Which extinguisher: water, foam, CO2, powder or wet chemical?

The fire classes

• Class A — solids: paper, wood, fabric, plastic.
• Class B — flammable liquids: petrol, paint, oils (not cooking oils).
• Class C — flammable gases: LPG, methane.
• Class D — flammable metals: magnesium, sodium.
• Class F — cooking oils and fats in commercial kitchens.
• Electrical — not a class, but a key consideration.

Water

The traditional Class A workhorse. Cheap, effective on paper/wood/fabric, and the staple of most office and retail environments. Never use on electrical equipment or burning liquids. Mist and additive variants extend the use case but for most premises a plain 9-litre water extinguisher does the job.

Foam (AFFF)

Covers Class A and Class B. The most versatile general-purpose extinguisher and the default choice if you can have only one type. Safe to use on electrical equipment only if it's been dielectrically tested to 35kV — read the label.

CO2

Class B and electrical. The standard extinguisher for server rooms, comms cupboards and office IT areas. Leaves no residue, but cools dramatically — never grip the horn during discharge, and ventilate after use in enclosed spaces.

Dry powder

ABC powder covers Class A, B and C plus electrical. Versatile but messy — discharge in an internal space causes huge visibility loss and damages electronics. Best reserved for external use (forklifts, plant rooms, LPG storage) where the disruption is acceptable.

Wet chemical

Class F only — designed specifically for cooking oils and fats. Discharges as a fine mist that saponifies the burning oil, smothering it. Mandatory for any commercial kitchen with a deep-fat fryer. Do not use water or foam on a fryer fire — it will violently spread the burning oil.

Picking the mix

Most offices: foam plus CO2. Restaurants: foam, CO2 and wet chemical. Warehouses: foam, CO2 and (often) external powder. The fire risk assessment will specify the exact provision and locations — and we'll quote you the most cost-effective compliant mix.