ABC powder fire extinguishers are a very versatile extinguisher that can be used on Class A (carbonaceous items), Class B (flammable liquids), Class C (flammable gases) and Electrical fires. Monoammonium phosphate, an extinguishing agent that spreads easily and melts over flames, is what’s used in Dry Powder extinguishers. It’s a one-to-one mixture of ammonia (NH3) and phosphoric acid (H3PO4). This works by depriving the fire of a fuel source by the fine powder MAP, which separates fire from oxygen.