What is the primary purpose of the foam created by a foam extinguisher?

The primary purpose of the foam created by a foam extinguisher is to smother the fire. Foam extinguishers work by creating a barrier between the fuel and the fire while also cooling the burning material. This foam sits atop the burning liquid or surface, effectively sealing off the fire from the air and preventing oxygen from reaching it. By smothering the flames, the foam not only helps to extinguish the fire but can also prevent re-ignition by suppressing the release of flammable vapors.

While cooling the fire is a factor involved in firefighting, the main mechanism of action for foam extinguishers is the smothering effect they provide. The creation of a foam blanket helps to remove the heat from the fire, but its most critical role is to cut off the oxygen supply, thereby starving the fire of its fuel source effectively. This makes foam extinguishers particularly effective for certain types of fires, especially those involving flammable liquids, where controlling the vapors is crucial for fire suppression.