What type of foam should be used for direct attack on flames?

Using Class A foam for a direct attack on flames is appropriate due to its composition and effectiveness in extinguishing ordinary combustible materials. Class A foams are specifically formulated to enhance the water's ability to penetrate and cool burning materials. They include surfactants that reduce the surface tension of water, allowing it to better soak into solid materials such as wood and vegetation, which is critical in wildland urban interface (WUI) environments.

Class A foam is particularly advantageous when tackling flames that are fueled by combustible solids, making it a preferred choice for structural fires and wildland fires involving dense vegetation. Its ability to create a blanket over a fire helps to suppress flames by cooling the fuel and preventing the release of flammable vapors.

In contrast, other foam types are designed for different applications. For example, Class B foam targets flammable liquids and is used in situations where there are petroleum-based fires. Alcohol-resistant foam is formulated for fires involving polar solvents, while water-based foam is more general-purpose but may not have the same effectiveness as Class A foam for direct application on solid combustibles.