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JR Oldroyd writes: > The algorithm suggested was to get the spare tank. Then, IF AND ONLY IF > no DCS symptoms were present, to get back into the water. Then descend > to: > > 12m for 1/4 of your originally-planned 3m deco time > 9m for 1/3 of your originally-planned 3m deco time > 6m for 1/2 of your originally-planned 3m deco time > and > 3m for 1.5 of your originally-planned 3m deco time >... > Now, I have not had a need to try this out. I'm wondering if anyone > else here has. Specifically, I'm interested in comments on the actual > algorithm here. If you had to do this, would you use these timings and > depths? I think this applies mostly to open water divers, since cave divers generally have a much easier and safer situation for decompressing and should be able to avoid the problem this is designed to solve. I'm referring only to missing stops, not to danger such as undesireable profiles which may be forced upon cave divers. Answering only for myself, I doubt that I would ever need to do this, and not just because of the greater safety of decompressing in cave diving. There are aren't any caves in Florida which are so remote that it would be impossible to get to a chamber within a reasonable length of time. It is also doubtful that I'd be able to get out of the water, leave my doubles, run up to my truck for another tank, get a regulator and put it on the tank, run back to the water, and descend within the five minute limit given in the DAN booklet describing this procedure. All the exertion involved in doing that would be a very bad idea, anyway. I also figure before the dive that a tank in my truck isn't going to do me any good. It only takes a few minutes to get the tank ready and place it in the water at the start of the dive just in case. That few minutes of preparation avoids a possible dilemma later. But in principle I don't see anything wrong with trying the procedure above, provided it can be done without unreasonable delay and exertion, especially if oxygen is available for the 20 and 10 foot stops. > If you'd broken decompression deeper than 12m, would you restart > deeper? My understanding of the procedure is that you make up any missed stops deeper than 40 feet (12m) before starting this modified schedule. This is a difficult call, though. If you've missed a stop that deep you are looking at a very high probability of getting bent if you do nothing, and more risk of developing a serious problem either before you can manage to go back down (in which case you shouldn't go back down) or after you go down. You are also most likely looking at a rather long decompression schedule, with 2 7/12 times the already long 10 foot stop spent at 40 feet and above. If you can't complete that and you don't have oxygen available you should think twice about going down and soaking up more nitrogen. Although in water treatment of DCS is a different matter than prevention by quickly making up missed decompression I think some comments from the instructions for using trimix tables by Hamilton Research are relevant. Note especially the last sentence. "In Australia where distances to dive sites are great and chambers are often not immediately available, a procedure for inwater [sic] recompression treatment using oxygen has been developed (Edmonds et al, 1983). This table is included in Appendix B. [It is also in Gilliam's book.] This procedure should of course only be used with oxygen. It is less effective than treatment in a chamber, but when conducted properly it is regarded as being better than no treatment at all. In any case the operational factors should be weighed carefully, and this should clearly be the proper course before it is undertaken. We do not advise against using these procedures (with great care), but we strongly advise against getting into a situation where they might be needed." Bill Mayne
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