What is the potential result of mixing two different foam concentrates together during a Class B fire?

• A. The dominant foam will suppress the lesser foam that is mixed
• B. The mixed foams could congeal and plug the foam system
• C. Nothing will happen if the foams are the same brand
• D. Operators would need to flow water at a higher rate to overcome possible friction

Answer: (B)

Mixing two foam concentrates with different chemistries can create incompatibility. Foam concentrates are designed to mix with water to form a stable foam solution, but when incompatible products are combined, they can separate or react to form a gel or congealed mass. That gel can travel into and clog the foam lines, eductor, proportioner, and other components, effectively plugging the system and preventing proper foam delivery. This is why compatibility is critical and why you should never mix different concentrates. The key risk here is the formation of a solid or gel that blocks the system, rather than any change in required water flow or a simple dominance of one product.