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It seems to me that in a normal course of diving you would never expose yourself to a situation where you go from a heavier gas to a lighter gas unless you are going down, which means that counterdiffusion would not be a problem anyway. The only way it could be a problem, *IF* indeed it is ever a problem, is going from a heavy gas to a light gas, and going up (or remaining at the same depth). I can think of 2 scenarios where this could happen. 1) Very deep dive using high HE mix Switch to Nitrox 50% at 70 fsw RUN OUT OF THAT GAS SOMEHOW Go back on your remaining back gas to finish the deco. If this happens, you wouldn't know if you got bent because you decoed on the wrong gas or because of counterdiffusion, plus your alternative is drowning, so you have no choice anyway! This makes the whole discussion on counterdiffusion totally academic in this case. 2) You happen to have a bottle filled with heliox 50/50. You do a deep dive on air (dumb idea) you switch to your heliox at 70 fsw to do your deco. Now this is obviously so stupid that I can't imagine anyone doing it, but if the theory on counterdiffusion is right, then this might be problem...or not, depending on how darwinian you are ;-) In any case, if you follow proper procedures I don't see how counterdiffusion could ever be a problem in diving, but maybe I'm missing something? Cheers. George Irvine wrote: ~ >Bullshit, and again from the usual do nothing bullshitters. Imbert knows >less about deco than a dog. We changed all of Bullmanns stuff completely >around, and when you can do it like we do it, moron, you can tell me that >those who have long ago been proven wrong are right. > >It does not occur in any situation that involves diving where the gradients >are not violated. The only time the sum of the partial pressures is out of >balance is due to the oxygen window, and that certainly does NOT cause any >problems. > >Now maybe you can tell us all how this fairy tale applies to diving, and wh= y >saying asinine things like "get off the helium as fast as you can" is >anything but crap. > >You rack up my experience and the combined decompression experience of the >WKPP and then tell us all about deco. Funny , we are the ones that the >parties who have an interest now study, not any of the once upon a times >that you mention. >----- Original Message ----- >From: "Matthias Voss" <mat.voss@t-*.de*> >To: "Trey" <trey@ne*.co*> >Cc: "Alain T=E9sio" <alain@on*.or*>; <scottk@nw*.co*>; "Techlist" ><techdiver@aquanaut.com> >Sent: Friday, April 20, 2001 7:54 AM >Subject: Re: Counter diffusion > > >> You are wrong, Trey, and Alain is right. >> I would only modify the essence to : >> If bubbles occur during a static gas change, this happens because of >> counterdiffusion, and because of a certain choice of gases, and switch >> depth. >> It can be avoided if the above conditions are not met. >> If you need know more, get in touch with Dr. Aspacher ( he wrote a >> monography on isobaric counterdiffusion, there you may find the evidence >> , and why some ( few) are affected, majority not. >> B=FChlmann ( page 67-71), Lambertsen et.al., Lettnin, ( page 223) / Imbe= rt >> proved, that the sum of partial pressures , when certain conditions are >> met, can be eqal or greater than ambient pressure. >> However, this holds mostly for chamber situations. >> >> Horseshit physicians and PH D's, arent't they ? >> >> Matthias >> >> Trey schrieb: >> > >> > Total and complete bullshit. This is the stupidest thing I have read o= n >here >> > in years. Partial pressures are not going to create bubbles, only >absolute >> > differentials. Otherwise we would all get bent going to oxygen, right? >You >> > obviously do not dive, do you. >> > >> > This is a fairy tale used to explain why misfits get bent. It is total >and >> > complete bullshit. We in WKPP do dives involving five gas changes and >the >> > fastest deco from saturation on the planet, and nobody gets bent in an= y >> > fashion. >> > >> > If this horseshit were even close to true, we would not be using deco >gases, >> > now would we. >> > >> > -----Original Message----- >> > From: Alain T=E9sio [mailto:alain@on*.or*] >> > Sent: Thursday, April 19, 2001 6:38 PM >> > To: scottk@nw*.co*; Techlist >> > Subject: Re: Counter diffusion >> > >> > Counter diffusion occurs when switching gases, the common >> > picture is "isobaric counter diffusion" because bubbles >> > appear though you don't change the depth, which can't happen >> > in theory with no gas change : >> > when you change from nitrox to heliox, as helium diffuses >> > faster than nitrogen gases out, for some time the total >> > partial pressure of inert gases will increase which can >> > mean bubbles. >> > >> > It isn't something which is absolutely required to know >> > for tech diving, at least if you follow the common >> > procedures and don't play the random gas wizard, but it's >> > a must for hyperbaric specialists. >> > >> > They know how to deal with decompression illness with gases >> > other than air, at least in Europe when professional divers >> > use heliox for 30 years, however it may be a problem >> > in areas having experience only with recreational >> > diving. >> > >> > If there is one thing to remember, it is that you shouldn't >> > breath nitrox when you go to the chamber after of a >> > trimix accident. >> > >> > The other way is ok though, it's essentially a specialist >> > affair, but using heliox 50 for air accident is ok. >> > >> > Alain >> > >> > ----- Original Message ----- >> > From: "Scott" <scottk@nw*.co*> >> > To: "Techlist" <techdiver@aquanaut.com> >> > Cc: "Trey" <trey@ne*.co*> >> > Sent: Thursday, April 19, 2001 6:38 PM >> > Subject: Counter diffusion >> > >> > > George, >> > > >> > > Can you put the issues of "counter diffusion" into language a Jarhea= d >can >> > > understand? >> > > >> > > I was accosted this past week by a "Master Diver" who warned us that >"If >> > you >> > > have to take a chamber ride after breathing that shit (helium) it wi= ll >> > kill >> > > you." >> > > >> > > I was so stunned by his position and attitude that I just nodded and >> > > listened. >> > > >> > > Plus, I have no idea what counter diffusion is, or if or why it is a= n >> > issue >> > > to SCUBA divers. >> > > >> > > Scott >> > > >> > > -- >> > > 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'= =2E >> > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com= '. >> > >> > -- >> > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'= =2E >> > 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'. -- Paul B. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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