Understanding UK Fire Classes
Every portable fire extinguisher is designed to tackle specific types of fire. Using the wrong extinguisher — such as water on a flammable liquid fire, or water on live electrical equipment — can cause the fire to spread or create an electrocution hazard. The European fire class system provides a standardised framework for categorising fires by the type of material burning, making it straightforward to match the correct extinguishing agent to the risk.
The Fire Classes Explained
- Class A — Fires involving solid, organic combustibles that form a glowing ember on burning. Materials include wood, paper, cardboard, textiles, rubber, and many plastics. Water, foam, and ABC powder extinguishers are effective. The most common class in offices and residential premises.
- Class B — Fires involving flammable liquids or liquefiable solids, including petrol, diesel, oils (excluding cooking oils), paint, solvents, and wax. Foam or CO2 extinguishers should be used. Never use water — it can cause burning liquid to scatter.
- Class C — Fires involving flammable gases such as propane, butane, methane, and hydrogen. The correct approach is to shut off the gas supply rather than extinguish the flame; extinguishing without isolating the source risks an explosion from unburned gas.
- Class D — Fires involving combustible metals such as magnesium, titanium, lithium, sodium, and potassium. These require specialist dry powder extinguishers formulated for the specific metal. Standard extinguishers should never be used on Class D fires.
- Class F — Fires involving cooking oils and fats at high temperature, such as in deep fat fryers and chip pans. These are among the most dangerous fire types — burning oil can reach over 360 °C, well above its autoignition temperature. A wet chemical extinguisher is the only suitable agent; never use water.
What About Electrical Fires?
"Electrical fire" is not an official fire class — it describes a fire in which live electrical equipment is involved or adjacent. The underlying fire is usually Class A or B. The concern is the risk of electrocution to the user. CO2 and dry powder extinguishers are non-conductive and safe to use near live electrical equipment up to 1,000 V (CO2) or 1,000 V (dry powder) according to BS EN 3. Water and foam must never be used on live electrical equipment.
Matching Extinguishers to Fire Classes
Under BS 5306-8, fire extinguishers must be selected to cover the fire risks present in the premises. In most offices and commercial buildings, a combination of water or foam extinguishers (for Class A) and CO2 extinguishers (for electrical risks) is the standard provision. Commercial kitchens require a wet chemical extinguisher for Class F risk alongside CO2 for electrical equipment.
The number and rating of extinguishers required depends on the floor area and risk category of the premises — a risk assessment and selection exercise by a competent person, qualified to the BFC EAL Level 3 Fire Extinguisher standard, ensures the correct provision.