Evacuation of Occupants

Egress design

Egress design should be based upon an evaluation of a building’s total fire protection system (see figure 41.5).

Figure 41.5 Principles of exit safety

People evacuating from a burning building are influenced by a number of impressions during their escape. The occupants have to make several decisions during the escape in order to make the right choices in each situation. These reactions can differ widely, depending upon the physical and mental capabilities and conditions of building occupants. The building will also influence the decisions made by the occupants by its escape routes, guidance signs and other installed safety systems. The spread of fire and smoke will have the strongest impact on how the occupants make their decisions. The smoke will limit the visibility in the building and create a non-tenable environment to the evacuating persons. Radiation from fire and flames creates large spaces that cannot be used for evacuation, which increases the risk. In designing means of egress one first needs a familiarity with the reaction of people in fire emergencies. Patterns of movement of people must be understood.

The three stages of evacuation time are notification time, reaction time and time to evacuate. The notification time is related to whether there is a fire alarm system in the building or if the occupant is able to understand the situation or how the building is divided into compartments. The reaction time depends on the occupant’s ability to make decisions, the properties of the fire (such as the amount of heat and smoke) and how the building’s egress system is planned. Finally, the time to evacuate depends on where in the building crowds are formed and how people move in various situations.  In specific buildings with mobile occupants, for example, studies have shown certain reproducible flow characteristics from persons exiting the buildings. These predictable flow characteristics have fostered computer simulations and modelling to aid the egress design process.

The evacuation travel distances are related to the fire hazard of the contents. The higher the hazard, the shorter the travel distance to an exit. A safe exit from a building requires a safe path of escape from the fire environment. Hence, there must be a number of properly designed means of egress of adequate capacity. There should be at least one alternative means of egress considering that fire, smoke and the characteristics of occupants and so on may prevent use of one means of egress. The means of egress must be protected against fire, heat and smoke during the egress time. Thus, it is necessary to have building codes that consider the passive protection, according to evacuation and of course to fire protection. A building must manage the critical situations, which are given in the codes concerning evacuation. For example, in the Swedish Building Codes, the smoke layer must not reach below 1.6 + 0.1H (H is the total compartment height), maximum radiation 10 kW/m² of short duration, and the temperature in the breathing air must not exceed 80 °C. An effective evacuation can take place if a fire is discovered early and the occupants are alerted promptly with a detection and alarm system. A proper mark of the means of egress surely facilitates the evacuation. There is also a need for organization and drill of evacuation procedures.

Human behaviour during fires

How one reacts during a fire is related to the role assumed, previous experience, education and personality; the perceived threat of the fire situation; the physical characteristics and means of egress available within the structure; and the actions of others who are sharing the experience. Detailed interviews and studies over 30 years have established that instances of non-adaptive, or panic, behaviour are rare events that occur under specific conditions. Most behaviour in fires is determined by information analysis, resulting in cooperative and altruistic actions. Human behaviour is found to pass through a number of identified stages, with the possibility of various routes from one stage to the next. In summary, the fire is seen as having three general stages:

1. The individual receives initial cues and investigates or misinterprets these initial cues.

2. Once the fire is apparent, the individual will try to obtain further information, contact others or leave.

3. The individual will thereafter deal with the fire, interact with others or escape.

Pre-fire activity is an important factor. If a person is engaged in a well-known activity, for example eating a meal in a restaurant, the implications for subsequent behaviour are considerable.

Cue reception may be a function of pre-fire activity. There is a tendency for gender differences, with females more likely to be recipients of noises and odours, though the effect is only slight. There are role differences in initial responses to the cue. In domestic fires, if the female receives the cue and investigates, the male, when told, is likely to “have a look” and delay further actions. In larger establishments, the cue may be an alarm warning. Information may come from others and has been found to be inadequate for effective behaviour. Individuals may or may not have realized that there is a fire. An understanding of their behaviour must take account of whether they have defined their situation correctly. When the fire has been defined, the “prepare” stage occurs. The particular type of occupancy is likely to have a great influence on exactly how this stage develops. The “prepare” stage includes in chronological order “instruct”, “explore” and “withdraw”. The “act” stage, which is the final stage, depends upon role, occupancy, and earlier behaviour and experience. It may be possible for early evacuation or effective fire-fighting to occur.

Building transportation systems

Building transportation systems must be considered during the design stage and should be integrated with the whole building’s fire protection system. The hazards associated with these systems must be included in any pre-fire planning and fire protection survey. Building transportation systems, such as elevators and escalators, make high-rise buildings feasible. Elevator shafts can contribute to the spread of smoke and fire. On the other hand, an elevator is a necessary tool for fire-fighting operations in high-rise buildings. Transportation systems may contribute to dangerous and complicated fire safety problems because an enclosed elevator shaft acts as a chimney or flue because of the stack effect of hot smoke and gases from fire. This generally results in the movement of smoke and combustion products from lower to upper levels of the building. High-rise buildings present new and different problems to fire-suppression forces, including the use of elevators during emergencies. Elevators are unsafe in a fire for several reasons:

1. Persons may push a corridor button and have to wait for an elevator that may never respond, losing valuable escape time.

2. Elevators do not prioritize car and corridor calls, and one of the calls may be at the fire floor.

3. Elevators cannot start until the lift and shaft doors are closed, and panic could lead to overcrowding of an elevator and the blockage of the doors, which would thus prevent closing.

4. The power can fail during a fire at any time, thus leading to entrapment. (See figure 41.6)

Figure 41.6 An example of a pictographic warning message for elevator use

Fire drills and occupant training

A proper mark of the means of egress facilitates the evacuation, but it does not ensure life safety during fire. Exit drills are necessary to make an orderly escape. They are specially required in schools, board and care facilities and industries with high hazard. Employee drills are required, for example, in hotel and large business occupancies. Exit drills should be conducted to avoid confusion and ensure the evacuation of all occupants. All employees should be assigned to check for availability, to count occupants when they are outside the fire area, to search for stragglers and to control re-entry. They should also recognize the evacuation signal and know the exit route they are to follow. Primary and alternative routes should be established, and all employees should be trained to use either route. After each exit drill, a meeting of responsible managers should be held to evaluate the success of the drill and to solve any kind of problem that could have occurred.