IIRC, the average air consumption is about 1 cu. ft./ min. at atmospheric pressure. Assuming the bladder is not pressurized, at a guess it could hold ~2 cu. ft

IIRC, the average air consumption is about 1 cu. ft./ min. at atmospheric pressure. Assuming the bladder is not pressurized, at a guess it could hold ~2 cu. ft., so maybe a couple minutes worth of air. If you could manage to submerge, that would be substantially longer than the average person can hold their breath, maybe enough to be worth it. (Notice the "if".)