# Air-Conditioning, Heating, and Refrigeration Institute (AHRI) — Hazardous Materials Safety Interpretation **Citation:** 21-0011 **Type / status:** guidance / guidance **Agency:** Pipeline and Hazardous Materials Safety Administration **Effective:** Not stated **Published:** 2021-04-13 21-0011 response to Air-Conditioning, Heating, and Refrigeration Institute (AHRI) concerning 173.307. ## Document text <<>> U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration 1200 New Jersey Avenue, SE Washington, DC 20590 April 13, 2021 Helen Walter-Terrinoni VP Regulatory Affairs Air-Conditioning, Heating, and Refrigeration Institute (AHRI) 2311 Wilson Boulevard Suite 400 Arlington, VA 22201 Reference No. 21-0011 Dear Ms. Walter-Terrinoni: This letter is in response to your February 4, 2021, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to exceptions for compressed gases in refrigerating machines and their components. Specifically, you ask questions regarding the exceptions provided in §§ 173.307(a)(4)(iii) and (v). We have paraphrased and answered your questions as follows: Q1. You ask whether the exception provided in § 173.307(a)(4)(iii) would apply to refrigerating machines containing 12 kg or less of a flammable, non-toxic liquefied gas, such as “UN3252, Difluoromethane, 2.1” or “UN3161, Liquefied gas, flammable, n.o.s., 2.1,” so long as such units are not offered or transported by air. A1. The answer is yes. Refrigerating machines and components thereof, containing 12 kg or less of a flammable, non-toxic gas, including a liquefied gas, are not subject to the requirements of the HMR provided they are not offered or transported by aircraft. Q2. You ask whether the exception provided in § 173.307(a)(4)(v) would apply to refrigerating machines containing 100 g or less of a flammable, non-toxic liquefied gas, such as “UN3252, Difluoromethane, 2.1” or “UN3161, Liquefied gas, flammable, n.o.s., 2.1, ” regardless of the mode of transportation. <<>> A2. The answer is yes. Refrigerating machines and components thereof, containing 100 g or less of a flammable, non-toxic liquefied gas, are not subject to the requirements of the HMR, regardless of the mode of transportation. 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 <<>> Patrick 21-0011 From: INFOCNTR (PHMSA) To: Subject: Date: Attachments: Dodd, Alice (PHMSA); Hazmat Interps FW: AHRI Request for PHMCSA Letter of Interpretation Friday, February 5, 2021 1:56:22 PM AHRI Request for PHMSA Letter of Interpretation CFR 49 173.pdf image002.png image004.png Good afternoon Alice, Please see the attached request for a letter of interpretation. Please contact our office with any questions. Thank you, Sarah (HMIC) From: Kelley, Shane (PHMSA) Sent: Thursday, February 4, 2021 12:03 PM To: INFOCNTR (PHMSA) ; Dodd, Alice (PHMSA) Cc: DerKinderen, Dirk (PHMSA) ; Foster, Glenn (PHMSA) ; Nickels, Matthew (PHMSA) ; Constantino, Lindsey (PHMSA) ; Pfund, Duane (PHMSA) Subject: FW: AHRI Request for PHMCSA Letter of Interpretation Folks. Please process as a formal interp request. Management Team – let me know who is assigned please, and include me in the concurrence chain. Let’s include our international team on this one as well please. Thank you From: Walter-Terrinoni, Helen Sent: Thursday, February 04, 2021 11:47 AM To: Constantino, Lindsey (PHMSA) Cc: Kelley, Shane (PHMSA) ; Koban, Mary ; Carpizo, Marie ; Maureen Beatty (mbeatty@refrigerants.com) Subject: AHRI Request for PHMCSA Letter of Interpretation CAUTION: This email originated from outside of the Department of Transportation (DOT). Do not click on links or open attachments unless you recognize the sender and know the content is safe. Shane (PHMSA) Constantino, Lindsey (PHMSA) Dear Lindsey, <<>> Thank-you for taking the time to discuss our questions regarding a potential request for a letter of interpretation late last year. Please see our request attached to this email. We look forward to continuing to work with you on this question. Please contact me if you have any questions. I hope that you and your family are doing well. Best Regards, Helen Helen Walter-Terrinoni Air Conditioning, Heating, and Refrigeration Institute (AHRI) VP Regulatory Affairs 302-598-4608 Hwalter-terrinoni@ahrinet.org ## Provenance - Official: Yes - Source: - Source ID: `phmsa` - SHA-256: `5a403f50fa0e5433692d7aa210f98de702c8f9d120c4c0344da87fafd04a173d` - Retrieved: 2026-08-20T00:59:31.977Z - Exported: 2026-08-23T23:45:41.146Z - Document slug: `phmsa-interpretation-21-0011` ### Source metadata ```json { "materialSubtype": "interpretation", "interpretationArea": "hazardous_materials", "representation": "full_text_from_official_pdf", "companies": [ "Air-Conditioning, Heating, and Refrigeration Institute (AHRI)" ], "individuals": [ "Helen Walter-Terrinoni" ], "refIds": [ "21-0011" ], "catalogDates": [ "2021-04-13" ], "catalogParts": [ 173 ], "catalogRowCount": 1, "sourceRecordUrls": [ "https://www.phmsa.dot.gov/node/72596" ], "linkedAttachmentUrls": [], "unavailableResponseUrls": [], "duplicateRepresentationUrls": [], "citedSections": [ "173.307", "173.307(a)(4)(iii)" ], "catalogPageUrls": [ "https://www.phmsa.dot.gov/regulations/title49/section/173307" ], "pdfUrls": [ "https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/standards-rulemaking/hazmat/interpretations/74901/210011.pdf" ], "representations": [ { "viewUrl": "https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/standards-rulemaking/hazmat/interpretations/74901/210011.pdf", "detailUrl": null, "detailHtmlPath": null, "pdfUrl": "https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/standards-rulemaking/hazmat/interpretations/74901/210011.pdf", "pdfArtifactPath": "data/sources/phmsa-interpretations/21-0011-47f670f70a.pdf", "pdfArtifactSha256": "f60d78d2e1fd14ea257bdf85a2e5862f4dc5d584ac1ac7e6db6ec48608bbe618", "extractedTextPath": "data/sources/phmsa-interpretations/21-0011-47f670f70a.v2.txt", "extractedTextSha256": "285fe2ca69d904a8d7b7086b64248a88fccf49401f860a6e953b2be0269909ff", "pageCount": 4, "extractionVersion": 2 } ], "caveat": "Interpretations apply regulations to the facts presented and do not create independently enforceable requirements.", "jurisdiction": "US" } ```