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Interpretation Response #06-0243 ([Alloy Custom Products] [Mr. Everett Snoeberger ])

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

Interpretation Response Details

Response Publish Date:

Company Name: Alloy Custom Products

Individual Name: Mr. Everett Snoeberger 

Location State: IN Country: US

View the Interpretation Document

Response text:

Jan 3, 2007


Mr. Everett Snoeberger                 Reference No. 06-0243
Alloy Custom Products
9701 SR 25 North
Lafayette, IN 47905

Dear Mr. Snoeberger:


This is in response to your October 19, 2006 letter and enclosed video regarding the use of MC-338  cargo tank motor vehicles as specified under the Hazardous Materials Regulations HMR; 49 CFR Parts 171-180). Your scenarios revolve around the shipment of hazardous materials in vacuum insulated MC-338 cargo tank motor vehicles. Your questions are paraphrased and answered as follows:

Q1:      Section 173.33(g) requires each liquid filling and liquid discharge line in an
MC-338 cargo tank to be provided with a remotely controlled internal self-closing stop valve except when the MC-338 cargo tank is used to transport argon, carbon dioxide, helium, krypton, neon, nitrogen, and xenon. Section 178.338-11(b) specifies that for
MC-338 cargo tanks, each liquid filling and liquid discharge line must be provided with
a shut-off valve located as close to the tank as practicable and, unless the valve is manually operable at the valve, the line must also have a manual shut-off valve. This provision allows for either an internal or an external stop valve placed as close to the
tank as possible. We have found that most vacuum insulated MC-338 cargo tanks operate at temperatures below the reliable operating temperature of available internal self-closing stop valves, and currently no manufacturer builds an internal self-closing stop valve that will operate reliably at temperatures that may reach minus 452 °F. Therefore, is a
MC-338 required to have a remotely controlled internal self-closing stop valve as specified in § 173.33(g)?

Al:        The answer is no. MC-338 cargo tanks that utilize an external self-closing stop valve for compliance with the requirements in § 178.338-11(b) may be used to transport hazardous materials in commerce, notwithstanding the provisions in § 173.33(g). This issue will be clarified in a future rulemaking.

Q2:      Section 177.834 requires cargo tanks to be transported with all valves and other closures in liquid discharge systems to be closed and free of leaks unless transported in accordance with § 173.29(b)(2). This provision was added as a result of HM-222B (May 30, 1996; 61 FR 27166) to consolidate the closure requirements for cargo tanks transporting Class 3 (flammable liquid) materials, class 8 (corrosive) materials, and Division 6.1 (poisonous) materials. This rule did not consider the impact this provision
would have on MC-338 cargo tanks that transport cryogenic liquids. These tanks have
external self-closing valves that are normally transported in an open position. These valves are designed to close with a tremendous amount of force to ensure proper closure. Subsequently, these valves require a large amount of force and effort to open. As a result, the potential for physical injury to employee personnel is increased and the ability of the valve system to operate is potentially compromised as a result of repeated cycling opening, closing, and testing). Does § 177.834 permit emergency self-closing valves on MC-338 cargo tanks to be either open or closed during transit?

A2:       The answer is yes. External emergency self-closing valves on MC-338 cargo tanks containing cryogenic liquids may remain either open or closed during transit. We will clarify this issue in a future rulemaking.

I hope this information is helpful. If you have further questions, please do not hesitate to contact this office.



Hattie Mitchell
Chief, Regulatory Review and Reinvention
Office of Hazardous Materials, Standards

173.33(g), 177.834

Regulation Sections

Section Subject
173.33 Hazardous materials in cargo tank motor vehicles
177.834 General requirements