Which type of fire extinguisher uses foam to extinguish fires?

The correct answer is that a Class B extinguisher uses foam to extinguish fires. Foam extinguishers are specifically designed for use on flammable liquid fires, which are classified as Class B fires. These fires can involve substances like gasoline, oils, and solvents that can burn rapidly and produce intense heat.

Foam works by forming a barrier between the fuel and the oxygen in the air, effectively smothering the flames and preventing re-ignition. While there are other classes of extinguishers, they each target different types of fires. For instance, Class A extinguishers are suitable for ordinary combustibles, Class K extinguishers are intended for cooking oils and fats, and Class C extinguishers are used for electrical fires. Therefore, understanding the specific application of foam and its efficacy on flammable liquids is crucial for effective firefighting in those scenarios.