Author: rusty

Please note the following product safety notice issued by Abysmal Diving, a distributor of Luxfer scuba cylinders. Although the notice refers to Thermo scuba valves used with Luxfer cylinders, Luxfer Gas Cylinders wishes to emphasize that the notice is not a result of any action or omission on the part of Thermo Valve Corporation.

JULY 15, 2002

TO: ABYSMAL DIVING CUSTOMERS:

Abysmal Diving Inc. of Lake Havasu City, Arizona has been notified that some scuba cylinder valves manufactured by Thermo Valve Corp. and sold by Abysmal Diving Inc. as prepared for oxygen/nitrox service between August 2000 and July 9, 2002, may not be compatible with 100% pure Oxygen (when introduced at 200 psi and above) or Oxygen Enriched Air Nitrox mixtures greater than 21% oxygen content.

If you currently introduce into your scuba cylinder 100% pure oxygen or oxygen enriched air gas mixtures with an oxygen content greater than 21% and you are using one of the valves listed below, you must immediately discontinue such practice due to a RISK OF SPONTANEOUS FIRE AND SERIOUS PERSONAL INJURY OR DEATH.

If you use your valves for AIR only then this Safety Notice does not apply to you.

Valves Subject to Safety Notice

• Val-131 Thermo valve 3000 PSI: K 3/4 - 14 NGS thread
• Val-132 Thermo valve 2400 PSI K 3/4 - 14 NGS thread
• Val-133 Thermo valve 3300 PSI K 3/4 - 14 NGS thread
• Val-300 Thermo valve 2400 PSI, 300bar DIN 3/4 - 14 NGS thread
• Val-301 Thermo valve 3000 PSI, 300bar DIN 3/4 - 14 NGS thread
• Val-302 Thermo valve 3300 PSI, 300bar DIN 3/4 - 14 NGS thread
• Val-303 Thermo valve 3180 PSI, 300bar DIN 3/4 - 14 NGS thread
• Val-157 Thermo 200 bar twin Isolation manifold DIN/INT 3/4 - 14 NGS thread
• Val-357 Thermo 300 bar twin Isolation manifold DIN 3/4 - 14 NGS thread
• Val-351 Thermo 200 bar DIN/INT right hand modular valve 3/4 - 14 NGS thread
• Val-355 Thermo 200 bar H connector / Right hand
• Val-352 Thermo 200 bar DIN/INT left hand modular valve 3/4 - 14 NGS thread
• Val-356 Thermo 200 bar H connector/ Left hand Val-358 Thermo manifold cross bar with shutoff isolation
• Val-359 Thermo manifold cross bar without shutoff

*This Product Safety Notice is not a result of any action or omission on the part of Thermo Valve.

DANGER: DO NOT USE THE ABOVE LISTED VALVES WITH 100% PURE OXYGEN OR OXYGEN ENRICHED AIR NITROX MIXTURES.

Abysmal Diving Inc. of Lake Havasu City, Arizona has been notified that some scuba cylinder valves manufactured by Thermo Valve Corp. and sold by Abysmal Diving Inc. as prepared for oxygen/nitrox service between August 2000 and July 9, 2002 may contain one or more soft good materials (O-ring, seat) that may not be compatible with 100% pure Oxygen (when introduced at 200psi and above) or Oxygen Enriched Air Nitrox mixtures greater than 21% oxygen content.

You must stop using the valve and manifold combinations listed above immediately if being used with 100% pure high pressure oxygen (200 psi or more) or oxygen enriched air mixtures greater than 21% oxygen content or if the valve or manifold is exposed to high pressure oxygen (200 psi or greater) during a partial pressure mixing process. You must immediately return the item (s) to Abysmal Diving Inc.where they will be serviced and returned to you at no charge.

If you now use or intend to use your valve and scuba tank for AIR use, only, and if you have no intention of introducing 100% pure Oxygen (when introduced at 200psi and above) or Oxygen Enriched Air Nitrox mixtures greater than 21% oxygen content through it, then this Product Safety Notice does not apply to you.

INSTRUCTIONS:

If your valves are subject to this Product Safety Notice, please e-mail, call or write Abysmal Diving Inc. immediately at: 2099 Acoma Boulevard West, Suite C, Lake Havasu City, Arizona, 86403 USA Phone: (928) 854-9470 Fax: (928) 854-9473, and request an SMA # (Service Merchandise Authorization #). Then pack your valves in an appropriate container and return them to Abysmal Diving Inc. When your valves arrives they will undergo a complete teardown, inspection, cleaning and will be fitted with any required oxygen compatible materials and lubricants. Your serviced valves will then be shipped back to you free of charge.

As of July 20th, 2002 Abysmal Diving Inc. has received no reports of any valve failing or exhibiting any oxygen compatibility problems. However this Product Safety Notice has been issued and a free retrofit offer made, in an attempt to ensure our customers have all the components originally intended in these valves for oxygen/nitrox service. Abysmal Diving Inc. strives to produce the finest and safest diving equipment, and protect its customers from the unreasonable risk of injury.

Again, if you currently introduce 100% pure oxygen or oxygen enriched air gas mixtures with an oxygen content greater than 21% you must immediately discontinue use of the above listed valves until such time as they have been returned to Abysmal Diving Inc. for a complete inspection and any required retrofitting and preparation for oxygen service. DO NOT CONTINUE TO USE THESE VALVES IN OXYGEN-RELATED SERVICE BECAUSE OF THE POSSIBILITY OF FIRE AND SERIOUS INJURY OR DEATH.

Any questions can be directed to Abysmal Diving Inc.

SYDNEY, Australia (June 13, 2002)-Luxfer Gas Cylinders has announced an updated inspection and replacement policy for scuba cylinders manufactured at its facility in Australia. The primary purpose for the new policy is to clarify inspection and testing procedures for the two different aluminium alloys from which Luxfer scuba cylinders have been manufactured. The text of the policy is as follows:

Section I: Inspection and Testing of Luxfer Scuba Cylinders Manufactured from 6351 Aluminium Alloy

Luxfer scuba cylinders were manufactured from 6351 aluminium alloy during the following periods:

• Australia: 1975 through 1990
• United States: 1972 through mid-1988
• England: 1967 through 1995

Luxfer requires that every Luxfer 6351-alloy all-aluminium scuba cylinder be visually inspected at least every 2.5 years by a properly trained inspector. As part of this inspection, Luxfer further requires that the cylinder neck be tested with an eddy-current device such as Visual Plus, Visual Eddy or equivalent non-destructive testing equipment. When properly used, eddy-current devices contribute significantly to early detection of difficult-to-observe sustained-load cracks in the necks of 6351-alloy cylinders. If the cylinder passes the inspection, the inspector will document that fact. If the cylinder fails the inspection, it must be removed from service immediately. Do not use Luxfer 6351-alloy scuba cylinders that have not been both visually inspected and eddy-current tested and then properly documented.

This Luxfer-required visual and eddy-current inspection is in addition to periodic requalifications (including retesting and inspections) required or recommended by various regulatory agencies around the world. The intervals between retests and inspections vary from country to country.

In addition to the required inspection and testing described above and in keeping with Australian and New Zealand scuba industry standards, Luxfer recommends that all Luxfer 6351-alloy scuba cylinders be visually inspected at least once each year by a properly trained inspector.

For cylinders in heavy use (for example, those filled five or more times a week), Luxfer recommends visual inspection every four months. For more information, refer to Luxfer's Scuba Cylinder Inspection Guide, which is available by calling Luxfer at 61-2-9830-0999 or by visiting the Luxfer web site at www.luxfercylinders.com.

Section II: Inspection and Testing of Luxfer Scuba Cylinders Manufactured from 6061 Aluminium Alloy

Luxfer began manufacturing scuba cylinders from a proprietary 6061 aluminium alloy in 1990 in Australia, in mid-1988 in the United States and in 1995 in England. The majority of Luxfer scuba cylinders currently in service are made from this proprietary 6061 alloy, which Luxfer is still using.

Cylinders made from Luxfer's proprietary 6061 alloy are not susceptible to sustained-load cracks. Therefore, Luxfer does not deem it necessary to test these cylinders with eddy-current devices such as Visual Plus and Visual Eddy. In fact, field experience has shown that using such eddy-current devices with Luxfer 6061-alloy cylinders can result in misleading "false-positive" readings.

In keeping with Australian and New Zealand scuba industry standards, Luxfer recommends annual visual inspection of Luxfer 6061-alloy cylinders by a properly trained inspector. For cylinders in heavy use (for example, those filled five or more times a week), Luxfer recommends visual inspection every four months. These recommended inspections are in addition to periodic requalifications (including retesting and inspections) required or recommended by various regulatory agencies around the world. The intervals between retests and inspections vary from country to country.

For more information, refer to Luxfer's Scuba Cylinder Inspection Guide, which is available by calling Luxfer at 61-2-9830-0999 or visiting the Luxfer web site at www.luxfercylinders.com.

Section III: Luxfer Scuba Cylinder Replacement Policy

This replacement policy applies only to the original owner of a Luxfer scuba cylinder. If a properly inspected Luxfer scuba cylinder is found to have either sustained-load cracking (in the case of 6351-alloy cylinders) or a manufacturing defect (i.e., any imperfection that fails to meet product specifications at the time of manufacture), Luxfer will honor the following replacement policy:

• If the cylinder is 10 years old or less (based on the original hydrotest date), Luxfer will replace the cylinder at no charge with a new 6061-alloy cylinder. However, Luxfer will not replace cylinders that have been damaged, abused or mistreated.
• If the cylinder is more than 10 years old, the original owner may purchase an equivalent replacement 65, 75, 85 or 95 cu. ft. cylinder, 3500 psi fill pressure, for A$137.50 or NZ$186 for cylinders manufactured in Australia.
• For DOT 80 cu. ft. cylinders, 3000 psi fill pressure, manufactured in Australia or the United States, the replacement prices are A$110 and NZ$152. For 20 cu ft cylinders, 3100 psi fill pressure, manufactured in Australia, the replacement prices are A$110 and NZ$152. Australian and New Zealand prices include GST.
• Luxfer cylinder owners in Australia should contact Luxfer Gas Cylinders at 61-2-98300999 to obtain replacement cylinders. Luxfer cylinder owners in New Zealand should contact Luxfer's New Zealand agent, Tank Test Laboratories, at 64-9-2623628 to obtain replacement cylinders.
• For the Scuba Replacement Policy, it is the owner's responsibility to pay the freight to Luxfer Gas Cylinders or TTL. The return freight will be at Luxfer's or TTL's cost, provided that the cylinder qualifies for replacement or trade-in.
• Please ensure that all cylinders are returned without valve or accessories. Luxfer Gas Cylinders and TTL will not be held responsible for any accessories that remain on the cylinder at the time of claim.
• Return freight will be at the owner's cost for any invalid claim. Any invalid claim will also incur an inspection fee by TTL as nominated by TTL. All claims lodged for trade-in are to be paid for within 3 months of lodgment. If payment is not received within this time, the cylinders will be condemned and the claim will be null and void.

For more information about this policy, contact Luxfer Gas Cylinders, 350 Vardys Road, Kings Park, NSW 2148, Australia; telephone 61-2-9830-0999; fax 61-2-9622-9227; on the web at www.luxfercylinders.com.

NOTTINGHAM, England - July 17, 2000 -- Luxfer Gas Cylinders has announced a new inspection and replacement policy for scuba cylinders manufactured at its facilities in the United Kingdom. The primary purpose for the new policy is to clarify inspection and testing procedures for the two different aluminium alloys from which Luxfer scuba cylinders have been manufactured. The policy conforms to British Standards and has been approved for publication by the Health & Safety Executive. The text of the policy is as follows:

Section I: Inspection and Testing of Luxfer Scuba Cylinders Manufactured from Aluminium Alloy 6351 (AA6351)

Luxfer scuba cylinders were manufactured from Aluminium Alloy 6351 during the following periods:

• England: 1963 through 1995
• United States: 1972 through mid-1988
• Australia: 1975 through 1990

In compliance with United Kingdom legislation (Health and Safety at Work Act 1974 and Consumer Protection Act 1987), Luxfer requires that every Luxfer 6351-alloy all-aluminium scuba cylinder be visually inspected at least every two years by a properly trained inspector in accordance with BS5430, Part 3 or 6. As part of this inspection, Luxfer recommends that the cylinder neck be tested with an eddy-current device such as Visual Plus, Visual Eddy or equivalent non-destructive testing equipment. When properly used, eddy-current devices contribute significantly to early detection of difficult-to-observe sustained-load cracks in the necks of 6351-alloy cylinders. Do not fill Luxfer 6351-alloy scuba cylinders that have not been visually inspected in accordance with BS5430, Part 3 or 6, eddy-current tested (see next paragraph) and properly documented.

In exceptional circumstances where eddy-current testing equipment is not yet available, a visual inspection (performed in accordance with BS5430, Part 3 or 6) is acceptable until the next required visual inspection, which must include an eddy-current test; all subsequent required visual inspections must also include an eddy-current test.

If the cylinder passes the inspection, the inspector will document that fact. If the cylinder fails the inspection, it must be removed from service immediately.

Section II: Inspection and Testing of Luxfer Scuba Cylinders Manufactured from Aluminium Alloy 6061 (AA6061)

Luxfer has manufactured scuba cylinders exclusively from a proprietary 6061 aluminium alloy since 1995 in England, since mid-1988 in the United States, and since 1990 in Australia. The majority of Luxfer scuba cylinders currently in service globally are made from this proprietary 6061 alloy, which Luxfer still uses.

Cylinders made from Luxfer's proprietary Aluminium Alloy 6061 are not susceptible to sustained-load cracks. Therefore, Luxfer does not deem it necessary to test these cylinders with eddy-current devices such as Visual Plus and Visual Eddy. In fact, field experience has shown that use of such eddy-current devices with Luxfer 6061-alloy cylinders can result in misleading "false-positive" readings.

In compliance with United Kingdom legislation (Health and Safety at Work Act 1974 and Consumer Protection Act 1987), Luxfer requires visual inspection of Luxfer 6061-alloy cylinders at least every two years by a properly trained inspector in accordance with BS5430, Part 3 or 6.

Section III: Identifying the Alloy of Manufacture of Luxfer Scuba Cylinders

The aluminium alloy from which a Luxfer scuba cylinder is manufactured can be determined from the stamping on the shoulder and around the base of the cylinder.

Identifying Aluminium Alloy 6351 (AA6351)

Luxfer cylinders stamped with any of the following markings are manufactured from Aluminium Alloy 6351:

• HOAL 1
• HOAL 2
• HOAL 3
• HOAL 4
• BS5045/3/B
• BS5045/3/B/S
• AA6351
• HE30
• P****X (as part of serial number)
• P****P (as part of serial number)

On some small cylinders manufactured at Luxfer's Aldridge plant, the above markings may not be present. In that case, the alloy can be determined from the three-digit type number stamped around the base. If the three-digit number is of the form 1**, 3** or 5**, then the alloy of manufacture is AA6351.

Identifying Aluminium Alloy 6061 (AA6061)

Luxfer cylinders stamped with any of the following markings are manufactured from Aluminium Alloy 6061:

• BS5045/3/C
• BS5045/3/C/S
• AA6061
• P****Z (as part of serial number)

On some small cylinders manufactured at Luxfer's Aldridge plant, the above markings may not be present. In that case, the alloy can be determined from the three-digit type number stamped around the base. If the three-digit number is of the form 2**, 4** or 6**, then the alloy of manufacture is AA6061.

If there is any doubt, please contact Luxfer Gas Cylinders, Colwick, Nottingham, England NG4 2BH; telephone: (0)115 980 3800; fax: (0) 115 980 3899.

Section IV: Luxfer Scuba Cylinder Replacement Policy

This replacement policy applies only to the original owner of a Luxfer scuba cylinder. If a properly inspected Luxfer scuba cylinder is found to have either sustained-load cracking (in the case of 6351-alloy cylinders) or a manufacturing defect (i.e., any imperfection that fails to meet product specifications at the time of manufacture), Luxfer will honor the following replacement policy for cylinders manufactured in England:

• If the cylinder is 10 years old or less (based on the original hydro-test date), Luxfer will replace the cylinder at no charge with a new 6061-alloy cylinder. However, Luxfer will not replace cylinders that have been damaged, abused or mistreated.
• If the cylinder is more than 10 years old, the original owner may purchase an equivalent replacement cylinder from the current product range at the following prices: £42 for a 7-litre cylinder; £55 for a 10-litre or 12-litre cylinder; Prices for other sizes are available on request.

For cylinders manufactured elsewhere, the purchase price of the replacement cylinder will be determined in the country of origin based on local currency rates.

For more information about this policy, contact Luxfer Gas Cylinders, Colwick, Nottingham, England NG4 2BH; telephone: (0) 115 980 3800; fax: (0) 115 980

RIVERSIDE, Calif. - March 1, 2000 - Luxfer Gas Cylinders, the world's largest manufacturer of high-pressure aluminum and composite cylinders for most major gas markets, today announced that it would make downloadable versions of its Guide to SCBA Cylinder Inspection and Guide to SCUBA Cylinder Inspection available to its customers for free on its website at www.luxfercylinders.com.

Any customers wishing to download these free inspection guides may go to the "Product Information" section of the Luxfer site, where they will find links to the guides. Customers must first complete a short questionnaire before downloading the documents, which are available in .pdf format and can be viewed with Adobe's free Acrobat Reader.

Both cylinder inspection guides are part of Luxfer's "Safety First" initiative, which includes a variety of safety-related products for technicians, inspectors, and consumers. Bound, printed copies of the SCUBA and SCBA inspection guides may also be ordered on the Luxfer website for a small fee.

For more information about the "Safety First" program or Luxfer products, please contact Luxfer Gas Cylinders, 3016 Kansas Avenue, Riverside, Calif. 92507 USA; telephone 951-684-5110; fax 951-781-6598.

10 January 2000

Recently Luxfer Gas Cylinders announced a global policy on the care and maintenance of scuba cylinders and a new replacement program. Given that the inspection regime is different in Europe, we would like to clarify exactly what this means for our local markets.

For some time Luxfer has been concerned about the difficulty of finding sustained load cracks in the threaded area in aluminium scuba cylinders at the annual visual inspection (in accordance with BS5430, pt 3 or equivalent national regulations). After 5 years of evaluation, Luxfer USA has found a relatively inexpensive device which can help with the visual inspection of aluminium cylinders. The unit is an eddy current machine marketed by AIT in the USA under the brand name "Visual Plus".

Luxfer requires that all test stations use the Visual Plus unit (or alternative non-destructive testing equipment specifically designed for neck crack detection) as an additional safety precaution when annually inspecting Luxfer aluminium cylinders that are 15 years old or older.

During February of next year AIT will be touring the UK to explain to Test Stations how to use the unit. For further details please contact Chris Clarke at Luxfer, on (+44) 0115 9803842 or email chris.clarke@eu.luxfercylinders.com

Please note that Luxfer has no financial interest in Visual Plus. We are only concerned with improving safety standards for the Dive Industry.

Luxfer Europe offers the following program in support of the global initiative.

Luxfer Europe Aluminium Cylinders 10 years old or less:

Luxfer will replace at no charge any Luxfer aluminium scuba cylinder 10 years old or less that fails to pass the testing procedure detailed in BS5430, pt 3 [or equivalent national regulations] and is condemned because of a manufacturing defect or because of sustained load cracking. Please send the undamaged cylinder together with the test certificate to the above address, attention Mrs Chris Clarke. The owner is responsible for the cost of freight to Luxfer; Luxfer will pay the return freight. Any invalid claim will be to the owner's cost.

Luxfer Europe Aluminium Cylinders more than 10 years old:

For any aluminium scuba cylinder more than 10 years old that fails to pass the BS5430, pt 3 [ or equivalent national regulations] testing procedure and is condemned because of a manufacturing defect or sustained load cracking, Luxfer will offer the following trade-in deal:

• For 10 and 12 litre cylinders: forward a bank cheque for £50 made payable to Luxfer Gas Cylinders plus the condemned cylinder to Luxfer, and Luxfer Gas Cylinders will replace with a new cylinder of the same capacity.
• For 7 litre cylinders: forward a bank cheque for £38 made payable to Luxfer Gas Cylinders plus the condemned cylinder to Luxfer, and Luxfer will replace with a new cylinder of the same capacity.
• For 3 litre 'pony' cylinders: forward a bank cheque for £15 made to Luxfer Gas Cylinders plus the condemned cylinder to Luxfer Gas Cylinders, and Luxfer will replace with a new cylinder of the same capacity.
• Replacement prices for sizes other than those listed above will be handled on request.

With all the trade-in cylinders, the owner is responsible for paying the cost of freight to Luxfer. Luxfer will carry the cost of freighting the new cylinder to the owner. Please note that the undamaged cylinder (without a valve or any accessories) must be accompanied by the test certificate and preferably the Visual Plus printout from the Certificated Gas Cylinder Test Station. Luxfer Gas Cylinders will take no responsibility for any valves or accessories returned with the cylinder. The trade-in cylinders are to be forwarded to Customer Service, at the above address. Any invalid claim will be to the owner's cost.

An undamaged cylinder denotes a cylinder that has not been rendered unusable. In the event that there is mutual agreement that no sustained load crack or manufacturing defect exists, the cylinder will be returned to the owner.

Please note that as part of the inspection procedure Luxfer will use the Visual Plus unit in conjunction with the visual inspection to confirm that the cylinder should be condemned. So please ensure that the threads are undamaged.

If you require any further information or clarification on the Global Scuba Policy please contact Chris Clarke on (+44) 0115 9803842

John Mellors, Market Sector Manager Scuba

October 28, 1999

BH: I formed PSI, Inc. (initially called Professional Scuba Inspectors) in 1982, following three years of research. I had completed four years as NAUI's president and was looking for another way to serve the diving community. Our first seminar was conducted in January 1983. We have trained over 10,000 inspectors for military, government, hydrostatic retesting, dive and fire industries in North America, and at numerous international locations. We have 65 instructors in ten countries conducting nearly 200 seminars each year.

What are the main reasons for an aluminium cylinder being condemned and withdrawn from service?

Aluminium cylinders have received a great deal of attention in the USA since an explosion in Riviera Beach, Florida in February 1998. This was widely discussed on the Internet. Before that event, the occasional explosion of either steel or aluminium cylinders was largely ignored by the dive industry. Internal and external corrosion are the main causes of steel cylinders failing inspection or test. Aluminium cylinders fail less often, but when they do the cause is either excessive corrosion, often in the thread area or beneath the boot, or from a crack discovered during a visual inspection.

What does your organisation consider to be the main cause of these problems?

Corrosion damage is usually the fault of the cylinder owner or the fill station. Water, especially salt water, causes metal to corrode. Water lies in contact with the cylinder for days beneath a boot. If air fill stations have poorly maintained filters and water separators, water will be pumped into the cylinder during fills. Sustained load cracking is a defect that appears in some cylinders made from 6351 alloy. In the USA, this alloy was used by Luxfer Gas Cylinders from 1971 through to 1987. All Walter Kidde scuba cylinders were also made from 6351.

Is it hydro testing or visual testing that shows if there is a problem with a cylinder?

Hydro testing does not appear to be the best means to detect a sustained load crack in at-risk cylinders. Most cracks in cylinders are found by visual inspectors. Considering both steel and aluminium, over 90% of the cylinders failed by a hydro retester are failed by visual inspection prior to a pressure test.

Do you have an idea of the percentage of cylinders which fail out of those tested?

If you mean hydrostatic tested cylinders which failed that pressure test, then the number is very small, since most cylinders are failed based upon damage observed by visual inspection. The following example from one of our PSI affiliate instructors who is also a federally licensed hydrostatic retester may help. His retest business is primarily limited to scuba cylinders. He tests about 2000 scuba cylinders each year - these cylinders are visually inspected annually and hydro tested with visual inspection every five years. Of those 2000, he condemns nearly 12% prior to the actual pressure test, due to damage observed that exceeds the allowable limits. Of those that pass the pre-test visual examination and are then pressure tested, he condemns only one or two aluminium cylinders and about ten steel cylinders. This example is consistent with enquiries we have made of other hydrostatic retesters on other occasions.

What can divers do to ensure their aluminium cylinders are safe?

The final responsibility for cylinder safety lies with the cylinder owner. They must realise that an 80 cubic foot capacity cylinder contains more than one million foot/lbs of potential energy, very likely equal to a hand grenade. Divers should clean their cylinders, dry them and store them away from excessive heat, always with some internal pressure. They can demand that the fill station have properly functioning filter/separator systems, fill the cylinder slowly, and not overfill it. Cylinders should be inspected frequently, both internally and externally, by a technician who actually knows what to look for in the way of damage. In North America we found that, regardless of how many years of experience an inspector may have handling cylinders, without formal training they cannot properly assess damage.

Do you have any recommendations for filling/test stations to ensure the safety of their staff and customers ?

I have written several articles and produced a booklet that details safe practices for fill station operations. There are many things fill stations can do. Unfortunately, many dive stores in North America fail to appreciate the power of compressed air. Since most cylinder explosions occur during the filling process, there needs to be a separation of the operator and the cylinder. Separation can be accomplished by either distance or a barrier. Only cylinders that have been inspected by a trained visual inspector and are within the retest period should be accepted for filling.

What staff training procedures are recommended in the USA to ensure that people testing and filling cylinders are competent?

In Canada and the USA there are federal requirements and licensing for hydrostatic retesters. The test procedures are established by law, and enforcement is administered by the Department of Transportation (DOT) or Transport Canada (TC). By law, the retester must take training every three years and be examined by federal enforcement personnel every five years to retain their license. Unfortunately, enforcement is incomplete and there are many hydro retesters who are inadequately trained and certify improperly evaluated cylinders. The retester must conduct a visual inspection as part of the hydro retest, but many don't know what that entails. The North American dive industry has established its own standard of an annual or more frequent visual inspection. This standard is rather well enforced by dive stores and other air fill stations. There is no legal mandate that the inspectors be trained. However, untrained inspectors have no legal defence if a cylinder they inspected fails explosively. Most dive industry entities - including PADI, NAUI, Luxfer, Catalina, Compair/Mako, most dive stores and several court jurisdictions - accept the PSI training protocol as the industry standard.

What is the number one thing that divers do to affect the structural strength of their steel or aluminium cylinders?

Cylinder owners are probably most guilty of not regularly removing and cleaning the cylinder beneath the boot; and, for salt water divers, not washing and drying the valve/cylinder interface.

What are your recommendations to divers for maintaining their cylinders?

Cylinder owners should insist that a trained visual inspector inspect both the interior and exterior of the cylinder at least annually. In North America we have to recommend that a visual inspector look into the cylinder after the hydro retest to ensure no water or other foreign material has been left inside. Store the cylinder in a dry, cool location with some pressure. Secure the cylinder during transport. Don't drop the cylinder or allow it to bang against hard objects. If corrosion is noted, clean it away, assess the damage against allowable limits and protect the area from future deterioration.

Does storing a full cylinder for long periods - several weeks or months - have a detrimental effect on its structural strength?

There are several considerations when making this decision. In a clean dry cylinder, clean dry air will store quite nicely for long periods, certainly a year or more. Poorly filtered air containing various hydrocarbons or other contaminants could deteriorate in quality over weeks or months. The cylinder itself is designed for a sustained pressure load during its entire life. If moisture is left in the cylinder, then the increased oxygen in a full cylinder will contribute to more rapid corrosion that in turn could weaken the cylinder dramatically over a matter of months.

More importantly, internal corrosion activity will reduce the oxygen content of the air. In the USA we have two examples of oxygen depletion in steel cylinders (corrosion is more rapid in steel). Following three months of storage, a corroded cylinder contained only 15% oxygen, a near-deadly deficiency. Analysis of a dead diver's air supply in a heavily corroded steel cylinder revealed a deadly 6% oxygen content. The University of Rhode Island's study of cylinder internal corrosion reveals that under equal conditions of moisture in cylinders, aluminium cylinders fare much better, so air stored in aluminium cylinders may retain its quality longer.

There is one additional consideration for aluminium cylinders. Because of its low tolerance for heat, and where there is potential for the aluminium cylinder to be involved in a fire, there is merit in storing the cylinder either full or nearly empty (about 20 psig). A 3000 psig aluminium cylinder containing less than about 1500 psig is at risk of exploding in a fire. The metal will lose its strength before the heat causes a rise in internal pressure sufficient to activate the pressure relief device (burst disc).

Do you have any comment on the effect of hydrotesting on the material of aluminium cylinders?

I am not an expert in metallurgy, so can say very little about material integrity. However, there are specialists who believe that the hydro test procedure may not adequately test aluminium cylinders. The manufacturers cycle many test cylinders to hydro test pressure thousands of times with no apparent damage. I have not heard any expert suggest that the hydro test causes damage to the cylinder.

In New Zealand and Australia, cylinders are currently tested every two years, and this may change to every year. In the USA, it is currently every five years and may change to every ten years! What are your thoughts on the wide difference in the period over which cylinders must be hydro-tested?

The hydro test alone is not a very good assessment of a cylinder's condition. Cylinders with obvious cracks and pinholes have passed hydro retest. US rules for retest were written more than 50 years ago, when cylinders were used very differently to how they are used by divers today. Experience in the USA shows that a five year interval seems to work for most gas industry cylinders. I can't speak about the logic used by the rulemakers in New Zealand and Australia. Whether the retest is one year, two years, or five years is irrelevant for scuba cylinders unless a technical visual inspection is part of the test. Remember, 90% of the cylinders failed by a retester fail the visual inspection, not the pressure test.

In a test conducted by the University of Rhode Island in 1971, a steel cylinder with a small amount of salt water inside was damaged in 100 days to a point of imminent explosion. If I were only given a choice of my cylinder being either hydro retested by one of our less diligent retesters or by a PSI trained visual inspector, I would take a frequent visual inspection and skip the hydro test. There is a proposal before DOT to eliminate hydro retest and replace it with an ultrasound examination at ten year intervals. The vast majority of gas industry users oppose this dramatic change. Ultrasound cannot test for heat damage, the impact of continual overpressurisation, or a number of other forms of damage. Because of the outcry from the dive industry and others, DOT has delayed its decision on this matter. Scuba cylinders cannot possibly remain in service for ten years without a formal examination. Should this rule pass, the frequency of cylinder explosions will increase rapidly.

Do you think aluminium cylinders should have a finite life, then be removed from service?

I have followed closely the issue of sustained load cracking of aluminium cylinders since 1985. As yet, I have not found a correlation between age and the formation of a crack. We do see more cracked cylinders now than we saw ten years ago. That probably means that we now have more people looking, and we have better tools such as the Visual Plus apparatus to conduct the assessment. Some of the cracked cylinders were made in the 1980s, while many thousands from the 1970s remain in service.

Since the cracks propagate slowly over several years, technical visual inspection of the suspect area at least annually should identify defective cylinders. Our records show less than ten aluminium scuba cylinders exploded in North America and several international locations, including Australia, that were most likely caused by sustained load cracking. Statistically, that is a very small number (several million were made), although tragic for those persons injured.

We know some of those cracks should have been found by the visual inspectors who last looked at the cylinder. Unfortunately they were not properly trained. PSI does not have information that would cause us to urge a condemnation of scuba cylinders over a certain age. We believe that no cylinder owner should imagine that his cylinder must last forever. It could last a lifetime, or as little as a few months. It all depends on its treatment while in service. Scuba cylinders are very well made and pass through a variety of rigorous tests both by the manufacturer and by third party examiners. Almost without exception, those that have exploded would have been removed from service by trained inspectors well before the failure, if the opportunity to inspect them had been there. This suggests that the opportunity for technical visual inspections should exist and be available to all cylinder owners. The cylinder owners then must be willing to have their cylinders condemned when damage beyond allowable limits is found.

Thanks, Bill, for your time in providing our readers with this invaluable information. You have brough up some important points that all divers and cylinder owners should be aware of.