Fire Fighting Foam is an aggregate of gas filled bubbles formed from solutions fomulated foaming agents. In most cases the gas used is normal air, however, an inert gas may be used in special circumstances.
Some foams are thick and viscous forming strong heat resistance blankets over flammable liquid fires and vertical surfaces, others are thinner and spread more easily.
Fire Fighting foam is generally defined by its expansion ratio.
Low Expansion Foam up to 20:,
Medium Expansion Foam between 20:1 and 200:1
High Expansion Foam between 200:1 and 1000:1
Low Expansion Foam is primarily used in the extinguishment of flammable liquid fires either in pools or involving tanks by developing a cooling coherent blanket.
The blanket of foam covering the liquid surface will assist in preventing the formation and transmission of vapours.
Medium & High Expansion Foam is typically used to fill enclosures such as basements and ship holds where fire may be difficult to reach. In this case the foam acts to limit convection and access to air. The water content also cools and results in oxygen displacement by steam.
Where Fixed Foam Suppression Systems are required, the foam generating and distribution systems are normally installed intergrally with the hazard. These fixed devices are then piped to a source of foam solution. Such systems can be designed to operate manually or automatically on the activation of a fire detector.
A foam-water sprinkler system is a system that is pipe-connected to a source of foam concentrate and to a water supply may be any type of sprinkler system Wet, Dry, Preaction, or Deluge . The system is equipped with appropriate discharge devices for extinguishing agent discharge and for distribution over the area to be protected. The piping system is connected to the water supply through a control valve that usually is actuated by operation of automatic detection equipment that is installed in the same areas as the sprinklers. When this valve opens, water flows into the piping system, foam concentrate is injected into the water, and the resulting foam solution discharging through the discharge devices generates and distributes foam.