Fire extinguisher types and placement

The fire classes, briefly

• Class A — solid combustibles: paper, wood, textiles, most rubbish.
• Class B — flammable liquids: petrol, solvents, paints.
• Class C — flammable gases, which are normally tackled by isolating the supply, not by extinguisher.
• Class D — metals such as magnesium and lithium swarf, requiring specialist powder.
• Class F — cooking oils and fats, requiring wet chemical.
• Electrical — not a class in its own right, but CO2 is the usual answer because it leaves no residue.

Choosing the right extinguisher

Water extinguishers are the cheapest and best Class A performers, with additive versions giving a higher rating from a smaller unit. Foam covers Class A and B and is the practical default in mixed premises. CO2 handles live electrical risk and is placed alongside server rooms, distribution boards and workshop machinery — but it is poor on Class A and the horn gets dangerously cold. Powder is versatile outdoors and in plant rooms but should be avoided indoors in occupied spaces, since discharge severely reduces visibility and damages electronics. Wet chemical is essential wherever deep-fat frying takes place.

How many, and what rating

Provision is based on the fire rating stamped on the unit, not the size of the bottle. BS 5306-8 guidance points to at least two Class A extinguishers per floor with a combined rating of 26A, which is commonly two 6-litre foam or water units at 13A each. Above roughly 400m² you add units to keep the ratio near one 13A per 200m². Specific risks are then covered separately: a CO2 by the comms room, a wet chemical in the kitchen, a foam near a fuel store.

Where to put them

Site extinguishers on escape routes, next to exit doors and stair enclosures, at a consistent point on each floor so people learn where they are. Nobody should travel more than 30 metres for a Class A unit. Specific-risk extinguishers go near the hazard, positioned so the user reaches them without passing the fire. Keep units off the floor on brackets or stands, keep them visible, and never behind a door or inside a cupboard.

Mounting and signage

Handles at about 1.5 metres for units up to 4kg, about 1 metre for heavier units. Every position should have a compliant sign at a height visible from a distance, identifying the extinguisher type. In corridors, a projecting sign helps far more than a flat one. Where extinguishers must be moved for cleaning, mark the position on the floor so they get returned.

Common siting mistakes

• Extinguishers stored in a cupboard "so they do not get vandalised" — nobody finds them.
• CO2 units next to a fryer, where they will spread burning oil.
• Powder units in small offices, where discharge will incapacitate the room.
• Units moved during a refit and left in a corner unmounted and unsigned.
• Provision that no longer matches the risk after new machinery or a new kitchen arrived.

Keeping them ready

Check monthly that each unit is in place, unobstructed, undamaged, with the pressure gauge in the green and the pin and tamper seal intact. Service annually to BS 5306-3, with extended service at five years for most water-based types and ten-year overhaul or replacement for CO2. Train staff on which unit to use and, just as importantly, when to leave the building instead.