The LWF Blog

Fire Engineering for Healthcare Premises – The Human Element – Part 54

September 27, 2021 11:44 am

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 53 of Fire Engineering for Healthcare Premises, LWF looked at the human element of fire safety management, by discussing staff response to fire alarms. In part 54, we will continue to look at the reactions of people to the fire alarm in a healthcare building.

When assessing the likely response to a fire alarm, it is important to understand the speed of movement. Speed of movement of independent people (that is, those people who can move independently and do not require assistance) is well-established in studies. It is possible to utilise empirical data on walking speed given the variables of crowd density (people per square metre), flow rates in corridors and up/down stairs, the rate at which queues of people pass through doorways or any restricted-width passageway or other construction.

Due to people preferring what is familiar to them, all potential exits are not utilised equally. Not all exit doors are used at optimum levels, whereas some will potentially be over-utilised, such as the main entrance to a building.

Research has been carried out to establish the capabilities of dependent and very high dependency patients and those persons with disabilities and mobility issues. Of course, this group of people will move more slowly and may find some obstacles impassable. This data allows the movement-time portion of the total evacuation time to be estimated fairly accurately, however, the movement-time portion is not the largest component of the overall time evacuation takes.

During the evacuation process, people within the healthcare building may be exposed to smoke and other toxic products of combustion. Such exposure is quantified in terms of a fractional effective dose (FED), which is dependent on the concentration of certain toxins within the cocktail of fire gases – and the duration of the exposure.

When the FED for a particular person is reached – and FEDs vary per person – they are overcome by the smoke. Some products of combustion have an almost instantaneous effect, rather than a cumulative one and concentration is the key parameter.

The tenability of a room may be expressed in a number of ways:

  • The time for a person’s FED to reach unity (if they were to remain there for the duration indicated);
  • The value of the concentration of a given product sufficient to prevent escape.


In Part 55 of LWF’s blog series, LWF will discuss pre-movement time. 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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