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----- Original Message ----- From: <Jsuw@ao*.co*> To: <techdiver@aquanaut.com> Sent: Tuesday, July 15, 2003 1:48 AM Subject: Re: What ppO2 for bottom mix? > Jan: > > Using standard mixes simplifies things. As someone else mentioned, you begin to know the deco for the dive with that mix because you use it often. It also helps your team of divers to have the same mix for a dive. That way you are all staying a team and doing the same deco. What about different standards for "standard mixes"? There is difference in standards beetween WKPP and GUE. Aren't GUE standards developed from WKPP? For 0-190 ft WKPP recommends trimix 18/35 for bottom gas. Personally I see no practical reason to use trimix for 50 ft dive for dives _I_ make. > The lower PO2 (e.g. 1.2) is to avoid both Central Nervous System Oxygen Toxicity, but more importantly, to avoid seeing the respiratory degradation which occurs with whole body oxygen toxicity. The respiratory effects will cause inefficient off-gassing on long exposures. This is also the reason to incorporate "back-gas" breaks during the deco. This is where you'd switch to the lowest PO2 mix breathable at a given depth during deco. An example of this for oxygen deco at 20' (6M) would be to breathe O2 for 12 minutes and then the back gas for 6 and then O2 for 12, etc. This helps prevent the respiratory effects. Yes, but for the same reason some organisations and divers say 1,4 is safe limit. 1,2 is only for exceptionally long exposures. And there are always exceptions when somebody can get a oxtox hit or something well before reaching limits proposed by you but is it enough reason for others to follow? Tech diving is risky activity and risk is what tech divers are used to live with. As for a oxygen breaks I agree. > > Most decompression tables and programs are based on Buhlmann algorithms for decompression modeling. Buhlmann assumed, without testing, that helium would lengthen the decompression schedule. Actual experience with helium mixtures proves otherwise. Helium on-gasses and off-gasses quickly, and can be off-gassed very cleanly when doing "deep stops" and using slow ascent rates. Not only will you be coherent on dives with helium, but you will feel much better, less tired (and less other symptoms "decompression stress"), etc. after the dive. I will not try to be smarter than tables because of actual experience. If there is actual experience you state why there is no tables using this advantage? It's bee a few years since we know it and still no programs and tables??? Why??? New algorythms are developed and we still have to dive like those legendary Egyptian divemasters diving 80 meters on air without computers just counting on feeling good? :-) > You need at least 35% helium in the mix to make any real difference. Less than that is a token amount and not effective enough. Well, actually I felt the difference having 23% He on my last dive to 43 meters. I'm like most divers very aware of nitrogen narcosis, and can detect it without problem. > When I plan a dive using software, such as DecoPlanner, I use the table provided by the program, add deep stops, add time at gas switches to have at least 5 minutes at a switch, and then I trim a few minutes from the shallower stops, following the shape of the decompression curve. Why to add 5 minutes for gas switch? > As far as solo diving, I encourage you to develop a group of safety minded divers that are qualified to do the dives you wish to do. Begin diving as a team. By team, I do not mean independent divers in the water at the same time. Plan your dives together. Execute the dives together. Support each other during the dive. Watch each other perform gas switches, etc. It's safer and more fun. Agree, but then there is reality. I don't know _any_ diver 40 km radius from my city ever diving wreck on Baltic sea, same with trimix. Nearest diver able dive tx whom I know lives about 90 km away and his schedulle make it impossible to dive together. So maybe in Florida it's different situation but not here. Thank you for a lot of info. Jan Werbiński O0oo....._[:]) bul, bul, bul Strona domowa http://www.janwer.com/ [ http://pa54.zgora.sdi.tpnet.pl/jw/ ] Nasza sieć http://www.fredry.net/ [ http://pa54.zgora.sdi.tpnet.pl/ ] -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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