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---- Microsoft Mail "VMS Mail" message ---- From: HeimannJ on Mon, Feb 15, 1993 1:10 PM Subject: RE: Trimix + Re: Hose wars To: techdiver Reply to Jouni Polkko: >Are trimix fills comercially available for sport divers anywhere ? >Do trimix divers generally mix their gases themselves and how is >that usually done ? I suppose, that easiest way is first to put helium >into the tank and then fill it full with air. Or is the helium first >enriched by O2 to get different O2/N2 relations ? >How soon should the mix be used after the mixing so that helium doesn't >run away from the tank ? Or are ordinary valves and sealings enough >helium proof that this isn't a problem ? There are a few places in the eastern US where mix is sold to certified sport divers; these include Key West Divers in FL, Island Scuba Center in Freeport, NY (home of Ed Betts and ANDI), and the Gas Station in Gloucester, NJ. Commercial gas supply houses will sometimes supply premix as well. Most people seem to buy gas in bulk, and pump it in their basements with a Haskel booster. I should note that I am not trimix certified but am signed up for a course with Randy Bohrer this month which may actually happen. The way home mix seems to be done, according to those who do it, is to compute the partial pressures of He and O2 to be added to a tank for a particular mix, assuming that air is used to top it off. Next, He is added to a tank until the right pressure is achieved. The tank is allowed to cool, and the pressure measured again, and He may be added or vented. Next, O2 is added by pressure, and the tank is rolled around to facilitate mixing, again allowed to cool and rechecked. At this stage, the FO2 (and by computation, the FHe) can be checked with an O2 analyzer. Finally, air is added by pressure, the tank is mixed by rolling it, and it is allowed to cool. The FO2 is checked for the final mix, and O2, He, or air is added if necessary to correct the mix. The new book "Mixed Gas Diving" by Tom Mount/Brett Gilliam/Randy Bohrer/John Crea describes the procedures in detail. When I asked him about He leakage, Billy Deans assured me that he has done experiments and found that it isn't significant. >Could somebody kindly send me the ISBN numbers of the Gilliam's et. al. >books "Deep Diving: ..." and "Mixed Gas Diving" ? Are they worht of reading >and can anyone recommend any other books about the subject ? Aquacorps journal is a good source of info. The "Deep Diving" and "Mixed Gas Diving" books are pretty good, but I'm convinced that there is only a fixed amount of technical diving text and photos that can exist in the world, since the same articles and photos keep reappearing in all the books and magazines. I have both books at home and can get you the ISBN #s.
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