Which class of fire extinguisher should NOT be used for fires involving live electrical equipment?

Class B fire extinguishers are specifically designed for fires involving flammable liquids, such as gasoline, oil, and grease, and are not suitable for live electrical equipment. Class A/B extinguishers, which combine the capabilities of Class A and Class B extinguishers, also pose a risk when used on live electrical fires because they may have components that conduct electricity.

The correct choice, in this case, is Class B because it emphasizes the hazards associated with using extinguishers not designated for electrical fires. On the other hand, Class C extinguishers are specifically designed for use on fires involving live electrical equipment, and Class D extinguishers are meant for combustible metals. Therefore, choosing a Class B or Class A/B extinguisher for an electrical fire is unsafe, as it could lead to serious injuries or exacerbate the fire.