Class A foam reduces which property of water to improve firefighting effectiveness?

• A. Increasing the surface tension of water, making penetration harder.
• B. Lowering the surface tension of water, allowing better penetration into the fuel.
• C. Causes water to become more viscous.
• D. Has no effect on water properties.

Answer: (B)

Class A foam works by changing how water interacts with fuels. It adds surfactants that lower water’s surface tension, so water spreads and wets surfaces more easily. That reduced surface tension lets the water penetrate into porous fuels and reach hidden pockets, improving cooling and knockdown. Because of this, the most accurate statement is that the foam lowers surface tension to enhance penetration into the fuel. Increasing surface tension would make wetting harder, making water bead up instead of spread; making water more viscous would hinder flow; saying there’s no effect ignores the actual wetting improvement Class A foam provides.