The LWF Blog

Fire Safety for Facilities Management Personnel – Means of Escape – Part 123

November 8, 2021 1:35 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 122, LWF continued discussing means of escape, including stairway capacity and how to calculate it. In part 123, we begin to look at floor space factors when calculating occupant capacity for means of escape.

In some buildings, it is simple to estimate the likely occupancy. A restaurant at capacity will be filled when each of the tables is full and so that number, plus staff, will be the maximum occupancy. Other types of building can present more of a challenge. At the design stage, it is important to be able to make an educated assumption about the number of people who will occupy a building, unless it is known and acknowledged that only a specific number of occupants will be possible.

In order to calculate the ‘educated assumption’, floor space factors are used. A floor space factor is the area per person adopted for the purpose of calculating the occupant capacity of a room, area or storey of a building. The purpose is to ensure that adequate provision is made for the occupants in terms of the number and width of exits.

The calculation is as follows:

Area of the room or storey in m2 divided by the floor space factor in m2 per person.

If the area contains stairways, lifts and sanitary accommodation, this is to be excluded from the overall area of the room or storey.

The floor space factor per person varies depending on the intended type of area usage. Some typical floor space factors are as follows:

Standing and spectator areas, bar areas (within 2 m of serving point) and similar refreshment areas – 0.3 m2 per person

Bar areas (without fixed seating) bingo halls, dance halls, general purpose assembly halls – 0.5m2 per person

Restaurants, lounges, bars (other than examples above), dining rooms, staff rooms, meeting rooms – 1.0 m2 per person

Sales areas of shops, including department stores and supermarkets 2.0 m2 per person

Offices – 6.0 m2 per person

Lightly occupied sales areas of shops, such as furniture and white goods departments, cash and carries – 7.0 m2 per person

Warehouses – 30.0 m2 per person

These figures are given in Approved Document B, which supports the Building Regulations in England and Wales.

In part 124 of this series, LWF will continue to discuss floor space factors. 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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