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Aqueous Film Forming Foam (AFFF) is a detergent-based compound, frequently containing sodium alkyl sulphate, and/or perfluoro telomere as surfactants, which have the ability to spread over the surface of hydrocarbon-based liquids. This gives an effective vapour seal and fast knockdown on hydrocarbon fires, even when low application rates are used and only a thin layer of foam is present. Due to the film-forming characteristic, this type of foam can be applied by non-aspirated nozzles.
In AFFF systems a bladder tank containing a nylon reinforced elastomeric bladder is used to store the foam concentrate. System water pressure is used to squeeze the bladder providing firefighting foam concentrate, at the same pressure, to the proportioner. With bladder tank foam systems, no external power is required, and little maintenance is needed.
Alcohol-resistant foams are based on AFFF chemistry to which a polymer has been added. ARCs are the most versatile of the firefighting foam agents in that they are effective on fires involving polar solvents like methanol as well as hydrocarbon fires such as gasoline.
A foam system requires proportioning equipment to mix the foam with water in the required concentration. Automatic pressure balancing valves regulate the foam concentrate pressure to match the water pressure