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On Tue, 7 Apr 1998, Jesse Armantrout wrote: > >From the 1996-1997 TDI Exams Book - Decompression Procedures Exam - page > 1 - question 7: > > 7. Oxygen can be employed to increase safety regarding DCS or it can > be used to shorten decompression time by permitting the diver to conduct > the 10fsw stop at 20fsw. > True/False. > > TDI Answer: False > > The track record speaks for itself. I didn't do my tech training with TDI, so I can't speak for their record or training first hand, but actually, the answer to the above question is "False" according to most deco models, including Bulhmann, which is the predominant deco model used for decompression today (WKPP secret funky homebrew aside). According to the Buhlmann model, there is absolutely no deco difference between breathing O2 at 20, 10, or 60ft - depth won't shorten your hang time. Why? Well, under Buhlmann, the only thing that makes a difference in your deco time is the partial pressure of N2 and/or He in your deco mix, as this affects the relative gradient between the gas dissolved in your tissues and the partial pressure of the gas it is working against (what you are breathing). And *that* affects your off-gassing rate. Your PN2 will vary with depth, so as long as you are breathing a mix that contains *any* N2 or He, depth matters, but as soon as you go onto 100% O2, there is no diluent in the mix, so depth makes absolutely no difference - you are at your maximum off-gassing gradient, and because there's no He or N2 in the mix, the partial pressure of these gasses can't increase. -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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