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Richard and others, Thanks for your comments. To those who asked, I don't have references to the work on narcotic potency of oxygen vs nitrogen. All I know about it is what others have mentioned here on techdiver. Maybe John Crea or Chris Parrett can provide references ? On the issue of depth, I perhaps shouldn't have mentioned the air diving records of Gilliam et al. The depth range I would like the discussion to focus on is the 50-80m (160'-260') range. This is a range that quite a few people push air diving into (see "Deep Diving" by Gilliam). Richard Pyle <deepreef@bi*.bi*.Ha*.Or*> writes: > >On Mon, 6 Feb 1995, David Giddy wrote: > >> Has anyone tried an alternative of Reduced air Nitrox ? By this I mean air >> to which *Nitrogen* has been *added* to reduce the FO2. > >The interesting thing about air (Nitrox-21) is that it happens to be about >the optimum blend for deep diving of any nitrogen and oxygen mixture. The >reason for this is that both oxygen toxicity and narcotic limits for most >people are achieved at about the same depth when breathing air. Many >people prefer to limit their oxygen exposure to about 1.4 ATA, which on >air occurs at about 190fsw, at which depth most people are feeling strong >effects of narcosis. A few people set their PO2 limit at 1.6ATA, >which is ~220fsw on air, a depth where only a very few individuals are not >seriously incapacitated by narcosis. In other words, O2 toxicity and >narcosis are almost equally limiting factors for depth when breathing air. Agreed. However, for those people who do wish to push air deeper, I think that it would be safer to reduce the chance of O2 toxicity and have narcosis as the limiting factor. > [deleted] > >I actually believe that breathing Nitrox-10 at, say 240fsw, would be >slightly less narcotic than breathing air at 240fsw (nothing to back this >up...just a hunch). But what would the point be? Any reduction in >narcosis would be subtle, at best, and would likely be dwarfed by other >variables affecting narcosis intensity (water temp, CO2 buildup, water >clarity, etc). I think the point is not to reduce narcosis, but to reduce the O2 risk significantly while *not increasing* the narcosis level. > >It's true that the risk of acute O2 toxicity might be reduced somewhat, >but that becomes unimportant if narcosis is incapacitating. Although a few >individuals like Bret Gilliam, Dan Manion, and others have pushed beyond >400 or even 500 fsw and lived to tell about it, even they wouldn't >advocate nitrogen/oxygen bimixes as a *practical* breathing gas for deep >water. I guess it depends on the depth range you are aiming for. My primary suggestion is that in the range of 50-80m (160'-260'), something like Nitrox-10 or even Nitrox-5 may be a safer breathing gas than air. (To those who wrote about using Trimix and Heliox: I fully realise that they would be even safer, but that is not the point I am interested in exploring) > >I'm sorry if this doesn't satisfactorily answer the question...I'd sum up >by saying that: any advantages gained by increasing the nitrogen content >of air at deeper depths are tiny compared with the advantages of diluting >air with helium (even when considering the relative price of the two >gases). So, except for some highly unusual situations, it would be better >to use air, trimix, or heliox for deeper dives. The interest may be particularly local as here in Australia, medical grade Helium is roughly 5 times the price of medical grade oxygen. In addition, there are as yet very few places which will provide Trimix and Heliox fills. Cheers, David. ______________________________________________________________________________ David Giddy, | Voice: +61 3 253 6388 Telstra Corporation, | Fax: +61 3 253 6144 P.O. Box 249, Rosebank MDC, 3169, AUSTRALIA | Internet: d.giddy@tr*.oz*.au* ------------------------------------------------------------------------------
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