Fire extinguishers · BS 5306-8
How many fire extinguishers does a building need?
The rules of thumb for how many extinguishers each storey needs, how far anyone should walk to one, and where they go on the wall.
The rule for each storey
Extinguishers are provided storey by storey, using the fire rating of the extinguishers (the Class A rating, such as 13A or 21A) added together:
| Storey size | What is needed |
|---|---|
| 50 m² or less | At least one extinguisher, with a total Class A rating of at least 26A |
| More than 50 m², up to 400 m² | At least two extinguishers, totalling at least 26A |
| Over 400 m² | A total of 0.065 × the floor area in m². That is about 13A for every 200 m² |
These are the figures from BS 5306-8. They are a starting point. The fire risk assessment decides whether a particular building needs more.
Two worked examples
A 300 m² storey. It is over 50 m² and under 400 m², so it needs at least two extinguishers totalling 26A or more. Two 13A extinguishers make exactly 26A.
A 600 m² storey. It is over 400 m², so the total is 0.065 × 600 = 39A. Three 13A extinguishers make 39A. There must always be at least two extinguishers on a storey this size, and the total rating is what counts.
The free numbers calculator does this sum from the floor area, so you can check a storey quickly and print the working.
How far should anyone have to walk?
Nobody should have to walk more than 30 m to reach a Class A extinguisher. For Class B risks (flammable liquids) and Class F risks (cooking oil and fat) the distance is 10 m.
Take 5 m off for every door someone has to open on the way. A 30 m limit becomes 25 m with one door in the way, and 20 m with two.
Where they go on the wall
Extinguishers are mounted on the wall, on a stand or on a plinth, not left on the floor. The handle goes at no more than 1 m from the floor, or 1.5 m for extinguishers with a total mass under 4 kg.
Choosing the right type
The number of extinguishers is only half of it. The type has to suit what could burn:
- Class A: solids such as wood and paper
- Class B: flammable liquids
- Class C: flammable gases
- Class D: metals
- Class F: cooking oils and fats
The body is red, and a colour band shows the contents: water has no band, foam is cream, ABC powder is blue, CO2 is black, wet chemical is canary yellow and Class D powder is signal violet. For live electrical equipment, use only extinguishers whose contents do not conduct electricity, such as CO2 or powder. Water-based extinguishers should not be used on live equipment.
Common questions
How many fire extinguishers does a 100 m² floor need?
At least two, with a total Class A rating of at least 26A. A floor of 50 m² or less needs at least one, again totalling at least 26A.
How far should anyone have to walk to an extinguisher?
No more than 30 m to a Class A extinguisher, and 10 m for Class B and Class F risks. Take 5 m off for each door that has to be opened.
What height should a fire extinguisher be mounted at?
The handle should be no more than 1 m from the floor, or 1.5 m for extinguishers with a total mass under 4 kg.
Can I use a water extinguisher on electrical equipment?
No. Water-based extinguishers conduct electricity. Use CO2, powder or clean agent extinguishers, and isolate live equipment before you discharge where you can.
This guide is general information for UK fire & security companies, not legal or engineering advice. Always work to the current edition of the relevant standard and your own competent-person judgement.
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