Fire Extinguisher Types Explained

There is no single extinguisher that puts out every fire. Use the wrong one — water on a chip-pan fire, or CO2 on burning wood — and you can make the situation far more dangerous. UK fire extinguishers are split into five main types, each colour-coded under BS EN 3 and each designed for a specific set of fire classes. This guide explains the fire classes, the five extinguisher types, where each should and should not be used, how to read the colour codes, and the PASS technique for using one safely.

Understanding fire classes

Every extinguisher is rated against the classes of fire it can safely tackle. The class depends on what is burning — and matching the extinguisher to the fuel is the single most important decision you make.

• Class A — ordinary combustible solids such as wood, paper, fabric and furniture.
• Class B — flammable liquids such as petrol, diesel, oil, paint, solvents and alcohol.
• Class C — flammable gases including methane, propane and butane.
• Class D — flammable metals such as magnesium, aluminium powder and potassium.
• Class F — cooking oils and fats, typically in deep-fat fryers and chip pans.
• Electrical — fires involving live electrical equipment, treated separately because of the shock risk.

Electrical fires are not given a letter because, in principle, electricity is an ignition source rather than a fuel — but live equipment demands non-conductive agents (CO2 or, with care, foam), so it is always considered in its own right. Class D fires involving metals require specialist powders only and are never tackled with standard extinguishers.

The five extinguisher types at a glance

There are five extinguisher types found across UK workplaces: water, foam, CO2, dry powder and wet chemical. Under BS EN 3, the body of every extinguisher must be predominantly signal red, with a coloured band or label identifying the type — at least 95% red with no more than 5% showing the identification colour. Knowing these colours on sight lets anyone pick the right unit in seconds during an emergency.

*Standard ABC powder is rated for Class A, B, C and electrical fires; BC powder covers only Class B and C, and specialist Class D powder covers flammable metals only. A water-mist (white label) extinguisher is also available and tackles multiple classes, but the five types above remain the standard for most premises.

Water extinguishers

Water extinguishers carry a red label and are rated for Class A fires only. They work by cooling: water reduces the temperature of burning solids below their ignition point, while the steam produced helps displace oxygen and saturation prevents re-ignition. They are the most common and cost-effective choice for premises that contain mainly solid combustibles.

Typical settings include offices, schools, libraries, museums, warehouses storing non-flammable goods, retail units and homes. Common sizes are 6-litre (13A rating) and 9-litre (21A rating).

Water must never be used on flammable-liquid (Class B) fires, where it spreads the burning liquid; on flammable gases (Class C); on live electrical equipment, where it presents an electrocution risk; or on cooking-oil (Class F) fires, where it causes dangerous splattering.

Foam extinguishers

Foam extinguishers carry a cream label and tackle both Class A and Class B fires, making them one of the most versatile options for mixed-risk premises. The foam forms a blanket that cuts off the oxygen supply while its water content cools the fire. On solid materials it smothers and penetrates fabric and wood; on flammable liquids it seals the surface, preventing re-ignition — ideal for petrol, oil and paint.

Many AFFF foam extinguishers also have non-conductive spray nozzles and have passed the BS EN 3 35,000-volt dielectric test, so they can be used near (but not directly on) live electrical equipment. Modern foam units are lighter than equivalent water models — a 6-litre foam can match the 13A rating of a 9kg water extinguisher. Foam is not suitable for flammable gases (Class C) and should not be applied directly to live electrical equipment.

CO2 extinguishers

CO2 (carbon dioxide) extinguishers carry a black label and are rated for Class B and electrical fires. They work by displacing the oxygen around the fire, effectively suffocating it. The gas is stored under pressure and expands rapidly on discharge, reaching temperatures below -78°C. Because CO2 is non-conductive and leaves no residue, it is the go-to choice for electrical panels, switchboards, computers, servers and laboratory equipment, as well as flammable-liquid spills. Common sizes are 2kg and 5kg.

CO2 should not be used on Class A fires, where the lack of cooling allows re-ignition; on cooking-oil (Class F) fires, where the blast can splash burning oil; or on gas fires, which it cannot shut off. One important safety point: never touch the discharge horn during use — it becomes extremely cold and can cause frostbite. Ensure good ventilation when used indoors, as CO2 displaces breathable air.

Dry powder extinguishers

Dry powder extinguishers carry a blue label and are sometimes called the "multi-purpose" extinguisher because standard ABC powder covers Class A, B, C and electrical fires. The powder smothers flames and chemically interrupts combustion, forming a barrier that cuts off oxygen.

Several formulations exist for different risks: MAP 50 (50% monoammonium phosphate) for general use, MAP 90 (90%) for higher-risk environments, B+ and standard BC powder for flammable liquids and gases only, Monnex for industrial settings, and sodium-chloride-based Class D powder for flammable metals such as magnesium and lithium.

Powder has real drawbacks. It creates a sudden loss of visibility and is therefore not recommended for small, enclosed indoor spaces; it leaves a corrosive residue that can damage electronics and is difficult to clean; and the cloud should not be inhaled, so stand well back and ventilate afterwards. It is also unsuitable for chip-pan and deep-fat-fryer fires — use a wet chemical extinguisher for those.

Wet chemical extinguishers

Wet chemical extinguishers carry a yellow label and are the only type designed primarily for Class F cooking-oil and fat fires; many also handle Class A, and some models cover Class B. They discharge a potassium-based solution as a fine mist that reacts with the hot oil to form a soapy film through a process called saponification, sealing the surface from oxygen while the mist cools the fuel below its ignition point.

This makes them essential for commercial kitchens, chip shops, burger bars, restaurants and hotels — anywhere with deep-fat fryers or chip pans. They use an extended hose with a lance; keep at least one metre from the flames and apply in slow, circular movements. Wet chemical extinguishers must not be used on flammable gases (Class C) or live electrical equipment, and adequate ventilation should be maintained. Professional kitchens usually pair them with foam and CO2 units to cover every risk on site.

How to use an extinguisher: PASS

Once you have the right extinguisher, the PASS technique applies to all of them. Only tackle a fire if it is small, you have a clear escape route behind you, and you have raised the alarm first.

• P — Pull the safety pin, breaking the tamper seal.
• A — Aim the nozzle at the base of the flames, not the top.
• S — Squeeze the handle slowly and steadily to release the agent.
• S — Sweep from side to side across the base of the fire.

Most extinguishers hold only around 10 seconds of discharge, so aim accurately and keep the sweeping motion going. After the flames are out, watch the area for several minutes, as a fire can reignite if hot material remains. If the fire does not go out quickly or grows, leave immediately and let the fire and rescue service deal with it.

Selection, placement and maintenance

Choosing the correct extinguishers starts with your fire risk assessment, which is a legal duty under the Regulatory Reform (Fire Safety) Order 2005. As a guide, one 13A extinguisher covers roughly 200 m² of floor area — so a 450 m² office would need three (450 ÷ 200 = 2.25, rounded up). Maximum travel distance to reach an extinguisher is 30 metres for Class A and C units and 10 metres for Class B and F units. Mount lighter extinguishers (up to 4kg) with the handle about 1.5 metres from the floor, and heavier ones at roughly 1 metre.

Maintenance keeps them reliable. Carry out a monthly visual check of position, pressure, seals and condition, and arrange annual professional servicing in line with BS 5306. Water, foam and powder extinguishers need an extended discharge service (refilling) every five years; CO2 units need refurbishment after ten. Any extinguisher that has been used — even partially — must be replaced or recharged, because its pressurised system is compromised. Always use a service provider with recognised certification, such as those approved by the Fire Industry Association (FIA) or BAFE.

Mark McShane

Fire Safety Training Specialist, Online CPD Academy

Mark writes about workplace fire safety, compliance and accredited training for Fire Marshal Training, part of Online CPD Academy.