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William Mayne > > Dave Story writes: > > > > ... I disagree that this air-based > > "missed deco" procedure is worth trying. This procedure is one of > > those which has percolated around and bubbles up everywhere, despite > > the best efforts of some people to stop it. > [... good discussion elided ...] > The question then is how far above a required stop can you go and > how long can you take to get back down before you should give up > and head for a chamber. Maybe 10 feet is too much. Maybe 5 minutes > is too long. Where do you draw the line? I agree, there is no black and white --- not with today's models. I should also point out that it's easy to argue from a smug position, e.g., "I'd never let that happen," and I'm glad Bill has carefully culled out the real question. Let me carefully state my objections to this "missed deco" method: 1) The procedure appears formal and authoritative, thus engendering trust, yet it is based on the misapplication of invalid information. As such, it is semi-fraudulent to perpetuate this method. 2) The steps in this procedure appear arbitrary and thus are suspect. The theory does not appear to be trustworthy. Has anyone ever seen an explanation of this? Where did this 1/4, 1/3, 1/2 stuff come from? What happens on deep stops? Does this apply to EANx and heliox? I also seem to recall an earlier version in which the initial stop was 5/4 @ 40', not 1/4 @ 40'! > Realistically if I can't get back down within a matter of seconds, > which I would choose to try, I would have little chance of making it > within five minutes, anyway. So for me the grey area doesn't matter much. I'm not saying I think 5 minutes couldn't be realistic, for some dives. I would be willing to wager (theoretically, not with my body!) that for a long, looong, shallow dive in which you missed a long stop at 10 or even 20fsw, 5 minutes might not be enough time to form symptomatic bubbles. I don't think 5 minutes of high-stress and probably high-exertion surface time is valid for the common case of deep decompression dives. Bubbles have formed in those 5 minutes if your fast tissues are controlling! Recompressing on air will force bubbles trapped in the lung's capillary bed through the bed and into the arterial circulation, where they are guaranteed to be trapped in capillaries that are not as tolerant. I'd rather have those bubbles in my lungs than in my brain, especially since my lungs have a lower dissolved pN2 than remote tissues that are still offgassing. That said, I don't know where to draw the line either, but I refuse to recommend any procedure which has nothing to recommend it. If someone were to present the theory underlying this procedure, I might rethink, but I don't think the theory exists. In the meanwhile, I consider this procedure an old, inapplicable, and untested, most likely copied incompletely from some Navy scrimshaw ages ago, and resurfacing anew when these problems are being faced by the next generation. History repeats.... Safe diving, David Story NAUI AI Z9588, PADI DM 43922, EMT story@be*.wp*.sg*.co* Every dive is a decompression dive.
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