What type of fire requires a foam extinguisher for effective suppression?

Foam extinguishers are specifically designed for use on Class B fires, which involve flammable liquids such as gasoline, oil, and solvents. The chemical composition of foam creates a blanket over the burning liquid, suppressing the flames and preventing the re-ignition by cutting off the oxygen supply. This makes foam extinguishers particularly effective for combating fires fueled by such flammable liquids, as they can not only extinguish the fire but also help in preventing the spread of the burning liquid.

Class A fires, which involve solid combustible materials like wood and paper, are better served by water-based extinguishing agents or dry chemicals that can handle the combustion of solids. Class C fires involve electrical equipment, and while they can sometimes be fought with foam, there are more suitable extinguishing agents like carbon dioxide (CO2) or dry chemical extinguishers that are preferred for their non-conductive properties. Class D fires pertain to combustible metals, requiring specialized extinguishing agents that can smother such fires without reacting negatively with the burning metal.

Thus, the effectiveness of foam extinguishers in suppressing flammable liquid fires makes them essential tools on vessels and in industrial settings where such hazards are prevalent.