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Excerpts from tech: 19-Apr-95 Re: Final decompression gas.. Mike Sandler@in* (1592) *snip* except for the fact that pure O2 IS easy to aquire, I personally feel that a 80% O2 nitrox mix would be desirable because; the difference in deco times as opposed to 100% O2 would be negligible AND the safety margin with respect OTU's is greatly increased with a 80% mix consider the 200+ ft air diver with a twenty-five minute or more bottom time. Also its more forgiving while trying to maintain that 20 ft. stop in open seas. *snip* First I assume Mike means CNS%, not OTUs here. It quite a serious dive if you can rack up enough OTUs to matter, and even if so I can live with 2-3% vital capacity reduction as the result of going over the OTU limit. Secondly, whereas EANx80 gives a greater CNS% advantage at 20' and drifting to 23' isn't probably won't be devastating (although the nitrogen offgassing will be reduced), the diver using EANx80 will have to perform a 10' stop on the nose in order to elimante enough nitrogen according to their tables. Using pure O2 the diver can pull their 20' stop at 19-20' and then pull their 10' stop anywhere between 10-18' and have the same offgassing rate. On another note, NOAA has produced tables for Po2 limits while at rest which read 45mins at 1.9 ATA. VERY few (I can't think of any of the top of my head) accidents have been recorded resulting from CNS O2 tox while at the 20' stop. Now that I think about it, I do recall a few stories (unverified), but they all involved the diver "accidentaly" drifting to 30-40' and then convulsing. Either way, they both work. -Pete Goutmann
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