Foam fire extinguishers (or AFFF fire extinguishers) are more versatile than water and are lighter in weight compared with water equivalents delivering similar suppressant performance. Foam fire extinguishers can be used for Class A & B fires but are not recommended for fires involving electricity unless the electrical current can be disconnected first. Foam fire extinguishers are colour coded with a cream label. A foam fire extinguisher discharges a foam solution under pressure that forms a blanket or film on the surface of a burning liquid creating a barrier between the fire vapours and the air necessary to support combustion thereby smothering the fire.
How to use a foam fire extinguisher on Class B liquid fires
Where the liquid on fire is in a container, direct the spray at the back edge of the container or at an adjoining vertical surface above the level of the burning liquid. This allows the foam to build up and flow across the surface of the liquid to smother the fire.
- Where this is not possible stand well back, direct the spray over the fire with a gentle sweeping movement, allow the foam to drop down and lie on the surface of the burning liquid. (This procedure should also be used to tackle Class A type fires involving solids).
- Do not aim the spray directly into the liquid as this will drive the foam beneath the liquid surface and render it ineffective. In addition aiming foam directly into the liquid may splash the fire onto the surroundings, potentially spreading the fire.
