The main idea is that the materials used for foam solution piping must be compatible with the foam concentrate and the system environment, and galvanized steel is permitted as a valid option. This means you can design foam piping using galvanized steel, provided you follow the rest of the system requirements (like proper coatings, fittings, and maintenance) and ensure the foam concentrate chemistry won’t corrode or degrade the piping. Galvanized steel is acceptable because it offers adequate corrosion resistance in typical foam system conditions and is cost-effective and widely available. It’s not restricted to copper-nickel or limited to unprotected carbon steel; those options either impose too strict a limitation or raise corrosion concerns in this application. So, recognizing galvanized steel as an allowed material aligns with standard practice for many foam piping installations, assuming all other design and maintenance guidelines are met.