What are the two major types of firefighting foams?

• A. AFFF and Protein
• B. Class A and Class B Foam
• C. Fluoroprotein and Protein
• D. Alcohol-Resistant Foam and AFFF

Answer: (B)

Foams are categorized by the type of fuel they’re meant to fight: ordinary combustibles versus flammable liquids. That broad split is what most training emphasizes.

For ordinary combustibles like wood and paper, foam acts mainly as a cooling and soaking agent. It creates a stable, foamy blanket that helps the water in the foam soak into porous fuels, rapidly cooling the fuel and reducing the chance of reignition. The foam blanket also helps separate the fuel from the air, slowing or stopping the burn as heat and fuel release are controlled.

For flammable liquids such as gasoline or solvents, foam is designed to sit on the liquid surface and form a barrier between the fuel and air. Many foams also create a thin film that promotes fast vapor suppression and keeps the flame from re-igniting. Different formulations exist within this category to handle various kinds of hydrocarbon and polar solvents, but the key idea is protection of the surface and reduction of vapor release.

So, the two major types reflect the fuels they target: Class A for ordinary combustibles and Class B for flammable liquids.