Fire fighting foam agents suppress fire by separating the liquid fuel from the air (oxygen). Depending upon the type of foam agent, this is done in several ways

• The foam blankets the fuel surface, smothering the fire
• The foam blanket separates the flames from the fuel surface
• The foam cools the fuel and adjacent heat and ignition sources 

The foam blanket suppresses the release of flammable vapors that can mix with air.