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Certain metals burn in contact with air or water (for example, sodium), which exacerbates this risk. Therefore, even a small metal fire can spread and become a larger fire in the surrounding ordinary combustible materials. Metal fires represent a unique hazard because people are often not aware of the characteristics of these fires and are not properly prepared to fight them. Chemicals such as FM-200 are now the recommended halogenated suppressant.Ĭlass B (US)/Class C (EU/AU): Flammable gases Ĭlass D fires involve combustible metals - especially alkali metals like lithium and potassium, alkaline earth metals such as magnesium, and group 4 elements such as titanium and zirconium. Halon has fallen out of favor in recent times (except for aircraft fire extinguishing systems) because it is an ozone-depleting material the Montreal Protocol declares that Halon should no longer be used. The most effective way to extinguish a liquid fire is by inhibiting the chemical chain reaction of the fire, which is done by dry chemical and Halon extinguishing agents, although smothering with CO 2 or, for liquids, foam is also effective. A solid stream of water should never be used to extinguish this type because it can cause the fuel to scatter, spreading the flames. These fires follow the same basic fire tetrahedron (heat, fuel, oxygen, chemical reaction) as ordinary combustible fires, except that the fuel in question is a flammable liquid such as gasoline, or gas such as natural gas. In the European/Australian system, flammable liquids are designated "Class B" having flash point less than 100 ☌ (212 ☏). The US system includes flammable gases in their "Class B". A carbon dioxide fire extinguisher rated for flammable liquids and gassesĬlass B fires are those where the fuel is flammable or combustible liquid.