STEVE HORRELL / SCIENCE PHOTO LIBRARY STEVE HORRELL / SCIENCE PHOTO LIBRARY
Fire extinguisher. Gas cylinder of a dry powder fire extinguisher. This cylinder contains an inert gas under pressure which forces out a powder that smothers flames. Chemicals used for this powder include sodium or potassium bicarbonate, urea potassium bicarbonate, potassium chloride or ammonium phosphate. The powder works by covering the burning materials, separating them from the oxygen in the air that they need for combustion. The bicarbonates also release carbon dioxide when heated, an inert gas which further isolates the burning material. Dry powder fire extinguishers are useful for electrical fires, where the use of water could cause firefighters to be electrocuted.
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