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Luxfer clarifies difference between bowed and bulged aluminum cylinders

Luxfer Gas Cylinders has received an increasing number of inquiries about the difference between “bowed” and “bulged” aluminum cylinders. The pictures and information below are intended to clarify this important difference.

Bowed Cylinder

A bow is a slight curve in the sidewall of an aluminum cylinder (see image above). A fairly common cosmetic feature, a bow is not dangerous and does not affect cylinder performance. A bow is an occasional by-product of the manufacturing process, not a manufacturing defect. Bows occur most often in taller cylinders, including scuba cylinders with a capacity of 80 cubic feet or more. A typical bowed cylinder has one convex side curving slightly outward and an opposite concave side (180° degrees away) curving slightly inward. The curves are long and gradual, covering much of the length of the cylinder sidewall. Most bows are barely discernible with the naked eye, but they sometimes become noticeable when you hold a straight edge against the cylinder wall and rotate the cylinder to reveal both the convex and concave sides. More severely bowed cylinders are sometimes called “banana shaped,” and even these cylinders are safe to use. Infrequently a cylinder will have one straight side and one slightly convex (outward curving) side. Such a condition, called an unparallel sidewall or a plano-convexity, is also a type of bow. It does not affect cylinder performance. Inspectors should be careful not to misidentify the harmless, slightly convex side of a bowed cylinder as a bulge, which is completely different and a very rare condition.

A bow is often so subtle that the naked eye has difficulty detecting it. (In the picture above, the bow has been exaggerated somewhat to make it clearly visible.) Using a straight edge will usually reveal convexity and concavity. Bear in mind that the convex (outward curving) side is sometimes more pronounced than the concave side. Do not mistake the convexity of a bow for a bulge! (For more information about bulges, see the following section.)

Bulged Cylinder

A bulge (pictured above) is an extremely rare, dangerous condition. Bulged cylinders must be immediately condemned and removed from service. Unlike a bow, which is usually slight and sometimes difficult to see, a bulge is generally very pronounced and obvious, even to the naked eye. Bulges occur in cylinders that have been overheated or in cylinders with sidewalls thinned by severe corrosion. There are two basic types of bulges. A long, convex bulge protrudes outward noticeably on one side or around the entire circumference of the cylinder (as in the yellow cylinder shown above on the left); such a bulge occurs when an entire cylinder has been exposed to high heat. A smaller, “goose-egg-shaped” bulge (cylinder at right, above) usually indicates localized overheating, which is the result of “spot annealing.”

If you are uncertain whether a cylinder is bulged, remove it from service and contact Luxfer Customer Service before condemning the cylinder.

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Update to Luraville, Florida incident

Investigators continue to believe that the July 27, 2004 incident in Luraville, Florida was caused when an operator was about to fill oxygen into a scuba cylinder that was not designed for oxygen use, and most probably the valve and/or cylinder had not been purged of all organic matter. Ignition from the fall caused the organic matter in the cylinder to burn, which caused the resulting fire and explosion.

Investigators have determined that the cylinder was made of aluminum alloy 6061. Investigators have ruled out the cylinder as a cause of the explosion.

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Cylinder incident in Luraville, Florida

Regulatory authorities are investigating the death of a woman who was injured while attempting to fill a scuba cylinder with pure oxygen. The cylinder fell over, burned and exploded at Cave Excursions dive shop in Luraville, Florida, on July 27, 2004.

Sara Frances Slaughter, 50, a dive shop employee, was attempting to add 98 percent oxygen to the Luxfer 30-cubic-foot scuba cylinder—which was not prepared by Luxfer for such pure oxygen service—when the accident occurred. Witnesses said that the cylinder fell and immediately exploded in a fiery flash on impact. Three bystanders suffered injuries, including burns. The dive shop was also damaged, but was subsequently repaired.

Investigators attributed the fire and explosion to the presence of an organic contaminant, noting that any organic material can ignite in the presence of pure oxygen and an ignition source. Federal law and industry standards require that any high-pressure cylinder intended for oxygen use must be scientifically cleaned of organic material before being filled with oxygen. Such cylinders must remain in this “oxygen clean” condition while being used with oxygen. Investigators said that the cylinder or valve—or both—involved in the accident either had not been properly cleaned or had become contaminated. Impact from the fall may also have contributed to the explosion, investigators said. They also noted that labeling on the cylinder did not indicate whether the cylinder had been properly visually inspected for damage, thread conditions or imperfections other than corrosion.

As the investigation continues, authorities will determine whether federal or state laws were violated and announce their complete findings at a later date. Participating in the investigation are the U.S. Department of Transportation, OSHA and the Suwanee County Sheriff’s Department.

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Dates when Luxfer changed its aluminum alloy from 6351 to 6061

Between 1987 and 1988, Luxfer Gas Cylinders discontinued use of 6351 aluminum alloy and began using a proprietary version of 6061 aluminum alloy for all its aluminum cylinder models manufactured in the United States. Listed below are the dates by model number when the transitions to the new alloy occurred. Any current Luxfer models that do not appear on this list were never made from 6351 alloy in the first place and have always been made from Luxfer's proprietary 6061 alloy.


S30, S63 -May 1988

S40 - June 1988

S50, S92 - April 1988

S72, S100 - August 1987

S80 - January 1988

S808 - May1987


L7, L8, L13 - September 1987

L13 - May 1988

L15 - January 1989

L26 - February 1988

L45 - November 1987


C1.2, C1.5 - January 1989

C2 - November 1988

C10 - August 1988

C5 - June 1988

C15 - November 1987

C20, C35 - April 1988

C50 - February 1988


M9 - January 1988

MD15, ME24 - December 1987

Industrial Gas

N22, N150 - May 1988

N33 - November 1988

N60, N122 - December 1987

N88 - December 1988

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Dates of SCUBA cylinder aluminum alloy changes

Dates by models when Luxfer changed the aluminum alloy in its scuba tanks from 6351-T6 to Luxfer’s proprietary 6061-T6 alloy.

S808 - May 1987

S72 - August 1987

S100 - August 1987

S80 - January 1988

S50 - April 1988

S92 - April 1988

S30 - May 1988

S63 - May 1988

S40 - June 1988

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Product safety notice: potential scuba valve oxygen incompatibility

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.


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.


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.


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.


Any questions can be directed to Abysmal Diving Inc.

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Unauthorized metal-removing modifications to Luxfer aluminum gas cylinders used in North America

Certain unauthorized modifications to Luxfer aluminum cylinders could remove metal or alter the cylinder design to such an extent that the cylinder no longer meets 3AL cylinder design specifications defined by the U.S. Department of Transportation (DOT), Transport Canada (TC) and the Compressed Gas Association (CGA).1 2

Unauthorized modifications and activities include grinding, cutting, sand-blasting, shot-blasting, media-blasting, sanding, brushing, polishing, engraving, scraping3 and any other activity that removes metal and thins cylinder walls. Additional unauthorized activities include subjecting Luxfer cylinders to various harsh chemicals (e.g., certain cleaners, caustics, acids and other corrosive substances); exposing cylinders to heat processes that could anneal or otherwise adversely affect the aluminum; recutting or resurfacing O-ring glands; and rethreading cylinders.

Luxfer warranty provisions forbid unauthorized modifications to Luxfer cylinders, including any metal-removing modification performed by unauthorized persons or companies. Such modifications will immediately void the warranties on Luxfer cylinders. In addition, such modified cylinders may be unsafe to fill and use.

Luxfer accepts no responsibility or liability for the condition or performance of any cylinder modified by unauthorized persons or companies. Moreover, in accordance with DOT and TC specifications and CGA guidelines, Luxfer requires that the wall thickness of any Luxfer cylinder modified by unauthorized means be checked to ensure that the cylinder still meets the minimum DOT and TC wall-thickness requirements.

Luxfer offers authorized cylinder refurbishing and polishing services through its factories and service centers. Such authorized Luxfer services will not adversely affect Luxfer cylinder warranties.

1 This Luxfer Gas Cylinders Technical Bulletin supersedes all other Luxfer technical bulletins and publications related to this subject and to the cylinder-modifying activities described herein.

2 Refer to U.S. Department of Transportation (DOT) specifications in Section 178.46-7 of Title 49, Code of Federal Regulations (CFR); to Canadian specifications CTC 3AL and Transport Canada (TC) 3ALM; and to Compressed Gas Association (CGA) publication C-6.1–2002.

3 Scraping to remove labels is allowed as long as the activity does not remove metal.