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> I'd say you CANNOT buddy-breathe with a rebreather. Tell that to the German military guys who train for it. I believe they do it with the buddy breather holding on the back of the other diver, and the front guy (with the working rebreather) passes the mouthpiece up behind his head. > - What do you do with the exhalation when you don't have the mouthpiece? Hold it, unless you are ascending. > - Throw it out, like you do on OC? > - Of course, this will deplete the rebreather gas supply in a jiffy. Then, > to avoid gas depletion, do you keep it in your lungs until you have the > mouthpiece back? Yes, unless you are ascending. > - If you keep it, what do you do if you are ascending, which is perhaps the > likeliest thing to do when one rebreather goes on the fritz? Then you exhale it as you ascend. This won't cause any greater gas loss than the rebreather loses anyway -- remember, the loop/countelungs of a rebreather have to be vented during ascent anyway. This just vents the loop via the divers lungs' (which is what I do anyway when ascending with a rebreather - inhale through mouth, exhale through nose - same thing). > >2) Probably the biggest risk of rebreather diving (at least for > >fully-closed systems) is hypoxia-induced blackout, followed closely by > >hyperoxia-induced convulsions. Both of these are non-fatal per se if > >rectified quickly; so having an attentive buddy could save a life (if the > >buddy corrects the O2 managament problem quickly, and the afflicted > >diver hasn't already drowned). > > Since convulsion is a likely thing to happen, how about using a FFM? This > way, in case of convulsions, the diver does not risk losing the mouthpiece. > In addition, a FFM would likely to reduce the amount of accidental gas > venting (I think). Well, of course a FFM (=full face mask for the acronymically challenged - sorry, Mr. Appleyard ;-) would increase the probability of survival in the event of convulsion or hypoxia-induced blackout *IF* somebody else was around to correct the problem. On a solo rebreather dive, you would die if it was hypoxia. I'm not sure what the probability of surviving an O2-induced convulsion on a rebreather with a FFM is if nobody is around to help correct the problem. Maybe the probability is high? I dunno - I've never convulsed so I don't know how incapacitated one is after such an episode. > Then, I'd say that if you dive a rebreather, whether solo or with someone > else, you get yourself a good bailout system, whether an independant OC or > something integrated with the rebreather. If your point is that all rebreather divers should assume themselves to be alone, and assume they must be able to get themselves out of any situation without assistance, then YES! I totally agree. But that's a separate issue. Buddies on rebreather dives are most useful for helping to solve problems that happen before the afflicted diver ever has a chance to make use of the bailout equipment (such as convulsions or hypoxia). > - When you plan your dive, do you ABSOLUTELY have to plan it around your > bail-out system capacities? I'm not sure what you mean. I will say that about 90% of the logistics of my decompression rebreather dives have to do with providing for open-circuit bailout. If I could reduce the need for OC bailout (such as with a redundant rebreather), these dives would be a helluva lot simpler, and therefore, a helluva lot safer. > - If you buddy-dive with rebreathers, could you conceivably plan your dive > SAFELY around the COMBINED bailout sytem capacities? That's an excellent question that we haven't yet resolved. Here's the deal: To provide for realistic OC bailout, you need to carry with you enough volume of proper mixtures to allow for a controlled return to the nearest staged bottles. The problem, of course, is that the more cylinders you carry with you, the bulkier the rig, which can be a safety problem by itself. The question, then, is should you split the OC bailout supply between two divers, lightening each diver's load. To do this, you need to acknowledge two assumptions: 1) Both divers won't need to conduct an OC bailout simultaneously; and 2) The divers will be close enough to each other throughout the whole dive that, in the event of an emergency, the time delays in initiating the buddy-abort are small enough that they do not lead to wasting too much precious OC gas. I don't have enough experience yet to decide whether the benefits of split-OC bailout supply (less bulk on the diver) outweigh the costs (the two assumptions above, plus the assorted costs of having two people owing big decompression in the water at the same time, plus all other buddy-related costs). My feeling now is to stick with self-sufficiency. Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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