Not all sprinklers are created equal, and its the foam concentrate that makes the difference.

Aqueous Film Forming Foam (AFFF) and Alcohol Resistant-Aqueous Film Forming Foam (AR-AFFF) concentrates are used to extinguish flammable and combustible liquids either in surface or spill type fires. Flammable liquids emit volatile vapors in normal storage. Combustible liquids do not emit volatile vapors in normal storage; they emit flammable vapors when heated.

In surface- and spill-type fires, the liquid does not burn, the vapor burns. When you see a large pan fire of heptane burning, the fire starts out calmly. The base of the fire will actually be above the liquid. As the pan heats, the vapors are emitted at a higher rate. The longer the liquid burns, the higher the rate of vapor being expelled and the higher the base of the fire above the liquid.