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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. I submit that the efficacy of the missed deco procedure is not matter of black and white. It depends, among other things, on how bad the violation was. Can we agree that if you blow a stop by some short interval going back down to do the stop, and possibly extending it a bit, up to the recommendations we've been discussing , is a good idea? If so, unless you consider violating a stop by 10 feet for even a few seconds is too much to try to make up this becomes a question of where to draw the line? Somewhere between a few seconds and five minutes, I would think. The schedules we find in tables aren't so precise that going one foot past a stop for five seconds is likely to get you bent if you go back down and finish the stop. At least you'd have a much better chance of not getting bent than if you just say "I've blown it!" and surface after such a minor violation with several minutes left to do. That is why computers have alarms which give you a chance to correct a mistake and back off a bit. Aladins allow two minutes above the indicated stop depth before recording a violation. The instruction manual even says that you can do dives with stops below 80 feet, which is the deepest stop it will display, by feeling for the ceiling using the deco alarm. (I am not saying that I like that idea, nor that I would want to be doing a dive involving a stop below 80 feet using air. If the dive is not too deep for air but is long and deep enough to require a 90 foot stop I believe that the length of the decompression would be unreasonable. Deeper stops are normal on even minimal trimix dives, using nitrox and oxygen to accelarate decompression, but I wouldn't be using my computer for these dives. Actually my deepest stop so far using air has been 50 feet, and most of the times my computer has shown a 50 foot stop it has cleared to 40 or less before I reached 50 feet. Has anyone on this mailing list had to do a stop deeper than 80 feet on an air dive?) 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? How about if you just hit the surface when you meant to stop at 10 feet, because of carelessness, task loading, or some other problem? A buddy of mine (not diving with me at the time) once got blown past his stop coming out of a high flow cave. I don't know all the circumstances. He was inexperienced at the time, especially in high flow and low visibility. He may also have been distracted by the task of winding in the guide line. This was at Little River (Branford, Florida) when the river was high and there was tannic water in basin, for those who know the place. He was able to go back down immediately and did not get bent. Had he not gone back down he most likely would have been bent. Would you say he should have just headed straight for the hospital without going back down? > While we all know that prevention is better than cure, a cure is > sometimes necessary. I would toss out this air-based recompression > procedure and instead look seriously at adding the necessary support > for the Australian method. It's main selling point in my eyes is that > it can be interrupted whenever more qualified help arrives without > worsening symptoms. Also, since you breathe pure O2 during the entire > treatment, your nitrogen accumulation never increases. The Australian method is intended for circumstances where qualified help is not going to arrive within the two to three hours this kind of treatment takes. In any case the Australian method and the missed deco method are intended for different circumstances. But by all means if enough oxygen and a full face mask and attendant are available breathe pure O2 during any reimmersion intended to prevent DCS, too. I'd even say that for me availability of oxygen for use at 20 and 10 feet would move the line of when to attempt to make up missed deco a bit further into the violation zone. I'm not sure exactly where I would draw the line either, though it would surely be on the safe side of the five minute limit. And I hope never to be in this situation. 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. Bill Mayne
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