Evacuation strategy

An evacuation strategy is the planned way in which the occupants of a building respond to a fire: who leaves, in what order, by which route and to which place of safety. The main types are simultaneous evacuation of the whole building, phased evacuation of the most threatened floors first, progressive horizontal evacuation to an adjacent fire compartment, and strategies in which occupants stay where they are. The chosen strategy determines the alarm and communication systems a building needs, the capacity of its stairs and the role of staff during a fire.

Traditional practice is to evacuate everyone as soon as the alarm sounds. This is simple, but in tall buildings it can leave the people most at risk queuing behind everyone else. Managed strategies move those people first, but they rely on reliable detection, clear announcements and trained staff. In Australia, the 2020 data sheets for the Fire Safety Verification Method require the evacuation management strategy to be specified as part of the fire safety strategy. Its expected performance must also be stated, because evacuation procedures can change during the life of a building.

Types of strategy

The International Fire Engineering Guidelines (2005) describe the traditional practice as starting the evacuation of occupants in response to fire alarms, following an evacuation management plan. In this simultaneous or total evacuation, every occupant leaves at once. Proulx calls it uncontrolled total evacuation, because the order of movement depends mainly on how people give way to one another on the stairs.

In high-rise buildings with an emergency warning and intercommunication system, trained personnel can manage the evacuation instead. Occupants on floors far from the fire are first placed on alert and evacuated progressively only if the fire continues to develop. This is known as phased evacuation or controlled selective evacuation. Its success depends on the type of control and on a voice communication system. In the World Trade Center investigation, phased evacuation meant that the occupants of the fire floor and the floors immediately around it went down to three floors below the fire floor. The report notes that this approach is also known as defend-in-place.

In hospitals the first response is different. Nursing staff move patients horizontally to an adjacent smoke zone or fire compartment, and they are moved further, or other floors evacuated, only if the fire threat keeps developing. This progressive horizontal evacuation relies on staff, because in hospitals and aged care nearly all residents may need help to leave.

A fourth group of strategies keeps people where they are. In some buildings occupants go to a fire-safe refuge, a special fire compartment where they wait for rescue by the fire service. A more recent development is the protect-in-place concept, used particularly in fully sprinklered residential buildings. Occupants are encouraged to remain where they are rather than escape through corridors and stairs that may be full of smoke. Such approaches are also called a stay-put strategy or stay-in-place strategy. In these cases the detection system is used to inform occupants about the location and extent of the fire, and instructions are then given to the people concerned.

Four types of evacuation strategy: simultaneous evacuation, phased evacuation, progressive horizontal evacuation and staying in place. Based on National Research Council of Canada et al. (2005), pp. 1.8-2 and 2.8-2.

New Zealand's C/VM2 (second edition, 2025) groups these under delayed evacuation strategies. They apply where occupants must stay in place or move to a place of safety inside the building. Examples are people who are detained or who are being treated in an operating theatre, a hyperbaric chamber or a dialysis unit. Such spaces must meet the definition of a place of safety. Because they are usually climate-controlled, smoke detection and the smoke control of the air handling system need special care.

Total versus phased evacuation

Proulx compares the two strategies for a hypothetical 15-storey office building with 70 people per floor and two stairs 1,120 mm wide. In a total evacuation, each stair discharges about one person per second, and people descend at about 3.6 floors per minute, or 0.5 m/s along the stair. In both cases about 9 minutes are needed to move everyone below a presumed fire on the tenth floor. The selective procedure takes about as long to bring 490 people below the ninth floor as the total evacuation takes to bring all 980 people to the ground. Starting and controlling a selective evacuation takes time.

The comparison does not show that total evacuation is better. If there really were a fire on the tenth floor and everyone left at the same time, the people on the most threatened floors would queue near those floors for several minutes. With the stair doors open on the fire floor, smoke would reach all the upper floors, and people coming down from above would have to move through it. Uncontrolled total evacuation makes few demands on building management systems. It is, however, increasingly seen as too disruptive for occupants who are evacuated indiscriminately, if they can be persuaded to leave at all with ambiguous alarms. Selective evacuation needs more sophisticated systems and training, which are expensive and can delay the moment at which the right people are told to leave.

Drills give practical numbers. In 1972, 1,453 people left a 15-storey office building by four stairs 1,140 mm wide in a total evacuation. The stairs emptied after 6.6 to 9.3 minutes, 7.8 minutes on average, against a predicted 7.0 minutes. In the same drill, 73 people who would have found the stairs too arduous, together with their assistants, used a fifth stair reserved for them. The time differences between the stairs came mainly from unequal numbers of people using each stair.

For the 21-storey building of the Ottawa drill described below, Proulx estimates that an uncontrolled total evacuation of its 2,100 occupants by two stairs would take a minimum of nearly 20 minutes. If everyone stood at the stair doors at once, there would be only 0.17 m² of stair, about half a tread, per person. The selective procedure used in that drill could have been stopped after 6 minutes, once the presumed fire floor and the two adjacent floors were clear.

The World Trade Center investigation simulated both strategies for one tower. A phased evacuation of 600 occupants from three floors took 3.5 to 4 minutes when everyone started at once, and 11 to 11.5 minutes with random delays of up to 10 minutes. A total evacuation of a fully occupied tower of 19,800 people would have taken at least 92 to 112 minutes. NIST concluded that phased evacuation was not appropriate for an emergency on the scale of 11 September 2001. Under certain circumstances, though, it moves the people most at risk to relative safety much more quickly and with less disruption than a full evacuation. It works well for routine emergencies that fall within the design envelope of the life safety systems.

Simulated times for a phased evacuation of three floors and for full evacuations of one World Trade Center tower. Based on Averill et al. (2005), pp. xxxv and 160.

Alarm and communication

A managed strategy needs a way to tell different groups of people different things. In Australia, alarm systems for phased evacuation commonly use two tones. An alert tone means prepare for evacuation, for example by switching off equipment and waiting for instructions, and an evacuation tone means leave immediately. Because the alarm then reaches some areas later, those delays must be included in the evacuation analysis. On floors far from the fire, access to the stair may be delayed on purpose to give priority to the fire floor.

In a phased evacuation, floors at risk receive the evacuation tone while other floors receive an alert tone and wait for instructions. Based on Australian Building Codes Board (2020a), Data Sheet D1, pp. 243–244 and 246.

The way the message is given matters. The book Introduction to Fire Safety Engineering notes that a slow-whoop alarm signal is known to be less effective than the spoken word. An automatic evacuation alarm system is generally less effective than a live announcement, by public address, in person or by telephone. The effect of an automatic alarm depends strongly on the culture of the people in the building. Where a well-trained evacuation organisation is present, the chance that the alarm is taken seriously is many times greater.

New Zealand's C/VM2 reflects this in its design values. For retail shops and restaurants, a voice alarm halves the pre-travel activity time from 60 to 30 s in the room of fire origin. For sleeping hotel guests away from the fire, it halves the time from 600 to 300 s.

Design pre-travel activity times in C/VM2 for a standard alarm signal and a voice alarm signal. Based on Ministry of Business, Innovation and Employment (2025b), p. 30.

Announcements can also fail. In 1971, one of the first large controlled selective evacuation drills was held in a 21-storey office building in Ottawa, with the fire assumed on the third floor. Because of an incorrectly set switch, the first announcement came through only after nearly 3 minutes, and it was ambiguous. Up to 350 people left their floors too early, which delayed the floors that should have gone first. With only the alarm bell ringing, 17 % of the people surveyed thought there was a fire, nearly 60 % thought it was a fault and 16 % a drill. In the World Trade Center in 2001, an announcement in the second tower telling people to return to their offices was cited by many survivors as a constraint on their evacuation.

Strategy and building design

The evacuation strategy and the physical fire safety measures must fit together. The Australian data sheets point out that the deemed-to-satisfy provisions of the National Construction Code assume typical strategies. Patient care areas in hospitals and aged care buildings must be divided into smoke compartments of at most 500 m². Horizontal exits there need a clear area of at least 2.5 m² per patient on the far side of the fire wall. These rules match a phased evacuation with staff assistance. Emergency warning and intercommunication systems are required, among other cases, in buildings with an effective height of more than 25 m.

The strategy also affects other systems. The number of stair doors open at the same time, and therefore the design of stair pressurisation, depends on whether a staged evacuation or refuge concept is part of the emergency plan. Dividing a tall stair into pressurised compartments only works with a staged evacuation, not when the whole building leaves by the stairs at once. For very tall buildings, the Australian handbook mentions protect-in-place or partial evacuation strategies and the use of lifts as possible enhancements.

The evacuation strategy is therefore a part of the wider fire safety strategy. The Australian data sheets state that the description of the fire safety strategy must include clear details of the evacuation management strategy and the performance expected from it. They also warn that changes to the evacuation management strategy should not be used on their own to justify relaxing the prescriptive requirements. Both the proposed design and the reference building are expected to have an optimised strategy.

Use in evacuation analysis

In a time-based analysis, the strategy changes the inputs. New Zealand's C/VM2 takes the notification time as 30 s for standard evacuation strategies. For non-standard strategies, such as management investigating the activation of a single detector before raising the alarm, the longer notification time must be included. In Australia, the data sheets describe levels of emergency management organisation. These range from long-term occupants with floor wardens and regular drills to small residential buildings with no permanent staff, where managing the evacuation falls to the fire brigade.

Training, drills and a reliable intercom system make occupant behaviour more uniform and predictable, as is common in health care, most workplaces and larger public buildings. With simple alarms and an informal organisation, human behaviour varies much more, which is typical of small and medium-sized residential buildings. The analysis must therefore reflect the strategy that will actually be in place. Scenarios with a failed alarm or intercom system also need to be considered.

Limits and failure modes

Every strategy rests on assumptions that can fail. A phased evacuation assumes that the fire stays on the floor of origin. The Australian data sheets warn that it may be sensitive to rapid fire spread over several floors via the façade, and that procedures for that case should be described. At the World Trade Center in 2001, the scale of the event made a phased approach unsuitable. In the first stages a full-building evacuation took place from all floors not badly affected by the impacts. Had stair pressurisation been installed, this would have lowered the pressure in the stairs below the required value.

Strategies in which people stay put depend on the protection around them and on reliable information about the fire. NIST observed that current strategies generally required mobility-impaired occupants to shelter in place and wait for assistance. It recommended that new procedures should consider full building evacuation, so that these occupants have a way to leave on their own. The Australian data sheets state more generally that the fire safety strategy must show how the safety of all occupants is achieved, usually by combining physical fire safety features with evacuation management procedures.

See also

• Fire safety management
• Evacuation of people with disabilities
• Evacuation lift
• Pre-movement time

References

• Australian Building Codes Board. (2020a). Data sheets: Fire Safety Verification Method (Handbook annex, Print version 1.1).
• Australian Building Codes Board. (2020b). Handbook: Fire Safety Verification Method (Print version 1.1).
• 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.
• Ferreira, M. J., & Strege, S. M. (2005). Smoke management systems (NIST NCSTAR 1-4D). National Institute of Standards and Technology.
• Klote, J. H. (2002). Smoke control. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-274–4-291). National Fire Protection Association; Society of Fire Protection Engineers.
• Ministry of Business, Innovation and Employment. (2025b). Verification Method C/VM2: Framework for fire safety design (2nd ed.).
• National Institute of Standards and Technology. (2005). Final report on the collapse of the World Trade Center towers (NIST NCSTAR 1).
• National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). International fire engineering guidelines (2005 ed.). Australian Building Codes Board.
• 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.
• Schifiliti, R. P., Meacham, B. J., & Custer, R. L. P. (2002). Design of detection systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-1–4-43). National Fire Protection Association; Society of Fire Protection Engineers.
• Van Rossum, E. (2027). Introduction to Fire Safety Engineering. Fire Safety Academy.