How does AFFF work to suppress fire?

Aqueous Film-Forming Foam (AFFF) is specifically designed to combat flammable liquid fires, such as those involving fuels. It works primarily by smothering the fire, creating a barrier between the fuel and the oxygen in the air, while also forming a film that helps to isolate the fuel from the atmosphere. This smothering effect reduces the availability of oxygen, which is crucial for maintaining combustion, thereby helping to extinguish the fire.

Additionally, the foam creates a blanket over the flammable liquids, preventing vapor release, which can further assist in controlling the fire. The ability of AFFF to separate the fuel from air is a fundamental principle of fire suppression and makes it particularly effective in situations involving flammable liquids. This aspect of AFFF's operation is why the answer accurately reflects its primary function in firefighting scenarios.