Which type of fire should never be fought with water?

Water should not be used on fuel, oil, grease, or electrical fires. Water on burning fuel or oil floats the burning liquid across a wider area and can splash flaming material onto the firefighter. Water on an energized electrical fire conducts current and creates a serious shock hazard. Class B fires (flammable liquids) require a foam, dry chemical, or CO2 extinguisher. Class C fires (electrical) require a non-conductive agent like CO2 or dry chemical. Most commercial vehicles carry a B:C-rated dry chemical extinguisher. Water is acceptable on Class A fires: wood, paper, fabric, and rubber. For a tire fire, water can help if you can get enough flow on it, but for a small contained fire on a paper or cloth load, water is the right call.