The Marine Approval Authorities such as SOLAS and Lloyds Register of Shipping recognise that foam is the accepted and preferred means of controlling and extinguishing fires involving flammable liquids.

Foam is a mixture of foam concentrate, water and air that forms a blanket of bubbles over the surface of the flammable liquid thereby suppressing the release of flammable vapours, separating the vapours from the air necessary for combustion; and cooling the fuel and hot surfaces.

Marine foam systems comprise of a system distribution control valve, a tank, a foam proportioner, a pumped sea water supply distribution pipework and discharge devices such as nozzles, branchpipes and monitors.  Water and foam concentrate are fed to the proportioner, which meters the foam concentrate into the water at a predetermined rate, usually 3% (3 parts foam concentrate to 97 parts water). This “foam solution” flows through the distribution pipework to the discharge devices, which mix air into the foam solution (aspirate) to deliver foam onto the fire.

The foam may be delivered as ‘low expansion’ having an expansion ratio of less than 20:1; as “medium expansion” foam with an expansion ratio of between 20 and 200:1; or “high expansion” foam with an expansion ratio of greater than 200:1.

Foam for marine applications is usually based on low or medium expansion systems depending on the type of risk involved. For example, Machinery spaces containing oil fired boilers, oil fuel units (including internal combustion machinery), or steam turbines of aggregate total output greater than 375 kW require protecting with a high expansion foam system and a foam applicator comprising a branchpipe, portable inductor, and 2x20 litres foam concentrate.

Cargo spaces on ships over 1000 gross tonnage require protection with a high Expansion foam system whilst Tankers of over and under 20,000 tonnes dead-weight require a fixed deck foam system, 4 x 400 litres per minute foam applicators on deck and high expansion foam systems in the cargo pump rooms.

The different types of Foam systems include: