On what class of fire are compressed air foam systems most effective?

Compressed air foam systems are most effective on Class A fires, which typically involve ordinary combustible materials such as wood, paper, cloth, and some plastics. These types of fires benefit greatly from the properties of foam, which not only cools the burning material but also provides a barrier between the fuel and the oxygen supporting the combustion process.

When a compressed air foam system is utilized, the foam expands and forms a thick blanket that forms a protective layer over the burning materials, effectively smothering the flames and preventing the fire from reigniting. This dual action of cooling and smothering makes it particularly suitable for Class A fires.

In contrast, Class B fires, which involve flammable liquids and gases, typically require different firefighting agents that are specially designed to handle flammable substances. Class C fires involve energized electrical equipment, necessitating the use of non-conductive agents to prevent electric shock. Similarly, Class D fires, involving combustible metals, require agents that can smother the reaction without causing an explosive reaction or additional hazards. Thus, while compressed air foam systems can be versatile, their primary effectiveness lies with Class A fires, where their cooling and smothering capabilities can be maximally utilized.