Under what condition should foam concentrates from different manufacturers be mixed?

• A. Always mix.
• B. Only if MILSPEC AFFF is designed to be compatible.
• C. Never mix, ever.
• D. Mix only with water.

Answer: (B)

Foam concentrates are formulated with specific surfactants, solvents, and stabilizers that work together to create a stable, film-forming foam. Mixing concentrates from different manufacturers can cause unpredictable chemical interactions, leading to unstable foam, poor expansion, degraded film integrity, or even precipitates that clog equipment. The only time mixing is acceptable is when compatibility is explicitly confirmed by MILSPEC AFFF compatibility data or manufacturer guidelines, meaning those brands have tested and approved blending them. If compatibility isn’t documented, use a single approved concentrate and avoid mixing.