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Will - I really know nothing about rebreathers but isn't open circuit oxygen quicker offgassing? Ie/ isn't the rebreather going to start giving you the inerts back through the loop that is coming out of your lungs in the first place, causing the p. pressure gradient to drop? At 10:43 AM 7/24/98 -0400, "William M. Smithers" <will@tr*.co*> wrote: >You would probably burn through about 25 cu. ft of >O2 in the process, if you include a 7-8 hour deco. > >Regards, > >-Will > > > > > >> ---------- >> > From: William M. Smithers <will@tr*.co*> >> > To: CHKBOONE@ao*.co*; techdiver@aquanaut.com >> > Subject: Re: Helium Deco / Wil >> > Date: Thursday, July 23, 1998 9:14 PM >> > >> > >> > On Thu, 23 Jul 1998, William M. Smithers wrote: >> > >> > > Incidentally, that's also why Heliox is a much safer gas >> > > for repetetive multi-day diving - it clear almost completely >> > > out of your system overnight, unlike N2, which takes >> > > 36 hours or so. >> > >> > BTW, for this and several other good reasons, I've been >> > diving with NO nitrogen anywhere in the bottom >> > and deco mixes for about seven months now - I dive >> > Heliox10 end-to-end, with pure O2 for deco starting >> > at 20ft. And I feel *great* after the dives. Unless >> > I'm cruising a reef at 80fsw on Nitrox with an AL80, it's the devil >> > gas for me. >> > >> > The extra hang time is shorter than you'd think. >> > Compared to an appropriate trimix, you're typically looking >> > at an extra 10 minutes or so for an hour-long deco. >> > >> > Of course, diving heliox can start to get more than a bit >> > pricey, unless you're on a closed circuit rebreather. ;) >> > (I typically burn through all of four cubic feet of >> > heliox for a typical two or three hour dive to > 250fsw). >> > >> > Regards, >> > >> > -Will >> > >> > >> > >> > > >> > > > Regardless of the rates of diffusion of two different gasses such >> as He >> > > > and N2, given a fixed period of time for on-gassing and a symmetrical >> cycle >> > > > each gas should off-gas completely in the same period of time. >> > > > If at the same time you pore red marbles into a bucket at a rate >> of 50 per >> > > > second and blue marbles into the same bucket at a rate of 100 per >> second for >> > > > 10 seconds then pore them out at the same rates for 10 seconds the >> bucket >> > > > should be empty of both groups of marbles at the same moment. >> > > > If, however, they are each pored in at different rates that >> decrease >> > > > exponentially and then out at linear rates (or close on both counts) >> then >> > > > there can be a divergence of the points in time at which each is >> totally clear >> > > > of the bucket. >> > > > This would be true of all tissues, not just the slow ones, and >> this is >> > > > what I suspect is happening but I am looking for confirmation and a >> more >> > > > thorough description of the process. I am not sure that the >> exponential / >> > > > linear model is valid or uniformly applicable. >> > > > >> > > > I can see possible merrit in your suggestion if helium diffuses >> to points >> > > > beyond the influence of the blood stream but this would seem to make >> the >> > > > process dangerously unpredictable. I agree that the use of helium >> would >> > > > probably shift the controlling tissue to a slower one for a portion >> of the >> > > > dive. >> > > > Actually you are making two dives and two decompressions when >> using trimix >> > > > and I suspect that the procedures we customarily use are not the most >> > > > effective way to manage them. I suspect that we are making a >> descending >> > > > excursion on nitrogen at the first gas switch so that we can blow off >> helium >> > > > earlier in the deco schedule than may be necessary. >> > > > Something like this may be behind George's insistance that 50/50 >> is a >> > > > better deco mix than 36 - because it delays that descending excursion >> on >> > > > nitrogen rather than jumping the helium deco gun and paying for it >> throughout >> > > > the rest of the deco by having to dump the nitrogen you took on to do >> it. >> > > > I may be way off base but if I can get a few questions cleared up >> I might >> > > > be able to shorten and improve the effectiveness of my deco >> procedures. >> > > > This post is the first question. >> > > > >> > > > I appreciate your response, Wil, and I hope that the explanation >> turns out >> > > > to be as simple as you suggest but I fear that I am in for some big >> headaches >> > > > over the next few days, especially if I can get Bill Mee, Eric >> Maiken, or John >> > > > Crea to bite on this. >> > > > >> > > > Does the above seem reasonable or is my brain so fogged with >> thinking >> > > > about this stuff that I am missing something obvious ? >> > > > >> > > > Chuck Boone >> > > > >> > > > >> > > > >> > > > -- >> > > > 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'. >> -- >> 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'. > > -------------------------------------------------- Kevin Connell <kevin@nw*.co*> Northwest Labor Systems http://www.nwls.com Lake Stevens, WA -------------------------------------------------- -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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