Which extinguishing agent is commonly used in Class B foam extinguishers?

Class B fires involve flammable liquids such as gasoline, oil, and solvents, which do not mix with water and can spread quickly. To effectively combat these types of fires, a specialized extinguishing agent is required that can not only suppress the flames but also prevent re-ignition.

Alcohol-resistant foam is specifically designed to fight Class B fires involving polar solvents and is capable of creating a barrier that both smothers the fire and prevents the vapor from escaping, thus mitigating the risk of re-ignition. This type of foam is effective because it can adhere to surfaces and form a protective layer, making it particularly valuable in situations involving volatile flammable liquids.

While water can be used in certain situations, it is not suitable for Class B fires as it can cause the burning liquid to spread. Dry chemical agents and carbon dioxide, while useful for some types of fires, do not provide the same level of efficacy against the re-ignition risks associated with flammable liquids as alcohol-resistant foam does.