Indeed, copper is not allowed for natural gas distribution systems or in home pipe infrastructure, but is still allowed in most areas when being used in compound fittings. Copper would corrode over time in distribution systems because of trace amounts of moisture within the gas fuel, but fittings used to make final connections to an appliance are not exposed to this same level of moisture. In fact, there are some copper components used within certain gas valves as well. That being said, some municipalities have indeed outlawed copper completely, simply to avoid confusion about what is and what is not allowed, but this was not to do with safety of compound fittings such as this item.
Tyler M. - NFI Master Hearth Professional
on October 3, 2019