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.


For any story in a building with a floor area equal to or less than 400 m² there should be

a minimum of 2 x class 'A' extinguishers with a minimum combined fire rating of 26A.



floor area 130m2 ..........  2 x 13A extinguishers

floor area 390m2 ..........  2 x 13A extinguishers



For any story in a building with a floor area greater than 400 m² there should be a minimum of two class A extinguishers with a minimum combined fire rating of 0.065 x floor area (m2)


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.





Normal practice is to use carbon dioxide (CO2) for fires involving live electrical equipment, however several different types of extinguisher are now suitable for use on 'electrical' fires. Surprisingly, some of these are water-based, such as water or foam spray in which case they will have passed the dielectric test specified in BS EN 3 - 7. This information can be found on the extinguisher label and will indicate the extinguisher has passed the 35 kV dielectric test at 1m (or similar).


The maximum distance to reach a fire extinguisher from electrical equipment should not be more than 10m.





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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