What type of fires is a foam extinguisher useful for?

A foam extinguisher is specifically designed to combat fires involving flammable liquids, such as gasoline, oils, and solvents. The foam works by creating a barrier between the fuel and the fire, suppressing flames and preventing re-ignition by cooling the burning material and smothering the fire. This makes foam extinguishers particularly effective for Class B fires, which involve combustible liquids.

While foam extinguishers can also be somewhat effective on Class A fires (ordinary combustibles like wood and paper) to a degree, their primary purpose is to handle flammable liquids. It's critical to avoid using foam extinguishers on electrical fires, as the foam is conductive and could potentially create a serious hazard. Therefore, while foam extinguishers have a wider range of uses, their most appropriate application is in situations involving flammable liquids.