Interpretation Response #25-0115
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: NeoWave S.A.S. de C.V.
Individual Name: Francisco Davila
View the Interpretation Document
Response text:
March 19, 2026
Francisco Davila
Registered Inspector
NeoWave S.A.S. de C.V.
Hacienda Monte Real 107
Hacienda El Campanario
Apodaca, Nuevo Leon, Mexico 66643
Reference No. 25-0115
Dear Mr. Davila:
This letter is in response to your August 7, 2025 letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to cargo tank modifications. Specifically, you state that you are inquiring about modifying a cargo tank to a different specification than that which it was originally built. You state that some manufacturers, repair facilities, and registered inspectors are under the assumption that a Motor Carrier (MC) 300-series cargo tank can have its name plate modified to reflect a current Department of Transportation (DOT) 400-series specification if that cargo tank meets the requirements outlined in §§ 178.345 through 178.348. You ask a series of questions regarding the modification of MC 300-series cargo tanks.
We have paraphrased and answered your questions as follows:
Q1. You ask whether § 180.405(b)(2) allows for the recertification of MC 306, MC 307, and MC 312 cargo tanks to their original specification.
A1. Yes, § 180.405(b)(2) allows cargo tanks originally manufactured as MC 306, MC 307, and MC 312 cargo tanks to be recertified to their original specification. This serves as an exception to paragraph (b)(1) of that section which states that no cargo tank may be marked or certified after August 31, 1995, to the applicable MC 306, MC 307, MC 312, MC 331, or MC 338 standard for that specification in effect on December 30, 1990. This allows a registered inspector to recertify an MC 306, MC 307, or MC 312 cargo tank after it has been modified.
Q2. You ask whether § 180.405(c)(2) allows MC 300-series cargo tanks to have their pressure relief devices (PRDs) and outlets modified to conform to DOT 400-series cargo tank specifications.
A2. Yes, MC 300-series cargo tanks may have their PRDs and outlets modified to meet certain DOT 400-series specifications as authorized by § 173.33(d)(3) and § 180.405(c)(2). PHMSA previously amended the HMR in a final rule, HM-183, to discontinue the construction of MC 300-series cargo tanks and authorized the use of DOT 400-series PRDs on the remaining in-service MC 300-series cargo tanks.1
Q3. You ask whether it is permissible, if a cargo tank complies with the regulations applicable to a DOT 400-series cargo tank, to change the specification on the nameplate from showing MC 300-series to show DOT 400-series.
A3. Yes, the HMR allows for the modification, stretching, or rebarrelling of only those listed MC 300-series cargo tanks to the corresponding DOT 400-series specifications specified in § 180.413(d)(2)(i) through (iii). All the provisions in § 180.413(d)(1) through (d)(4) must be met for modifications, including the installation of a supplemental specification plate, nameplate, or both containing the information that reflects the cargo tank as modified, stretched, or rebarrelled.
I hope this information is helpful. Please contact us if we can be of further assistance.
Sincerely,
Alexander Wolcott
Acting Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division
173.33(d)(3) 178.345 through 178.348 180.405(b)(2) 180.405(c)(2) 180.413(d)(2)(i) through (iii) 180.413(d)(1) through (d)(4)