What is the dominant extinguishing agent in Class A foam?

In fire suppression, Class A foam is specifically designed to combat ordinary combustible materials such as wood, paper, and textiles. The dominant extinguishing agent in Class A foam is water. When Class A foam is mixed with water, it creates a foam solution that enhances the water's effectiveness.

Water plays a critical role in cooling the fire, reducing temperature, and preventing re-ignition. The foam expands and encapsulates the burning materials, creating a barrier that smothers the fire by cutting off the oxygen supply. Additionally, the use of foam helps in generating a larger surface area compared to water alone, allowing for more effective penetration and saturation of the burning materials.

While the foam and the chemical film barrier (which refers to the action of the foam forming a protective layer on materials) are also important components of the foam's effectiveness, they do not act as the primary extinguishing agent. Foam and air support the extinguishment process but do not provide the cooling and direct extinguishing capability that water does.