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> >> My understanding is that emptying the breathing bag 2 or 3 times by exhaling >> through the nose should work, > > My understanding is that purging n times wastes n bagfuls and n lungfuls of >oxygen and grossly shortens the dive. I see no need for more than: empty bag >and your lungs as far as you can, then start breathing from the set, then >purge once. Am I the only one this makes nervous? We've got someone who apparently has a rebreather they have neither directions or training for, and two levels of "I gather" type notions to guide him in how to use it. Or is this just a troll? Anyhow, I'll bite.... My copy of BASIC SCUBA DIVING, circa 1964 (and surely one of the last introductory SCUBA texts to give full directions for rebreather use!) recommends purging three or four cycles. An older US Navy dive manual says to do it until the bag is completely flat, then every hour and before beginning an ascent. This is for a plain jane manually operated straight 02 rig. There are a lot of newer ones offering one degree or another of automation, mixture control, or gas mix options, each of which requires specialized techniques and training. Exhaling during the purge cycles, "I gather" is not just a matter of exhaling through the nose, since any exhaled gasses that make it back into the bag defeat the process - it's necessary to have either a three way valve that allows blocking the flow back to the bag, or else to crimp the hose with your fingers to block it off. Has anyone else had any experience using a rebreather just for decom use? It doesn't seem like an optimum use at all, because of the chances of water getting into the bag while the outfit is hanging (doubly a problem with any rebreather not made specifically for diving and using absorbents like caustics and hyperoxides which are intolerant of water), and the difficulty of effectively doing an effective initial purge underwater. It would also probably be a good idea to purge more often, in decom use, since one would be outgassing significant amounts of nitrogen. Experienced, trained rebreather divers still manage to die using rebreathers, and the record is much worse for rebreathers not specifically designed for diving (like the mine gas masks common in the USA after WW2, or the surplus Soviet ones turning up on the surplus market now). Anyone considering using one should be very sure of the accuracy of their information and their understanding of the subtleties involved. >--
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