What is the primary function of aqueous film forming foam agents?

The primary function of aqueous film forming foam (AFFF) agents is to cool and smother fires, especially those involving flammable liquids. When applied, these agents form a film that spreads over the surface of the burning liquid, both cooling the fuel beneath and preventing the release of flammable vapors into the atmosphere. This dual action is particularly effective in suppressing fires since it not only reduces the temperature but also limits oxygen availability to the fire, effectively smothering the flames and inhibiting combustion.

Other options provided may relate to different fire suppression techniques but do not encompass the core function of AFFF agents as clearly as the cooling and smothering effect. While breaking the chain reaction and removing oxygen are concepts associated with fire suppression in general, they do not capture the primary operational mechanics of AFFF, which rely on the physical properties of the foam to control and extinguish fires effectively. Sealing off flames might be a secondary effect, but it is the cooling and smothering that is the hallmark of how AFFF functions in fire suppression situations.