Which extinguishing agent is commonly used in a Class A fire extinguisher?

The commonly used extinguishing agent in a Class A fire extinguisher is water. Class A fires involve ordinary combustible materials such as wood, paper, and cloth. Water is effective on these types of fires because it cools the burning material and reduces the heat to below the ignition point, allowing the fire to extinguish.

Water also helps to prevent re-ignition by soaking the materials involved. In many firefighting scenarios for Class A fires, water is the first choice due to its availability, cost-effectiveness, and efficiency in cooling the burning materials. Other agents have specific applications; for example, foam is more suitable for Class B fires involving flammable liquids, carbon dioxide is used primarily for electrical and flammable liquid fires, and dry powder extinguishers are best for certain types of flammable metals and gases. However, for the ordinary materials classed under Class A, water remains the primary and most effective extinguishing agent.