What could happen if you mix different types of foam concentrate 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 different foam concentrates creates incompatibilities that can cause the mixture to congeal or gel. Each foam type is formulated to work with specific chemicals and a particular proportioning setup. When you combine types, their ingredients can interact or separate, forming thick gels that can clog foam lines, proportioners, strainers, or nozzles. In a Class B fire, this blockage prevents proper foam generation and blanket formation, compromising the foam’s ability to control the fire. So, the main risk is that the blend could congeal and plug the foam system. It’s not about one foam overpowering another, and the issue isn’t simply needing more water flow; the problem is the potential for the mixture to clog the system.