The color codes for marking pipes used for hazardous materials include background colors of red, orange, yellow, brown, green and blue with lettering in either black or white. Purple, white, gray and black are also used as background colors, with black and white lettering for user defined materials.
Labels with white lettering on a red background are used for fire quenching fluids, while a yellow background with black lettering is for flammable fluids. Toxic and corrosive fluids use an orange background with black lettering, and combustible fluids have a brown background with white lettering. Water pipes use a green background with white lettering, and compressed air uses blue and white. The user defined labels use a purple background with white letters, white background with black letters, gray background with white letters and black background with white lettering.
All pipe labels are placed where they are easiest to see by workers in the area. They must also have lettering of at least 1/2 inch. The lettering on the labels grows larger with pipe size, with the largest minimum letter requirement being that of 3 1/2 inches for pipes over 10 inches in diameter. Pipes that are less than 3/4 inch in diameter use a permanent tag instead of labels for identification of the contents.