Which type of fires involve materials that are not combustible when energized?

Class C fires specifically involve energized electrical equipment and materials. This type of fire can occur with appliances, wiring, circuit breakers, and other electrical devices that are operational. The defining characteristic of Class C fires is that the involved materials are not considered combustible when they are energized; instead, they become a fire hazard only when electrical current is present.

In contrast, other classes of fires involve different types of materials and conditions. Class A fires involve ordinary combustible materials like wood, paper, and cloth; Class B fires deal with flammable liquids and gases; and Class D fires are associated with combustible metals. Therefore, Class C is the only category that pertains specifically to fires initiated in energized electrical equipment, distinguishing it from the other classes that relate to non-electrical materials.