What do the A B C ratings mean on Fire Extinguishers?
Fire extinguishers with a Class A rating are effective against fires involving paper, wood, textiles, and plastics. The primary chemical used to fight these fires is mono ammonium phosphate, because of its ability to smother fires in these types of materials.
Fire extinguishers with a Class B rating are effective against flammable liquid fires. These can be fires where cooking liquids, oil, gasoline, kerosene, or paint have become ignited. Two commonly used chemicals are effective in fighting these types of fires. Mono ammonium phosphate effectively smothers the fire, while sodium bicarbonate induces a chemical reaction which extinguishes the fire.
Fire extinguishers with a Class C rating are suitable for fires in “live” electrical equipment. Both mono ammonium phosphate and sodium bicarbonate are commonly used to fight this type of fire because of their non-conductive properties.
Fire Extinguisher Ratings
Fire extinguishers are classified by fire type. The A, B, C rating system defines the kinds of burning materials each fire extinguisher is designed to fight. The number in front of the A, B, or C indicates the rating size of fire the unit can extinguish.
To achieve a Class “A” rating, the extinguisher must be capable of putting out the wood crib, wood panel and excelsior (shredded paper) tests. Ratings are based on the size of the material that can be repeatedly extinguished.
To achieve a class “B” rating, the extinguisher must repeatedly put out a flaming liquid fire. Ratings are based on the size of the fire.