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George, Frankly, I would have to completely agree. You can come up with theoretical tables all day long to predict decompression from trimix dives, but you are probably just fooling yourself. Any kind of serious exposure to trimix and you simply cannot decompress without some type of sub clinical physiological damage. You and I and the others have done our share of these kinds of dives and there is no hiding the fact that no matter how good shape you're in there is a tangible "beating" factor. I'm sick of it. My guess is that the real problem is nitrogen and that the effect is not so much partial pressure dependent as it is simply pressure dependent. It is well known in chemical engineering that many reactions require external pressures to occur. For instance certain polymerization reactions are pressure dependent. Really, who knows what nitrogen is doing. We do know that it affects the mechanical characteristics of erythrocytes (red blood cells). The ability of erythrocytes to deform is critical to their passage through some of the capillary beds and who would argue that gas transfer at the microcapillary level is not relevant to decompression? Heliox seems to give far superior results and this should not be surprising since the commercial dive industry has compiled an historically impressive safety record for saturation diving. I don't know what this will mean for technical diving, but I guess it will ceratinly help the market for booster pumps when everyone realizes that "trimix" is a bust. At least with the rebreathers you can operate at much lower drive gas pressures; however I am not recommending that everyone run out and buy rebreathers as these devices pose all sorts of other risks. As you know I have been using straight heliox for the 120ft and 70ft deco gases with the Halcyon with drive gas pressures of 2000-2400 and had lot's of gas left over, even with the 40cf bottles after long decos. I have also jacked the bottom gas to 75% helium with great results. Where do we go from here? Bill -----Original Message----- From: Katherine Irvine <kirvine@sa*.ne*> To: techdiver@aquanaut.com <techdiver@aquanaut.com> Cc: rose@cs*.sc*.ed* <rose@cs*.sc*.ed*>; wwm@sa*.ne* <wwm@sa*.ne*> Date: Tuesday, July 27, 1999 3:14 PM Subject: Deco not working? Could be the gas....is "trimix" worthless? >I get questions all of the time as to recommendations for improving >deco that others are not satisfied that they are doing advantageously. >Many times it is obvious as to wrong shape of the deco or wrong gas, but >lately it is less clear. > > For my own account I have been more interseted than ever in >minimizing damage and maximizing my available workout time since I am >training for an Iron Man this fall - I can't have any down time from >training since I have to work three disciplines and workout twice per >day . My teammates have become more interested in marathons, bike >races, swim races, triathelons and in more conditioning, and have taken >the same attitide that I have taken, and that is we do not want diving >to get in the way of our training, even though diving was why we started >training in the first place. > > You have seen the progression of our deco, and may have noticed that >we started incorporating helium into the deco gasses, and increasing the >amount of helium in the mixes. As we got higher and higher on the helium >percentage , the truth has become clearer and clearer - nitrogen is the >problem, and "trimix" as we knew it is basicly worthless. > > Sure, I can walk away from most trimix dives, but I run away from >helium dives. We may have to revamp our entire structure on this issue. >Heliox may in fact be the correct gas for diving, and the answer to >deco, not anything more or less. > > The Navy asked us about loss of vital capacity. We can measure that >on the track , in the pool, and on the speedometer in one word ; >nitrogen. > > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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