Which of the following is not an agent used for extinguishing Class B fires?

Water is not an effective agent for extinguishing Class B fires, which involve flammable liquids such as gasoline, oils, and solvents. Using water on a Class B fire can be dangerous because it may cause the burning liquid to spread, leading to a more extensive fire. Water can either evaporate or be pushed away from the burning fuel, and if the flammable liquid is lighter than water, it can float on the surface and continue to burn.

In contrast, agents such as foam, dry chemicals, and carbon dioxide (CO2) are specifically designed to smother flames, suppress vapors, and prevent the re-ignition of burning liquids. Foam creates a barrier that cools the fire and blocks the oxygen, while dry chemicals interrupt the chemical reaction of the fire. CO2 works by displacing oxygen in the vicinity of the fire, effectively suffocating it. This understanding of fire behavior and effective extinguishment methods is crucial for firefighting safety and effectiveness.