US +1800 764 0366 | Europe & Middle East +44 (0)115 980 3800 | Asia-Pacific: +61 2 7227 5369

Home / FAQs




Aluminum scuba cylinders in oxygen-enriched and oxygen service – are Luxfer scuba cylinders ready for oxygen service when they leave the Luxfer factory?

New Luxfer scuba cylinders manufactured from January 1, 2000, until December 31, 2004, were cleaned for oxygen service at the factory and sealed with an oxygen-compatible cap before being shipped. However, starting on January 1, 2005, Luxfer began providing oxygen-clean scuba cylinders only by special order. Unless specifically ordered “oxygen clean,” new Luxfer scuba cylinders will be cleaned for gas mixtures containing only up to 23.5% oxygen. (Of course, it will still be possible to have these cylinders cleaned for use with higher concentrations of oxygen by following the DOT-specified procedures cited above.)


Aluminum scuba cylinders in oxygen-enriched and oxygen service – how do I keep my cylinder clean for use with oxygen or oxygen-enriched gas mixtures?

Here are some basic guidelines for keeping your cylinder clean and for using it with oxygen and oxygen-enriched gas mixtures (more detailed guidelines are available from CGA):

  • Only use an oxygen-clean, oxygen-compatible valve installed by a properly trained, competent technician familiar with the procedures described in current CGA guidelines.
  • Either use no lubricants at all—or use only lubricants that the lubricant manufacturer explicitly recommends for use with oxygen systems and cylinders containing oxygen under pressure. Once you have found an oxygen-safe lubricant, always strictly follow the application and use instructions of the lubricant manufacturer. If a lubricant manufacturer does not specifically state that a lubricant is suitable for compressed oxygen service, don’t use it.
  • Have your cylinder filled only with contaminant-free gas pumped by oxygen-clean systems, including fill lines that are clean and dedicated only to oxygen service and compressors that will not release oils or other contaminants into the gas.
  • Make sure that the inside of your cylinder does not become contaminated by water, dirt, oil residues, body fluids or other contaminants during use and storage. If the cylinder does become contaminated, it must be re-cleaned and tested before being used with oxygen again.
  • If a hydrocarbon or other contaminant is discovered on the outside of the valve-to-cylinder connection, the cylinder must be depressurized and tested to make sure that it is still oxygen-clean. If the cylinder is not clean, then it must be re-cleaned for oxygen and tested again before being filled with oxygen or an oxygen-enriched gas mixture.
  • Ensure that your cylinder is inspected and requalified only by properly trained, competent technicians who are familiar with government requirements regarding oxygen cleanliness and use. If you suspect that your cylinder has been handled by someone who lacks this requisite knowledge, do not use the cylinder for oxygen or oxygen-enriched service until the cylinder has been tested by competent people.
  • A valve should only be removed and reinstalled by a properly trained, competent technician who is familiar with procedures described in current CGA guidelines (see CGA P-38). Attempting to remove a valve without following the proper safety procedures can cause death or serious injury.
  • If a cylinder owner, user, inspector, requalifier, distributor or filler has any doubts concerning the proper cleanliness of a cylinder intended for oxygen or oxygen-enriched service, the cylinder must be tested for oxygen cleanliness before being filled or used.
  • When your cylinder has been exposed to possible contaminants, have it cleaned and tested for oxygen-cleanliness before filling or using it.


Aluminum scuba cylinders in oxygen-enriched and oxygen service – what is the difference between “formal” and “informal” oxygen cleaning?

The terms “formal oxygen cleaning” and “informal oxygen cleaning,” which appear in some non-Luxfer scuba manuals, are intended to differentiate between formal, government-mandated oxygen-cleanliness documentation required in the gas and medical industries, as opposed to less-formal documentation used in the recreational diving industry.

Unfortunately, some scuba technicians and divers have erroneously interpreted “informal cleaning” to mean that a less-rigorous, less-thorough level of oxygen cleaning is required for scuba equipment—even though the scuba manuals that use these terms make it quite clear that the same careful cleaning procedures and acceptable cleanliness levels should be used with all equipment in oxygen service. Moreover, the term “informal” is often associated with the so-called “40% rule,” from which some divers and technicians have wrongly inferred that the recreational diving industry somehow has special dispensation to clean cylinders to a less-stringent standard and at a higher oxygen-content threshold than other industries (see Question 4, above).

Because of these erroneous and potentially dangerous misinterpretations, Luxfer chooses not to use the terms “formal” and “informal” when referring to oxygen cleanliness. Oxygen clean is oxygen clean—there are not different levels of cleanliness.

As for documentation, it is always a good idea to thoroughly document all aspects of your oxygen-cleaning procedures and maintenance. Such careful record-keeping can be very valuable if an oxygen-related incident occurs.


Aluminum scuba cylinders in oxygen-enriched and oxygen service – how clean does my cylinder actually need to be for oxygen service?

It needs to be “oxygen clean”—which means free from contaminants that can be the fuel for an oxygen-fed fire. Cleanliness on surfaces is measured by milligrams (mg) of hydrocarbon per square foot of surface area (mg/ft2). In the U.S., DOT (in RRC 901c) requires that the cleanliness of cylinders used in oxygen service be proven to be less than 2.5 mg/ft2, which is a level considerably below what can be seen by the naked eye. For this reason, a visual inspection after cleaning is not enough. A test must be performed to verify that the required cleanliness level has been achieved. In CFR49 173.302(b), DOT specifies an approved cleaning method and a standard test to determine the cleanliness of cylinders.


Aluminum scuba cylinders in oxygen-enriched and oxygen service – why does Luxfer require cleaning for oxygen concentrations above 23.5%?

Few concepts have caused more confusion and controversy in the recreational diving industry than the so-called “40% rule.” While there seems to be general agreement that special cleaning is required when a pressurized oxygen concentration reaches a particular “threshold” percentage, there is disagreement about exactly what that threshold should be and at what pressure it becomes important. Some say 40%; others say 23.5%; still others say anything more than 21% when a gas mixture is pressurized more than 100 psig. It would be helpful to explore the background of this confusion briefly before discussing Luxfer’s position on this vital subject.

The 40% threshold is cited in a single Federal CFR published by the Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labor: 29CFR910.430, which applies to “Commercial Diving Operations” and states in the section titled “Oxygen safety” on page 854: “(1) Equipment used with oxygen or mixtures containing over forty percent (40%) by volume oxygen shall be designed for oxygen service. (2) Components (except umbilicals) exposed to oxygen or mixtures containing over forty percent (40%) by volume oxygen shall be cleaned of flammable materials before use.”

Please note that OSHA also provides a very specific definition about who should—and should not—be considered a “commercial diver” to whom the 40% threshold applies: “Commercial diver means a diver engaged in underwater work for hire excluding sport and recreational diving and the instruction thereof” (46CFR197, page 409; italics added for emphasis).

Even though OSHA clearly excludes sport and recreational divers from the CFR that specifies a 40% threshold, some professionals in the recreational diving industry have nonetheless been citing the OSHA “rule” for many years and maintaining that special cleaning of recreational diving equipment is not necessary with oxygen concentrations of 40% or less. These advocates of the “40% rule” have often stated that the U.S. Navy supports their position, which at one time was true—but no more. In the current applicable military specification (Mil-Std-1330D), the Navy specifies a 25% threshold for oxygen cleaning. Compounding the confusion is the fact that two other OSHA documents, 29CFR1910.146 and 29CFR1910.134, specify an oxygen threshold of 23.5%.

For the sake of clarity, here’s a summary of the oxygen threshold percentages at which various key U.S. agencies and organizations require special cleaning of oxygen-handling equipment and systems:

Organization Oxygen threshold Reference

U.S. Navy



U.S. Compressed Gas Association (CGA)


CGA Pamphlet 4.4

National Fire Prevention Association (NFPA)

>21 – 25%

NFPA standards

American Society for Testing & Materials (ASTM)


G126, G128, G63, G94

National Aeronautical & Space Administration (NASA)

>21%/>100 psig

Various KSC & JSC

Occupational Safety & Health Administration (OSHA)









The reasons for Luxfer’s position: Luxfer supports an oxygen-cleaning threshold of 23.5% and does not support the alleged “40% rule.” This means that when a pressurized oxygen concentration used in a Luxfer cylinder exceeds 23.5%, the cylinder must have been cleaned to the same cleanliness standard mandated for a cylinder containing 100% oxygen. Luxfer’s reasons for this position are:

  • All key U.S. regulatory and gas industry references except one advocate an oxygen threshold of 21% to 25%.
  • Luxfer is a member of the Compressed Gas Association and therefore supports the CGA-specified threshold of 23.5%. Furthermore, Luxfer defers to CGA on all safety matters related to oxygen handling and containment, as do OSHA and DOT.
  • As an international manufacturer, Luxfer works with regulatory authorities and industry associations around the world—the overwhelming majority of which support a threshold value from 21% to 25% (for example, this is true in the United Kingdom, Australia, France, Germany and Japan).
  • United Nations compressed air packaging guidelines (see UN 1002) indicate that when compressed air contains oxygen as the only oxidizing gas and the oxygen concentration exceeds 23.5%, then the entire gas mixture must be listed as an oxidizing gas.

Some within the recreational diving community contend that the supposed “40% rule” is justified by an excellent scuba safety record and should therefore be maintained—despite the fact that so many agencies and organizations have specified much lower threshold values for oxygen cleaning. Luxfer finds this “history-of-use” argument unconvincing for the following reasons:

  • Compared to other industries and organizations that use pressurized oxygen, oxygen usage in the recreational diving industry has not been sufficiently widespread, nor are available oxygen-use statistics sufficiently comprehensive, to declare a successful history of use for the 40% threshold.
  • Oxygen-related fires and explosions are inherently low-probability, high-consequence events—which means that they occur very infrequently, but are usually catastrophic when they do. Forensic evidence has shown that undetected, non-propagating fires happen within scuba oxygen systems more frequently than is generally known. It is possible to operate “on the edge” of a fire for years without knowing it—and to be lulled into complacency by seemingly “safe” performance.
  • As use of higher oxygen concentrations at higher pressures increases in the recreational diving industry, the risk of serious accidents will also increase.

Under these circumstances, Luxfer believes that requiring thorough oxygen cleanliness at a threshold of 23.5% makes very good sense not only for the sake of individual safety, but also from the business standpoint of prudent risk management.


Aluminum scuba cylinders in oxygen-enriched and oxygen service – why is it necessary to clean scuba tanks for oxygen service?

To remove contaminants that can become the fuel for an oxygen-fed fire.

Oxygen, an oxidizing gas, does not burn, but it supports combustion and causes other materials to burn. In the presence of pressurized oxygen concentrations exceeding that in standard air, most materials become progressively more flammable and ignitable as the oxygen concentration and pressure increase. Even materials that would not easily catch fire in standard air under normal atmospheric pressure will ignite and burn furiously in a pressurized oxygen-enriched environment. It cannot be overemphasized that rising pressure increases the risk of ignition.

For an oxygen-fed fire to occur, three things must be present: oxygen, fuel (something to burn), and heat (an ignition source)—this is the classic “fire triangle.” When dealing with pressurized oxygen or EAN in a scuba cylinder, remember this important variation on the classic three factors needed for a fire:

  1. Oxygen or gas containing oxygen, under pressure (higher concentrations of oxygen and significant pressure greatly increase the need for oxygen cleanliness and diligent safety practices).
  2. An ignition (flame, spark, heat source, etc., including impact from dropping or striking a pressurized cylinder).
  3. A contaminant (i.e., fuel—but the reason the term “contaminant” is preferred in this case is that in an properly cleaned oxygen system, no fuel is present. If fuel is present, it is contaminating the system and making it no longer safe for use with oxygen). Common contaminants include:
    • Machining oils (including residual oil film)
    • Hydrocarbon-based grease and lubricants (including compressor oil)
    • Some soaps, detergents, solvents and cleaning solutions, especially those that contain organic compounds
    • Skin lotions and emollients and cosmetics
    • Sun-tanning oils and lotions
    • Human skin oil and bodily fluids
    • Insects and insect body parts
    • Paint, wax, and marking crayons
    • Carbon dust from filtration systems
    • Metal fines, filings, scale and burrs
    • Chrome chips (usually from valves and other chrome-plated parts)
    • Rust particles and dust
    • Metallic oxides in general
    • Airborne soot and dust
    • Pipe thread sealants
    • Residue from soapy water and leak-detection fluids used to check for leaks
    • Lint from cloths used in cleaning
    • Any other material containing organic compounds and hydrocarbons

Any of these contaminants—many of which are very difficult to detect—can be the initial fuel for an ignition event, the technical term for starting a fire. Once an oxygen-fed fire gets going, even metal components—including a scuba cylinder itself—can burn vigorously. Aluminum melts at 1,220 degrees F (660 degrees C); after an oxygen-related cylinder fire, it is not unusual to find large areas of melted aluminum—which shows just how hot and energetic such a fire can be.

That’s why it’s so essential to remove contaminants and to keep the oxygen system clean. Proper oxygen cleaning need not be excessively costly or time-consuming, but it does need to be effective. Removing contaminants and keeping equipment oxygen-clean is the best way to make sure that an oxygen-fed fire never starts.

A number of agencies and organizations in the United States provide certification courses in oxygen cleaning. For example, American Nitrox Divers International (ANDI) offers a particularly comprehensive training course that defines “oxygen cleaning” as “the process of contaminant removal from component parts or assemblies intended for contact with gases containing Oxygen concentrations of 23.5% or more by volume.”1

1EAN and Oxygen Equipment Servicing Procedures, ANDI International: 1999, p. 19.


Aluminum scuba cylinders in oxygen-enriched and oxygen service – can I fill my Luxfer aluminum scuba cylinder with pure oxygen so that I can use it for decompression?

Yes, if you follow the Luxfer requirements listed below, which must be met both for pure oxygen and gas mixtures containing more than 23.5% oxygen:

  • The cylinder must have been properly cleaned, tested for cleanliness and maintained in a proper state of cleanliness for oxygen service in strict accordance with the Code of Federal Regulations (CFR), specifically U.S. Department of Transportation (DOT) CFR49 173.302(b).
  • The cylinder must be equipped with an oxygen-compatible valve and be filled only by oxygen-clean, properly maintained filling equipment dedicated to oxygen service.
  • The cylinder must never be fast-filled or over-pressurized.
  • Proper safety procedures for handling and dispensing oxygen prescribed by the DOT and U.S. Compressed Gas Association (CGA) must be followed at all times. In fact, Luxfer further recommends that anyone in the scuba industry who handles pure oxygen in a Luxfer cylinder become familiar with and follow current guidelines concerning cleanliness, filling, storage, usage and maintenance of oxygen cylinders provided by the U.S. Food and Drug Administration (FDA). As the world’s largest manufacturer of aluminum and composite medical oxygen cylinders, Luxfer has a great deal of experience with cylinders in pure oxygen service and with the FDA guidelines that promote safe oxygen usage. Luxfer’s experience has shown that following FDA guidelines is a practical and effective way of preventing oxygen-related accidents.


Sustained-load cracking – if Luxfer 6061-alloy cylinders are not susceptible to SLC, why has Luxfer exchanged 6061 cylinders that have been reported to have cracks?

  • After the introduction of eddy-current technology, Luxfer received reports of cracking in 6061-alloy cylinders. We accepted returns on about 1,200 of these cylinders to conduct extensive tests. Not a single cylinder was found to be cracked.
  • On Luxfer 6061-alloy cylinders, eddy-current devices sometimes show harmless “indications” that lead to “false-positive” readings for SLC.


Should I be doing anything different for my aluminum alloy 6061 composite cylinders than I have done in the past?

If you have properly maintained, used, tested and stored your cylinders in accordance with applicable regulations and manufacturer recommendations, the answer is no. If you continue following these proper procedures, your cylinders should provide many years of dependable service.

For more information about proper care and maintenance for your aluminum and aluminum-lined composite cylinders, please see the “Support” section of the Luxfer website at


Will my aluminum-lined composite cylinder have a shortened life from being hydrostatically tested with tap water?

No. The field record of cylinders in use for many years shows no evidence of reduced service life from periodic hydrostatic testing with tap water. This test is normally conducted quickly, and the cylinder only holds tap water for a few minutes. After the test, the cylinder must be dried. As long as this procedure is properly followed, there is no cause for concern.