The LWF Blog

Fire Engineering for Healthcare Premises – The Human Element – Part 55

October 4, 2021 12:03 pm

In LWF’s blog series for healthcare professionals, our aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 54 of Fire Engineering for Healthcare Premises, LWF looked at the reactions of people to the sounding of the fire alarm in a healthcare building. In part 55, we will discuss pre-movement time.

When evacuation time is discussed as part of a fire safety design, it comprises two key parts – travel time and pre-movement time.

Required safe egress time (abbreviated to RSET) also includes the time for a fire to be detected and the alarm raised, whether the alarm is automatic or manual.

Pre-movement time can be further sub-divided into two areas of consideration:

  • Recognition time – the time taken for a building occupant to recognise that an alarm has been sounded and they need to take action, and;
  • Response time – the time taken for all other activities performed prior to evacuation, whether advisable or not.

The response time component may encompass various different types of action, some of which may be appropriate or even necessary – such as investigating the threat, taking first-aid firefighting action if the fire is small, assisting or ordering other building occupants to leave, or assisting patients in the case of healthcare buildings.

Other actions taken may be inadvisable and should be discouraged, but when considering human reactions to a fire alarm, they should be taken into account in any case. These may include gathering personal possessions or looking for family members, for instance.

A modelling short-cut aims to represent all pre-movement activities with a single time delay before a person moves (and when ‘moves’ is used in this context, it relates to the building occupant moving towards a place of safety as a response to the fire alarm, all other movements not to that end are counted as pre-movement). The probability distribution for this delay is hard to quantify without considering the activities explicitly.

Evacuation modelling aims to predict the pre-movement activity phase, the majority using a distribution of delay times – some examples are CRISP, EXODUS, EvacSim etc.

After pre-movement time is considered, travel time must be analysed and the first part of this is speed of movement, which is affected by the type of person evacuating and potential crowd density.


In Part 56 of LWF’s blog series, LWF will discuss speed of movement, patient dependency and disabilities. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact LWF on freephone 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.


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