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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #24-0010

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:


Individual Name: Patrick Schoenhoff

Location State: MO Country: US

View the Interpretation Document

Response text:

May 10, 2024

Mr. Patrick Schoenhoff
General Manager
10271 Bach Boulevard
Saint Louis, MO  63132

Reference No. 24-0010

Dear Mr. Schoenhoff:

This letter is in response to your February 20, 2024, letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the overpack marking requirements in § 173.25 as they relate to cylinders.

We have paraphrased and answered your questions as follows:

Q1. You present a scenario where oxygen is shipped in Department of Transportation (DOT) 3AA or 3HT specification cylinders, placed in a fiberboard box, and marked "UN1072, Oxygen, Compressed." You ask whether the fiberboard box must be marked "OVERPACK" as described in § 173.25(a)(4).

A1. The answer is yes, provided the configuration meets the definition of an overpack, as defined in § 171.8, and the specification markings on the cylinders are not visible through the overpack. As prescribed in § 173.25(a)(4), the word "OVERPACK" is required to be marked on an overpack if package specification markings—when required—are not visible.

Q2. In connection to question Q1, you ask whether it is a violation of the HMR to mark a fiberboard box with "OVERPACK" if it does not meet the definition of an overpack as defined in § 171.8.

A2. The answer is yes. Marking a fiberboard box with "OVERPACK" is a violation of the HMR if it does not meet the definition of an overpack as defined in § 171.8.

Q3. You present a scenario where fire extinguishers are shipped under DOT Special Permits (SPs)—DOT SP-7945, DOT SP-8495, and DOT SP-12726 —and marked "UN1044, Fire Extinguishers." You ask whether the "OVERPACK" mark is required on the fiberboard box containing fire extinguisher cylinders shipped under DOT SP 7945, DOT SP 8495, and DOT SP 12726.

A3. Except when transported in DOT specification cylinders (see DOT-SP 12726 paragraph 7.a), the answer is no. The SPs referenced in your letter—DOT SP 7945 and DOT SP 8495—state: "non-DOT specification cylinder conforming with all regulations applicable to a DOT specification 4DS cylinder." Though specification 4DS cylinders do require the "OVERPACK" marking when enclosed in a fiberboard box, in accordance with § 173.25(a)(4), the overpack marking is not required for DOT-SP 7945 and DOT SP 8495, since the cylinders in question are not considered to be DOT specification cylinders (please also see answer A4). As such, the "OVERPACK" marking is also not required under DOT SP 12726, when non-DOT specification cylinders are used as specified in paragraph 7.a.

Q4. In connection to question Q3, you ask whether it is a violation of the HMR to mark a fiberboard box with "OVERPACK" if it does not meet the definition of an overpack as defined in § 171.8.

A4. See answer A2. However, when the SP requires the use of a strong outer packaging—as in DOT-SP 7945 paragraph 8.g. or DOT-SP 8495 paragraph 8.g.—the outer packaging does not meet the definition of an overpack, and therefore, "OVERPACK" is not an appropriate marking.

Also note, DOT-SP 12726 paragraph 7.a. authorizes the use of both non-DOT specification cylinders and DOT specification cylinders, and—when DOT specification cylinders are used—the "OVERPACK" marking is required unless the markings representative of each package type contained in the overpack are visible from outside of the overpack.

I hope this information is helpful. Please contact us if we can be of further assistance.


Steven Andrews
Acting Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

173.25(a)(4), 171.8

Regulation Sections

Section Subject
171.8 Definitions and abbreviations
173.25 Authorized packagings and overpacks