For which class of fire are water-based extinguishing agents generally not effective?

Water-based extinguishing agents are generally not effective for Class C fires, which involve energized electrical equipment. The primary reason for this is that water is a conductor of electricity. Using water on electrical fires can not only fail to extinguish the fire but can also create the risk of electric shock to the person trying to use the extinguisher.

In contrast, water is very effective for Class A fires, which involve ordinary combustible materials like wood, paper, and fabric. Class B fires, involving flammable liquids such as gasoline or oil, are typically addressed with foam or other agents specifically designed for suppressing flammable liquid fires, as using water can spread the flames. Class D fires, which consist of combustible metals like magnesium or sodium, require special extinguishing agents compatible with the specific type of metal burning, as water can react violently with these metals.

Therefore, understanding the nature of fire classes and the characteristics of different extinguishing agents is crucial for effective fire response.