Required safe egress time - Revision history

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2026-11-02T17:14:51Z

Add Intermediate SVG figures with Fire Safety Academy watermark at planned locations; preserve article text

← Older revision		Revision as of 18:14, 2 November 2026
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	== Components ==		== Components ==
	Most sources split the RSET into four or five consecutive periods. C/VM2 uses a detection time, a notification time, a pre-travel activity time and a travel or flow time.<ref name="MBIE25-26" /> The Australian data sheets for the Fire Safety Verification Method use the same four parts.<ref name="ABCB-242">Australian Building Codes Board (2020a), Data Sheet D1, p. 242.</ref> Nelson and Mowrer split the time before movement into two parts: until occupants decide to act, and from that decision until evacuation starts.<ref name="NM-367" /> The International Fire Engineering Guidelines speak of a cue period, a response period, a delay period and a movement period.<ref name="IFEG-1.8-2">National Research Council of Canada et al. (2005), p. 1.8-2.</ref>		Most sources split the RSET into four or five consecutive periods. C/VM2 uses a detection time, a notification time, a pre-travel activity time and a travel or flow time.<ref name="MBIE25-26" /> The Australian data sheets for the Fire Safety Verification Method use the same four parts.<ref name="ABCB-242">Australian Building Codes Board (2020a), Data Sheet D1, p. 242.</ref> Nelson and Mowrer split the time before movement into two parts: until occupants decide to act, and from that decision until evacuation starts.<ref name="NM-367" /> The International Fire Engineering Guidelines speak of a cue period, a response period, a delay period and a movement period.<ref name="IFEG-1.8-2">National Research Council of Canada et al. (2005), p. 1.8-2.</ref>

			[[File:fse-required-safe-egress-time-v1.svg\|thumb\|upright=1.5\|alt=Timeline from ignition: detection, notification, pre-movement and movement make up RSET; a longer ASET bar ends at untenable conditions.\|The components of the required safe egress time and its comparison with the available safe egress time. Based on Ministry of Business, Innovation and Employment (2025b), p. 26, and Van Rossum (2027), §7.1.]]

	The detection time runs from ignition until an automatic system or a person detects the fire. C/VM2 requires it to be found from deterministic modelling of the detectors or sprinklers, using fixed detector properties regardless of the products to be installed.<ref name="MBIE25-26" /><ref name="MBIE25-27">Ministry of Business, Innovation and Employment (2025b), p. 27.</ref> Methods to calculate it are described under [[detector activation time]]. The notification time covers the delay between detection and the alarm reaching the occupants. C/VM2 takes it as 30 s for standard evacuation strategies, and longer where the alarm is first investigated by staff.<ref name="MBIE25-29">Ministry of Business, Innovation and Employment (2025b), p. 29.</ref>		The detection time runs from ignition until an automatic system or a person detects the fire. C/VM2 requires it to be found from deterministic modelling of the detectors or sprinklers, using fixed detector properties regardless of the products to be installed.<ref name="MBIE25-26" /><ref name="MBIE25-27">Ministry of Business, Innovation and Employment (2025b), p. 27.</ref> Methods to calculate it are described under [[detector activation time]]. The notification time covers the delay between detection and the alarm reaching the occupants. C/VM2 takes it as 30 s for standard evacuation strategies, and longer where the alarm is first investigated by staff.<ref name="MBIE25-29">Ministry of Business, Innovation and Employment (2025b), p. 29.</ref>
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	The relation applies to the occupants of one room or location. For the room of fire origin, C/VM2 assumes that the occupants are spread evenly, so that the larger of the travel and flow times governs.<ref name="MBIE25-26" /> For routes through several spaces, the analysis must cover the whole route, so that a restriction closer to the final exit is not missed.<ref name="MBIE25-33">Ministry of Business, Innovation and Employment (2025b), p. 33.</ref> The travel speed falls with crowd density and is capped at 1.2 m/s on level routes.<ref name="MBIE25-32">Ministry of Business, Innovation and Employment (2025b), p. 32.</ref> The flow through a door is calculated from its effective width and a density of 1.9 persons/m², and is limited to 50 people per minute for each self-closing door leaf.<ref name="MBIE25-33" /><ref name="MBIE25-34">Ministry of Business, Innovation and Employment (2025b), p. 34.</ref>		The relation applies to the occupants of one room or location. For the room of fire origin, C/VM2 assumes that the occupants are spread evenly, so that the larger of the travel and flow times governs.<ref name="MBIE25-26" /> For routes through several spaces, the analysis must cover the whole route, so that a restriction closer to the final exit is not missed.<ref name="MBIE25-33">Ministry of Business, Innovation and Employment (2025b), p. 33.</ref> The travel speed falls with crowd density and is capped at 1.2 m/s on level routes.<ref name="MBIE25-32">Ministry of Business, Innovation and Employment (2025b), p. 32.</ref> The flow through a door is calculated from its effective width and a density of 1.9 persons/m², and is limited to 50 people per minute for each self-closing door leaf.<ref name="MBIE25-33" /><ref name="MBIE25-34">Ministry of Business, Innovation and Employment (2025b), p. 34.</ref>

			[[File:fse-required-safe-egress-time-v2.svg\|thumb\|upright=1.5\|alt=Line chart of horizontal travel speed against crowd density: flat at 1.2 m/s up to 0.54 persons per m², then falling linearly to zero at about 3.8.\|Design travel speed on level routes in C/VM2 (second edition, 2025) as a function of crowd density. Based on Ministry of Business, Innovation and Employment (2025b), pp. 32–33.]]

	Like other hydraulic methods, this calculation assumes that all occupants start at the same moment and move without interruptions, and that most are free of disabilities that would slow the group.<ref name="NM-367" /> The ''Introduction to Fire Safety Engineering'' adds that a hand calculation requires a homogeneous group of people and a simple geometry.<ref name="VR-7.5">Van Rossum (2027), §7.5.</ref> Its eight-step method determines the people per space, the flow capacity of each exit, the distribution of people over the exits and the governing exit. It then adds the walking time of the first person, the flow time of the governing exit and the walking time of the last person to safety.<ref name="VR-7.5" />		Like other hydraulic methods, this calculation assumes that all occupants start at the same moment and move without interruptions, and that most are free of disabilities that would slow the group.<ref name="NM-367" /> The ''Introduction to Fire Safety Engineering'' adds that a hand calculation requires a homogeneous group of people and a simple geometry.<ref name="VR-7.5">Van Rossum (2027), §7.5.</ref> Its eight-step method determines the people per space, the flow capacity of each exit, the distribution of people over the exits and the governing exit. It then adds the walking time of the first person, the flow time of the governing exit and the walking time of the last person to safety.<ref name="VR-7.5" />
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	<math display="block">\mathrm{RSET} = 66 + 30 + 30 + \max(68,\ 150) = 276\ \mathrm{s}</math>		<math display="block">\mathrm{RSET} = 66 + 30 + 30 + \max(68,\ 150) = 276\ \mathrm{s}</math>
	For the people who leave through the foyer, the commentary adds another 150 s of flow time, giving 426 s.<ref name="MBIE13-206">Ministry of Business, Innovation and Employment (2013), p. 206.</ref> The modelled tenability limit for carbon monoxide was not reached within the 1,200 s simulated, so ASET exceeds RSET by more than 924 s in the ballroom.<ref name="MBIE13-206" /> The commentary notes that, strictly, the dose must be calculated at the locations of the moving occupants, which may mean using data from different rooms for different periods.<ref name="MBIE13-206" />		For the people who leave through the foyer, the commentary adds another 150 s of flow time, giving 426 s.<ref name="MBIE13-206">Ministry of Business, Innovation and Employment (2013), p. 206.</ref> The modelled tenability limit for carbon monoxide was not reached within the 1,200 s simulated, so ASET exceeds RSET by more than 924 s in the ballroom.<ref name="MBIE13-206" /> The commentary notes that, strictly, the dose must be calculated at the locations of the moving occupants, which may mean using data from different rooms for different periods.<ref name="MBIE13-206" />

			[[File:fse-required-safe-egress-time-v3.svg\|thumb\|upright=1.5\|alt=Stacked bars: ballroom 66 + 30 + 30 + 150 = 276 s; via foyer 426 s; a vertical line marks ASET beyond 1,200 s.\|RSET in the commentary example: detection, notification, pre-travel and flow time for the ballroom and for the route through the foyer, compared with the ASET. Based on Ministry of Business, Innovation and Employment (2013), pp. 203–206.]]

	The ''Introduction to Fire Safety Engineering'' gives a simpler example of the movement part alone. Three hundred people are divided equally over four stairs, and the two narrowest stairs of 1.6 m govern. Each passes 1.2 persons per second, so 75 people need about 63 s.<ref name="VR-7.5" /> Adding 5 s for the first person to reach the stair and 10 s for the last person to reach safety gives a movement time of 78 s.<ref name="VR-7.5" />		The ''Introduction to Fire Safety Engineering'' gives a simpler example of the movement part alone. Three hundred people are divided equally over four stairs, and the two narrowest stairs of 1.6 m govern. Each passes 1.2 persons per second, so 75 people need about 63 s.<ref name="VR-7.5" /> Adding 5 s for the first person to reach the stair and 10 s for the last person to reach safety gives a movement time of 78 s.<ref name="VR-7.5" />
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	In the Netherlands, the standards for large fire compartments, NEN 6060 and NEN 6079, include an ASET/RSET comparison with safety factors.<ref name="VR-7.1" /> For new buildings assessed with the rule-of-thumb method and conservative inputs, the factor is 1.5 when RSET is up to 3 minutes and 2.0 when it is longer.<ref name="VR-7.1" /> With nominal inputs, the factors are 2.0 and 2.5. Existing buildings have lower factors, between 1.0 and 1.5.<ref name="VR-7.1" /> Proulx suggests that, in a conservative approach, the time available should be at least twice the time required.<ref name="Proulx-363" />		In the Netherlands, the standards for large fire compartments, NEN 6060 and NEN 6079, include an ASET/RSET comparison with safety factors.<ref name="VR-7.1" /> For new buildings assessed with the rule-of-thumb method and conservative inputs, the factor is 1.5 when RSET is up to 3 minutes and 2.0 when it is longer.<ref name="VR-7.1" /> With nominal inputs, the factors are 2.0 and 2.5. Existing buildings have lower factors, between 1.0 and 1.5.<ref name="VR-7.1" /> Proulx suggests that, in a conservative approach, the time available should be at least twice the time required.<ref name="Proulx-363" />

			[[File:fse-required-safe-egress-time-v4.svg\|thumb\|upright=1.5\|alt=Grouped bars of required ASET/RSET factors for new and existing buildings, conservative and nominal inputs, RSET up to and over 3 minutes; values 1.0 to 2.5.\|Safety factors on RSET in NEN 6060 and NEN 6079 for the rule-of-thumb method, as reproduced in the Introduction to Fire Safety Engineering. Based on Van Rossum (2027), §7.1.]]

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

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

2026-11-01T22:55:59Z

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

New page

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

== Notes ==
<references />

== References ==
* Australian Building Codes Board. (2020a). ''Data sheets: Fire Safety Verification Method'' (Handbook annex, Print version 1.1).
* Averill, J. D., Mileti, D. S., Peacock, R. D., Kuligowski, E. D., Groner, N., Proulx, G., Reneke, P. A., & Nelson, H. E. (2005). ''Occupant behavior, egress, and emergency communications'' (NIST NCSTAR 1-7). National Institute of Standards and Technology.
* Ministry of Business, Innovation and Employment. (2013). ''Commentary for Building Code clauses C1–C6 and Verification Method C/VM2''.
* Ministry of Business, Innovation and Employment. (2025b). ''Verification Method C/VM2: Framework for fire safety design'' (2nd ed.).
* National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Nelson, H. E., & Mowrer, F. W. (2002). Emergency movement. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-367–3-380). National Fire Protection Association; Society of Fire Protection Engineers.
* Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-342–3-366). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Human Behaviour & Evacuation]]