Interpretation Response #26-0032
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: American Cylinder and Safety, LLC
Individual Name: Myles TenBroeck
Location State: MI Country: US
View the Interpretation Document
Response text:
April 22, 2026
Myles TenBroeck
President
American Cylinder and Safety, LLC
P.O. Box 84
Traverse City, MI 49685
Reference No. 26-0032
Dear Mr. TenBroeck:
This letter is in response to your March 9, 2026 email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the inspection and requalification of compressed gas cylinders that are dual marked with both U.S. Department of Transportation (DOT) specification markings and United Nations (UN) pressure receptacle markings manufactured in accordance with International Organization for Standardization (ISO) standards. You explain that for some dual marked cylinders, the visual inspection or requalification requirements, or both, may differ depending on the applicable standard. In addition, the service life of certain composite cylinders may vary depending on the standard. Therefore, you seek clarification on how a person should manage cylinders that bear both DOT and UN/ISO markings.
We have paraphrased and answered your questions as follows:
Q1. When a cylinder is dual marked with both DOT and UN/ISO markings, which standard takes precedence for inspections and requalification?
A1. A dual-marked cylinder must be maintained and requalified in accordance with the applicable requirements associated with each marking, as authorized with the HMR. The regulations do not establish an order of precedence; instead, the cylinder must comply with the applicable requalification provisions for its maintenance and authorized use.
Q2. If there is no precedence for which standard the cylinder is inspected or tested to, is documentation required on which standard was applied and the reason why that standard was chosen?
A2. No. Requalification must be performed using an authorized method applicable to the cylinder, and the requalifier must maintain required records and markings identifying the method used and the results. The HMR do not require documentation of a "choice" between standards or justification for selecting one standard over another; however, the method applied must be appropriate for the cylinder and must be compliant with applicable regulatory requirements. Please note that any marking that could misrepresent the cylinder as meeting a different specification or standard should be removed, covered, or otherwise obliterated to prevent confusion or misinterpretation.
Q3. If there is a precedence for which standard takes priority, where is this referenced in the HMR, in CGA pamphlets, or ISO guidelines?
A3. See answer A1.
I hope this information is helpful. Please contact us if we can be of further assistance.
Sincerely,
Dirk Der Kinderen
Chief, Standards Development Branch
Standards and Rulemaking Division