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David Giddy writes: > In the recreational Nitrox community I believe that the most common mixture > being promoted is NOAA Nitrox I (32% O2). This mixture reaches a PPO2 of 1.6 > at 40m which is the recreational depth limit. I know I keep saying this but this isn't true world-wide. 40m is the recreational limit only for certain organisations. The assumption that most dives are done on NNI may be valid but there are a significant number done on 36% O2. You can't just ignore them. > At this PPO2, the O2 toxicity limit for CNS toxicity is 45 minutes (DCIEM > manual). As the recreational use of nitrox is strictly no-decompression, > then the NDL will be far more restrictive than the O2 toxicity limit. > Hence, an O2 hit with Nitrox I in recreational profiles is extremely unlikely. No it's not. It is for a pulmonary hit, which for all but the most aggressive recreational divers isn't a concern. And again only certain organisations define recreational diving as being no-decompression. Many divers in the UK regularly do decompression dives sanctioned by their organisation. > If the only gasses being used > are Air and Nitrox I, then the consequences of a swapped tank aren't quite > so serious - well, DCS (which may occur if one is diving Nitrox tables with air) > IS serious, but not as bad as an O2 hit!. Only valid if your limit is 40m and you only have NNI around. We regularly have mixes from 30% to 38% O2 around. Everyone should test their mix prior to entering the water. [Easy to preach. Is there anyone who can honestly say they have done this?] Alan
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