Aqueous Film Forming Foam. Fire-fighting foam is a foam used for fire suppression. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion. Fire-fighting foam was invented by the Russian engineer and chemist Aleksandr Loran in 1902. The surfactants used must produce foam in concentration of less than 1%. Other components of fire-retardant foams are organic solvents (e. g. trimethyltrimethylene glycol and hexylene glycol), foam stabilizers (e. g. , lauryl alcohol), and corrosion inhibitors. Low-expansion foams have an expansion rate less than 20 times. Foams with expansion ratio between 20 and 200 are medium-expansion. Low-expansion foams such as AFFF are low-viscosity, mobile, and able to quickly cover large areas. High-expansion foams have an expansion ratio over 200. They are suitable for enclosed spaces such as hangars, where quick filling is needed. Alcohol-resistant foams contain a polymer that forms a protective layer between the burning surface and the foam, preventing foam breakdown by alcohols in the burning fuel. Alcohol-resistant foams should be used in fighting fires of fuels containing oxygenates, e. g. MTBE, or fires of liquids based on or containing polar solvents