What type of fire is a pressurized water extinguisher designed to extinguish?

A pressurized water extinguisher is specifically designed for Class A fires, which involve ordinary combustibles such as wood, paper, and cloth. The reason pressurized water extinguishers are effective for Class A fires is that water cools the burning material and removes heat from the fire triangle, which consists of heat, fuel, and oxygen. This cooling effect can help to extinguish the flames and prevent re-ignition.

In contrast, using water on Class B fires (such as flammable liquids), Class C fires (involving electrical equipment), Class D fires (involving combustible metals), or Class K fires (related to cooking oils and fats) can be dangerous or ineffective. For example, applying water to a Class B fire can spread the flammable liquid and worsen the fire, while water can conduct electricity in a Class C fire, posing a shock hazard. Therefore, the design and purpose of the pressurized water extinguisher make it suitable exclusively for Class A fires.