Which type of pipe is not permitted in a Halon 1301 system?

In a Halon 1301 system, cast iron pipe is not permitted due to its material properties and behavior during a fire suppression event. Halon systems are designed for rapid discharge of the agent to suppress fires effectively, and the piping must ensure not only the durability and integrity under pressure but also compatibility with the Halon agent.

Cast iron, while strong, can be brittle and may fracture under certain conditions, specifically in high-pressure situations that can arise during the activation of a suppression system. Furthermore, in the case of a fire, the cast iron could produce harmful byproducts or fail to adequately transport the halon agent, compromising the system's effectiveness.

Materials such as flexible pipe, steel pipe conforming to ASTM A 120, and nonmetallic pipe can be appropriate alternatives in a Halon 1301 system, as they can be designed for better flexibility, strength, and compatibility with Halon, thus ensuring the reliable and efficient operation of the fire suppression system.