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> Yes, of course, but the rebreather DEPENDS on the exhalate to replenish > the breathable gas supply, so one is compelled to exhale back in to the > rebreather, a difficult thing to do when you don't have the mouthpiece in > your mouth. You'd have to hold your breath until you get back the > mouthpiece, exhale quickly, then inhale. Since you'll most likely be > ascending, I don't think it's a good idea to hold your breath while going up... As I've said before, you need to purge the gas out of the loop of a rebreather during ascent anyway, so there is no extra gas loss. Think of it this way: at a given depth, the total loop volume of a buddy pair breathing from a rebreather consists of the gas in the rebreather loop, plus the gas in the two divers' lungs. As the divers ascend, this gas expands. Whether there is only one diver or two breathing off the unit, gas has to be vented in order to maintain the total loop volume relatively constant. If done correctly, the diver without the moutpiece does all this venting during the ascent (i.e., they trade off venting during the ascent, who ever is without the moutpiece). For clarity, lets plug in some very simple numbers. Suppose the ambient pressure is reduced by one half during a given buddy-breathe cycle (this is unrealistic - they will be passing the mouthpiece back and forth much more frequently than this, but it doesn't matter for illustative purposes, so we'll keep the numbers simple). O.K. This means that the diver without the mouthpiece (will call him/her the "1st diver") must exhale a minimum of one half of the gas molecules in his/her lungs during this ascent interval so as not to experience AGE/pneumothorax. Meanwhile, the diver with the mouthpiece (2nd diver) is not exhaling anything into the water, so the volume of gas in the rebreather plus the 2nd diver's lungs has just doubled. Unless the first diver's lung capacity exceeds the combined volume of the 2nd divers lungs *and* the rebreather loop (not figgin' likely), then the net volume of the total system (rebreather plus both divers lungs) has increased during the ascent interval, even though the 1st diver exhaled half his/her lung volume. In other words, they'll have to vent more gas than the non-mouthpiece diver must exhale to avoid lung overexpansion. There is a relatively large margin for error, because in addition to venting off the excess volume, the rebreather loop must be purged even *more* to flush out the excess diluent and replace with O2 (assuming constant PO2). Trust me on this: buddy-breathing rebreather divers will not lose any more gas volume on ascent than a single rebreather diver would under normal circumstances, as long as the buddy breathing drill and ascent is done correctly. The problem with all of this is that doing it correctly is a very tricky process that requires lots and lots of practice/training. In my experience, it make more logistic sense to provide each diver with his/her own OC bailout route to the surface. Aloha, Rich
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