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>From: Rodney Nairne <rnairne@sy*.DI*.oz*.au*> > >Here in Sydney Australia we descend as quickly as possible, in order to >maximise time spent on the wrecks. When the conditions are good, we have >exeeded descent rates of 50 mtrs (165ft) per min. > >Hearing about Shecks problems with descent rates, I was wondering if the huge >gas pressure gradients produced by fast descents could be detremental in the >75 to 120mtr range, on Helair mixes. Rod, I used to descend as fast as possible for the reasons you state, however, recently I have been slowing down due to something I read in Edmonds "Diving and subaquatic medicine" textbook. He mentioned that one possible explanation for Dysbaric Osteonecrosis was the large tissue pressure gradients caused by rapid descent. I suspect the deeper you go, the more significant this problem. The other thing to consider is that the table models assume a specified descent rate (e.g: 18 m/min) and by exceeding this, you are bending the model as you will be spending more time at depth than the model calculates. So for very fast descent rates, you should probably assume a longer than measured bottom time when calculating decompression requirements. These effects would become more pronounced with increasing bottom depth. Cheers, David. ______________________________________________________________________________ David Giddy, | Voice: +61 3 253 6388 Telstra Corporation, | Fax: +61 3 253 6144 P.O. Box 249, Rosebank MDC, 3169, AUSTRALIA | Internet: d.giddy@tr*.oz*.au* ------------------------------------------------------------------------------
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