What is the primary extinguishing agent used in Class B fire extinguishers?

The primary extinguishing agent used in Class B fire extinguishers is carbon dioxide (CO2) or dry chemical agents. Class B fires involve flammable liquids such as gasoline, oil, and paints, which require extinguishing agents that can effectively suppress vapors and interrupt combustion.

Carbon dioxide is particularly effective because it displaces oxygen in the vicinity of the fire, thereby suffocating it and preventing it from spreading. Dry chemical agents, such as monoammonium phosphate or sodium bicarbonate, work by interrupting the chemical reaction of the fire. These agents are versatile and can quickly extinguish flames, making them suitable for various scenarios involving flammable liquids.

While water is effective for Class A fires involving ordinary combustibles, it can be dangerous when used on Class B fires, as it can spread flammable liquids. Foam is also used for Class B fires but is not the primary agent. Class K agents are specifically formulated for cooking oils and fats and are used in kitchen fires, making them irrelevant for the broad category of Class B fires.