In roll-on foam tactics for UHP, what is the key functional characteristic of the foam concentration (1%/3%)?

• A. It works only by cooling
• B. It works mainly by roll-on
• C. It is unaffected by foam concentration
• D. It reacts with air to form solid barriers

Answer: (B)

Roll-on foam tactics rely on the foam concentration to create a blanket that spreads across the surface as it flows, covering the fuel and forming a continuous film. At 1% or 3% concentrate, the foam expands and lays down smoothly, allowing the foam to roll onto and blanket the area rather than just sitting as droplets. This roll-on action is the primary way the foam controls a fire by separating fuel from air and cooling the surface, while still benefiting from the cooling effect as a secondary aid.

The other ideas don’t fit because cooling is a helpful side effect, not the main mechanism in roll-on tactics; changing concentration changes how well and how far the foam blankets the surface, so it isn’t “unaffected” by concentration; and foam doesn’t react with air to form solid barriers—the protection comes from the foamy film and the water content reducing heat and vapor release.