AFFF is primarily used for which types of fires?

Aqueous Film Forming Foam (AFFF) is a specialized fire suppression agent designed primarily for use on flammable liquid fires, which fall under Class B fires. The correct answer refers to its effectiveness on Class A and B fires. Class A fires involve ordinary combustible materials like wood and paper, while Class B fires involve flammable liquids such as gasoline or oil.

AFFF works by creating a barrier that prevents oxygen from reaching the fuel, thereby extinguishing the fire. Its unique formulation allows it to also cool the surface of burning Class A materials, making it versatile for various fire scenarios. This dual effectiveness—suppressing both Class A and B fires—illustrates why the answer identifies these classes specifically.