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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 #23-0035

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

Interpretation Response Details

Response Publish Date:

Company Name: Superior Plus Propane

Individual Name: Mr. Tim Decker

Location State: NY Country: US

View the Interpretation Document

Response text:

April 19. 2024

Mr. Tim Decker
Field Health and Safety Specialist
Superior Plus Propane
1870 South Winton Rd.
Rochester, NY 14618

Reference No. 23-0035

Dear Mr. Decker:

This letter is in response to your March 13, 2023, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to cargo tank inlet and outlet markings. Specifically, you ask about the applicability of marking requirements in § 178.337-9(c) where the HMR states that, except for gauging devices, thermometer wells, and pressure relief valves, each cargo tank inlet and outlet must be marked "liquid" or "vapor" to designate whether it communicates with liquid or vapor when the cargo tank is filled to the maximum permitted filling density.

We have paraphrased and answered your questions as follows:

Q1. You ask what is considered a cargo tank "inlet" under § 178.337-9(c).

A1. Under § 178.320, an "outlet" is defined as "any opening in the shell or head of a cargo tank, (including the means for attaching a closure), except that the following are not outlets: a threaded opening securely closed during transportation with a threaded plug or a threaded cap, a flanged opening securely closed during transportation with a bolted or welded blank flange, a manhole, a gauging device, a thermometer well, or a pressure relief device." It is the opinion of this office that for the purposes of § 178.337-9(c), an inlet and an outlet are the same.

Q2. You ask whether the piping in your attached photographs require marking under § 178.337-9(c).

A2. It is unclear from your photographs whether the piping is an inlet/outlet, as it is unclear whether the piping does or does not communicate directly with the cargo tank or how the fittings connection is used. Therefore, this Office is unable to determine if the piping is subject to the marking requirements under § 178.337-9(c).

Q3. You ask whether the marking shown in the attached photographs meet the requirements of § 178.337-9(c).

A3. Provided the marking is readily visible, legible, durable to withstand transport conditions, and clearly associated with the corresponding inlet or outlet, marking in the locations you describe would satisfy the requirements of the HMR. The marking requirement may be satisfied using various locations and methods, including marking on the cargo tank shell.

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

178.320, 178.337-9(c)

Regulation Sections

Section Subject
178.320 General requirements applicable to all DOT specification cargo tank motor vehicles
178.337-9 Pressure relief devices, piping, valves, hoses, and fittings