What is one of the main functions of Class B foam in fire suppression?

Class B foam is primarily used in fire suppression to create a vapor barrier. This is crucial in fighting flammable liquid fires, as it helps to prevent the release of flammable vapors that can ignite and cause the fire to spread. The foam forms a blanket over the burning liquid, which reduces the likelihood of vapor ignition by limiting the interaction between the vapor phase of the fuel and the air, thus cutting off the oxygen supply needed for combustion.

Creating a vapor barrier also plays a significant role in suppressing the fire, as it decreases the intensity of the fire, allowing firefighters to manage the situation more effectively. By preventing the formation of flammable vapors, Class B foam not only helps to suffocate the fire but also creates a safer working environment for the firefighting personnel.

The other options focus on functions that while relevant to fire dynamics, do not capture the primary role of Class B foam in the context of vapor mitigation. Foam's ability to reduce vapor release is a distinctive and critical aspect of its effectiveness in combatting fires involving flammable liquids.