# Fleener Consulting LLC — Hazardous Materials Safety Interpretation - **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:** Not available - **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:** <<>> 1200 New Jersey Avenue, SE Washington, DC 20590 U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration January 14, 2026 Art Fleener Fleener Consulting LLC 3741 Mathews Road Ames, Iowa 50014 Reference No. 25-0035 Dear Mr. Fleener: This letter is in response to your March 27, 2025 email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to cargo tanks. Specifically, your inquiry is related to the required frequency of the external and internal visual inspections of insulated and non-insulated MC 331 cargo tanks. We have paraphrased and answered your questions as follows: Q1. If you are unable to conduct the annual external visual inspection on an insulated MC 331 cargo tank, are you required to conduct an internal visual inspection once a year? A1. Yes, for those areas of the cargo tank unable to be externally inspected. Each specification cargo tank must be tested and inspected as specified in § 180.407(c) and in accordance with § 180.407(d)(1), where insulation precludes a complete external visual inspection, the cargo tank must also (emphasis added) be given an internal visual inspection in accordance with § 180.407(d)(1). Q2. If you are unable to conduct the annual external visual inspection on a non-insulated MC 331 cargo tank that has a coating, or vinyl wrap applied to the external shell, are you required to conduct an internal visual inspection once a year? A2. Yes. If external visual inspection is precluded because any part of the cargo tank wall is externally lined, coated, or designed, to prevent an external visual inspection, those areas of the cargo tank must be visually inspected in accordance with § 180.407(d)(1). Q3. It is your understanding that PHMSA has required an internal visual inspection once every 5 years for insulated MC 331 cargo tanks and an internal visual inspection annually for non-insulated MC 331 cargo tanks that have wraps or other external coverings of the tank. <<>> If this understanding is still accurate, why are non-insulated MC 331 cargo tanks with a coating or vinyl wrap required to conduct an internal visual inspection every year? A3. Insulated and non-insulated MC 331 cargo tanks are not treated differently with regard to internal visual inspections. In both cases, a complete internal visual inspection is required once every five years as reflected in the table of § 180.407(c). The external visual inspection is required annually for MC 331 cargo tanks. For both cases in accordance with § 180.407(d)(1), if insulation precludes complete external visual inspection or if any portion of a cargo tank is externally covered (i.e., lined, coated, or designed to prevent external visual inspection), then an internal visual inspection of those areas affected by the covering is required in conjunction with the external visual inspection for the remaining areas of the cargo tank wall. Because the interval for external visual inspection is annually, the interval for the partial internal visual inspection is also annually. I hope this information is helpful. Please contact us if we can be of further assistance. Sincerely, Dirk DerKinderen Chief, Standards and Development Branch Standards and Rulemaking Division <<>> Horne 25-0035 From: Kelley, Shane (PHMSA) To: Hazmat Interps Subject: Fw: Request interp Date: Friday, March 28, 2025 3:01:06 AM Please process accordingly. From: art fleener Sent: Thursday, March 27, 2025 5:30:01 PM To: Kelley, Shane (PHMSA) Subject: Request interp You don't often get email from fleenerconsulting@yahoo.com. Learn why this is important 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: Hope all is well with you, and you are surviving. I would like clarification and for PHMSA to reconsider the current stance on doing an internal visual on when you cannot see the outside of the tank. PHMSA has issued several interps over the years that for an insulated 330, 331 and 338 cargo tank that you are not required to do an internal visual inspection every year to satisfy the external visual and that we are only required to do the internal visual every 5 years, this is consistent with the regulations. In the 180.407 test and inspection table it tells us that we have to do an internal inspection every year for an insulated tank, except for a 330, 331 and 338, and that these tanks are required to be internally visually inspected every 5 years. PHMSA also has issued several interps that tells us if we have a 331 cargo tank and we cannot see the outside of the tank due to wraps and even paint, then we have to do an internal visual as part of the external visual inspection every year. These interps tells us since we cannot see the actual outside of the tank as part of an external that we have to go inside, and IMO these interps are in conflict with the prior interps for an insulated tank. PHMSA tells us in interps that if we have a 331 cargo tank with a spray on coating to help protect the tank the that we have to do an internal every year as part of the external visual. That same tank if it was insulated and we cannot see the outside of the tank we would only need to do the internal once every 5 years. IF that tank had any corrosion that started on the outside, we would most likely never find that issue by doing an internal visual inspection as the pressure in the tank would of most likely caused the tank to leak prior to any visual evidence seen on the inside. <<>> 1. For an insulated 331 are you required to do an internal visual at least once a year as part of the external visual since you are not able to see the tank proper? 2. For a non insulated 331 that has a coating, or a vinal wrap applied to the external shell where you can potentially see if there are any issues with the external portion of the cargo tank, are you required to do an internal annually as part of the external visual? 3. Historically PHMSA has answered question 1 that you are required to do an internal only once every 5 years and for question 2 that you would have to do the internal every year. If those answers are still current, please explain why when we have a non insulated 331 with a coating or vinal wrap and we can see more of the outside shell we are required to do an internal every year. thanks art Fleener Consulting LLC. 515 291 9208 fleenerconsulting.com - **truncated:** false - **body characters:** 6619