How does fire fighting foam extinguish flames?

Firefighting foam extinguishes flames primarily by smothering the fire and excluding oxygen, which is essential for combustion. When foam is applied to a fire, it forms a blanket that covers the burning material. This blanket prevents oxygen from reaching the flames and simultaneously acts to inhibit the release of flammable vapors, effectively interrupting the fire's ability to sustain itself.

The smothering effect of the foam disrupts the combustion process, which relies on the presence of fuel, heat, and oxygen, known as the fire triangle. By eliminating oxygen from this equation, the foam effectively extinguishes the fire. Additionally, many types of firefighting foam also cool down the surface of the burning fuel, which further aids in fire suppression.

Other methods referenced in the choices, such as cooling the flames, while beneficial, do not fully encompass the primary action of foam in fire suppression. The release of carbon dioxide is not a characteristic action of firefighting foam and increasing the fuel surface area is counterproductive as it would typically lead to more combustion rather than extinguishing flames. Thus, the key function of fighting foam lies in its ability to smother the fire and exclude oxygen.