OSHA does not specifically require compressed air pipes to be labeled. Employers may wish to check with state and local authorities to see if there are any state regulations which would apply. If no requirements apply, employers may wish to use the standard color scheme recommended by the American Society of Mechanical Engineers (ASME) in ASME Standard A13.1-2020, Scheme for the Identification of Piping Systems, which calls for white letters on a blue background.
ANSI A13.1- 2020 calls for pipe markings to include the identity of the materials in the pipe and an arrow(s), as well as any other information to alert the marking observer to any other hazards, e.g., pressure and temperature. In addition to the color and legend provisions, the standards offer legend examples, definitions, and further provisions on marking locations and intervals, marking approaches, the size and style of marking letters, marking visibility, and alternatives to the marking scheme itself.