USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

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

Interpretation Response #22-0035

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

Interpretation Response Details

Response Publish Date:

Company Name: Linde Gas & Equipment Inc.

Individual Name: Mike Stephens

Location State: IL Country: US

View the Interpretation Document

Response text:

December 5, 2022

Mr. Mike Stephens
Manager Distribution Compliance
Linde Gas & Equipment Inc.
217 Loren Street
Washington, IL 61571

Reference No. 22-0035

Dear Mr. Stephens,

This letter is in response to your March 29, 2022, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the transportation requirements for dual-marked Department of Transportation (DOT) 3AA and United Nations International Organization for Standardization (UN ISO) 9809 cylinders that are also pi-marked. Specifically, you state that your company fills and ships dual-marked, pi-marked cylinders, without pressure relief devices (PRDs), and with the valves protected by steel caps, which are secured to the cylinders. You have included a picture of the steel cap assembly that protects the valve in your email.

We have paraphrased and answered your questions as follows:

Q1. You ask whether pi-marked DOT 3AA/UN ISO 9809 cylinders meet the provisions in § 173.301(f)(5)(iv) in that a PRD is not required on these cylinders for domestic and foreign transportation.

A1. Section 173.301(f)(5)(iv) states that a PRD is not required on a UN pressure receptacle transported in accordance with paragraph (k) or (l) of § 173.301. The reference to paragraphs (k) and (l) in § 173.301(f)(5) is incorrect. This appears to have been an oversight in a previous rulemaking and will be addressed in a future rulemaking. The provisions in § 173.301(k) and (l) are now found in § 171.23(a)(4) and (5). A PRD is not required on a UN pressure receptacle imported for discharge within a single port area, provided the conditions of § 171.23(a)(4)(i) through (iii) are met, or on a UN pressure receptacle filled with a gas and offered for transportation and transported for export, provided the conditions in § 171.23(a)(5)(i) through (iii) are met. Further, § 171.23(a)(6) specifies additional conditions for DOT specification and UN cylinders not equipped with PRDs provided they are offered for transportation and transported for export.  These exceptions do not apply to cylinders offered for domestic transportation.

Q2. You ask whether the use of a steel cap conforming to ISO 11117:2008 meets the requirements of § 173.301b(c)(2).

A2. The answer is yes. In accordance with § 173.301b(c)(2)(ii), a UN pressure receptacle must have its valves protected from damage that could cause inadvertent release of the contents of the UN pressure receptacle by one of the methods listed in paragraphs (c)(2)(i) through (vi) of that section. One of the permitted methods listed in paragraph (c)(2)(ii) entails equipping the UN pressure receptacle with a valve cap conforming to the requirements in ISO 11117:2008(E) and Technical Corrigendum 1.

Q3. You ask whether the use of a steel cap referenced in question Q2 is considered a "metal attachment," as stated in § 173.301(k).

A3. The answer is yes. As stated in § 173.301(k), metal attachments to cylinders must have rounded or chamfered corners, or be otherwise protected, to prevent the likelihood of causing puncture or damage to other hazardous materials packages. This requirement applies to anything temporarily or permanently attached to the cylinder, such as metal skids. The steel cap shown in your picture may meet this requirement.

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

173.301(f)(5)(iv), 173.301(k), 173.301(l), 173.301(f)(5), 171.23(a)(4), 171.23(a)(5), 171.23(a)(4)(i) through (iii), 171.23(a)(5)(i) through (iii), 171.23(a)(6), 173.301b(c)(2)

Regulation Sections

Section Subject
171.23 Requirements for specific materials and packagings transported under the ICAO Technical Instructions, IMDG Code, Transport Canada TDG Regulations, or the IAEA Regulations
173.301 General requirements for shipment of compressed gases and other hazardous materials in cylinders, UN pressure receptacles and spherical pressure vessels
173.301b Additional general requirements for shipment of UN pressure receptacles