I have a question. Does this have anything to do with the fact that although the ppO2 on 50% at 22m is the same as 100% at 6m, your nitrogen gradient is not as you are still breathing N2 in the 50% mix? I thought about this when I read the "why we don't use 80%" post. "nor does it work as well as pure oxygen without an inert gas at any depth" Thoughts? James Dibbs Sydney, Australia jdibbs@ma*.co*.au* -----Original Message----- From: Paltz, Art [mailto:Art.Paltz@R2*.CO*] Sent: Thursday, 13 January 2000 5:42 AM To: 'Oystein Mehus'; Manos Manoli Cc: Tech Diver Subject: RE: I think I don't understand I don't think it's that cut and dry. I think it depends on the amount of nitrogen in the bottom mix. According to Buhlman (since it was referenced), if you've got a lot of nitrogen in the bottom mix then the O2 is going to get your our faster (greater N2 difference in the bottom mix). Less nitrogen in the bottom mix and the 50/50 is going to get you out faster (the He difference is 100% and it comes out faster then N2). According to straight Buhlman (using Decom with N2/He M's set to 0%) I get the following. Same simple dive 130 feet for 45 minutes. Using air you'll get out of the water in the following times. Deep stops, O2 deco - 87 minutes Deep Stops, 50/50 deco - 90 minutes No deep stops, O2 deco - 85 minutes No deep stops, 50/50 deco - 89 minutes. Using air O2 wins both times by 3-4 minutes. Say you are using a helium rich mixture, say 50% He, 21% O2 (want to keep the O2 the same when comparing. What you would be doing with this mix in your tanks I don't know. 130 ft, 45 minutes, 50% He, 21% O2. Deep stops, O2 deco - 130 minutes Deep stops, 50/50 deco - 117 minutes No deep stops, O2 deco - 128 minutes No deep stops, 50/50 deco - 114 minutes 50/50 wins both times by 13-14 minutes. With a lower Nitrogen bottom mix you're better off with 50/50 then the O2. I think it naturally comes back to picking the right gases for the dive. Naturally this is Buhlman's interpretation. Hope this helps, Art. -----Original Message----- From: Oystein Mehus [SMTP:oymehus@on*.no*] Sent: Wednesday, January 12, 2000 8:50 AM To: Manos Manoli Cc: Tech Diver Subject: Re: I think I don't understand Manos Manoli wrote: > > Jeff i made many many tests with diferent Ean mixtures belive me > 100% oxygen on 6 meters does a hell of a lot diference than 50% on all stops. > This subject interests me. Do you have any references to why this might be so? And why does not deco-programs reflect this knowledge? According to the algorithms (at least Buhlman) you'll get out sooner if you use 50% from 21m than if you go straight to O2 on 6m. Oystein -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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