What is the general term for the tubing, piping, or conduit of a system?

The correct answer is the general term "Piping," which encompasses all forms of conveyance systems used to transport gases or fluids within medical gas systems. In the context of NFPA 99, piping refers to the network of tubes and pipes designed to handle gas distribution safely and effectively in healthcare settings. This terminology is broad enough to include various forms of conveyance such as tubing and conduit, allowing for a more inclusive understanding of the medical gas system infrastructure.

While "tubing" specifies a type of material that can transport gases, it does not adequately cover the entire system, which could include rigid or flexible components as well as different sizes and shapes of pipes. "Conduit" typically refers to a casing that protects electrical wiring rather than gas or fluid flow. "Flex lines" specifically denote flexible tubing used for certain applications, generally limiting their scope and not representing the entire system of gas transportation. Therefore, "Piping" accurately reflects the comprehensive nature of the question, making it the best choice.