Portable fire extinguishers, made for personal use, are designed to fight small confined fires. These seals certify that the unit has been type tested and passed for the specified type and size of fire listed. It must be large enough to put out the fire. Class A fires involve ordinary combustibles such as wood, cloth, paper, rubber, and many plastics. Class A extinguishers are water based, often using compressed air to deliver the water.
Water acts a cooling agent to extinguish the fire.
Class B fires involve flammable liquids such as gasoline, oil, grease, tar, oil-based paint, lacquer, and flammable gas. Class B extinguishers use carbon dioxide gas, dry chemical or foam to cover the fire and exclude air. Class C fires involve energized electrical equipment including wiring, fuse boxes, circuit breakers, machinery, and appliances. Class C extinguishers require the use of non-conductive agents such as carbon dioxide or dry chemicals. Carbon dioxide is the preferred agent, as it leaves no residue to be cleaned up.