Which statement about foam expansion is true?

• A. It is the process of adding foam concentrate to water.
• B. It is the process of aerating the foam solution after the proportioner.
• C. It is the result of introducing air into the foam solution, creating foam bubbles for finished foam.
• D. It is the ratio of foam concentrate to water.

Answer: (C)

Foam expansion is about how much finished foam volume you get from a relatively small amount of foam solution, and the key is air being added to that solution to form bubbles. When the foam solution is discharged through the nozzle or foam proportioner, air is drawn in and dispersed throughout the liquid, creating countless foam bubbles. That air incorporation is what makes the foam occupy many times the liquid’s original volume, producing the foamy blanket used for fire attack. The statement describing introducing air into the foam solution to create foam bubbles for finished foam captures this essential process. The other ideas describe mixing or diluting concentrate, which govern concentration or flow but not the expansion of foam into a finished foam blanket.