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At 10:44 AM 6/26/96 -0700, you wrote: >T.J. > >On Wed, 26 Jun 1996 tjm@ea*.ne* wrote: > >> Besides, I will have to modify mine for tech-stuff - >> computer, O.C. bailout, gas switches, etc... Will drive the cost up >> considerably. > >The issue of a computer is an interesting one. All the computers, that >this slack-jawed "prosumer" has seen, use variations of the standard >algorithms where the inspired concentration of gas is constant and the >partial pressure of the gas varies. To get the max out of your CCR, you >need a computer that takes into account the variation throughout the >dive of your FiN2 as well as depth. > >Now the Pg = Fg x depth equation would indicate that all you need to do is >substitute the computer algorithm. But the laws of physics, while constant >sometimes have hidden variables in physiologic systems. What if the >absorption of nitrogen is dependent not only on the FiN2, but also on the >ratio of FiN2/FiO2? As the CCR varies the FiO2, this ratio will change. >e.g., you want to keep your pPO2 at about 1.2 At 50 fsw your >FiO2:FiN2 is 48:52, at 100 fsw the ratio is 30:70, about half. Why do I >think this might make a difference? Murphy's Law of Medicine and the fact >that the solubilities of the two gasses (O2 and N2) are not the same. >Basically I'm asking if all that matters is the pPN2 or if the relative >concentrations of other gasses, have an effect on the absorption of >nitrogen (..like the oxygen window effect). > >> Let's do get a couple (of CCRs) and go diving! > >Absolutely, but before I plunge to depths where time at decompression >stops is important, I would like to be sure that the assumptions I make >about nitrogen absorption when the FiN2 is constant remain true when it >varies. > >I'm hoping that some of the mavens on the net can show this bu(r)bbling >diver the light. > >Peter FWIW.... There are several issues that have been bothering us as we develope the internals for the rebreather module in Abyss. So far as we have seen most of the models that are generating "Rebreather" tables are just simple variations on the standard algorithm. The only thing we can really be sure of is that it is NOT the same as using Open Circuit, and that the gases in the loop have their own subtle variations that need to be taken into account to come up with reasonable tables. For the realtime computer, we have a little more input, so the model should be even more accurate. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Christopher M. Parrett, President Abysmal Diving Inc. 6595 Odell Place, Suite G. Boulder CO, 80301 USA Makers of ABYSS, Advanced Dive Planning Software. Phone: (303) 530-7248 Fax: (303) 530-2808 File Transfer Site: ftp://abysmal.com/users/abysmal NEW WWW Site... World Wide Web Site: http://www.flinet.com/gulfstream/abyss/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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