You are in fact giving away your bailout, but the fact of the matter is if your diving as a team you are only planning for one failure. ie Say for example you are planning a cave dive with another CCR diver. The rule is you need 1.5 times the amount of bailout gas to get
one diver out. So thoeretically what should happen is when the diver on the bailout only breaths down his B/O lets say a third and then while swimming you and your buddy should swap B/O's so that in that case you would always have a B/O with some sort of gas in them. This is a skill that we practice cave diving
Now if your diving with and O/C buddy that could be a bit different. I usally carry an 80 because most of the time that equals at least 1/3 of the O/C divers back gas. The same rule still applies in this situation as well except your relying on the O/C diver using the rule of thirds with his back gas for you to use. The best configuration for the CCR diver in my mind would be to split the bailout gas. ie if you need 80 cuft carry 2 X 40's or CCR diver carry one and get the O/C diver to carry the other
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Scott