Nitrox workshop dings - Divers Alert Network

Rubicon Foundation Archive (http://rubicon-foundation.org)Lang (ed.): DANNitrox Workshop, Divers Alert Network, November 2000.Background Considerations: Making and Handling OEA MixesBefore physiological issues can be of concern, it is necessary to prepare and handle theoxygen-enriched breathing mixtures. There are several aspects to this.Air to be mixed with oxygenBreathing mixtures for some of the early operational use of OEA at the NOAA UnderseaResearch Center at the University of North Carolina at Wilmington were made by mixing puregases, oxygen and nitrogen, to form 32% or 36% oxygen-nitrogen mixes. This is expensive, andinherently dangerous because it involves using a pure inert gas. This was done because a sourceof air clean enough to mix with oxygen could not be identified or even specified. This was laterresolved.Use of mixes up to 40% oxygenFrom the earliest use of oxygen-enriched mixtures it was considered that mixtures of up to40% oxygen could be handled in the same way and with the same equipment configurations asfor air. Although this "40% rule" has been widely disseminated (for example, it is in the OSHAstandard for commercial diving), it appears that limited testing has been done to validate this,and it remains a matter of uncertainty in the minds of some.Mixes should be analyzedUnlike medical prescriptions, in the present-day recreational diving industry it is considered,and experience has shown, that the diver should check the analysis of tanks of mix prepared by adive shop or gas supplier. The custom is for divers to confirm the analysis of the oxygen fractionin OEA mixes in their scuba tanks. Normally this is performed at the shop providing the "fill" atthe time a tank is taken. When to do the analysis and the procedures to be followed shouldsomehow meet some as-yet-undefined minimum standards.Tanks should be properly and prominently labeledThe analysis has essentially no meaning unless the user of the tank is aware of it. To ensurethis, it is essential that scuba tanks containing gas other than air be labeled unambiguously.Names such as "NNI" are not unambiguous. Some diving groups also label tanks with anindication of the maximum operating depth (MOD) for a given mix, based on the PO2 selected asthe "limit" of exposure. The MOD, in large letters, is visible to other divers for added safety.The MOD banner is useful, but the actual values of each of the major components should showon the tank.History of Diving with Oxygen-Enriched AirThe history of diving with oxygen-enriched, nitrogen-based mixtures can be roughly dividedinto 3 phases. The first would include the early operations and studies that used rebreathers.This phase, as a part of the development of enriched air diving, goes to about the 1960s.The next phase was commercial operations, most of which were using conventional hose andmask apparatus with on-line blenders. This was done mostly in the 1970s and 1980s.