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Northwest Dive News, Volume 3 Issue 11

November 1999

 Tank Safety and Professional Inspection


By Jack Hornsby,

Professional Scuba Inspector and PADI Instructor

ASK Water Sports, Dublin, Ohio


            A standard 80 cubic foot scuba tank pressurized to 3000 PSI has an explosive force of approximately 1.3 million pounds.  That is equivalent to a hand grenade.  Over the years there have been many reported explosions of both steel and aluminum cylinders.  Some incidents caused deaths; many more caused serious injuries.  More than 80% of those explosions happened during the fill process.  As employees at ASK Water Sports, we are very concerned about our safety during the fill process as well as your safety while using dive cylinders.

            To maintain a high level of safety we depend upon training, safety check standards, and tools provided by Professional Scuba Inspectors, Inc.  This group is based in Seattle, Washington and is headed by the noted tank inspection expert Bill High.  The organization that has basically set the standards nationwide for tank inspection and all professional dive centers abide by them.

            As most scuba divers are aware, scuba tanks must be hydrostatically tested every five years.  This test assures that the tank has not lost its elasticity and become brittle through abuse or heat damage, etc.  However, simply passing a hydro test does not assure that a tank is safe.  Visual inspections must be done at least once a year to assure that other defects or dangers do not exist.  Most tank failures and injuries are due to factors normally found during the visual inspection process.  Some of these defects are cracks in tank walls or threads, corrosion and pitting, the wrong valve, heat damage, the wrong burst disk, etc.  Because of our concern for our and your safety, we thoroughly inspect each tank in several areas before applying an Evidence of Inspection Sticker.  This sticker is our assurance - and yours - that a professional inspection has been performed.

            At ASK Water Sports all tanks are inspected both inside and outside for any evidence of damage or abuse.  This inspection can take up to 30 minutes for each tank.  The process requires specialized tools and gauges to insure that minimum standards are met.  All boots, bands, and mesh coverings are removed as well as all old inspection stickers.  This allows a thorough check to be made for corrosion, pitting, bulges and paint or heat damage.

            The interior is checked for unwanted contents such as moisture, dust, corrosion, flakes or other particles.  The tank interior is also checked for discoloration, scale, pitting, cracks and other defects.  Coated tank interiors are looked at very closely and often rejected if there is obvious damage that could indicate corrosion under the coating.  Often older steel tanks must be tumbled with abrasives to remove corrosion, scale and coatings in order to see possible underlying damage.  Any time metal is removed by tumbling, the tank must be re-hydrostatically tested to insure integrity.

            Tank threads and the interior crown are checked for shape, folds in the metal, cracks, or corrosion, etc. , that could indicate danger.  The O-ring seating surface is checked for proper seat and sealing of the valve.  As an additional safety measure we have purchased an electronic thread testing device at a cost of over $1500.  All valves are checked for function, corrosion, burst disks, o-rings, leaks, etc.

            At ASK Water Sports we do FAIL tanks!  This is not always due to one major defect.  Sometimes it is due to an uneasy feeling due to several marginal issues with a tank.  We normally destroy a failed tank by damaging the threads so the tank can not be restored to use.  This is done only after a thorough, professional inspection.  While we do fail tanks, those failures are usually less than one percent of the tanks we inspected.  Regardless of the failure rate, safety for ourselves and you is our primary goal.

            Recently, Luxfer Gas Cylinders, the worlds leading manufacturer of aluminum scuba cylinders for underwater diving, announced a new policy concerning the periodic inspection and replacement of it's scuba cylinders.

            Effective immediately, Luxfer requires that every Luxfer scuba cylinder 15 years old or older be visually inspected annually by a properly trained inspector, as well as inspected with Visual Plus or equivalent non-destructive testing equipment.  If the cylinder passes the inspection, it will be certified for use by the inspector.  Cylinders that are not inspected and not certified should not be used.  Cylinders that fail the inspection should be removed from service.

            I f a properly inspected scuba cylinder is found to have either a manufacturing defect or sustained-load cracking, Luxfer will honor the following replacement policy: If the cylinder is 10 years old or less (based on the original hydro test date), Luxfer will replace the cylinder at no charge.  Luxfer will not replace cylinders that have been damaged in normal use or due to abuse or mistreatment.

If the cylinder is more than 10 years old, the customer may purchase an equivalent replacement cylinder for US$50 for cylinders manufactured in the United States.  For Luxfer aluminum cylinders manufactured elsewhere, the purchase price will be determined in the country of origin based on local currency rates.

A "manufacturing defect" is any imperfection that fails to meet product specifications at the time of manufacture.

Jack Ward, Luxfer's market manager in charge of scuba products, said that the new Luxfer policy is an extension of the company's well publicized "Safety First" program, as well as Luxfer's previous public recommendations concerning cylinder inspection.  "We want to make sure that all Luxfer cylinders are safe to fill and safe to use, regardless of age, and we want to get damaged cylinders out of circulation," he said.  "That's why we are requiring the use of Visual Plus or equivalent testing, which helps take the guesswork out of cylinder inspection."  Ward explained that scuba is the most demanding application for cylinders because of the corrosive effects of seawater and the need for higher pressures and frequent fills.  "Our experience has also shown that there is a much higher potential for cylinder abuse, including overfilling and fast-filling, in scuba than in other cylinder applications," he notes.

For more information about the new scuba policy or Luxfer scuba products, please contact Luxfer Gas Cylinders, 3016 Kansas Avenue, Riverside, Calif. 92507


Advanced Inspection Technology
14020 Eagle View Rd.
Lake Mathews, CA USA    92570

Within the US: 1-800-611-9077 
Outside the US: 1-951-776-9994 
FAX: 951-776-9995
Customer Support: support@visualplus.net
Sales: sales@visualplus.net