What type of copper tube is prohibited for use in fuel gas systems?

In fuel gas systems, Type M copper tubing is prohibited due to its thinner walls compared to Type L and Type K. The wall thickness of Type M is not sufficient to withstand the pressures and potential impacts associated with fuel gas installations, which require a degree of robustness to ensure safety and reliability. Using a tubing type that can handle the operational demands is critical; therefore, Types L and K, which have thicker walls suitable for such applications, are acceptable. Type R, while not commonly referenced for fuel gas, generally indicates specific uses that may not be relevant here. The prohibition of Type M is rooted in safety protocols to prevent accidents caused by inadequate material strength in gas distribution systems.