Since there has been a reference to the Luxfer position as a CYA, I thought I would pull it up and post it below. From my reading of it, Luxfer's, and now apparently PSI's, position is not that unreasonable. Some people on this board may claim it is too conservative and that the uneducated are too willing to accept these standards, but that is just their opinion. I am not aware that any of the participants in this thread are actual experts in the field. Do any of you serve on any of the agencies or trade associations that set the standards? Are your opinions sought out by anyone in the compressed gas industry?
MHK has made the comment that the percentages chosen are arbitrary and that 23.6%could not possibly be put you in danger. Maybe, maybe not, but why the need to push the limits? The leap in logic that since the standards are arbitrary they should in effect be ignored is amazing. Most standards outside of certain scientific laws are to some degree arbitrary. You have to pick some number or you have no standard. If everyone is then free to interpret the standard as they see fit, you no longer have a standard. If you don't like 23.5%, why settle on 40%? How could 41% be a problem? If 66 MPH is okay, why not 76?
To the extent that a dive shop has chosen a standard 23.5% or 40%, or refuses to put air in a tank with a Nitrox sticker their customers ought to abide by the rules or go elsewhere. Deceiving a shop because you think they are too conservative, or everyone else is doing it, or whatever justification you want to attach to it is just plain wrong. Yes there are better, more expensive, more time consuming and intrusive ways of dealing with the issue and that is generally what you get when people flaunt a voluntary system. No more fills without a tank analysis. No nitrox, trimix, etc. pumped into anything but (you take your pick) shop tanks or commercial/military tanks. Play games with the shops and (again take your pick) get banned, have your tank confiscated, have your agency pull your C card or all of the above. Yep, following those simple rules about the stickers and respecting the rules of the individual dive shops was such a joke.
Excerpt from Luxfer position:
"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 >25% Mil-Std-1330D
U.S. Compressed Gas Association (CGA) >23.5% CGA Pamphlet 4.4
National Fire Prevention Association (NFPA) >21 – 25% NFPA standards
American Society for Testing & Materials (ASTM) >25% G126, G128, G63, G94
National Aeronautical & Space Administration (NASA) >21%/>100 psig Various KSC & JSC
Occupational Safety & Health Administration (OSHA) >23.5% 29CFR1910.146
OSHA >23.5% 29CFR1910.134
OSHA >40% 29CFR1910.430
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"
