Which of the following is a characteristic of Class A fires?

Class A fires are characterized by the presence of ordinary combustibles, such as wood, paper, cloth, and some types of plastics. When these materials burn, they typically leave behind ashes once they are extinguished. This residue is an indicator of the carbonaceous materials that were consumed during the combustion process.

While options involving flammable liquids, electrical equipment, or reactions to water are important, they refer to different classes of fires. For instance, flammable liquids are associated with Class B fires, electrical equipment pertains to Class C fires, and materials that react violently with water, like certain metals, fall under Class D. Thus, the characteristic of leaving behind ashes is definitively associated with Class A fires, highlighting their consumable nature and distinguishing them from other fire classifications.