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    Extinguishing Agents for Fire Extinguishers

    By Mark Conroy

    Do you know your extinguishing agents? Check your knowledge with this summary of extinguishing agents used in fire extinguishers.

    Dry Chemical
    An agent made up of very small particles of sodium bicarbonate, potassium bicarbonate, or ammonium phosphate with additives to enhance flow and prevent packing and caking. Extinguishers with sodium bicarbonate and potassium bicarbonate are rated for Class B and Class C fires. Extinguishers with ammonium phosphate are rated for Class A, B, and C fires

    Wet Chemical
    A water solution with additives that chemically reacts with fats in a cooking-oil fire, creating a thick foam blanket that floats on the surface of the oil. These extinguishers are intended for Class K fires.

    Clean Agent
    An electrically nonconductive extinguishing agent, that evaporates and leaves no residue. The currently acceptable clean agents used in extinguishers include halocarbons, such as Halotron I and FE36, Halon 1211, and carbon dioxide. Carbon dioxide extinguishers are rated for Class B and C fires. Extinguishers containing halocarbons and Halon 1211 are rated for Class B and C fires, while larger units are rated for Class A fires.

    Water Stream (Extinguisher)
    This is an extinguisher with a 2.5 gallon capacity, containing tap water or a loaded stream charge that is discharged through a hose assembly as a solid stream. This type of extinguisher is rated 2-A for use on Class A fires only.

    Water Mist (Extinguisher)
    An extinguisher with a special nozzle for discharging de-ionized water as a fine mist. This type of extinguisher is rated for Class A and C fires.

    This extinguishing agent is either aqueous film-forming foam (AFFF) or film-forming fluoroprotein (FFFP) foam. Extinguishers containing foam solution have a hose with a special nozzle that introduces air to the solution, which creates foam as it leaves the extinguisher. Foam extinguishers are intended for Class B fires.

    Dry Powder
    An extinguishing agent made up of powder or granular particles that are intended for the extinguishment of Class D combustible metal fires. Typical dry powder agents include sodium chloride, graphite, and copper. Extinguishers containing dry powder are listed for the extinguishment of specific combustible metals.

    With this summary, you can now discuss portable fire extinguisher applications more confidently with your customers. Selection of the proper extinguishing agent for any application is dependent on your understanding of this material. For extinguisher placement, always follow NFPA or locally adopted standards and consult with the Authority Having Jurisdiction (AHJ) as needed.

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