High-Pressure Gas Cylinder Inspections

There are misunderstandings surrounding the inspection requirements for high-pressure gas cylinders used as part of aircraft standard and supplementary systems.


49 CFR Part 173.1 (a)(2) specifically includes air transportation — “Requirements to be observed in preparing hazardous materials for shipment by air, highway, rail, or water, or any combination thereof…”

49 CFR Part 173.1 (a)(3) refers to the inclusion of inspection and testing requirements — “Inspection, testing, and retesting responsibilities for persons who retest, recondition, maintain, repair, and rebuild containers used or intended for use in the transportation of hazardous materials.”

49 CFR Part 173.301 (a)(1) describes the general requirements for shipment of compressed gases in cylinders and spherical pressure vessels and specifically states that — “Compressed gases must be in metal cylinders and containers built in accordance with the DOT and ICC specifications…”

49 CFR Part 173.301 (a)(2) further requires that “A cylinder may be repaired and requalified only as prescribed in subpart C of Part 180 of this subchapter.”

49 CFR Part 180.205 titled “General requirements for re-qualification of cylinders” defines who can perform the required inspections and tests:

“(b) Persons performing re-qualification functions. No person may represent that a repair or re-qualification of a cylinder has been performed in accordance with the requirements in this subchapter unless that person holds a current approval issued under the procedural requirements prescribed in subpart I of Part 107 of this chapter. No person may mark a cylinder with a RIN and a re-qualification date or otherwise represent that a DOT specification or exemption cylinder has been re-qualified unless all applicable requirements of this subpart have been met. A person who re-qualifies cylinders must maintain the records prescribed in § 180.215 at each location at which it inspects, tests, or marks cylinders.”

49 CFR Part 180.205 also provides a detailed description of visual inspection requirements for cylinders:

“(f) Visual inspection. Except as otherwise provided in this subpart, each time a cylinder is pressure tested, it must be given an internal and external visual inspection…”

49 CFR Part 180.205 also describes the pressure test requirements for cylinders:

“(g) Pressure test. (1) Unless otherwise provided, each cylinder required to be retested under this subpart must be retested by means suitable for measuring the expansion of the cylinder under pressure. Bands and other removable attachments must be loosened or removed before testing so that the cylinder is free to expand in all directions.”

It is under “Cylinder Condemnation” that we find the familiar replacement requirement for 3HT bottles:

“(i) Cylinder condemnation. (1) A cylinder must be condemned when — (v) For a DOT 3HT cylinder — (C) The cylinder bears a manufacture or an original test date older than 24 years or after 4,380 pressurizations, whichever occurs first. If a cylinder is refilled, on average, more than once every other day, an accurate record of the number of rechargings must be maintained by the cylinder owner or the owner’s agent.”

The listing of bottles and their test period or intervals is contained under 49 CFR Part 180.209 titled “Requirements for re-qualification of specification cylinders.” The common test periods we’re familiar with haven’t changed but it is easier to find and understand what needs to be done and how often.

The requirement for hand-held fire extinguishers is found in 49 CFR Part 180.209 “(j) Cylinder used as a fire extinguisher.”

The reorganization of 49 CFR for DOT cylinder re-qualification requirements provides all interested parties with a much simpler rule. All of us will have an easier time finding and understanding the requirements applicable to the aircraft equipment. I suspect that it will be years before all of the aircraft manufacturer maintenance manuals are revised to include the new regulatory reference, but remember, just because the reference is wrong in the maintenance manual doesn’t mean that you are not responsible for the new requirements.

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