{"operation":"document","citation":"25-0020","title":"Boyd Pro Service, LLC — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2025-09-23","effective_on":null,"summary":"25-0020 response to Boyd Pro Service, LLC concerning 173.33, 178.345, 178.348, 180.407.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0020.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0020.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0020","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2026-01/250020.pdf","body":"<<<PAGE 1>>>\n\n1200 New Jersey Avenue, SE\nWashington, DC 20590\nU.S. Department\nof Transportation\nPipeline and Hazardous\nMaterials Safety\nAdministration\nSeptember 23, 2025\nFloyd A. Boyd\nBoyd Pro Service LLC\n993 Pruden Ave.\nDayton, OH 45403\nReference No. 25-0020\nDear Mr. Boyd:\nThis letter is in response to your February 13, 2025 letter requesting clarification of the\nHazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to pressure relief\ndevices (PRDs) on Motor Carrier (MC) 312 cargo tank motor vehicles (CTMVs). Specifically,\nyou state that your company has a customer who owns several MC 312 CTMVs used exclusively\nfor the transportation of “UN1791, Hypochlorite solutions, 8, II,” each fitted with a single-use,\nnon-reclosing, 35 psi PRD. You further state that these cargo tanks were built in the 1980’s. You\nask if single-use PRDs on MC 312 CTMVs can be replaced with 35 psi reclosing PRDs.\nSection 173.33(d)(1) specifies that non-reclosing PRDs are not authorized in any cargo tank\nexcept when in series with a reclosing PRD; however, a cargo tank marked or certified before\nAugust 31, 1995, which is fitted with non-reclosing PRDs, may continue to be used in any\nhazardous material service for which it is authorized. Section 173.33(d)(3) specifies that for MC\n312 CTMVs, PRDs or outlets may be modified to meet the applicable requirement for a\nDepartment of Transportation (DOT) 412 CTMV. Further, § 180.407(j)(1)(iii)(B) states that MC\n312 cargo tanks modified with reclosing PRDs meeting DOT 412 specifications must meet the\npressures set forth for a DOT 412 cargo tank in § 178.348-4. Paragraph (c) of § 178.348-4 states\nthat the setting of PRDs must be in accordance with § 178.345-10(d), which specifies that the set\npressure of each primary relief valve must be no less than 120 percent of the maximum allowable\nworking pressure (MAWP), and no more than 132 percent of the MAWP, and that the valve\nmust reclose at not less than 108 percent of the MAWP and remain closed at lower pressures.\nI hope this information is helpful. Please contact us if we can be of further assistance.\nSincerely,\nAlexander Wolcott\nActing Chief, Regulatory Review and Reinvention Branch\nStandards and Rulemaking Division\n\n<<<PAGE 2>>>\n\nFeb.13.2025 2:26PM\nNo.1607 P. 1\nFebuary 13,2025\n25-00020\nLarson\nBoyd Pro Service LLC.\n993 Pruden Ave.\nDayton, Oh. 45403\n(937) 751-5964\nBoydproservice@gmail.com\nU.S. DOT\nResearch and Special Programs\nAttn: Approvals PHH-31\n1200 New Jersey Ave, SE\nWashington, D.C. 20590-0001\nTo Whom it may concern: Ref: HMR 178.345�10\nWe have a customer that has a few MC-312 cargo tanks that were built in the B0's that\ntransport Sodium Hypochlorite ( UN 1791) only. They currently have single use/changeable 35\nP .S.I. pressure relief (graphite) Disk on them. I am writing to you to ask if that single use disk\nmay be removed & replaced with a Teflon Lined 35 P.S.I. rec/osing Pressure relief valve. Will you\nplease clarify.\nSincerely,\n�,d/?,./\nFloyd A. Boyd\n1","truncated":false,"body_characters":2992}