{"operation":"document","citation":"25-0035","title":"Fleener Consulting LLC — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2026-01-14","effective_on":null,"summary":"25-0035 response to Fleener Consulting LLC concerning 180.407.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0035.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0035.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0035","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2026-01/250035.pdf","body":"<<<PAGE 1>>>\n\n1200 New Jersey Avenue, SE\nWashington, DC 20590\nU.S. Department\nof Transportation\nPipeline and Hazardous\nMaterials Safety\nAdministration\nJanuary 14, 2026\nArt Fleener\nFleener Consulting LLC\n3741 Mathews Road\nAmes, Iowa 50014\nReference No. 25-0035\nDear Mr. Fleener:\nThis letter is in response to your March 27, 2025 email requesting clarification of the Hazardous\nMaterials Regulations (HMR; 49 CFR Parts 171-180) applicable to cargo tanks. Specifically,\nyour inquiry is related to the required frequency of the external and internal visual inspections of\ninsulated and non-insulated MC 331 cargo tanks.\nWe have paraphrased and answered your questions as follows:\nQ1. If you are unable to conduct the annual external visual inspection on an insulated MC 331\ncargo tank, are you required to conduct an internal visual inspection once a year?\nA1. Yes, for those areas of the cargo tank unable to be externally inspected. Each\nspecification cargo tank must be tested and inspected as specified in § 180.407(c) and in\naccordance with § 180.407(d)(1), where insulation precludes a complete external visual\ninspection, the cargo tank must also (emphasis added) be given an internal visual inspection in\naccordance with § 180.407(d)(1).\nQ2. If you are unable to conduct the annual external visual inspection on a non-insulated MC\n331 cargo tank that has a coating, or vinyl wrap applied to the external shell, are you required to\nconduct an internal visual inspection once a year?\nA2. Yes. If external visual inspection is precluded because any part of the cargo tank wall is\nexternally lined, coated, or designed, to prevent an external visual inspection, those areas of the\ncargo tank must be visually inspected in accordance with § 180.407(d)(1).\nQ3. It is your understanding that PHMSA has required an internal visual inspection once\nevery 5 years for insulated MC 331 cargo tanks and an internal visual inspection annually for\nnon-insulated MC 331 cargo tanks that have wraps or other external coverings of the tank.\n\n<<<PAGE 2>>>\n\nIf this understanding is still accurate, why are non-insulated MC 331 cargo tanks with a coating\nor vinyl wrap required to conduct an internal visual inspection every year?\nA3. Insulated and non-insulated MC 331 cargo tanks are not treated differently with regard to\ninternal visual inspections. In both cases, a complete internal visual inspection is required once\nevery five years as reflected in the table of § 180.407(c). The external visual inspection is\nrequired annually for MC 331 cargo tanks. For both cases in accordance with § 180.407(d)(1), if\ninsulation precludes complete external visual inspection or if any portion of a cargo tank is\nexternally covered (i.e., lined, coated, or designed to prevent external visual inspection), then an\ninternal visual inspection of those areas affected by the covering is required in conjunction with\nthe external visual inspection for the remaining areas of the cargo tank wall. Because the interval\nfor external visual inspection is annually, the interval for the partial internal visual inspection is\nalso annually.\nI hope this information is helpful. Please contact us if we can be of further assistance.\nSincerely,\nDirk DerKinderen\nChief, Standards and Development Branch\nStandards and Rulemaking Division\n\n<<<PAGE 3>>>\n\nHorne\n25-0035\nFrom: Kelley, Shane (PHMSA)\nTo: Hazmat Interps\nSubject: Fw: Request interp\nDate: Friday, March 28, 2025 3:01:06 AM\nPlease process accordingly.\nFrom: art fleener <fleenerconsulting@yahoo.com>\nSent: Thursday, March 27, 2025 5:30:01 PM\nTo: Kelley, Shane (PHMSA) <shane.kelley@dot.gov>\nSubject: Request interp\nYou don't often get email from fleenerconsulting@yahoo.com. Learn why this is important\nCAUTION: This email originated from outside of the Department of Transportation (DOT). Do\nnot click on links or open attachments unless you recognize the sender and know the content\nis safe.\nShane:\nHope all is well with you, and you are surviving.\nI would like clarification and for PHMSA to reconsider the current stance on doing an\ninternal visual on when you cannot see the outside of the tank.\nPHMSA has issued several interps over the years that for an insulated 330, 331 and\n338 cargo tank that you are not required to do an internal visual inspection every year\nto satisfy the external visual and that we are only required to do the internal visual\nevery 5 years, this is consistent with the regulations. In the 180.407 test and\ninspection table it tells us that we have to do an internal inspection every year for an\ninsulated tank, except for a 330, 331 and 338, and that these tanks are required to be\ninternally visually inspected every 5 years.\nPHMSA also has issued several interps that tells us if we have a 331 cargo tank and\nwe cannot see the outside of the tank due to wraps and even paint, then we have to\ndo an internal visual as part of the external visual inspection every year. These\ninterps tells us since we cannot see the actual outside of the tank as part of an\nexternal that we have to go inside, and IMO these interps are in conflict with the prior\ninterps for an insulated tank.\nPHMSA tells us in interps that if we have a 331 cargo tank with a spray on coating to\nhelp protect the tank the that we have to do an internal every year as part of the\nexternal visual. That same tank if it was insulated and we cannot see the outside of\nthe tank we would only need to do the internal once every 5 years. IF that tank had\nany corrosion that started on the outside, we would most likely never find that issue\nby doing an internal visual inspection as the pressure in the tank would of most likely\ncaused the tank to leak prior to any visual evidence seen on the inside.\n\n<<<PAGE 4>>>\n\n1. For an insulated 331 are you required to do an internal visual at least once a year\nas part of the external visual since you are not able to see the tank proper?\n2. For a non insulated 331 that has a coating, or a vinal wrap applied to the external\nshell where you can potentially see if there are any issues with the external portion of\nthe cargo tank, are you required to do an internal annually as part of the external\nvisual?\n3. Historically PHMSA has answered question 1 that you are required to do an\ninternal only once every 5 years and for question 2 that you would have to do the\ninternal every year. If those answers are still current, please explain why when we\nhave a non insulated 331 with a coating or vinal wrap and we can see more of the\noutside shell we are required to do an internal every year.\nthanks\nart\nFleener Consulting LLC.\n515 291 9208\nfleenerconsulting.com","truncated":false,"body_characters":6619}