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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #23-0009

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: DOT Training Solutions

Individual Name: Rex Railsback

Location State: KS Country: US

View the Interpretation Document

Response text:

March 21, 2024

Mr. Rex Railsback
Safety Consultant
DOT Training Solutions
P.O. Box 25311
Overland Park, KS  66225

Reference No. 23-0009

Dear Mr. Railsback:

This letter is in response to your January 30, 2023, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to cargo tank void spaces. Specifically, you wish to clarify the question from a previously issued letter of interpretation (Reference No. 22-0028).

You state in your email that you "... did not intend to ask if the void space between compartmented cargo tanks built with double bulkheads, between compartments, was considered a 'compartment'." Rather, you intended to ask whether the individual tanks of a multi-tank cargo tank motor vehicle (CTMV)—utilizing double bulkheads between tanks which remain at atmospheric pressure during leakage and pressure test-are considered adjacent cargo tanks, as it relates to §§ 180.407(g)(1)(vi) and (h)(1).

The answer is yes. As noted in our previous letter of interpretation (Reference No. 22-0028), §§ 180.407(g)(1)(vi) and (h)(1) both state that "each cargo tank of a multi-tank cargo tank motor vehicle must be tested with the adjacent cargo tanks empty and at atmospheric pressure" (emphasis added). In addition, §§ 180.407(g)(1)(vi) and (h)(1) do not contain provisions specifically excepting CTMVs configured with bulkheads.

I hope this information is helpful. Please contact us if we can be of further assistance.


Steven Andrews
Acting Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

180.407(g)(1)(vi), 180.407 (h)(1)

Regulation Sections

Section Subject
180.407 Requirements for test and inspection of specification cargo tanks