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

Every fire needs three things: heat, oxygen and fuel. Remove any one and the fire goes out. Different fuels behave differently, so they are sorted into classes. Each class has an extinguishing agent that works best for it — and using the wrong one can spread the fire, cause an explosion or give you a severe electric shock. Here is a plain-English run-through of each class and the extinguisher that matches it.

The class of a fire is defined by what is burning. Identify the fuel first, and the right extinguisher choice follows naturally.

Class A — ordinary combustibles

Class A fires involve everyday solid materials: wood, paper, cardboard, textiles, furniture and most plastics. These are the most common fires in homes and offices. They leave ash — a useful clue. The best agent is water, which cools the fuel below its ignition temperature. Foam also works well on Class A fires.

Class B — flammable liquids

Class B covers flammable and combustible liquids such as petrol, diesel, paint, solvents, oil and spirits. Water must never be used here — it can cause the burning liquid to splash and spread. The right agents are foam, which forms a blanket that smothers the surface, dry powder, or CO₂ for smaller fires.

Class C — flammable gases

Class C fires involve flammable gases such as propane, butane, methane or natural gas. The safest action is almost always to isolate the gas supply if you can do so safely — cutting off the fuel starves the fire. Dry powder is the extinguisher most often used on Class C fires, but tackling a gas fire is high risk, and evacuation is frequently the wiser choice.

Class D — combustible metals

Class D fires involve burning metals such as magnesium, titanium, aluminium swarf, sodium or lithium. These are mostly an industrial and laboratory concern. They burn extremely hot and react violently with water and many ordinary agents. They require a specialist dry powder (Class D) extinguisher formulated for the specific metal — standard extinguishers must not be used.

Class F — cooking oils and fats

Class F fires involve cooking oils and fats, the kind found in kitchens and deep-fat fryers. They burn at very high temperatures, and using water on them causes a violent, explosive reaction. The correct agent is a wet chemical extinguisher, which cools the oil and forms a soapy layer that seals the surface. A fire blanket is also valuable for a small pan fire.

Electrical fires

Electrical fires — involving live equipment such as computers, machinery, switchboards and chargers — are sometimes labelled "Class E", but strictly speaking electricity is a source of ignition rather than a fuel. The danger is that conductive agents like water and foam can give you a fatal shock. The safe choices are CO₂, which leaves no residue and is gentle on electronics, or a suitable dry powder. Switching off the power, where safe, turns it back into whatever class the burning material actually is.

Matching the extinguisher to the class

Once you know the class, choosing the extinguisher becomes straightforward. The quick summary below pairs each class with its safe agent.

• Class A (combustibles): water or foam.
• Class B (flammable liquids): foam, dry powder or CO₂.
• Class C (flammable gases): dry powder — isolate the supply first.
• Class D (metals): specialist Class D powder only.
• Class F (cooking oils): wet chemical or a fire blanket.
• Electrical: CO₂ or dry powder — never water or foam on live equipment.

Knowing the class is only half the skill — you also need to operate the extinguisher correctly. See our guide on how to use a fire extinguisher for the PASS method.

Reading the chart is easy; making the right call in a real emergency takes training. A certified Fire course teaches your team to recognise every class of fire and respond correctly — for just €35 per person. Explore all our safety courses and equip your people with knowledge that protects lives.