Water fire extinguishers are used on Class A fires, which usually involve freely burning solid materials such as paper, wood, straw, fabrics and coal. The extinguisher works by spraying a jet of water onto the fire, which penetrates the fire and extinguishes the flames by cooling the burning materials and preventing them re-igniting. Ordinary water fire extinguishers should not be used on fires with electrical equipment because water is conductive so could lead to an electric shock if used on anything electrical. There are several main types of water fire extinguishers, which are the standard ones, spray mist extinguishers and water additive extinguishers. Standard models use ordinary tap water which is sprayed out in a jet under pressure from compressed air.
Foam fire extinguishers have come a long way in 30 years. The original foam was thick, gloopy and smelled appalling, due to its high animal protein content. Modern Aqueous Film Forming Foam (AFFF) fire extinguishers are another breed altogether, one of the best all-round units available. Foam extinguishers are red with a cream panel above the operating instructions.
CO2 fire extinguishers (carbon dioxide) are the only fire extinguisher recommended for fires involving electrical equipment. CO2 is safe to use on and around electrical equipment, as the gas itself is non-conductive, and once used, there is no sticky foam or messy powder left behind. They are also effective on Class B fires (flammable liquids). Carbon dioxide fire extinguishers are painted bright red with a black panel above the operating instructions. They have a distinctive horn-shaped nozzle at the side on the smaller models with 5kgs and above having a hose and horn.
Dry powder fire extinguishers are excellent all-round fire extinguishers, often recommended for use on vehicles and in the home. All powder fire extinguishers are red with a blue panel, are either ABC or BC rated and are safe to be used on fires involving electrical equipment. (Remember to look for the electrical safety pictogram.) Dry powder extinguishers are not suitable for use in enclosed spaces such as offices, hotels, schools, etc, as the fire-fighting agent creates a cloud that can obscure vision. The contents may also create breathing problems.
Wet chemical fire extinguishers are the new kids on the fire extinguisher scene, developed specifically for use on deep fat cooking fires. The first such extinguisher on the market was the Chubb FryFighter, and its appearance gave rise to a new fire class, Class F and a new British Standard, BS 7937: 2000. Wet chemical fire extinguishers are red with a yellow panel above the operating instructions.
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