A Class B fire extinguisher is designed to extinguish fires involving flammable liquids, such as gasoline, oil, and paint. The rating is based on the type of material that the extinguisher is effective against. Class B extinguishers typically use a dry chemical agent, such as monoammonium phosphate, to extinguish fires. These agents work by smothering the fire and creating a barrier between the fuel and the oxygen, which cuts off the fire’s oxygen supply.
Class B fire extinguishers are generally not recommended for use on fires involving electrical equipment, as the dry chemical agents can be conductive and create a new hazard. They can also be known as “foam type” or “chemical extinguisher”.