The LWF Blog

Fire Safety for Facilities Management Personnel – Means of Escape – Part 124

November 15, 2021 12:31 pm

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 123, LWF began to look at floor space factors when calculating occupant capacity for means of escape. In part 124, we continue to discuss floor space factors.

Floor Space Factors

As noted in the last blog, the accepted and typical floor space factor figures for common occupancies are given in Approved Document B. However, those figures are not ‘set in stone’ and may be altered somewhat by discussion with and approval by the enforcing authority. The need to vary the figures may arise from the occupancy not fitting the categories given in the code, or where a large chain of identical premises has proven a more accurate basis for the calculation.

The floor space factor calculation is intended as a tool to determine the number of occupants for whom exit capacity must be provided. It is not designed to limit the number of occupants allowed within a space. The capacity limit is determined by the exit widths.


Fire-resisting Construction

Fire-resisting construction refers to the walls, floors, ceilings, doors etc. constructed in a specific manner and capable of resisting fire for a specified amount of time. Commonly, in order to protect means of escape, a fire resistance of 30 minutes is provided. This period of time is considered sufficient for building occupants to effect a safe evacuation from the premises to a place of safety, and for the Fire Service to attend and fight the fire.

Fire-resistant construction can be applied to higher-hazard areas for an increased duration of fire resistance, if required. It may be necessary, as per the building regulations, to minimise the spread of fire.


Escape route protection

When the term ‘protected’ is used in reference to means of escape, such as protected stairway and protected lobby when discussing travel distance, it means that the escape route or part thereof is enclosed by construction that is fire-resisting. When installed, maintained and used as intended, it stops fire spreading to the escape route and ensures conditions do not deteriorate due to smoke and particulate matter for the time indicated.


In part 125 of this series, LWF will continue to discuss means of escape by looking at the three stages of escape: travel within rooms; horizontal travel and vertical travel. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

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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