What is the foam-concentrate mixing rule?

• A. Always mix concentrates from different manufacturers.
• B. Never mix even if MILSPEC compatibility is claimed.
• C. Do not mix different manufacturers in apparatus tanks unless MILSPEC AFFF designed to be compatible.
• D. Mix only with water.

Answer: (C)

Foam concentrates are formulated with different chemistries, and not all blends mix cleanly. If you pour concentrates from different manufacturers into the same tank, they can misbehave, causing incomplete film formation, poor foam quality, or even solidified residue that can clog lines and equipment. The safe rule is to avoid mixing different manufacturers in apparatus tanks unless the MILSPEC AFFF product is specifically designed and labeled to be compatible with others. That MILSPEC compatibility indicates testing shows the concentrates can be combined without compromising performance or safety, and you should follow the manufacturer’s instructions for compatibility, mixing ratios, and use. This keeps foam performance reliable and protects equipment and personnel.

The other options break with practical safety and performance considerations. Mixing everything from different manufacturers ignores compatibility issues; requiring mixing never if MILSPEC compatibility is claimed is too strict because the claim means it’s acceptable when properly specified; and mixing only with water omits the essential need to use the correct foam concentrate as part of the foam solution.