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 #04-0168 ([Florida House of Representatives] [The Honorable Julio Robaina])

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

Interpretation Response Details

Response Publish Date:

Company Name: Florida House of Representatives

Individual Name: The Honorable Julio Robaina

Location State: FL Country: US

View the Interpretation Document

Response text:

Oct 19, 2004

The Honorable Julio Robaina

Florida House of Representatives                 Reference No. 04-0168

402 House Office Building

402 South Monroe Street

Tallahassee, FL 32399

Dear Mr. Robaina:

This is in response to your e-mail and telephone conversations with members of my staff concerning the reluctance of some dive shops in the State of Florida to service and refill certain older DOT 3AL cylinders made of aluminum alloy 6351 and used as self-contained underwater breathing apparatus (SCUBA cylinders). You stated that some dive shops are refusing to fill these older SCUBA cylinders based on information received from the Department of Transportation's Office of Hazardous Materials Safety that the cylinders "are unsafe and are unable to be serviced or refilled and are to be thrown out."

There appears to be a misunderstanding about our position on cylinders made of aluminum alloy 6351. We issued a notice of proposed rulemaking [ No. RSPA 03-14405 (HM-220F)} that proposes to amend the Hazardous Materials Regulations (HMR) to enhance the requalification procedures for DOT 3AL cylinders made of aluminum alloy 6351. The intended effect of the notice of proposed rulemaking, should it be adopted into a final rule, is to facilitate the detection of sustained loading cracking (SLC) and reduce the risk of the cylinder rupturing. Under the proposal, cylinders showing no evidence of SLC and passing the periodic requalification are suitable for continued hazardous material service. We also issued several safety alert notices to inform users of the identity, proper maintenance and precautionary measures for cylinders made of aluminum alloy 6351, including those used as SCUBA cylinders. The safety alert notices and the notice of proposed rulemaking on the DOT 3AL cylinders are available for review at the Office of Hazardous Materials Safety's internet web site at [Web Editor's Note: the website has changed and this information can now be accessed at]

You also stated that some dive shops are refusing to fill certain aluminum alloy cylinders that have the manufacturer's name marked on the lower base, which is sometimes referred to as the cylinder heel. Some cylinder requalifiers may be condemning these cylinders on the mistaken belief that these base roll markings are on the sidewall. Based on information provided to us, most of the cylinders were manufactured before 1989 and formed by the extrusion technique. These cylinders have a thick bottom base area; the larger the diameter, the thicker the base. The manufacturer's markings on these particular cylinders are in a low stress area and are acceptable under § 178.35(f)(6) of the HMR. See the enclosed sketches.


Also please note that whether or not a refiller will refill a particular cylinder is a matter within the refiller's discretion and over which this Department has no control. The same applies to a requalifier who may decline to requalify for continuing use cylinders of questionable linage.

I hope this information is helpful. If I can provide further information or assistance, please feel free to call me.


Robert A. McGuire

Associate Administrator for Hazardous Materials Safety



Regulation Sections

Section Subject
173.301 General requirements for shipment of compressed gases and other hazardous materials in cylinders, UN pressure receptacles and spherical pressure vessels