NFPA 54 National Fuel Gas Code Practice Test

Labeling colors are used to distinguish fuel types so technicians can identify the correct gas supply at a glance and avoid cross-connecting lines or mis-servicing equipment. For dual-fuel systems, natural gas is designated by yellow labeling, while LP (propane) is designated by green labeling. This color separation helps ensure valves, meters, regulators, and piping are associated with the right fuel source, reducing the risk of delivering the wrong gas to an appliance. Therefore, seeing yellow indicates natural gas, and green indicates LP gas, aligning with standard practice for dual-fuel labeling.