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Interpretation Response #13-0147 ([Hazmat Resources, Inc.] [Mr. Danny Shelton])

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

Interpretation Response Details

Response Publish Date:

Company Name: Hazmat Resources, Inc.

Individual Name: Mr. Danny Shelton

Location State: TX Country: US

View the Interpretation Document

Response text:

October 23, 2013

Mr. Danny Shelton
Hazmat Resources, Inc.
124 Rainbow Drive, Suite 2471
Livingston, TX 77399

Ref. No.: 13-0147

Dear Mr. Shelton:

This responds to your July 16, 2013 letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to pressure relief devices on specification DOT 400 series cargo tank motor vehicles.  Specifically, you ask what the requirements are for testing and inspection of specification DOT 400 series cargo tank motor vehicles pertaining to pressure relief valves and pressure relief systems.

As provided in § 180.407(d)(3), all reclosing pressure relief valves must be externally inspected for any corrosion or damage which might prevent safe operation.  Additionally, all reclosing pressure relief valves on cargo tanks carrying lading corrosive to the valve must be removed from the cargo tank for inspection and testing.  Finally, each reclosing pressure relief valve required to be removed and tested must open at no less than the required set pressure and no more than 110 percent of the required set pressure, and must reseat to a leak-tight condition at no less than 90 percent of the start-to-discharge pressure or the pressure prescribed for the applicable cargo tank specification.

Under the general design and construction requirements applicable to specification DOT 400 series cargo tank motor vehicles (see § 178.345), the pressure relief system requirements provided in § 178.345-10(d) state that the set pressure of the pressure relief system is the pressure at which it starts to open, allowing discharge.  The set pressure of each primary relief valve must be no less than 120 percent of the maximum allowable working pressure (MAWP), and no more than 132 percent of the MAWP.  Additionally, the valve must reclose at not less than 108 percent of the MAWP and remain closed at lower pressures.  Finally, the set pressure of each pressure relief valve used as a secondary relief device must be not less than 120 percent of the MAWP.  This standard equally applies to original construction and requalification under parts 178 and 180 of the HMR, respectively.

I hope this satisfies your inquiry.  Please contact us if we can be of further assistance.


T. Glenn Foster
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

180.407, 178.345-10(d)

Regulation Sections

Section Subject
178.345-10 Pressure relief
180.407 Requirements for test and inspection of specification cargo tanks