Fire Extinguisher Types and When to Use Them

Fire Classes: The Letters That Tell You What to Use

Before you shop for extinguishers, it helps to understand what you are actually fighting. UK fire classifications run from A to F, based on the fuel involved, and every extinguisher carries a label showing which classes it can tackle.

• Class A – solid combustibles such as wood, paper, cardboard, textiles and soft furnishings.
• Class B – flammable liquids including petrol, paint thinners, solvents and paraffin.
• Class C – flammable gases such as propane, butane and natural gas.
• Class D – combustible metals like magnesium and sodium, common in specialist manufacturing.
• Class F – cooking oils and fats, the ones behind most commercial kitchen fires.
• Electrical fires – not a class of their own, but they need care because the equipment may still be live.

Using the wrong extinguisher can make a small fire much worse. A jet of water onto chip-pan fat, or onto live electrical equipment, is a genuinely dangerous mistake. So let us walk through each type.

Water Extinguishers: The Class A Workhorse

Water extinguishers are the classic red-bodied unit, and for years they were the only colour on the wall. They work by cooling the fuel below its ignition temperature, which is why they are excellent on paper, wood, fabric and similar materials. They are cheap, simple and easy to refill.

They are also the wrong choice almost everywhere else. Never use water on electrical equipment, on flammable liquids, or on cooking oil. In an office with plenty of paper and cardboard, a couple of six-litre water extinguishers near the exits is a sensible starting point. In a workshop full of solvents, they are close to useless.

Foam Extinguishers: The Versatile Middle Ground

Foam extinguishers carry a cream label and are a popular choice for small businesses because they cover more ground than water. The foam forms a blanket over burning liquid, smothering the flames and stopping vapour from escaping, which makes them effective on Class A and Class B fires.

Think of a garage, a paint store or a workshop where both solid materials and flammable liquids are present. Foam handles both. One limitation worth knowing: standard foam sprays contain water, so they should not be used on live electrical equipment or on cooking oils. Newer foam formulations are often more environmentally friendly than the older ones, which is worth asking about when you buy.

CO2 Extinguishers: For Electrical Equipment and Server Rooms

Carbon dioxide extinguishers are the black-labelled units, usually recognisable by their heavy horn and lack of a pressure gauge. CO2 works by displacing oxygen, and because it leaves no residue, it is the go-to choice for anything electrical: computers, printers, switchboards, servers and specialist equipment.

They are rated for Class B fires too, so they suit a workplace with small quantities of flammable liquids. The practical drawback is that CO2 clouds disperse quickly and can be blown about by draughts, so you may need to get close to the fire. The horn also becomes extremely cold during discharge, so hold the handle only. In small, unventilated rooms, be mindful of the risk of asphyxiation.

Powder and Wet Chemical: The Specialists

Powder extinguishers are blue-labelled and cover the widest range of fires in one unit, typically Classes A, B, C and electrical risks. They are often found on vehicles and in industrial settings. The trade-off is the mess: powder gets everywhere, and it can cause damage to sensitive electronics and machinery even when the fire itself did not. Never use powder in a confined space where you might breathe it in.

Wet chemical extinguishers carry a yellow label and exist for one main reason: Class F cooking fires. If you run a café, takeaway or commercial kitchen, a wet chemical unit is essential. It reacts with the fat to form a soapy layer that cools and seals the surface, which water and foam simply cannot do.

Choosing, Siting and Looking After Your Extinguishers

A small business rarely needs one of everything. Start with the risks in each room and work backwards. A typical office might have a water or foam extinguisher near the door and a CO2 unit beside the IT equipment. A workshop with solvents leans on foam. A kitchen needs wet chemical. Anywhere with gas appliances should be assessed for Class C coverage.

• Site extinguishers on brackets at a sensible height, close to exits and escape routes, so nobody has to reach past a fire to grab one.
• Make sure the correct signage is visible. A hidden extinguisher is no extinguisher at all.
• Commission new units promptly, then arrange annual servicing through a competent person, with extended servicing at the intervals your provider advises.
• Carry out a quick monthly visual check: pressure gauge in the green, no obvious damage, pins and seals intact.
• Train your team. A two-minute briefing on which extinguisher to grab, and when to walk away instead, is worth more than any wall chart.

Finally, remember that extinguishers are for small, early-stage fires and for clearing an escape route. If a fire is spreading, the room is filling with smoke, or you have any doubt at all, get everyone out, call 999 and let the professionals handle it. Your fire risk assessment should record what you have, where it is and who checks it, and it is worth reviewing whenever your premises or activities change.