From 12m, all you'd need to do is hold your breath and surface rapidly to give yourself a potentially fatal lung injury. Note that this is exactly what you woul

From 12m, all you'd need to do is hold your breath and surface rapidly to give yourself a potentially fatal lung injury. Note that this is exactly what you would reflexively want to do in nearly any emergency or if you just got claustrophobic in the mask and reg (common) or had a sudden abyss panic (not uncommon) or even a trivial even like having your mask kicked off by a buddy. Recreational training should include a half dozen or so pool dives to practice skills. This gives you the training and confidence to cleanly handle minor emergencies, followed by three or four supervised training dives to test those skills in a real environment, and to give you a comfort level that gelps prevent panicy action later. Those first few dives to shallow depth are actually among the most dangerous you ever do, because you're a novice in an environment where your reflexes will kill you.