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On Fri, 20 Aug 1999 tgunther@co*.co* wrote: > May I assume, than, that your gas profile of choice (from shallow to deeper > depths) would be: > > Nitrox -----> Trimix -------> Heliox Tod, HeliOx is probably the perfect gas for the extreme dives that George and the WKPP do. That is, about 280ffw. However, there's an effect which is currently unrecognized in the scientific literature when diving HeliOx beyond about 250-280fsw. It's what a few of us call "the anti-narc", and has also been referred to as "pre-HPNS". You feel like you've had about four cups of espresso, and generally feel scattered as a result. Proper HPNS (shaking limbs, etc) doesn't set in until much deeper (around 500-600ft), but it's not just me - several people have noticed problems as shallow as 240. The simple answer (long accepted among commercial divers in dealing with actual HPNS) is to squirt in a couple or few percent of nitrogen. This seems to offset the effect. So, the answer to me, in order of descending depth, is Nitrox-->trimix-->heliox-->trimix. That sequence factors in gas cost, as well as efficiency. -Will -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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