Classes of Fire Explained: A, B, C, D, F and Electrical

Fires are classified by what is burning, because the fuel decides which extinguisher will work and which will make things worse. This guide covers each class with workplace examples, the right and wrong extinguishers, how electrical fires fit in, and why UK and US classes use different letters.

What are the 5 classes of fire?

The five classes are A, B, C, D and F, set out in the European standard BS EN 2, Classification of fires. The standard groups fires by the material that is burning, and the same five classes appear in the government’s fire risk assessment guidance for offices and shops.

Source: BS EN 2; London Fire Brigade Guidance Note 08 (Rev 20, 2025); Warwickshire Fire and Rescue Service; HM Government, Fire safety risk assessment: offices and shops.

Class A fires: solid materials

Class A fires involve ordinary solid combustibles. They are the most common type in offices, shops, warehouses and schools, because paper, cardboard, furniture and packaging are everywhere.

Water is the traditional Class A agent. It soaks into the material and cools it below the point where it will keep burning. Foam and dry powder also work on Class A, as does water mist. CO2 is not listed for Class A fires because it does little to cool the burning material, so the fire can reignite once the gas clears.

Extinguishers that work on Class A carry an “A” rating such as 13A. The number reflects the size of test fire it put out, so a higher number means more firefighting capacity.

Class B fires: flammable liquids

Class B covers flammable liquids and solids that melt into liquids when heated, such as waxes and some plastics. Workshops, vehicle maintenance areas, print rooms, cleaning stores and anywhere that uses solvents or fuels can have a Class B risk.

Do not use a standard water extinguisher on a burning liquid. The water can spread the liquid and the fire with it. (Some water extinguishers with additives carry a B rating as well; the label will say so.) Foam smothers the surface and seals in the vapours, CO2 displaces the oxygen, and dry powder knocks the flames down. Class B ratings look like 34B or 55B.

Where flammable liquids or vapours could form an explosive atmosphere, the Dangerous Substances and Explosive Atmospheres Regulations also apply. Our guide to the DSEAR regulations explains what that means.

Class C fires: flammable gases

Class C fires involve gases such as propane, butane, natural gas and acetylene. The first and most effective action is to shut off the gas supply, but only if that can be done safely.

Putting out a gas flame while the gas is still escaping can be more dangerous than the flame itself, because unburnt gas can build up and then ignite explosively. Dry powder extinguishers are rated for Class C, but London Fire Brigade guidance advises seeking specialist advice for Class C risks. If in doubt, evacuate and call 999.

Class D fires: combustible metals

Class D fires involve metals such as magnesium, aluminium in powder or swarf form, titanium and lithium metal. They are mostly found in specialist manufacturing, machining and laboratories.

Metal fires burn extremely hot and can react badly with ordinary agents, including water. Only a specialist Class D powder (London Fire Brigade lists its colour code as signal violet) or dry sand should be used, and the choice should come from specialist advice based on the specific metal. Standard dry powder extinguishers are not suitable.

Class F fires: cooking oils and fats

Class F fires involve cooking oils and fats at very high temperatures, typically in deep fat fryers in commercial kitchens. Cooking oil fires have their own class because they behave differently from other liquid fires, and need their own type of extinguisher. Government fire safety guidance describes Class F extinguishers as particularly suitable for commercial kitchens with deep-fat fryers, and says foam extinguishers are not suitable for deep-fat fryers or chip pans.

Wet chemical extinguishers are designed for Class F. The agent bonds with the burning fat or oil, smothering the fire and cooling it. A fire blanket can smother a small pan fire. Never use water: Essex County Fire and Rescue Service warns never to throw water on hot or burning oil. Turn off the heat if it is safe and call 999.

Are electrical fires a class of fire?

No. BS EN 2 states that it does not define a particular class of fire involving an electrical risk. Electricity is a source of ignition rather than a fuel, and once the power is off, the fire is usually a Class A or Class B fire.

While the equipment is live, though, the extinguisher must not conduct electricity back to the user. That rules out water and foam. CO2 is the usual choice: Warwickshire Fire and Rescue Service lists it for computer equipment and other electrical appliances. Dry powder also works, and London Fire Brigade lists water mist as suitable for electrical fires. Isolate the power first if you can do so safely. This is why extinguisher charts and signs often show “electrical” as an extra category, even though the standard does not.

Why do UK and US classes of fire differ?

The US uses a different system, set by the National Fire Protection Association, with five classes: A, B, C, D and K. The letters do not line up with BS EN 2, which causes confusion when people read American websites or safety data sheets.

If you work in the UK, use the BS EN 2 letters. An extinguisher marked for “Class C” in the UK is rated for gas fires, not electrical ones.

How the classes of fire link to your fire risk assessment

Your fire risk assessment should identify which classes of fire could occur in each area, and the extinguishers provided should match. Under Article 13 of the Regulatory Reform (Fire Safety) Order 2005, the responsible person must, where necessary, make sure the premises are equipped with appropriate firefighting equipment, and that any manual equipment is easily accessible, simple to use and indicated by signs.

In practice that means water or foam for general areas, CO2 near electrical equipment and server rooms, wet chemical in kitchens with fryers, and specialist advice for gas and metal risks. Our guide to fire extinguisher colours and types shows how to tell them apart, and the fire triangle explains how each one puts a fire out.

Some hazards should not be tackled at all. Warwickshire Fire and Rescue Service and the government guidance both advise that it is not safe to fight fires involving aerosols with extinguishers.

Frequently asked questions

Where to learn more

• Fire Awareness Training: classes of fire and choosing the right extinguisher, for all staff
• Fire Warden and Fire Marshal Training: a full day including an extinguisher practical
• Fire extinguisher colours and types explained
• The fire triangle explained
• Fire marshal duties: a UK guide