In the United States, Occupational Safety and Health Administration regulations recommend following American Society of Mechanical Engineers Standard A13.1-2015 - Scheme for the Identification of Piping Systems.
[3] The standard states that labels should be placed where easily viewed by a person standing near the pipe at any of the following points:[4] 2015 revisions added oxidizing materials to the existing 'Flammables' classification.
[6] The National Fire Protection Association have a special labeling system in the standard for Health Care Facilities, such as hospitals and dentistry offices.
The labels used on pipes must be positioned visibly in the vicinity of the most hazardous points, such as valves and joints; at both sides of bulkheads and floor penetrations; and at reasonable intervals.
This is ISO 14726:2008 Ships and marine technology — Identification colours for the content of piping systems.
Basic identification colours and warning symbols identify the pipe contents and any hazards.
RAL colour standard charts are used by architects, construction industry and road safety.