The primary extinguishing agent for Class B fires is what?

The primary extinguishing agent for Class B fires is foam. Class B fires involve flammable liquids such as gasoline, oils, and solvents, which can spread quickly and are difficult to control with regular extinguishing agents. Foam is effective because it smothers the fire by creating a barrier between the burning liquid and the oxygen in the air. This suppression method not only cools the fire but also helps to prevent the flammable vapors from reigniting.

While other agents like dry powder can also be used for these types of fires, foam is commonly preferred due to its ability to blanket the surface of the burning liquid and prevent re-ignition. Water, in contrast, is not suitable for Class B fires as it can spread the burning liquid and exacerbate the situation. Similarly, carbon dioxide may not provide the same level of suppression for larger Class B fires, since it works by displacing oxygen rather than cooling the fire or preventing flammable vapors. Thus, foam stands out as the most effective primary extinguishing agent for dealing with Class B fires.