Fire classes
Class A: solids such as wood, paper and fabric. Class B: flammable liquids. Class C: flammable gases. Class D: burning metals. Class F: cooking oils and fats. Electrical fires are not a class; they are shown by a spark symbol.
Extinguisher colours
In the UK, extinguishers have a red body with a coloured band showing what is inside. Red: water, for Class A. Cream: foam, for Class A and B. Blue: dry powder, for A, B and C and often electrical (it can reduce visibility and affect breathing in small rooms, so use it indoors only where your risk assessment says so). Black: CO2, for Class B and electrical (it does not cool, so it is not for solids). Yellow: wet chemical, for Class F cooking oil fires.
Which to use where
- Offices: water or foam, plus CO2 near electrical equipment.
- Kitchens: wet chemical near fryers, a fire blanket, and CO2 for electrical.
- Workshops: foam or powder where there are flammable liquids, plus CO2.
- Server rooms: CO2, as it leaves no residue.
- Gas: turning off the supply comes first.
How many you need
BS 5306-8:2023 sets the minimum for Class A cover on each floor (storey).
- Up to 50 square metres: at least one Class A extinguisher with a total rating of at least 26A.
- Over 50 and up to 400 square metres: at least two Class A extinguishers with a combined rating of at least 26A.
- Over 400 square metres: at least two, with a combined rating of 0.065 times the floor area (so 1,000 square metres needs at least 65A).
A standard 9 litre water extinguisher is rated 13A. Nobody should have to travel more than 30 metres to reach a Class A extinguisher, or more than 10 metres for Class B and Class F risks. Your fire risk assessment decides the final mix.