It's time to ditch the CESA. It's not healthy for instructors and it really doesn't teach what we want them to know. The biggest problem is that you should really try to take a breath on the way up. If they do, they get failed. When I first started diving in 1969, I had the worst instructor anyone could ever have. He gave all of his instruction pool side and never even got in the water with the two of us. Back then, I didn't have an SPG, I had a j-valve. Oh, there were SPGs available, but he said we didn't need them. When you breathed it down to your last, you simply reached by your left butt and pulled the rod. Well, that's if the rod wasn't already down. if you were really, really out of gas, swimming to the surface was pretty intuitive. You never had a full breath, and you tried to breath a few time as you made your way up. The bad part was when you reached the surface. We dove without BCs back then, so there was no inflating or floating. We had to swim back to the shore in such a manner that we could breathe. It was incredibly important to be as neutral as possible so you wouldn't drown after.
Caveat: since I started diving with an SPG, I have yet to run out of air. It's my belief that a lack of sufficient neutral buoyancy results in a distraught diver who is so distracted that they can easily run out of air. Most standards don't address being neutral near enough, nor do they address gas management near enough. The best way to do a CESA is never to have to do a CESA. I've done more than enough of them to know I don't ever want my students to have to do them.
Pete,
Given the data that
@boulderjohn has presented, I think more data is required to consider. I'll insert some comments with in his statement:
Actually, something changed, although it has not had an impact on that training.
A few years after this thread ended, PADI and DAN did a study to determine the most common reasons for dive accidents, other than health issues, and see how training could be adjusted accordingly. The number one factor in diver deaths, it turned out, was an air embolism following a diver reaching the surface after a panicked ascent in which the diver likely held his or her breath. This usually followed an OOA event.
In other words, the most likely cause of death was an improperly performed emergency ascent.
Now we are all familiar with Boyle's Law (and I learned what it stands for from you Pete). And we all know that the norm in open water courses is that students are on their knees and overweighted. And we know that extra amount of gas required in a BCD (and/or drysuit) is going to contribute to the ascent rate if not dumped appropriately. So the overweighting is likely. I don't have the data to back this though, just an (un)educated guess. We do know however that the 2016 DAN report found here:
https://www.diversalertnetwork.org/medical/report/AnnualDivingReport-2016Edition.pdf, calls for improved buoyancy control and proper weighting.
I still hear crickets from ALL mainstream agencies (though I could be wrong about a couple agencies) not addressing this, which honestly drives me crazy. We all know that a diver is properly weighted when at the safety stop with a nearly empty cylinder, empty BCD/dry suit, they neither sink nor rise, except with their breath. AND the weight they have is distributed so that they are comfortably (i.e., no sculling) in the horizontal position.
Why this is not explicitly stated in every agencies' open water student manual/materials is beyond me. Why agencies don't require instructors to do weight checks at the end of dives as well, draining cylinders down at the end of the safety stop, and making appropriate adjustments, is also beyond me.
Ladies and gentlemen, we are not quantum physicists. We are not brain surgeons. This isn't complicated stuff. Is it laziness? Incompetence? Rectal-cranial inversion? Why cannot we move forward and not have "get off my lawn" types like me ranting about this?
Following that, PADI training did change in that they made a significantly greater emphasis in training on using the buddy system and especially frequent checking of air supplies. It left the CESA in the course.
Years ago, a thread on ScubaBoard that argued for the elimination of CESA included the fact that BSAC no longer taught CESA. I wrote to BSAC's leadership, and in our email exchange, I was told that their training emphasized making sure that the diver never needs to do a CESA by making sure they cannot run out of air. OK, I said, but what does a diver do if that happens anyway? What does a diver do if they are out of air with no nearby alternate air source? The reply was that they will have to do a CESA--they just will not have been trained on how to do it.
I'd want to see the data from the yearly BSAC report to see if they have the same issue in the incidents in the UK. Obviously BSAC doesn't have 100% of the market there, but I'd gather it is rather sizeable. If they don't have air embolisms at the same rate as the rest of the world, that's a possible red flag for the training conducted in the rest of the world relative to what BSAC provides.
I'm mulling all the statements over, but I don't feel enough data is available.