Using the wrong extinguisher on a fire can make it worse. Here’s what each type is for, how to recognise it, and what never to use it on.
Classes of fire
Fires are grouped by what is burning:
| Class | What’s burning | Examples |
|---|---|---|
| A | Solid materials | Paper, wood, textiles, plastics |
| B | Flammable liquids | Petrol, diesel, paint, solvents |
| C | Flammable gases | Propane, butane, natural gas |
| D | Metals | Magnesium, aluminium swarf |
| F | Cooking oils and fats | Deep fat fryers |
Fires involving electrical equipment aren’t a class of their own, but they need care because of the risk of electric shock. Once the power is off, an electrical fire usually behaves like the class of whatever is burning.
How to recognise each type
Since 1997, the body of every new extinguisher in the UK has been red, with a coloured band or label showing the type:
| Type | Label colour | Use on | Don’t use on |
|---|---|---|---|
| Water | Red | Class A: paper, wood, textiles | Electrical equipment, burning liquids, cooking oil |
| Foam | Cream | Class A and Class B (liquids) | Cooking oil fires; electrical equipment unless the extinguisher is marked as tested for it |
| Carbon dioxide (CO2) | Black | Electrical equipment, Class B (liquids) | Cooking oil fires; not effective on deep-seated solid fires |
| Dry powder | Blue | Class A, B and C, and electrical equipment | Enclosed spaces where people are working, and cooking oil |
| Wet chemical | Yellow | Class F: cooking oil and fat | Electrical equipment |
Water
Water extinguishers cool burning solids and are the standard choice for offices, shops and other buildings where the main fire risk is paper, furniture and fabrics. Never use water on burning oil or fat, or on live electrical equipment.
Foam
Foam extinguishers work on solids and on flammable liquids, by smothering the surface of the liquid. That makes them a useful general-purpose choice where both are present.
Carbon dioxide
CO2 extinguishers smother a fire by displacing the oxygen around it, and leave no residue, which is why they’re the usual choice for computer rooms, comms cupboards and electrical equipment. The horn gets extremely cold when used, so hold the extinguisher by its handle, and remember that CO2 disperses quickly, so a fire can re-ignite. Don’t use CO2 in a small, enclosed space where people will remain.
Dry powder
Powder extinguishers work on many kinds of fire, but the powder spreads widely, makes it hard to see and breathe, and causes a lot of damage. That’s why they’re generally kept for outdoor areas, garages, vehicles and plant rooms, rather than offices or other enclosed spaces where people work.
Wet chemical
Wet chemical extinguishers are designed for cooking oil and fat fires. They cool the oil and form a layer on its surface that stops it re-igniting. Any commercial kitchen with a deep fat fryer should have one close by.
Which do you need?
Most premises need a combination: water or foam for the general fire risk, CO2 near electrical equipment, and specialist types where there’s a particular hazard. Your fire risk assessment and BS 5306-8, the code of practice for choosing and siting extinguishers, decide the mix.
If you’d like us to check that you have the right types in the right places, see extinguisher supply and installation or read how many extinguishers a business needs.