Why almost nothing in the dive industry is labeled "Suitable for 100% Oxygen Service"
Thermo is a brand name of SCUBA valves currently manufactured by XS Scuba, a US based corporation. A disclaimer label appeared on Thermo brand SCUBA valves following a specific accident involving 100% oxygen. One of the components involved was a Thermo valve that was delivered to the victim still sealed in the bag with a product information card making it clear the valve was not intended for use with 100% oxygen. Thermo brand Nitrox SCUBA valves have ALWAYS been documented by Thermo as "for use with enriched air having maximum oxygen content of 40%", it just was not labeled on the valve. As a result of this accident, now "40% MAX OXYGEN PREMIXED" is clearly labeled on the valve itself. The statement does not mean the valve is unclean as supplied by Thermo. In fact, Thermo brand Nitrox SCUBA valves have always been the finest quality available: the design uses oxygen compatible materials and when sealed in the original factory packaging is also free of organic and particle contamination. More recently, Thermo brand PRO DIN/K 200-bar Nitrox SCUBA valves have been tested by an independent laboratory as meeting the CGA V9-2009 Compressed Gas Association Standard for Compressed Gas Cylinder Valves.
The reason for such labels is rooted in the fact that there is a small but consistent incidence of compressed oxygen gas handling related injuries and fatalities in SCUBA. While the equipment often takes the blame, like "pilot error", in most cases the cause of the accident can be traced to gross violations of best practices for the handling of oxygen. Not surprising, given the recreational diving industry has virtually no safety mechanism in place to educate dive shop fill station operators and technical divers in the proper handling of oxygen.
While the use of oxygen rich gas mixtures and pure oxygen is widespread in technical diving, there is no diver C-card for "Oxygen Handling Safety Procedures" and technical diver training rarely includes even a cursory review of best practices of compressed oxygen gas handling. Most technical divers know their equipment must be specially qualified for use with oxygen rich decompression gases, but they usually don't precisely understand the meaning of oxygen clean, oxygen compatible, oxygen service, or how to establish and maintain such conditions.
"Oxygen compatible" is described as: gas handling equipment whose high pressure gas flow path design and contact surface materials meet standards for use with oxygen. "Oxygen clean" is described as: the flow path and material surfaces which meet standards for absence of contaminates that can become a source for ignition. Equipment which simultaneously meet standards for both "oxygen compatible" and "oxygen clean" is said to be "oxygen service".
One of the problems the recreational diving industry faces is, other than Nitrox labeling, there are no diving-related industry-wide consensus or peer reviewed standards for the handling of the specialty compressed gases used in diving. So the dive industry has to fall back on the standards and guidelines of other industries. In the US, they are established and maintained primarily by the Compressed Gas Association (most often referenced by industry) and ASTM International (most often referenced by aerospace). This means there is no strong voice for the diving industry in establishing standards that are entirely compatible with diving industry practices.
Outside of diving, the use of oxygen enriched air Nitrox is virtually unknown, and the CGA has been vague as to whether Nitrox should be handled as air or oxygen. The CGA has recently clarified that equipment and systems handling any gas in excess of 23.5% oxygen by volume shall be designed, cleaned, and prepared as if the gas was PURE oxygen. The regulations of the US DOT - Hazardous Materials Administration, a US government agency, incorporate many of the CGA standards and guidelines by reference, meaning the CGA statement that anything greater than 23.5% oxygen is handled as 100% oxygen has essentially become US Federal law.
Nitrox is no longer just "enriched air." Now, for the purposes of handling, it's considered pure oxygen. The establishment of a legal definition for Nitrox has created issues for the recreational Nitrox and technical diving marketplace. One issue is that guidelines for oxygen service valves imply SCUBA valves are, in some regards, inherently unsuitable for use with pure oxygen. The SCUBA valve was designed when the only recreational diving breathing gas was air, thus the SCUBA valve was not originally intended for oxygen service. Just cleaning a SCUBA valve with Simple Green® detergent, lubricating it with Christo-Lube® , and assembling it with Viton® o-rings will not make it suitable for oxygen service.
Another issue is that dive equipment, which may initially meet compressed gas industry standards for oxygen service, rarely remains clean for any significant period of actual diving use. The cause is three fold: (1) the dive industry relies heavily upon mechanical gas compressors which must be lubricated. (2) The dive industry has a widespread ignorance of what is required to establish and maintain equipment conditions that meet oxygen service standards. (3) Divers don't practice their sport in cleanroom conditions. The fact is that before a diver fills their new tank at a local dive shop and goes diving with their new regulator is probably the last time that such equipment might ever be able to meet any standard for being oxygen clean.
Almost all dive industry suppliers, including Dive Gear Express, are thus reluctant to explicitly label any dive equipment as "Suitable for Oxygen Service", knowing that it almost certainly won't be, immediately after delivery to consumers. Some suppliers vaguely label products as "clean" or "compatible" but not both, and there are various versions of "40% MAX OXYGEN" disclaimers. Sometimes the labels include the limitation of "prior to initial use." The CGA standard that any gas greater than 23.5% must be handled as if it was 100% oxygen also creates a further labeling dilemma when several different pieces of equipment with different (perhaps conflicting) supplier definitions and disclaimers are daisy-chained together.
Many dive equipment suppliers attempt to address these issues by substituting the term "Nitrox Ready" to describe their products intended for use with anything other than air. Unfortunately, there is not widespread agreement as to the meaning of "Nitrox Ready," although we like our Dive Gear Express definition of Nitrox Ready as a definition that meets the needs of divers. To avoid conflicts with various supplier disclaimers, Dive Gear Express uses the more technically accurate CGA phrase "suitable for service with compressed gases containing greater than 23.5% oxygen" to describe products that are both oxygen clean and oxygen compatible, rather than "suitable for oxygen service".
Given the widespread ignorance regarding oxygen safety and that the design of SCUBA valves may be inherently unsuitable for use with pure oxygen, it is unlikely any reputable supplier would label them for oxygen service. Dive Gear Express is not aware of ANY brand of SCUBA valve offered by a US based manufacturer that is explicitly labeled for "oxygen service." There are some SCUBA valves in the European Union that are labeled as "oxygen service," based on EU standards. However, the oxygen service SCUBA valves in the EU use intentionally incompatible M26X2 threads on the outlet. Some valves are explicitly labeled "Air Only" service, but in the absence of labeling, the valve must be assumed to be ONLY suitable for use with air.
Please recognize this is not a discussion of who has legal liability, that will be of little consolation if you are the individual involved in an oxygen fire. Rather, it is about whether something is in fact suitable for oxygen service. Keep in mind that it's highly unlikely that dive equipment not explicitly labeled is suitable for use with oxygen just because other divers have used the equipment with oxygen without incident, or that the equipment has been aftermarket "cleaned" in order to convert it for use with oxygen. The CGA pamphlet G4.1 "Cleaning Equipment for Oxygen Service" describes the methods for cleaning and testing the suitability of the equipment used with oxygen.
To technically trained divers, who tend to think more about partial pressures than percentages, it might seem that the oxygen absolute pressure (not the oxygen percentage) is the primary concern in oxygen fires. In practice, at the gas service pressures encountered in the scuba industry, it is extremely difficult to get an ignition that will start a kindling chain resulting in an oxygen fire when oxygen is mixed with an inert gas like nitrogen. Experience within the dive industry has demonstrated that, for gas pressures typical of scuba cylinders, the likelihood of an ignition becomes a genuine concern only when the gas mixture contains 50% or more oxygen.
The diving industry does not have a significant history of ignition problems with sport diving mixtures of the Nitrox gas itself. That's what is so frustrating about the legal definition of Nitrox as pure oxygen: the handling of nitrogen-oxygen gas mixtures containing less than 50% oxygen (aka sport Nitrox) has an excellent safety record in the dive industry, it's when pure oxygen is involved that oxygen service concerns become paramount. Unfortunately, the cost effective production of small quantities of Nitrox involves adding oxygen to air. Thus, the issues regarding oxygen handling safety continue to surround Nitrox.
One confusing issue is the so-called "40% Rule" that says equipment may be used interchangeably with CGA Grade "E" air as long as the product never contacts gas mixtures in excess of 40% oxygen. According to the 40% Rule, equipment used with Nitrox up to 40% does not have to be oxygen compatible nor does it have to be oxygen clean. Compressed gas handling experts consider the 40% Rule to be completely invalid and, as previously explained, it also violates U.S. Federal law. Expert opinion considers equipment and handling as either suitable for use with pure oxygen or only suitable for use with air, there is no in-between.
Various oxygen and nitrox disclaimers on dive equipment have triggered many discussions at local dive shops that offer Nitrox or oxygen fills. Technically incorrect wording found on many scuba tank evidence-of-inspection labels (aka "VIP stickers") in particular may cause conversation between the diver and the shop about responsibilities for the proper handing of the cylinder and the gas. When one or both parties is not fully informed and up-to-date about the facts of oxygen safety standards and practices, these discussions can have some undesirable outcomes as a result of inadequate knowledge or dogmatic adherence to opinion.
If the local dive shop owner and/or fill station operator (FSO) does not want to accept responsibility for handling oxygen, they should only sell air fills. The reality is that an unsafe condition may exist if the FSO is upset about 40% disclaimers yet also filling Nitrox and/or pure oxygen. Objection to such statements could mean the FSO has an inadequate working knowledge of the technical and procedural issues surrounding the handling of oxygen within the recreational diving industry.
If the FSO is willing to accept responsibility and fill your cylinder, then a relationship of trust must be established between the FSO and the person presenting the cylinder to be filled. Establishing and maintaining that trust requires that the people involved in handling the cylinder are following, whenever possible, the best practices for oxygen service. Like sexually transmitted disease, this is particularly problematic for the FSO because they are also trusting everyone previously filling and servicing the cylinder.
The good news is that Nitrox disclaimers have become widely used in the industry to limit manufacturer liability yet indicate a product is (at least initially) oxygen compatible and oxygen clean. By now it's very likely that most fill station operators will have encountered this situation, thus having more clearly established their Nitrox and/or oxygen fill policies, needing only to have a discussion about handling best practices with customers previously unknown to them.
The bottom line is that, in the opinion of Dive Gear Express, filling a SCUBA tank with oxygen can not be done while simultaneously following all the compressed gas industry guidelines and best practices for the handling of high pressure compressed oxygen gas. Regardless, by following those practices as closely as practical, the risks will be greatly reduced but the risk of an oxygen fire cannot be eliminated.
OXYGEN-RELATED FIRES AND EXPLOSIONS CAN RESULT IN SERIOUS INJURY OR DEATH. ULTIMATELY, YOU MUST MAKE THE FINAL DECISION TO ASSUME ALL RISKS ASSOCIATED WITH THE USE OF ANY COMPRESSED GASES, INCLUDING THOSE IN EXCESS OF 23.5% OXYGEN.