- https://www.grainger.com/content/qt-safety-ansi-pipe-marking-standard-203
- ASME A13.1-2007 (R2013) Scheme for the Identification of Piping Systems
https://webstore.ansi.org/standards/asme/asmea132007r2013
- ANSI/NEMA Z535.1-2006 (R2011) Safety Colors
https://webstore.ansi.org/standards/nema/ansinemaz5352006r2011