Interpretation Response #26-0054
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: Eaton, Mission Systems Division
Individual Name: Austin Proctor
Location State: NY Country: US
View the Interpretation Document
Response text:
October 6, 2026
Austin Proctor
Mechanical Design Engineer
Eaton, Mission Systems Division
10 Cobham Drive
Orchard Park, NY, 14127
Reference No. 26-0054
Dear Mr. Proctor:
This letter is in response to your April 29, 2026 email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to limited quantities of compressed gases. Specifically, you ask about transporting a pressure vessel two cubic inches in volume containing helium as a limited quantity. You reference a previously issued letter of interpretation for the same article, except that instead of being filled to 7,000 psig, it is now filled to approximately 9,500 psig. You also note the article is associated with an EX approval (i.e., EX2021052492) issued by the Pipeline and Hazardous Materials Safety Administration (PHMSA).
We have paraphrased and answered your questions as follows:
Q1. Is a pressurized vessel that meets the requirements of § 173.306(a)(1) excepted from all requirements of § 178.65 (Department of Transportation (DOT) Specification 39 non-reusable (non-refillable) cylinders), and other sections of the HMR, except §§ 173.27, 174.24, and 177.817 as listed in § 173.306?
A1. Yes. Containers such as the one you describe meeting the capacity limit of § 173.306(a)(1) are not subject to specification packaging requirements (e.g., § 178.65). As you indicate, limited quantities of compressed gases are further excepted from certain requirements of the HMR depending on the mode of transportation. For example, limited quantities of compressed gases shipped by rail meeting applicable conditions of § 173.306 are not subject to Part 174, carriage by rail requirements except for shipping papers (§ 174.24). However, the material may be further excepted if meeting the conditions of § 173.306(i).
Q2. Does a pressurized vessel need to be a DOT specification cylinder (or sphere) to have the ability to be shipped under § 173.306(a)?
A2. No. As stated in § 173.306(a) introductory text, unless required as a condition of use for an exception, limited quantities of compressed gases are excepted from specification packaging requirements of the HMR when packaged in accordance with provisions of the section, such as paragraph (a)(1).
Q3. What documentation would be needed other than an EX approval letter to ship under § 173.306, if any?
A3. There are no documentation requirements for limited quantities of compressed gases transported in accordance with § 173.306. However, the shipment would be subject to any additional requirements specified in the EX approval.
Q4. Would an assembly that integrates the described pressure vessel that is also equipped with a pyrotechnic pressure relief device (PRD) (which is not regulated as Class 1 based on the EX approval letter) still be eligible for transport by air under § 173.306?
A4. Yes. If the assembly was evaluated with the PRD and assigned Division 2.2 via the EX approval, it is eligible for exceptions provided in § 173.306. However, for transportation by air, there may be additional requirements in accordance with § 173.27.
Q5. Is the pressure vessel referenced above still subject to the specification cylinder marking requirements of the HMR (i.e., § 178.35) if shipped as a limited quantity under § 173.306?
A5. No. The exception from specification packages provided in § 173.306(a) removes the need for specification markings required by § 178.35.
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