Protective action decision model

A protective action decision model is a model of the decision process that leads people who notice signs of a threat to a protective action. Such an action may be evacuating, moving to a refuge or staying where they are. The SFPE Handbook of Fire Protection Engineering (2002) and the International Fire Engineering Guidelines (2005) describe such a protective-action decision process. So does a study of the 2001 World Trade Center evacuation by the National Institute of Standards and Technology (NIST). None of them uses the name protective action decision model. The decision process takes place during the pre-movement time, the period between the first cue and the start of purposeful movement to a safe place.

NIST calls its own model a model of evacuation delay. The model was built on a review of about 300 studies of how people respond to risk events and risk information for natural and technological hazards. These studies included events in which protective actions other than evacuation were warranted, and research on evacuation in high-rise fires was used as well. The model explained about half of the variation in the time occupants waited before starting to evacuate. Research on human behaviour in fire shows that a fire alarm on its own rarely triggers evacuation. The delay to start depends on the information and cues people receive, the risk they perceive and the behaviour of others.

From cue to protective action

The International Fire Engineering Guidelines (2005) divide the time from ignition to safety into a sequence of events. A cue first signals the fire. It may come from an automatic alarm, from the fire itself or from other people. The occupant then recognises the cue as a sign of fire, and after a delay, during which other actions or no action may take place, starts to move.

The time from the cue to the start of movement is the pre-movement phase. It consists of a response period, until the cue is recognised, and a delay period after it. The movement itself ends when the occupant reaches a safe area.

The movement chapter of the SFPE Handbook splits the delay time to start into three parts: perception, interpretation and action. Occupants first perceive the alarm signal, a fire cue or a warning from others. They then interpret this information, often investigating or searching for more information before deciding to evacuate. Even after that decision, they usually carry out other actions first, such as getting dressed, gathering children or collecting valuables. Introduction to Fire Safety Engineering describes the same sequence as three phases: awareness, decision-making and execution.

Evacuation is not the only possible protective action. The guidelines mention progressive evacuation in high-rise buildings, in which floors far from the fire are first placed on alert. Other options are a fire-safe refuge where occupants wait for the fire service, and the newer concept of protection in place, in which occupants stay where they are. In the protect-in-place concept, staying is itself the intended protective action, chosen to avoid smoke-filled corridors and stairs.

Stages of the decision process

The behaviour chapter of the SFPE Handbook describes the decision process of an individual in a fire as six linked processes, based on work by Withey. In recognition, a person identifies ambiguous cues as a sign of a fire. Many people first interpret such cues in terms of the most familiar and harmless explanation, partly because they feel personally invulnerable to risk. In validation, the person tries to confirm the first impression, often by seeking reassurance or more information from others who have noticed the same cues.

In definition, the person relates the information to the situation, such as the location and size of the fire. Stress and anxiety rise fastest before the ambiguous cues have been given a clear meaning. In evaluation, the person weighs possible responses, such as escaping, fighting the fire or raising the alarm. Because fires develop quickly, this evaluation may have to be completed within a few seconds. The location of exits, the presence of other people, the perceived effects of the fire and the actions of others all influence this choice.

In commitment, the person carries out the chosen response. If it fails, reassessment follows, which may be the most stressful stage. With each failure, more energy goes into the response, the person becomes less selective about the risks taken, and the chance of success falls. At the Arundel Park fire, more people chose windows as an escape route when they were involved in a second attempt to get out.

Cues and warnings

People become aware of a fire in many ways. In a study of 569 participants in residential fires, 26.0 per cent first noticed the fire by smelling smoke, 21.3 per cent were told by others and 18.6 per cent heard noises. Another 13.4 per cent were told by family members, 9.1 per cent saw smoke and 8.1 per cent saw the fire. The way people are alerted may influence how serious they think the threat is.

The alarm signal is probably the least reliable cue, because false alarms, test alarms and pranks have reduced its credibility. Three or more false alarms in six months can be regarded as a large number, and in such buildings the delay to start may be extended almost without limit. Smelling or seeing smoke is ambiguous and tends to start an investigation rather than an evacuation. A warning from another person is a better sign of a real problem. Messages from a voice communication system, or directly from staff, are taken most seriously. An evacuation alarm system with live, informative voice messages is probably the best way to start a fast response, while prerecorded messages are rarely as effective.

Introduction to Fire Safety Engineering reports the same pattern: a slow-whoop tone is less effective than spoken words, and live messages are followed faster than automatic alarms. If a message conflicts with other cues, such as the smell or sight of smoke, its credibility may be questioned and the information disregarded. In a fire in the World Trade Center in 1975, occupants on smoke-logged floors were told to return to their offices but stayed in the core lobbies. An evacuation message followed six minutes later.

Perceived risk and information seeking

In the NIST model, the delay before evacuation depended on six factors. These were environmental cues, the starting floor, information received without asking for it, perceived risk, the search for more information and other actions taken before leaving. Perceived risk was preferred to actual risk, because people act on what they believe to be true. In both towers, perceived risk rose mainly with the starting floor and with exposure to cues such as smoke, damage or fire. Information that people received had a weaker effect.

Seeking information is a typical response in sudden emergencies, because people need to make sense of an event before they act on it. This behaviour is known as milling, and cues were its strongest predictor. Pre-evacuation actions included making telephone calls, gathering belongings and finishing other tasks. The model explained between 49 and 56 per cent of the variation in evacuation delay, which its authors describe as extraordinarily high for a study of human evacuation.

The delays themselves were spread widely. In WTC 1 the mean delay was 5.61 minutes, the median 3.00 minutes and the most frequent value 1 minute. In WTC 2 these values were 6.04, 4.00 and 5 minutes. The reported delays peaked in the first or second minute and then tailed off. Their distribution was approximately lognormal or gamma-shaped, and the delay tended to increase with the height of the floor.

Social influences

Other people strongly shape each step of the decision. In experiments by Latane and Darley, smoke was let into a room where students were filling in a questionnaire. Of the students who were alone, 75 per cent reported the smoke, but only 10 per cent did so when two passive companions were present. Social inhibition, diffusion of responsibility and imitation of others explain this effect. It can make people in restaurants, hotels and other public buildings ignore early cues. Introduction to Fire Safety Engineering links this to the conformity experiments of Asch and notes that group behaviour can also help, when a well-trained part of the group takes the right decision and others follow.

Staff and wardens have a large effect. In an unannounced drill in a department store, the fast response of staff led customers to start moving after 25 s on average, with a maximum of 55 s. In an underground station, passengers did not respond to the fire alarm at all, but moved at once when staff prompted them, and within 15 s of a precise live message. People also follow authority: some wait for permission from a manager before leaving.

Responsibility and social ties play a part as well. People at home react quickly to a smoke alarm because they know nobody else will deal with it, while visitors to a public building assume that someone will tell them if something is really wrong. Occupants also tend to gather the people to whom they have emotional ties, such as family members, before they leave. This affiliative behaviour takes time, especially when the members of a group are not together at the start of the incident.

Use in fire safety engineering

The decision process enters a design through the pre-movement time in the comparison of available and required escape time. In the past, engineers assumed that occupants would start to evacuate as soon as they perceived the alarm or a fire cue. Reports by fire victims have always challenged this assumption. Earlier editions of the handbook chapter suggested doubling the calculated movement time, while many fire safety engineers preferred to add 15 to 30 s. The 2002 edition argues that values should instead be based on research findings.

Data from drills and real fires show a wide range. In drills in seven residential buildings in Canada, announced weeks ahead without a date or time, the delay depended strongly on how well the alarm could be heard. In the three buildings with a clearly audible alarm, the mean delay to start was 2 min 49 s, about three-quarters of the total evacuation time. In two buildings where more than a fifth of the occupants found the alarm too quiet, some occupants started within 2 minutes, but others took up to 25 minutes, with a mean of 9 minutes. In three office buildings with trained occupants, the mean was 50 s, although many people still finished telephone calls, saved computer data or gathered belongings first. In real fires, delays of about 2.5 minutes were found in a high-rise office fire without an alarm, and about 10 minutes in a residential fire at night.

These differences follow less from the type of occupancy than from the characteristics of the building and its occupants. The building characteristics include the type of warning system, the layout, visual access to other people, any focal point such as a stage, training and the frequency of false alarms. The occupant characteristics include familiarity with the building, responsibility, social ties, commitment to an activity, alertness and physical or mental limitations. Well-trained staff and wardens can shorten the delay to start dramatically.

Limits and uncertainty

Human behaviour is one of the least predictable aspects of fire safety. Although many data from fires are available, they have not yet led to generally valid models for predicting pre-evacuation times. Researchers hesitate to suggest numbers because the research findings are limited. The SFPE Handbook regards unannounced drills as perfectly representative of a fire in which the only sign is the sudden sound of the alarm. Some argue that real fires should cause faster responses, but interviews with victims show that the first signs of a real fire are usually judged extremely ambiguous, which further increases the delay.

Statistical models of the decision process also have limits. Even the NIST model left about half of the variation in delay unexplained. Its data came from survivors, so occupants of the upper floors of WTC 2 who waited too long were missing from the sample. Comparisons between the towers need care, because the cues that led people to evacuate differed between them. Night-time fires, sleeping occupants and people with limited mobility or alertness are likely to need a longer time to start.

Common misconceptions

A widespread belief is that people in a fire tend to panic. Research shows the opposite. Deliberate, purposeful behaviour is the most frequent response, and panic is an infrequent or unusual reaction in most fires. Introduction to Fire Safety Engineering adds that a lack of awareness of the danger is usually a greater problem than panic, and that people find it hard to judge how fast a fire develops.

A second misconception is that an alarm leads straight to evacuation. A fire alarm on its own rarely triggers evacuation unless training and other information are provided. It works best as a way to alert occupants and prepare them for further information. A third misconception concerns the choice of route. People prefer the way by which they entered the building and attractive, transparent routes. Exit signs in their usual form have little influence on this choice, and emergency doors meant only for incidents are hardly used at all.

See also

• Evacuation modelling
• Required safe egress time
• Stay-put strategy
• Phased evacuation
• Escape signage

References

• Averill, J. D., Mileti, D. S., Peacock, R. D., Kuligowski, E. D., Groner, N., Proulx, G., Reneke, P. A., & Nelson, H. E. (2005). Occupant behavior, egress, and emergency communications (NIST NCSTAR 1-7). National Institute of Standards and Technology.
• Bryan, J. L. (2002). Behavioral response to fire and smoke. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-315–3-341). National Fire Protection Association; Society of Fire Protection Engineers.
• National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). International fire engineering guidelines (2005 ed.). Australian Building Codes Board.
• Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-342–3-366). National Fire Protection Association; Society of Fire Protection Engineers.
• Van Rossum, E. (2027). Introduction to Fire Safety Engineering. Fire Safety Academy.