______ pipe and fittings shall not be used unless specifically listed with the system.

• A. Copper
• B. PVC
• C. Aluminum
• D. Galvanized

Answer: (D)

Material compatibility and listing requirements drive how piping is chosen for Class K wet chemical extinguishing systems. The piping and fittings must be compatible with the wet chemical agent (potassium acetate) and with the system as designed by the manufacturer, so only materials specifically listed by the system can be used. Galvanized pipe is not compatible with the wet chemical agent because the potassium acetate solution can corrode galvanized steel, compromising the system’s integrity and reliability. That’s why galvanized pipe shall not be used unless the manufacturer has specifically listed it as acceptable for that system. Copper, PVC, and aluminum can be used if the system manufacturer lists them as compatible, but the key point is that any material must be explicitly listed for the particular system.