An aqueous film forming foam (AFFF) portable extinguisher is intended for use on which class of fire?

The correct answer is B, as an aqueous film-forming foam (AFFF) portable extinguisher is specifically designed for use on Class Bravo fires. These types of fires involve flammable liquids such as gasoline, oil, and grease. AFFF extinguishers work by forming a film on the surface of the burning liquid, which helps to smother the fire and prevent re-ignition by reducing the release of flammable vapors.

AFFF is particularly effective on Class Bravo fires because it can suppress vapor release, which is critical for extinguishing fires fueled by liquids that can spread or reignite quickly. The foaming action not only helps to cool the flames but also creates a barrier that isolates the fuel source from oxygen, thus extinguishing the fire.

Other classes of fires, such as Class Alpha (ordinary combustibles), Class Charlie (electrical fires), and Class Delta (reactive metals), require different types of extinguishing agents or methods, making AFFF unsuitable for those applications. For instance, water is often used on Class Alpha fires, but could worsen electrical fires in Class Charlie. Understanding which extinguishing agent to use for different fire classes is essential for effective fire safety and suppression.