USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

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

Interpretation Response #23-0031

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

Interpretation Response Details

Response Publish Date:

Company Name: Essex Industries, Inc.

Individual Name: Ario Estrada

Location State: MO Country: US

View the Interpretation Document

Response text:

June 7, 2023

Ario Estrada
Senior Quality Manager
Essex Industries, Inc.
8007 Chivvis Drive
St. Louis, MO  63123-2395

Reference No. 23-0031

Dear Mr. Estrada:

This letter is in response to your March 20, 2023, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to general requirements for DOT specification cylinders. In your email, you state that your company manufacturers DOT 4L cylinders with a water capacity of 1,220 cubic inches at a facility in the United States. In reference to the inspection and analyses requirements of § 178.35(b)(2), you ask whether your company is able to use a competent inspector of the manufacturer or must instead use an independent inspection agency approved in writing by the Associate Administrator. Specifically, you seek confirmation of your understanding that the water capacity threshold limit of 1,100 cubic inches for use of a competent inspector of the manufacturer for domestic manufacturing applies only to DOT 4D cylinders and not to the other cylinders listed including DOT 4L cylinders.

Your understanding is correct, the 1,100 cubic-inch limit only applies to DOT 4D cylinders. A domestic manufacturer of DOT 4L cylinders may use a "competent inspector of the manufacturer" for performance of inspections and verification of the cylinders. Specifically, your 1,220 cubic inch DOT 4L cylinders may be inspected by a competent inspector of the manufacturer.

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


Dirk Der Kinderen
Chief, Standards Development Branch
Standards and Rulemaking Division


Regulation Sections

Section Subject
178.35 General requirements for specification cylinders