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On 1 Jul 1994, HeimannJ wrote: > Has anyone out there tried using an O2 rebreather for the 10 and 20 fsw > stops? It seems like it would pay for itself pretty quickly (especially if a > surplus one were available) - I probably average $5 per wreck dive just on O2 > fills. I would guess it would have to be modified to keep water out of the > scrubber when it wasn't being used. One of the fundamental problems of using an O2 rebreather on the decompression line is inert-gas buildup in the loop. The point of decompressing is to allow the excess inert gas(es) (diluents) to diffuse across the alveolar membranes from the blood into the exhaled breath. On open circuit, these diluent molecules in the exhale leave the body in the form of bubbles, and each new breath contains 100% oxygen. On closed-circuit, however, the exhaled breath is recirculated. Thus, over time, as your body off-gases N2 (and He), the inert-gas content of the breathing mixture starts to rise. This means that you are no longer breathing 100% oxygen, which means the concentration gradient across the alveolar membranes is reduced, which means the rate of gas elimination from your blood is reduced, which means you're no longer decompressing as efficiently as you would if you were breathing open circuit oxygen. Does this significantly affect decompression? The real answer is that 1) nobody really knows for sure, and 2) the extent to which it would affect decompression depends on the nature of the dive. However, according to John Crea (whose opinions on the topic of diving physiology I often trust more than scientifically documented stuff), it CAN significantly effect decompression efficiency. The solution, therefore is to periodically flush the breathing loop of the rebreather. I haven't yet heard anyone put forth a recommended frequency of flushing, though. Despite this complication, I think you are right - an O2 rebreather would be an effective tool for decompression. It would ALSO be a very useful tool for anyone attempting in-water recompression to treat DCS. For this reason, I asked the rebreather manufacturers at the Key West forum if they might be making inexpensive oxygen rebreathers for such purposes. The general answer I felt I got was that the liability concerns (apparently THE MAJOR road-block to rebreather availability) were GREATER for the O2 rebreathers than for the mixed-gas ones (believe it or not). Translation: "Don't expect them anytime soon". Hope this helps. Aloha, Rich
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