Purple-K, also known as PKP, potassium bicarbonate dry powder, is a dry-chemical fire suppression agent used in some dry chemical fire extinguishers. It is the second most effective dry chemical in fighting class B (flammable liquid) fires after Monnex (potassium allophanate), and can be used against some energized electrical equipment fires (USA class C fires). It has about 4–5 times more effectiveness against class B fires than carbon dioxide, and more than twice that of sodium bicarbonate. Some fire extinguishers are capable of operation in temperatures down to ?54 °C or up to +49 °C. Dry chemical works by directly inhibiting the chemical chain reaction which forms one of the four sides of the fire tetrahedron (Heat + Oxygen + Fuel + Chemical Chain Reaction = Fire). To a much smaller degree it also has a smothering effect —by excluding oxygen from the fire. "Dry chemical" extinguishers, such as Purple-K, are different from "dry powder" extinguishers that are used to fight Class D flammable metal fires.
Purple-K powder has an acrid taste and odor, is free-flowing, floating on most liquids, non-abrasive, does not wet with water and is compatible with most foam concentrates. It has violet color, to distinguish it from other dry agents.
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