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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 #22-0129

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 Bureau of Shipping

Individual Name: Ms. Simone Goncalves

Location State: TX Country: US

View the Interpretation Document

Response text:

March 21, 2023

Ms. Simone Goncalves 
Technical Manager
American Bureau of Shipping
1701 City Plaza Drive
Spring, TX  77389

Reference No. 22-0129

Dear Ms. Goncalves:

This letter is in response to your November 30, 2022, email and subsequent telephone conversations with a member of my staff requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the testing of portable tanks. Specifically, you ask whether there are any “exemptions” from the dynamic longitudinal impact test requirement, specified in § 178.274(j)(6), for portable tanks containing “UN1977, Nitrogen, refrigerated liquid, 2.2” by highway transportation only.

As specified in § 178.274(j)(6), United Nations (UN) portable tanks used for the dedicated transportation of “Helium, refrigerated liquid,” UN1963, and “Hydrogen, refrigerated liquid,” UN1966, that are marked “NOT FOR RAIL TRANSPORT” in letters of a minimum height of 10 cm (4 inches) on at least two sides of the portable tank are excepted from the dynamic longitudinal impact test.  However, there are certain scenarios where non-specification portable tanks may be used when transported by highway.  For example, § 173.320(a) states that “atmospheric gases and helium, cryogenic liquids, in Dewar flasks, insulated cylinders, insulated portable tanks, insulated cargo tanks, and insulated tank cars, designed and constructed so that the pressure in such packagings will not exceed 25.3 psig under ambient temperature conditions during transportation …” are excepted from the requirements of subchapter C of the HMR, provided all the requirements of § 173.320 are met.  Therefore, a highway shipment of “UN1977, Nitrogen, refrigerated liquid, 2.2” may be transported in a non-specification insulated portable tank, provided the portable tank is constructed so that the pressure will not exceed 25.3 psig under ambient temperature conditions during transportation and all other requirements of
§ 173.320 are met. 

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


T. Glenn Foster 
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

173.320, 173.320(a), 178.274(j)(6),

Regulation Sections

Section Subject
173.320 Cryogenic liquids; exceptions
178.274 Specifications for UN portable tanks