Just as a final point, I believe that almost all agencies do a very poor job teaching emergency ascents. During my 17 years as professional, I have twice had extensive discussions with PADI about this. I did not convince them either time, and they did not convince me. The main benefit to those discussions is that I really know well what their beliefs are.
One problem I have is that they do not include the information I posted above about the regulator being able to deliver air during the ascent. Their explanation for that is that while it may be true in a normal OOA ascent, it is possible that there was some sort of regulator failure that would make it inoperable at any depth. (That is what they are really training you for--a truly rare regulator failure, not going OOA.)
A second problem is the exercise they do in the pool sessions called the air depletion exercise. In that exercise, the instructor is supposed to shut off the student's air, and the student is supposed to signal OOA upon realizing they have no air. I imagine that for the last couple decades, people have wondered what the point of that might be. Well, if you go back and read the literature when the idea was first hatched, you see the point of it. Regulators were not as good then, and it would feel harder to breathe as you got close to zero. The point was to get you to recognize that you were about to run out of air so you could prepare for it. With modern regulators, you will not experience that with your air shut off in the bottom of a swimming pool. It will, however, happen at depth with a tank that is low on air. You should have a warning of a couple breaths before you are OOA. The air depletion exercise teaches students the opposite of its original intent. (In this exercise, you can mimic a true OOA experience by almost, but not quite, shutting off the student's air. In that case, they will feel it getting harder to breathe.)
The main problem is the horizontal CESA in the pool. Students have to swim relatively slowly for 30 feet while exhaling the whole way. Most students find that difficult, and instructors resort to a host of tricks to get them to make it the whole way. Many have to try it more than once to make it. It is difficult because even if they ascend on a diagonal from the deep end of the pool, they are not getting the true expanding air experience. This teaches them the exact wrong thing--in a real emergency from any deeper than that, I won't make it!
A joint PADI/DAN study about a decade ago found that the most common cause of death in a scuba accident (not talking about things like heart attacks) is an air embolism following a panicked ascent to the surface, usually following an OOA incident. In other words, the divers likely died because they held their breath doing an emergency ascent after going OOA. I fully believe that many of those deaths were caused by the "I'm never going to make it!" belief instilled in students during their initial training.
One problem I have is that they do not include the information I posted above about the regulator being able to deliver air during the ascent. Their explanation for that is that while it may be true in a normal OOA ascent, it is possible that there was some sort of regulator failure that would make it inoperable at any depth. (That is what they are really training you for--a truly rare regulator failure, not going OOA.)
A second problem is the exercise they do in the pool sessions called the air depletion exercise. In that exercise, the instructor is supposed to shut off the student's air, and the student is supposed to signal OOA upon realizing they have no air. I imagine that for the last couple decades, people have wondered what the point of that might be. Well, if you go back and read the literature when the idea was first hatched, you see the point of it. Regulators were not as good then, and it would feel harder to breathe as you got close to zero. The point was to get you to recognize that you were about to run out of air so you could prepare for it. With modern regulators, you will not experience that with your air shut off in the bottom of a swimming pool. It will, however, happen at depth with a tank that is low on air. You should have a warning of a couple breaths before you are OOA. The air depletion exercise teaches students the opposite of its original intent. (In this exercise, you can mimic a true OOA experience by almost, but not quite, shutting off the student's air. In that case, they will feel it getting harder to breathe.)
The main problem is the horizontal CESA in the pool. Students have to swim relatively slowly for 30 feet while exhaling the whole way. Most students find that difficult, and instructors resort to a host of tricks to get them to make it the whole way. Many have to try it more than once to make it. It is difficult because even if they ascend on a diagonal from the deep end of the pool, they are not getting the true expanding air experience. This teaches them the exact wrong thing--in a real emergency from any deeper than that, I won't make it!
A joint PADI/DAN study about a decade ago found that the most common cause of death in a scuba accident (not talking about things like heart attacks) is an air embolism following a panicked ascent to the surface, usually following an OOA incident. In other words, the divers likely died because they held their breath doing an emergency ascent after going OOA. I fully believe that many of those deaths were caused by the "I'm never going to make it!" belief instilled in students during their initial training.
