PHMSA letter of interpretation

Qualification Markings on DOT 4BA Cylinders

Pipeline and Hazardous Materials Safety Administration · Dec 15, 1999 · Reference No. 99-0243

PHMSA says to use caution with this letter. On August 8, 2002, RSPA finalized Docket HM-220D, which consolidated the requirements for qualification, use, and maintenance of cylinders in Part 180, Subpart C. As a result, the references provided in this guidance are no longer accurate. Please see Part 180, Subpart C for the current requirements for the qualification, use, and maintenance of cylinders. Although not all references to requirements previously codified in § 173.34 have parallel requirements in Part 180, Subpart C, you may wish to review § 180, Subpart C for additional information.

Reggie’s quick take

A company that ships refrigerant cylinders asked whether a 5-year retest due date marked on DOT 4BA cylinders could be removed and replaced with a 10-year due date. The agency said the rules do not require a next due date marking on DOT specification cylinders. So the existing due date may be removed, since it counts as additional information under § 173.34(c)(1). The agency also noted that the retest date marked on a cylinder must be the month and year the test was actually done, per § 173.34(e)(1) and (7).

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.

This is in response to your letter dated August 27, 1991, requesting clarification on the periodic qualification of DOT 4BA cylinders used exclusively for refrigerant gases which are commercially free of corroding components. Specifically, you state that the cylinders were marked with a 5-year retest due date at the time of manufacture. You asked whether this 5-year due date may be removed and replaced with a 10-year due date.

The HMR contains no requirement to mark a DOT specification cylinder with the next due date. Therefore, the due date marking, which would be considered as additional information under § 173.34(c)(1), may be removed. Please note that the retest date marked on a cylinder is the date (month and year) the test is actually performed. See § 173.34(e)(1) and (7).

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.