I currently teach reg in the mouth. I was addressing the OP that I, too, learned to jettison the reg in initial training 37 years ago and the thought process for it at the time.
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It's all about limits. Before you dive, you should agree on both turn and thumb pressures. Turn pressure is half your gas less the thumb pressure. Thumb pressure is your depth x10 (imperial), with 600psi as an absolute limit. This is in addition to figuring out if you have enough gas to do the dive you want to do. Say my SAC is 0.8 and I want to dive to 100 ft.Something I don't understand about gas planning.
Ken, if they were given the power of control in their classes, then neither would happen. It's not hard, but instructors have to make a commitment to turn out divers who are in control of their depth with a modicum of situational and buddy awareness.
I understood your point and it has some merit. It's my opinion that an out of control diver is so preoccupied by trying to establish control that they neglect things like gas pressures and buddy whereabouts. Teach your diver proper trim and neutral buoyancy and they can easily track these two things. A diver who's plummeting, followed by an uncontrolled ascent, followed by another plunge is already so dangerously close to panicking that they don't have the mental resources to read their SPG much less keep track of their buddy. Imagine when this near hysterical diver actually runs out of air? His training has already failed him, so we can't expect him to resort to it now. Their near hysteria will instantly devolve into sheer panic and the diver is well on their way to injuring or killing themselves. The one or two CESAs they did in their OW class are the furthest thing from their mind. If you want to give a diver confidence: teach them trim and buoyancy. The best CESA is the one you avoid having to make. An ounce of this prevention is worth a ton of CESA cure.My point is
My thinking is more that one will become more comfortable with the situation of having to rely on only the gas that is in one's lungs to reach the surface. Obviously if someone is unable to both learn freediving and remember to exhale while ascending after breathing SCUBA they ought not learn both. Or either, I imagine.Free diving classes will teach you to hold your breath and ascend rapidly. Not exactly the best training to fall back on when your lungs are even partially filled with compressed gas.
If I aa relative of mine died after a panicked OOG ascent, and I found out you told them they had no safe option without an alternate air source and were going to die under those circumstances, you can you would lose that lawsuit big time.My point is that the instructor givens them an ‘easy out’. If you believe a CESA is an option then you still have an option so can afford to be less diligent about the rest of it. If on the other hand the instructor tells you that if you run out of gas without an alternatively or a buddy you will very likely die then maybe the instructor is properly emphasising the need for awareness and so forth.
Finally, as I pointed out earlier, as you ascend to shallower depths and lesser ambient pressures, the regulator will once again be able to give you air. That will only happen, though, if the regulator is in the mouth.