Dual Marking of Cylinders
Pipeline and Hazardous Materials Safety Administration · Aug 4, 1978 · Reference No. 78-0002
Interprets: 49 CFR § 171.1, 49 CFR § 173.300a, 49 CFR § 173.300b
Reggie’s quick take
A company asked whether cylinders can carry both a Canadian (CTC) and a DOT marking. The agency's answer is yes, but only if the cylinders were made in full compliance with §§ 173.300a and 173.300b and the applicable specifications in Part 171. If so, the CTC/DOT mark goes before the specification marking, followed by the service pressure, as in "CTC/DOT 3AA X 1800." The letter says the order cannot be reversed to DOT/CTC under any circumstances.
Written by AI (Claude) on Oct 22, 2026. Robots make mistakes and leave things out, so the letter below is what counts. Not legal advice.
Thank you for your letter received May 11, 1978 requesting my comments on dual marking of cylinders.
If it can be determined that the cylinders in question were manufactured in full compliance with Title 49. Code of Federal Regulations, Sections 173.300a and 173.300b, an applicable, and the applicable specifications in Part 171.1, then the cylinders may be marked CTC/DOT preceding the specification marking followed by the service pressure (for example, CTC/DOT 3AA X 1800, etc.). Under no circumstances are the cylinders to be marked DOT/CTC, etc.
I trust this is helpful to you.
A letter of interpretation applies the regulations to the facts the requester described. It isn’t a regulation and isn’t legal advice. The agency’s copy.