“A foam system is used in firefighting to deliver free retardant foam for the purpose of extinguishing a fire or protecting unburned areas. Typical components include a water source, a centrifugal pump, foam concentrate tanks, a direct-injection foam proportioning system on the discharge side of the pump, a mixing chamber or device, a rotary air compressor, and control systems to ensure the correct mixes of concentrate, water, and air.”
Reference: Robert G. Taylor, Compressed Air Foam Systems in Limited Staffing Conditions. 1997. Morristown Fire Bureau, Morristown, New Jersey
Comment: Foam is used to fight fires of organic liquid pools. By covering the liquid surface, foam both insulates the liquid from the hot flame so that the vapor mass rate feeding the flame is reduced, and impedes the access of oxygen.