Foam Extinguishing System

Last updated: December 15, 2019

What Does Foam Extinguishing System Mean?

Foam extinguishing systems are fire extinguishing systems that rely on firefighting foam as the primary fire suppressant agent. Firefighting foam is comprised of a solution of water and a chemical foaming agent.

There are a number of different types of foam extinguishing systems, which reflect that different types of firefighting foam are used to extinguish different types of fire. The technical requirements for foam extinguishing systems vary depending on the extinguishing system and type of foaming agent used. For example, the foaming agent and water are often held in separate containers and mixed together only once the extinguishing system has been activated for use.

Safeopedia Explains Foam Extinguishing System

Foam extinguishing systems are used to fight a wide variety of different fire types. Typically, foam-based extinguishing systems are thought of in relation to their use in fighting liquid-based fires, such as oil fires; however, foam-based extinguishing systems are also used to fight ordinary structural fires as well. The type of foam these systems use is; however, different.

Foam extinguishers used for liquid fires use “Class B” foam, so-called because liquid fires are classified as being “Class B” fires, while foam used for extinguishing combustible solids are referred to as “Class A” foam for the same reason. The classification used for fire types varies geographically; however, they all use Class A for combustible solids and Class B for liquids.

Class B foam extinguishing systems are effective at extinguishing liquid fires due to their ability to remain on-top of whatever liquid (ignition source) they are sprayed upon. By separating the ignition source from its fuel (usually oxygen), the foam prevents the combustion reaction from continuing, and further inhibits the combustion reaction by cooling the ignited liquid.

Foam extinguishing systems are required for use in industries in which liquid chemical fires pose a significant hazard; however, the specific Class B foam that needs to be used varies depending on the specific types of fire that must be protected against. Some types of liquid fire render certain Class B foams ineffective, and certain fire hazards can be extinguished more effectively by types of foam with specific physical properties—such as high-expansion foam, which can be used in situations where it is desirable to rapidly fill an enclosed space.

Class A extinguisher systems are similar to regular water extinguisher systems; however, they contain a foaming agent designed to reduce the surface tension of the water. This allows the water to more effectively wet and saturate the material to which it is applied.


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