A fire extinguisher works by breaking the fire triangle of heat, fuel, and oxygen. Most extinguishers both cool the fire and remove the oxygen. They use a variety of materials to extinguish the fire. The majority of fire extinguishers found in welding shops use foam, carbon dioxide, a pump tank, or dry chemicals. When using a foam extinguisher, do not spray the stream directly into the burning liquid. Allow the foam to fall lightly on the base of the fire. When using a carbon dioxide extinguisher, direct the discharge as close to the fire as possible, first at the edge of the flames and gradually to the center. When using a dry chemical extinguisher, direct the extinguisher at the base of the flames. In the case of type A fires, follow up by directing the dry chemicals at the remaining material still burning. The extinguisher must be directed at the base of the fire where the fuel is located.