For extinguishing a Class B fire, what should NOT be used?

In the context of extinguishing a Class B fire, which involves flammable liquids such as gasoline, grease, or oil, using water is not appropriate. Water can exacerbate a Class B fire because it can spread the burning liquid, leading to a larger fire and increasing the risk of injury or further property damage. When water is applied to a burning liquid, it can cause the liquid to splatter and create additional flames, ultimately making the situation worse.

Extinguishing agents like Halon, dry chemical, and foam extinguishers are specifically designed for Class B fires. Halon extinguishers work by interrupting the chemical reaction of the fire, dry chemical extinguishers create a barrier between the fuel and the oxygen, and foam extinguishers create a blanket that smothers the fire and prevents re-ignition. Thus, they are effective options for safely and efficiently putting out Class B fires, while water is counterproductive in this scenario.