Foam

Foam fire extinguishing systems are specialized suppression systems intended to control and extinguish flammable and combustible liquid fires by forming a stable blanket over the fuel surface. Their primary function is to separate fuel from oxygen, suppress flammable vapors, and provide cooling to prevent re-ignition. This makes them particularly effective for hazards where liquid fuels can spread, pool, or rapidly release vapors.

Foams are categorized by expansion ratio. Low-expansion foam (up to ~20:1), such as AR-SFFF, is commonly used for hydrocarbon and polar solvent fuels in applications like fuel storage tanks, loading racks, and aircraft hangars. Medium-expansion foam (20:1 to ~200:1) is used for spill control and confined areas. High-expansion foam (200:1 to 1000:1) is designed for total flooding of large enclosed volumes such as aircraft hangars, warehouses, or tunnels, rapidly filling the space to suppress fire.

System components include foam concentrate storage tanks, proportioning devices (eductors or bladder tanks), and discharge devices such as foam chambers, foam makers, monitors, and open nozzles. These systems are typically actuated through deluge-type valves, allowing simultaneous discharge over the hazard.

Foam systems are used instead of standard wet or dry sprinklers where water alone is ineffective, as water cannot adequately control vapor release or prevent re-ignition of flammable liquid surfaces.