What is the purpose of using AFFF when dealing with flammable liquids?

Aqueous Film-Forming Foam (AFFF) is specifically designed to combat flammable liquid fires by creating a blanket over the surface of the liquid. This blanket serves multiple critical functions, one of the most important being the creation of a barrier against ignitable vapors that can lead to a fire spreading or reigniting. By suppressing these vapors, AFFF effectively minimizes the risk of the fire escalating, thereby helping to control and extinguish the flames more efficiently. This vapor suppression capability is essential as many flammable liquids can produce vapors that are both hazardous and highly flammable, making the use of AFFF vital during firefighting operations.

While the other choices mention aspects like visibility, intensity of fire, or cleanup, these are not fundamental purposes of AFFF. In contrast, the barrier against vapor formation is a primary and critical function of this firefighting foam, confirming its essential role in effectively managing fires involving flammable liquids.