The LWF Blog

Fire Engineering | Fire Evacuation Strategies

March 12, 2014 11:35 am

When designing a new building or considering a change of use prior to a renovation, most architects and design teams are surprised to hear that the fire evacuation strategy should be considered at such an early stage of their fire safety and building plans.

To the casual building user, it must seem that a fire alarm sounds and an evacuation takes place. However, this is not always the case and in some situations, it is not possible or desirable that it should be so.

Fire engineers design appropriate evacuation strategies, dependent upon the building and its occupants.  In relation to a new build development, the evacuation strategy must be decided upon at a very early stage as it will have a significant impact on the overall design, including requirements for fire compartmentation, escape route dimensions and the fire alarm cause and effect.

The most commonly used fire evacuation strategies fall into the following categories:

Simultaneous Evacuation

This is the most common strategy and is often termed ‘one out, all out’.  Effectively, in the event of fire alarm activation, everybody leaves the building and makes their way to an assembly point.  This evacuation strategy is simple, in that all occupants follow the same instruction, i.e. evacuate.  However, it can lead to unnecessary evacuation for occupants, for instance, in cases where occupants are so remote from the fire that they are in no danger. This can lead to business disruption and associated downtime.

Phased Evacuation

Phased evacuation is frequently adopted in high rise developments, or very large buildings.  This strategy is effectively based on those most at risk (in close proximity to the fire) evacuating first, with occupants who are separated from immediate danger by fire resisting construction and/or distance on a delayed evacuation.  

Phased evacuation prioritises those most at risk, which presents obvious benefits.  Additional building design related benefits can include reduced escape route sizes, with the stair cores a significant advantage.  However, to use a ‘stay put’ policy, or delay full evacuation, other measures need to be introduced.  The fire compartmentation requirements will be greater than a simultaneous evacuation and due to the reliance on compartmentation, it must be ensured that it is maintained for the life of the building.  Additionally, the fire alarm system will need to be more complex to allow for evacuation zones.

In addition to the requirements above, psychological factors must be taken into account.  For the evacuation to be successful, occupants are required to react in accordance to the strategy and this should therefore be considered in great detail.  The design must carry some resilience to compensate for occupants reacting in alternative ways.  Such considerations of behaviour can be predicted using specialist fire engineering techniques and software which take into account all possibilities and likely timings. 

Progressive Horizontal Evacuation

This is effectively a deviation of phased evacuation and is most commonly used in environments where the vertical descent of occupants may not be desirable, the most common example being a hospital.  

Should a fire occur within a hospital, full evacuation outside of the building is not normally desirable.  Similarly, patients may not be able to use the stairs for escape; therefore, it is desirable to move them horizontally, whilst maintaining clinical care.  To ensure this is possible, fire compartmentation is required to ensure occupants can move from the fire to a place of relative safety.  Once more, this scenario requires a more complex fire alarm system with an evacuation signal provided to given zones and an alert (pre-evacuation) signal given to adjacent zones.  Fire safety management training is also required to ensure staff have a full understanding of the evacuation procedures and carry them out as prescribed.

It is clear that there are a variety of evacuation strategies available and the evacuation strategy must be selected to suit the needs of the eventual occupant.  Adopting the wrong strategy for a building will lead to problems in evacuation and could potentially put building occupiers in danger.

If you would like to know more, or would like to arrange an appointment with one of our senior fire safety advisers, please call Peter Gyere on 020 8668 8663

Lawrence Webster Forrest Limited is a fire engineering and fire risk management consultancy established in 1986, with extensive experience in the development of fire engineered technology and the application of fire safety standards including fire engineered techniques.

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