviour, even where the wall and damper remain in the same positions.<ref name="Kl_4-274" /><ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref>

The penetration treatment also depends on its construction context. C/VM2's orientation requirement distinguishes a seal's intended application from its material identity. The same principle prevents a general description of a sealing material from establishing every installed crossing. The evidence concerns the arrangement in which the material performs its protective function.<ref name="CVM_13" /><ref name="N_F-44" />

== Inspection and changes to the building ==

The 2005 International Fire Engineering Guidelines distinguish static barriers from operable protective features. Construction checks establish whether components match the specification and whether operable systems work as intended. Operational testing addresses a different question from visual continuity of a wall. Both observations are relevant where a boundary includes a moving closure.<ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Repairs and modifications can overlook the role of passive fire-separating construction. The guidelines therefore emphasise continued identification of boundaries and preservation of their integrity. For a duct crossing, that includes retaining the connection between the opening protection and the surrounding separation. A local change can otherwise affect a boundary whose full extent is not visible.<ref name="IFEG_1.6-9" /><ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

Maintenance documentation records the required functions and the outcomes of inspection or operational tests. The guidelines do not provide one universal test interval for every protective device, and their emphasis is on maintaining the designed arrangement and recording its condition. Product-specific and jurisdiction-specific details require the applicable supporting documents.<ref name="IFEG_1.6-9" />

== See also ==

* [[Fire door]]
* [[Passive fire protection]]
* [[Smoke control]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire compartmentation

2026-11-02T18:41:57Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Fire compartmentation''' is the division of a building into spaces separated by construction intended to restrict the spread of fire and its effects. Walls, floors, closures and protected penetrations work together as a boundary. Its performance depends on maintaining the required structural, integrity and heat-transmission functions under the relevant exposure.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="N_F-24">Iqbal and Salley (2004), p. F-24.</ref><ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

The separation is not defined by a wall alone. Doors, ventilation openings, service penetrations, junctions and supporting construction can determine how a fire reaches another space. Some routes exist from the outset, while others develop through opening, damage or structural failure. Concealed voids and shafts can connect spaces beyond the room of origin.<ref name="IFEG_1.6-6_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-8.</ref>

Smoke movement adds a further consideration because intact construction can still contain leakage paths. Pressure differences drive flow through those paths and through open doors. Compartmentation consequently interacts with evacuation, ventilation and smoke control, as well as the fire resistance of its materials and assemblies.<ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

== The compartment boundary ==

A compartment is a volume separated from other spaces by construction intended to restrict fire effects, and its boundary can include walls, floors, a roof and closures within those elements. New Zealand's C/VM2, second edition of 2025, calls the enclosed volume a firecell. Its definition allows contiguous spaces on the same or different levels, rather than limiting a firecell to one room.<ref name="CVM_64" />

The boundary is therefore a complete system of construction and protected openings. The definition of a fire barrier in NUREG-1805 includes supports, penetration seals, closures, doors and dampers alongside walls and floors. That report was prepared for the United States nuclear regulatory inspection programme. Its terminology usefully identifies the interacting components without establishing requirements for every other building type.<ref name="N_F-24" />

[[File:fse-fire-compartmentation-v1.svg|thumb|upright=1.5|alt=Firecell bounded by walls, floor, roof, fire door, damper and penetration seals.|A firecell is a complete separating system. Based on Ministry of Business, Innovation and Employment (2025), p. 64.]]

[[Fire resistance]] describes how the construction maintains specified functions under an exposure. Those functions include structural adequacy, integrity and insulation where applicable: the first concerns load-bearing performance, the second passage of flames or hot gases, and the third heat transmission. A compartment boundary can lose one function while retaining another.<ref name="KH_1-155" /><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref><ref name="CVM_64" />

A [[Fire wall]] is one form of separating construction, but its precise role depends on the governing framework. Iqbal and Salley distinguish a wall intended to remain stable through an uncontrolled fire from a barrier used with other protective measures. That distinction belongs to their discussion of United States practice. It does not make every internal partition a structurally independent fire wall.<ref name="N_17-7_17-8">Iqbal and Salley (2004), pp. 17-7–17-8.</ref>

== Routes by which fire can spread ==

[[Fire spread]] between compartments can follow openings that already exist or openings created during the fire, and the 2005 International Fire Engineering Guidelines treat both categories explicitly. Doors and windows may be open initially, while glazing breakage or damage can create further routes. The state of each route can change as the event develops.<ref name="IFEG_1.6-1">Australian Building Codes Board et al. (2005), p. 1.6-1.</ref><ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref>

An opening can also result from missing or inadequate sealing around services. Pipes, cable trays and ventilation ducts cross boundaries to perform normal building functions. Those crossings need their own representation in the separating system. A sound wall surface does not describe the behaviour of an unprotected opening through it.<ref name="IFEG_1.6-6" /><ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

Concealed spaces can connect locations that appear separate in an occupied room, and the guidelines identify ceiling voids, hollow construction, spaces under floors and spaces behind external cladding. Shafts and large service ducts can provide vertical routes. In the analysis, these spaces become further enclosures with their own connections and boundaries.<ref name="IFEG_1.6-6" />

The route can also pass outside the building before re-entering another space, and the guidelines discuss flames projecting from windows, radiation and burning debris. Adjacent buildings can be exposed through openings or external surfaces. Compartmentation therefore cannot be assessed solely by tracing internal partition lines on a floor plan.<ref name="IFEG_1.6-5_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-7.</ref>

[[File:fse-fire-compartmentation-v3.svg|thumb|upright=1.5|alt=Fire and smoke passing through a door, duct, cable penetration, cavity and wall end.|Openings and junctions can bypass a fire-rated wall. Based on Australian Building Codes Board et al. (2005), p. 1.6-7 and Iqbal and Salley (2004), p. 17-8.]]

== Thermal, integrity and stability failures ==

Heat can pass through an intact boundary by conduction. The unexposed surface may then become hot enough to breach an insulation criterion or ignite nearby material under suitable conditions. This mechanism does not require a visible hole. The thermal properties, thickness and exposure history influence the resulting temperature distribution.<ref name="IFEG_1.6-7" /><ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

Loss of integrity introduces a path through the boundary. Cracks, fissures and failed penetration protection can permit hot gases or flames to pass. Whether adjacent material ignites depends on its location and response to the exposure. The International Fire Engineering Guidelines distinguish this physical sequence from a simplified analysis that equates barrier failure with spread.<ref name="IFEG_1.6-6_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-7.</ref>

Loss of stability means that the barrier or its supporting construction can no longer remain in place, so a wall can fail because another structural element supporting it fails. The guidelines identify this dependency explicitly. The endurance of an isolated wall specimen is therefore not sufficient evidence for a boundary whose support fails earlier.<ref name="IFEG_1.6-7_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-7–1.6-8.</ref>

[[File:fse-fire-compartmentation-v2.svg|thumb|upright=1.5|alt=Three panels: heat through an intact wall, cracks with smoke and a collapsed wall.|Compartment boundaries can fail thermally, through integrity or through stability. Based on Australian Building Codes Board et al. (2005), p. 1.6-7.]]

These mechanisms can interact during the same fire. An opening can change ventilation as well as permit spread into another enclosure. Structural loss can damage several boundaries together. The analysis therefore follows changes in the building and exposure, rather than assigning every component an unrelated failure time.<ref name="IFEG_1.6-4">Australian Building Codes Board et al. (2005), p. 1.6-4.</ref><ref name="IFEG_1.6-8">Australian Building Codes Board et al. (2005), p. 1.6-8.</ref>

== Doors, ducts and service penetrations ==

A [[Fire door]] protects an opening that must also permit normal access and evacuation, and its closed-state performance is part of the compartment boundary. Its open state creates a different route for heat and smoke. The International Fire Engineering Guidelines consequently connect door-opening times to the analysis of occupant movement.<ref name="CVM_64" /><ref name="IFEG_1.6-7" />

A [[Fire damper]] addresses the internal path through a ventilation opening or duct. Iqbal and Salley describe devices that close in response to a fusible link or remote signal. Their account distinguishes the fire-resistance function from the conditions under which the damper can close against airflow. Those conditions depend partly on whether ventilation is stopped.<ref name="N_F-19">Iqbal and Salley (2004), p. F-19.</ref>

[[Firestopping]] addresses gaps and penetrations that would otherwise weaken the separation. Around a duct, it protects the path between the duct assembly and the surrounding boundary. Closing the air passage inside the duct is a different function. A design can therefore need both a closure and a suitable seal at the same crossing.<ref name="N_F-19" /><ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref>

New Zealand's 2025 C/VM2 construction provisions connect these details to the completed design, and its commentary calls for proprietary firestopping suited to the orientation and the separating element. It also identifies testing of rated closures under an internationally recognised standard. These provisions concern the installed construction, not a material name or an isolated product label.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref>

== Smoke separation and pressure differences ==

Restricting fire spread and restricting smoke movement are related but distinct functions. Smoke can pass through cracks and leakage paths while a boundary remains intact. Klote identifies gaps around doors, pipe penetrations and wall-to-floor junctions as examples. The pressure difference across the boundary determines the driving force for that leakage.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

Several forces can create the pressure difference. Klote discusses buoyancy from heating, stack effect, wind and mechanical ventilation, and these can act together, so smoke movement is not determined by temperature alone. Stopping ventilation fans removes one influence but does not eliminate movement driven by the others.<ref name="Kl_4-274">Klote (2002), p. 4-274.</ref><ref name="Kl_4-277">Klote (2002), p. 4-277.</ref>

Mechanical smoke control can use pressure differences across closed boundaries and airflow through open doorways. The appropriate assessment changes when a door opens. A pressure difference across a mostly closed barrier is not equivalent to the airflow required through a large opening. Klote therefore distinguishes closed-door and open-door conditions.<ref name="Kl_4-278_4-279">Klote (2002), pp. 4-278–4-279.</ref>

C/VM2, second edition of 2025, likewise distinguishes fire separations, smoke separations and unrated construction within the trial design. The method applies different assumptions to their continued presence during a fire. Those assumptions describe the analysis framework and the evidence attributed to each separation. They are not predictions that every physical partition disappears at one identical temperature.<ref name="CVM_14_15">Ministry of Business, Innovation and Employment (2025), pp. 14–15.</ref>

== Representing openings in an analysis ==

The International Fire Engineering Guidelines begin with the enclosure geometry, openings and properties of barriers and structural elements. They also require the location and ignition characteristics of material in adjacent spaces, and this information establishes what can be exposed if a route opens. A boundary failure and the ignition of another fuel item are separate events unless the method deliberately combines them.<ref name="IFEG_1.6-5_1.6-7" />

The guidelines permit simplifying assumptions for specified analyses. Examples include treating barrier failure as spread or using flashover as an opening-related event. They also identify conditions that can invalidate a simplification, such as direct flame contact on an unrated boundary. An assumption is therefore part of the model definition, rather than an observed fact about every fire.<ref name="IFEG_1.6-6" />

Door use provides a practical example. Under New Zealand's 2025 C/VM2, a self-closing fire or smoke-control door is assumed closed except when occupants use it. With low occupant demand, it is modelled open for three seconds per occupant. Where occupants queue, the method instead considers the sustained opening associated with that queue.<ref name="CVM_15">Ministry of Business, Innovation and Employment (2025), p. 15.</ref>

The same document uses half the door width for smoke-flow modelling while the door is being used for egress. Its commentary explains that a moving leaf and passing occupants restrict the unobstructed opening, and this is a smoke-modelling assumption within C/VM2. It is not a rule that halves the physical escape width of every doorway.<ref name="CVM_15_16">Ministry of Business, Innovation and Employment (2025), pp. 15–16.</ref>

The concealed-space scenario in New Zealand's 2025 C/VM2 provides a specific example of protecting a route that is not visible from an occupied room. It applies within the stated scope to buildings containing rooms with more than 50 occupants and concealed spaces. The document identifies separating elements, suppression and detection as approaches to that scenario. Their acceptance depends on the scenario conditions, rather than an unrestricted exchange between systems.<ref name="CVM_41">Ministry of Business, Innovation and Employment (2025), p. 41.</ref>

Where its separating-element approach is used without automatic detection, C/VM2 specifies at least 30 minutes for integrity and insulation and limits the concealed-space area to 500 m². These figures belong to the particular 2025 New Zealand scenario; they do not define a universal compartment size or barrier rating. The example shows how the route, detection assumptions and separating construction are connected within a stated method.<ref name="CVM_41" />

== Integration with the fire safety strategy ==

Compartmentation forms part of [[Passive fire protection]], but it interacts with systems that operate during an incident. A door may need to close, and a ventilation closure may depend on a signal or the state of a fan. The International Fire Engineering Guidelines distinguish static barriers from operable closures. Describing the whole strategy as having no operational dependencies would conceal those differences.<ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref><ref name="N_F-19" />

The expected duration of separation follows its purpose in the strategy. The guidelines connect times of spread and structural failure to evacuation, firefighting and protection of adjoining property. Different objectives can therefore require different outputs from the same physical analysis. A nominal duration without an endpoint or objective does not define the required performance.<ref name="IFEG_1.6-2">Australian Building Codes Board et al. (2005), p. 1.6-2.</ref><ref name="IFEG_1.6-4" />

Compartmentation can also be evaluated alongside suppression. Iqbal and Salley's distinction between fire walls and barriers specifically refers to whether other protective measures are credited. The consequences of losing that support differ from the behaviour assumed when it operates. The design basis therefore identifies which systems and operating conditions form part of the assessment.<ref name="N_17-7">Iqbal and Salley (2004), p. 17-7.</ref>

Structural support is another dependency within the strategy. A protected boundary may rely on columns, beams or floors to remain in place. The guidelines require consideration of failure of those supporting elements and its effects on other boundaries. Treating each rating independently would omit a physical route by which several protections can be lost together.<ref name="IFEG_1.6-8" />

== Construction, alterations and continued performance ==

Construction and commissioning establish whether the intended boundaries exist and their components match the specification. The International Fire Engineering Guidelines identify barrier integrity, specified materials and operation of automatic closures as distinct checks. They also include operation and maintenance documents. The completed system therefore includes both physical construction and information about its required functions.<ref name="IFEG_1.6-9" />

Later repairs or alterations can change that system. The guidelines note that passive barriers are liable to be overlooked during building modifications. Their continued identification helps connect a new service opening or construction change to the original fire strategy. Without that connection, a local alteration can change a boundary whose role is not visible from the room alone.<ref name="IFEG_1.6-9" />

Static barriers and operable closures have different maintenance needs. The guidelines describe relatively limited routine maintenance for passive barriers, while calling for operational testing of automatic closures. Inspection and records preserve evidence about both. A wall remaining in place and a door closing correctly are separate observations within the same compartmentation system.<ref name="IFEG_1.6-9" />

Evidence of performance remains tied to the construction and conditions assessed. A standard test demonstrates specified functions of its assembly, while modelling represents selected exposures, openings and dependencies; their combined interpretation identifies where the boundary is expected to remain effective. It also identifies the assumptions that cease to hold when the building or its operating conditions change.<ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref><ref name="IFEG_1.6-5_1.6-9">Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-9.</ref>

== See also ==

* [[Cavity barrier]]
* [[Protected escape route]]
* [[Stay-put strategy]]
* [[Progressive horizontal evacuation]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Timber in fire

2026-11-02T18:41:52Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

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

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

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

== Heating, decomposition and combustion ==

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

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

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

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

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

== Charring rate and grain direction ==

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

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

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

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

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

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

== A worked charring example ==

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

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

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

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

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

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

== The remaining section and structural capacity ==

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

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

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

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

== Heat penetration is not char depth ==

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

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

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

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

== Membranes and protected assemblies ==

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

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

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

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

== Reaction to fire and fire resistance ==

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

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

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

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

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

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

== Exposure limits and model evidence ==

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

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

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

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

== See also ==

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

== Notes ==

<references />

== References ==

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

[[Category:Structural Fire Engineering]]

Steel in fire

2026-11-02T18:41:47Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Steel in fire''' describes the heating, expansion and loss of mechanical performance of steel members exposed to fire. Steel can remain noncombustible while its strength and stiffness decrease. Structural performance therefore depends on temperature, loading, geometry, protection and support conditions, rather than combustibility alone.<ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="M_4-209">Milke (2002), p. 4-209.</ref><ref name="M_4-211_4-212">Milke (2002), pp. 4-211–4-212.</ref>

Assessment connects three stages: defining the fire exposure, calculating heat transfer into the steel and evaluating structural response. The gas temperature is an input to this sequence, not automatically the temperature of the member. Exposed surface, steel mass and protection determine how rapidly the member heats, while mechanical properties determine the consequences.<ref name="M_4-209" /><ref name="M_4-222_4-224">Milke (2002), pp. 4-222–4-224.</ref>

A standard furnace exposure provides one basis for comparing protected and unprotected assemblies, while a natural fire requires its own description of the thermal environment. Neither approach supplies one failure temperature for every steel product or structural system. The selected endpoint must remain connected to the load and conditions it represents.<ref name="VR_8.6">Van Rossum (2027), §8.6.</ref><ref name="KH_1-163">Kodur and Harmathy (2002), p. 1-163.</ref>

== From fire exposure to steel temperature ==

The fire environment supplies heat to the surface of an exposed member. Radiation transfers energy from flames and hot surroundings, while convection transfers energy between the gases and the surface. Conduction then redistributes that energy within the steel. The member temperature follows this combined heat balance rather than simply equalling the surrounding gas temperature.<ref name="M_4-209" /><ref name="M_4-222">Milke (2002), p. 4-222.</ref>

The exposure history must therefore be defined before a heating calculation can begin. A furnace curve supplies one repeatable history, while a natural compartment fire develops according to the fuel, ventilation and enclosure. Heat release rate and gas temperature are different quantities within that description. Van Rossum treats standard temperature curves as prescribed exposures, rather than predictions of every room fire.<ref name="VR_8.6" />

The exposed faces also matter: a column surrounded by fire receives a different boundary condition from a beam connected to a concrete slab. The slab can shield the upper part of the beam and take heat from it. Milke explains that these effects can create appreciable temperature differences between the lower and upper flanges.<ref name="M_4-223_4-224">Milke (2002), pp. 4-223–4-224.</ref>

A thermal model can treat the member as uniformly hot or calculate a temperature distribution; the first approach is simpler and can suit some exposed sections. The second becomes relevant when temperature gradients affect the structural response. Choosing between them depends on the exposure, section and purpose of the calculation.<ref name="M_4-222_4-224" />

== Geometry and section factor ==

[[Section factor]] relates the heated surface to the amount of steel being heated. For a member with a constant cross-section, the heated perimeter divided by the cross-sectional area expresses this relationship. More heated perimeter per unit area generally gives a greater heating response under otherwise equal conditions. The comparison concerns exposure and thermal storage together.<ref name="M_4-222_4-224" />

Milke also uses the inverse form: mass per unit length divided by heated perimeter, and its SI unit is kilograms per square metre. A large value represents more steel mass behind each unit of heated surface and therefore greater thermal storage. Confusing this ratio with the perimeter-to-area section factor reverses the interpretation of which section heats faster.<ref name="M_4-219">Milke (2002), p. 4-219.</ref><ref name="M_4-222_4-224" />

[[File:fse-steel-in-fire-v1.svg|thumb|upright=1.5|alt=Two steel sections with different exposed perimeters and masses receiving the same nominal heat flux.|Section geometry affects steel heating. Based on Milke (2002), pp. 4-222–4-224.]]

Protection can alter the relevant heated boundary. An insulating enclosure around a section need not follow every recess of the steel profile, and its thermal resistance and exposed perimeter form part of the protected-member model. The geometry used for an unprotected contour cannot automatically describe an enclosing board system.<ref name="M_4-213_4-214">Milke (2002), pp. 4-213–4-214.</ref><ref name="M_4-223">Milke (2002), p. 4-223.</ref>

Shielding by adjacent construction likewise changes the surface receiving heat. Milke provides separate perimeter diagrams for different arrangements and connections to slabs, and these diagrams distinguish steel area from the boundary exposed to the thermal environment. The resulting section factor describes a particular exposure configuration, rather than a permanent property of the section designation.<ref name="M_4-223" />

The two geometry ratios can be converted through density. Milke's steel density of 7,860 kg/m³ divided by the example mass-to-perimeter ratio of 39.3 kg/m² gives 200 m⁻¹. This is the corresponding heated-perimeter-to-area ratio for that example. The conversion leaves the physical section unchanged while expressing the same thermal-storage relationship in another form.<ref name="M_4-211">Milke (2002), p. 4-211.</ref><ref name="M_4-219" /><ref name="M_4-224">Milke (2002), p. 4-224.</ref>

The conversion also provides a dimensional check. A perimeter divided by an area has units of inverse metres, whereas mass divided by heated area has units of kilograms per square metre. Values expressed in these units cannot be substituted directly for each other. The intervening density and the direction of the ratio determine their relationship.<ref name="M_4-222_4-224" />

== A simplified heating calculation ==

In a lumped-capacity model, the steel is assumed to have one temperature throughout its section, and the heat entering over a short interval increases the energy stored in the steel. Dividing the incoming heat by the steel's heat capacity gives the temperature increment. Milke expresses the model using the mass-to-heated-perimeter ratio.<ref name="M_4-222" />

<math display="block">\Delta T_s=\frac{h_{\mathrm{tot}}}{c_s(m'/P)}(T_g-T_s)\Delta t</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\Delta T_s</math> || Steel temperature increment || K
|-
| <math>h_{\mathrm{tot}}</math> || Combined convection and linearised radiation coefficient || W/(m²·K)
|-
| <math>c_s</math> || Steel specific heat || J/(kg·K)
|-
| <math>m'</math> || Steel mass per unit member length || kg/m
|-
| <math>P</math> || Heated perimeter || m
|-
| <math>T_g,T_s</math> || Gas and steel temperatures || °C
|-
| <math>\Delta t</math> || Calculation interval || s
|}

The temperature difference in this equation has the same numerical value in kelvins and degrees Celsius. Radiation calculations used to determine the combined coefficient, however, require absolute temperatures. Milke separates the radiative and convective contributions and recommends short calculation intervals for this approximation. The equation is then applied repeatedly as the exposure and steel temperature change.<ref name="M_4-222_4-223">Milke (2002), pp. 4-222–4-223.</ref>

A calculation of the convective contribution illustrates the role of the inputs. Milke gives a mass-to-perimeter ratio of 39.3 kg/m² for the contour of a W8 × 28 section. His A36 specific-heat expression gives 430 J/(kg·K) at 20 °C. Taking his example temperature level of 538 °C as an assumed gas temperature permits a simple initial-step comparison.<ref name="M_4-219" /><ref name="M_4-211" /><ref name="KH_1-163" />

With a convective coefficient of 25 W/(m²·K) and an interval of 10 s, the calculated convection-only rise is 7.7 K. The arithmetic uses the unrounded specific heat of 430.2 J/(kg·K). Radiation has deliberately been excluded from this component calculation, so 7.7 K is not a complete fire-heating prediction. The chosen gas temperature is an illustrative boundary condition, not a measured exposure for that section.<ref name="M_4-211" /><ref name="M_4-222_4-223" />

== Strength, stiffness and steel type ==

[[Strength reduction at elevated temperatures]] changes the load that a hot member can resist. Yield strength describes the onset of substantial permanent deformation in the adopted material model, and the modulus of elasticity describes stiffness before that stage. A reduction in stiffness can increase deformation and affect stability even before the nominal yield-strength limit is reached.<ref name="M_4-211_4-212" />

The response is not identical for all steel products. Fleischmann and Buchanan distinguish hot-rolled reinforcing steel, cold-drawn prestressing steel and high-strength alloy steel, and their chapter presents different strength-temperature relationships for these materials. It also distinguishes yield strength from tensile strength where the relevant design property differs.<ref name="FB_4-240">Fleischmann and Buchanan (2002), p. 4-240.</ref>

[[File:fse-steel-in-fire-v2.svg|thumb|upright=1.5|alt=Schematic strength curves for hot-rolled, prestressing and alloy steel that fall at different temperatures and cross.|Steel products respond differently to elevated temperature. Based on Fleischmann and Buchanan (2002), p. 4-240.]]

Heating can also introduce creep, which is deformation that develops with time under sustained stress. Milke explains that creep depends on stress, heating rate and temperature. Some fire-design material relationships incorporate its effects implicitly. Combining data from incompatible test histories can therefore misrepresent the response even when the nominal steel temperature is the same.<ref name="M_4-212">Milke (2002), p. 4-212.</ref>

Room-temperature strength consequently supplies only part of the required information; a thermal analysis determines where and when the steel heats. Temperature-dependent mechanical properties then connect those temperatures to the structural calculation. The assessment still requires the applied load and the relevant support conditions.<ref name="M_4-209" /><ref name="M_4-211_4-212" />

== Critical temperature and structural endpoints ==

[[Critical steel temperature]] is a temperature associated with an unacceptable structural condition under stated assumptions, and it depends on the load to be supported and the material's remaining capacity. The concept can simplify a thermal calculation when those structural conditions have already been established. It does not replace them with a universal failure temperature.<ref name="KH_1-163" /><ref name="M_4-209" />

Kodur and Harmathy describe historical North American examples of 538 °C for structural steel, 593 °C for reinforcing steel and 426 °C for prestressing steel. The structural-steel example is associated with particular ASTM E119-related assumptions, including full design loading in the discussion of columns. These figures illustrate method-dependent endpoints. They do not represent melting temperatures or limits applicable to every steel member.<ref name="KH_1-163" />

[[File:fse-steel-in-fire-v3.svg|thumb|upright=1.5|alt=Critical-temperature examples 538, 593 and 426 °C for three steel uses.|Critical-temperature examples depend on steel use and method. Based on Kodur and Harmathy (2002), p. 1-163.]]

Milke's description of A36 steel provides the mechanical context. At approximately 538 °C, its yield strength in the cited relationship is about 60% of the room-temperature value. The significance of that reduction depends on the stress already imposed on the member. A lightly loaded and a heavily loaded member need not reach their structural endpoints at the same temperature.<ref name="M_4-212" />

A temperature endpoint and a structural endpoint therefore answer related questions: the thermal calculation can determine when a specified temperature is reached. A structural calculation evaluates the resulting stresses, deformation and capacity under the adopted loading and restraint. Where a temperature criterion is used, its connection to those structural conditions remains part of the method.<ref name="M_4-209" /><ref name="M_4-222" />

== Expansion, restraint and structural response ==

Steel expands as its temperature rises. If supports or surrounding construction limit that movement, [[Restrained thermal expansion]] changes the forces and deformations within the system. The member then responds to more than its original mechanical loading. Milke consequently includes thermal expansion and end conditions in the structural assessment.<ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref>

Test restraint is a defined condition rather than an informal description of a connection. Milke reproduces historical ASTM examples distinguishing different floor and framing arrangements, and the classification considers how the surrounding structure resists movement. A restrained test result therefore requires interpretation in relation to the proposed construction and its actual boundaries.<ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref>

Temperature gradients add another complication: a beam beneath a slab can have a hotter lower flange and a cooler upper flange. A uniform-temperature model does not explicitly describe that difference. Where the gradient affects the structural question, Milke identifies the need for a more suitable analytical approach.<ref name="M_4-223_4-224" />

[[Structural fire engineering]] combines these effects rather than treating steel temperature as a complete outcome, and it uses the exposure to calculate temperatures, then applies temperature-dependent properties within a structural model. Loads, geometry and end conditions determine how the member responds. The required result may involve deformation and stability as well as a nominal strength comparison.<ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref>

== Protection systems and their behaviour ==

Protection reduces the rate of heat transfer into the steel. Milke describes insulating boards, spray-applied materials, concrete encasement and enclosing membranes. Their mechanisms and attachment details differ. The relevant evidence concerns the protected assembly, including the protection material and the way it remains attached during exposure.<ref name="M_4-212_4-214">Milke (2002), pp. 4-212–4-214.</ref>

[[Intumescent material]] expands during heating to form an insulating layer. The change is part of the protective mechanism, so the layer cannot always be represented by its original thickness and properties. Van Rossum identifies swelling as one of several processes that change the heat-conduction path during fire. Milke includes intumescent products among spray-applied protection methods.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="M_4-214">Milke (2002), p. 4-214.</ref>

Board systems rely on suitable enclosure and attachment. Milke specifically identifies the means of securing boards as a factor affecting assembly performance. Spray-applied products require properties such as adhesion, durability and uniform application. These considerations connect the material's thermal performance to its condition on the actual member.<ref name="M_4-212_4-214" />

Protection can also store heat. Milke distinguishes simplified models that neglect its heat capacity from models that include it. Gypsum and concrete protection are examples where that contribution can matter. Omitting the protection's thermal storage is therefore an assumption to assess, rather than a property of every protected-steel calculation.<ref name="M_4-223" />

A protected member can receive heat through the insulation while the insulation itself is warming. Part of the incoming energy then increases the protection's temperature instead of immediately heating the steel. Milke includes this storage in the denominator of a protected-member temperature-increment expression. The effect differs from thermal resistance, which describes the rate of energy transfer through the layer.<ref name="M_4-223" />

An intact thermal barrier also needs to survive handling and its surrounding environment. Milke includes bond strength, durability, weathering resistance and consistent application among relevant protection characteristics, and these requirements concern maintaining the protective arrangement that the thermal model assumes. A conductivity value alone cannot establish whether the applied protection will retain that arrangement throughout service and exposure.<ref name="M_4-212" />

== Evidence and modelling limits ==

Empirical protection formulas are linked to the tests from which they were developed. Milke cautions that their ranges can be restricted by member shapes, protection thickness and other conditions. A result outside those ranges has a different evidential basis from a result within them. The fire exposure, loading and span also limit the applicability of test-based correlations.<ref name="M_4-209" /><ref name="M_4-219" />

A more detailed thermal calculation does not remove uncertainty in its inputs. Heating conditions, temperature-dependent material properties and insulation behaviour still affect the result, and a structural calculation introduces additional assumptions about loads and restraint. The accuracy of the combined prediction depends on the relationship between all these stages.<ref name="M_4-209_4-210" />

Tests provide evidence about interactions that simplified models may omit. Milke emphasises their role in establishing material behaviour and checking protected assemblies. The resulting evidence describes the tested exposure and configuration. Its application to another member depends on whether the model represents the changes in geometry, heating and structural conditions.<ref name="M_4-210_4-211" />

== See also ==

* [[Progressive collapse]]
* [[Tensile membrane action]]
* [[Fire resistance]]

== Notes ==

<references />

== References ==

* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Structural Fire Engineering]]

Fire resistance

2026-11-02T18:41:42Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Fire resistance''' is the ability of a building member or assembly to maintain specified functions for a stated time under a defined fire exposure. Depending on the assembly, these functions include carrying loads, preventing the passage of flames and limiting heat transmission. A rating records performance against particular criteria, rather than a general resistance to every possible fire.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref>

Assessment concerns the complete construction and its conditions. Materials, dimensions, protection, loading, connections and restraint can all affect the result. A standard furnace test provides one means of evaluation, while suitable calculations can connect the exposure to temperatures and structural response. Both approaches require a defined endpoint.<ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref>

The duration in a rating is therefore inseparable from the method used to establish it. It is not automatically the time available for evacuation, the time to collapse in a natural fire or a measure of combustibility. Understanding the exposure and performance criteria is necessary to interpret what the rating demonstrates.<ref name="M_4-209_4-210" /><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref><ref name="VR_8.6">Van Rossum (2027), §8.6.</ref>

== The functions being assessed ==

[[Fire resistance criteria]] identify the functions that an assembly must maintain. Structural adequacy concerns carrying the specified load without unacceptable structural response. Integrity concerns the passage of flames or hot gases through a separating assembly. Insulation concerns heat transmission to the unexposed side. These functions can reach their endpoints at different times.<ref name="KH_1-155" /><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref><ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

A separating wall illustrates the difference between integrity and insulation. Heat can conduct through an intact wall and raise the temperature of its unexposed surface. No visible opening is needed for that heat transfer to become excessive under an insulation criterion. Conversely, a crack can permit hot gases or flames to pass even where most of the wall remains comparatively cool.<ref name="IFEG_1.6-7" />

Structural adequacy is a further, separate question. A load-bearing member can lose strength or stiffness as its temperature rises, and its response also depends on applied loads and the conditions at its supports. A thermal result therefore cannot establish structural endurance unless it is connected to a suitable structural criterion or model.<ref name="M_4-209_4-210" />

New Zealand's C/VM2, second edition of 2025, expresses the fire resistance rating through three times in minutes, and the stated order is structural adequacy, integrity and insulation. That notation makes the separate functions explicit. Other test and classification systems require their own interpretation rather than an assumed transfer of symbols or values.<ref name="CVM_64" />

[[File:fse-fire-resistance-v1.svg|thumb|upright=1.5|alt=Three panels for load support, flame separation and limited heat transmission.|Fire resistance has three distinct performance criteria. Based on Ministry of Business, Innovation and Employment (2025), p. 64.]]

== How a furnace test establishes a rating ==

A [[Fire resistance test]] exposes a defined specimen to a prescribed heating history while monitoring the required endpoints. Milke describes this approach through the United States ASTM E119 framework in the 2002 handbook, and a successful specimen receives a rating for the stated test duration and conditions. The rating belongs to the tested assembly and its permitted applications.<ref name="M_4-209_4-210" />

The specimen can include several materials and components. Protection around a steel member, for example, changes the heat entering the steel and its temperature history, and the test observes the interaction between the protection and the member. This is one reason separate material properties do not always reproduce the behaviour of an assembled construction.<ref name="M_4-209_4-210" />

Loads and restraint form part of the test arrangement. Restraint describes the extent to which surrounding construction prevents thermal movement. Milke explains that framing geometry and connections affect the distinction between restrained and unrestrained test systems. A result obtained under one arrangement cannot automatically represent another arrangement with different movement conditions.<ref name="M_4-210_4-211" />

The monitored endpoints also depend on the assembly. They can include maintaining the applied load, limiting temperatures and preventing the passage of flames or gases capable of igniting a specified target. Some historical ASTM procedures include a hose-stream exposure. These observations have distinct purposes, so a report identifies which endpoints and procedures apply to its specimen.<ref name="M_4-210_4-211" />

[[File:fse-fire-resistance-v2.svg|thumb|upright=1.5|alt=Standard furnace curve heats an assembly and leads to structural, flame and temperature endpoints.|Fire-resistance testing links exposure to assembly endpoints. Based on Milke (2002), pp. 4-209–4-210.]]

An unlisted assembly and a failed assembly are not the same evidential category. Milke explains that an assembly without a listing has no established rating unless acceptable performance is demonstrated. That demonstration may involve a standard test, a special experiment or an analytical method. Absence of a rating therefore concerns the available evidence, rather than an observed failure time.<ref name="M_4-209">Milke (2002), p. 4-209.</ref>

== Reading temperature criteria correctly ==

A temperature rise is a difference from the starting temperature, so it is not the same quantity as an absolute temperature. Confusing them changes the interpretation of an insulation criterion, even when both are printed using degrees Celsius. The initial condition therefore belongs with the stated limit and measurement location.<ref name="M_4-211">Milke (2002), p. 4-211.</ref>

Milke's historical ASTM E119 table gives wall-insulation examples of a 139 °C average rise and a 181 °C single-point rise. These values apply to measurements on the unexposed side of the stated wall or partition assemblies; they are not limiting furnace temperatures. The table also contains other endpoints for steel members, which require their own interpretation.<ref name="M_4-211" />

[[File:fse-fire-resistance-v3.svg|thumb|upright=1.5|alt=Wall with average 139 °C and single-point 181 °C temperature-rise criteria marked on the unexposed side.|ASTM E119 wall-insulation endpoint examples (temperature rise). Based on Milke (2002), p. 4-211.]]

An average and a single-point limit address different aspects of the temperature field: the average represents the group of measured locations, while the single-point value constrains a local high temperature. Keeping both avoids replacing the endpoint definition with one convenient measurement. Neither value alone describes the complete fire exposure or the structural condition of the specimen.<ref name="M_4-211" />

A structural temperature criterion is different again. Kodur and Harmathy explain that a critical temperature corresponds to the material becoming unable to support the applied load under the adopted conditions. It consequently depends on loading and material behaviour. A temperature used in a simplified test-based method is not a universal temperature at which every member collapses.<ref name="KH_1-163">Kodur and Harmathy (2002), p. 1-163.</ref><ref name="M_4-209" />

== Standard exposure and a worked example ==

A [[Standard fire curve]] prescribes temperature as a function of time. It provides a repeatable exposure for comparing assemblies. It does not directly describe the heat release rate of a burning object or the temperature in every real room. Van Rossum distinguishes these quantities because they serve different purposes in a fire analysis.<ref name="VR_8.6" />

Milke presents the following approximation for the ISO 834 furnace-temperature history, and the logarithm describes the continuing rise in prescribed temperature, while the initial temperature is added separately. In this expression, time is entered in seconds. The coefficient 0.133 carries reciprocal-second units, making the quantity inside the logarithm dimensionless.<ref name="M_4-223">Milke (2002), p. 4-223.</ref>

<math display="block">T_f=T_0+345\log_{10}(0.133t+1)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>T_f</math> || Prescribed furnace temperature || °C
|-
| <math>T_0</math> || Initial temperature || °C
|-
| <math>t</math> || Elapsed heating time || s
|}

Using an initial temperature of 20 °C gives approximately 841 °C at 1,800 s and 945 °C at 3,600 s. These calculations use the rounded coefficient printed by Milke, and they illustrate the prescribed thermal environment at 30 min and 60 min. They do not predict the temperature of the specimen, which requires a separate heat-transfer calculation.<ref name="M_4-211" /><ref name="M_4-223" />

The equation contains no material thickness, conductivity, loading or support condition, so it cannot calculate whether a particular wall or beam survives either exposure duration. Two assemblies in the same furnace can develop different internal temperatures and structural responses. The standard curve supplies one input to the assessment, not its final result.<ref name="M_4-209" /><ref name="M_4-223" />

== Material and assembly behaviour ==

Materials perform different functions within an assembly. Steel provides load-bearing capacity but changes strength and stiffness when heated. Concrete can carry load while delaying heat transfer to reinforcement. Insulating materials can protect a structural component without carrying significant load themselves. The complete assembly combines these roles under the imposed exposure.<ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="FB_4-239">Fleischmann and Buchanan (2002), p. 4-239.</ref>

Combustible construction can also retain structural function for a specified period. White describes timber endurance through protective membranes, the extent of charring and the capacity of the remaining uncharred wood. Char itself has very little load-bearing capacity. The existence of combustion therefore does not, by itself, establish the time at which the member loses its required function.<ref name="W_4-257">White (2002), p. 4-257.</ref><ref name="W_4-260">White (2002), p. 4-260.</ref>

Conversely, noncombustibility does not establish fire resistance: a material can remain unburned while its mechanical properties deteriorate or its unexposed surface becomes too hot. This is the distinction from [[Reaction to fire]], which concerns the material's contribution to fire development. Different tests are needed because the two assessments follow different physical outcomes.<ref name="KH_1-155" /><ref name="KH_1-157" /><ref name="J_3-38_3-39">Janssens (2002), pp. 3-38–3-39.</ref>

Changes to an assembly can affect several outcomes together. White explains that changing membranes, member spacing or insulation can fall outside the tested timber arrangement. Adding insulation does not produce an automatic improvement in every floor or roof assembly. The relevant evidence is the behaviour of the revised construction, including how its layers remain supported during heating.<ref name="W_4-257_4-259">White (2002), pp. 4-257–4-259.</ref>

Heat transfer through protection can involve physical and chemical changes as well as ordinary conduction. Van Rossum describes moisture evaporation, release of chemically bound water and swelling as processes that change thermal response. These processes can consume energy or alter the heat-conduction path. An assembly calculation using fixed room-temperature properties may therefore miss part of the protective behaviour.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

The relevant time is also a property of the complete sequence. The furnace heats the surface, energy moves through the construction, and the specified endpoint is reached at a measurement location or structural state. A material's conductivity describes only one part of this sequence. It cannot by itself supply a duration without geometry, boundary conditions and the selected endpoint.<ref name="M_4-209" /><ref name="VR_5.2" />

== Fire resistance within compartmentation ==

[[Fire compartmentation]] uses separating construction to restrict the spread of fire between spaces, and the wall or floor is only part of that separation. Existing openings, closures and penetrations can provide other routes for spread. The 2005 International Fire Engineering Guidelines therefore consider spread through openings separately from failure of the barrier material.<ref name="IFEG_1.6-3">Australian Building Codes Board et al. (2005), p. 1.6-3.</ref><ref name="IFEG_1.6-7" />

The guidelines distinguish conduction, loss of integrity and loss of stability as different barrier-failure mechanisms. Conduction can heat nearby combustible material without opening the barrier. Loss of integrity includes cracks and failure of firestopping, while loss of stability involves collapse. A fire-resistance rating must be interpreted alongside the boundary details relevant to those mechanisms.<ref name="IFEG_1.6-7" />

Door use also changes the separation during evacuation, and the same guidelines treat the time of opening a door as information supplied by the occupant-movement analysis. A closed-door test does not describe the period when the door is open. Compartmentation performance consequently depends on the states of its openings as well as the endurance of closed components.<ref name="IFEG_1.6-7" />

[[Passive fire protection]] includes the barriers and protective materials that support these functions. Their performance is expressed through particular constructions and conditions, rather than a general promise that fire remains contained. This connection explains why rated construction and its installation details belong to the same design. A rating on one component cannot close an unprotected route around it.<ref name="IFEG_1.6-7" /><ref name="M_4-212_4-214">Milke (2002), pp. 4-212–4-214.</ref>

== Calculation methods and validation ==

[[Structural fire engineering]] connects fire exposure, heat transfer and structural response. The first stage defines the thermal environment. The second calculates temperatures within the member, using material properties and boundary conditions. The third evaluates the consequences for stresses, deformation and load-carrying capacity. A calculation of one stage does not independently establish the others.<ref name="M_4-209" />

Empirical correlations provide a simpler route where sufficient test data exist. Milke explains that such correlations are limited by the exposure, loading and span represented in their underlying tests. Their numerical simplicity does not remove those limits. Applying a correlation outside its supporting range introduces a different problem from interpolating within the tested conditions.<ref name="M_4-209" />

Thermal models can represent either standard exposure or a specified nonstandard fire, and their output may be the time to a chosen temperature or a temperature distribution for structural analysis. Temperature-dependent properties and the description of heating both affect accuracy. A model with detailed geometry can still produce a misleading result if those physical inputs are unsuitable.<ref name="M_4-209" />

Testing remains relevant even where calculation is available, and it supplies material behaviour, checks assembly interactions and provides evidence for judging model predictions. New Zealand's 2025 C/VM2 definition explicitly connects its calculation route to verification against standard fire-resistance tests. That connection identifies the evidence supporting a rating rather than treating calculation as evidence by itself.<ref name="M_4-210_4-211" /><ref name="CVM_64" />

== Limits when applying a rating ==

A furnace test is a controlled representation with practical size and support constraints. Milke notes that these constraints make some results comparative rather than exact reproductions of entire structures. An extended continuous frame can behave differently from an isolated specimen. The tested configuration and the proposed application therefore remain part of the interpretation.<ref name="M_4-210">Milke (2002), p. 4-210.</ref>

A real compartment fire can grow, reach a maximum and decay. Its temperature history depends on the fuel, ventilation and enclosure, while the standard curve serves a repeatable testing purpose. A stated rating is therefore not a direct forecast of survival time in every natural fire. Connecting the two requires a method that represents the relevant exposure and structural conditions.<ref name="VR_8.6" /><ref name="M_4-209" />

The same rating also does not establish the time available for occupants to escape. The International Fire Engineering Guidelines treat barrier performance, fire spread and other subsystem results as interacting parts of an analysis. Smoke and opening conditions can affect adjacent spaces before a closed assembly reaches its furnace-test endpoint. Escape and containment consequently require related but distinct assessments.<ref name="IFEG_1.6-3" /><ref name="IFEG_1.6-7" />

== See also ==

* [[Concrete in fire]]
* [[Timber in fire]]
* [[Critical steel temperature]]
* [[Time equivalence]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-38–3-62). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* White, R. H. (2002). Analytical methods for determining fire resistance of timber members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-257–4-273). National Fire Protection Association.

[[Category:Structural Fire Engineering]]

Concrete in fire

2026-11-02T18:41:37Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Concrete in fire''' describes the heating, material changes and structural response of concrete members exposed to fire. Concrete is noncombustible and can delay the heating of embedded reinforcement through its relatively low thermal conductivity, and its cooler interior can continue carrying load while the exposed surface becomes hot. These advantages do not prevent all forms of thermal damage or structural failure.<ref name="FB_4-239">Fleischmann and Buchanan (2002), p. 4-239.</ref>

The response depends on the complete member, rather than compressive strength alone. Aggregate, moisture, cover depth, geometry, applied load and support conditions affect different stages of the assessment. Surface material can also break away during heating, changing the protection available to the reinforcement. A calculation that considers only intact concrete may then miss an influential change in the section.<ref name="KH_1-156">Kodur and Harmathy (2002), p. 1-156.</ref><ref name="KH_1-163_1-164">Kodur and Harmathy (2002), pp. 1-163–1-164.</ref><ref name="FB_4-239" />

Assessment normally connects a defined fire exposure to an internal temperature distribution and then to structural performance. Separating elements also have a heat-transmission function. Each calculation therefore needs a stated endpoint and material data suitable for the relevant temperature range.<ref name="FB_4-239_4-242">Fleischmann and Buchanan (2002), pp. 4-239–4-242.</ref>

== Material structure and fire exposure ==

Concrete combines aggregates with a cement paste containing pores and moisture, and these constituents respond differently when heated, so concrete cannot be represented as one chemically uniform solid. Aggregate type, density, porosity and moisture influence its thermal behaviour. The properties needed for a fire calculation consequently extend beyond its specified compressive strength at ordinary temperature.<ref name="KH_1-155_1-156">Kodur and Harmathy (2002), pp. 1-155–1-156.</ref>

The material can perform both a structural and an insulating role. Concrete around steel reinforcement absorbs and conducts heat before the reinforcement reaches a high temperature. Meanwhile, cooler parts of a concrete section can continue to carry load. These functions are related, but they require different calculations and different material properties.<ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="FB_4-239" />

Fire exposure is the boundary condition for those calculations. A prescribed furnace temperature history differs from a natural compartment fire, whose development depends on fuel, ventilation and enclosure properties. A temperature curve also differs from a heat release rate curve: one describes temperature, while the other describes thermal power. Confusing them would change the physical problem being assessed.<ref name="VR_8.6">Van Rossum (2027), §8.6.</ref>

The exposed faces matter as much as the nominal temperature history. A slab or separating wall may receive fire exposure predominantly on one side. A beam can be heated on several sides, while a column can be exposed around its perimeter. Fleischmann and Buchanan describe these arrangements separately because they produce different internal temperature distributions.<ref name="FB_4-242">Fleischmann and Buchanan (2002), p. 4-242.</ref>

== Heat penetration and material properties ==

Heat entering the exposed surface moves through solid concrete mainly by conduction. [[Thermal conductivity]] describes how readily a temperature difference drives that transfer. Density and specific heat describe the energy stored as the material warms. Together, these quantities determine how rapidly a temperature disturbance spreads into the section.<ref name="FB_4-242" /><ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

The exposed surface and the interior therefore need not reach the same temperature. During early heating, a substantial temperature gradient can exist through a thick section. The cooler interior is one reason a concrete member may continue functioning while its surface becomes very hot. A single furnace temperature does not represent the temperature of every reinforcement bar.<ref name="FB_4-239" /><ref name="FB_4-242" /><ref name="VR_5.2" />

Moisture changes the energy balance because evaporation consumes heat. Heating also changes the material itself, including its microstructure and relevant thermal properties. Van Rossum consequently treats calculations with constant properties as approximations. The diffusivity used at one stage of heating need not describe the entire fire exposure.<ref name="VR_5.2" /><ref name="KH_1-157" />

A steady calculation assumes that the temperature profile through the whole construction has already developed. That assumption can be unsuitable during the initial heating of a thick wall. A transient calculation instead follows the changing temperatures as energy enters and spreads through the material. This distinction affects both reinforcement temperature and heat transfer to the unexposed side.<ref name="VR_5.2" /><ref name="FB_4-239" />

== A worked heat-penetration example ==

Thermal diffusivity divides conductivity by the volumetric heat capacity, which is density multiplied by specific heat. For a sudden surface-temperature change, the square root of diffusivity multiplied by time gives a characteristic penetration depth. This depth describes a scale of temperature change, rather than a sharp front separating hot and cold concrete.<ref name="VR_5.2" />

<math display="block">\alpha=\frac{\lambda}{\rho c_p},\qquad d\approx\sqrt{\alpha t}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\alpha</math> || Thermal diffusivity || m²/s
|-
| <math>\lambda</math> || Thermal conductivity || W/(m·K)
|-
| <math>\rho</math> || Density || kg/m³
|-
| <math>c_p</math> || Specific heat || J/(kg·K)
|-
| <math>t</math> || Heating duration || s
|-
| <math>d</math> || Characteristic penetration depth || m
|}

Van Rossum's comparison of thick concrete and timber walls uses rounded concrete properties of 1.7 W/(m·K), 2,300 kg/m³ and 900 J/(kg·K). With these inputs, the calculated diffusivity is 8.21 × 10⁻⁷ m²/s. After 3,600 s, the characteristic depth is approximately 0.054 m, or 54 mm. The calculation reproduces the source example using unrounded intermediate values.<ref name="VR_5.2" />

That result does not mean that concrete outside a 54 mm layer remains exactly at its initial temperature. Nor does it identify a spalling depth, a damaged zone or the position of a failure boundary. The model has no mechanical failure criterion and uses fixed thermal properties. Its purpose is to explain the scale of transient heating in a thick material.<ref name="VR_5.2" />

A separate example in the same section considers a 200 mm concrete wall over the first 900 s. It uses a different stated diffusivity, 9.88 × 10⁻⁷ m²/s. The source's approximate boundary between thermally thick and thin behaviour, twice the penetration depth, is then 60 mm. The 200 mm wall is thermally thick for that example, but this observation does not assign it a fire-resistance rating.<ref name="VR_5.2" />

== Spalling and loss of cover ==

[[Spalling]] is the breaking away of concrete from the heated surface. Kodur and Harmathy distinguish early explosive loss from later loss associated with weakened material. The process matters because the section can lose both material and thermal protection. Reinforcement formerly enclosed by concrete may then receive more direct heating.<ref name="KH_1-163_1-164" />

One proposed mechanism involves moisture movement and pressure within the pores. Heating drives moisture towards cooler regions, where a relatively saturated zone can impede further transport. Pressure can rise if vapour cannot escape readily. The handbook also discusses explanations based on thermal stresses and fracture, so pore pressure is not the sole mechanism considered.<ref name="KH_1-163">Kodur and Harmathy (2002), p. 1-163.</ref>

[[File:fse-concrete-in-fire-v1.svg|thumb|upright=1.5|alt=Heat drives moisture into a low-permeability concrete clog, raising pressure and cracking the surface.|Moisture clog and pressure can contribute to spalling. Based on Kodur and Harmathy (2002), p. 1-163.]]

The source illustrates the pressure mechanism using approximately 8 MPa vapour pressure at 300 °C and approximately 5 MPa tensile strength for high-strength concrete. This comparison demonstrates how internal pressure can exceed a resisting tensile stress; it is an explanatory example, not a universal pressure-temperature failure rule. Actual spalling also depends on permeability, moisture, loading and the heating conditions.<ref name="KH_1-163_1-164" />

[[File:fse-concrete-in-fire-v3.svg|thumb|upright=1.5|alt=Example vapour pressure 8 MPa versus tensile strength 5 MPa at 300 °C.|Example of internal pressure exceeding concrete tensile strength. Based on Kodur and Harmathy (2002), p. 1-163.]]

High compressive strength at room temperature does not by itself prevent spalling. Dense, low-permeability concrete can restrict moisture escape during rapid heating. Once surface material is lost, deeper concrete and reinforcement heat more rapidly. A model that retains the original section throughout the exposure cannot automatically represent that change.<ref name="KH_1-163_1-164" />

Thermal stress offers a different way for cracking to develop. The heated surface tends to expand while cooler material restricts that movement. Kodur and Harmathy discuss fracture-based explanations in which these stresses contribute to surface loss. An analysis based only on vapour pressure therefore addresses one proposed contribution, rather than demonstrating that other mechanisms are absent.<ref name="KH_1-163" />

The distinction between tensile and compressive behaviour is also relevant. The pressure example compares internal pressure with tensile resistance, whereas the familiar concrete grade describes compressive strength; these are different material quantities. Increasing the specified compressive strength cannot by itself resolve a cracking mechanism involving internal pressure, restrained expansion and tensile fracture.<ref name="KH_1-163_1-164" />

== Reinforcement and load-carrying capacity ==

[[Strength reduction at elevated temperatures]] affects both the concrete and the embedded steel. Fleischmann and Buchanan distinguish hot-rolled reinforcement from cold-drawn prestressing steel and high-strength alloy steel, and their strength-temperature relationships differ, reflecting the materials and mechanical properties considered. A single generic steel curve cannot represent every reinforced or prestressed member.<ref name="FB_4-239_4-240">Fleischmann and Buchanan (2002), pp. 4-239–4-240.</ref>

Concrete strength also depends on aggregate and on the conditions of the material test. The handbook compares specimens heated under load with specimens heated before being loaded to failure, and these procedures can produce different measured strengths at the same temperature. Material data therefore need an accompanying description of the loading and heating history.<ref name="FB_4-240_4-241">Fleischmann and Buchanan (2002), pp. 4-240–4-241.</ref>

The modulus of elasticity describes stiffness, or resistance to elastic deformation, and it can decrease substantially during heating even when part of the compressive strength remains. Consequently, a strength calculation and a deformation calculation address different effects. Thermal expansion adds another source of deformation and can alter the forces arising in restrained construction.<ref name="FB_4-240_4-241" />

[[File:fse-concrete-in-fire-v2.svg|thumb|upright=1.5|alt=Concrete section with cover, reinforcement and spalled region reducing protection and stiffness.|Concrete and reinforcement respond together to heat and section loss. Based on Fleischmann and Buchanan (2002), pp. 4-241–4-242 and Kodur and Harmathy (2002), p. 1-164.]]

In a simplified thermal analysis, the reinforcement temperature may be approximated by the concrete temperature at the bar centre. This connects the heat-transfer calculation to the subsequent structural calculation. The cover depth, exposed faces and heating duration then affect the steel properties used in that analysis. The approximation belongs to the stated modelling approach, rather than every possible member configuration.<ref name="FB_4-242" />

The load present during heating affects how a property curve is established. In the concrete results discussed by Fleischmann and Buchanan, some specimens carried 40% of their compressive strength while being heated. They were then loaded to failure at the temperature of interest. That procedure describes strength while hot, rather than a measurement of residual strength after cooling.<ref name="FB_4-240">Fleischmann and Buchanan (2002), p. 4-240.</ref>

A temperature-dependent property curve consequently carries more information than its axes alone, and its concrete type, initial condition and testing sequence affect what the result represents. A curve measured for one aggregate and load history cannot be assumed to describe another without supporting evidence. This is separate from uncertainty in the furnace temperature or the calculated temperature within the member.<ref name="FB_4-240_4-241" />

== Beams, slabs and structural continuity ==

A simply supported slab provides a useful starting model: its ends permit expansion and rotation under the idealised support conditions described by Fleischmann and Buchanan. As reinforcement heats and weakens, the section's resistance to bending decreases. Structural failure is assessed by comparing that remaining resistance with the bending demand from the applied load.<ref name="FB_4-245">Fleischmann and Buchanan (2002), p. 4-245.</ref>

Concrete near the compression face may remain cooler than reinforcement near the fire-exposed underside. The structural calculation therefore uses the temperature distribution, rather than applying one reduction to the entire section. If part of the compression zone becomes sufficiently hot, the source method reduces its contribution. That step depends on the chosen material model and calculation procedure.<ref name="FB_4-245" />

A continuous member behaves differently because it can redistribute bending moments between the span and its supports. Redistribution can extend endurance, but the remaining sections must still resist the transferred demand. Fleischmann and Buchanan describe failure through the formation of a mechanism involving several yielding regions. Continuity is therefore a structural condition, not an automatic allowance added to a rating.<ref name="FB_4-246">Fleischmann and Buchanan (2002), p. 4-246.</ref>

[[Structural fire engineering]] combines this structural response with the preceding fire and thermal calculations. The assessment depends on loads, geometry, reinforcement and support conditions as well as temperature. More specialised structural behaviour is addressed in the related topic [[Tensile membrane action]]. The heat-penetration example above does not calculate any redistribution or membrane resistance.<ref name="FB_4-239" /><ref name="FB_4-245_4-246">Fleischmann and Buchanan (2002), pp. 4-245–4-246.</ref>

== Testing and fire-resistance assessment ==

[[Fire resistance]] is evaluated against specified functions under a defined exposure. A separating concrete floor may need to support loads and limit heat transfer to the space above. A column has a different structural role and exposure arrangement. The required endpoints follow the assembly and assessment method, rather than the material name alone.<ref name="FB_4-239" /><ref name="FB_4-242" />

For standard exposure, empirical methods can relate dimensions and other parameters to results from furnace tests. Nonstandard exposure generally requires a more explicit thermal analysis followed by structural evaluation. Fleischmann and Buchanan describe both approaches and their different information requirements. A correlation derived from a standard test does not independently establish performance for an arbitrary natural fire.<ref name="FB_4-239" />

New Zealand's C/VM2, second edition of 2025, defines a fire resistance rating using three durations, and their order is structural adequacy, integrity and insulation. The definition permits standard testing or a specified calculation method verified against standard fire-resistance tests. This is the terminology of that New Zealand document, rather than a universal notation for every jurisdiction.<ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

== Limits of simplified predictions ==

A numerical model can follow changing temperatures with more detail than a penetration-depth estimate. The concrete chapter describes models that include temperature-dependent properties and changing boundary conditions, but it also notes that the cited implementations did not explicitly model moisture migration. Representing evaporation through adjusted thermal properties does not itself calculate pore-pressure-driven spalling.<ref name="FB_4-243">Fleischmann and Buchanan (2002), p. 4-243.</ref><ref name="KH_1-163" />

The same distinction applies to a good match with measured temperatures. Such a match supports the thermal calculation for the tested conditions, but it does not independently demonstrate the correct structural restraint, reinforcement strength or response to section loss. Those questions require evidence relevant to the mechanical model and the construction being assessed.<ref name="FB_4-239" /><ref name="FB_4-243" /><ref name="KH_1-164">Kodur and Harmathy (2002), p. 1-164.</ref>

A source value also carries limits associated with its concrete and test history. Aggregate type, moisture and applied load can affect the measured response, while rapid heating can introduce additional damage mechanisms. These dependencies explain why the handbook presents several material relationships and calculation approaches. Selecting one requires identifying the physical conditions it represents.<ref name="FB_4-240_4-241" /><ref name="KH_1-163_1-164" />

== See also ==

* [[Conduction]]
* [[Steel in fire]]
* [[Restrained thermal expansion]]

== Notes ==

<references />

== References ==

* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Structural Fire Engineering]]

Reaction to fire

2026-11-02T18:41:31Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

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

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

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

== Contribution to a developing fire ==

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

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

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

== Heating, ignition and flame spread ==

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

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

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

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

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

== Heat release and mass loss ==

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

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

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

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

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

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

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

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

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

== What tests measure ==

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

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

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

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

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

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

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

== Why total energy and peak power differ ==

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

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

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

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

== Classification and use in buildings ==

Classification connects specified test results with a defined regulatory framework. The intended use matters because a wall lining, floor covering and structural member serve different functions. New Zealand's C/VM2, second edition of 2025, treats rapid spread over internal surface linings as a specific design scenario. Its criteria depend on location, building use and importance level.<ref name="CVM_50_52">Ministry of Business, Innovation and Employment (2025), pp. 50–52.</ref>

In that New Zealand method, exposed internal wall and ceiling surfaces receive material Group Numbers. The commentary associates ordinary timber products with Group 3 and many fire-retardant-treated timbers with Group 2, and it identifies exposed polyurethane foams as examples associated with Group 4. These are explanatory examples, rather than classifications transferable to every product bearing the same material name.<ref name="CVM_50_52" />

Flooring is assessed through critical radiant flux in the same document. A higher critical flux corresponds to better performance in the specified flooring assessment. For sleeping areas and exitways in care or detention buildings, the 2025 table gives 4.5 kW/m² without sprinklers and 2.2 kW/m² with sprinklers. These are New Zealand scenario requirements, not general ignition thresholds for all materials.<ref name="CVM_52">Ministry of Business, Innovation and Employment (2025), p. 52.</ref>

[[File:fse-reaction-to-fire-v3.svg|thumb|upright=1.5|alt=Critical radiant flux values 4.5, 2.2 and 1.2 kW/m² for three C/VM2 situations.|C/VM2 critical radiant flux depends on occupancy and sprinklers. Based on Ministry of Business, Innovation and Employment (2025), p. 52.]]

The distinctions reflect the role of the space. C/VM2 gives greater emphasis to linings along escape routes, where they may form a substantial part of the available fuel. Occupants' ability to evacuate and the presence of sprinklers also affect the specified criteria. Applying one classification requirement throughout every occupancy would remove these distinctions.<ref name="CVM_52" />

== Smoke production and treatment effects ==

Heat release and smoke-related hazards are connected but are not interchangeable measurements. Janssens expresses the production rate of a toxic gas as its yield multiplied by the mass loss rate. A high yield alone does not establish the largest total release. The burning rate and its variation during the exposure are also part of the assessment.<ref name="J_3-38">Janssens (2002), p. 3-38.</ref>

A fire-retardant treatment can change more than one measured property. Janssens discusses treatments that increase a toxic-gas yield while reducing mass loss sufficiently to reduce the assessed hazard. That example explains why treatment performance cannot be judged from one isolated number. Its interpretation depends on the complete combination of burning rate, yields and exposure conditions.<ref name="J_3-38" />

Smoke obscuration is another measurement available in calorimetry. It describes the effect of suspended products on transmitted light, rather than directly measuring structural endurance or the complete toxic hazard. A test reporting smoke obscuration therefore answers a different question from a furnace test of a separating assembly. The measurements become useful when each remains connected to its own physical quantity.<ref name="J_3-39" /><ref name="M_4-209_4-210" />

== Evidence and uncertainty ==

Heat-release measurements contain both systematic bias and random variation. Babrauskas describes calibration with a metered gas supply as one means of addressing bias. Comparisons between laboratories reveal variability that a single test cannot show. The historical interlaboratory results in the handbook are evidence about those apparatuses and trials, rather than permanent uncertainty allowances for every later test.<ref name="B_3-32_3-33" />

A model that uses small-specimen results introduces a further step between measurement and application. Material properties derived from those results must reproduce the processes relevant to the larger fire. Janssens describes approaches ranging from full-scale experiments to calculations using bench-scale data. Their suitability depends on the fire scenario, the available measurements and the treatment of enclosure feedback.<ref name="J_3-38_3-39" />

Even the same product can present different exposed areas and orientations in different applications. A room-corner arrangement provides different heat feedback from an isolated specimen, while a mounting method can alter burning. A defensible comparison consequently identifies the product, construction, exposure, measured quantity and test configuration together. Removing those conditions can turn a valid measurement into an unsupported prediction.<ref name="J_3-39" /><ref name="J_3-56" />

== See also ==

* [[Flame retardant]]
* [[Heat release rate]]
* [[Ignition]]

== Notes ==

<references />

== References ==

* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-38–3-62). National Fire Protection Association.
* Kanury, A. M. (2002). Flaming ignition of solid fuels. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-229–2-245). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Quintiere, J. G. (2002). Surface flame spread. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-246–2-257). National Fire Protection Association.

[[Category:Materials & Fire Testing]]

Passive fire protection

2026-11-02T18:14:38Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Passive fire protection''' uses building construction and protective materials to restrict fire spread, delay heating and preserve specified structural or separating functions. Examples include fire-resisting barriers and insulation around structural members. The mechanisms depend on the physical and thermal behaviour of the installed construction.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="M_4-212_4-214">Milke (2002), pp. 4-212–4-214.</ref>

Passive does not mean that every component remains unchanged during fire. Materials can release moisture, char or swell as they heat. A broader compartmentation system can also contain doors or other closures that must operate. Static barriers, heat-responsive materials and movable protective features therefore have different dependencies.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Performance belongs to a defined assembly and exposure, rather than a material label alone. Thickness, continuity, attachment, supports and installation details can affect the result. The protective function also needs to remain intact through later alterations and use. Testing, calculation and inspection provide different parts of the evidence for that continuing performance.<ref name="M_4-209_4-214">Milke (2002), pp. 4-209–4-214.</ref><ref name="IFEG_1.6-9" />

== Protective functions within a building ==

Passive protection uses the physical behaviour of construction to limit fire effects. A boundary can restrict passage between spaces, while an insulating layer can delay heating of a structural member. A material can also perform several functions together. Kodur and Harmathy distinguish load-bearing, insulating and combined roles when describing building materials.<ref name="KH_1-155" /><ref name="KH_1-157" />

[[Fire compartmentation]] applies the separating function to a volume within the building. Its boundary includes the walls and floors as well as their protected openings and supporting construction. The performance of one wall surface cannot describe the whole enclosure. The International Fire Engineering Guidelines identify several routes by which fire can pass beyond that boundary.<ref name="IFEG_1.6-6_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-8.</ref>

Thermal protection of a steel member addresses another function. Milke describes insulation, membranes, shielding and heat sinks as ways to reduce heating. These measures affect the temperature history used in the structural assessment. Their purpose is not to make the steel immune to fire, but to change the rate and distribution of heat transfer.<ref name="M_4-212_4-214" />

[[File:fse-passive-fire-protection-v1.svg|thumb|upright=1.5|alt=Compartment, insulation and doors provide passive protection beside active alarm and sprinkler.|Passive measures and active systems have different roles. Based on Iqbal and Salley (2004), p. F-44.]]

A complete strategy can combine these functions with detection, warning and suppression. New Zealand's C/VM2 defines fire safety systems as the combination of active and passive measures serving evacuation, firefighting, spread control and structural stability. The category passive therefore describes how particular measures work. It does not mean that the entire building strategy has no operational dependencies.<ref name="CVM_65">Ministry of Business, Innovation and Employment (2025), p. 65.</ref><ref name="IFEG_1.6-9" />

== How thermal protection changes heating ==

An insulating layer alters the route by which heat reaches a protected member. Its thickness, conductivity and physical condition affect that route. The layer can also absorb energy as its own temperature rises. Milke distinguishes models that neglect this thermal storage from models that include it, particularly for materials such as concrete and gypsum.<ref name="M_4-223">Milke (2002), p. 4-223.</ref>

The initial temperature and exposure at the surface are also needed for a heat-transfer calculation. Rockett and Milke explain that the surface condition can be specified through temperature or heat flux. Those conditions can vary over the surface and with time. A material conductivity alone consequently cannot determine the temperature reached by a complete protected member.<ref name="RM_1-29">Rockett and Milke (2002), p. 1-29.</ref>

Protection can change chemically and physically during heating. Van Rossum describes evaporation, charring, loss of material and swelling as processes that alter thermal response. Gypsum also absorbs energy through release of chemically bound water. A model using fixed properties and unchanged geometry may omit part of the protection's behaviour.<ref name="VR_5.2" />

An [[Intumescent material]] expands under heating and develops an insulating structure. This is a heat-induced response within a passive protective system. It differs from an electrically or mechanically commanded closure. Describing passive protection as completely unchanged during fire would therefore misrepresent one of its recognised mechanisms.<ref name="VR_5.2" /><ref name="M_4-214">Milke (2002), p. 4-214.</ref>

== Boundaries, doors and concealed spaces ==

A [[Fire door]] provides a closure where access interrupts a separation. Its rating concerns the specified doorset, while its closing function establishes the state credited during fire. The International Fire Engineering Guidelines distinguish operable barriers from static construction. A compartment containing an automatically closing door therefore includes an operating dependency as well as passive materials.<ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref><ref name="IFEG_1.6-9" />

[[Firestopping]] protects penetrations and narrow gaps that would otherwise interrupt the boundary. New Zealand's 2025 C/VM2 definition includes services and joints within or through fire separations. Its construction commentary links the product to the orientation and separating element. This connects the protective function to its installed arrangement.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref><ref name="CVM_65" />

A [[Cavity barrier]] addresses spread within a concealed space. C/VM2 distinguishes this function from sealing a penetration through a separation. The International Fire Engineering Guidelines identify ceiling voids, hollow construction and spaces behind cladding as possible spread routes. A continuous surface visible from an occupied room does not demonstrate that these concealed paths are interrupted.<ref name="CVM_62">Ministry of Business, Innovation and Employment (2025), p. 62.</ref><ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref>

The boundary also depends on its supports. A fire-resisting wall or floor can fail when the construction carrying it loses stability. The guidelines therefore connect supporting-member failure with the continued function of barriers. Treating every rated component independently can omit a shared physical dependency in the completed building.<ref name="IFEG_1.6-8">Australian Building Codes Board et al. (2005), p. 1.6-8.</ref>

== Fire-resistance evidence and failure modes ==

[[Fire resistance]] concerns specified functions maintained under a defined exposure. Structural adequacy addresses carrying loads, integrity addresses passage of flames or hot gases, and insulation addresses heat transmission. The applicable functions depend on the assembly and method. A quoted duration has meaning only alongside those conditions and endpoints.<ref name="KH_1-155" /><ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref><ref name="CVM_64" />

The International Fire Engineering Guidelines describe conduction, integrity loss and stability loss as separate barrier-failure mechanisms. An intact wall can transmit excessive heat without forming a hole. A crack or failed penetration treatment can permit passage while most of the wall remains sound. Collapse creates another form of loss, possibly involving the wall's supports.<ref name="IFEG_1.6-7_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-7–1.6-8.</ref>

A test establishes evidence for a particular assembly. Milke explains that standard furnace conditions include defined exposure, loading and restraint. Analytical methods can also be used, but their inputs and range of validity remain relevant. A test-based correlation does not automatically describe another exposure, span or loading condition.<ref name="M_4-209_4-211" />

Material combustibility is a separate question. Steel can remain unburned while its mechanical properties deteriorate, while timber can retain an uncharred load-bearing section during charring. Kodur and Harmathy distinguish these thermal, structural and fuel roles. A noncombustible label therefore cannot replace evidence for the claimed protective function of an assembly.<ref name="KH_1-157" /><ref name="W_4-257">White (2002), p. 4-257.</ref><ref name="W_4-260">White (2002), p. 4-260.</ref>

A fire-retardant treatment makes another, more limited claim. C/VM2 defines it as a substance or treatment that suppresses or delays combustion under specified conditions. White explains that treatment intended to limit surface flame spread does not automatically provide fire-resistive protection to a timber member. The outcome being claimed therefore determines the evidence required. An improved surface-burning result is not itself a structural endurance result.<ref name="CVM_64" /><ref name="W_4-259">White (2002), p. 4-259.</ref>

The assembly route can include calculation as well as testing. New Zealand's 2025 C/VM2 definition permits a specified calculation method verified against standard fire-resistance tests. Milke separates empirical correlations, heat-transfer analysis and structural analysis because they answer different questions. An empirical estimate inherits its test range, while a thermal result still needs a structural endpoint. The more detailed calculation does not eliminate the need to establish what performance is being demonstrated.<ref name="CVM_64" /><ref name="M_4-209">Milke (2002), p. 4-209.</ref>

Protection of a timber assembly further illustrates the interaction between layers and structure. White identifies the membrane's behaviour, the amount of charring and the capacity of the remaining wood as separate contributions. A change in the protective layer can affect the later condition of the load-bearing member. The overall rating consequently cannot be inferred from a favourable description of either component in isolation.<ref name="W_4-257" />

== Thickness, continuity and attachment ==

A thermal model represents a physical arrangement of protection around or in front of a member. Gaps and changes in thickness alter that arrangement. Carino and colleagues' investigation of World Trade Center protection specifically examined gaps and thickness variability. Their work connects the assumed insulation geometry to the thermal analysis.<ref name="WTC_iii">Carino et al. (2005), p. iii.</ref>

[[File:fse-passive-fire-protection-v2.svg|thumb|upright=1.5|alt=Uniform insulation beside a gap and thin region forming thermal bridges to a member.|Insulation gaps and thickness variation create thermal bridges. Based on Carino et al. (2005), p. iii and Rockett and Milke (2002), p. 1-29.]]

Attachment determines whether protective layers remain in their intended positions. Milke identifies the means of fixing board systems as a factor in assembly performance. He also includes bond strength, durability and resistance to damage among relevant properties of applied insulation. These characteristics concern retaining the thermal barrier, rather than conductivity alone.<ref name="M_4-212_4-214" />

The protection can be affected during construction or later modifications. Iqbal and Salley discuss sprayed mineral-fibre coatings being knocked from steel members during such work. The report therefore distinguishes an effective applied layer from a damaged installation over time. The protective material's original test description does not establish its condition after alteration.<ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

Different protection forms also require different models. A board enclosure can surround a section without following its full contour, while an applied coating follows another thermal path. Some systems store appreciable heat within the protection itself. The calculation must represent the arrangement being credited, including its geometry and relevant material changes.<ref name="M_4-213_4-214">Milke (2002), pp. 4-213–4-214.</ref><ref name="M_4-223" />

== A World Trade Center specification example ==

NIST NCSTAR 1-6A investigates passive protection in the World Trade Center towers in connection with the 2001 disaster. Carino and colleagues review design decisions, construction records, material properties and available measurements of installed protection. They also examine adhesion, gaps and variability in thickness. The report describes that historical investigation, not a general specification for other buildings.<ref name="WTC_iii" />

Its historical review identifies an issue in rewritten sprayed fire-resistive material specifications. A requirement linking finished thickness to particular ratings was apparently omitted during rewriting in 1969. The authors reproduce the relevant correspondence in their account. This is documentary evidence about the specification history, rather than a direct measurement of every installed member.<ref name="WTC_12_13">Carino et al. (2005), pp. 12–13.</ref>

The omitted wording linked the protection of specified support beams and steel deckwork to a three-hour rating. It linked the specified pick-up girders and columns to four hours. These values belonged to that historic specification and its identified components. They are not general requirements for all beams and columns, nor proof of the actual endurance of every tower member.<ref name="WTC_13">Carino et al. (2005), p. 13.</ref>

[[File:fse-passive-fire-protection-v3.svg|thumb|upright=1.5|alt=Specification links finished insulation thickness to 3-hour and 4-hour member ratings.|WTC example links specification, thickness and fire rating. Based on Carino et al. (2005), p. 13.]]

The example separates intended performance, written specification and installed condition. The report treats construction records and in-place measurements as different forms of evidence. Its analysis of thickness and material properties then supports thermal-structural modelling. None of these steps can be replaced simply by stating that the building contained fireproofing.<ref name="WTC_iii" /><ref name="WTC_12_13" />

== Coordination with suppression and smoke control ==

A [[Fire suppression system]] acts on the developing fire, while passive measures restrict its effects on construction or adjacent spaces. The distinction does not make their credited performance independent. Iqbal and Salley describe a fire barrier used in conjunction with other protective measures. A design that relies on suppression consequently has different assumptions from one considering an uncontrolled fire.<ref name="N_F-29">Iqbal and Salley (2004), p. F-29.</ref><ref name="N_17-7">Iqbal and Salley (2004), p. 17-7.</ref>

Smoke separation also depends on the building's pressure conditions. Klote describes leakage through door gaps, penetrations and construction cracks. Mechanical smoke control can use pressure differences across barriers and airflow through openings. A physical boundary and an operating fan system can therefore contribute to the same protective objective.<ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref>

Opening a door changes that interaction during evacuation. The International Fire Engineering Guidelines obtain opening times from the occupant-movement analysis. New Zealand's 2025 C/VM2 similarly specifies different door-opening assumptions for intermittent passage and continuous queues. A strategy cannot infer the open-state performance solely from the rating of the closed doorset.<ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref><ref name="CVM_15">Ministry of Business, Innovation and Employment (2025), p. 15.</ref>

C/VM2's concealed-space scenario illustrates another form of coordination. For its stated scope, it permits separating elements, suppression or automatic detection as approaches to the specified concern. Those alternatives belong to the scenario's criteria and limitations. They do not establish unrestricted substitution between any passive measure and any active system elsewhere in a building.<ref name="CVM_41">Ministry of Business, Innovation and Employment (2025), p. 41.</ref>

== Construction, management and change ==

The International Fire Engineering Guidelines identify three physical checks during construction and commissioning: boundary integrity, conformity with specifications and operation of movable protective features. They also call for appropriate operation and maintenance information. These checks connect the design assumptions with the completed building. Each addresses a different part of the protective system.<ref name="IFEG_1.6-9" />

The guidelines note that passive features can be overlooked when a building is repaired or modified. Their continuing identification therefore forms part of preserving the strategy. A new service route or local construction change may affect a larger compartment boundary. The importance of that boundary may not be evident from the location of the work alone.<ref name="IFEG_1.6-9" />

Inspection and operational testing serve different purposes. The guidelines describe limited routine maintenance for static passive barriers while calling for operational tests of automatically closing features. Written maintenance requirements and recorded outcomes retain evidence of the resulting condition. The word passive therefore does not mean that the construction can be forgotten after installation.<ref name="IFEG_1.6-9" />

A maintained system preserves the arrangement supported by its evidence. Material data, assembly tests, calculation assumptions and construction records describe different parts of that arrangement. When geometry, exposure or operation changes, the relationship between those parts also changes. The technical assessment then concerns the revised system and the functions still supported by its evidence.<ref name="M_4-209_4-214" /><ref name="IFEG_1.6-9" />

== See also ==

* [[Fire safety strategy]]
* [[Structural fire engineering]]
* [[Fire wall]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Carino, N. J., Starnes, M. A., Gross, J. L., Yang, J. C., Kukuck, S. R., Prasad, K. R., & Bukowski, R. W. (2005). ''Passive fire protection'' (NIST NCSTAR 1-6A). 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Rockett, J. A., & Milke, J. A. (2002). Conduction of heat in solids. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-27–1-43). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* White, R. H. (2002). Analytical methods for determining fire resistance of timber members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-257–4-273). National Fire Protection Association.

[[Category:Passive Fire Protection]]

Firestopping

2026-11-02T18:14:32Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Firestopping''' is the use of materials or construction details to restrict fire spread through penetrations and gaps in separating construction. It preserves the boundary's intended function where services or joints would otherwise interrupt it. The function is part of assembly fire resistance, particularly the integrity of the separation.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="CVM_65">Ministry of Business, Innovation and Employment (2025), p. 65.</ref><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

A firestop is assessed in its installed context. The surrounding wall or floor, the penetrating service, the orientation and the relevant test evidence determine what performance is supported. A material described as fire resistant does not automatically establish the performance of every opening filled with it. New Zealand's 2025 C/VM2 explicitly links the product to the orientation and separating element.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref><ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref>

Related terms need careful distinction. A duct closure, a barrier within a concealed space and a feature limiting spread along a cable tray address different routes. The same broad firestopping terminology can otherwise obscure which physical function an installation is intended to perform.<ref name="N_F-19">Iqbal and Salley (2004), p. F-19.</ref><ref name="N_F-29">Iqbal and Salley (2004), p. F-29.</ref><ref name="CVM_62">Ministry of Business, Innovation and Employment (2025), p. 62.</ref>

== The route being sealed ==

Services often need to cross the walls or floors that form [[Fire compartmentation]]. Pipes, cables, cable trays and ventilation ducts can create openings through an otherwise continuous boundary. A penetration seal addresses the route around those services. Its purpose is to preserve the intended separating function of the construction.<ref name="N_F-44" /><ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

New Zealand's C/VM2, second edition of 2025, defines a fire stop as a material or construction method restricting spread within or through a fire separation. Its definition includes sealing around penetrations and narrow gaps between building elements. The stated fire resistance must be no less than that of the separation. This is a requirement within that New Zealand method.<ref name="CVM_65" />

[[File:fse-firestopping-v1.svg|thumb|upright=1.5|alt=Unsealed tray carrying flame and sealed penetration blocking it, with backing and contact shown.|Firestopping closes service paths through a fire separation. Based on Ministry of Business, Innovation and Employment (2025), p. 65.]]

A visible gap and heat transmission through intact construction are different paths. The International Fire Engineering Guidelines distinguish failed firestopping from excessive conduction through a barrier. Sealing an opening addresses the first mechanism but does not independently establish the thermal performance of the entire wall. The required functions remain those of the completed separation.<ref name="IFEG_1.6-7" /><ref name="KH_1-155" />

The surrounding construction matters to the seal's performance. C/VM2's construction commentary specifies proprietary products appropriate to the orientation and separating element. An installation in a floor and one in a wall are therefore not assumed interchangeable merely because their materials look similar. The evidence follows the application and construction in which the product is used.<ref name="CVM_13" />

== Materials and complete systems ==

A firestop is defined by the function of its installed arrangement. The opening, service and surrounding separation form part of that arrangement. Iqbal and Salley's penetration-seal definition expressly includes wiring, cables, pipes, ducts and building joints. The same material name does not establish performance across all those geometries and duties.<ref name="N_F-44" /><ref name="CVM_13" />

An [[Intumescent material]] expands when heated and can develop an insulating layer. Van Rossum identifies swelling as a process that changes thickness and heat transfer during fire. This explains one possible protective-material mechanism. It does not establish a universal expansion factor, seal depth or application for an unspecified firestop product.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

Other aspects of an assembly can also change during exposure. The International Fire Engineering Guidelines include damaged service pipes and cable trays among conditions that can create openings. Integrity therefore depends on more than the initial appearance of the filled gap. The assessment concerns whether the intended boundary remains effective through the relevant event.<ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref>

Product evidence and installation details consequently answer different but connected questions. Testing supports a stated construction under defined conditions. Installation establishes whether that construction has been reproduced in the building. New Zealand's 2025 verification method explicitly connects construction detailing to the developed design.<ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref><ref name="CVM_13" />

== Distinction from dampers and cavity barriers ==

A [[Fire damper]] closes the passage inside a ventilation duct or opening. A penetration seal addresses the path around that assembly where it crosses a wall or floor. Those paths can exist at the same location but require different protective functions. Closing one does not demonstrate that the other has been protected.<ref name="N_F-19" /><ref name="N_F-44" />

[[File:fse-firestopping-v2.svg|thumb|upright=1.5|alt=Damper stops airflow inside duct while firestop seals the gap between duct and wall.|Damper and firestop perform complementary functions. Based on Iqbal and Salley (2004), p. F-19 and p. F-44.]]

A [[Cavity barrier]] restricts spread within a concealed space or closes an opening within that space. C/VM2 defines it separately from the fire stop used at a separation. The distinction concerns the route and location being protected. It prevents every concealed barrier or service seal from being treated as the same type of construction.<ref name="CVM_62" /><ref name="CVM_65" />

Building joints are another distinct application. Iqbal and Salley's list of standards separates through-penetration firestop tests from tests for building joint systems. A joint and a service penetration therefore have different evidential descriptions in that source. Their performance cannot be established by ignoring what the cited test actually evaluates.<ref name="N_C-15">Iqbal and Salley (2004), p. C-15.</ref>

Terminology can also vary between technical contexts. The NUREG glossary uses fire stop for a feature restricting propagation along cables or towards nearby combustible material. It separately defines penetration seals at rated boundaries. A cable-tray fire stop described in an incident report is consequently not automatically a wall-penetration seal of the same design.<ref name="N_F-29" /><ref name="N_F-44" />

== Tests and the limits of a classification ==

A [[Fire resistance test]] evaluates specified functions under a defined exposure. The assembly, measurement criteria and duration belong together. A generic material description does not provide these details. The evidence therefore needs to identify the tested protective arrangement and the function claimed from it.<ref name="KH_1-155" /><ref name="M_4-209_4-210" />

The 2004 NUREG report identifies ASTM E814 and UL 1479 as through-penetration firestop test standards. It separately lists UL 2079 for building joint systems. These references establish which test subjects the report distinguishes. The list is not a substitute for the full standards or a current classification of an installed product.<ref name="N_C-15" />

The source's regulatory setting also remains relevant. NUREG-1805 supports the United States nuclear fire-protection inspection programme, while C/VM2 provides a New Zealand verification method. Their definitions and examples can explain physical functions without becoming universal installation rules. Any stated requirement retains the country, document and edition from which it comes.<ref name="N_F-44" /><ref name="CVM_13" /><ref name="CVM_65" />

Smoke performance requires its own interpretation. Klote explains that pressure differences can drive smoke through leakage paths around penetrations and construction joints. A fire-endurance description does not quantify that flow by itself. The credited smoke-separation function therefore needs evidence about the relevant path and operating conditions.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

== An incident showing the importance of configuration ==

NUREG-1805 includes an account of the Waterford 3 switchgear fire, drawing on United States regulatory reports issued in 1995. In that incident, propagation along a horizontal cable tray stopped at a raceway fire stop. In a vertical riser, the fire passed beyond a fire stop and continued. The account describes different outcomes within one event.<ref name="N_H-23">Iqbal and Salley (2004), p. H-23.</ref>

[[File:fse-firestopping-v3.svg|thumb|upright=1.5|alt=Horizontal stop holds fire while vertical tray fire jumps the stop and continues.|Waterford incident shows different firestop outcomes by orientation. Based on Iqbal and Salley (2004), p. H-23.]]

The authors state that it was unclear whether the vertical fire stop delayed propagation. That uncertainty matters: continued spread does not establish the size of any delay, and no delay should be invented from the account. The observed horizontal outcome likewise does not prove that every horizontal arrangement performs the same way. The evidence concerns the reported installation and incident.<ref name="N_H-23" />

The example also needs the correct object of comparison. These were cable-tray propagation features, not a controlled comparison of every wall and floor penetration system. The NUREG terminology distinguishes those uses. Treating the incident as a universal product test would extend the observation beyond what the report establishes.<ref name="N_H-23" /><ref name="N_F-29" /><ref name="N_F-44" />

Configuration nevertheless has direct relevance to construction evidence. C/VM2's separate requirement for appropriate orientation and separating element identifies the same need to retain application conditions. A result or observation becomes less informative when those conditions are removed. The evidence describes an arrangement, rather than the word firestop in isolation.<ref name="CVM_13" /><ref name="N_H-23" />

== Construction, alterations and inspection ==

The International Fire Engineering Guidelines identify barrier integrity and conformity with specifications as construction and commissioning concerns. Firestopping contributes to that integrity at services and joints. The completed boundary therefore includes the penetration treatment as well as the visible wall or floor. Missing treatment can create a spread route without any general failure of the main element.<ref name="IFEG_1.6-6" /><ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Later modifications can change the original arrangement. New services, altered openings or repairs can affect boundaries whose fire-safety role is not obvious locally. The guidelines note that passive components are liable to be overlooked during such work. Continued identification connects the alteration to the separation it crosses.<ref name="IFEG_1.6-9" />

Inspection and records preserve information about the resulting condition. The guidelines call for maintenance requirements to be documented and outcomes recorded. They do not provide one universal seal recipe or inspection interval. The relevant product evidence and construction details remain necessary to assess the actual installed system.<ref name="IFEG_1.6-9" /><ref name="CVM_13" />

== See also ==

* [[Fire wall]]
* [[Passive fire protection]]
* [[Fire resistance]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire wall

2026-11-02T18:14:27Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''fire wall''' is a separating wall intended to restrict fire spread while maintaining the required resistance and structural stability. Its role combines the thermal and structural functions of building construction. In NUREG-1805's description of United States practice, a fire wall is distinguished from a barrier used alongside other protective measures.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="N_17-7">Iqbal and Salley (2004), p. 17-7.</ref>

The complete separation includes the wall's supports, ends, roof junction and protected openings. Fire can pass around an otherwise effective wall or through a damaged penetration. Some fire walls are designed to remain stable after construction collapses on either side, but that capability must be part of the stated design.<ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref><ref name="IFEG_1.6-6_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-8.</ref>

A fire-resistance duration alone does not describe all these conditions. The construction, exposure, support and required endpoints determine what the evidence demonstrates. Wall terminology and detailing provisions also differ between regulatory frameworks. Historical examples therefore need their document and jurisdictional context to remain explicit.<ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref><ref name="N_17-7" />

== Fire wall and fire barrier terminology ==

NUREG-1805 distinguishes two related forms of separating construction in its discussion of United States practice. A fire wall separates buildings or subdivides a building while providing resistance and structural stability. A fire barrier restricts spread and extends to the floor or roof deck above. The distinction follows the report's description of NFPA 221.<ref name="N_17-7" />

The same account differentiates the assumed fire conditions. The fire wall is intended to remain stable during an uncontrolled fire without effective sprinkler protection. The barrier is considered alongside other protective measures, such as sprinklers. This identifies the performance basis within that framework rather than making the terminology universal across countries.<ref name="N_17-7" />

[[File:fse-fire-wall-v1.svg|thumb|upright=1.5|alt=Fire wall stable during uncontrolled fire and fire barrier working with sprinklers.|Fire wall and fire barrier have different design roles. Based on Iqbal and Salley (2004), p. 17-7.]]

Both constructions can contribute to [[Fire compartmentation]], but their structural assumptions can differ. A wall's label does not independently explain whether surrounding construction may fail while the wall remains standing. That condition needs to be part of the design basis. Iqbal and Salley state that some fire walls are specifically designed to survive collapse on either side.<ref name="N_17-7_17-8">Iqbal and Salley (2004), pp. 17-7–17-8.</ref>

A time rating is also a different description from structural independence. The rating concerns specified performance under a defined exposure. Independence concerns the relationship between the wall and the structures around it. A design needs evidence for whichever combination of those functions it claims.<ref name="KH_1-155" /><ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref><ref name="N_17-8" />

== Heat transmission, openings and stability ==

[[Fire resistance criteria]] distinguish structural adequacy, integrity and insulation where those functions apply. Heat can pass through a wall even if the wall remains standing and has no opening. Cracks can permit gases or flames to pass before widespread collapse. These different mechanisms cannot be represented by observing only whether the wall is visibly upright.<ref name="KH_1-155" /><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

The insulation function depends on heat transfer through the construction. A thick material can develop a hot exposed surface while its interior remains cooler. Conductivity, heat capacity and exposure duration affect this temperature distribution. A description of noncombustibility does not by itself establish how long the unexposed surface remains within a specified limit.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref>

Integrity concerns routes through the wall. Openings may be present initially or develop through damage, cracking or failed protection around services. The International Fire Engineering Guidelines consider these routes separately from conduction through intact material. The neighbouring fuel and its exposure determine whether passage through a route develops into another fire.<ref name="IFEG_1.6-6_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-7.</ref>

Stability includes the wall and any structural support it relies on. The guidelines note that a barrier may fail when its supporting member fails. They also require consideration of the effects on other barriers after structural failure. A separate wall rating cannot remove this dependency from the assembled building.<ref name="IFEG_1.6-8">Australian Building Codes Board et al. (2005), p. 1.6-8.</ref>

== Continuity at roofs, ends and penetrations ==

A wall can be bypassed at its edges even if the main surface performs as intended. Iqbal and Salley describe exterior wing walls at the ends of fire walls to restrict spread around them. They also describe a parapet continuing through and above the roof. These are examples of completing the separation in their United States technical context.<ref name="N_17-8" />

[[File:fse-fire-wall-v2.svg|thumb|upright=1.5|alt=Wing walls close the ends and a parapet carries the fire wall through and above the roof.|Wing walls and parapets close fire-wall bypass routes. Based on Iqbal and Salley (2004), p. 17-8.]]

The roof junction can otherwise connect the spaces on either side of the wall. The 2005 International Fire Engineering Guidelines identify concealed roof and ceiling spaces as possible routes between enclosures. A separating line in an occupied room does not automatically close those spaces. The boundary must be understood through its full extent and connections.<ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref><ref name="N_17-8" />

Service crossings require their own protection. [[Firestopping]] addresses the paths around pipes, conduits, cables and ducts where they pass through the boundary. Personnel or vehicle openings require suitable closures within the arrangement described by Iqbal and Salley. The wall, penetration protection and closures form complementary parts of the separating system.<ref name="N_17-8" /><ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref>

Service support can also influence the wall's condition during collapse. NUREG-1805 describes routing pipes, conduits and cables near floor level to reduce the risk of damaging the wall when construction collapses on one side. This is a specific detailing consideration in that report. It illustrates why the location of a penetration can matter beyond its initial seal.<ref name="N_17-8" />

== Historical resistance examples ==

[[Fire resistance]] is established for an assembly and stated conditions, rather than assigned from a generic material name. NUREG-1805 nevertheless provides a table of historical rules of thumb for common wall constructions. The report labels these as typical estimates. They are useful examples of the influence of construction, but they are not current approvals for unspecified walls.<ref name="N_17-7" /><ref name="M_4-209_4-210" />

The table associates a 12-inch brick wall with a ten-hour estimate. It associates an 8-inch concrete-brick wall with six hours and a 16-inch nominal concrete-block wall with four hours. The corresponding nominal dimensions are approximately 305 mm, 203 mm and 406 mm. These conversions retain the original construction distinctions and do not create new tested specifications.<ref name="N_17-7" />

[[File:fse-fire-wall-v3.svg|thumb|upright=1.5|alt=Typical values: 12-inch brick 10 h, 8-inch concrete brick 6 h and 16-inch concrete block 4 h.|Typical wall fire-resistance examples from NUREG-1805. Based on Iqbal and Salley (2004), p. 17-7.]]

The concrete-block row also distinguishes nominal from actual thickness. Its stated actual thickness is 15⅝ inches, approximately 397 mm, rather than the nominal 406 mm. That detail demonstrates why a rounded product description can differ from the tested or tabulated geometry. It also prevents the table from being read as a simple universal thickness-to-rating formula.<ref name="N_17-7" />

A contemporary application needs the evidence relevant to its actual wall and jurisdiction. Milke explains that test-based correlations remain limited by the conditions represented in their supporting tests. An old tabulated estimate does not independently resolve changes in loading, support or construction. The estimate and a verified rating are therefore different forms of evidence.<ref name="M_4-209_4-210" /><ref name="N_17-7" />

== Internal and external fire spread ==

A wall can address separation within one building and contribute to limiting [[Fire spread between buildings]]. The routes differ because external exposure can involve radiation, projecting flames and burning debris. The International Fire Engineering Guidelines treat these mechanisms explicitly. The adjacent building's openings and combustible surfaces are part of that assessment.<ref name="IFEG_1.6-5_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-7.</ref>

Radiation can expose material through glazing without the glass first falling out. A broken window can also change both the outgoing fire exposure and ventilation into the room. The guidelines therefore connect opening events to the fire-development analysis. A fire wall assessment cannot represent every external route solely through the temperature of the wall surface.<ref name="IFEG_1.6-7" />

The relative positions of boundaries and openings determine which routes require consideration. Vertical shafts and concealed spaces can connect different levels, while openings can connect neighbouring enclosures horizontally. The guidelines treat those connected spaces as enclosures within the analysis. The wall's function is therefore evaluated within a network of possible paths.<ref name="IFEG_1.6-6" />

Fire-separating and smoke-separating performance also differ. Klote describes smoke movement through construction cracks under pressure differences. An intact wall can consequently restrict flames while permitting some gas leakage. Where the strategy assigns a smoke-control function, the pressure and leakage conditions require attention alongside fire endurance.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

== Testing, installation and continued condition ==

A standard test represents a specified wall construction, load and support arrangement. Milke describes practical furnace and specimen constraints that limit direct reproduction of whole buildings. The result provides evidence for the assembly and permitted applications. Changes in the proposed wall therefore need to remain connected to the supporting test or calculation method.<ref name="M_4-209_4-211" />

New Zealand's C/VM2, second edition of 2025, gives one example of this connection in construction provisions. Details must match the developed design, while its commentary links penetration protection to the relevant orientation and separating element. These are requirements within that method. They do not convert a historical United States wall estimate into a New Zealand classification.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref>

The International Fire Engineering Guidelines identify barrier integrity and conformity with specifications as construction checks. They also note that passive features may be overlooked during later repairs and modifications. Continued identification of the wall's fire-safety role connects such work to the original strategy. This is particularly relevant where new openings or services alter its continuity.<ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Inspection records concern the condition that exists, while the test or calculation describes the condition credited in the design. Both are needed to keep those descriptions aligned. The guidelines include documentation of maintenance requirements and recorded outcomes. They do not supply one universal inspection interval or wall detail for every application.<ref name="IFEG_1.6-9" />

== See also ==

* [[Passive fire protection]]
* [[Fire door]]
* [[Protected escape route]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire door

2026-11-02T18:14:22Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''fire door''' is a rated doorset that protects an opening in a fire separation. It allows access through the boundary while providing specified resistance when closed. The thermal and integrity functions concern the complete construction, while closing and latching establish the operating state on which that performance depends.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

A door is consequently more than its leaf material. Its installation, associated components and evidence of assembly performance matter to the claimed rating. Smoke control may require additional performance beyond the fire-resistance function. New Zealand's C/VM2, second edition of 2025, distinguishes those requirements explicitly.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref><ref name="CVM_15">Ministry of Business, Innovation and Employment (2025), p. 15.</ref><ref name="CVM_64" />

A fire door also forms a changing part of [[Fire compartmentation]]. Occupants open it during evacuation, while pressure differences can move smoke through gaps or the open doorway. Understanding its role therefore requires both the closed-state evidence and the conditions under which it opens and closes during the event.<ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref><ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref>

== The complete doorset ==

A fire door belongs to the separating construction surrounding its opening. New Zealand's C/VM2, second edition of 2025, defines it as a single-leaf or multiple-leaf doorset with a specified rating. The definition includes automatic closing and self-latching during fire if the door is not already closed. Smoke-control capability is an additional feature in specified situations.<ref name="CVM_64" />

The word doorset keeps attention on the assembled opening protection. A door leaf operates within a frame and a surrounding separation, while the closing and latching functions establish its intended state. A claim about one material does not describe all these functions. The rating concerns the construction and conditions supported by the relevant test evidence.<ref name="CVM_13" /><ref name="CVM_64" /><ref name="N_C-10">Iqbal and Salley (2004), p. C-10.</ref>

[[File:fse-fire-door-v1.svg|thumb|upright=1.5|alt=Fire door with labelled leaf, frame, intumescent seal, closer and latch in a fire separation.|A fire door is a complete doorset, not only a leaf. Based on Ministry of Business, Innovation and Employment (2025), p. 64 and Iqbal and Salley (2004), p. C-10.]]

An [[Intumescent material]] swells during heating and can change the thermal path through an assembly. Van Rossum describes that general protective mechanism without defining the performance of a particular doorset. Its presence does not replace evidence for the complete door. The construction, operation and claimed fire performance remain separate parts of the assessment.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="CVM_13" />

[[Fire-resistant glazing]] likewise concerns a complete assembly rather than glass alone. C/VM2's definition includes the glazing, frame, fixings and associated components. The source therefore distinguishes a rated glazing arrangement from an unspecified glazed opening. A glazed door requires evidence relevant to the assembled construction in which that glazing is used.<ref name="CVM_64" /><ref name="CVM_13" />

== Fire resistance and smoke performance ==

[[Fire resistance criteria]] identify the functions evaluated under the prescribed exposure. Integrity addresses the passage of flames or hot gases, while insulation addresses heat transmission. A separating element may require different evidence for these outcomes. Neither can be inferred solely from the appearance or combustibility of the door material.<ref name="KH_1-155" /><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref>

[[Smoke movement]] introduces leakage paths and pressure differences. Klote identifies cracks around closed doors as paths through which gases can move. A closed leaf therefore does not imply an airtight boundary. The amount and direction of movement depend on both the available path and the forces acting across it.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

New Zealand's 2025 C/VM2 explicitly separates fire-door and smoke-control-door provisions. A fire door with smoke-control capability must satisfy both sets of provisions identified by that method. This distinction prevents a fire rating from being read as a complete smoke-leakage specification. It also identifies which function is being credited in the analysis.<ref name="CVM_15" />

A smoke separation need not have the same fire-resisting capability as a fire separation. C/VM2 applies different assumptions to their continued presence as conditions become more severe. Its discussion explains why a boundary credited early in a fire may not be credited after flashover. That is a modelling distinction, not a universal physical failure temperature for every door.<ref name="CVM_14_15">Ministry of Business, Innovation and Employment (2025), pp. 14–15.</ref>

== Testing and interpretation of ratings ==

A [[Fire resistance test]] places the doorset under a defined exposure and evaluates specified endpoints. The 2004 NUREG-1805 report summarises United States NFPA 252 door-assembly testing. It describes tests continuing to the selected rating period or an earlier performance failure. The report is a historical technical summary, not the full standard or a current product approval.<ref name="N_C-10" />

The summary includes rated periods such as 20, 30, 45, 60, 90 and 180 minutes. These durations belong to the reported test framework. They do not establish a universal duration required for every door or every location. The required performance follows the building context and the applicable classification and design provisions.<ref name="N_C-10" /><ref name="CVM_13" />

The same summary describes a hose-stream exposure following the fire-endurance test. Its purpose is to apply impact, erosion and cooling to the heated assembly. The report identifies an exception in which the hose stream is optional for the stated 20-minute-rated assemblies. It is therefore inaccurate to describe this stage as mandatory for every door test worldwide.<ref name="N_C-10" />

[[File:fse-fire-door-v3.svg|thumb|upright=1.5|alt=Door in furnace followed by hose-stream impact, erosion and cooling.|Fire-door testing includes endurance and hose-stream response. Based on Iqbal and Salley (2004), p. C-10.]]

Test evidence also retains its construction context. New Zealand's 2025 verification method requires details during construction to match the developed design. Its commentary connects rated closures to testing under an internationally recognised standard. This links the installed doorset to its evidence instead of assigning a rating from its thickness or material name alone.<ref name="CVM_13" />

== Door use during evacuation ==

A door protecting [[Means of escape]] must be considered in both its closed and open states. When occupants pass through, they temporarily change the separating boundary. The International Fire Engineering Guidelines therefore obtain opening times from the evacuation analysis. A closed-door furnace result does not describe those periods of use.<ref name="IFEG_1.6-7" />

C/VM2, second edition of 2025, provides a specific modelling convention for this interaction. Fire and smoke-control doors with self-closers are assumed closed unless occupants are using them. For low occupant demand, the model allows three seconds of opening per occupant. The commentary connects that interval to opening the leaf, passing through and allowing it to close.<ref name="CVM_15" />

Where a queue keeps occupants passing continuously, the same document treats the door as open for the queuing period. This is a different physical state from isolated short openings. Applying the low-demand convention while a continuous queue holds the leaf open would misrepresent the intended assumption. The distinction belongs to the New Zealand method's movement and smoke analyses.<ref name="CVM_15" />

[[File:fse-fire-door-v2.svg|thumb|upright=1.5|alt=Door opens for three seconds per occupant and remains open during a queue before closing.|Fire-door state changes during evacuation. Based on Ministry of Business, Innovation and Employment (2025), p. 15.]]

For smoke-flow calculations during egress, C/VM2 represents the open door using half its width. The commentary explains that the moving leaf and occupants obstruct part of the opening. This is an effective opening assumption for that analysis. It does not redefine the constructed door width or the width available under separate escape provisions.<ref name="CVM_15_16">Ministry of Business, Innovation and Employment (2025), pp. 15–16.</ref>

== Pressure differences and open doorways ==

A closed door and an open doorway present different airflow problems. With a closed door, the paths may consist mainly of small gaps. With an open door, a much larger passage connects the spaces. Klote distinguishes pressure control across mostly closed barriers from airflow control through large openings.<ref name="Kl_4-278_4-279">Klote (2002), pp. 4-278–4-279.</ref>

Mechanical pressurisation can oppose smoke entry through leakage paths. Its intended airflow is from the protected side towards the smoke-exposed side. When a door opens, however, low air velocity may permit smoke to flow back through part of the opening. The closed-door pressure condition does not by itself establish the open-door performance.<ref name="Kl_4-278">Klote (2002), p. 4-278.</ref>

The forces moving smoke can also come from outside the mechanical system. Buoyancy, stack effect and wind affect the pressure field within a building. Klote explains that fan shutdown alone does not stop movement through all available paths. A door's leakage and operating state therefore interact with the surrounding building conditions.<ref name="Kl_4-274">Klote (2002), p. 4-274.</ref><ref name="Kl_4-277">Klote (2002), p. 4-277.</ref>

These interactions explain why fire separation and smoke control cannot be assessed as completely independent systems. The same opening can support evacuation, interrupt a smoke boundary and influence airflow. The analysis identifies which state is assumed during each part of the event. It then connects that state to the function attributed to the doorset.<ref name="Kl_4-278_4-279" /><ref name="IFEG_1.6-7" />

== Closing functions and commissioning ==

A rating establishes performance under its tested conditions; it does not prove that an installed door will reach the necessary closed state. Closing and latching are operating functions in C/VM2's definition. Their role is distinct from the material's thermal response. Both are needed where the strategy relies on an automatically closed opening.<ref name="CVM_64" /><ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

The International Fire Engineering Guidelines include operable systems among construction and commissioning checks. Components must match the specification, and automatically closing doors must perform their intended function. The guidelines also include operating and maintenance information. This creates an evidence chain from the design description to the completed and functioning installation.<ref name="IFEG_1.6-9" />

The state assumed in a model can depend on use and management. C/VM2 explains its short opening convention through a well-maintained self-closing door and intermittent occupant arrivals. That convention does not describe a door permanently held open. Its use therefore rests on the operational condition stated in the method.<ref name="CVM_15" />

== Inspection, alterations and continuing evidence ==

The 2005 International Fire Engineering Guidelines distinguish routine inspection of static barriers from operational testing of active closures. A fire door may combine both types of concern: the physical separation and the movement required to restore it. Inspection of the wall alone cannot demonstrate the closing function. An operating check alone cannot establish the wall's complete fire-resisting construction.<ref name="IFEG_1.6-9" />

Repairs and modifications can affect the original boundary. The guidelines note that passive components may be overlooked during building changes. Continued identification of the separation links local work to its wider fire-safety role. That includes the opening protection as well as the surrounding construction.<ref name="IFEG_1.6-9" />

Maintenance records identify the required functions and document observed outcomes. The guidelines do not prescribe one universal inspection interval or one component specification for every doorset. Those details require the applicable standard and product evidence. The general framework preserves the connection between the designed boundary, the installed assembly and its continuing operation.<ref name="IFEG_1.6-9" /><ref name="CVM_13" />

== See also ==

* [[Passive fire protection]]
* [[Stair pressurisation]]
* [[Protected escape route]]
* [[Fire-induced pressure]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire damper

2026-11-02T18:14:17Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

A '''fire damper''' is an automatic closure in an air-distribution passage intended to resist the passage of heat and flame. It protects an opening that would otherwise interrupt a fire-separating wall or floor. The detailed definition in NUREG-1805 distinguishes its fire-resistance function from its ability to close under particular airflow conditions.<ref name="N_F-19">Iqbal and Salley (2004), p. F-19.</ref>

The device forms part of a complete boundary. Its closed state addresses the path through the ventilation opening, while the surrounding penetration requires suitable treatment. Smoke can also move through a building under pressure differences caused by buoyancy, wind and ventilation. A closure specification therefore needs more information than a nominal fire duration.<ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref><ref name="Kl_4-274">Klote (2002), p. 4-274.</ref><ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

Fire dampers and smoke dampers have related but different functions. The evidence needed for resisting fire is not identical to the evidence needed for limiting leakage or operating against airflow. The selected arrangement must correspond to the functions assigned to the opening in the building's fire strategy.<ref name="N_F-19" /><ref name="N_C-11">Iqbal and Salley (2004), p. C-11.</ref>

== The opening that a damper protects ==

Ventilation ducts connect spaces that may otherwise be separated by walls or floors. An open air passage can therefore bypass part of the intended [[Fire compartmentation]]. The damper supplies a closure within that passage. Its function is different from the wall's ability to resist heating through its solid material.<ref name="N_F-19" /><ref name="IFEG_1.6-6_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-7.</ref>

There can also be a separate path around the duct or damper assembly. [[Firestopping]] protects the surrounding penetration so that the crossing does not impair the barrier's intended performance. Closing the duct does not automatically seal this outside path. Both functions belong to the completed boundary.<ref name="N_F-19" /><ref name="N_F-44" />

[[File:fse-fire-damper-v1.svg|thumb|upright=1.5|alt=Open duct with airflow and closed damper blocking fire, with firestop around the frame.|A fire damper closes the duct; firestopping seals the surrounding penetration. Based on Iqbal and Salley (2004), p. F-19 and p. F-44.]]

The separating construction also provides the damper's installation context. New Zealand's C/VM2, second edition of 2025, links construction details to the approved design. Its commentary specifies firestopping appropriate to the orientation and separating element. This illustrates why evidence about an opening protection cannot be detached from the construction containing it.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref>

A damper is consequently assessed as part of an opening-protection arrangement. The duct, surrounding separation and penetration treatment perform complementary roles. The International Fire Engineering Guidelines identify both unprotected openings and failed firestopping as possible routes of spread. The presence of a closure alone does not describe every route through the boundary.<ref name="IFEG_1.6-6_1.6-7" />

== Closure and airflow conditions ==

The NUREG-1805 glossary describes assemblies of blades or louvers released by a fusible link or a remote activation signal. A fusible link responds to heat by melting and allowing closure. A remote signal provides another means of initiating the movement. These are alternative arrangements in the source, rather than a description of every product.<ref name="N_F-19" />

The conditions during closure matter as well as the closed-state fire performance. Iqbal and Salley distinguish a fire-resistance rating from an airflow-closure rating. The latter depends on whether the ventilation system is stopped when fire is detected. The design therefore needs to connect the assumed fan state to the damper's closing duty.<ref name="N_F-19" />

A static closure arrangement is associated with stopped airflow. A dynamic arrangement is intended to close under the relevant airflow conditions. These labels concern the operating condition against which closure is assessed. They do not, by themselves, describe smoke leakage, the surrounding wall or every subsequent control action.<ref name="N_F-19" />

[[File:fse-fire-damper-v2.svg|thumb|upright=1.5|alt=Static closure in stopped air and dynamic closure against fan pressure.|Static and dynamic fire-damper closure conditions. Based on Iqbal and Salley (2004), p. F-19.]]

Stopping a fan also does not remove every force moving gases through a building. Klote identifies stack effect, buoyancy and wind as additional drivers. These can continue moving smoke through ventilation passages even after mechanical supply stops. The intended closure function therefore remains distinct from the instruction to switch off a fan.<ref name="Kl_4-274" /><ref name="Kl_4-277">Klote (2002), p. 4-277.</ref>

== Fire dampers and smoke dampers ==

[[Smoke movement]] depends on available paths and the pressure differences driving flow through them. A smoke damper is intended to restrict that movement within a ventilation system. Its leakage performance is consequently relevant even when flames are not passing through the opening. Iqbal and Salley distinguish this role from resisting heat and flame.<ref name="Kl_4-277_4-278" /><ref name="N_F-19" />

Their account describes smoke dampers used in systems that stop airflow and in engineered systems that continue operating selected fans. The latter use controlled pressure differences to restrict smoke spread. Closure and fan operation therefore form part of a coordinated strategy. A universal instruction that every ventilation component must take the same state would omit these different functions.<ref name="N_F-19" /><ref name="Kl_4-278_4-279">Klote (2002), pp. 4-278–4-279.</ref>

The source states that a smoke damper need not meet every design function of a fire damper. Its smoke-damper test summary identifies leakage class, pressure, velocity, installation orientation and temperature. A fire-endurance claim therefore does not automatically demonstrate the separate leakage and operating characteristics. Evidence of one function cannot silently substitute for evidence of the other.<ref name="N_F-19" /><ref name="N_C-11" />

[[File:fse-fire-damper-v3.svg|thumb|upright=1.5|alt=Fire-damper flame rating beside smoke-damper leakage, pressure and velocity classes.|Fire dampers and smoke dampers have different evaluation criteria. Based on Iqbal and Salley (2004), p. F-19 and p. C-11.]]

The distinction also changes the question asked about an installed device. For fire separation, the question concerns the required resistance under the specified exposure. For smoke control, it also concerns the flow permitted under the relevant pressure and temperature conditions. The complete specification follows the functions assigned to that opening.<ref name="N_C-11" /><ref name="N_F-19" />

== Test evidence and material behaviour ==

[[Fire resistance criteria]] define the performance being claimed during a stated exposure. The 2004 NUREG report identifies UL 555 in its summary of fire-damper testing and UL 555S for smoke dampers. These references describe the report's historical United States context. The summary is not the complete text of either standard or a current product classification.<ref name="N_C-11" /><ref name="N_C-15">Iqbal and Salley (2004), p. C-15.</ref>

Test duration is only one part of that evidence. The smoke-damper summary expressly includes operating pressure, velocity and installation mode. Fire-damper application also includes the airflow condition during closure. Two products with a similar quoted duration can therefore represent different operating duties.<ref name="N_C-11" /><ref name="N_F-19" />

An [[Intumescent material]] changes through swelling when heated, which can alter the heat-conduction path. Van Rossum describes this as a general protective-material mechanism. It is distinct from the fusible-link and remote-signal closure mechanisms described for dampers. The general material behaviour alone does not establish the performance of a particular opening-protection assembly.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="N_F-19" />

The surrounding barrier has its own thermal, integrity and stability functions. The International Fire Engineering Guidelines show that barrier failure can arise through conduction, cracking or collapse. A damper assessment addresses an opening within that system. It does not independently establish the performance of the entire supporting wall or floor.<ref name="IFEG_1.6-7_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-7–1.6-8.</ref>

== Installation and operational dependencies ==

The installed arrangement joins building construction and ventilation control. Its assumed conditions include the protected boundary, the air passage and the state of the ventilation system during fire. The damper's closure duty must correspond to that operating state. Otherwise, the design would rely on a function different from the one described by the selected evidence.<ref name="N_F-19" /><ref name="CVM_13" />

The opening can be affected by changes elsewhere in the system. Klote explains that fan operation and other pressure drivers influence smoke movement. A revised ventilation arrangement can therefore change the physical conditions at the closure. This relationship follows from the system behaviour, even where the wall and damper remain in the same positions.<ref name="Kl_4-274" /><ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref>

The penetration treatment also depends on its construction context. C/VM2's orientation requirement distinguishes a seal's intended application from its material identity. The same principle prevents a general description of a sealing material from establishing every installed crossing. The evidence concerns the arrangement in which the material performs its protective function.<ref name="CVM_13" /><ref name="N_F-44" />

== Inspection and changes to the building ==

The 2005 International Fire Engineering Guidelines distinguish static barriers from operable protective features. Construction checks establish whether components match the specification and whether operable systems work as intended. Operational testing addresses a different question from visual continuity of a wall. Both observations are relevant where a boundary includes a moving closure.<ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref>

Repairs and modifications can overlook the role of passive fire-separating construction. The guidelines therefore emphasise continued identification of boundaries and preservation of their integrity. For a duct crossing, that includes retaining the connection between the opening protection and the surrounding separation. A local change can otherwise affect a boundary whose full extent is not visible.<ref name="IFEG_1.6-9" /><ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

Maintenance documentation records the required functions and the outcomes of inspection or operational tests. The guidelines do not provide one universal test interval for every protective device. Their emphasis is on maintaining the designed arrangement and recording its condition. Product-specific and jurisdiction-specific details require the applicable supporting documents.<ref name="IFEG_1.6-9" />

== See also ==

* [[Fire door]]
* [[Passive fire protection]]
* [[Smoke control]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Fire compartmentation

2026-11-02T18:14:12Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Fire compartmentation''' is the division of a building into spaces separated by construction intended to restrict the spread of fire and its effects. Walls, floors, closures and protected penetrations work together as a boundary. Its performance depends on maintaining the required structural, integrity and heat-transmission functions under the relevant exposure.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="N_F-24">Iqbal and Salley (2004), p. F-24.</ref><ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

The separation is not defined by a wall alone. Doors, ventilation openings, service penetrations, junctions and supporting construction can determine how a fire reaches another space. Some routes exist from the outset, while others develop through opening, damage or structural failure. Concealed voids and shafts can connect spaces beyond the room of origin.<ref name="IFEG_1.6-6_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-8.</ref>

Smoke movement adds a further consideration because intact construction can still contain leakage paths. Pressure differences drive flow through those paths and through open doors. Compartmentation consequently interacts with evacuation, ventilation and smoke control, as well as the fire resistance of its materials and assemblies.<ref name="Kl_4-277_4-279">Klote (2002), pp. 4-277–4-279.</ref><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref>

== The compartment boundary ==

A compartment is a volume separated from other spaces by construction intended to restrict fire effects. Its boundary can include walls, floors, a roof and closures within those elements. New Zealand's C/VM2, second edition of 2025, calls the enclosed volume a firecell. Its definition allows contiguous spaces on the same or different levels, rather than limiting a firecell to one room.<ref name="CVM_64" />

The boundary is therefore a complete system of construction and protected openings. The definition of a fire barrier in NUREG-1805 includes supports, penetration seals, closures, doors and dampers alongside walls and floors. That report was prepared for the United States nuclear regulatory inspection programme. Its terminology usefully identifies the interacting components without establishing requirements for every other building type.<ref name="N_F-24" />

[[File:fse-fire-compartmentation-v1.svg|thumb|upright=1.5|alt=Firecell bounded by walls, floor, roof, fire door, damper and penetration seals.|A firecell is a complete separating system. Based on Ministry of Business, Innovation and Employment (2025), p. 64.]]

[[Fire resistance]] describes how the construction maintains specified functions under an exposure. Those functions include structural adequacy, integrity and insulation where applicable. The first concerns load-bearing performance, the second passage of flames or hot gases, and the third heat transmission. A compartment boundary can lose one function while retaining another.<ref name="KH_1-155" /><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref><ref name="CVM_64" />

A [[Fire wall]] is one form of separating construction, but its precise role depends on the governing framework. Iqbal and Salley distinguish a wall intended to remain stable through an uncontrolled fire from a barrier used with other protective measures. That distinction belongs to their discussion of United States practice. It does not make every internal partition a structurally independent fire wall.<ref name="N_17-7_17-8">Iqbal and Salley (2004), pp. 17-7–17-8.</ref>

== Routes by which fire can spread ==

[[Fire spread]] between compartments can follow openings that already exist or openings created during the fire. The 2005 International Fire Engineering Guidelines treat both categories explicitly. Doors and windows may be open initially, while glazing breakage or damage can create further routes. The state of each route can change as the event develops.<ref name="IFEG_1.6-1">Australian Building Codes Board et al. (2005), p. 1.6-1.</ref><ref name="IFEG_1.6-6">Australian Building Codes Board et al. (2005), p. 1.6-6.</ref>

An opening can also result from missing or inadequate sealing around services. Pipes, cable trays and ventilation ducts cross boundaries to perform normal building functions. Those crossings need their own representation in the separating system. A sound wall surface does not describe the behaviour of an unprotected opening through it.<ref name="IFEG_1.6-6" /><ref name="N_17-8">Iqbal and Salley (2004), p. 17-8.</ref>

Concealed spaces can connect locations that appear separate in an occupied room. The guidelines identify ceiling voids, hollow construction, spaces under floors and spaces behind external cladding. Shafts and large service ducts can provide vertical routes. In the analysis, these spaces become further enclosures with their own connections and boundaries.<ref name="IFEG_1.6-6" />

The route can also pass outside the building before re-entering another space. The guidelines discuss flames projecting from windows, radiation and burning debris. Adjacent buildings can be exposed through openings or external surfaces. Compartmentation therefore cannot be assessed solely by tracing internal partition lines on a floor plan.<ref name="IFEG_1.6-5_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-7.</ref>

[[File:fse-fire-compartmentation-v3.svg|thumb|upright=1.5|alt=Fire and smoke passing through a door, duct, cable penetration, cavity and wall end.|Openings and junctions can bypass a fire-rated wall. Based on Australian Building Codes Board et al. (2005), p. 1.6-7 and Iqbal and Salley (2004), p. 17-8.]]

== Thermal, integrity and stability failures ==

Heat can pass through an intact boundary by conduction. The unexposed surface may then become hot enough to breach an insulation criterion or ignite nearby material under suitable conditions. This mechanism does not require a visible hole. The thermal properties, thickness and exposure history influence the resulting temperature distribution.<ref name="IFEG_1.6-7" /><ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

Loss of integrity introduces a path through the boundary. Cracks, fissures and failed penetration protection can permit hot gases or flames to pass. Whether adjacent material ignites depends on its location and response to the exposure. The International Fire Engineering Guidelines distinguish this physical sequence from a simplified analysis that equates barrier failure with spread.<ref name="IFEG_1.6-6_1.6-7">Australian Building Codes Board et al. (2005), pp. 1.6-6–1.6-7.</ref>

Loss of stability means that the barrier or its supporting construction can no longer remain in place. A wall can consequently fail because another structural element supporting it fails. The guidelines identify this dependency explicitly. The endurance of an isolated wall specimen is therefore not sufficient evidence for a boundary whose support fails earlier.<ref name="IFEG_1.6-7_1.6-8">Australian Building Codes Board et al. (2005), pp. 1.6-7–1.6-8.</ref>

[[File:fse-fire-compartmentation-v2.svg|thumb|upright=1.5|alt=Three panels: heat through an intact wall, cracks with smoke and a collapsed wall.|Compartment boundaries can fail thermally, through integrity or through stability. Based on Australian Building Codes Board et al. (2005), p. 1.6-7.]]

These mechanisms can interact during the same fire. An opening can change ventilation as well as permit spread into another enclosure. Structural loss can damage several boundaries together. The analysis therefore follows changes in the building and exposure, rather than assigning every component an unrelated failure time.<ref name="IFEG_1.6-4">Australian Building Codes Board et al. (2005), p. 1.6-4.</ref><ref name="IFEG_1.6-8">Australian Building Codes Board et al. (2005), p. 1.6-8.</ref>

== Doors, ducts and service penetrations ==

A [[Fire door]] protects an opening that must also permit normal access and evacuation. Its closed-state performance is part of the compartment boundary. Its open state creates a different route for heat and smoke. The International Fire Engineering Guidelines consequently connect door-opening times to the analysis of occupant movement.<ref name="CVM_64" /><ref name="IFEG_1.6-7" />

A [[Fire damper]] addresses the internal path through a ventilation opening or duct. Iqbal and Salley describe devices that close in response to a fusible link or remote signal. Their account distinguishes the fire-resistance function from the conditions under which the damper can close against airflow. Those conditions depend partly on whether ventilation is stopped.<ref name="N_F-19">Iqbal and Salley (2004), p. F-19.</ref>

[[Firestopping]] addresses gaps and penetrations that would otherwise weaken the separation. Around a duct, it protects the path between the duct assembly and the surrounding boundary. Closing the air passage inside the duct is a different function. A design can therefore need both a closure and a suitable seal at the same crossing.<ref name="N_F-19" /><ref name="N_F-44">Iqbal and Salley (2004), p. F-44.</ref>

New Zealand's 2025 C/VM2 construction provisions connect these details to the completed design. Its commentary calls for proprietary firestopping suited to the orientation and the separating element. It also identifies testing of rated closures under an internationally recognised standard. These provisions concern the installed construction, not a material name or an isolated product label.<ref name="CVM_13">Ministry of Business, Innovation and Employment (2025), p. 13.</ref>

== Smoke separation and pressure differences ==

Restricting fire spread and restricting smoke movement are related but distinct functions. Smoke can pass through cracks and leakage paths while a boundary remains intact. Klote identifies gaps around doors, pipe penetrations and wall-to-floor junctions as examples. The pressure difference across the boundary determines the driving force for that leakage.<ref name="Kl_4-277_4-278">Klote (2002), pp. 4-277–4-278.</ref>

Several forces can create the pressure difference. Klote discusses buoyancy from heating, stack effect, wind and mechanical ventilation. These can act together, so smoke movement is not determined by temperature alone. Stopping ventilation fans removes one influence but does not eliminate movement driven by the others.<ref name="Kl_4-274">Klote (2002), p. 4-274.</ref><ref name="Kl_4-277">Klote (2002), p. 4-277.</ref>

Mechanical smoke control can use pressure differences across closed boundaries and airflow through open doorways. The appropriate assessment changes when a door opens. A pressure difference across a mostly closed barrier is not equivalent to the airflow required through a large opening. Klote therefore distinguishes closed-door and open-door conditions.<ref name="Kl_4-278_4-279">Klote (2002), pp. 4-278–4-279.</ref>

C/VM2, second edition of 2025, likewise distinguishes fire separations, smoke separations and unrated construction within the trial design. The method applies different assumptions to their continued presence during a fire. Those assumptions describe the analysis framework and the evidence attributed to each separation. They are not predictions that every physical partition disappears at one identical temperature.<ref name="CVM_14_15">Ministry of Business, Innovation and Employment (2025), pp. 14–15.</ref>

== Representing openings in an analysis ==

The International Fire Engineering Guidelines begin with the enclosure geometry, openings and properties of barriers and structural elements. They also require the location and ignition characteristics of material in adjacent spaces. This information establishes what can be exposed if a route opens. A boundary failure and the ignition of another fuel item are separate events unless the method deliberately combines them.<ref name="IFEG_1.6-5_1.6-7" />

The guidelines permit simplifying assumptions for specified analyses. Examples include treating barrier failure as spread or using flashover as an opening-related event. They also identify conditions that can invalidate a simplification, such as direct flame contact on an unrated boundary. An assumption is therefore part of the model definition, rather than an observed fact about every fire.<ref name="IFEG_1.6-6" />

Door use provides a practical example. Under New Zealand's 2025 C/VM2, a self-closing fire or smoke-control door is assumed closed except when occupants use it. With low occupant demand, it is modelled open for three seconds per occupant. Where occupants queue, the method instead considers the sustained opening associated with that queue.<ref name="CVM_15">Ministry of Business, Innovation and Employment (2025), p. 15.</ref>

The same document uses half the door width for smoke-flow modelling while the door is being used for egress. Its commentary explains that a moving leaf and passing occupants restrict the unobstructed opening. This is a smoke-modelling assumption within C/VM2. It is not a rule that halves the physical escape width of every doorway.<ref name="CVM_15_16">Ministry of Business, Innovation and Employment (2025), pp. 15–16.</ref>

The concealed-space scenario in New Zealand's 2025 C/VM2 provides a specific example of protecting a route that is not visible from an occupied room. It applies within the stated scope to buildings containing rooms with more than 50 occupants and concealed spaces. The document identifies separating elements, suppression and detection as approaches to that scenario. Their acceptance depends on the scenario conditions, rather than an unrestricted exchange between systems.<ref name="CVM_41">Ministry of Business, Innovation and Employment (2025), p. 41.</ref>

Where its separating-element approach is used without automatic detection, C/VM2 specifies at least 30 minutes for integrity and insulation and limits the concealed-space area to 500 m². These figures belong to the particular 2025 New Zealand scenario. They do not define a universal compartment size or barrier rating. The example shows how the route, detection assumptions and separating construction are connected within a stated method.<ref name="CVM_41" />

== Integration with the fire safety strategy ==

Compartmentation forms part of [[Passive fire protection]], but it interacts with systems that operate during an incident. A door may need to close, and a ventilation closure may depend on a signal or the state of a fan. The International Fire Engineering Guidelines distinguish static barriers from operable closures. Describing the whole strategy as having no operational dependencies would conceal those differences.<ref name="IFEG_1.6-9">Australian Building Codes Board et al. (2005), p. 1.6-9.</ref><ref name="N_F-19" />

The expected duration of separation follows its purpose in the strategy. The guidelines connect times of spread and structural failure to evacuation, firefighting and protection of adjoining property. Different objectives can therefore require different outputs from the same physical analysis. A nominal duration without an endpoint or objective does not define the required performance.<ref name="IFEG_1.6-2">Australian Building Codes Board et al. (2005), p. 1.6-2.</ref><ref name="IFEG_1.6-4" />

Compartmentation can also be evaluated alongside suppression. Iqbal and Salley's distinction between fire walls and barriers specifically refers to whether other protective measures are credited. The consequences of losing that support differ from the behaviour assumed when it operates. The design basis therefore identifies which systems and operating conditions form part of the assessment.<ref name="N_17-7">Iqbal and Salley (2004), p. 17-7.</ref>

Structural support is another dependency within the strategy. A protected boundary may rely on columns, beams or floors to remain in place. The guidelines require consideration of failure of those supporting elements and its effects on other boundaries. Treating each rating independently would omit a physical route by which several protections can be lost together.<ref name="IFEG_1.6-8" />

== Construction, alterations and continued performance ==

Construction and commissioning establish whether the intended boundaries exist and their components match the specification. The International Fire Engineering Guidelines identify barrier integrity, specified materials and operation of automatic closures as distinct checks. They also include operation and maintenance documents. The completed system therefore includes both physical construction and information about its required functions.<ref name="IFEG_1.6-9" />

Later repairs or alterations can change that system. The guidelines note that passive barriers are liable to be overlooked during building modifications. Their continued identification helps connect a new service opening or construction change to the original fire strategy. Without that connection, a local alteration can change a boundary whose role is not visible from the room alone.<ref name="IFEG_1.6-9" />

Static barriers and operable closures have different maintenance needs. The guidelines describe relatively limited routine maintenance for passive barriers, while calling for operational testing of automatic closures. Inspection and records preserve evidence about both. A wall remaining in place and a door closing correctly are separate observations within the same compartmentation system.<ref name="IFEG_1.6-9" />

Evidence of performance remains tied to the construction and conditions assessed. A standard test demonstrates specified functions of its assembly, while modelling represents selected exposures, openings and dependencies. Their combined interpretation identifies where the boundary is expected to remain effective. It also identifies the assumptions that cease to hold when the building or its operating conditions change.<ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref><ref name="IFEG_1.6-5_1.6-9">Australian Building Codes Board et al. (2005), pp. 1.6-5–1.6-9.</ref>

== See also ==

* [[Cavity barrier]]
* [[Protected escape route]]
* [[Stay-put strategy]]
* [[Progressive horizontal evacuation]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* 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.
* Klote, J. H. (2002). Smoke control. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-274–4-291). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Passive Fire Protection]]

Timber in fire

2026-11-02T17:54:15Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

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

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

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

== Heating, decomposition and combustion ==

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

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

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

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

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

== Charring rate and grain direction ==

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

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

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

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

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

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

== A worked charring example ==

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

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

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

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

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

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

== The remaining section and structural capacity ==

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

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

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

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

== Heat penetration is not char depth ==

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

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

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

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

== Membranes and protected assemblies ==

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

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

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

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

== Reaction to fire and fire resistance ==

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

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

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

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

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

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

== Exposure limits and model evidence ==

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

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

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

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

== See also ==

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

== Notes ==

<references />

== References ==

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

[[Category:Structural Fire Engineering]]

Steel in fire

2026-11-02T17:54:10Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Steel in fire''' describes the heating, expansion and loss of mechanical performance of steel members exposed to fire. Steel can remain noncombustible while its strength and stiffness decrease. Structural performance therefore depends on temperature, loading, geometry, protection and support conditions, rather than combustibility alone.<ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="M_4-209">Milke (2002), p. 4-209.</ref><ref name="M_4-211_4-212">Milke (2002), pp. 4-211–4-212.</ref>

Assessment connects three stages: defining the fire exposure, calculating heat transfer into the steel and evaluating structural response. The gas temperature is an input to this sequence, not automatically the temperature of the member. Exposed surface, steel mass and protection determine how rapidly the member heats, while mechanical properties determine the consequences.<ref name="M_4-209" /><ref name="M_4-222_4-224">Milke (2002), pp. 4-222–4-224.</ref>

A standard furnace exposure provides one basis for comparing protected and unprotected assemblies. A natural fire requires its own description of the thermal environment. Neither approach supplies one failure temperature for every steel product or structural system. The selected endpoint must remain connected to the load and conditions it represents.<ref name="VR_8.6">Van Rossum (2027), §8.6.</ref><ref name="KH_1-163">Kodur and Harmathy (2002), p. 1-163.</ref>

== From fire exposure to steel temperature ==

The fire environment supplies heat to the surface of an exposed member. Radiation transfers energy from flames and hot surroundings, while convection transfers energy between the gases and the surface. Conduction then redistributes that energy within the steel. The member temperature follows this combined heat balance rather than simply equalling the surrounding gas temperature.<ref name="M_4-209" /><ref name="M_4-222">Milke (2002), p. 4-222.</ref>

The exposure history must therefore be defined before a heating calculation can begin. A furnace curve supplies one repeatable history, while a natural compartment fire develops according to the fuel, ventilation and enclosure. Heat release rate and gas temperature are different quantities within that description. Van Rossum treats standard temperature curves as prescribed exposures, rather than predictions of every room fire.<ref name="VR_8.6" />

The exposed faces also matter. A column surrounded by fire receives a different boundary condition from a beam connected to a concrete slab. The slab can shield the upper part of the beam and take heat from it. Milke explains that these effects can create appreciable temperature differences between the lower and upper flanges.<ref name="M_4-223_4-224">Milke (2002), pp. 4-223–4-224.</ref>

A thermal model can treat the member as uniformly hot or calculate a temperature distribution. The first approach is simpler and can suit some exposed sections. The second becomes relevant when temperature gradients affect the structural response. Choosing between them depends on the exposure, section and purpose of the calculation.<ref name="M_4-222_4-224" />

== Geometry and section factor ==

[[Section factor]] relates the heated surface to the amount of steel being heated. For a member with a constant cross-section, the heated perimeter divided by the cross-sectional area expresses this relationship. More heated perimeter per unit area generally gives a greater heating response under otherwise equal conditions. The comparison concerns exposure and thermal storage together.<ref name="M_4-222_4-224" />

Milke also uses the inverse form: mass per unit length divided by heated perimeter. Its SI unit is kilograms per square metre. A large value represents more steel mass behind each unit of heated surface and therefore greater thermal storage. Confusing this ratio with the perimeter-to-area section factor reverses the interpretation of which section heats faster.<ref name="M_4-219">Milke (2002), p. 4-219.</ref><ref name="M_4-222_4-224" />

[[File:fse-steel-in-fire-v1.svg|thumb|upright=1.5|alt=Two steel sections with different exposed perimeters and masses receiving the same nominal heat flux.|Section geometry affects steel heating. Based on Milke (2002), pp. 4-222–4-224.]]

Protection can alter the relevant heated boundary. An insulating enclosure around a section need not follow every recess of the steel profile. Its thermal resistance and exposed perimeter form part of the protected-member model. The geometry used for an unprotected contour cannot automatically describe an enclosing board system.<ref name="M_4-213_4-214">Milke (2002), pp. 4-213–4-214.</ref><ref name="M_4-223">Milke (2002), p. 4-223.</ref>

Shielding by adjacent construction likewise changes the surface receiving heat. Milke provides separate perimeter diagrams for different arrangements and connections to slabs. These diagrams distinguish steel area from the boundary exposed to the thermal environment. The resulting section factor describes a particular exposure configuration, rather than a permanent property of the section designation.<ref name="M_4-223" />

The two geometry ratios can be converted through density. Milke's steel density of 7,860 kg/m³ divided by the example mass-to-perimeter ratio of 39.3 kg/m² gives 200 m⁻¹. This is the corresponding heated-perimeter-to-area ratio for that example. The conversion leaves the physical section unchanged while expressing the same thermal-storage relationship in another form.<ref name="M_4-211">Milke (2002), p. 4-211.</ref><ref name="M_4-219" /><ref name="M_4-224">Milke (2002), p. 4-224.</ref>

The conversion also provides a dimensional check. A perimeter divided by an area has units of inverse metres, whereas mass divided by heated area has units of kilograms per square metre. Values expressed in these units cannot be substituted directly for each other. The intervening density and the direction of the ratio determine their relationship.<ref name="M_4-222_4-224" />

== A simplified heating calculation ==

In a lumped-capacity model, the steel is assumed to have one temperature throughout its section. The heat entering over a short interval increases the energy stored in the steel. Dividing the incoming heat by the steel's heat capacity gives the temperature increment. Milke expresses the model using the mass-to-heated-perimeter ratio.<ref name="M_4-222" />

<math display="block">\Delta T_s=\frac{h_{\mathrm{tot}}}{c_s(m'/P)}(T_g-T_s)\Delta t</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\Delta T_s</math> || Steel temperature increment || K
|-
| <math>h_{\mathrm{tot}}</math> || Combined convection and linearised radiation coefficient || W/(m²·K)
|-
| <math>c_s</math> || Steel specific heat || J/(kg·K)
|-
| <math>m'</math> || Steel mass per unit member length || kg/m
|-
| <math>P</math> || Heated perimeter || m
|-
| <math>T_g,T_s</math> || Gas and steel temperatures || °C
|-
| <math>\Delta t</math> || Calculation interval || s
|}

The temperature difference in this equation has the same numerical value in kelvins and degrees Celsius. Radiation calculations used to determine the combined coefficient, however, require absolute temperatures. Milke separates the radiative and convective contributions and recommends short calculation intervals for this approximation. The equation is then applied repeatedly as the exposure and steel temperature change.<ref name="M_4-222_4-223">Milke (2002), pp. 4-222–4-223.</ref>

A calculation of the convective contribution illustrates the role of the inputs. Milke gives a mass-to-perimeter ratio of 39.3 kg/m² for the contour of a W8 × 28 section. His A36 specific-heat expression gives 430 J/(kg·K) at 20 °C. Taking his example temperature level of 538 °C as an assumed gas temperature permits a simple initial-step comparison.<ref name="M_4-219" /><ref name="M_4-211" /><ref name="KH_1-163" />

With a convective coefficient of 25 W/(m²·K) and an interval of 10 s, the calculated convection-only rise is 7.7 K. The arithmetic uses the unrounded specific heat of 430.2 J/(kg·K). Radiation has deliberately been excluded from this component calculation, so 7.7 K is not a complete fire-heating prediction. The chosen gas temperature is an illustrative boundary condition, not a measured exposure for that section.<ref name="M_4-211" /><ref name="M_4-222_4-223" />

== Strength, stiffness and steel type ==

[[Strength reduction at elevated temperatures]] changes the load that a hot member can resist. Yield strength describes the onset of substantial permanent deformation in the adopted material model. The modulus of elasticity describes stiffness before that stage. A reduction in stiffness can increase deformation and affect stability even before the nominal yield-strength limit is reached.<ref name="M_4-211_4-212" />

The response is not identical for all steel products. Fleischmann and Buchanan distinguish hot-rolled reinforcing steel, cold-drawn prestressing steel and high-strength alloy steel. Their chapter presents different strength-temperature relationships for these materials. It also distinguishes yield strength from tensile strength where the relevant design property differs.<ref name="FB_4-240">Fleischmann and Buchanan (2002), p. 4-240.</ref>

[[File:fse-steel-in-fire-v2.svg|thumb|upright=1.5|alt=Schematic strength curves for hot-rolled, prestressing and alloy steel that fall at different temperatures and cross.|Steel products respond differently to elevated temperature. Based on Fleischmann and Buchanan (2002), p. 4-240.]]

Heating can also introduce creep, which is deformation that develops with time under sustained stress. Milke explains that creep depends on stress, heating rate and temperature. Some fire-design material relationships incorporate its effects implicitly. Combining data from incompatible test histories can therefore misrepresent the response even when the nominal steel temperature is the same.<ref name="M_4-212">Milke (2002), p. 4-212.</ref>

Room-temperature strength consequently supplies only part of the required information. A thermal analysis determines where and when the steel heats. Temperature-dependent mechanical properties then connect those temperatures to the structural calculation. The assessment still requires the applied load and the relevant support conditions.<ref name="M_4-209" /><ref name="M_4-211_4-212" />

== Critical temperature and structural endpoints ==

[[Critical steel temperature]] is a temperature associated with an unacceptable structural condition under stated assumptions. It depends on the load to be supported and the material's remaining capacity. The concept can simplify a thermal calculation when those structural conditions have already been established. It does not replace them with a universal failure temperature.<ref name="KH_1-163" /><ref name="M_4-209" />

Kodur and Harmathy describe historical North American examples of 538 °C for structural steel, 593 °C for reinforcing steel and 426 °C for prestressing steel. The structural-steel example is associated with particular ASTM E119-related assumptions, including full design loading in the discussion of columns. These figures illustrate method-dependent endpoints. They do not represent melting temperatures or limits applicable to every steel member.<ref name="KH_1-163" />

[[File:fse-steel-in-fire-v3.svg|thumb|upright=1.5|alt=Critical-temperature examples 538, 593 and 426 °C for three steel uses.|Critical-temperature examples depend on steel use and method. Based on Kodur and Harmathy (2002), p. 1-163.]]

Milke's description of A36 steel provides the mechanical context. At approximately 538 °C, its yield strength in the cited relationship is about 60% of the room-temperature value. The significance of that reduction depends on the stress already imposed on the member. A lightly loaded and a heavily loaded member need not reach their structural endpoints at the same temperature.<ref name="M_4-212" />

A temperature endpoint and a structural endpoint therefore answer related questions. The thermal calculation can determine when a specified temperature is reached. A structural calculation evaluates the resulting stresses, deformation and capacity under the adopted loading and restraint. Where a temperature criterion is used, its connection to those structural conditions remains part of the method.<ref name="M_4-209" /><ref name="M_4-222" />

== Expansion, restraint and structural response ==

Steel expands as its temperature rises. If supports or surrounding construction limit that movement, [[Restrained thermal expansion]] changes the forces and deformations within the system. The member then responds to more than its original mechanical loading. Milke consequently includes thermal expansion and end conditions in the structural assessment.<ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref>

Test restraint is a defined condition rather than an informal description of a connection. Milke reproduces historical ASTM examples distinguishing different floor and framing arrangements. The classification considers how the surrounding structure resists movement. A restrained test result therefore requires interpretation in relation to the proposed construction and its actual boundaries.<ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref>

Temperature gradients add another complication. A beam beneath a slab can have a hotter lower flange and a cooler upper flange. A uniform-temperature model does not explicitly describe that difference. Where the gradient affects the structural question, Milke identifies the need for a more suitable analytical approach.<ref name="M_4-223_4-224" />

[[Structural fire engineering]] combines these effects rather than treating steel temperature as a complete outcome. It uses the exposure to calculate temperatures, then applies temperature-dependent properties within a structural model. Loads, geometry and end conditions determine how the member responds. The required result may involve deformation and stability as well as a nominal strength comparison.<ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref>

== Protection systems and their behaviour ==

Protection reduces the rate of heat transfer into the steel. Milke describes insulating boards, spray-applied materials, concrete encasement and enclosing membranes. Their mechanisms and attachment details differ. The relevant evidence concerns the protected assembly, including the protection material and the way it remains attached during exposure.<ref name="M_4-212_4-214">Milke (2002), pp. 4-212–4-214.</ref>

[[Intumescent material]] expands during heating to form an insulating layer. The change is part of the protective mechanism, so the layer cannot always be represented by its original thickness and properties. Van Rossum identifies swelling as one of several processes that change the heat-conduction path during fire. Milke includes intumescent products among spray-applied protection methods.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref><ref name="M_4-214">Milke (2002), p. 4-214.</ref>

Board systems rely on suitable enclosure and attachment. Milke specifically identifies the means of securing boards as a factor affecting assembly performance. Spray-applied products require properties such as adhesion, durability and uniform application. These considerations connect the material's thermal performance to its condition on the actual member.<ref name="M_4-212_4-214" />

Protection can also store heat. Milke distinguishes simplified models that neglect its heat capacity from models that include it. Gypsum and concrete protection are examples where that contribution can matter. Omitting the protection's thermal storage is therefore an assumption to assess, rather than a property of every protected-steel calculation.<ref name="M_4-223" />

A protected member can receive heat through the insulation while the insulation itself is warming. Part of the incoming energy then increases the protection's temperature instead of immediately heating the steel. Milke includes this storage in the denominator of a protected-member temperature-increment expression. The effect differs from thermal resistance, which describes the rate of energy transfer through the layer.<ref name="M_4-223" />

An intact thermal barrier also needs to survive handling and its surrounding environment. Milke includes bond strength, durability, weathering resistance and consistent application among relevant protection characteristics. These requirements concern maintaining the protective arrangement that the thermal model assumes. A conductivity value alone cannot establish whether the applied protection will retain that arrangement throughout service and exposure.<ref name="M_4-212" />

== Evidence and modelling limits ==

Empirical protection formulas are linked to the tests from which they were developed. Milke cautions that their ranges can be restricted by member shapes, protection thickness and other conditions. A result outside those ranges has a different evidential basis from a result within them. The fire exposure, loading and span also limit the applicability of test-based correlations.<ref name="M_4-209" /><ref name="M_4-219" />

A more detailed thermal calculation does not remove uncertainty in its inputs. Heating conditions, temperature-dependent material properties and insulation behaviour still affect the result. A structural calculation introduces additional assumptions about loads and restraint. The accuracy of the combined prediction depends on the relationship between all these stages.<ref name="M_4-209_4-210" />

Tests provide evidence about interactions that simplified models may omit. Milke emphasises their role in establishing material behaviour and checking protected assemblies. The resulting evidence describes the tested exposure and configuration. Its application to another member depends on whether the model represents the changes in geometry, heating and structural conditions.<ref name="M_4-210_4-211" />

== See also ==

* [[Progressive collapse]]
* [[Tensile membrane action]]
* [[Fire resistance]]

== Notes ==

<references />

== References ==

* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Structural Fire Engineering]]

Fire resistance

2026-11-02T17:54:04Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Fire resistance''' is the ability of a building member or assembly to maintain specified functions for a stated time under a defined fire exposure. Depending on the assembly, these functions include carrying loads, preventing the passage of flames and limiting heat transmission. A rating records performance against particular criteria, rather than a general resistance to every possible fire.<ref name="KH_1-155">Kodur and Harmathy (2002), p. 1-155.</ref><ref name="M_4-209_4-210">Milke (2002), pp. 4-209–4-210.</ref>

Assessment concerns the complete construction and its conditions. Materials, dimensions, protection, loading, connections and restraint can all affect the result. A standard furnace test provides one means of evaluation, while suitable calculations can connect the exposure to temperatures and structural response. Both approaches require a defined endpoint.<ref name="M_4-209_4-211">Milke (2002), pp. 4-209–4-211.</ref>

The duration in a rating is therefore inseparable from the method used to establish it. It is not automatically the time available for evacuation, the time to collapse in a natural fire or a measure of combustibility. Understanding the exposure and performance criteria is necessary to interpret what the rating demonstrates.<ref name="M_4-209_4-210" /><ref name="IFEG_1.6-7">Australian Building Codes Board et al. (2005), p. 1.6-7.</ref><ref name="VR_8.6">Van Rossum (2027), §8.6.</ref>

== The functions being assessed ==

[[Fire resistance criteria]] identify the functions that an assembly must maintain. Structural adequacy concerns carrying the specified load without unacceptable structural response. Integrity concerns the passage of flames or hot gases through a separating assembly. Insulation concerns heat transmission to the unexposed side. These functions can reach their endpoints at different times.<ref name="KH_1-155" /><ref name="M_4-210_4-211">Milke (2002), pp. 4-210–4-211.</ref><ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

A separating wall illustrates the difference between integrity and insulation. Heat can conduct through an intact wall and raise the temperature of its unexposed surface. No visible opening is needed for that heat transfer to become excessive under an insulation criterion. Conversely, a crack can permit hot gases or flames to pass even where most of the wall remains comparatively cool.<ref name="IFEG_1.6-7" />

Structural adequacy is a further, separate question. A load-bearing member can lose strength or stiffness as its temperature rises. Its response also depends on applied loads and the conditions at its supports. A thermal result therefore cannot establish structural endurance unless it is connected to a suitable structural criterion or model.<ref name="M_4-209_4-210" />

New Zealand's C/VM2, second edition of 2025, expresses the fire resistance rating through three times in minutes. The stated order is structural adequacy, integrity and insulation. That notation makes the separate functions explicit. Other test and classification systems require their own interpretation rather than an assumed transfer of symbols or values.<ref name="CVM_64" />

[[File:fse-fire-resistance-v1.svg|thumb|upright=1.5|alt=Three panels for load support, flame separation and limited heat transmission.|Fire resistance has three distinct performance criteria. Based on Ministry of Business, Innovation and Employment (2025), p. 64.]]

== How a furnace test establishes a rating ==

A [[Fire resistance test]] exposes a defined specimen to a prescribed heating history while monitoring the required endpoints. Milke describes this approach through the United States ASTM E119 framework in the 2002 handbook. A successful specimen receives a rating for the stated test duration and conditions. The rating belongs to the tested assembly and its permitted applications.<ref name="M_4-209_4-210" />

The specimen can include several materials and components. Protection around a steel member, for example, changes the heat entering the steel and its temperature history. The test observes the interaction between the protection and the member. This is one reason separate material properties do not always reproduce the behaviour of an assembled construction.<ref name="M_4-209_4-210" />

Loads and restraint form part of the test arrangement. Restraint describes the extent to which surrounding construction prevents thermal movement. Milke explains that framing geometry and connections affect the distinction between restrained and unrestrained test systems. A result obtained under one arrangement cannot automatically represent another arrangement with different movement conditions.<ref name="M_4-210_4-211" />

The monitored endpoints also depend on the assembly. They can include maintaining the applied load, limiting temperatures and preventing the passage of flames or gases capable of igniting a specified target. Some historical ASTM procedures include a hose-stream exposure. These observations have distinct purposes, so a report identifies which endpoints and procedures apply to its specimen.<ref name="M_4-210_4-211" />

[[File:fse-fire-resistance-v2.svg|thumb|upright=1.5|alt=Standard furnace curve heats an assembly and leads to structural, flame and temperature endpoints.|Fire-resistance testing links exposure to assembly endpoints. Based on Milke (2002), pp. 4-209–4-210.]]

An unlisted assembly and a failed assembly are not the same evidential category. Milke explains that an assembly without a listing has no established rating unless acceptable performance is demonstrated. That demonstration may involve a standard test, a special experiment or an analytical method. Absence of a rating therefore concerns the available evidence, rather than an observed failure time.<ref name="M_4-209">Milke (2002), p. 4-209.</ref>

== Reading temperature criteria correctly ==

A temperature rise is a difference from the starting temperature. It is not the same quantity as an absolute temperature. Confusing them changes the interpretation of an insulation criterion, even when both are printed using degrees Celsius. The initial condition therefore belongs with the stated limit and measurement location.<ref name="M_4-211">Milke (2002), p. 4-211.</ref>

Milke's historical ASTM E119 table gives wall-insulation examples of a 139 °C average rise and a 181 °C single-point rise. These values apply to measurements on the unexposed side of the stated wall or partition assemblies. They are not limiting furnace temperatures. The table also contains other endpoints for steel members, which require their own interpretation.<ref name="M_4-211" />

[[File:fse-fire-resistance-v3.svg|thumb|upright=1.5|alt=Wall with average 139 °C and single-point 181 °C temperature-rise criteria marked on the unexposed side.|ASTM E119 wall-insulation endpoint examples (temperature rise). Based on Milke (2002), p. 4-211.]]

An average and a single-point limit address different aspects of the temperature field. The average represents the group of measured locations, while the single-point value constrains a local high temperature. Keeping both avoids replacing the endpoint definition with one convenient measurement. Neither value alone describes the complete fire exposure or the structural condition of the specimen.<ref name="M_4-211" />

A structural temperature criterion is different again. Kodur and Harmathy explain that a critical temperature corresponds to the material becoming unable to support the applied load under the adopted conditions. It consequently depends on loading and material behaviour. A temperature used in a simplified test-based method is not a universal temperature at which every member collapses.<ref name="KH_1-163">Kodur and Harmathy (2002), p. 1-163.</ref><ref name="M_4-209" />

== Standard exposure and a worked example ==

A [[Standard fire curve]] prescribes temperature as a function of time. It provides a repeatable exposure for comparing assemblies. It does not directly describe the heat release rate of a burning object or the temperature in every real room. Van Rossum distinguishes these quantities because they serve different purposes in a fire analysis.<ref name="VR_8.6" />

Milke presents the following approximation for the ISO 834 furnace-temperature history. The logarithm describes the continuing rise in prescribed temperature, while the initial temperature is added separately. In this expression, time is entered in seconds. The coefficient 0.133 carries reciprocal-second units, making the quantity inside the logarithm dimensionless.<ref name="M_4-223">Milke (2002), p. 4-223.</ref>

<math display="block">T_f=T_0+345\log_{10}(0.133t+1)</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>T_f</math> || Prescribed furnace temperature || °C
|-
| <math>T_0</math> || Initial temperature || °C
|-
| <math>t</math> || Elapsed heating time || s
|}

Using an initial temperature of 20 °C gives approximately 841 °C at 1,800 s and 945 °C at 3,600 s. These calculations use the rounded coefficient printed by Milke. They illustrate the prescribed thermal environment at 30 min and 60 min. They do not predict the temperature of the specimen, which requires a separate heat-transfer calculation.<ref name="M_4-211" /><ref name="M_4-223" />

The equation contains no material thickness, conductivity, loading or support condition. It therefore cannot calculate whether a particular wall or beam survives either exposure duration. Two assemblies in the same furnace can develop different internal temperatures and structural responses. The standard curve supplies one input to the assessment, not its final result.<ref name="M_4-209" /><ref name="M_4-223" />

== Material and assembly behaviour ==

Materials perform different functions within an assembly. Steel provides load-bearing capacity but changes strength and stiffness when heated. Concrete can carry load while delaying heat transfer to reinforcement. Insulating materials can protect a structural component without carrying significant load themselves. The complete assembly combines these roles under the imposed exposure.<ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="FB_4-239">Fleischmann and Buchanan (2002), p. 4-239.</ref>

Combustible construction can also retain structural function for a specified period. White describes timber endurance through protective membranes, the extent of charring and the capacity of the remaining uncharred wood. Char itself has very little load-bearing capacity. The existence of combustion therefore does not, by itself, establish the time at which the member loses its required function.<ref name="W_4-257">White (2002), p. 4-257.</ref><ref name="W_4-260">White (2002), p. 4-260.</ref>

Conversely, noncombustibility does not establish fire resistance. A material can remain unburned while its mechanical properties deteriorate or its unexposed surface becomes too hot. This is the distinction from [[Reaction to fire]], which concerns the material's contribution to fire development. Different tests are needed because the two assessments follow different physical outcomes.<ref name="KH_1-155" /><ref name="KH_1-157" /><ref name="J_3-38_3-39">Janssens (2002), pp. 3-38–3-39.</ref>

Changes to an assembly can affect several outcomes together. White explains that changing membranes, member spacing or insulation can fall outside the tested timber arrangement. Adding insulation does not produce an automatic improvement in every floor or roof assembly. The relevant evidence is the behaviour of the revised construction, including how its layers remain supported during heating.<ref name="W_4-257_4-259">White (2002), pp. 4-257–4-259.</ref>

Heat transfer through protection can involve physical and chemical changes as well as ordinary conduction. Van Rossum describes moisture evaporation, release of chemically bound water and swelling as processes that change thermal response. These processes can consume energy or alter the heat-conduction path. An assembly calculation using fixed room-temperature properties may therefore miss part of the protective behaviour.<ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

The relevant time is also a property of the complete sequence. The furnace heats the surface, energy moves through the construction, and the specified endpoint is reached at a measurement location or structural state. A material's conductivity describes only one part of this sequence. It cannot by itself supply a duration without geometry, boundary conditions and the selected endpoint.<ref name="M_4-209" /><ref name="VR_5.2" />

== Fire resistance within compartmentation ==

[[Fire compartmentation]] uses separating construction to restrict the spread of fire between spaces. The wall or floor is only part of that separation. Existing openings, closures and penetrations can provide other routes for spread. The 2005 International Fire Engineering Guidelines therefore consider spread through openings separately from failure of the barrier material.<ref name="IFEG_1.6-3">Australian Building Codes Board et al. (2005), p. 1.6-3.</ref><ref name="IFEG_1.6-7" />

The guidelines distinguish conduction, loss of integrity and loss of stability as different barrier-failure mechanisms. Conduction can heat nearby combustible material without opening the barrier. Loss of integrity includes cracks and failure of firestopping, while loss of stability involves collapse. A fire-resistance rating must be interpreted alongside the boundary details relevant to those mechanisms.<ref name="IFEG_1.6-7" />

Door use also changes the separation during evacuation. The same guidelines treat the time of opening a door as information supplied by the occupant-movement analysis. A closed-door test does not describe the period when the door is open. Compartmentation performance consequently depends on the states of its openings as well as the endurance of closed components.<ref name="IFEG_1.6-7" />

[[Passive fire protection]] includes the barriers and protective materials that support these functions. Their performance is expressed through particular constructions and conditions, rather than a general promise that fire remains contained. This connection explains why rated construction and its installation details belong to the same design. A rating on one component cannot close an unprotected route around it.<ref name="IFEG_1.6-7" /><ref name="M_4-212_4-214">Milke (2002), pp. 4-212–4-214.</ref>

== Calculation methods and validation ==

[[Structural fire engineering]] connects fire exposure, heat transfer and structural response. The first stage defines the thermal environment. The second calculates temperatures within the member, using material properties and boundary conditions. The third evaluates the consequences for stresses, deformation and load-carrying capacity. A calculation of one stage does not independently establish the others.<ref name="M_4-209" />

Empirical correlations provide a simpler route where sufficient test data exist. Milke explains that such correlations are limited by the exposure, loading and span represented in their underlying tests. Their numerical simplicity does not remove those limits. Applying a correlation outside its supporting range introduces a different problem from interpolating within the tested conditions.<ref name="M_4-209" />

Thermal models can represent either standard exposure or a specified nonstandard fire. Their output may be the time to a chosen temperature or a temperature distribution for structural analysis. Temperature-dependent properties and the description of heating both affect accuracy. A model with detailed geometry can still produce a misleading result if those physical inputs are unsuitable.<ref name="M_4-209" />

Testing remains relevant even where calculation is available. It supplies material behaviour, checks assembly interactions and provides evidence for judging model predictions. New Zealand's 2025 C/VM2 definition explicitly connects its calculation route to verification against standard fire-resistance tests. That connection identifies the evidence supporting a rating rather than treating calculation as evidence by itself.<ref name="M_4-210_4-211" /><ref name="CVM_64" />

== Limits when applying a rating ==

A furnace test is a controlled representation with practical size and support constraints. Milke notes that these constraints make some results comparative rather than exact reproductions of entire structures. An extended continuous frame can behave differently from an isolated specimen. The tested configuration and the proposed application therefore remain part of the interpretation.<ref name="M_4-210">Milke (2002), p. 4-210.</ref>

A real compartment fire can grow, reach a maximum and decay. Its temperature history depends on the fuel, ventilation and enclosure, while the standard curve serves a repeatable testing purpose. A stated rating is therefore not a direct forecast of survival time in every natural fire. Connecting the two requires a method that represents the relevant exposure and structural conditions.<ref name="VR_8.6" /><ref name="M_4-209" />

The same rating also does not establish the time available for occupants to escape. The International Fire Engineering Guidelines treat barrier performance, fire spread and other subsystem results as interacting parts of an analysis. Smoke and opening conditions can affect adjacent spaces before a closed assembly reaches its furnace-test endpoint. Escape and containment consequently require related but distinct assessments.<ref name="IFEG_1.6-3" /><ref name="IFEG_1.6-7" />

== See also ==

* [[Concrete in fire]]
* [[Timber in fire]]
* [[Critical steel temperature]]
* [[Time equivalence]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines''. Australian Building Codes Board.
* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-38–3-62). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* White, R. H. (2002). Analytical methods for determining fire resistance of timber members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-257–4-273). National Fire Protection Association.

[[Category:Structural Fire Engineering]]

Concrete in fire

2026-11-02T17:53:59Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

'''Concrete in fire''' describes the heating, material changes and structural response of concrete members exposed to fire. Concrete is noncombustible and can delay the heating of embedded reinforcement through its relatively low thermal conductivity. Its cooler interior can continue carrying load while the exposed surface becomes hot. These advantages do not prevent all forms of thermal damage or structural failure.<ref name="FB_4-239">Fleischmann and Buchanan (2002), p. 4-239.</ref>

The response depends on the complete member, rather than compressive strength alone. Aggregate, moisture, cover depth, geometry, applied load and support conditions affect different stages of the assessment. Surface material can also break away during heating, changing the protection available to the reinforcement. A calculation that considers only intact concrete may then miss an influential change in the section.<ref name="KH_1-156">Kodur and Harmathy (2002), p. 1-156.</ref><ref name="KH_1-163_1-164">Kodur and Harmathy (2002), pp. 1-163–1-164.</ref><ref name="FB_4-239" />

Assessment normally connects a defined fire exposure to an internal temperature distribution and then to structural performance. Separating elements also have a heat-transmission function. Each calculation therefore needs a stated endpoint and material data suitable for the relevant temperature range.<ref name="FB_4-239_4-242">Fleischmann and Buchanan (2002), pp. 4-239–4-242.</ref>

== Material structure and fire exposure ==

Concrete combines aggregates with a cement paste containing pores and moisture. These constituents respond differently when heated, so concrete cannot be represented as one chemically uniform solid. Aggregate type, density, porosity and moisture influence its thermal behaviour. The properties needed for a fire calculation consequently extend beyond its specified compressive strength at ordinary temperature.<ref name="KH_1-155_1-156">Kodur and Harmathy (2002), pp. 1-155–1-156.</ref>

The material can perform both a structural and an insulating role. Concrete around steel reinforcement absorbs and conducts heat before the reinforcement reaches a high temperature. Meanwhile, cooler parts of a concrete section can continue to carry load. These functions are related, but they require different calculations and different material properties.<ref name="KH_1-157">Kodur and Harmathy (2002), p. 1-157.</ref><ref name="FB_4-239" />

Fire exposure is the boundary condition for those calculations. A prescribed furnace temperature history differs from a natural compartment fire, whose development depends on fuel, ventilation and enclosure properties. A temperature curve also differs from a heat release rate curve: one describes temperature, while the other describes thermal power. Confusing them would change the physical problem being assessed.<ref name="VR_8.6">Van Rossum (2027), §8.6.</ref>

The exposed faces matter as much as the nominal temperature history. A slab or separating wall may receive fire exposure predominantly on one side. A beam can be heated on several sides, while a column can be exposed around its perimeter. Fleischmann and Buchanan describe these arrangements separately because they produce different internal temperature distributions.<ref name="FB_4-242">Fleischmann and Buchanan (2002), p. 4-242.</ref>

== Heat penetration and material properties ==

Heat entering the exposed surface moves through solid concrete mainly by conduction. [[Thermal conductivity]] describes how readily a temperature difference drives that transfer. Density and specific heat describe the energy stored as the material warms. Together, these quantities determine how rapidly a temperature disturbance spreads into the section.<ref name="FB_4-242" /><ref name="VR_5.2">Van Rossum (2027), §5.2.</ref>

The exposed surface and the interior therefore need not reach the same temperature. During early heating, a substantial temperature gradient can exist through a thick section. The cooler interior is one reason a concrete member may continue functioning while its surface becomes very hot. A single furnace temperature does not represent the temperature of every reinforcement bar.<ref name="FB_4-239" /><ref name="FB_4-242" /><ref name="VR_5.2" />

Moisture changes the energy balance because evaporation consumes heat. Heating also changes the material itself, including its microstructure and relevant thermal properties. Van Rossum consequently treats calculations with constant properties as approximations. The diffusivity used at one stage of heating need not describe the entire fire exposure.<ref name="VR_5.2" /><ref name="KH_1-157" />

A steady calculation assumes that the temperature profile through the whole construction has already developed. That assumption can be unsuitable during the initial heating of a thick wall. A transient calculation instead follows the changing temperatures as energy enters and spreads through the material. This distinction affects both reinforcement temperature and heat transfer to the unexposed side.<ref name="VR_5.2" /><ref name="FB_4-239" />

== A worked heat-penetration example ==

Thermal diffusivity divides conductivity by the volumetric heat capacity, which is density multiplied by specific heat. For a sudden surface-temperature change, the square root of diffusivity multiplied by time gives a characteristic penetration depth. This depth describes a scale of temperature change, rather than a sharp front separating hot and cold concrete.<ref name="VR_5.2" />

<math display="block">\alpha=\frac{\lambda}{\rho c_p},\qquad d\approx\sqrt{\alpha t}</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\alpha</math> || Thermal diffusivity || m²/s
|-
| <math>\lambda</math> || Thermal conductivity || W/(m·K)
|-
| <math>\rho</math> || Density || kg/m³
|-
| <math>c_p</math> || Specific heat || J/(kg·K)
|-
| <math>t</math> || Heating duration || s
|-
| <math>d</math> || Characteristic penetration depth || m
|}

Van Rossum's comparison of thick concrete and timber walls uses rounded concrete properties of 1.7 W/(m·K), 2,300 kg/m³ and 900 J/(kg·K). With these inputs, the calculated diffusivity is 8.21 × 10⁻⁷ m²/s. After 3,600 s, the characteristic depth is approximately 0.054 m, or 54 mm. The calculation reproduces the source example using unrounded intermediate values.<ref name="VR_5.2" />

That result does not mean that concrete outside a 54 mm layer remains exactly at its initial temperature. Nor does it identify a spalling depth, a damaged zone or the position of a failure boundary. The model has no mechanical failure criterion and uses fixed thermal properties. Its purpose is to explain the scale of transient heating in a thick material.<ref name="VR_5.2" />

A separate example in the same section considers a 200 mm concrete wall over the first 900 s. It uses a different stated diffusivity, 9.88 × 10⁻⁷ m²/s. The source's approximate boundary between thermally thick and thin behaviour, twice the penetration depth, is then 60 mm. The 200 mm wall is thermally thick for that example, but this observation does not assign it a fire-resistance rating.<ref name="VR_5.2" />

== Spalling and loss of cover ==

[[Spalling]] is the breaking away of concrete from the heated surface. Kodur and Harmathy distinguish early explosive loss from later loss associated with weakened material. The process matters because the section can lose both material and thermal protection. Reinforcement formerly enclosed by concrete may then receive more direct heating.<ref name="KH_1-163_1-164" />

One proposed mechanism involves moisture movement and pressure within the pores. Heating drives moisture towards cooler regions, where a relatively saturated zone can impede further transport. Pressure can rise if vapour cannot escape readily. The handbook also discusses explanations based on thermal stresses and fracture, so pore pressure is not the sole mechanism considered.<ref name="KH_1-163">Kodur and Harmathy (2002), p. 1-163.</ref>

[[File:fse-concrete-in-fire-v1.svg|thumb|upright=1.5|alt=Heat drives moisture into a low-permeability concrete clog, raising pressure and cracking the surface.|Moisture clog and pressure can contribute to spalling. Based on Kodur and Harmathy (2002), p. 1-163.]]

The source illustrates the pressure mechanism using approximately 8 MPa vapour pressure at 300 °C and approximately 5 MPa tensile strength for high-strength concrete. This comparison demonstrates how internal pressure can exceed a resisting tensile stress. It is an explanatory example, not a universal pressure-temperature failure rule. Actual spalling also depends on permeability, moisture, loading and the heating conditions.<ref name="KH_1-163_1-164" />

[[File:fse-concrete-in-fire-v3.svg|thumb|upright=1.5|alt=Example vapour pressure 8 MPa versus tensile strength 5 MPa at 300 °C.|Example of internal pressure exceeding concrete tensile strength. Based on Kodur and Harmathy (2002), p. 1-163.]]

High compressive strength at room temperature does not by itself prevent spalling. Dense, low-permeability concrete can restrict moisture escape during rapid heating. Once surface material is lost, deeper concrete and reinforcement heat more rapidly. A model that retains the original section throughout the exposure cannot automatically represent that change.<ref name="KH_1-163_1-164" />

Thermal stress offers a different way for cracking to develop. The heated surface tends to expand while cooler material restricts that movement. Kodur and Harmathy discuss fracture-based explanations in which these stresses contribute to surface loss. An analysis based only on vapour pressure therefore addresses one proposed contribution, rather than demonstrating that other mechanisms are absent.<ref name="KH_1-163" />

The distinction between tensile and compressive behaviour is also relevant. The pressure example compares internal pressure with tensile resistance, whereas the familiar concrete grade describes compressive strength. These are different material quantities. Increasing the specified compressive strength cannot by itself resolve a cracking mechanism involving internal pressure, restrained expansion and tensile fracture.<ref name="KH_1-163_1-164" />

== Reinforcement and load-carrying capacity ==

[[Strength reduction at elevated temperatures]] affects both the concrete and the embedded steel. Fleischmann and Buchanan distinguish hot-rolled reinforcement from cold-drawn prestressing steel and high-strength alloy steel. Their strength-temperature relationships differ, reflecting the materials and mechanical properties considered. A single generic steel curve cannot represent every reinforced or prestressed member.<ref name="FB_4-239_4-240">Fleischmann and Buchanan (2002), pp. 4-239–4-240.</ref>

Concrete strength also depends on aggregate and on the conditions of the material test. The handbook compares specimens heated under load with specimens heated before being loaded to failure. These procedures can produce different measured strengths at the same temperature. Material data therefore need an accompanying description of the loading and heating history.<ref name="FB_4-240_4-241">Fleischmann and Buchanan (2002), pp. 4-240–4-241.</ref>

The modulus of elasticity describes stiffness, or resistance to elastic deformation. It can decrease substantially during heating even when part of the compressive strength remains. Consequently, a strength calculation and a deformation calculation address different effects. Thermal expansion adds another source of deformation and can alter the forces arising in restrained construction.<ref name="FB_4-240_4-241" />

[[File:fse-concrete-in-fire-v2.svg|thumb|upright=1.5|alt=Concrete section with cover, reinforcement and spalled region reducing protection and stiffness.|Concrete and reinforcement respond together to heat and section loss. Based on Fleischmann and Buchanan (2002), pp. 4-241–4-242 and Kodur and Harmathy (2002), p. 1-164.]]

In a simplified thermal analysis, the reinforcement temperature may be approximated by the concrete temperature at the bar centre. This connects the heat-transfer calculation to the subsequent structural calculation. The cover depth, exposed faces and heating duration then affect the steel properties used in that analysis. The approximation belongs to the stated modelling approach, rather than every possible member configuration.<ref name="FB_4-242" />

The load present during heating affects how a property curve is established. In the concrete results discussed by Fleischmann and Buchanan, some specimens carried 40% of their compressive strength while being heated. They were then loaded to failure at the temperature of interest. That procedure describes strength while hot, rather than a measurement of residual strength after cooling.<ref name="FB_4-240">Fleischmann and Buchanan (2002), p. 4-240.</ref>

A temperature-dependent property curve consequently carries more information than its axes alone. Its concrete type, initial condition and testing sequence affect what the result represents. A curve measured for one aggregate and load history cannot be assumed to describe another without supporting evidence. This is separate from uncertainty in the furnace temperature or the calculated temperature within the member.<ref name="FB_4-240_4-241" />

== Beams, slabs and structural continuity ==

A simply supported slab provides a useful starting model. Its ends permit expansion and rotation under the idealised support conditions described by Fleischmann and Buchanan. As reinforcement heats and weakens, the section's resistance to bending decreases. Structural failure is assessed by comparing that remaining resistance with the bending demand from the applied load.<ref name="FB_4-245">Fleischmann and Buchanan (2002), p. 4-245.</ref>

Concrete near the compression face may remain cooler than reinforcement near the fire-exposed underside. The structural calculation therefore uses the temperature distribution, rather than applying one reduction to the entire section. If part of the compression zone becomes sufficiently hot, the source method reduces its contribution. That step depends on the chosen material model and calculation procedure.<ref name="FB_4-245" />

A continuous member behaves differently because it can redistribute bending moments between the span and its supports. Redistribution can extend endurance, but the remaining sections must still resist the transferred demand. Fleischmann and Buchanan describe failure through the formation of a mechanism involving several yielding regions. Continuity is therefore a structural condition, not an automatic allowance added to a rating.<ref name="FB_4-246">Fleischmann and Buchanan (2002), p. 4-246.</ref>

[[Structural fire engineering]] combines this structural response with the preceding fire and thermal calculations. The assessment depends on loads, geometry, reinforcement and support conditions as well as temperature. More specialised structural behaviour is addressed in the related topic [[Tensile membrane action]]. The heat-penetration example above does not calculate any redistribution or membrane resistance.<ref name="FB_4-239" /><ref name="FB_4-245_4-246">Fleischmann and Buchanan (2002), pp. 4-245–4-246.</ref>

== Testing and fire-resistance assessment ==

[[Fire resistance]] is evaluated against specified functions under a defined exposure. A separating concrete floor may need to support loads and limit heat transfer to the space above. A column has a different structural role and exposure arrangement. The required endpoints follow the assembly and assessment method, rather than the material name alone.<ref name="FB_4-239" /><ref name="FB_4-242" />

For standard exposure, empirical methods can relate dimensions and other parameters to results from furnace tests. Nonstandard exposure generally requires a more explicit thermal analysis followed by structural evaluation. Fleischmann and Buchanan describe both approaches and their different information requirements. A correlation derived from a standard test does not independently establish performance for an arbitrary natural fire.<ref name="FB_4-239" />

New Zealand's C/VM2, second edition of 2025, defines a fire resistance rating using three durations. Their order is structural adequacy, integrity and insulation. The definition permits standard testing or a specified calculation method verified against standard fire-resistance tests. This is the terminology of that New Zealand document, rather than a universal notation for every jurisdiction.<ref name="CVM_64">Ministry of Business, Innovation and Employment (2025), p. 64.</ref>

== Limits of simplified predictions ==

A numerical model can follow changing temperatures with more detail than a penetration-depth estimate. The concrete chapter describes models that include temperature-dependent properties and changing boundary conditions. It also notes that the cited implementations did not explicitly model moisture migration. Representing evaporation through adjusted thermal properties does not itself calculate pore-pressure-driven spalling.<ref name="FB_4-243">Fleischmann and Buchanan (2002), p. 4-243.</ref><ref name="KH_1-163" />

The same distinction applies to a good match with measured temperatures. Such a match supports the thermal calculation for the tested conditions. It does not independently demonstrate the correct structural restraint, reinforcement strength or response to section loss. Those questions require evidence relevant to the mechanical model and the construction being assessed.<ref name="FB_4-239" /><ref name="FB_4-243" /><ref name="KH_1-164">Kodur and Harmathy (2002), p. 1-164.</ref>

A source value also carries limits associated with its concrete and test history. Aggregate type, moisture and applied load can affect the measured response, while rapid heating can introduce additional damage mechanisms. These dependencies explain why the handbook presents several material relationships and calculation approaches. Selecting one requires identifying the physical conditions it represents.<ref name="FB_4-240_4-241" /><ref name="KH_1-163_1-164" />

== See also ==

* [[Conduction]]
* [[Steel in fire]]
* [[Restrained thermal expansion]]

== Notes ==

<references />

== References ==

* Fleischmann, C., & Buchanan, A. (2002). Analytical methods for determining fire resistance of concrete members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-239–4-256). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Structural Fire Engineering]]

Reaction to fire

2026-11-02T17:53:54Z

Emma: Revise Basic article against FSE writing guidelines: sourced explanations, examples and references (GPT-6)

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

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

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

== Contribution to a developing fire ==

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

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

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

== Heating, ignition and flame spread ==

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

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

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

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

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

== Heat release and mass loss ==

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

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

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

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

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

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

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

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

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

== What tests measure ==

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

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

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

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

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

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

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

== Why total energy and peak power differ ==

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

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

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

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

== Classification and use in buildings ==

Classification connects specified test results with a defined regulatory framework. The intended use matters because a wall lining, floor covering and structural member serve different functions. New Zealand's C/VM2, second edition of 2025, treats rapid spread over internal surface linings as a specific design scenario. Its criteria depend on location, building use and importance level.<ref name="CVM_50_52">Ministry of Business, Innovation and Employment (2025), pp. 50–52.</ref>

In that New Zealand method, exposed internal wall and ceiling surfaces receive material Group Numbers. The commentary associates ordinary timber products with Group 3 and many fire-retardant-treated timbers with Group 2. It identifies exposed polyurethane foams as examples associated with Group 4. These are explanatory examples, rather than classifications transferable to every product bearing the same material name.<ref name="CVM_50_52" />

Flooring is assessed through critical radiant flux in the same document. A higher critical flux corresponds to better performance in the specified flooring assessment. For sleeping areas and exitways in care or detention buildings, the 2025 table gives 4.5 kW/m² without sprinklers and 2.2 kW/m² with sprinklers. These are New Zealand scenario requirements, not general ignition thresholds for all materials.<ref name="CVM_52">Ministry of Business, Innovation and Employment (2025), p. 52.</ref>

[[File:fse-reaction-to-fire-v3.svg|thumb|upright=1.5|alt=Critical radiant flux values 4.5, 2.2 and 1.2 kW/m² for three C/VM2 situations.|C/VM2 critical radiant flux depends on occupancy and sprinklers. Based on Ministry of Business, Innovation and Employment (2025), p. 52.]]

The distinctions reflect the role of the space. C/VM2 gives greater emphasis to linings along escape routes, where they may form a substantial part of the available fuel. Occupants' ability to evacuate and the presence of sprinklers also affect the specified criteria. Applying one classification requirement throughout every occupancy would remove these distinctions.<ref name="CVM_52" />

== Smoke production and treatment effects ==

Heat release and smoke-related hazards are connected but are not interchangeable measurements. Janssens expresses the production rate of a toxic gas as its yield multiplied by the mass loss rate. A high yield alone does not establish the largest total release. The burning rate and its variation during the exposure are also part of the assessment.<ref name="J_3-38">Janssens (2002), p. 3-38.</ref>

A fire-retardant treatment can change more than one measured property. Janssens discusses treatments that increase a toxic-gas yield while reducing mass loss sufficiently to reduce the assessed hazard. That example explains why treatment performance cannot be judged from one isolated number. Its interpretation depends on the complete combination of burning rate, yields and exposure conditions.<ref name="J_3-38" />

Smoke obscuration is another measurement available in calorimetry. It describes the effect of suspended products on transmitted light, rather than directly measuring structural endurance or the complete toxic hazard. A test reporting smoke obscuration therefore answers a different question from a furnace test of a separating assembly. The measurements become useful when each remains connected to its own physical quantity.<ref name="J_3-39" /><ref name="M_4-209_4-210" />

== Evidence and uncertainty ==

Heat-release measurements contain both systematic bias and random variation. Babrauskas describes calibration with a metered gas supply as one means of addressing bias. Comparisons between laboratories reveal variability that a single test cannot show. The historical interlaboratory results in the handbook are evidence about those apparatuses and trials, rather than permanent uncertainty allowances for every later test.<ref name="B_3-32_3-33" />

A model that uses small-specimen results introduces a further step between measurement and application. Material properties derived from those results must reproduce the processes relevant to the larger fire. Janssens describes approaches ranging from full-scale experiments to calculations using bench-scale data. Their suitability depends on the fire scenario, the available measurements and the treatment of enclosure feedback.<ref name="J_3-38_3-39" />

Even the same product can present different exposed areas and orientations in different applications. A room-corner arrangement provides different heat feedback from an isolated specimen, while a mounting method can alter burning. A defensible comparison consequently identifies the product, construction, exposure, measured quantity and test configuration together. Removing those conditions can turn a valid measurement into an unsupported prediction.<ref name="J_3-39" /><ref name="J_3-56" />

== See also ==

* [[Flame retardant]]
* [[Heat release rate]]
* [[Ignition]]

== Notes ==

<references />

== References ==

* Babrauskas, V. (2002). Heat release rates. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association.
* Janssens, M. (2002). Calorimetry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-38–3-62). National Fire Protection Association.
* Kanury, A. M. (2002). Flaming ignition of solid fuels. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-229–2-245). National Fire Protection Association.
* Kodur, V. K. R., & Harmathy, T. Z. (2002). Properties of building materials. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 1-155–1-181). National Fire Protection Association.
* Milke, J. A. (2002). Analytical methods for determining fire resistance of steel members. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-209–4-238). National Fire Protection Association.
* Ministry of Business, Innovation and Employment. (2025). ''C protection from fire: Verification method C/VM2'' (2nd ed.).
* Quintiere, J. G. (2002). Surface flame spread. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-246–2-257). National Fire Protection Association.

[[Category:Materials & Fire Testing]]

Vapour cloud explosion

2026-11-02T16:17:18Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

A '''vapour cloud explosion''' is an explosion arising when a flammable gas or vapour cloud ignites and its combustion produces a blast wave. Zalosh describes large clouds burning among densely arranged process equipment as an important example. The resulting blast depends on flame speed and confinement, as well as the combustible material present. The released fuel mass alone therefore does not determine the pressure imposed on surrounding equipment or structures.<ref name="Z420">Zalosh (2002), p. 3-420.</ref>

The assessment connects a release, mixing with air, ignition, flame propagation and pressure loading. Each stage can change the location and extent of the hazard. A cloud may remain outside, enter a building through ventilation openings, or spread between interconnected compartments. The hydrogen scenarios in the EPRI/NRC methodology illustrate these alternative pathways within US nuclear power facilities.<ref name="N8">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-8–N-11.</ref>

== Formation and ignition of a cloud ==

A release does not necessarily ignite at its source. Fuel can mix with air before encountering an ignition source elsewhere. The resulting concentration field depends on the release and its dispersion. For outdoor hydrogen releases, the EPRI/NRC methodology considers rising gas, wind direction and atmospheric conditions when examining whether a cloud reaches an ignition location.<ref name="N8" />
[[File:fse-vapour-cloud-explosion-v1.svg|thumb|upright=1.5|alt=A release branches into immediate jet combustion or a dispersed cloud that ignites later.|Immediate and delayed ignition require different exposure scenarios. Based on Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-7–N-9.]]

The [[Flammability limits|flammability limits]] identify concentration conditions within which flame propagation is possible under specified test conditions. They do not define the shape of a real cloud. Concentration can vary between locations, and the entire released inventory need not belong to one combustible mixture. Zalosh also distinguishes concentration limits from the ignition energy needed to initiate combustion.<ref name="Zlimits">Zalosh (2002), pp. 3-402–3-405.</ref>

The distinction between immediate and delayed ignition changes the scenario. The EPRI/NRC report treats immediate ignition of a pressurised hydrogen leak as a jet flame. It separately considers gas accumulation followed by ignition and possible return of combustion towards a continuing release. These branches require different exposure descriptions because the combustible material occupies different locations when burning begins.<ref name="N7">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-7–N-8.</ref>

Release duration and the time to ignition therefore influence the material available for combustion. In the report's analytical approach, the time for gas to reach an ignition source can also be compared with possible isolation actions. That comparison does not establish an automatic successful intervention. Its probability belongs to the scenario assessment and requires evidence about the relevant equipment and actions.<ref name="N8" />

== Flame propagation, congestion and confinement ==

An [[Explosion|explosion]] assessment must distinguish the fuel's chemical energy from the rate and geometry of its release. A [[Deflagration|deflagration]] propagates through the unburned mixture at subsonic speed. Expansion of the hot burned gases drives motion in the surrounding mixture. The flame speed seen by a stationary observer consequently differs from the burning velocity relative to the unburned gas.<ref name="Zprop">Zalosh (2002), pp. 3-407–3-410.</ref>

Turbulence can increase burning through faster local propagation or a more distorted flame with greater surface area. This helps explain why a cloud among obstructions cannot be represented by combustible mass alone. The handbook associates vapour cloud blast strength with the flame speed that develops and the degree of confinement. The equipment arrangement is therefore part of the physical problem.<ref name="Zprop" /><ref name="Z420" />

Congestion and confinement describe related but different features of that arrangement. The handbook's example combines a high density of process equipment with restrictions in and around the cloud. An outdoor process area can contain extensive obstructions even without forming a closed room. Conversely, gas entering a building can encounter a substantially different boundary arrangement from the outdoor release location.<ref name="Z420" /><ref name="N8" />

A cloud explosion is not automatically a detonation. A detonation involves supersonic propagation through the unburned mixture and a strongly nonuniform transient pressure field. The possibility of [[Deflagration-to-detonation transition|deflagration-to-detonation transition]] depends on mixture reactivity and the geometry available for flame acceleration. The handbook also identifies roughness and obstructions as relevant influences in elongated enclosures.<ref name="Zdet">Zalosh (2002), pp. 3-410–3-412.</ref>

These distinctions affect protection and structural assessment. A slowly developing enclosure pressure and a rapidly travelling pressure wave do not impose the same loading history. Zalosh therefore treats detonation protection separately from closed-vessel deflagration protection. A method selected for one propagation regime cannot be assumed suitable for the other simply because the fuel is identical.<ref name="Zdet" />

== Pressure, impulse and ideal blast scaling ==

Blast pressure varies with time at a receiving location. The incident pressure describes the arriving wave, while reflection at a surface can alter the pressure applied there. The duration of the positive pressure phase also matters. Its accumulated effect, called impulse, is relevant to dynamic structural response.<ref name="Z419">Zalosh (2002), p. 3-419.</ref>
[[File:fse-vapour-cloud-explosion-v2.svg|thumb|upright=1.5|alt=Two ideal point sources have the same scaled radius at 50 m and 100 m with energies of 100 MJ and 800 MJ.|Eightfold energy corresponds to twice the distance at equal scaled radius in this idealised example. Based on Zalosh (2002), p. 3-419.]]

Ideal blast theory simplifies the source to energy released instantaneously at one point. The handbook defines a dimensionless radius by combining actual distance, ambient pressure and blast energy. This provides a useful way to explain the scaling assumption, although it does not establish its validity for a particular vapour cloud.<ref name="Z419" />

<div class="fse-equation">R̄ = R(P<sub>0</sub>/E)<sup>1/3</sup></div>

{| class="wikitable"
! Symbol !! Meaning !! Unit
|-
| R̄ || Dimensionless radius in ideal blast scaling || dimensionless
|-
| R || Distance from the assumed point source || m
|-
| P<sub>0</sub> || Ambient absolute pressure || Pa
|-
| E || Assumed energy contributing to the blast || J
|}

The pressure-to-energy ratio has units of inverse cubic metres. Its cube root therefore cancels the length dimension of the distance. At unchanged ambient pressure, maintaining the same scaled radius requires distance to vary with the cube root of blast energy. This is a mathematical consequence of the stated expression, not a separate prediction of cloud combustion.<ref name="Z419" />

For illustration, select a distance of 50 m, ambient pressure of 101,325 Pa and assumed blast energy of 100 MJ. The resulting dimensionless radius is approximately 5.02. Doubling the distance to 100 m gives the same scaled radius only if energy increases eightfold, to 800 MJ. These selected values demonstrate scaling and do not describe a measured accident.<ref name="Z419" />

No pressure or safe separation distance follows from that calculation alone. It still requires an applicable pressure relationship and a justified blast-energy input. The chemical energy of released fuel is not automatically equal to the energy contributing to the blast. The handbook identifies uncertain energy yield as one weakness of early vapour cloud assessments.<ref name="Z420" />

== Why a single equivalent energy is insufficient ==

[[TNT equivalence|TNT equivalence]] is relevant when an explosion is represented through an equivalent compact-explosive source. The handbook explains that ideal blast correlations draw on theory and tests involving compact condensed-phase explosives. Their assumed instantaneous point release differs from combustion developing through an extended vapour cloud. Matching an energy number does not remove that difference.<ref name="Z419" /><ref name="Z420" />

Zalosh reports that early ideal-blast assessments were unsuccessful for two related reasons. Much of the practical interest concerned locations near the cloud, where a point-source representation was inadequate. Even farther away, the reported pressure and impulse decayed differently from ideal blast predictions. An arbitrary yield adjustment consequently could not correct every part of the pressure field.<ref name="Z420" />

The 2002 handbook describes two alternative modelling approaches. One estimates flame speed empirically and uses calculations of nonideal wave generation. The other represents two-dimensional or three-dimensional flame propagation and calculates acceleration as part of the solution. This is a description of the approaches discussed in that edition, rather than an inventory of present-day software.<ref name="Z420" />

Both approaches require more information than total released mass. The flame-speed representation and geometry must correspond to the scenario being examined. The EPRI/NRC methodology likewise leaves tool selection and suitability to the analyst; its hydrogen appendix does not verify or validate a particular explosion model. A named computational method is therefore not itself evidence of adequate validation.<ref name="Z420" /><ref name="N11">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-11.</ref>

== Hydrogen migration and connected spaces ==

[[Hydrogen safety|Hydrogen safety]] illustrates why the release location and explosion location need separate treatment. The EPRI/NRC report considers an outdoor cloud reaching a building's ventilation intake. The relevant assessment then includes concentration at the intake, mixing within the ventilation system and possible ignition locations. Ignition outside the building and ignition inside it are distinct scenarios.<ref name="N9">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-9.</ref>
[[File:fse-vapour-cloud-explosion-v3.svg|thumb|upright=1.5|alt=Gas from an outdoor release may enter an air intake and move through ducts into connected rooms.|Gas migration can connect an outdoor release with indoor explosion scenarios. Based on Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-8–N-11.]]

The same report considers migration through ceiling openings, wall openings and ventilation ducts between compartments. A release in one space can therefore require examination of connected spaces. The report separates explosions confined to the compartment of origin from those involving several compartments. Its conservative damage assumptions were developed for nuclear-plant risk assessment and are not universal physical damage laws.<ref name="N10">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-10–N-11.</ref>

For connected compartments, the proposed analysis examines the quantity needed to create combustible mixtures and the time required to release that quantity. It then considers failure to isolate the leak within the available period. This sequence links accumulation with system response. It avoids treating the presence of a gas source as proof that every connected room contains the same mixture simultaneously.<ref name="N10" />

== Interpretation and evidence limits ==

A consequence assessment needs a consistent chain from source conditions to target loading. The release and dispersion define where combustible mixtures can occur. Ignition and flame propagation define how energy is released. Pressure histories and the response of the exposed equipment then determine the consequence being assessed.<ref name="N8" /><ref name="Z419" /><ref name="Z420" />

The scope of supporting evidence remains attached to that chain. The EPRI/NRC appendix uses historical nuclear-industry events to support its scenario rules. Those rules do not provide a calibrated general-purpose overpressure model for every industrial site. Its explicit separation between scenario development and model verification preserves that distinction.<ref name="N1">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-1 and N-11.</ref>

An output expressed only as peak pressure also leaves part of the loading unspecified. Reflection, duration and impulse can influence structural response. Likewise, a quoted distance requires a defined source geometry and consequence criterion. The ideal scaling example demonstrates one relationship between inputs; it does not supply those missing physical and response assumptions.<ref name="Z419" /><ref name="Z420" />

== See also ==
* [[Detonation]]

== Notes ==
<references />

== References ==
* Electric Power Research Institute, & U.S. Nuclear Regulatory Commission. (2005). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Volume 2, Detailed methodology'' (EPRI 1011989; NUREG/CR-6850).
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-402–3-421). National Fire Protection Association.

[[Category:Explosions & Industrial Fires]]

Minimum ignition energy

2026-11-02T16:17:12Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

'''Minimum ignition energy''' is the smallest spark energy capable of igniting a specified combustible mixture under the conditions of a test. Commonly abbreviated MIE, it describes sensitivity to an electrical discharge. The value depends on the material, mixture composition and discharge characteristics, rather than being an unrestricted constant for every situation involving that substance.<ref name="B-181">Beyler (2002), p. 2-181.</ref><ref name="Z-405">Zalosh (2002), p. 3-405.</ref>

The quantity helps assess whether an [[Ignition source|ignition source]] can initiate combustion. It is distinct from the minimum temperature needed for ignition and from the pressure developed after an explosion. Those properties require different measurements and answer different safety questions.<ref name="Z-404-406">Zalosh (2002), pp. 3-404–3-406.</ref> A comparison between a possible spark and a measured MIE therefore retains the type of discharge, the fuel concentration and the surrounding conditions. Gas mixtures near their flammability boundaries generally require more ignition energy than more readily ignited compositions within the flammable range.<ref name="B-181" /><ref name="N-4">Iqbal and Salley (2004), p. 16-4.</ref>

== What the measured quantity describes ==

Ignition energy concerns the initiation of combustion by a particular source. The experimental arrangement supplies energy to a prepared mixture and determines whether ignition occurs. For dust clouds, Zalosh describes a standardised electrical-spark test. For gases, Beyler relates the required energy to mixture composition and to the loss of heat near surrounding surfaces.<ref name="Z-405" /><ref name="B-181-182">Beyler (2002), pp. 2-181–2-182.</ref>

The energy is commonly reported in millijoules, where one millijoule is one thousandth of a joule. Electrical energy calculations often use joules with capacitance, voltage, inductance and current in their corresponding SI units. Converting the measured threshold before making that comparison prevents a thousandfold unit error. The handbook's worked example explicitly converts millijoules to joules.<ref name="Z-405" />

The word minimum refers to the conditions examined in obtaining the value. The most readily ignited concentration can differ between materials. Zalosh states that his tabulated dust results represent the most sensitive concentration for each tested sample. A result for another concentration can therefore exceed the reported minimum without contradicting it.<ref name="Z-405" />

An ignition-energy result is not an explosion-severity measurement. The pressure following ignition depends on flame propagation, confinement and the thermal state of the burned gases. Zalosh treats that pressure calculation separately from the ignition-source assessment. A material that is easily ignited does not have its eventual pressure determined by MIE alone.<ref name="Z-402">Zalosh (2002), p. 3-402.</ref><ref name="Z-406">Zalosh (2002), p. 3-406.</ref>

The distinction also separates energy from ignition temperature. Dust-cloud temperature tests expose dispersed material in a heated apparatus, while dust-layer tests use a heated surface. An electrical spark delivers energy through a different exposure. The resulting values cannot be substituted for each other simply because all concern ignition.<ref name="Z-404">Zalosh (2002), p. 3-404.</ref>

== Gas concentration and surrounding conditions ==

A gas must be mixed with oxidant in suitable proportions for a flame to propagate. [[Flammability limits]] identify the boundaries of that range under specified conditions. Inside the range, the energy needed for ignition still varies with composition. Being within the flammable range therefore does not imply that every possible electrical disturbance will ignite the mixture.<ref name="B-181" />

Beyler reports ignition energies of the order of a few tenths of a millijoule for many near-stoichiometric mixtures in air. Stoichiometric composition supplies fuel and oxygen in the proportions required by the combustion reaction. The minimum does not necessarily occur exactly at that composition. The source discusses shifts towards richer mixtures associated with preferential diffusion for certain fuels.<ref name="B-181" />

As a mixture approaches either flammability boundary, its required ignition energy rises sharply. This dependence means that one measured minimum cannot reproduce the complete concentration-dependent response. It is useful for identifying a sensitive condition, while a particular scenario still needs its actual mixture considered. The nuclear inspection guidance describes the same general trend for hydrogen in air.<ref name="B-181" /><ref name="N-4" />
[[File:fse-minimum-ignition-energy-v1.svg|thumb|upright=1.5|alt=A qualitative curve shows higher required spark energy near the lean and rich boundaries and a lower intermediate region.|Required ignition energy changes within the flammable concentration range. Based on Beyler (2002), p. 2-181, and Iqbal and Salley (2004), p. 16-4.]]

The oxidant mixture also influences ignition. Beyler notes much smaller energy scales for mixtures in oxygen than for corresponding discussions of mixtures in air. NUREG-1805 describes increased ignition energy when a diluent such as steam is added to hydrogen and air. A threshold therefore needs the oxidant and diluent conditions alongside the fuel name.<ref name="B-181" /><ref name="N-4" />

Pressure is another part of the reported experimental condition. The hydrogen figure reproduced in NUREG-1805 presents separate ignition-energy curves for different pressures. These curves vary with hydrogen concentration and do not collapse into one fixed threshold. The figure supports retaining pressure when interpreting its data, without supplying a universal correction for every gas and discharge.<ref name="N-4" />

== Hydrogen as an ignition-sensitivity example ==

The importance of low-energy sparks is evident in [[Hydrogen safety|hydrogen safety]]. NUREG-1805 identifies electrical equipment and small static discharges as possible ignition sources when a hydrogen-air mixture becomes flammable. Its discussion concerns dry, relatively still mixtures and shows how required energy changes with composition. These conditions remain part of the evidence.<ref name="N-4" />

The same report distinguishes hydrogen's low spark-energy requirement from its comparatively high ignition temperature. The properties describe different ignition mechanisms. A relatively high temperature criterion therefore does not mean that small electrical sparks can be disregarded. Conversely, a spark-energy value does not specify the temperature of every surface capable of initiating combustion.<ref name="N-2">Iqbal and Salley (2004), p. 16-2.</ref><ref name="N-4" />

Hydrogen flammability limits also depend on the flame-propagation direction used in the test. NUREG-1805 distinguishes upward, horizontal and downward propagation. This illustrates that ignition and sustained propagation are evaluated within a defined experimental arrangement. Combining an ignition-energy measurement with unrelated mixture limits can conceal differences in what the experiments actually assessed.<ref name="N-2" /><ref name="N-4" />

The report's plotted curves and approximate prose statement serve different purposes. The curves show concentration and pressure dependence, while the prose conveys the small energy scale. Treating the approximate statement as one exact minimum for every hydrogen mixture would discard the variation shown on the same page. The article therefore does not assign a universal hydrogen threshold.<ref name="N-4" />

== Dust-cloud tests and sample dependence ==

For a [[Dust explosion|dust explosion]] assessment, the relevant fuel is a suspended particulate cloud. Zalosh describes measuring MIE in a 1.2 litre cylindrical apparatus, commonly called a modified Hartmann tube. An electrical discharge is applied to the prepared cloud. The account refers to the historical test method described in the 2002 handbook.<ref name="Z-405" />

The tested powder is more specific than its commercial material name. The handbook reports particle-size information with the results and identifies concentration, temperature and mixture motion as influences. These conditions can differ between a laboratory sample and a process cloud. A tabulated value consequently requires the associated sample and test description.<ref name="Z-404" /><ref name="Z-405" />

The following examples retain the median particle sizes reported in Zalosh's table. The MIE results were obtained using relatively long inductive discharges and the most sensitive dust concentration. They demonstrate variation among particular tested powders. They are not universal constants for all sugar, milk powder or starch products.<ref name="Z-table">Zalosh (2002), pp. 3-404–3-405, Table 3-16.2.</ref>

{| class="wikitable"
! Tested material !! Reported median particle size !! Minimum ignition energy
|-
| Sugar || 10 μm || 14 mJ
|-
| Milk powder || 165 μm || 75 mJ
|-
| Corn starch || Less than 10 μm || 300 mJ
|}

Differences between these rows cannot isolate a particle-size effect because the materials also differ. The table combines several characteristics of each sample. An assessment of one influence would require otherwise comparable test conditions and material. The numbers support sample-specific comparison, rather than a simple ranking based only on the displayed particle diameters.<ref name="Z-table" /><ref name="Z-405" />

Minimum explosible concentration is a separate dust property. Its test examines whether a cloud of a given concentration supports the relevant combustion response, using an ignition source specified by that method. Zalosh notes that those results can themselves be sensitive to igniter energy and turbulence. A concentration test does not automatically determine the material's minimum spark energy.<ref name="Z-404" />

The milk-powder row also reports a cloud ignition temperature of 460 °C and a layer ignition temperature of 330 °C. These temperatures accompany an MIE of 75 mJ for the stated sample. The three numbers describe different experimental exposures. Their different units and test arrangements prevent interpreting one as a direct conversion of another.<ref name="Z-table" />
[[File:fse-minimum-ignition-energy-v2.svg|thumb|upright=1.5|alt=Three test concepts distinguish the milk-powder sample’s spark energy, cloud ignition temperature and layer ignition temperature.|The same powder sample has distinct energy, cloud-temperature and layer-temperature results. Based on Zalosh (2002), pp. 3-404–3-405.]]

Zalosh attributes lower layer ignition temperatures to reduced heat dissipation within deposited material compared with a dispersed cloud. The distinction helps explain why a hot deposited layer can present a different ignition problem from the same material suspended in air. A spark-energy result for the cloud consequently does not evaluate sustained heating of the deposit.<ref name="Z-404-406" />

Temperature and motion can also change the spark test itself. Zalosh reports decreasing dust MIE with increasing mixture temperature and increasing MIE with greater dust-air velocity. Those influences are separate from the choice of powder and concentration. A result obtained in one prepared cloud therefore does not establish the same threshold under every hotter or faster-moving process condition.<ref name="Z-405" />

The test record consequently needs more than a material label and an energy number. Sample description, concentration, temperature and discharge duration identify what was actually assessed. Keeping these details together permits a meaningful comparison with a proposed ignition scenario.<ref name="Z-405" />

== Discharge duration and stored energy ==

The duration of an electrical spark affects its ability to ignite a dust cloud. Zalosh describes lower measured MIE values for longer discharges produced by adding inductance or resistance to a capacitive circuit. The total energy and its release history are therefore related but distinct characteristics. Comparing only the energy numbers can overlook the duration difference.<ref name="Z-405" />

This matters when laboratory results are compared with electrostatic discharges. The source distinguishes relatively short capacitive sparks from longer discharges associated with electrical equipment. A dust threshold obtained with a long inductive spark cannot automatically be treated as the matching threshold for every capacitive spark. The discharge type accompanies the reported MIE.<ref name="Z-405" />

Theoretical stored energies for ideal capacitive and inductive circuits follow the equations below. Their variables use SI units so that the calculated energy is in joules. These expressions describe the stated ideal electrical storage. They do not independently establish the fraction of that energy transferred to a real combustible mixture.<ref name="Z-405" />

<div class="fse-equation">E<sub>C</sub> = ½ C U²</div>
<div class="fse-equation">E<sub>L</sub> = ½ L I²</div>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| E<sub>C</sub> || Ideal capacitive stored energy || J
|-
| E<sub>L</sub> || Ideal inductive stored energy || J
|-
| C || Capacitance || F
|-
| U || Potential difference before discharge || V
|-
| L || Inductance || H
|-
| I || Current || A
|}

The square dependence means that voltage and energy do not change in direct proportion at fixed capacitance. Halving the voltage gives one quarter of the stored energy. The corresponding inductive expression has the same square dependence on current at fixed inductance. These mathematical relationships help interpret changes within the stated circuit model.<ref name="Z-405" />

Mechanical sparks require another assessment. Zalosh states that their associated energy is much more difficult to determine than energy in simple electrical circuits. Hot spots produced by sustained friction also differ from brief impact sparks. The capacitive formula therefore cannot be used as a complete description of every possible ignition source.<ref name="Z-405" />

== A worked comparison of discharge types ==

Zalosh gives an illustrative powder silo with a capacitance of 500 picofarads. The stated powder has a minimum ignition energy of 10 mJ for inductive sparks and 50 mJ for capacitive sparks. The question concerns a capacitive discharge, so the matching comparison uses 50 mJ. The lower inductive result describes a different discharge history.<ref name="Z-405" />
[[File:fse-minimum-ignition-energy-v3.svg|thumb|upright=1.5|alt=The capacitive threshold connects to the stored-energy calculation, while the inductive threshold is shown as an incompatible input.|The theoretical electrostatic comparison uses the threshold for the same discharge type. Based on Zalosh (2002), p. 3-405.]]

Rearranging the capacitive equation gives U = √(2E<sub>C</sub>/C). Converting the inputs gives an energy of 0.050 J and a capacitance of 500 × 10⁻¹² F. The calculated voltage is approximately 14,100 V, or 14 kV to two significant figures. This reproduces the handbook's rounded theoretical result.<ref name="Z-405" />

Using the 10 mJ inductive threshold in that capacitive calculation would instead give approximately 6.3 kV. This is a calculated illustration of the error introduced by changing the threshold definition. It does not establish a second valid capacitive ignition criterion. The difference arises from comparing unlike discharge conditions.<ref name="Z-405" />

The source connects the example to charge generation during powder handling. It also notes that grounding the silo addresses charge on that conductive object. Isolated objects inside it and a sufficiently resistive powder can retain their own charge hazards. The energy calculation therefore identifies one mechanism without demonstrating that every electrostatic source has been controlled.<ref name="Z-405" /><ref name="Z-406" />

== Engineering use and limits ==

One prevention approach is to limit electrical equipment so that its worst fault condition cannot supply sufficient ignition energy for the specified gas. Beyler describes this as intrinsic safety. Another approach contains an internal ignition and prevents its flame from propagating outside the enclosure. These approaches address ignition in different ways and require their own design basis.<ref name="B-181" />

Flame quenching depends on heat lost as a flame passes through a sufficiently small gap. Beyler distinguishes the quenching distance from the minimum experimental safe gap, which also reflects possible ignition outside by emerging hot gases. Neither distance is simply an energy value. Their relationship to ignition sensitivity does not make them interchangeable equipment parameters.<ref name="B-181-182" />

These source-control concepts are relevant to the separate topic [[Hazardous area classification|Hazardous area classification]]. The ignition-energy discussion here does not establish a zone or division, an equipment category or a permissible installation. It describes the physical basis for comparing certain ignition sources with specified combustible mixtures.<ref name="B-181" /><ref name="Z-402" />

Finally, an assessment retains both the ignition conditions and the consequences if ignition occurs. Mixture formation, electrical or mechanical source characteristics and subsequent flame propagation are separate parts of that sequence. A favourable comparison with one measured MIE does not evaluate every alternative source or mixture state. The source data remain conditional on their material and experimental context.<ref name="Z-402" /><ref name="Z-405" /><ref name="N-4" />

== See also ==
* [[Deflagration index]]

== Notes ==
<references />

== References ==
* Beyler, C. (2002). Flammability limits of premixed and diffusion flames. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 2-7). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-16). National Fire Protection Association.

[[Category:Explosions & Industrial Fires]]

Jet fire

2026-11-02T16:17:06Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

A '''jet fire''' is a flame sustained by a directed release of combustible material that mixes with surrounding air as it burns. The release can arise from a pressurised leak or from an intentionally operated flare. Its momentum influences the flame's direction and shape, while buoyancy and the surrounding wind also affect its development. Beyler describes these fires as turbulent diffusion flames, meaning that fuel and air mix during combustion.<ref name="B291">Beyler (2002), pp. 3-291–3-292.</ref>

The distinction between exposure outside the flame and direct flame impingement is central to assessing the hazard. A distant surface may receive predominantly thermal radiation, whereas an engulfed target also experiences strong convective heating. The release direction, flame dimensions and target position therefore matter alongside the total heat release rate. A radiation calculation for a distant target cannot represent every consequence of a nearby jet.<ref name="B298">Beyler (2002), p. 3-298.</ref><ref name="B302">Beyler (2002), p. 3-302.</ref>

== Release conditions and possible fire sequences ==

Beyler's release event tree distinguishes immediate ignition from ignition after fuel has accumulated or dispersed. Immediate ignition of a release through a relatively small opening can produce a jet flame. The material can be gas or liquid, with a liquid release potentially involving flashing into vapour and accumulation. The flame representation must therefore match the state and behaviour of the released material.<ref name="Bevent">Beyler (2002), pp. 3-268–3-269.</ref>
[[File:fse-jet-fire-v1.svg|thumb|upright=1.5|alt=A release branches into jet, pool and cloud-fire pathways.|A release can lead to different fire types and a changing sequence. Based on Beyler (2002), pp. 3-268–3-269.]]

A [[Pool fire|pool fire]] involves burning associated with an accumulated liquid surface. A directed jet and an accumulated pool can arise within the same release sequence, but their geometries differ. Delayed ignition of a dispersed cloud can also propagate back towards the release and establish subsequent steady burning. Treating the initial event and the continuing fire as separate stages preserves these differences.<ref name="Bevent" />

An intentionally operated flare shares important flame characteristics with an accidental jet fire. However, flare composition, outlet diameter and stack height may be known design inputs. For an accidental release, those inputs can require estimation from the failed equipment and release conditions. Similar combustion physics does not mean that the source uncertainty is the same.<ref name="B291" />

The EPRI/NRC methodology provides examples involving hydrogen relief valves, valve packing and flange leaks. It distinguishes jet flames from tank explosions and delayed cloud ignition. The report was prepared for fire risk assessment at US nuclear power facilities. Its scenario categories can clarify the sequence being considered, while its numerical screening assumptions remain tied to that purpose.<ref name="N7">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-7–N-8.</ref>

The distinction also matters when considering a [[BLEVE|boiling liquid expanding vapour explosion]]. A sustained jet exposure and a sudden vessel failure are different stages or outcomes. Beyler describes accidents in which burning released fuel heated neighbouring liquefied-gas vessels before later failures. A calculation of the original jet therefore does not automatically describe every subsequent exposure.<ref name="B302" />

== Momentum, buoyancy and flame stability ==

Fuel emerging from an opening carries momentum. Mixing with surrounding air supports combustion and changes the moving stream, while hot gases experience buoyancy. Depending on their relative influence, the flame can be predominantly momentum-controlled or buoyancy-controlled. Beyler consequently separates the corresponding flame-length relationships instead of assigning one universal length to a given release diameter.<ref name="Bgeometry">Beyler (2002), pp. 3-291–3-293.</ref>

At relatively low release velocities, the flame can remain attached near the outlet. Increasing velocity can cause its base to lift away. At still higher conditions, a stable flame may cease to be maintained and blowout can occur. An obstruction can also stabilise a flame, so the arrangement around the release belongs in the assessment.<ref name="B291" /><ref name="Bstability">Beyler (2002), pp. 3-296–3-297.</ref>

A lifted flame does not mean that fuel has stopped being released. Its burning region is displaced from the opening. The handbook explains this position through the balance between local flow velocity and turbulent burning velocity. Changes in release conditions can move the flame base to another location where that balance is possible.<ref name="Bstability" />

These mechanisms limit simple comparisons based only on outlet velocity. The same velocity does not uniquely determine flame length, attachment or radiation for every fuel and opening. Density, burning characteristics and the flow regime also enter the cited relationships. A prediction should retain those conditions instead of treating a laboratory observation as a universal jet-fire rule.<ref name="Bgeometry" /><ref name="Bstability" />

== Wind, geometry and the location of exposure ==

Crosswind can bend a jet flame and change its length and width. The handbook reviews experiments with several fuels and distinguishes vertical flame height from distance along an inclined flame. These geometric quantities answer different questions. A height above the outlet cannot be used directly as the full length of a tilted flame.<ref name="Bwind">Beyler (2002), pp. 3-293–3-296.</ref>

The correlations described in the chapter have stated experimental ranges. One group of wind-tunnel tests used burner diameters from 6 to 22 mm, jet velocities from 13 to 200 m/s, and crosswinds from 2.6 to 8.1 m/s. These conditions identify the supporting evidence. They do not establish equal accuracy for every large accidental release.<ref name="B294">Beyler (2002), p. 3-294.</ref>

Release direction can determine which equipment lies within the flame path. The EPRI/NRC hydrogen assessment explicitly considers orientation relative to potential targets. For a relief valve, the discharge direction may constrain the possible flame direction. For a less clearly defined leak, the assumed direction requires its own scenario basis.<ref name="N7" />

Distance also requires a defined reference. In the point-source radiation model, it is measured from a representative point near the flame centre. Distance from the pipe opening is generally a different quantity. A long flame can therefore place the representative radiating region substantially closer to a target than the release point itself.<ref name="B298" />

The receiving surface orientation further affects radiation. A surface facing the representative source receives a different projected exposure from the same surface turned obliquely. This geometric effect is separate from any change in flame power. Source location and surface orientation both need definition before numerical distances can be compared.<ref name="B298" />

One historical hydrogen incident in the EPRI/NRC appendix illustrates the importance of localisation. Direct impingement severely damaged equipment near the release, while damage decreased farther away. A later release through an excess-flow valve directed flame towards a fence. The account identifies changing release geometry rather than a uniform exposure around the original source.<ref name="N6">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-6.</ref>

== Radiation models and their limits ==

[[Flame radiation|Flame radiation]] depends on the amount of energy emitted and the geometric relationship to the target. A simple model replaces the flame by a point at its centre. Beyler gives the following expression for a target outside the flame, together with the relation between radiated power and total heat release.<ref name="B298" />

<div class="fse-equation">q̇″ = Q̇<sub>r</sub> cos θ / (4πR²)</div>
<div class="fse-equation">Q̇<sub>r</sub> = χ<sub>r</sub> Q̇</div>

{| class="wikitable"
! Symbol !! Meaning !! Unit
|-
| q̇″ || Incident radiative heat flux in the simplified model || kW/m²
|-
| Q̇<sub>r</sub> || Total power emitted as radiation || kW
|-
| Q̇ || Total heat release rate || kW
|-
| χ<sub>r</sub> || Fraction of heat release emitted as radiation || dimensionless
|-
| R || Distance from the representative flame centre to the target || m
|-
| θ || Angle between the surface normal and direction towards the source || degrees, used consistently in the cosine
|}

This expression distributes radiant power over a spherical area and includes the receiving surface's projected orientation. It does not resolve how emission varies along the flame. The chapter reports useful comparisons for flare radiation, but also identifies errors close to the source. The point approximation therefore requires separation large enough for the finite flame geometry to be adequately represented.<ref name="B298" /><ref name="B301">Beyler (2002), pp. 3-301–3-302.</ref>

A solid-flame model retains a simplified emitting shape, such as a tilted cylinder. Its result depends on surface emissive power, a geometric configuration factor and atmospheric transmission. A line-source model instead sums contributions along the flame length. These approaches expose different geometric detail; none eliminates the need to justify the flame and emission inputs.<ref name="B301" />

The radiative fraction is not a universal constant for a fuel. Beyler reviews effects of combustion efficiency, soot, mixing and heat transferred to entrained air. The chapter also reports changes with jet velocity and crosswind. Laboratory trends provide evidence of these influences, but their quantitative transfer to large flames requires care.<ref name="Bfraction">Beyler (2002), pp. 3-299–3-301.</ref>

Atmospheric attenuation is another separate influence. The basic point expression shown here contains no transmission factor. Its use therefore embodies that simplification. A more detailed assessment must retain consistency between emitted power, any attenuation model and the incident quantity being reported.<ref name="Bfraction" /><ref name="B301" />

The spatial distribution of emission is another source of approximation. Propane experiments reviewed by Beyler found the strongest radiation near the flame centre, decreasing towards either end. A uniformly emitting cylinder discards that variation. A line representation can retain variation along its length, provided the assigned distribution has supporting evidence.<ref name="Bfraction" /><ref name="B301" />

The chapter also describes a three-dimensional model incorporating flow, turbulence, combustion and soot. Its reported comparison with field experiments used methane jets up to 254 mm in diameter and obtained heat-flux agreement within 15%. That result belongs to the identified model and experiments. It is not a general accuracy statement for every computational jet-fire model.<ref name="B301" />

== Worked radiation comparison ==

Consider an illustrative 10 MW jet with an assumed radiative fraction of 0.20. The handbook lists a value of 0.20 among the reported methane results, but also explains its dependence on operating conditions. It is selected here solely to demonstrate the equation. It is not a recommended fraction for every methane release.<ref name="Btable">Beyler (2002), p. 3-299, Table 3-11.12.</ref>
[[File:fse-jet-fire-v2.svg|thumb|upright=1.5|alt=Three assumed point-source cases show radiation decreasing with distance and oblique orientation.|Distance and orientation change the calculated far-field radiation. Based on Beyler (2002), pp. 3-298–3-299.]]

The assumed radiated power is 2,000 kW. For a target facing the representative source at 50 m, the equation gives approximately 0.0637 kW/m². At 100 m, the result is approximately 0.0159 kW/m². Doubling distance reduces the calculated flux to one quarter because the spherical area increases with the square of distance.<ref name="B298" />

Keeping the target at 50 m but turning its normal through 60° halves the result to approximately 0.0318 kW/m². The calculation uses the same emitted power and changes only projected orientation. These three cases demonstrate the distance and angular terms independently. All intermediate calculations retain unrounded values.<ref name="B298" />

The example does not establish that an actual 10 MW jet has a particular flame length. It assumes that the chosen positions are sufficiently far from the flame for the point representation. Nor does it calculate atmospheric attenuation, direct contact or the thermal response of a target. Those omissions define the scope of the reported values.<ref name="B298" /><ref name="B301" />

A numerical flux is also not automatically a consequence criterion. The target's material, duration of exposure and response require separate treatment. The handbook frames its radiation methods as inputs to an assessment of particular impacts. A distance derived from the equation needs that additional basis before it can be interpreted as a protection distance.<ref name="Bintro">Beyler (2002), p. 3-268.</ref>

== Direct impingement and structural exposure ==

An impinging jet heats the target through both radiation and convection. The handbook reports particularly severe exposures where large-scale jet flames engulfed cylindrical targets. In the cited tests, average heat fluxes over the impingement area were approximately 200 kW/m² for sonic natural gas and 150 kW/m² for two-phase liquefied petroleum gas. These are results for those experimental arrangements.<ref name="B302" />
[[File:fse-jet-fire-v3.svg|thumb|upright=1.5|alt=A remote target receives radiation while an engulfed target also receives strong convective heating.|Direct impingement combines radiative and convective heating. Based on Beyler (2002), pp. 3-301–3-302.]]

The corresponding reported peaks reached approximately 300 and 250 kW/m² respectively. A peak local value differs from an average over the target area. Neither value describes every location on a vessel or every release condition. Retaining the fuel state and target geometry prevents those measurements from becoming universal design inputs.<ref name="B302" />

Beyler describes roughly comparable radiative and convective contributions in some high-flux regions. Other gaseous propane tests reported a different balance. A radiation-only estimate therefore cannot generally reproduce total impingement heating. The relevant exposure includes the local gas motion and thermal environment as well as radiation.<ref name="B302" />

A prescribed [[Hydrocarbon fire curve|hydrocarbon fire curve]] describes a temperature–time exposure associated with oil or gas fire testing. Van Rossum distinguishes such agreed histories from temperatures developing in an actual scenario. The curve and the local jet-impingement flux consequently describe different inputs. Substituting one for the other requires a thermal assessment rather than a change of label.<ref name="VR86">Van Rossum (2027), §8.6.</ref><ref name="B302" />

== Mitigation, continuing release and assessment scope ==

Water application can affect exposure without necessarily extinguishing the jet. Beyler reviews experiments showing reduced radiation at water-spray rates below complete suppression. Fleming likewise distinguishes cooling of exposed construction from successful extinction. A reduction in measured radiation is therefore a different result from stopping fuel flow or eliminating the flame.<ref name="Bwater">Beyler (2002), p. 3-300.</ref><ref name="F72">Fleming (2002), p. 4-72.</ref>

A [[Deluge system|deluge system]] supplies open discharge devices after a separate detection system operates its valve. That system description does not specify its effectiveness against a particular jet. Fleming emphasises the empirical basis and limits of suppression calculations. The cited jet-spray observations therefore cannot supply a general deluge application rate or guaranteed performance.<ref name="F72" /><ref name="F73">Fleming (2002), p. 4-73.</ref><ref name="Bwater" />

For [[Hydrogen safety|hydrogen safety]], continuing release and ignition sequence remain particularly relevant. The EPRI/NRC report explains that loss of a flame while gas continues escaping can permit a flammable cloud to form. Its discussion of source isolation reflects that change in scenario. Extinction and removal of the fuel source are consequently distinct outcomes in the hazard analysis.<ref name="N1">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-1–N-2.</ref>

The final assessment needs a defined release, flame representation, target geometry and exposure duration. It also needs the applicable model limitations and supporting experimental conditions. The EPRI/NRC report leaves selection and validation of detailed computational tools outside its hydrogen scenario rules. Its screening assumptions cannot replace a validated thermal model for a different application.<ref name="N11">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-11.</ref><ref name="Bintro" />

== See also ==
* [[Fireball]]

== Notes ==
<references />

== References ==
* Beyler, C. L. (2002). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-11). National Fire Protection Association.
* Electric Power Research Institute, & U.S. Nuclear Regulatory Commission. (2005). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Volume 2, Detailed methodology'' (EPRI 1011989; NUREG/CR-6850).
* Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 4-72–4-87). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''.

[[Category:Explosions & Industrial Fires]]

Inerting

2026-11-02T16:17:00Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

'''Inerting''' is the addition of a suitable diluent to prevent a combustible mixture from supporting flame propagation. In common gas-purging applications, an inert gas reduces the oxygen concentration below the limit relevant to the fuel and conditions. The method changes the mixture's ability to burn, rather than relying solely on excluding ignition sources.<ref name="B-179">Beyler (2002), p. 2-179.</ref><ref name="N-27">Iqbal and Salley (2004), p. B-27.</ref>

The limiting oxygen concentration depends on the fuel, diluent, temperature and pressure. An inerted state therefore requires a defined mixture and operating condition. A concentration that prevents flame propagation in one system cannot automatically be transferred to another.<ref name="B-179" /> Mixing during gas replacement also matters: the path from the initial composition to the final composition can cross a flammable region even when the endpoints do not.<ref name="B-180">Beyler (2002), pp. 2-180–2-181.</ref> Inerting calculations consequently consider mixture composition, dilution history and the continued control of oxygen. Practical application also depends on concentration nonuniformity and the performance of monitoring instruments.<ref name="Z-403">Zalosh (2002), p. 3-403.</ref>

== Preventing a combustible mixture ==

A premixed fire requires fuel and oxidant in proportions that support flame propagation. [[Flammability limits]] describe the boundaries of that composition range under specified test conditions. Adding a diluent changes the concentrations and thermal behaviour of the mixture. Beyond a sufficient dilution, a flame cannot propagate away from the ignition source under those conditions.<ref name="B-178">Beyler (2002), pp. 2-178–2-179.</ref>

This provides one way to interrupt the sequence leading to an [[Explosion|explosion]]. Zalosh describes three broad protection approaches: preventing a flammable mixture, excluding ignition sources and limiting the pressure generated after ignition. Inerting belongs to the first approach. Explosion venting and suppression address different stages, so their mechanisms are not interchangeable with mixture control.<ref name="Z-402">Zalosh (2002), p. 3-402.</ref>

NUREG-1805 distinguishes oxygen control from fuel-concentration control. An inert purge gas reduces the oxidant available to a mixture. Air dilution instead reduces fuel concentration while introducing additional oxygen. These approaches can move the composition along different paths and require different evidence that the resulting mixtures remain outside the flammable region.<ref name="N-27" /><ref name="B-180" />

The word inert describes the diluent's role in the specified combustion problem. It does not mean that the resulting atmosphere is suitable for breathing. The handbook's discussion of inert-gas agents identifies reduced oxygen as their principal physiological hazard. Fire prevention and the assessment of human exposure therefore remain separate questions.<ref name="D-184">DiNenno (2002), p. 4-184.</ref>

The supplied vessel-purging methods also have a defined application scope. NUREG-1805 discusses tanks and process vessels, while Beyler examines fuel, oxidant and diluent mixtures. These calculations do not constitute a complete design description for an [[Oxygen reduction system|oxygen reduction system]]. The shared oxygen-control principle does not supply every installation-specific operating requirement.<ref name="N-27" /><ref name="B-179" />

== Limiting oxygen concentration ==

The limiting oxygen concentration is the oxygen boundary below which the specified mixture cannot support the relevant combustion process. Beyler discusses it in terms of preventing premixed flame propagation. Zalosh relates the limiting oxidant concentration to explosion prevention. The intended test criterion matters when interpreting values obtained from different experimental arrangements.<ref name="B-179" /><ref name="Z-402" />

The limit is different from a fuel's lower flammable limit in ordinary air. The lower fuel limit concerns insufficient fuel in a specified oxidising mixture. The oxygen limit concerns insufficient oxidant after dilution. Controlling one variable does not remove the need to identify the other constituents of the mixture.<ref name="B-178" /><ref name="B-179" />

Diluent choice affects the limiting condition. Beyler compares nitrogen and carbon dioxide and relates their different performance to heat capacity. The added gas absorbs energy during combustion, influencing whether a flame can sustain itself. Equal volume fractions of two different diluents therefore need not produce the same flammability boundary.<ref name="B-179" />

Fuel identity also matters. The handbook describes hydrogen and carbon monoxide as having lower limiting oxygen concentrations than many common hydrocarbon fuels. A value selected for one hydrocarbon therefore cannot be treated as an oxygen limit for every combustible gas. The relevant fuel data remain part of the inerting calculation.<ref name="B-179" />

Temperature and pressure accompany the composition data. Beyler states that the limiting concentration depends on both and identifies the conditions attached to his tabulated results. A value measured near normal atmospheric conditions is not an unrestricted limit for a heated or pressurised process. The data and the proposed operating state need a compatible basis.<ref name="B-179" />

The experimental limit is also distinct from an operating setpoint. Zalosh discusses margins for nonuniform mixtures and for instrument accuracy, response and reliability. His numerical examples refer to the historical standard edition cited in that chapter. The underlying distinction remains that a measured boundary alone does not specify the margin or monitoring arrangement for an installation.<ref name="Z-403" />

== Reading the composition path ==

A flammability diagram represents mixtures of fuel, oxygen and diluent. In a three-axis diagram, each constituent has an explicit concentration coordinate. The three fractions sum to the complete mixture. A two-axis representation can carry the same information by obtaining the third fraction from the difference between the other two and the total.<ref name="B-178" />

The flammable region occupies only part of that composition space. A mixture can lie outside it because it contains too little fuel, too little oxygen or too much fuel relative to oxidant. These are different starting states. Their subsequent response to added air cannot be inferred from the simple statement that the initial mixture is nonflammable.<ref name="B-178" /><ref name="B-180" />

Adding one constituent moves the overall composition towards the point representing that pure gas. Adding air instead moves it towards the air composition. Beyler uses these paths to examine the dilution of fuel-rich mixtures. A straight path between an initial mixture and air can pass through the flammable region even though the initial rich mixture lies outside it.<ref name="B-180" />
[[File:fse-inerting-v1.svg|thumb|upright=1.5|alt=Composition diagram shows a direct air-mixing path crossing a flammable region and an alternative path around it.|The path through composition space matters as well as its endpoints. Based on Beyler (2002), pp. 2-178–2-181.]]

Adding nitrogen first can change the starting point for later air dilution. In the handbook example, a graphical tangent identifies a diluted composition whose subsequent mixing line avoids the flammable region. The result depends on the complete diagram and its stated conditions. It cannot be obtained merely by assuming that any reduction in fuel concentration is protective.<ref name="B-180" />

The same reasoning applies to gas leaving the system. An exhaust mixture that cannot burn inside the inerted volume can mix with external air and enter a flammable range. Beyler explicitly identifies this issue in his room-purging example. The discharge boundary is therefore part of the combustion assessment, rather than the point at which consideration ends.<ref name="B-181">Beyler (2002), p. 2-181.</ref>

== A model for well-mixed purging ==

Purging replaces some of the original gas with an introduced gas while material leaves through an outlet. If the entire volume remains well mixed, the outlet contains the same mixture as the interior. Newly added inert gas consequently leaves alongside the original gas. This loss makes mixed purging different from replacing one unmixed volume with another.<ref name="B-180" />

Beyler describes the decline in fuel concentration using an exponential relationship. The model assumes a fixed enclosed volume and uniform concentration during the addition of nitrogen. Added and exhausted gas volumes are expressed on a consistent basis. The formula concerns the idealised dilution process and does not establish that an actual space mixes uniformly.<ref name="B-181" />

<div class="fse-equation">C = C<sub>0</sub> exp(−V<sub>N</sub>/V)</div>
<div class="fse-equation">V<sub>N</sub> = −V ln(C/C<sub>0</sub>)</div>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| C || Fuel concentration after the modelled purge || Volume fraction or volume percent
|-
| C<sub>0</sub> || Initial fuel concentration, on the same basis || Volume fraction or volume percent
|-
| V<sub>N</sub> || Nitrogen volume introduced at the stated gas conditions || m³
|-
| V || Fixed volume being purged || m³
|}

The concentration ratio is dimensionless, so both concentrations must use the same convention. Volume percent can be used in both numerator and denominator without converting them separately to fractions. The logarithm is the natural logarithm. Mixing a percentage with a fraction would produce a different ratio and an erroneous purge quantity.<ref name="B-181" />

The expression predicts progressively smaller concentration reductions for successive equal gas additions. As the original gas becomes more dilute, less of it leaves with each unit of exhaust. A later addition therefore removes less original fuel than an equally large initial addition. This is the physical meaning of the exponential decline under the complete-mixing assumption.<ref name="B-181" />

Other mixing patterns require other descriptions. Beyler contrasts complete mixing with an ideal replacement in which only the original mixture is removed. Neither idealisation proves the flow pattern in a particular room or vessel. The selected model has to retain its assumptions when its calculated gas quantity is interpreted for an actual installation.<ref name="B-180" />

== Worked examples from the handbook ==

Beyler considers a 200 m³ room initially containing 30% methane by volume. His flammability diagram gives a methane concentration of 13% for the selected nitrogen-diluted endpoint before subsequent air mixing. These are inputs to a particular theoretical example. They are not breathable-atmosphere criteria or a general procedure for clearing a methane-filled room.<ref name="B-180" /><ref name="D-184" />

Using the mixed-purge expression gives −200 ln(13/30), approximately 167 m³ of nitrogen. Direct calculation with the displayed inputs gives 167.25 m³, consistent with the handbook's rounded result. The volume exceeds the amount obtained by assuming that the incoming nitrogen replaces only original gas. Under complete mixing, some nitrogen also leaves through the outlet.<ref name="B-181" />
[[File:fse-inerting-v2.svg|thumb|upright=1.5|alt=Methane concentration falls from 30% to 13% as the model adds about 167 cubic metres of nitrogen.|Complete mixing causes an exponential decline in the modelled concentration. Based on Beyler (2002), pp. 2-180–2-181.]]

For the ideal unmixed replacement comparison, the expression 200(30 − 13)/30 gives approximately 113 m³. The mixed-purge result is about 48% greater, using unrounded values. This difference illustrates the influence of the mixing assumption. It does not supply an installation allowance for leaks, poor distribution or uncertain concentration measurements.<ref name="B-180" /><ref name="B-181" />

The source also considers a continuous methane stream released at 1 kg/s. Its graphical construction uses methane and nitrogen proportions of 18% and 82% by volume. Those proportions correspond to molar proportions for the stated gas treatment. The required mass-flow ratio therefore additionally depends on the molecular weights of the two gases.<ref name="B-181" />

Using molecular weights of 16 for methane and 28 for nitrogen gives a nitrogen flow of approximately 7.97 kg/s in that example. Simply multiplying the methane mass flow by 82/18 would omit the molecular-weight conversion. The worked result demonstrates why a volumetric or molar mixture specification cannot be treated as a mass fraction.<ref name="B-181" />

Both examples depend on their selected composition path. Neither the final methane percentage nor the nitrogen flow is a universal target for every methane system. The source's warning about flammable mixing at the exhaust remains relevant. The numerical exercises describe a model of the mixture, not proof of personnel safety or of field performance.<ref name="B-180" /><ref name="B-181" /><ref name="D-184" />

== Dusts and changing process conditions ==

Inerting can also address a [[Dust explosion|dust explosion]] hazard when suspended combustible particles are mixed with air. Zalosh describes reducing oxygen where dust concentration cannot reliably be maintained below its minimum explosible concentration. The control variable is then the oxidant available to the cloud. The relevant limiting concentration remains material-specific.<ref name="Z-404">Zalosh (2002), p. 3-404.</ref>

Dust concentrations observed during normal operation may not represent abnormal conditions. Zalosh gives examples in which vibration or air blasts used to dislodge obstructions produce substantially greater suspended concentrations. Such changes affect the potential combustible cloud. An assessment based only on a routine concentration measurement can therefore miss the state against which inerting is intended to provide protection.<ref name="Z-404" />

Different dusts do not have one common oxygen limit. The handbook distinguishes organic materials from some metal powders requiring substantially lower concentrations. Temperature also affects the reported dust limits. Gas-phase data for a convenient reference fuel cannot replace evidence for the actual powder and process conditions.<ref name="Z-403" /><ref name="Z-404" />

Dust testing and gas testing also use different experimental arrangements. Zalosh describes controlled dispersion, ignition and pressure measurement for dust-cloud assessment. The resulting boundary is associated with those material and test conditions. Its use requires understanding what the test establishes rather than treating a tabulated value as independent of the experiment.<ref name="Z-403" /><ref name="Z-404" />

== Monitoring and interpretation ==

Practical concentration fields can be stratified or otherwise nonuniform. A well-mixed calculation assigns one concentration to the whole volume, while a real process can contain regions with different mixtures. Zalosh identifies that difference as a central issue in applying flammability data. A favourable average does not establish the same composition at every location.<ref name="Z-403" />
[[File:fse-inerting-v3.svg|thumb|upright=1.5|alt=Uniform model and nonuniform vessel mixture are compared alongside the properties of concentration measurement.|Nonuniform mixtures and instrument performance affect the interpretation of an inerting calculation. Based on Zalosh (2002), p. 3-403.]]

Instrument performance introduces another limitation. Accuracy affects how closely the measured concentration represents the gas at the sensor. Response time affects whether changing conditions are detected promptly, while reliability concerns continued availability of the measurement. The source treats these as reasons that an experimental limiting concentration cannot simply become the operating boundary without further assessment.<ref name="Z-403" />

The intended [[Oxygen depletion|oxygen depletion]] also affects people independently of whether flame propagation is prevented. DiNenno identifies oxygen reduction as the physiological concern associated with inert-gas agents. His discussion concerns a specific suppression context; it does not establish safe occupancy for the purge examples above. A combustion calculation cannot substitute for an exposure assessment.<ref name="D-184" />

Finally, maintaining an inerted state is different from calculating an initial gas addition. NUREG-1805 describes control of oxygen in dynamic processing equipment, and Zalosh emphasises changing mixtures and monitoring. The assessment therefore retains the process conditions under which the selected mixture boundary remains applicable. A successful arithmetic dilution result alone does not demonstrate that those conditions persist.<ref name="N-27" /><ref name="Z-403" />

== See also ==
* [[Flame extinction]]

== Notes ==
<references />

== References ==
* Beyler, C. (2002). Flammability limits of premixed and diffusion flames. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 2-7). National Fire Protection Association.
* DiNenno, P. J. (2002). Halon replacement clean agent total flooding systems. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 4-7). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-16). National Fire Protection Association.

[[Category:Explosions & Industrial Fires]]

Hydrogen safety

2026-11-02T16:16:54Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

'''Hydrogen safety''' concerns the assessment and control of fire and explosion hazards associated with hydrogen and its mixtures with an oxidiser. The central questions are whether a combustible mixture can form, whether it can ignite, and what consequences follow. The explosion-prevention principles described by Zalosh distinguish mixture composition from ignition and flame propagation. The EPRI/NRC hydrogen assessment applies that sequence to sources, release scenarios and exposed equipment in nuclear power facilities.<ref name="Z402">Zalosh (2002), pp. 3-402–3-405.</ref><ref name="N1">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-1–N-3.</ref>

Hydrogen presents several features that affect this assessment. It is much lighter than air at ordinary temperatures, can ignite from weak sparks, and burns with a flame that may be difficult to see in daylight. Its flammable range is broad, but depends on the conditions under which propagation is tested. Those properties need to be connected to the particular release and enclosure rather than treated as a complete description of the hazard.<ref name="I2">Iqbal and Salley (2004), p. 16-2.</ref><ref name="I4">Iqbal and Salley (2004), p. 16-4.</ref>

== Source characterisation and release conditions ==

A hydrogen assessment begins with the source rather than a generic concentration limit. The EPRI/NRC report identifies quantity, concentration, temperature and pressure as conditions that vary between applications. Its nuclear-plant examples include storage, generator cooling, process piping and gas generation during battery charging. These applications do not create identical release histories or surrounding conditions.<ref name="Nsource">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-2–N-3.</ref>
[[File:fse-hydrogen-safety-v1.svg|thumb|upright=1.5|alt=Hydrogen source inputs lead to different release, ignition and accumulation scenarios.|Hydrogen source conditions and ignition timing define different scenarios. Based on Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-1–N-3 and N-7–N-11.]]

Stored hydrogen can be supplied as pressurised gas or cryogenic liquid. The report describes gas distribution from storage to users through piping. It separately discusses hydrogen generated within equipment or battery rooms. A finite stored inventory and continuing generation require different descriptions of the amount available during the scenario.<ref name="Nsource" />

Potential release locations include valves, flanges, fittings and relief devices. The opening's position and direction can influence the subsequent flame or gas path. A relief discharge may have a more constrained direction than an unspecified equipment leak. The source description therefore needs both the released material and the physical arrangement through which it escapes.<ref name="N7">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-7–N-8.</ref>

The distinction between a release and its consequences also prevents premature assignment of a damage area. The report first characterises the hydrogen source, then develops scenarios and evaluates potential damage. Its simplified damage rules were devised for the nuclear facilities considered. They do not establish a universal separation distance for every hydrogen installation.<ref name="N1" /><ref name="N11">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-11.</ref>

== Flammable mixtures and propagation direction ==

The [[Flammability limits|flammability limits]] describe the limiting fuel concentrations that permit flame propagation under specified conditions. The lower limit concerns a fuel-lean mixture, while the upper limit concerns a fuel-rich mixture with relatively little available oxygen. A measured limit therefore belongs to a fuel, oxidiser and test condition. It is not simply a property of the hydrogen inventory.<ref name="Z402" /><ref name="I2" />

NUREG-1805 demonstrates the influence of propagation direction. Its room-temperature table gives a lower limit of approximately 4.1% hydrogen by volume for upward propagation, compared with 6.0% horizontally and 9.0% downwards. The listed upper value is 74% for all three directions. The surrounding discussion associates its 4.1% value with 25 °C, atmospheric pressure and saturated humidity.<ref name="Itable">Iqbal and Salley (2004), p. 16-2, Table 16-1.</ref>

{| class="wikitable"
! Propagation direction in the cited room-temperature data !! Lower hydrogen concentration !! Upper hydrogen concentration
|-
| Upward || 4.1% by volume || 74% by volume
|-
| Horizontal || 6.0% by volume || 74% by volume
|-
| Downward || 9.0% by volume || 74% by volume
|}

These differences show why a quoted concentration needs its test context. The higher downward-propagation limit does not make a mixture incapable of burning upwards. Nor does a room-average concentration identify every local mixture. The NUREG discussion of ventilation specifically recognises the possibility of trapped hydrogen pockets, particularly near a ceiling.<ref name="Itable" /><ref name="I11">Iqbal and Salley (2004), p. 16-11.</ref>

Dilution changes the mixture rather than removing the need for assessment. NUREG-1805 discusses added nitrogen, carbon dioxide and steam through flammability diagrams. The resulting combustible region depends on both fuel and oxidiser concentrations. A fuel concentration alone cannot describe the complete state when the oxidiser composition has also changed.<ref name="Idilute">Iqbal and Salley (2004), pp. 16-2–16-5.</ref>

A mixture outside a flammable region can also change as it mixes with another stream. The handbook's flammability-diagram treatment follows composition through dilution or addition of gas. This makes the path between operating states relevant alongside the initial and final states. A single concentration measurement cannot describe every intermediate mixture involved in changing the atmosphere.<ref name="Z402" />

== Ignition and the meaning of sensitivity ==

[[Minimum ignition energy|Minimum ignition energy]] refers to ignition under specified mixture and test conditions. NUREG-1805 shows that hydrogen's required spark energy varies with concentration and increases towards the flammability limits. Dilution can also change the energy requirement. A single quoted minimum therefore cannot describe every hydrogen-containing atmosphere.<ref name="I4" />

Electrical sparks and small static discharges are among the ignition mechanisms identified in that report. Their significance follows from hydrogen-air mixtures being ignitable by weak sources under favourable conditions. This does not mean that every spark ignites every mixture. Composition, the energy delivered and the conditions at the ignition location remain part of the physical problem.<ref name="I4" /><ref name="Z402" />

The EPRI/NRC report warns against inferring low ignition likelihood merely from a relatively high auto-ignition temperature. It discusses low-energy sources and the influence of materials present around the release. Spark ignition and heating to an auto-ignition condition are different mechanisms. A value associated with one does not exclude the other.<ref name="N2">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), p. N-2.</ref>

For lead-acid battery installations, NUREG-1805 identifies abnormal internal short circuits, heated terminals and leakage currents as possible ignition sources. Hydrogen generation and ignition can therefore be associated with the same equipment. That example supports examining equipment condition and local sources together. It does not provide a general electrical equipment classification scheme for every hydrogen application.<ref name="I5">Iqbal and Salley (2004), p. 16-5.</ref>

== Immediate ignition, accumulation and explosion ==

Immediate ignition of a pressurised leak can establish a [[Jet fire|jet fire]]. The direction of the release then helps determine which targets receive direct flame exposure. The EPRI/NRC methodology treats this separately from storage-vessel failure and ignition of an accumulated cloud. The distinction preserves the different source geometries and consequence mechanisms.<ref name="N7" />

Delayed ignition can involve a mixture that has travelled or accumulated before burning. A [[Vapour cloud explosion|vapour cloud explosion]] scenario therefore requires examination of dispersion and the surroundings of the cloud. The report includes outdoor ignition and gas entering a building as separate cases. The eventual ignition location need not coincide with the original equipment leak.<ref name="N8">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-8–N-9.</ref>

Flame propagation also affects the pressure loading. Zalosh distinguishes subsonic deflagration from detonation propagating supersonically through the unburned mixture. Expansion and turbulence can increase the flame speed observed within an enclosure. A description based only on total combustible energy omits the rate and spatial development of that release.<ref name="Zprop">Zalosh (2002), pp. 3-407–3-412.</ref>

The possibility of [[Deflagration-to-detonation transition|deflagration-to-detonation transition]] depends on conditions supporting flame acceleration. The handbook identifies mixture reactivity, elongated geometry, roughness and obstructions among the relevant influences. These factors require scenario-specific examination. The presence of hydrogen alone does not establish that a particular event will develop as a detonation.<ref name="Z412">Zalosh (2002), p. 3-412.</ref>

Thermal and pressure effects also require different target descriptions. Jet impingement concerns local heating, while an explosion imposes a transient pressure history. The same item of equipment can be exposed differently in alternative scenarios. A consequence assessment must identify which mechanism its chosen model actually represents.<ref name="N7" /><ref name="N8" /><ref name="Zprop" />

== Ventilation, migration and connected spaces ==

Hydrogen's low density encourages upward movement, but the surrounding flow and geometry remain relevant. The EPRI/NRC report considers rising outdoor gas together with wind direction and atmospheric conditions. Inside buildings, it considers openings and ventilation connections that allow migration. Buoyancy is consequently one influence on the path, not proof that every release immediately leaves the affected area.<ref name="I2" /><ref name="N8" />
[[File:fse-hydrogen-safety-v3.svg|thumb|upright=1.5|alt=Possible hydrogen paths connect an outdoor release with ducts, rooms and ceiling pockets.|Ventilation connections can transfer hydrogen between release and ignition locations. Based on Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-8–N-11; Iqbal and Salley (2004), p. 16-11.]]

A ventilation intake can connect an outdoor release with an indoor hazard. The report describes examining concentration at the intake, mixing in the ventilation system and possible ignition positions. It separately considers gas moving between compartments through openings and ducts. A building boundary does not automatically interrupt the gas pathway.<ref name="N9">Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-9–N-11.</ref>

Ventilation used to dilute hydrogen also needs a defined source rate and mixing assumption. NUREG-1805 discusses accumulation following loss of ventilation or conditions that permit local pockets. A flow expressed as air changes per hour does not by itself demonstrate uniform concentration. The distribution of supply and exhaust openings is part of the physical arrangement.<ref name="I7">Iqbal and Salley (2004), pp. 16-7–16-11.</ref>

The report's battery-room discussion treats loss of ventilation as a condition requiring attention. Its nuclear-plant provisions and concentration values refer to the particular US documents and editions cited in 2004. Those historical values should not be combined into a universal current setpoint. The relevant operating requirement needs its own applicable document and installation basis.<ref name="Icodes">Iqbal and Salley (2004), pp. 16-6–16-7.</ref>

== An idealised concentration model ==

NUREG-1805 gives a concentration-buildup expression for a constant gas source in a ventilated enclosure. The following form uses its perfect-mixing case, with the mixing factor set to one. It starts with no hydrogen in the represented volume and assumes constant generation and ventilation. The result describes the modelled homogeneous concentration.<ref name="Ieq">Iqbal and Salley (2004), p. 16-9, equation 16-3.</ref>
[[File:fse-hydrogen-safety-v2.svg|thumb|upright=1.5|alt=Two ideal concentration curves approach 0.20% and 0.10% as theoretical air changes increase.|Ideal mixing gives an asymptotic concentration under constant conditions. Based on Iqbal and Salley (2004), p. 16-9, equation 16-3.]]

<div class="fse-equation">C = (G/Q)[1 − exp(−N)]</div>

{| class="wikitable"
! Symbol !! Meaning in this idealised calculation !! Unit
|-
| C || Hydrogen concentration as a volume fraction || dimensionless
|-
| G || Constant hydrogen generation or discharge rate || m³/min
|-
| Q || Constant ventilation airflow rate || m³/min
|-
| N || Number of theoretical air changes elapsed || dimensionless
|}

Gas and air flow rates must use consistent volumetric reference conditions. Their ratio then gives a dimensionless concentration scale. Multiplication of C by 100 expresses the result as volume percent. Confusing a fraction with a percentage would change the reported value by a factor of one hundred.<ref name="Ieq" />

As the number of air changes increases, the exponential term decreases and concentration approaches G/Q in this model. At the start, concentration is zero under the selected initial condition. These features explain the shape of the accumulation history. They do not establish the spatial concentration field in a real room.<ref name="Ieq" />

For illustration, select hydrogen generation of 0.002 m³/min and airflow of 1 m³/min. The limiting model concentration is 0.002, equivalent to 0.20% by volume. After one, three and five theoretical air changes, the calculated values are approximately 0.126%, 0.190% and 0.199%. These selected inputs demonstrate the expression and are not ventilation design criteria.<ref name="Ieq" />

Doubling the selected airflow to 2 m³/min halves the limiting concentration to 0.10%. At the same numbers of theoretical air changes, the corresponding values are approximately 0.0632%, 0.0950% and 0.0993%. This comparison holds generation constant and changes ventilation. It compares air-change counts, not identical elapsed times.<ref name="Ieq" />

The expression contains ventilation flow in the denominator and cannot be evaluated by simply setting that flow to zero. Loss of ventilation requires a suitable accumulation balance and source history. Likewise, a changing source cannot automatically be represented by one constant value. Those changes require a different calculation or justified treatment of successive conditions.<ref name="Ieq" /><ref name="I7" />

== Battery generation and limits of source models ==

Lead-acid batteries provide a source example in NUREG-1805. The report associates substantial hydrogen evolution with charging near full charge and describes the importance of overcharge conditions. Its generation estimate uses cell count, battery capacity and a float-current input. The current depends on the identified cell technology, age, charging voltage and temperature assumptions.<ref name="Ibattery">Iqbal and Salley (2004), pp. 16-1, 16-7–16-8.</ref>

The report explicitly identifies the generation equation as a first-order approximation based on one vendor's recommendations. Its tabulated inputs concern stationary lead-acid cells. They are not evidence that every battery chemistry or operating condition releases the same amount of hydrogen. Applying the equation requires preserving the source's technological and operating scope.<ref name="Ilimit">Iqbal and Salley (2004), p. 16-10.</ref>

Source uncertainty and room mixing uncertainty are separate issues. A carefully calculated room-average concentration can still use an unsuitable generation input. Conversely, an appropriate generation estimate cannot establish the absence of a local pocket if the mixing assumption is unsuitable. The source model and transport model require their own supporting evidence.<ref name="Ilimit" /><ref name="I11" />

== Isolation, exposure and interpretation ==

Extinguishing a visible flame and stopping hydrogen release are different outcomes. The EPRI/NRC discussion highlights the possibility of a flammable cloud forming if gas continues escaping without burning. Its treatment therefore connects isolation actions with the scenario sequence. A changed flame condition does not necessarily mean that the combustible inventory has been removed.<ref name="N1" /><ref name="N7" />

Hydrogen's weakly luminous flame also limits visual interpretation of an exposure. NUREG-1805 notes that the flame may be invisible in daylight. Meanwhile, the SFPE jet discussion treats radiative power and flame impingement as physical quantities requiring appropriate models. Visual brightness alone cannot provide those quantities or justify importing hydrocarbon-jet measurements unchanged.<ref name="I2" /><ref name="Bjet">Beyler (2002), pp. 3-298–3-302.</ref>

Concentration monitoring provides information about the atmosphere at the measurement arrangement. NUREG-1805 identifies hydrogen measurement as part of implementing the battery-room protection measures it describes. The measured quantity remains distinct from a calculated room average or an assumed source rate. Interpreting one as the other would remove the spatial and operational assumptions behind the comparison.<ref name="Imonitor">Iqbal and Salley (2004), p. 16-1.</ref><ref name="I11" />

For structural explosion effects, peak pressure is only part of the loading description. Zalosh also identifies pressure duration, reflection and impulse as relevant to dynamic response. A hydrogen scenario must therefore connect the chosen propagation model with the target's response. Reporting combustible mass alone leaves both that loading history and the response criterion unspecified.<ref name="Z419">Zalosh (2002), p. 3-419.</ref>

The EPRI/NRC methodology explicitly separates scenario development from validation of computational models. Its appendix does not endorse one universal hydrogen consequence tool. A reported result therefore needs the source conditions, ignition branch, geometry, model assumptions and relevant validation. Those details define the consequence that has actually been assessed.<ref name="N11" />

== Notes ==
<references />

== References ==
* Beyler, C. L. (2002). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-11). National Fire Protection Association.
* Electric Power Research Institute, & U.S. Nuclear Regulatory Commission. (2005). ''EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Volume 2, Detailed methodology'' (EPRI 1011989; NUREG/CR-6850).
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.
* Zalosh, R. (2002). Explosion protection. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-402–3-421). National Fire Protection Association.

[[Category:Explosions & Industrial Fires]]

Fireball

2026-11-02T16:16:48Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

'''Fireball''' is a rapidly developing burning cloud that forms when a substantial release of volatile fuel ignites. The burning gases can expand and rise as surrounding air mixes into them. Engineering models commonly represent the cloud by an equivalent sphere, although real fireballs rarely maintain a spherical shape. Their changing dimensions and short lifetime distinguish their thermal exposure from a steady fire.<ref name="B-306">Beyler (2002), p. 3-306.</ref><ref name="B-302">Beyler (2002), pp. 3-302–3-303.</ref>

A fireball can accompany the failure of a pressurised vessel containing a flammable liquefied gas. The vessel failure, release and subsequent combustion are related parts of the event, with different consequences. Radiation from the burning cloud is assessed separately from the pressure effects and fragments associated with vessel rupture.<ref name="N-15">Iqbal and Salley (2004), p. 5-15.</ref> Estimating the thermal exposure requires the participating fuel mass, fireball geometry, burning duration and radiative properties. The position and orientation of the exposed object also influence the radiation it receives.<ref name="B-307-308">Beyler (2002), pp. 3-307–3-308.</ref>

== Formation and the release sequence ==

A pressurised liquid can partly vaporise when its container fails and the pressure falls. The resulting release can include vapour and entrained liquid. Rapid ignition can produce a large burning cloud before the material disperses over a wider area. The quantity participating in this process strongly influences the size of the resulting fireball.<ref name="B-268">Beyler (2002), pp. 3-268–3-269.</ref>

The release geometry helps determine the fire that follows. Immediate ignition of a substantial sudden release can produce a fireball. A continuing release through a relatively small opening can instead sustain a [[Jet fire|jet fire]]. The same stored substance can therefore produce different flame shapes and exposure histories under different failure conditions.<ref name="B-268" />
[[File:fse-fireball-v1.svg|thumb|upright=1.5|alt=Release sequence diagram distinguishing rapid fireball formation from a continuing jet and a delayed cloud fire.|The release and ignition sequence influence the form of the fire. Based on Beyler (2002), pp. 3-268–3-269.]]

Delayed ignition changes the sequence again. Vapour can travel downwind and mix with surrounding air before finding an ignition source. The flame can then propagate through the cloud towards the release location. Beyler describes this moving cloud fire separately from the rapid burning sphere used in the fireball model.<ref name="B-268" /><ref name="B-302" />

Burning can continue after the initial cloud has been consumed. A flame returning towards the release can ignite a remaining pool or a continuing jet. The short fireball or cloud-fire duration therefore does not necessarily describe the complete incident duration. A consequence assessment can require several successive fire exposures within one release scenario.<ref name="B-268" />

A [[BLEVE]] concerns the failure and rapid expansion of a vessel containing liquid above its atmospheric boiling temperature. A fireball describes combustion of released fuel. NUREG-1805 discusses their combined consequences for flammable contents, including radiant exposure and the container becoming a projectile. A radiation calculation alone does not evaluate those mechanical consequences.<ref name="N-15" />

The broader term [[Explosion|explosion]] consequently does not identify the geometry of a fireball or quantify its radiation. Vessel failure can arise through impact, deterioration or weakening under heat, as discussed in the nuclear inspection guidance. Identifying the failure mechanism and ignition sequence precedes selection of a thermal model. A visible burning cloud is only one part of that scenario description.<ref name="N-15" /><ref name="B-268" />

== Growth, buoyancy and burning duration ==

The fireball initially develops through the interaction of fuel release, combustion and mixing with air. Release momentum can dominate its early development. In the momentum-dominated description, the diameter grows rapidly and then changes relatively little during much of the burning period. The handbook illustrates this behaviour using a small LPG cylinder release.<ref name="B-306" /><ref name="B-307">Beyler (2002), p. 3-307.</ref>

Buoyancy provides another influence because the hot gases are less dense than their surroundings. In a buoyancy-dominated fireball, air entrainment governs growth while the burning cloud rises. The fireball can lift away from the ground before combustion ends. A fixed sphere touching the ground therefore represents only one simplified geometric condition.<ref name="B-307" />

These regimes have different time histories even when their predicted maximum diameters are similar. Beyler describes initial diameter growth proportional to the fourth root of time for momentum-dominated releases. The buoyancy-dominated description instead has initial growth proportional to time squared. Those relationships describe the cited idealisations, rather than every stage of an actual irregular flame.<ref name="B-306" /><ref name="B-307" />

The distinction also affects the choice of a representative source position. The average height of the fireball centre is used in simplified radiation geometry. The maximum elevation reached by the burning cloud is a different quantity. Substituting that maximum height for the mean centre would change the distance and angle used to calculate exposure.<ref name="B-307" />

For buoyancy-dominated fireballs, the handbook gives a separate estimate of the time to lift off. It scales with the same mass exponent as the buoyant burning duration and is approximately 40% of that duration. This connection helps describe the sequence of growth and rise. It does not establish a period during which nearby objects are protected from radiation.<ref name="B-307" />

== Estimating diameter and duration ==

The maximum equivalent diameter is primarily related to the mass of released fuel participating in the fireball. Beyler presents the following empirical relationship, with diameter in metres and fuel mass in kilograms. Its numerical coefficient belongs to those units. The equivalent spherical volume simplifies the geometry without asserting that the visible envelope is exactly spherical.<ref name="B-306" />

<div class="fse-equation">D = 5.8 m<sup>1/3</sup></div>

The corresponding duration expressions distinguish momentum-dominated and buoyancy-dominated behaviour. Each gives time in seconds when mass is in kilograms. They are alternative regime descriptions, rather than two consecutive periods that should be added together.<ref name="B-306" />
[[File:fse-fireball-v2.svg|thumb|upright=1.5|alt=Two curves show momentum and buoyancy duration estimates increasing at different rates with participating fuel mass.|The duration correlations use different mass exponents for two release regimes. Based on Beyler (2002), pp. 3-306–3-307.]]

<div class="fse-equation">t<sub>m</sub> = 0.45 m<sup>1/3</sup></div>
<div class="fse-equation">t<sub>b</sub> = 2.6 m<sup>1/6</sup></div>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| D || Maximum equivalent fireball diameter || m
|-
| m || Participating fuel mass || kg
|-
| t<sub>m</sub> || Momentum-dominated duration estimate || s
|-
| t<sub>b</sub> || Buoyancy-dominated duration estimate || s
|}

The diameter relationship does not contain storage pressure explicitly. Its stated independence from pressure assumes that the release conditions are sufficient to vaporise the relevant fuel. It therefore does not establish that pressure has no influence on the event. Pressure affects release dynamics and appears in the chapter's separate correlations for radiative behaviour.<ref name="B-306" /><ref name="B-307" />

For sufficiently large masses, the momentum expression gives a longer duration than the buoyancy expression. Beyler argues that buoyancy remains present and limits the appropriate duration. The chapter consequently uses the buoyancy expression for very large releases, described approximately as above 30,000 kg. Extending the momentum expression indefinitely would ignore this stated limitation.<ref name="B-307" />

Mass and diameter are not proportional. Doubling the participating mass increases the calculated diameter by the cube root of two, approximately 1.26. This follows directly from the diameter correlation. The result concerns maximum equivalent size; it does not establish that radiation at a particular target also increases by exactly the same factor.<ref name="B-306" />

== Representing thermal radiation ==

[[Flame radiation]] transfers energy from the burning cloud to exposed surroundings. The handbook presents point-source and spherical-source representations. Both simplify the changing fireball, but they describe its radiative output in different ways. The selected representation needs compatible geometry and radiative properties to produce a meaningful estimate at a target.<ref name="B-307-308" />

The point-source treatment places the radiative output at a representative centre. Its calculation depends on radiant power, the distance from that centre and the orientation of the target. Heat release is commonly averaged by dividing the available combustion energy by the selected fireball duration. This averaging replaces a changing energy-release history with a constant equivalent rate.<ref name="B-307" />

Only a fraction of the combustion energy is represented as radiation. Beyler reports radiative fractions generally between 0.1 and 0.4 in this treatment. The chapter also presents a pressure-dependent fit whose original data cover 0.2–1.4 MPa. Such a fitted range is part of the model evidence, rather than permission to extrapolate to arbitrary storage conditions.<ref name="B-307" />

The spherical-source treatment instead assigns an average surface emissive power to an equivalent sphere. Emissive power is energy leaving each unit of emitting surface per unit time. The incident flux follows by multiplying it by a geometric view factor and atmospheric transmissivity. These factors distinguish source emission from energy arriving at the receiving surface.<ref name="B-307-308" />

<div class="fse-equation">q″ = τ E F</div>
<div class="fse-equation">F = (r/L)<sup>2</sup> cos θ, when the complete sphere is visible to the target</div>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| q″ || Incident radiant heat flux || kW/m²
|-
| τ || Atmospheric transmissivity || Dimensionless
|-
| E || Average surface emissive power || kW/m²
|-
| F || Geometric view factor || Dimensionless
|-
| r || Equivalent sphere radius || m
|-
| L || Distance from target to sphere centre || m
|-
| θ || Angle between target normal and line to centre || rad
|}

The simple view factor requires the sphere to lie wholly within the receiving surface's field of view. When the surface orientation permits only a portion to be seen, the handbook supplies a different expression. A target facing directly towards the centre has zero angle in the formula above. The surface normal, rather than the surface plane, defines that angle.<ref name="B-307-308" />

Beyler reports measured fireball surface emissive powers between 100 and 450 kW/m². The chapter notes that 350 kW/m² is widely used for the described large-scale releases. This value is a modelling choice supported by that experimental context. It is not the incident heat flux at every object outside the fireball.<ref name="B-307-308" />

== An illustrative spherical-source calculation ==

Consider a selected participating mass of 1,000 kg. This is an illustrative input within the scale of releases discussed in the handbook, rather than a reconstruction of a particular experiment. The diameter correlation gives 58 m. The momentum and buoyancy duration expressions give approximately 4.5 s and 8.2 s respectively.<ref name="B-306" /><ref name="B-307-308" />

For a simplified momentum-dominated geometry, place the average centre at half the diameter above ground, giving 29 m. Select a ground-level target 100 m horizontally from the release. The distance to the centre is then approximately 104 m, obtained from the horizontal and vertical separations. It is this sloping distance that enters the view-factor calculation.<ref name="B-307" />
[[File:fse-fireball-v3.svg|thumb|upright=1.5|alt=A 58 metre equivalent fireball and target illustrate the difference between horizontal distance and distance to the centre.|The target distance is measured to the equivalent fireball centre. Based on Beyler (2002), pp. 3-306–3-308.]]

Assume that the target faces the centre and can see the complete sphere. Its angle is zero, and the calculated view factor is approximately 0.0776. Select the source's 350 kW/m² emissive power and set transmissivity to unity for this illustration. The resulting incident flux is approximately 27 kW/m², calculated without intermediate rounding.<ref name="B-307-308" />

The unity transmissivity assumption represents no atmospheric attenuation along the path. The example therefore isolates the chosen source and geometric factors. A calculation using a different transmissivity would give a different incident value. The result does not establish that the actual atmosphere, flame shape or target orientation matches these assumptions.<ref name="B-307-308" />

Holding that average flux constant for the selected 4.5 s momentum duration gives approximately 122 kJ/m² of incident radiant energy. This is the time integral of the illustrative constant flux. It is not an absorbed skin dose, a prediction of injury severity or a structural temperature. Those outcomes require their own response models and exposure assumptions.<ref name="B-302" /><ref name="B-307-308" />

== Observations and the limits of simple shapes ==

Accident observations illustrate how several consequences can develop within one event. Beyler describes a derailment at Oneonta involving multiple propane tank cars. An initial fireball was associated with a tank splitting open. Its thermal exposure then heated other tanks, followed by further vessel failures. The sequence demonstrates how a short initial release can contribute to continuing escalation.<ref name="B-302" />

The same chapter describes the Crescent City derailment, where impact between tank cars opened a propane container. The escaping gas produced an initial fireball, followed by further events over several hours. Such accounts support considering the surrounding inventory and subsequent fires. They do not mean that the first fireball itself burned for the entire incident duration.<ref name="B-302" />

Experiments provide a more controlled view of the changing geometry. The handbook's illustrated 7.5 kg LPG release has rapid early growth, a period with relatively little diameter change and later cooling with liftoff. Brightness also changes during this sequence. Representing the complete event by one diameter and one emissive power therefore averages physically different stages.<ref name="B-307" />

The assumed shape also needs evidence for the particular release. Beyler reviews an early model that represented unconfined vapour-cloud burning as a fireball, drawing on very small gas releases. Later cold-propane and LNG experiments did not universally exhibit that form. The chapter uses these observations to distinguish fireball calculations from the treatment of propagating cloud flames.<ref name="B-304">Beyler (2002), p. 3-304.</ref>

These different observations have different evidential roles. A documented accident establishes that a sequence can occur, while a controlled experiment can support a particular correlation. Neither automatically provides every input needed for another release. The source's event-tree approach therefore begins with the actual failure and ignition conditions before choosing a geometric model.<ref name="B-268" /><ref name="B-304" />

== Consequences and interpretation ==

The [[Effects of heat on people|effects of heat on people]] depend on both radiation intensity and exposure duration. The fireball's brief lifetime does not remove its potential to cause severe thermal exposure. Equally, a maximum emissive power does not specify what a person receives at a particular position. Distance, orientation and atmospheric transmission intervene between the flame and the exposed surface.<ref name="B-302" /><ref name="B-307-308" />

Property exposure also depends on the receiving object. NUREG-1805 identifies the participating fuel mass, diameter, duration and emissive power as principal fireball inputs. A consequence calculation then relates those inputs to the object being assessed. A single calculated radiation value is an exposure description, rather than a complete prediction of ignition or damage.<ref name="N-15" /><ref name="B-307-308" />

The thermal calculation must also remain separate from the vessel's mechanical hazards. Fragments and pressure effects require information beyond the equivalent radiating sphere. Neither the calculated diameter nor the duration supplies a fragment trajectory or blast pressure. Combining these consequences in an assessment requires identifying each mechanism explicitly.<ref name="N-15" />

Finally, these relationships are empirical engineering models. The participating mass, degree of vaporisation, release regime and representative geometry all influence their applicability. Beyler stresses that consequence methods require judgement about the actual scenario. Accurate arithmetic cannot compensate for assuming a fireball when the release instead produces a travelling cloud, a continuing jet or another fire configuration.<ref name="B-268" /><ref name="B-306" />

== See also ==
* [[Boilover]]

== Notes ==
<references />

== References ==
* Beyler, C. L. (2002). Fire hazard calculations for large, open hydrocarbon fires. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 3-11, pp. 3-268–3-314). National Fire Protection Association.
* Iqbal, N., & Salley, M. H. (2004). ''Fire dynamics tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission fire protection inspection program'' (NUREG-1805). U.S. Nuclear Regulatory Commission.

[[Category:Explosions & Industrial Fires]]

Reliability of fire protection systems

2026-11-02T16:16:42Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

'''Reliability of fire protection systems''' concerns their ability to perform the intended function under specified conditions for the required time or number of operating cycles. Modarres and Joglar-Billoch describe reliability in these terms and distinguish the physical mechanisms of failure from their probabilistic representation. In fire applications, the conditions include the demands and environmental stresses imposed by the fire.<ref name="M-24">Modarres and Joglar-Billoch (2002), pp. 5-24–5-25.</ref>

A reliability value therefore needs an explicit system boundary, success criterion and time basis. It cannot be interpreted adequately as a percentage attached to a product name. The Australian Building Codes Board (ABCB) Data Sheets require the performance level consistent with the system specification to be defined before reliability is estimated.<ref name="A-62">Australian Building Codes Board (2020a), pp. 62–64.</ref> Protection also depends on whether the functioning system is suitable, sufficiently capable and timely for the scenario. Distinguishing these questions makes reliability useful when evaluating an overall fire safety strategy.<ref name="B-194">Barry (2002), pp. 5-194–5-199.</ref>

== Function, boundaries and terminology ==

The intended function determines what counts as success. For a [[Sprinkler system|sprinkler system]], Barry describes the operational chain from water supply through pumps, valves and pipework to discharge at the heads. Whether the discharge controls the selected fire also depends on the design application. Operation and achievement of the protective objective therefore require related but distinct evidence.<ref name="B-203">Barry (2002), pp. 5-203–5-205.</ref><ref name="B-198">Barry (2002), pp. 5-198–5-199.</ref>

A [[Fire alarm system|fire alarm system]] similarly includes more than the sensing device. Barry's functional breakdown connects detection inputs, a control panel and alarms or interlocks. A reliability assessment that stops at detector operation may exclude a necessary downstream function. The boundary should extend to the output actually credited in the fire strategy.<ref name="B-205">Barry (2002), p. 5-205, Table 5-13.7.</ref>

Terminology differs between assessment frameworks. Barry separates response effectiveness, online availability and operational reliability. In this usage, response effectiveness concerns suitability, capacity, duration and response time; availability concerns whether the system is online; operational reliability concerns successful functioning on demand. These categories help identify different reasons why protection may be unsuccessful.<ref name="B-194" /><ref name="B-200">Barry (2002), pp. 5-200–5-203.</ref>
[[File:fse-reliability-of-fire-protection-systems-v1.svg|thumb|upright=1.5|alt=Three cards distinguish response effectiveness, online availability and operational reliability, with a note that definitions vary between sources.|The performance categories separate application, availability and operation in Barry’s framework. Based on Barry (2002), pp. 5-194–5-200, and Australian Building Codes Board (2020a), pp. 58–60.]]

The ABCB Data Sheets use a broader definition of reliability: performance consistent with the system specification. Their examples include isolation for maintenance, common-mode failures, construction defects and doors held open. Efficacy describes achievement of the objective when the system performs to specification in the relevant scenario. The definitions must be matched before numerical values from different studies are compared.<ref name="A-58">Australian Building Codes Board (2020a), pp. 58–60.</ref>

The distinction also matters for passive measures. A barrier does not normally operate in the same sense as a pump, although doors and dampers may need to move. The ABCB framework accommodates performance distributions and defects affecting passive construction. It warns that structural reliability calculations may omit gross defects that prevent the installed protection from meeting its specification.<ref name="A-58" />

Examples of gross defects include unprotected openings, omitted protection and substitution of materials with lower performance. The ABCB Data Sheets distinguish these from ordinary variations already included in an efficacy calculation. This distinction prevents an assessment of correctly constructed protection from being treated as evidence that the installed building necessarily has that protection.<ref name="A-58" />

Success must also retain the required level of fire performance. Barry distinguishes control, suppression and extinguishment when examining capacity. A system that limits growth may meet one objective without meeting another that requires extinction. A numerical probability is meaningful only when the assessment identifies which of these outcomes constitutes successful performance.<ref name="B-198" />

== Availability, demand and duration ==

A system can be unavailable even when none of its components has failed mechanically. Planned inspection, maintenance or testing may require isolation. Repairs, false trips or operational decisions can also leave protection offline. Barry distinguishes this known or projected downtime from hidden faults that prevent operation when an apparently available system is demanded.<ref name="B-200" />

For example, a valve intentionally shut during maintenance represents unavailability in Barry's framework. A valve that is believed ready but obstructs delivery because of hidden degradation represents operational failure on demand. Both can prevent protection, but their evidence and corrective actions differ. Combining them without definitions can omit failures or count the same failure twice.<ref name="B-203" />

The mission includes continued functioning for the required duration. Successful starting does not establish that delivery, power or another necessary function will persist long enough. Modarres and Joglar-Billoch define reliability over a stated time, while Barry includes mission-time failure when examining operational performance. The required duration must follow from the protective function being credited.<ref name="M-24" /><ref name="B-204">Barry (2002), p. 5-204.</ref>

Response time is a separate constraint on useful operation. Barry evaluates protective actions against the time at which critical conditions arise at the target. A technically functioning system can respond too late for the objective. Its activation probability and its probability of responding before that deadline therefore cannot be treated as interchangeable descriptions.<ref name="B-199">Barry (2002), pp. 5-199–5-200.</ref>

Inspection and testing influence more than one part of performance. Taking equipment offline temporarily reduces availability, while the same activity may reveal hidden failures and improve subsequent operation. Barry describes this balance explicitly. An assessment should retain both effects instead of treating maintenance frequency as an automatic increase or decrease in overall reliability.<ref name="B-202">Barry (2002), p. 5-202.</ref>

False activations can also affect future availability and response. Barry describes investigations and repairs that require shutdown, extended bypasses after nuisance alarms, and occupants becoming less responsive after repeated false alarms. These mechanisms illustrate why operational history matters. A description of the installed equipment alone does not capture the conditions under which protection will be demanded.<ref name="B-202" />

== Modelling system success ==

Reliability models describe the logical requirements for success. Modarres and Joglar-Billoch explain that a reliability block diagram need not reproduce the physical arrangement of equipment. A series representation means that every represented function is required. A parallel representation means that at least one alternative can meet the complete stated requirement.<ref name="M-31">Modarres and Joglar-Billoch (2002), pp. 5-31–5-32.</ref>

For two independent functions assessed over the same mission, the simple series and parallel expressions are shown below. R<sub>1</sub> and R<sub>2</sub> are their dimensionless success probabilities. The parallel expression applies only when either function alone is sufficient. Physical duplication does not establish either independence or sufficient capacity.<ref name="M-32">Modarres and Joglar-Billoch (2002), p. 5-32, equations 37 and 42–43.</ref>

<div class="fse-equation">R<sub>series</sub> = R<sub>1</sub> × R<sub>2</sub></div>
<div class="fse-equation">R<sub>parallel</sub> = 1 − (1 − R<sub>1</sub>)(1 − R<sub>2</sub>)</div>

{| class="wikitable"
|+ Symbols in the reliability expressions.<ref name="M-32" /><ref name="H-184" />
! Symbol !! Meaning !! Unit
|-
| R<sub>1</sub>, R<sub>2</sub> || Success probability of each modelled function over the specified mission || 1, dimensionless
|-
| R<sub>series</sub> || Success probability when both independent functions are required || 1, dimensionless
|-
| R<sub>parallel</sub> || Success probability when either independent alternative alone is sufficient || 1, dimensionless
|-
| R<sub>system</sub> || Complete-system success probability, including shared requirements || 1, dimensionless
|}

The first expression requires both functions to succeed. The second calculates the probability that both alternatives fail and subtracts it from one. The probabilities must refer to compatible conditions and durations. Changing the success requirement can change the model structure even when the physical equipment remains identical.<ref name="M-31" /><ref name="M-32" />

Standby arrangements require additional attention. A reserve function may depend on detecting the need for transfer, successfully switching and then operating for the remaining mission. Modarres and Joglar-Billoch discuss these requirements separately from simple parallel operation. Treating a standby unit as an automatically successful replacement can omit the functions needed to bring it into service.<ref name="M-33">Modarres and Joglar-Billoch (2002), pp. 5-33–5-34.</ref>

[[Fault tree analysis]] provides a way to represent combinations of failures that defeat a required function, including shared support and human actions. [[Event tree analysis]] places system success or failure within the sequence following initiation. The supporting reliability model and the event-tree branch must use the same operational requirement and scenario conditions.<ref name="M-35">Modarres and Joglar-Billoch (2002), pp. 5-35–5-38.</ref><ref name="B-194" />

== Worked example with a shared supply ==

Consider a hypothetical model with two alternative delivery paths. Either path alone can meet the full requirement for the same specified mission. Given that a necessary shared supply succeeds, each path has success probability 0.95. Their remaining failures are assumed independent under that condition. These values are teaching assumptions, not measured fire-pump or sprinkler reliabilities.<ref name="M-32" /><ref name="H-184">Hall (2002), p. 1-184.</ref>
[[File:fse-reliability-of-fire-protection-systems-v2.svg|thumb|upright=1.5|alt=A shared supply feeds two alternative successful delivery paths in a logical reliability block diagram.|The shared supply remains necessary even when either delivery path can meet the requirement. Based on Modarres and Joglar-Billoch (2002), pp. 5-31–5-32 and pp. 5-36–5-38; numerical inputs are hypothetical.]]

Under those assumptions, both paths fail with probability 0.05 multiplied by 0.05, or 0.0025. The probability that at least one succeeds is therefore 0.9975. This result describes the alternative paths conditional on successful shared supply. It does not yet describe the complete arrangement, because the necessary shared function has not been included.<ref name="M-32" /><ref name="H-184" />

Now assign the shared supply a hypothetical success probability of 0.98 over the required mission. The complete arrangement succeeds only when that supply succeeds and at least one delivery path succeeds. Hall's conditional-probability rule allows the shared probability to be multiplied by the conditional parallel result. The shared function is counted once.<ref name="H-184" /><ref name="M-37">Modarres and Joglar-Billoch (2002), pp. 5-36–5-38.</ref>

<div class="fse-equation">R<sub>system</sub> = 0.98 × 0.9975 = 0.97755 ≈ 0.978</div>

{| class="wikitable"
|+ Results for the hypothetical model, reported to three significant figures.<ref name="M-32" /><ref name="H-184" />
! Assessment boundary !! Success probability !! Failure probability
|-
| Alternative paths, given successful shared supply || 0.998 || 0.00250
|-
| Complete arrangement including shared supply || 0.978 || 0.0225
|}

The complete failure probability is approximately 0.0225, or 2.25%, compared with 0.250% for the alternatives when shared-supply success is certain. The difference arises from the necessary shared function. It does not mean redundancy has no benefit; it means the independent parallel calculation describes only part of the system boundary.<ref name="M-32" /><ref name="H-184" /><ref name="M-37" />
[[File:fse-reliability-of-fire-protection-systems-v3.svg|thumb|upright=1.5|alt=Two bars compare failure probabilities of 0.250% for the alternative paths and approximately 2.25% for the complete arrangement.|The model boundary changes the calculated failure probability when a necessary shared supply is included. Based on Modarres and Joglar-Billoch (2002), p. 5-32, and Hall (2002), p. 1-184; numerical inputs are hypothetical.]]

The same result can be checked by separating two mutually exclusive failure cases. Shared-supply failure contributes 0.02. When that supply succeeds, simultaneous residual failure of the two paths contributes 0.98 multiplied by 0.0025, or 0.00245. Adding these contributions gives the unrounded result 0.02245 without counting the shared failure twice. Intermediate products remain unrounded; final reported probabilities use three significant figures.<ref name="H-184" />

== Dependencies and common failures ==

[[Common cause failure]] can defeat several protective functions through one cause. Barry identifies loss of water or power, freezing, flooding and mechanical damage as relevant mechanisms. These cannot be represented adequately by assuming that every component or system fails independently. Their significance depends on which functions share the affected resource or exposure.<ref name="B-CCF">Barry (2002), pp. 5-201–5-204.</ref>

Modarres and Joglar-Billoch illustrate two suppression paths with shared water, power and actuation dependencies. Their example explicitly requires those dependencies to be included when quantifying failure. Separate pumps or nozzles do not remove a common dependency elsewhere in the chain. The analysis must follow each credited function back through its supporting functions.<ref name="M-37" />

Dependencies may also connect different types of protection. The ABCB handbook describes detection affecting occupant warning, notification of the fire service and smoke management. Their contributions cannot be evaluated solely as unrelated equipment percentages. The assessment must consider how one unsuccessful upstream function changes the conditions for each subsequent action.<ref name="A-H122">Australian Building Codes Board (2020b), pp. 120–122.</ref>

A useful model therefore identifies shared resources and common exposures before assigning independent probabilities. Where independence is not appropriate, conditional probabilities can represent the relevant relationships. Hall's definition makes clear that dependence does not require one event to cause another directly. Both may depend on a third condition that the model must retain.<ref name="H-184" /><ref name="B-CCF" />

== Data, uncertainty and continued validity ==

[[Fire statistics]] can inform reliability only when the observations match the success definition and assessed population. The ABCB Data Sheets identify historical data, fault and event trees, technical literature and expert judgement as available approaches. They also explain that evidence differs between active devices and passive construction, for which the pre-fire condition may be difficult to reconstruct.<ref name="A-62" />

Plant records can reflect the actual equipment, environment and maintenance programme, but their limitations remain important. Barry notes unrecorded failures, incomplete logs and short observation histories. Generic published data may cover different designs or operating conditions. Any adjustment requires an explicit basis rather than assuming the generic average describes the particular installation.<ref name="B-205206">Barry (2002), pp. 5-204–5-206.</ref>

Evidence at component level should not be mistaken for evidence at complete-system level. A recorded pump start does not, on its own, demonstrate that valves, distribution and discharge met the specified requirement. Barry's input, control and output breakdown identifies the interfaces that remain outside such an observation.<ref name="B-205" />

Failure rates and reliability probabilities are different quantities. A rate relates failures to time, whereas reliability concerns survival or successful performance over a specified interval. Modarres and Joglar-Billoch discuss several possible failure-time distributions. A constant-rate model is one assumption, not a universal property of fire protection equipment.<ref name="M-2529">Modarres and Joglar-Billoch (2002), pp. 5-25–5-29.</ref>

An absence of recorded failures does not establish perfect reliability. Modarres and Joglar-Billoch explain that estimates and confidence depend on the amount and quality of data and the assumed model. A short successful history leaves uncertainty about rare failures. The reported result should preserve that uncertainty rather than replace it with an unsupported value of one.<ref name="M-2529" />

The evidence basis can change during the building's life. Barry identifies age, environment, maintenance, testing, management of change and physical-damage exposure as relevant influences. The ABCB's 2020 data framework assumes appropriate installation, commissioning and continuing maintenance. Those historical assumptions need checking before its estimates are applied to an existing system.<ref name="B-207">Barry (2002), pp. 5-206–5-207.</ref><ref name="A-61">Australian Building Codes Board (2020a), pp. 61–62.</ref>

The practical consequence appears when comparing protection alternatives. The ABCB handbook presents two systems with equivalent outcomes when functioning but different failure probabilities. A deterministic assessment of successful operation alone would miss that difference. Probability information must therefore be combined with the consequences of each state before concluding that the alternatives provide equivalent protection. The same comparison must retain consequences of failure, rather than treating reliability as a complete measure of fire risk.<ref name="A-H118">Australian Building Codes Board (2020b), pp. 118–119.</ref>

A reliability assessment should retain the function, scenario, duration, boundary, dependencies, evidence and uncertainty supporting each value. These details allow later changes to be evaluated against the original assumptions. They also connect the numerical estimate to the maintenance and operational conditions needed for the credited protection to remain available and effective.<ref name="B-204" /><ref name="B-207" /><ref name="A-61" />

== See also ==
* [[Fire water supply]]
* [[Fire scenario]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Fire safety verification method data sheets: Handbook annex'' (Version 1.1).
* Australian Building Codes Board. (2020b). ''Fire safety verification method handbook'' (Version 1.1).
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 5-13, pp. 5-176–5-213). National Fire Protection Association.
* Hall, J. R., Jr. (2002). Probability concepts. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 1-11, pp. 1-182–1-192). National Fire Protection Association.
* Modarres, M., & Joglar-Billoch, F. (2002). Reliability. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 5-3, pp. 5-24–5-39). National Fire Protection Association.

[[Category:Fire Risk Analysis]]

Individual risk

2026-11-02T16:16:36Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

'''Individual risk''' expresses the likelihood of a specified injury or death affecting an individual at a defined location or under defined exposure conditions. Barry describes it relative to a fire or explosion source. His location-based contours show the expected frequency of events capable of causing the specified harm, regardless of whether anyone actually occupies the location.<ref name="B210">Barry (2002), p. 5-210.</ref>

The quantity therefore needs an explicit meaning before it can support a decision. A geographical measure for a continuously exposed hypothetical person differs from the risk experienced by somebody whose presence and protective actions vary. The ABCB Handbook also distinguishes individual risk from the likelihood of multiple deaths within a building. These measures answer related but different questions.<ref name="B210" /><ref name="A22">Australian Building Codes Board (2020), p. 22.</ref>

An assessment combines the frequency of relevant scenarios with their potential consequences. Its numerical result remains conditional on the selected harm endpoint, exposure assumptions and evidence. Presenting the result as a contour, profile or single value does not remove those conditions.<ref name="B176">Barry (2002), p. 5-176.</ref><ref name="B211">Barry (2002), p. 5-211.</ref>

== Defining the person, location and harm ==

The definition of harm sets the question being answered. A calculation concerned with fatality cannot be relabelled as a calculation of any injury. Barry notes uncertainties in fatal thermal, blast and toxic exposures. Assumptions and judgements about these endpoints require documentation, including when the assessment extends from fatalities to injuries.<ref name="B211" />

The exposure description is equally important. A location-based measure can describe the potential for harm at a fixed position without estimating the actual number of people present. This is useful for displaying a geographical pattern. It should not be interpreted as a population casualty estimate merely because the contour crosses an occupied area.<ref name="B210" />

An actual-person interpretation requires assumptions about the circumstances of exposure. Barry identifies population presence and the reliability of mitigation, including evacuation, when extending an assessment to people around a facility. These assumptions distinguish potential exposure from realised consequences. Their treatment needs to remain consistent between the scenario calculations and the reported risk measure.<ref name="B211" />

Within [[Fire risk|fire risk]] assessment, individual risk is therefore a defined output rather than a complete description of safety. It can identify locations or scenarios needing attention, but it does not describe every consequence of a fire. Property damage, interruption and the number of people affected may require other outputs alongside the individual measure.<ref name="B176" /><ref name="B210" />

The ABCB Handbook lists simple tenability limits, fractional effective dose models and [[Probit function|probit functions]] as forms of human exposure model. These categories describe alternative representations of human response. Their endpoint and interpretation need to be identified before using the outputs in an individual-risk calculation.<ref name="A110">Australian Building Codes Board (2020), p. 110.</ref><ref name="B211" />

== Combining scenario frequencies and conditional harm ==

The basic calculation connects how often a scenario occurs with what follows when it occurs. Barry expresses risk as event frequency multiplied by expected consequence and describes summing contributions from selected scenarios. For individual harm, a conditional probability can represent the consequence term, provided its endpoint and exposure assumptions are specified.<ref name="B176" /><ref name="B208">Barry (2002), pp. 5-208–5-209.</ref>
[[File:fse-individual-risk-v1.svg|thumb|upright=1.5|alt=Scenario frequencies and conditional harm probabilities combine into individual risk.|Individual risk combines distinct scenario contributions under stated exposure assumptions. Based on Barry (2002), pp. 5-176 and 5-208–5-210.]]

The following expression is a specialisation of that frequency–consequence approach. It represents the expected annual frequency of the selected harm at a location. The scenarios must be distinct contributions to the model, so that an initiating event and its own outcome branches are not counted twice.<ref name="B208" />

<div class="fse-equation">R(x) = Σ<sub>i</sub> f<sub>i</sub> p<sub>i</sub>(x)</div>

{| class="wikitable"
! Symbol !! Meaning !! Unit
|-
| R(x) || Expected frequency of the selected harm at location x || year<sup>−1</sup>
|-
| f<sub>i</sub> || Frequency of distinct scenario i || year<sup>−1</sup>
|-
| p<sub>i</sub>(x) || Conditional probability of the selected harm at x, given scenario i and the stated exposure assumptions || dimensionless
|-
| x || Defined location || location identifier or spatial coordinates
|}

Frequency and probability have different units. In this expression, a frequency per year multiplied by a dimensionless conditional probability produces a frequency per year. Calling that result an exact annual probability would introduce a further interpretation that the expression itself does not establish. The report should retain the quantity and units actually calculated.<ref name="B176" /><ref name="B210" />

The scenario frequencies already need to incorporate the relevant sequence of events. If a frequency includes failed suppression, that failure should not be applied again within the same contribution without a clear reason. Barry's scenario approach connects initiating conditions, protection performance and outcomes before combining their risk contributions.<ref name="B208" />

[[Quantitative risk assessment|Quantitative risk assessment]] supplies this broader structure. A single exposure calculation gives information about a consequence under selected conditions. It does not establish how often those conditions arise. Conversely, an initiating-event frequency cannot determine individual harm until the subsequent scenario and exposure have been represented.<ref name="B176" /><ref name="B208" />

== A numerical illustration ==

Consider three distinct hypothetical scenarios affecting one selected location. Assume a person is present there for the exposure represented in every case. The frequencies and conditional probabilities below are chosen solely to demonstrate arithmetic. They are neither incident data nor recommended design values.<ref name="B208" />

{| class="wikitable"
! Scenario !! Frequency (year<sup>−1</sup>) !! Conditional probability of harm !! Contribution (year<sup>−1</sup>)
|-
| A || 0.001 || 0.10 || 0.000100
|-
| B || 0.0002 || 0.50 || 0.000100
|-
| C || 0.00005 || 0.90 || 0.000045
|-
| Total || Not applicable || Not applicable || 0.000245
|}

Scenario A occurs five times as frequently as B, but its conditional probability of harm is one fifth as large. Their contributions are consequently equal. Scenario C has the highest conditional harm probability but the smallest contribution because its assumed frequency is lower. Ranking consequences alone would therefore give a different order from ranking these risk contributions.<ref name="B176" /><ref name="B208" />
[[File:fse-individual-risk-v2.svg|thumb|upright=1.5|alt=Scenarios A and B contribute equally; C contributes less despite its higher conditional harm probability.|Equal contributions can result from different frequencies and conditional probabilities in this hypothetical example. Based on Barry (2002), pp. 5-176 and 5-208–5-209.]]

The first two scenarios each contribute approximately 40.8% of the total; C contributes approximately 18.4%. These proportions can help identify which assumptions drive the result. They do not show which intervention is feasible, reliable or proportionate. Barry treats selecting risk-reduction measures as a subsequent analysis of the available options.<ref name="B211" />

For a second arithmetic case, reduce only B's conditional probability from 0.50 to 0.10. Its contribution becomes 0.000020 per year, and the total becomes 0.000165 per year. This illustrates consequence reduction with unchanged initiating frequencies. It does not demonstrate that a particular protection system can deliver the assumed change.<ref name="B176" /><ref name="B211" />

Neither total establishes acceptability. No acceptance threshold, justified scenario frequencies or validated harm relationships have been supplied in this illustration. The example shows how inputs combine and how one selected change affects the output. A building or facility conclusion requires evidence for those inputs and an independently defined decision criterion.<ref name="B208" /><ref name="A44">Australian Building Codes Board (2020), p. 44.</ref>

== Profiles, contours and population measures ==

A risk profile plots a selected measure against distance or another specified spatial path. A contour connects locations having the same potential individual risk. Barry describes both presentations as ways to communicate the geographical distribution of fire and explosion risk. The harm endpoint and exposure convention must accompany either display.<ref name="B210" />
[[File:fse-individual-risk-v3.svg|thumb|upright=1.5|alt=Two locations on one schematic contour share the same defined potential individual risk.|A contour joins locations with the same potential individual risk under a defined exposure convention. Based on Barry (2002), p. 5-210.]]

Contour geometry depends on the scenario analysis. The source presents an industrial layout with different activities and surrounding land uses, rather than a universal circular boundary. A schematic contour therefore cannot substitute for calculated exposure fields. Likewise, a profile along one direction does not describe every other direction around a facility.<ref name="B210" />

[[Societal risk|Societal risk]] additionally considers multiple casualties. Barry describes cumulative frequency–fatality curves and the information needed about the exposed population, its presence and mitigation. An individual-risk contour alone does not contain that population information. Two assessments can consequently have similar individual measures while involving different numbers of exposed people.<ref name="B210" /><ref name="B211" />

The ABCB Handbook calls for individual and societal risk to be considered together in its comparative building strategy. This makes the distinction relevant even when the assessment compares two designs rather than mapping an industrial site. A design change affecting occupancy can alter the population consequence without an equivalent change in the potential harm at one location.<ref name="A22" />

== Evidence, uncertainty and comparison ==

Scenario frequency estimates can draw on plant records, generic information and expert judgement. Barry discusses their quality alongside maintenance, testing and common-cause effects. A numerical estimate should therefore retain its origin and applicability. A rate drawn from another operating context is not automatically a measured rate for the installation being assessed.<ref name="B206">Barry (2002), pp. 5-206–5-207.</ref>

Uncertainty also enters the consequence calculation and the conversion from exposure to harm. Barry recommends documenting the judgements behind human-risk endpoints and discusses uncertainty bands when presenting results. Reporting many decimal places cannot compensate for uncertain inputs. The useful precision of the result depends on the evidence supporting the calculation.<ref name="B208" /><ref name="B211" />

The purpose of the comparison determines which output is useful. Barry distinguishes comparisons of design, operational and protection options and warns against presentation that hides resolution or introduces bias. The same endpoint, exposure convention and scenario basis are needed to interpret differences between alternatives. A changed definition can otherwise appear as a changed risk.<ref name="B211" />

The ABCB Handbook illustrates a reference-building approach for deriving comparative individual and societal risk criteria. That historical framework does not provide a universal numerical limit for every building or industrial installation. The selected reference and departures need to be documented so the calculated difference can be related to the assessment's objectives.<ref name="A44" />

Risk reduction can address scenario frequency, consequence severity or both. Barry identifies equipment reliability, ignition prevention, detection and protection among the available approaches. The resulting individual-risk estimate remains conditional on their assumed performance. A useful report therefore connects the numerical result with the specific conditions and measures needed to maintain it.<ref name="B211" />

== See also ==
* [[Acceptance criteria]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020). ''Fire safety verification method handbook'' (Version 1.1).
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 5-176–5-213). National Fire Protection Association.

[[Category:Fire Risk Analysis]]

Fire safety concepts tree

2026-11-02T16:16:29Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

The '''fire safety concepts tree''' is a graphical framework for relating fire safety objectives to alternative ways of preventing ignition or managing its consequences. Meacham describes it as a representation of the deliberations and professional judgements of the relevant NFPA technical committee. It provides one structured view of building fire safety and the functions needed to achieve its objectives.<ref name="M158">Meacham (2002), p. 5-158.</ref>

The two primary branches are preventing fire ignition and managing fire impact. If ignition is not prevented, the second branch directs attention to the building's ability to manage the fire and protect exposed people or things. The tree therefore connects an objective with strategies and supporting functions, rather than simply listing installed equipment.<ref name="M158" />

The framework can also help organise further analysis. The ABCB Handbook adapts part of it to show interactions among suppression, structural performance, occupant movement and fire brigade intervention. Such an adaptation needs additional information about timing, consequences and system performance before it becomes a quantitative risk assessment.<ref name="A120">Australian Building Codes Board (2020), p. 120.</ref>

== Objectives and the top-level alternatives ==

[[Fire safety objectives|Fire safety objectives]] define the outcome the strategy is intended to achieve. Meacham's wider risk framework identifies life, property, business continuity, heritage and environmental interests as possible concerns. These interests need not have identical measures of success. The objective at the top of a tree should therefore be meaningful for the assessment being undertaken.<ref name="M153">Meacham (2002), p. 5-153.</ref>

The top-level division separates prevention from management of impact. In the partial tree reproduced by Meacham, these branches form an alternative relationship. Achieving the objective requires the relevant prevention or impact-management function to succeed. This is a logical statement about the selected objective, rather than a claim that either branch always succeeds in practice.<ref name="M158" />
[[File:fse-fire-safety-concepts-tree-v1.svg|thumb|upright=1.5|alt=An objective branches to preventing ignition or managing fire impact, with the documented lower functions.|The top-level concepts connect the objective with ignition prevention and management of fire impact. Based on Meacham (2002), p. 5-158, Figure 5-12.4.]]

The prevention side identifies control of heat-energy sources, control of interactions between sources and fuel, and control of fuel. These headings direct attention to different parts of the ignition problem. They do not prescribe a particular detector, barrier or operating procedure. A project-specific assessment must identify how the relevant functions are implemented and supported.<ref name="M158" />

The impact-management side divides into managing the fire and managing those exposed. This distinction allows the assessment to examine both the development of the hazard and the circumstances of exposure. It also explains why preventing ignition is not the only route considered when a fire is already assumed to occur.<ref name="M158" />

The partial diagram in the handbook is attributed to [[NFPA]] and points to its guide for the complete tree. The diagram establishes the top-level concepts discussed here. It does not supply every lower branch, project-specific design condition or requirement that might appear in a separate edition of that guide.<ref name="M158" />

== Functions, equipment and causal sequences ==

A [[Fire safety strategy|fire safety strategy]] connects these functions with the measures available in a building. The ABCB Handbook's adaptation illustrates suppression by building users, automatic systems and the fire brigade. It also includes structural containment and occupant protection. Several measures can therefore contribute to related outcomes, while a single component can support more than one function.<ref name="A121">Australian Building Codes Board (2020), pp. 120–122, Figure 12.2.</ref>

Meacham's causal-sequence discussion provides another way to understand that distinction. It connects initiating events, outcomes, exposure and consequences. An intervention can act at different stages of this sequence. Altering the initiating conditions, blocking exposure and limiting a consequence are different forms of action, even when each contributes to the same ultimate objective.<ref name="M157">Meacham (2002), p. 5-157.</ref>

The source illustrates this with a shelter containing an open fire and obstructed ventilation. Possible interventions concern the heating arrangement, the obstruction, the fire itself or the occupants' exposure. The example shows why a strategy should identify what a measure changes. Naming the component alone does not explain its position in the causal chain.<ref name="M157" />

The tree can consequently guide an examination of a failed or unavailable function. Meacham explicitly describes evaluating fire-impact management when ignition prevention is unsuccessful. This preserves the connection with the objective while changing the conditions under consideration. It does not require pretending that the failed function remains available in the subsequent analysis.<ref name="M158" />

== Alternative and combined conditions ==

Different logical relationships occur within a strategy. Some outcomes can be achieved through alternatives, while others require several conditions together. The ABCB adaptation illustrates alternative interventions against structural collapse. Within that illustration, a successful intervention can interrupt progression towards the stated adverse outcome.<ref name="A122">Australian Building Codes Board (2020), p. 122.</ref>

The same source describes unassisted evacuation through a combined set of conditions. Detection and alarm must lead the occupant to move. Suitable movement means, a safe destination and the person's ability to evacuate without assistance are also required. Failure of a required condition can defeat that particular evacuation path.<ref name="A122" />
[[File:fse-fire-safety-concepts-tree-v2.svg|thumb|upright=1.5|alt=Five required conditions connect through AND to the illustrated unassisted evacuation outcome.|The illustrated unassisted evacuation path requires several conditions together. Based on Australian Building Codes Board (2020), p. 122.]]

Movement means include capacity, route completeness, protected paths and access to the route in the Handbook's description. A warning signal alone therefore does not establish successful evacuation. The combination concerns the complete function represented in the example, including the physical route and the person using it.<ref name="A122" />

These relationships explain the connection with [[Fault tree analysis|fault tree analysis]]. Meacham places fault and event trees among methods for examining initiating events and outcomes. However, a concepts diagram does not itself provide failure rates or prove that its branches are independent. A numerical model needs those additional definitions and supporting evidence.<ref name="M158" /><ref name="A120" /><ref name="A122" />

The interpretation also depends on the objective being tested. A successful action against collapse does not automatically demonstrate that all occupants avoided harmful exposure before that action. The ABCB discussion treats frequency analysis and consequence analysis separately, with consequence criteria selected for the scenario. The logical outcome and the performance criterion must remain connected.<ref name="A122" />

== Timing and a detector-dependency example ==

The order and timing of actions affect whether a function succeeds. The ABCB Handbook warns that many outcomes in its adapted diagram depend on relative timing. A box labelled suppression therefore represents more than eventual water application. The action must occur under conditions that allow it to achieve the outcome assigned to that branch.<ref name="A120" />

Consider the detection system in the Handbook's qualitative example. Its failure can affect occupant warning, delay the call to the fire brigade and prevent linked active smoke control from operating. These effects reach different parts of the strategy, despite originating in one failed system. Drawing three separate branches does not make their initiating support independent.<ref name="A122" />
[[File:fse-fire-safety-concepts-tree-v3.svg|thumb|upright=1.5|alt=A shared detector supplies occupant warning, the fire brigade call and linked smoke control.|One detection-system failure can affect several functions within the fire safety strategy. Based on Australian Building Codes Board (2020), p. 122.]]

The first step in reviewing this example is to identify each function that uses the detection output. The next is to examine what the assumed failure changes in each affected sequence. For occupant movement, this includes the warning and movement conditions. For intervention and smoke control, the source identifies corresponding delays or failures of activation.<ref name="A122" />

A model that credits every affected function as available would miss the stated dependency. A model that assigns unrelated failure probabilities without examining the shared detector could also misrepresent it. The source specifically calls for these interrelationships to be considered when comparing different protection approaches in reference and proposed buildings.<ref name="A122" />

The example does not establish a numerical probability of unsuccessful evacuation or a universal delay. No such inputs have been assigned. Its purpose is to show how the concepts help expose a shared dependency before the analyst selects detailed calculations. The eventual outcome still depends on timing, remaining functions and the consequence criteria.<ref name="A120" /><ref name="A122" />

== From a concepts tree to risk assessment ==

[[Fire risk assessment|Fire risk assessment]] requires information beyond the conceptual arrangement. Meacham distinguishes the valued interest, the hazard that can cause harm and the likelihood of the unwanted outcome. The tree can help organise the relationships among these elements. It cannot supply missing frequency or consequence evidence simply through additional branches.<ref name="M153" /><ref name="M158" />

The ABCB Handbook describes combining event-tree treatment of frequencies or probabilities with deterministic analysis of selected consequences. Its adapted concepts diagram is only a partial, stylised event tree. A single action box can require a more detailed event tree of its own when the underlying operation and failure modes matter to the assessment.<ref name="A119">Australian Building Codes Board (2020), pp. 119–120.</ref>

This distinction supports proportionate detail. An analyst may begin with the top-level functions to identify relevant interactions, then develop the branches needed to examine the design question. The level of frequency analysis in the Handbook depends on the scenarios and the differences between the reference and proposed solutions. More boxes alone do not establish a better-supported result.<ref name="A120" />

A review should preserve the objective, the meaning of success and failure, shared dependencies and relevant timing assumptions. The resulting structure can then direct attention to the evidence needed for each function. Its value lies in making those connections visible while keeping the qualitative framework distinct from the calculations used to evaluate it.<ref name="M158" /><ref name="A120" /><ref name="A122" />

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020). ''Fire safety verification method handbook'' (Version 1.1).
* Meacham, B. J. (2002). Building fire risk analysis. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 5-12). National Fire Protection Association.

[[Category:Fire Risk Analysis]]

Event tree analysis

2026-11-02T16:16:24Z

Emma: Add 3 watermarked SVG illustrations from the Advanced visual plan

'''Event tree analysis''' ('''ETA''') is an inductive method that follows an initiating event through possible subsequent events to distinct outcomes. In fire safety engineering, its branches describe how fire development, protection and human actions can alter the sequence. Barry identifies initiating events, intermediate events and outcomes as its principal elements, with the intermediate probabilities conditional on the preceding sequence.<ref name="B-180">Barry (2002), pp. 5-180–5-181.</ref>

An event tree makes the structure of a [[Fire scenario|fire scenario]] explicit. Each complete path describes one combination of events from initiation to a final state. Quantification adds probabilities or frequencies to this structure; assessing harm requires a further consequence analysis.<ref name="I-4">Australian Building Codes Board et al. (2005), p. 2.2-4.</ref><ref name="B-188">Barry (2002), pp. 5-188–5-190.</ref> The method therefore supports [[Quantitative risk assessment|quantitative risk assessment]] by connecting the likelihood of initiating conditions with the possible performance of protective measures. Its value depends on meaningful event definitions, appropriate conditional probabilities and a defensible account of the resulting consequences.<ref name="A-119">Australian Building Codes Board (2020), pp. 118–119.</ref>

== Boundaries and event sequence ==

An event tree begins with a clearly defined initiating event. This may be ignition in a particular enclosure, failure of equipment or release of a flammable substance. These starting points describe different populations of incidents. A release frequency cannot serve as a fire frequency unless the probability and circumstances of ignition are also represented.<ref name="B-181">Barry (2002), pp. 5-181–5-183.</ref>

The scope establishes what the analysis includes before branches are drawn. Barry places objectives, assessment boundaries and information gathering ahead of detailed quantification. Relevant information includes equipment, inventories, protection, operating conditions and maintenance arrangements. A tree based on the original design alone can misrepresent a facility whose equipment or operation has subsequently changed.<ref name="B-177">Barry (2002), pp. 5-177–5-179.</ref>

Intermediate events describe conditions that promote or limit the initiating event's development. Examples include detection, shutdown, isolation, automatic suppression and the performance of a barrier. An event can therefore represent a protective action or a condition that permits escalation. The headings should identify the required function rather than merely name the equipment installed.<ref name="B-180" /><ref name="B-182">Barry (2002), pp. 5-182–5-184.</ref>

The order of the headings follows the physical and operational sequence being represented. Early detection may allow isolation before a release grows, while a later intervention may act only after substantial exposure has occurred. Distinguishing these sequences prevents the same equipment from receiving identical credit regardless of when it responds.<ref name="B-182" />

A complete path ends in a defined outcome that can be assessed. The International Fire Engineering Guidelines illustrate paths involving sprinkler success, sprinkler failure followed by barrier success, and failure of both functions. These are useful structural examples. Their particular tenability outcomes depend on the assumptions of that example and cannot be assigned automatically to every protected building.<ref name="I-3">Australian Building Codes Board et al. (2005), pp. 2.2-3–2.2-4.</ref>

Fire control, suppression and extinguishment also describe different levels of performance. A successful control branch may mean that growth is limited sufficiently to meet the selected objective. It does not necessarily mean that combustion has ended. The outcome description should preserve this distinction when later assessment considers continuing heat, smoke or the duration of protection.<ref name="B-194" />

The tree is a model of the selected scenario family. Door positions, fire location, ventilation and occupant responses may require additional branches or separate initiating scenarios. The guidelines show separate fire-development and occupant-response trees, while acknowledging simplifying assumptions. Those assumptions require justification before the branches can represent an actual building.<ref name="I-56">Australian Building Codes Board et al. (2005), pp. 2.2-5–2.2-6.</ref>

== Defining success and response time ==

A branch labelled success needs a measurable functional meaning. Operation of a device and achievement of the fire safety objective are different questions. A sprinkler may operate without controlling the particular fire, while an alarm can function without producing evacuation in time. The scenario must establish which performance the branch represents.<ref name="I-3" /><ref name="A-122">Australian Building Codes Board (2020), pp. 120–122.</ref>

Barry separates response effectiveness, online availability and operational reliability when estimating protective-system success. Response effectiveness includes suitability, capacity, duration and timely action. Availability concerns whether the system is online, while operational reliability addresses its ability to perform when demanded. These distinctions support a more precise treatment of the [[Reliability of fire protection systems|reliability of fire protection systems]].<ref name="B-194">Barry (2002), pp. 5-194–5-200.</ref>

The event definition should identify a deadline where timing determines the outcome. Detection before loss of tenability differs from detection after occupants have been exposed. Similarly, isolation before a damaging release develops differs from eventual isolation. A generic probability of successful operation does not by itself establish successful operation within the required interval.<ref name="B-184">Barry (2002), p. 5-184.</ref><ref name="B-199">Barry (2002), pp. 5-199–5-200.</ref>
[[File:fse-event-tree-analysis-v2.svg|thumb|upright=1.5|alt=Two timelines compare protective action before and after the same critical-condition deadline.|A branch can require successful action before a scenario-specific deadline. Based on Barry (2002), p. 5-184 and pp. 5-199–5-200.]]

Timing also determines whether functions can be treated as alternatives or must occur together. The Australian Building Codes Board (ABCB) handbook illustrates evacuation as a combination of alarm, movement to safety, remaining safe and protection during exposure. Its simplified event tree is only a partial account of those interactions. More detailed analysis is needed where their relative timing affects success.<ref name="A-122" />

A branch should therefore retain the conditions under which its probability was estimated. These may include the particular fire, required output, available response time and the state of upstream systems. Replacing this description with a single percentage discards information needed to judge whether the value applies to another path or design.<ref name="B-194" /><ref name="B-190">Barry (2002), pp. 5-189–5-190.</ref>

Different levels of detail can be appropriate for different questions. A comparison involving one small change may use a simple tree, while interacting changes may require detailed supporting analysis. The ABCB handbook presents simplified probability assessment as a way to check whether differences in reliability could alter a conclusion based on deterministic modelling.<ref name="A-119" /><ref name="A-120">Australian Building Codes Board (2020), p. 120.</ref>

== Conditional probabilities and frequencies ==

Conditional probability is central to event-tree quantification. The probability assigned at a branch describes the event given the conditions already reached on that path. Hall defines the conditional probability of one event given another through their joint probability. Rearranging that definition gives the multiplication rule below, without requiring the events to be independent.<ref name="H-184">Hall (2002), p. 1-184.</ref>

<div class="fse-equation">P(A ∩ B) = P(A) × P(B | A)</div>

Here A and B are specified events, the intersection symbol denotes their joint occurrence, and the vertical bar means given. All terms are dimensionless probabilities. Applying the same rule successively gives a path probability from branch probabilities conditioned on the preceding sequence. Using unconditional probabilities instead requires an additional, justified independence assumption.<ref name="H-184" />

For a binary branch, success and failure must describe complementary outcomes under the same conditions. Their probabilities then sum to one. Across a complete set of mutually exclusive paths, the path probabilities also sum to one. These checks test the arithmetic and the stated partition of outcomes, although they cannot establish that the physical model is adequate.<ref name="H-183">Hall (2002), pp. 1-183–1-184.</ref><ref name="I-4" />

An initiating frequency adds a time basis to the calculation. Multiplying that frequency by the conditional probability of a path gives the frequency assigned to that path. This combines Barry's distinction between initiating frequencies and intermediate conditional probabilities with Hall's conditional-probability rule. The two quantities should remain separately identifiable in the results.<ref name="B-188" /><ref name="H-184" />

<div class="fse-equation">f<sub>i</sub> = f<sub>I</sub> × p<sub>i</sub></div>

Here f<sub>I</sub> is the initiating-event frequency, p<sub>i</sub> is the probability of path i given that initiation, and f<sub>i</sub> is its resulting frequency. If initiation is expressed in events per year, the path frequency has the same unit. A probability, by comparison, has no time unit.<ref name="B-188" /><ref name="H-184" />

{| class="wikitable"
|+ Symbols in the conditional-probability and frequency expressions.<ref name="H-184" /><ref name="B-188" />
! Symbol !! Meaning !! Unit
|-
| P(A) || Probability of event A || Dimensionless
|-
| P(B | A) || Probability of B conditional on A || Dimensionless
|-
| P(A ∩ B) || Probability that A and B both occur || Dimensionless
|-
| f<sub>I</sub> || Initiating-event frequency || year<sup>−1</sup> in this example
|-
| p<sub>i</sub> || Probability of path i conditional on initiation || Dimensionless
|-
| f<sub>i</sub> || Resulting frequency of path i || year<sup>−1</sup> in this example
|}

A frequency expressed per year should not be relabelled an annual probability. The former counts expected occurrences relative to time, while the latter concerns whether an event occurs within a specified interval. Keeping these meanings clear avoids mixing event frequencies, probabilities on demand and equipment failure rates in the same calculation.<ref name="B-188" />

== Worked conditional example ==

Consider a hypothetical fire initiation frequency of 0.020 per year. Automatic control succeeds with probability 0.90. If control fails, a barrier contains the fire with conditional probability 0.80. These invented values demonstrate the three-path structure illustrated in the guidelines; they do not describe measured sprinkler or barrier performance.<ref name="I-3" /><ref name="H-184" />
[[File:fse-event-tree-analysis-v1.svg|thumb|upright=1.5|alt=A fire branches into successful control, barrier containment after failed control, and failure of both functions, with calculated frequencies.|Three paths preserve the initiating frequency when conditional probabilities are applied consistently. Based on Australian Building Codes Board et al. (2005), p. 2.2-4, and Hall (2002), p. 1-184; numerical inputs are hypothetical.]]

The first path ends with control success and has probability 0.90. The second requires control failure and subsequent barrier success, giving 0.10 multiplied by 0.80, or 0.08. The third requires failure of control and failure of the barrier under that condition, giving 0.10 multiplied by 0.20, or 0.02.<ref name="H-184" />

{| class="wikitable"
|+ Hypothetical path probabilities and frequencies, calculated using Hall's conditional-probability rule.<ref name="H-184" />
! Outcome !! Probability given initiation !! Frequency (year<sup>−1</sup>)
|-
| Automatic control succeeds || 0.90 || 0.0180
|-
| Control fails; barrier contains || 0.08 || 0.0016
|-
| Both protective functions fail || 0.02 || 0.0004
|-
| Total || 1.00 || 0.0200
|}

The barrier probability belongs only to the population of fires for which control has already failed. It is therefore conditional on that failure, including whatever fire conditions remain. The calculation does not assume that a barrier has the same chance of success during controlled and uncontrolled fires. The first path requires no additional barrier branch for this simplified outcome classification.<ref name="H-184" /><ref name="I-3" />

The path probabilities sum to one and their frequencies sum to the initiating frequency. These checks confirm that the three declared outcomes account for the assumed initiation population. The frequency 0.0004 per year describes the last path in this model. It is neither a fatality probability nor a statement that all fires outside that path are harmless.<ref name="H-183" /><ref name="A-119" />

A sensitivity case reduces conditional barrier success to 0.40 while retaining the other assumptions. The last-path probability becomes 0.10 multiplied by 0.60, or 0.06. Its frequency increases to 0.0012 per year, three times the baseline value. Automatic-control success remains unchanged, while the contained-fire path falls to 0.0008 per year.<ref name="H-184" />
[[File:fse-event-tree-analysis-v3.svg|thumb|upright=1.5|alt=Two bars show final-path frequencies of 0.0004 and 0.0012 per year for conditional barrier success of 0.80 and 0.40.|Reducing conditional barrier success changes the final-path frequency while the initiating frequency remains fixed. Based on Hall (2002), p. 1-184; numerical inputs are hypothetical.]]

This change shows how a downstream conditional assumption can affect an outcome without changing initiation or the first protective function. It does not establish which barrier value is appropriate. That requires evidence about the barrier and the exposure produced on the failed-control path, together with the functional criteria used to define containment.<ref name="B-194" /><ref name="B-190" />

== Dependencies and consequence assessment ==

Separate branches do not establish physical independence. The ABCB handbook identifies detection as an example of a function influencing evacuation, fire-service notification and automatic smoke management. Failure to detect may affect several subsequent actions together. Their probabilities must therefore reflect the detection state already reached, rather than repeatedly granting an unconditional success probability.<ref name="A-122" /><ref name="H-184" />

Occupant response can introduce another sequence alongside fire development. The guidelines distinguish occupants alerted by direct sensory cues, an alarm or other people. These routes can lead to different response times and therefore different exposure conditions. Combining occupant-response paths with fire-development paths requires attention to their shared conditions, particularly whether detection and warning have already succeeded.<ref name="I-56" /><ref name="H-184" />

[[Fault tree analysis]] can support an event-tree branch by examining the combinations of equipment, human and external failures that defeat its function. Barry describes using these methods together when simple historical estimates are inadequate. The supporting failure model must correspond to the event definition and conditions used in the event tree.<ref name="B-188" /><ref name="I-4" />

Consequences remain a separate part of the assessment. An outcome such as failed suppression identifies a system state, but does not directly quantify temperature, smoke exposure, damage or casualties. The physical and occupant-response calculations must evaluate that state. The consequence measure should correspond to the design objective against which the alternatives are being compared.<ref name="B-182" /><ref name="A-122" />

The ABCB handbook demonstrates why equal consequences conditional on operation need not mean equal risk. Two systems can provide equivalent protection when working, yet differ in how often they fail. Including their failure probabilities can change the comparison. Conversely, a high operational probability cannot compensate automatically for an inadequate result whenever the system operates.<ref name="A-119" /><ref name="B-194" />

== Evidence, uncertainty and reporting ==

Probability assignments need a traceable evidence basis. Barry identifies relevant historical experience and synthesis using fault trees, human-reliability assessment and engineering judgement as complementary approaches. Generic historical values may require adjustment for the actual facility. Differences in equipment, operating practice and management can limit their applicability to the sequence being assessed.<ref name="B-188" />

Historical incident descriptions may reveal causes and consequences without providing a usable numerical frequency estimate for the facility. Barry notes that minor events are not always reported and that records can be incomplete. The analyst must distinguish evidence that a sequence is possible from evidence of how often it occurs. The population and observation period therefore matter when interpreting a numerical assignment.<ref name="B-177" /><ref name="B-188" />

A record should preserve each event's description, probability range, source, selected value and justification. Barry's documentation example includes these fields so that assumptions remain reviewable. Where expert judgement supplies missing information, the basis and relevant expertise should be recorded. An unsupported point value remains uncertain even when subsequent arithmetic is exact.<ref name="B-190" />

[[Monte Carlo simulation]] can propagate mathematically described input uncertainty through repeated calculations. Notarianni explains that correlations between inputs need representation when generating realistic scenarios. Sampling cannot establish the correctness of an unsupported branch structure or probability distribution. The resulting spread describes the uncertainty and variability encoded in the model.<ref name="N-51">Notarianni (2002), p. 5-51 and pp. 5-54–5-55.</ref>

Reporting should connect the event tree, its probability evidence and the consequence calculations. The reader needs to identify which paths control the conclusion and which assumptions could change it. This maintains the distinction between a transparent model of possible sequences and a demonstrated judgement about the acceptability of the resulting fire risk.<ref name="B-190" /><ref name="A-119" /><ref name="N-51" />

== See also ==
* [[Fire risk assessment]]
* [[Common cause failure]]

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020). ''Fire safety verification method handbook'' (Version 1.1).
* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing. (2005). ''International fire engineering guidelines''.
* Barry, T. F. (2002). Quantitative risk assessment in chemical process industries. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 5-13, pp. 5-176–5-213). National Fire Protection Association.
* Hall, J. R., Jr. (2002). Probability concepts. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 1-11, pp. 1-182–1-192). National Fire Protection Association.
* Notarianni, K. A. (2002). Uncertainty. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed., Chapter 5-4, pp. 5-40–5-64). National Fire Protection Association.

[[Category:Fire Risk Analysis]]

File:Fse-vapour-cloud-explosion-v3.svg

2026-11-02T16:16:17Z

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== Summary ==
Gas migration can connect an outdoor release with indoor explosion scenarios. Based on Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-8–N-11.

Original illustration for [[Vapour cloud explosion]], level 3 Advanced.

* Source basis: Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-8–N-11.
* Alt text: Gas from an outdoor release may enter an air intake and move through ducts into connected rooms.
* Accuracy notes: Paths are possibilities, not a computed dispersion field; do not imply uniform concentration.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-vapour-cloud-explosion-v2.svg

2026-11-02T16:16:11Z

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== Summary ==
Eightfold energy corresponds to twice the distance at equal scaled radius in this idealised example. Based on Zalosh (2002), p. 3-419.

Original illustration for [[Vapour cloud explosion]], level 3 Advanced.

* Source basis: Zalosh (2002), p. 3-419.
* Alt text: Two ideal point sources have the same scaled radius at 50 m and 100 m with energies of 100 MJ and 800 MJ.
* Accuracy notes: Do not depict a safe boundary or assign a TNT yield; no pressure values.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-vapour-cloud-explosion-v1.svg

2026-11-02T16:16:05Z

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== Summary ==
Immediate and delayed ignition require different exposure scenarios. Based on Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-7–N-9.

Original illustration for [[Vapour cloud explosion]], level 3 Advanced.

* Source basis: Electric Power Research Institute and U.S. Nuclear Regulatory Commission (2005), pp. N-7–N-9.
* Alt text: A release branches into immediate jet combustion or a dispersed cloud that ignites later.
* Accuracy notes: No event probabilities; no guaranteed explosion for every delayed ignition.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-minimum-ignition-energy-v3.svg

2026-11-02T16:15:59Z

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== Summary ==
The theoretical electrostatic comparison uses the threshold for the same discharge type. Based on Zalosh (2002), p. 3-405.

Original illustration for [[Minimum ignition energy]], level 3 Advanced.

* Source basis: Zalosh (2002), p. 3-405, Example2.
* Alt text: The capacitive threshold connects to the stored-energy calculation, while the inductive threshold is shown as an incompatible input.
* Accuracy notes: The result is a textbook theoretical comparison, not a guarantee of ignition or a permitted operating voltage.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-minimum-ignition-energy-v2.svg

2026-11-02T16:15:53Z

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== Summary ==
The same powder sample has distinct energy, cloud-temperature and layer-temperature results. Based on Zalosh (2002), pp. 3-404–3-405.

Original illustration for [[Minimum ignition energy]], level 3 Advanced.

* Source basis: Zalosh (2002), pp.3-404–3-405, Table3-16.2; redraw conceptual apparatus, not a test specification; redraw, do not copy.
* Alt text: Three test concepts distinguish the milk-powder sample’s spark energy, cloud ignition temperature and layer ignition temperature.
* Accuracy notes: Use spaced final labels; keep units distinct and do not imply conversion between millijoules and degrees Celsius.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-minimum-ignition-energy-v1.svg

2026-11-02T16:15:47Z

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== Summary ==
Required ignition energy changes within the flammable concentration range. Based on Beyler (2002), p. 2-181, and Iqbal and Salley (2004), p. 16-4.

Original illustration for [[Minimum ignition energy]], level 3 Advanced.

* Source basis: Beyler (2002), p. 2-181; Iqbal and Salley (2004), p. 16-4, Figure16-3; qualitative synthesis, not digitised data; redraw, do not copy.
* Alt text: A qualitative curve shows higher required spark energy near the lean and rich boundaries and a lower intermediate region.
* Accuracy notes: Do not assign one universal concentration or energy value; the minimum need not coincide exactly with stoichiometry.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-jet-fire-v3.svg

2026-11-02T16:15:41Z

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== Summary ==
Direct impingement combines radiative and convective heating. Based on Beyler (2002), pp. 3-301–3-302.

Original illustration for [[Jet fire]], level 3 Advanced.

* Source basis: Beyler (2002), pp. 3-301–3-302.
* Alt text: A remote target receives radiation while an engulfed target also receives strong convective heating.
* Accuracy notes: Do not depict equal radiation/convection for every fuel or location.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-jet-fire-v2.svg

2026-11-02T16:15:35Z

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== Summary ==
Distance and orientation change the calculated far-field radiation. Based on Beyler (2002), pp. 3-298–3-299.

Original illustration for [[Jet fire]], level 3 Advanced.

* Source basis: Beyler (2002), pp. 3-298–3-299.
* Alt text: Three assumed point-source cases show radiation decreasing with distance and oblique orientation.
* Accuracy notes: Distances start at flame centre; show no safety boundary and no impingement.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-jet-fire-v1.svg

2026-11-02T16:15:29Z

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== Summary ==
A release can lead to different fire types and a changing sequence. Based on Beyler (2002), pp. 3-268–3-269.

Original illustration for [[Jet fire]], level 3 Advanced.

* Source basis: Beyler (2002), pp. 3-268–3-269.
* Alt text: A release branches into jet, pool and cloud-fire pathways.
* Accuracy notes: No probabilities; a cloud fire is not automatically an explosion.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-inerting-v3.svg

2026-11-02T16:15:23Z

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== Summary ==
Nonuniform mixtures and instrument performance affect the interpretation of an inerting calculation. Based on Zalosh (2002), p. 3-403.

Original illustration for [[Inerting]], level 3 Advanced.

* Source basis: Zalosh (2002), p. 3-403; Beyler (2002), p. 2-181.
* Alt text: Uniform model and nonuniform vessel mixture are compared alongside the properties of concentration measurement.
* Accuracy notes: Do not portray the illustrated sensor location as a recommended installation or imply one reading establishes all local concentrations.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.

File:Fse-inerting-v2.svg

2026-11-02T16:15:16Z

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== Summary ==
Complete mixing causes an exponential decline in the modelled concentration. Based on Beyler (2002), pp. 2-180–2-181.

Original illustration for [[Inerting]], level 3 Advanced.

* Source basis: Beyler (2002), pp. 2-180–2-181, Example3 and mixed-purge equation.
* Alt text: Methane concentration falls from 30% to 13% as the model adds about 167 cubic metres of nitrogen.
* Accuracy notes: Use spaces in final number labels. Concentrations describe the textbook mixture example and must not be presented as safe for people.

== Licensing ==
New drawing by Fire Safety Academy. © Fire Safety Academy.