Are Aluminium Cylinders Safe?:
We at Luxfer Gas Cylinders are grateful to Dive New Zealand for seriously addressing the all-important issue of cylinder safety, and we appreciate the chance to express our point of view.
For many years, Luxfer has consistently emphasized safe use of our products through an active scuba safety education program, through our pioneering efforts in the development of Visual Plus non-destructive testing equipment, and through the most generous cylinder-replacement program in the scuba industry. We are currently organising seminars in Auckland and Wellington in mid-August to address directly the questions and concerns of New Zealand divers. However, Luxfer (or any other cylinder manufacturer) can only do so much to promote safety. Ultimately, safety is the responsibility of the individual diver, who must make sure that cylinders, as well as other equipment, remain in proper operating condition.
Luxfer takes full responsibility for the high quality and dependability of every cylinder that leaves our factories. Each cylinder is manufactured to specific, very demanding international standards (eg DOT, AS and BS). Government inspectors ensure that cylinders are thoroughly tested and approved before shipment. But once a cylinder leaves the factory, Luxfer has no control over what happens to it – and we have learned that, unfortunately, a great deal can happen to scuba cylinders to make them unsafe. All too often, scuba cylinders are fast-filled, over-filled, left filled at full pressure for long periods, left in the sun or in car boots, dumped filled (sometimes several times a day), gouged and dented, stripped and repainted, and generally mishandled or abused. All these conditions can shorten the useful life of a cylinder. Like any other important piece of equipment, high-pressure cylinders – whether made of aluminium, steel, nickel, composites or other materials – require proper care, maintenance and handling. Well-maintained cylinders can deliver decades of safe, reliable service. More than 30 million Luxfer cylinders are currently in use around the world in a wide variety of demanding applications.
To ensure safety, all high-pressure cylinders should be periodically inspected by qualified, accredited inspectors and re-tested or re-qualified. Between re-tests, cylinders should also be thoroughly visually inspected by trained, certified inspectors. In most countries, the industry standard is a complete visual inspection at least once each year. However, for cylinders in heavy service, Luxfer recommends visual inspections at least every four months, as well as Visual Plus inspections, if possible.
When discussing cylinder cracks and failures, it is imperative to make a distinction between actual scientific findings versus subjective opinions and proliferating myths. Luxfer is currently studying sustained load cracking in aluminium cylinders made of 6351 alloy, and we have engaged respected outside research organisations to assist in tests and analyses. Extensive international research has shown definitively that cracks in these cylinders generally do not grow quickly. For example, an independent research report (a copy of which is on file with OSH) revealed that the cylinder which injured Brian Schmidt in the much-publicized Tairua accident showed crack growth over a seven-year period. It is logical to ask why this cylinder was not condemned by a qualified inspector long before it became dangerous.
Unfortunately, we have found that there are a number of cylinder âinspectorsâ around the world – including even experienced and well-meaning divers and dive shop operators – who have not taken the time to learn proper procedures for detecting cracks in aluminium cylinders. Inspecting aluminium cylinders is very different from inspecting steel cylinders. For one thing, when checking an aluminium cylinder, the inspector should initially focus on the threads, which is where cracks occasionally start. Visual Plus testing equipment, which Luxfer helped develop, offers a fast, reliable method for removing the guesswork from crack detection; we highly recommend its use.
Divers have every right to be concerned about cylinder safety – in fact, Luxfer has been encouraging that concern for many years. But the secrets to safety are knowledge and prudence. Weâd like to conclude our comments with a published quotation from William L. High, president of Professional Scubu Inspectors, Inc (PSI), a highly-respected, independent authority on cylinder safety who has investigated cylinder failures around the world: âPerhaps the greatest responsibility of all for safe cylinders lies with cylinder owners. They must recognize that their cylinder contains over one million pounds of energy, that prudent handling, care and usage will help keep that explosive force contained, and they must insist that only trained professionals inspect, service or fill their cylinderâ (Sources, September/October 1994, p41).
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