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I really prefer to talk about strategies for AVOIDING ever having to think about things like BC breathing . . . come on, guys! The only reason you'd ever consider it would be if you were completely out of gas, too deep for a comfortable CESA, and out of reach of a buddy. There is no excuse for running out of gas, but there are a couple of reasons why one's equipment might stop delivering it (or overdeliver it). So at that point, you have a buddy to share with and you do an ascent as you were taught. If you are diving without a buddy nearby, you ought to have a redundant gas source.
Planning and avoidance beats a toolbox of reactions any day.