Which fittings shall not be used?

• A. Cast-iron fittings
• B. Brass fittings
• C. Class 150 fittings
• D. Plastic fittings

Answer: (C)

Fittings used in clean agent piping must be rated for the system’s design pressure and be compatible with the agent. Class 150 fittings have a maximum working pressure around 150 psi, and their pressure rating drops with temperature. Clean agent systems are designed to operate at pressures well above that, so using Class 150 fittings would create a weak point that could fail or leak and compromise agent discharge. For that reason they shall not be used. Cast-iron fittings are generally avoided for clean-agent piping due to compatibility and leakage concerns with halogenated agents, while brass and plastic fittings can be acceptable only when they are properly rated and listed for the specific agent and pressure.