Nitrox workshop dings - Divers Alert Network

Rubicon Foundation Archive (http://rubicon-foundation.org)Lang (ed.): DANNitrox Workshop, Divers Alert Network, November 2000Most of the special training one needs to safely dive with, and handle, enriched air relates toits higher oxygen content. The primary application of enriched air is to extend nodecompressionlimits beyond those of normal air. Based on NO AA tests, Navy tests dating backmore than 50 years, 20 years of field experience by scientific divers, plus field experience inthousands of recreational dives, the no decompression limits for enriched air are generallyconsidered as reliable as those for normal air tables and computers. However, there is a tradeoff. As you reduce nitrogen exposure, you increase oxygen exposure. Therefore, much of whatneeds to be taught to students deals with keeping oxygen exposures within safe limits.Practically speaking, depending upon the dive depth and breathing rate, dives may be limited byenriched air supply rather than no-decompression limits. Therefore, planned dive profiles andplanned repetitive dives may not be able to take advantage of the additional time enriched airoffers in some cases.Because you absorb less nitrogen using enriched air, you might expect that using enriched airwithin normal air no-decompression limits would substantially improve safety. This is probablynot true. The decompression sickness (DCS) incidence rate is already so low that it's unlikelythat simply reducing nitrogen can produce a meaningful risk reduction. Although there's been nostudy of this, statistical estimates suggest that using enriched air within normal air limits onlyreduces mathematical risk a fraction of a percent. After all, the DCS incident rate is estimated as.004 percent (one in 25,000 dives) to .001 percent (one in 100,000 dives). If you cut that rate byhalf, which is very unlikely, the best you could do is reduce incidence by .002 percent.Therefore, it's inaccurate to suggest that enriched air is "safer" than air in any meaningful way.Used properly, both are safe and have impressive safety records. Used improperly, enriched airhas more potential risk due to oxygen toxicity. Safety stops, avoiding factors that predispose youto DCS (such as dehydration), avoiding sawtooth profiles and following other safe divingpractices probably reduce your risk far more significantly than using enriched air within normalair limits. Admittedly, some divers feel any mathematical DCS incidence risk reduction, eventhough tiny, still makes it worthwhile to use enriched air for dives than can be expected to bemade safely with normal air. This is a personal choice without any safety concerns, providedenriched air procedures are followed.Although enriched air has a reduced nitrogen content, many diving physiologists don'tbelieve enriched air significantly reduces narcosis when making deeper dives (Bennett, 1970;Linnarsson, et al., 1990. This is because oxygen under pressure appears to have similar narcoticproperties to nitrogen under pressure. Thus, while enriched air has less nitrogen, it has about thesame potential for narcosis. Although some divers say they experience less narcosis withenriched air, it's wisest to assume enriched air will not reduce narcosis. Some divers claim they"feel better" after a dive with enriched air. There is little objective evidence for feeling less tiredor "better" after diving with enriched air, but it has been cited frequently. This may simply be apsychological effect.In comparison to air diving, diving with enriched air offers longer no-decompression times,but it also has five disadvantages and potential hazards:1. Potential for oxygen toxicity - Much of what is taught is the P ADI EANx program dealswith staying within oxygen time and depth limits. Exceeding safe oxygen limits can be46