In Class B foam generation, which component must be present with foam concentrate to create stable foam?

• A. Water only
• B. Air
• C. Chemical inhibitors
• D. Heat

Answer: (B)

Creating stable Class B foam relies on air being introduced into the foam solution. The foam concentrate, when mixed with water, forms a foam solution, but the bubbles and the bubbly, insulating blanket only appear when air is entrained into that mixture. An air-entraining nozzle or foam eductor pulls in air as the solution flows, producing a stable foam structure that blankets the hydrocarbon surface, cools the fuel, and helps separate it from the air. Without air, you’d get a runny liquid rather than foam, so the foam wouldn’t stay in place or provide the same protection. Heat or chemical inhibitors don’t generate the foam; they aren’t the mechanism that creates the foamy structure.