What is the main disadvantage of using water on Class B fires?

Using water on Class B fires is highly discouraged because it can spread the fire rather than extinguishing it. Class B fires involve flammable liquids such as gasoline, oil, and solvents. When water is applied to these types of fires, it can cause the flammable liquid to float on the water's surface and spread the flames to a larger area. This is due to the fact that water is denser than many flammable liquids, which leads to a dangerous situation where the fire can extend beyond the original ignition point.

In addition to this, applying water can turn the burning liquid into a vapor that can lead to a flashback or explosion. Firefighters and trained personnel are taught to use extinguishing agents specifically designed for Class B fires, such as foam or dry chemical extinguishers, which can effectively suffocate the fire and prevent its spread without creating additional hazards. Understanding this fundamental aspect of fire safety is crucial for preventing the exacerbation of a dangerous situation when dealing with flammable liquid fires.