Is it time to sink the CESA?

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I can't possibly improve upon @boulderjohn's post, but I completely agree. Doing the CESA horizontally in the pool gave me exactly that mistaken impression--that it was quite difficult to cover such a distance on a single breath, and basically impossible for someone of my marginal fitness level unless I started with full lungs and exhaled sparingly while kicking hard all the way to get there in time. Doing it vertically was a completely different experience, as I felt the air expanding to pour out of my lungs, while I became so buoyant I had to work to slow my ascent almost the whole way. Even if I never need to do a CESA in real life, I feel like this exercise made me understand Boyle's law in a visceral way that stayed with me far better than any classroom lesson. It also made me far less likely to panic in an OOA situation, because I know that ascending on one breath is much easier than swimming that distance in a pool on one breath.
 
I can't possibly improve upon @boulderjohn's post, but I completely agree. Doing the CESA horizontally in the pool gave me exactly that mistaken impression--that it was quite difficult to cover such a distance on a single breath, and basically impossible for someone of my marginal fitness level unless I started with full lungs and exhaled sparingly while kicking hard all the way to get there in time. Doing it vertically was a completely different experience, as I felt the air expanding to pour out of my lungs, while I became so buoyant I had to work to slow my ascent almost the whole way. Even if I never need to do a CESA in real life, I feel like this exercise made me understand Boyle's law in a visceral way that stayed with me far better than any classroom lesson. It also made me far less likely to panic in an OOA situation, because I know that ascending on one breath is much easier than swimming that distance in a pool on one breath.

What if (in a real situation) you lose the ability to get air from the tank AFTER you have exhaled? What if you were deliberately heavy when the problem developed, like say you were on the bottom and trying to be stable to take a photograph? What if there was no way to add air to your BC? What if you (as some people advocate) have zero ditchable ballast?

I can think of a lot of potential situations, which COULD make an actual CESA much more challenging than a relaxed 30 second swim in a pool where you know the surface is just a few feet above your head.
 
What if (in a real situation) you lose the ability to get air from the tank AFTER you have exhaled? What if you were deliberately heavy when the problem developed, like say you were on the bottom and trying to be stable to take a photograph? What if there was no way to add air to your BC? What if you (as some people advocate) have zero ditchable ballast?

I can think of a lot of potential situations, which COULD make an actual CESA much more challenging than a relaxed 30 second swim in a pool where you know the surface is just a few feet above your head.
Sure, that would be more difficult. I'm not saying the exercise taught me I don't need to monitor my air or stay with my buddy. I'm saying it helped me understand the physics and made me less prone to panic. FWIW, we started our OW vertical CESA with only half a breath, and I could still feel it filling and then overflowing my lungs. I could also feel how, even though I started out slightly negative, I quickly became positive and had to vent air from my BC. That's an important concept to internalize; doing it in the pool, I had to keep kicking the whole way, as I became increasingly desperate to take a breath; in the ocean, I just had to get moving, and then I actually had to slow my momentum.
 
What if (in a real situation) you lose the ability to get air from the tank AFTER you have exhaled?
Why would that be, to begin with? But it doesn't matter. Navy divers working on submarine escapes have done emergency ascents with no tanks at all, and they were trained to exhale before beginning the ascent so that their lungs would not have too much air. When you exhale, you only exhale about half the air in your lungs, so you still have plenty for the ascent.

What if you were deliberately heavy when the problem developed, like say you were on the bottom and trying to be stable to take a photograph?
Let's start by saying that if you are deliberately negatively buoyant to be stable for a photograph, you have really lousy buoyancy control and should take a class to get better before you destroy the environment you are trying to photograph. But if that was indeed the case, then you can ditch weights, inflate the BCD, or both.

What if there was no way to add air to your BC?
In a normal situation, there is no need to add air to the BCD. In a CESA (CONTROLLED emergency ascent), you dump air from the BCD to avoid an uncontrolled ascent.

What if you (as some people advocate) have zero ditchable ballast?
Those who advocate it say that you should be able to swim the weight you have up to the surface without difficulty. If not, you need redundant buoyancy.
 
In 30 years of open water diving I've never truly run out of air and had to do a CESA. I've been low on air and had to surface to keep from running out but never run out or had to make a mad dash to the surface. Then I use an AI computer and frequently check my air supply. I guess there's a minute chance of a catastrophic supply failure combined with buddy separation, but aside from that there is no excuse for running out of air.
 
Learning a cesa is one thing, and it's a good thing to know. But what is even more important is what to do when one surfaces. The diver likely ran out of air at depth ...20?...30 meters....and requires a safety stop or even deco.
So, grab another tank and descend again? Oxygen tank on board?
I remember the cesa in PADI classes 20 years ago. Looking back, from what I know now, a bit of free dive classes would be a good additive to an OW course.
 
Sure, that would be more difficult. I'm not saying the exercise taught me I don't need to monitor my air or stay with my buddy. I'm saying it helped me understand the physics and made me less prone to panic. FWIW, we started our OW vertical CESA with only half a breath, and I could still feel it filling and then overflowing my lungs. I could also feel how, even though I started out slightly negative, I quickly became positive and had to vent air from my BC. That's an important concept to internalize; doing it in the pool, I had to keep kicking the whole way, as I became increasingly desperate to take a breath; in the ocean, I just had to get moving, and then I actually had to slow my momentum.

I think it is probably good to practice an actual vertical CESA. I just wanted to throw out a few ideas that might be relevant to an actual loss of air supply. This is different than a diver being inattentive and running their tank down so low that it was beginning to be hard to inhale. Reducing the panic threshold and instilling confidence is a very valid reason for practicing it.
 
The diver likely ran out of air at depth ...20?...30 meters....and requires a safety stop or even deco.
A safety stop should be just an extra precaution on an NDL dive. Most experts contend that there is no reason to redescend and do one if it is missed for any reason, especially after the time needed to swap out a new tank.

According to common definitions (and some disagree, I know), if you owe a decompression stop, you are on a technical dive. The key difference between a technical dive and a recreational dive is a "ceiling" of some kind preventing you from going directly to the surface. A "hard ceiling" is the roof of a cave or wreck; a "soft ceiling" is a decompression obligation. If you are doing a decompression dive, you are supposed to have a redundant air source, because you know you cannot do a CESA. But what if you screw up and really do need to a CESA while having a decompression obligation? Different agencies advocate different things, but most do recommend an immediate return to depth for an extended decompression stop. If, however, you need to wait long enough to get another cylinder, the recommendation is that you do NOT redescend but rather watch carefully for DCS symptoms and breathe oxygen if available. If DCS symptoms do occur, head for a chamber ASAP. If it is not possible, in-water recompression can be done with the right equipment, but that need should be very rare--better to head for treatment.
 
I have had students bolt to the surface during the Basic Open Water and Advanced Open Water Courses, and also while DM'ing dives for groups. I would expect the divers to know not to ever hold their breath while breathing compressed air underwater. But task overloading and panic induced by whatever can cause a person to hold their breath unless some sort of positive muscle memory is developed during training. I strongly encourage the CESA remain in the curriculum. In fact, I have seen way more divers perform an improper ascent than I see equipment failures or out of air incidents. Some just plain bolt, some exceed the 30 fpm rule.
 
I found it useful and pretty easy to pass on the first attempt, which included manually inflating my BC.

I defer to the experts, but I think it was valuable so I knew it could be done easily, how to do it and to ensure I was at least physically and mentally present enough to inflate the BC manually once at the surface.
 

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