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Hi Rich, Sorry I could not get back to you sooner...I have to "work" sometimes....:) I ran into Jack Kellon yesterday, and mentioned the thread on bubble theory vs compartment theory, with the "Blow and Go" example. Apparently, Jack, and Morgan Wells, and the other guys who have been doing the deep dives and theory for 30 years, feel the math clearly proves the delta P between 10 ata and 6 ata indicates "Blow and Go" would be the safer, better way to approach decompression (better than a slow ascent to 100 feet)...i.e., 25 minutes at 10 ata, then fully inflate BC to 6 ata, dump BC, hang out a few minutes, and go slowly to a 60 foot first deco stop, and slow throughout the balance of the ascent/stops. They don't feel the change in pressure between 10 ata and 6 ata is large enough to justify the much larger saturation which would occurr in the slow "initial ascent" from extreme depth. This would still support adding a deeper first stop for the fit diver, and a much longer 10 and 20 foot stop for the "UNFIT" diver. Regards, Dan >> Ok, if I can paraphrase - The deeper one is the more nitrogen is being >> absorbed because of the higher PP. What you (Buehlmann?) seem to be >> saying is that the intention of the faster ascent rate from depth is to >> get the diver into a shallower depth, where the PP of nitrogen is less, >> in the quickest but safest time then slow the ascent to allow >> off-gassing to take place. That's probably a bit simplistic but in broad >> terms is that correct? > >Yes, that's what the compartment-based models sa - get the hell out of >deep water quicklyy. George is right that Eric can explain the bubble >physics better, but here's my visialization of it: > >The slow initial ascent is to keep the bubbles (which exist already >anyway for a variety of reasons) relatively small. A fast ascent in deep >water will allow the bubbles to get larger, and large bubbles take longer >to "offgas" into the surrounding blood/tissues because the pressure >inside the bubble isproportionally less. It's much more complicated than >this, but you can think of compartmentt-based models (like Buhlmann) as >managing dissolved gas molecules, and bubble-based models as managing >dissolved gas molecules in additio to gas-phase molecules (bubbles). The >upshot when you work out the math is that the bubble models suggest a >need for much deeper initial decompression stops (= slower deep ascents). > >But again, this is all theory - as Robb put it, our lab-coat >rationalization of how it works. All I know for sure is that I feel much >better after long deep decompression dives if I interject additional deep >stops. > >As for computers - I just spent more money getting two EDGE computers >overhauled than it would have cost me to get any one of the fancy new >computers. Why? Two reasons. One, the EDGE is the only computer that >displays whiat I consider to be the only useful information - the tissue >graph. And two, after thousands of dives I have come to learn how to >modify my decompression profile based on what the EDGE tells me - I'm not >sure if my modification algorithm will work on a different computer. >Tables are swell for certain dives, but they are useless to fish-nerds >(like myself) diving all over the place on vertical reef walls. > >Aloha, >Rich >-- >Send mail for the `techdiver' mailing list to `techdiver@terra.net'. >Send subscription/archive requests to `techdiver-request@terra.net'. > > Dan Volker SOUTH FLORIDA DIVE JOURNAL "The Internet magazine for Underwater Photography and mpeg Video" http://www.florida.net/scuba/dive 407-683-3592
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