Clarification of the Requirements for Pressure Relief Devices (PRD) on DOT Specification 2P Receptacles
Pipeline and Hazardous Materials Safety Administration · Jan 26, 2012 · Reference No. 11-0232
Interprets: 49 CFR § 173.304
Reggie’s quick take
A company asked whether a DOT 2P non-refillable metal receptacle holding 8 ounces of butane (a liquefied petroleum gas) needs a pressure relief device. PHMSA says no, if the receptacle holds no more than 31.83 cubic inches and is filled to no more than 35 psig at 70°F and 100 psig at 130°F, per § 173.304a(d)(3)(ii). A manufacturer may still install one if the receptacle meets Part 178 subpart B and those same conditions. But if it does, the device must meet all the applicable Part 173 subpart G requirements, or the manufacturer violates the rules when it fails to work.
Written by AI (Claude) on Oct 22, 2026. Robots make mistakes and leave things out, so the letter below is what counts. Not legal advice.
This responds to your letter requesting clarification of Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to pressure relief devices (PRD) on Department of Transportation (DOT) specification 2P non-refillable metal receptacles. Your questions are paraphrased and answered as follows:
Q1. Does a DOT specification 2P non-refillable metal receptacle containing 8 ounces of Butane (Liquefied petroleum gas) and charged to a pressure of 30 psig at 70o F and 80 psig at 130o F require a PRD?
A1. The answer is no. As specified in § 173.304a(d)(3)(ii), liquefied petroleum gases may be transported under specific conditions in a DOT specification 2P or 2Q non-refillable metal receptacle. Provided the maximum capacity of the receptacle does not exceed 31.83 cubic inches and a maximum filling pressure of 35 psig at 70o F and 100 psig at 130o F is not exceeded, no PRD is required for a DOT specification 2P or 2Q non-refillable metal receptacle containing liquefied petroleum gases. It should be noted that a DOT specification 2P container is considered a non-refillable metal receptacle, not a cylinder as you stated in your incoming letter.
Q2. If a DOT specification 2P non-refillable metal receptacle is excepted from the PRD requirements is a receptacle manufacturer still permitted to install one?
A2. Provided the DOT specification 2P non-refillable metal receptacle meets the applicable specification in Part 178 subpart B and the conditions specified in § 173.304a(d)(3)(ii), the answer is yes.
Q3. If a receptacle manufacturer installs a PRD on a DOT specification 2P non-refillable metal receptacle that is not required to include a PRD, does any violation exist if the PRD does not function properly?
A3. The answer is yes. If the package manufacturer chooses to install a PRD on a DOT specification 2P non-refillable metal receptacle that is excepted from the PRD requirements, the PRD must be in conformance with all the applicable requirements in Part 173, Subpart G specifically § 173.304a(d)(3)(ii), note 2.
A letter of interpretation applies the regulations to the facts the requester described. It isn’t a regulation and isn’t legal advice. The agency’s copy.