Which type of foam is used to combat flammable liquid fires?

AFFF, or Aqueous Film Forming Foam, is specifically designed to combat flammable liquid fires, such as those involving petroleum products and solvents. The effectiveness of AFFF lies in its ability to form a film on the surface of the burning liquid, which helps to suppress vapors and smother the fire by creating a barrier between the fuel and the air. This foam reduces the temperature of the fuel and minimizes the risk of re-ignition.

In contrast, protein foam is also used for flammable liquid fires but is generally less effective than AFFF in providing rapid fire control and vapor suppression. Water mist systems are effective in cooling burning materials and can mitigate fires, but they do not produce the film necessary to suppress flammable liquids effectively. Class D foam is specifically formulated for combustible metal fires and is unsuitable for flammable liquids. Hence, AFFF is the optimal choice for fighting flammable liquid fires due to its unique properties and effectiveness in these situations.