Using Foam in Firefighting Foam is used in firefighting to combat Class B fires (flammable liquids such as gasoline, oil, and alcohol) or to prevent their spread. It is also used to cool surfaces and prevent reignition in some Class A fires (solid combustibles like wood and paper). Foam works by cutting off oxygen and cooling the surface of the fuel. Types of Foam and Their Concentrations 1. AFFF (Aqueous Film Forming Foam): Concentration: 1% to 6% Application: Used for fires caused by flammable