Which statement best reflects piping material restrictions?

• A. Cast-iron pipes are prohibited unless allowed
• B. Copper pipes are prohibited
• C. All pipes are allowed
• D. Only plastic pipes are prohibited

Answer: (A)

Piping material restrictions for clean-agent systems focus on ensuring compatibility with the agent and reliable, leak‑free performance. Cast iron is not a preferred material for these systems because it is prone to corrosion and can shed rust or debris into the agent, potentially contaminating the discharge and compromising performance. For that reason, cast-iron piping is generally not allowed unless a specific design or the authority having jurisdiction expressly permits its use. This reflects an approach that there are restrictions on materials, rather than a blanket allowance of any material. Other materials may be used when they are compatible with the agent and approved by the design and AHJ, so the statement captures the nuanced requirement: there are restrictions, and cast iron is typically prohibited unless explicitly allowed.