Number of Fire Extinguishers Required

The following information is provided for guidance purposes, and should not be relied upon for the purposes of a fire risk assessment, in which case, British Standard 5306-8:2000 should be referred to.

Fire extinguishers for use on class A fires (flammable solids such as paper, wood, textiles etc) are ‘rated’ on their ability to extinguish test fires. The test rating can be found on the extinguisher label, e.g. 13A, 21A, 26A etc. Similarly, extinguishers for use on flammable liquids are given a class B rating e.g. 34B, however the calculation for these is different and is not covered here.

Class 'A' extinguishers

British Standard 5306 contains formulae for calculating the number of class A extinguishers as follows:

floor area (m2) x 0.065 divided by the extinguisher rating and round up.

e.g. For a floor area of 1250 m2:

For 13A extinguishers:     1250 x 0.065 ÷ 13 = 6.25       Round up to 7


For 21A extinguishers:     1250 x 0.065 ÷ 21 = 3.87       Round up to 4

(As a rule of thumb one 13A extinguisher covers 200 square metres of floor area)

There should be a minimum of 2 extinguishers per floor with a combined rating of at least 26A, unless the upper floor area is very small i.e. below 100m2, and in single occupancy, in which case, only a minimum rating of 13A is required on the upper floor.


The extinguishers should be positioned close to exits, for further information on siting see: siting

Where it is desirable to have smaller, lighter extinguishers, foam, or water with additives can be used to reduce weight whilst maintaining fire fighting capability. e.g. 6 Litre AFFF foam spray extinguishers are usually rated at 13A, but are approximately 30% lighter than 9 litre water.


Specialised extinguishers should also be provided to cover classes B (Liquids), D (Metals), E (fires involving electrical apparatus) and F (cooking oils and fats), e.g. foam, carbon dioxide or powder.


For an office environment we recommends the relevant number of 6L (or 3L) AFFF extinguishers plus an appropriate amount of CO2 extinguishers to cover any electrical risk.



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