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> For me, it all started from two factors some 10-15 years ago, when > 'deep' dives were 50-55m. It was customary to do a main (deep) dive out > in the English channel, then do a 20m or shallower dive close inshore > on the way in. [...] > Anyway, a few people got 'niggles', generally a few hours after the > second dive, and there was one or two cases of arm joint/ muscle bends > that required recompression. The Royal Navy 'pot' at Portland Bill > forcibly told these unfortunates that they thought two dives in one day > was a very bad thing to do when one or more was 'deep'. (They also > thought that letting divers control their own decompression stops was > crazy). The second dives were phased out after deep first dives, and > the niggles stopped occurring. Interestingly, in the old days I would tend to have problems much more frequently on days when I did a deep (>55m) dive followed by a shallowish (20-30m) second dive, than on days when I would do two or more deep dives. Surface interval was the same, decompression "conservatism" (staying 20ft below the ceiling, clearing at 20 feet, staying 15 extra minutes, etc.) was the same. Go figure... > 2. If you subscribe to the micro-bubble theory, you need to have a > long-enough surface interval such that no micro-bubbles remain in the > blood at the start of the second dive. Anyone know how long this is? I think the micronuclei are ALWAYS there (except some theories hold that deep dives might crush a few into oblivion). The differences is in how big the gas-phase bubbles are. That's why when I do multiple deep dives, I'm more "bubble conscious" than "tissue compartment conscious" in my decompression planning. Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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