Which type of fire extinguisher is typically required for class A fires involving ordinary combustibles?

A water extinguisher is typically required for Class A fires, which involve ordinary combustibles such as wood, paper, cloth, and some plastics. These materials burn readily and can be effectively extinguished by the cooling and smothering properties of water. The water extinguisher works by cooling the burning material below its ignition temperature and removing heat from the fire, thus suppressing the flames.

Other types of extinguishers, while they may extinguish Class A fires as well, are not as ideal for this specific class of fire. Foam extinguishers are more suited for flammable liquids (Class B fires) and may not effectively penetrate the materials involved in a Class A fire. Dry chemical extinguishers can be used on various classes of fires, including Class A, but they don't cool as efficiently as water extinguishers do. Carbon dioxide extinguishers are primarily used for electrical and flammable liquid fires (Classes B and C) and do not provide the cooling effect necessary for ordinary combustibles.

Therefore, the water extinguisher is the preferred and most effective choice for handling Class A fires involving ordinary combustibles.