BigboyDan:We only use the tanks in the same way that there are fire extinguishers hanging in the hallway at our dive shop, or the ones hanging onboard. They are never A PART of the dive plan; they're there for a total failure of a breathing system (eg. hose blows due to a rip or strong yank.) or emergency decos.
I see. So if you're reg get yanked off causing a total failure you just swim back to the line where you have more tanks waiting? I hope you're close...or can swim really fast.