CESA theory

[wetb4igetinthewater]

I am not an Einstein like you.

You have never posted anything more true on SB!

 

[Dody]

total

I try to explain, based on my experience, so that hopefully you will understand.
First of all, every human, if he stops breathing, has still at least one minute, usually two, before passing out. Probably, if CO2 builds up, he/she will feel the need to breath much earlier, but this "need" isn't real, CO2 will not make you to pass out, it is the lack of oxygen causing you to pass out.
At depth, the pp of Oxygen is high. So, even if you take two full minutes for surfacing, the risk of passing out is just in the last 2-3 meters, when you are almost at the surface.
If you manage to surface in less than 2 minutes, there is no risk of passing out; so, if you are down to 30m, or less, you are 100% sure to have enough time for surfacing at a reasonable speed.
But of course there are two other risks: lung over-expansion and drowning.
Lung over-expansion occurs, again, in the last few meters close to the surface, where the gas expansion is large and quick. And this is avoided if you leave your glottis valve open, so that, when the lungs become full during the ascent, the excess air can escape. No need to exhale voluntarily, nor to start exhaling before the lungs are full. For being sure the glottis is open you can emit some continuous sound, usually through your nose, doing "mmmmh".
The other risk is drowning. This happens when the CO2 goes up (as said, this occurs much earlier than the oxygen becomes so low that you pass away). CO2 gives a strong stimulus to breath. If you breath underwater you can inhale water, if the reg is not working, and so you could drown.
People who started as free divers, as me, and only later became scuba divers, are used to resist the urge to breath when the CO2 gives you the stimulus. Some "pure" scuba divers are unprepared to control their body under the pressure to breath. You should train to resist to it, and this training is better done on your sofa, where there is no risk of inhaling water if you cannot resist.
Last point: if you do not have decent free diving capabilities (particularly about kicking efficiently and resisting the urge to breath), then it is quite logic and correct that you are worried to perform a CESA. Nothing to be ashamed of.
In this case there are just two options:
1) Get trained to free diving to the same depth you plan to reach with a scuba system (say 30 meters) - if you can swim down and up again to this depth without breathing, a CESA from that depth will appear to you always feasible.
2) Equip as tech divers do, so that you never need to ascend for solving your problem. This is what I do (albeit having never done anything really "tech"). Instead of a single reg, I always use two fully independent regs, mounted on the two posts of my tank (which is also equipped with a good old reserve mechanism) - it is a 15 liters steel at 232 bars (albeit in some places they fill it up to just 200-210 bars), so I have plenty of air without making use of the reserve, which stays there "just in case" and is not planned to be used, except for true emergencies.
If my main first stage fails, I just close its valve and breath from the other reg. When people here were yet using old yoke regs, I have seen enough failures for understanding that relying on a single reg is barely stupid. Now all my regs are DIN, but I still use two of them: better being safe than sorry...

Thank you very much. But one thing disappointed me. You are one of my heroes in SB. I follow all your posts. I was sure that you were in fact a Tech diver. That I will never be.
I have started free diving training. Went from 30 seconds to 3 minutes but only in static and perfect conditions. I need to practice further.

 

[lexvil]

Simple physics, don’t breath, die.

 

[Angelo Farina]

Thank you very much. But one thing disappointed me. You are one of my heroes in SB. I follow all your posts. I was sure that you were in fact a Tech diver. That I will never be.

I will never be a tech diver, too. Rec is plenty enough!
But please understand, some agencies set the limit between "rec" and "tech" much lower than the organization which trained me (and for which I was a professional rec instructor many years ago), which is CMAS.
My fully-rec CMAS certification is for closed circuit rebreathers (pure oxygen, military-grade) down to 10 meters, and for air down to 50 meters and with mandatory deco, using twin tanks.
This is nowadays considered "tech" from some agencies...
Before all of this, when I was a teenager, I did practice some free diving. At the time everyone here was highly excited about the competition between Enzo Majorca and Jacques Majol, for reaching what, at the time, was considered "the limit": 100 meters. Majol won, reaching this depth before his rival.
So, for us youngsters, "diving" did mean always "free diving". But of course I was a low-level free diver, I think I did never manage to go below 25 meters while free diving, and just for a few seconds at depth.
Just a couple of years after I started diving, I had a severe OOA accident, at a time when both I and my girlfriend were still using a single reg. After that episode, which required to buddy-breath from just a single reg, we immediately purchased our second complete regs, and we did never regret that decision!
But also in that case of a sudden OOA (due to a valve unexpected closure), when I still was a decent free diver, the idea of performing a CESA did not cross my mind. Our training was that the CESA was always the very last solution, and that a diver should generally try first to solve any problem by staying underwater.
Of course it is all related: the usage of the military-style CC rebreather during our training, the fact that being in deco obligation was absolutely normal practice, and the widespread usage of twin tanks as the standard equipment even for novices, plus the fact that there was no BCD and that most scuba divers were not using long, efficient fins, did make a CESA a very bad option. So we were basically trained to avoid it as much as possible. And if you are not comfortable with it (as me), better to take actions which make its necessity a very remote chance.

 

[Dody]

I

I interpret what you've said as you do not have complete understanding of any of those three examples, but you have sufficient understanding to be comfortable using them. So what more do you need to understand about CESA to be comfortable using it? There is a wide range between understanding nothing and total, complete understanding of the physics and physiology. Where is your comfort zone in that range?

I might not have understood what you meant with your questions but you should not presume a lack of knowledge because we misunderstand each other. And the whole point of this thread is that I am not comfortable with CESA below 10 meters. Intellectually. Regardless of what the Instructors told me about rules that I already knew even before starting diving. It might be a mental affliction, I admit.
What I wanted and it might be a dream was that someone would trll me that I have x liters of O2, then between 30 m and 20 m, y happens and between 20 to 10, z happens and so on. Maybe I was asking for too much, asking for things people can’t answer. That’s fine. I will continue looking…

 

[TMHeimer]

Here's the deal. If you are out of gas at 30 meters you have two choices. Stay there and die or head for the surface. All of your questions are irrelevant if you're 30 meters deep and out of gas.

Bottom line is keep your airway open on the way up. If you end up bent so be it. Rather be bent on the surface than dead on the bottom.

Right. When I was doing my AOW years ago I asked the instructor what you do if you're down that deep and maybe too deep for a CESA?
He said "you do it anyway".

 

[Dody]

Right. When I was doing my AOW years ago I asked the instructor what you do if you're down that deep and maybe too deep for a CESA?
He said "you do it anyway".

Mine said the same thing. But he added: Pray. And that’s not good enough for me. I don’t believe in God

 

[tursiops]

I am not comfortable with CESA below 10 meters. Intellectually.

What is it about 10m that is so special? Could you imagine doing it from 11m? 12m? 13m?

You say you read your dive computer manual thoroughly and understand it. but that does not tell you how the DC actually works...what calculations it is making to tell you you have 7 more minutes of NDL. So you are clearly comfortable with less than total knowledge about a tool you are using. In fact, you are comfortable with a CESA from 10m without understanding the details of what is happening. I'm trying to understand what knowledge you need to expand your comfort zone, from 10m to, say, 20m. You know all the physics....so what is missing?

 

[lowwall]

Try this at home, get a large plastic bag and put it over your head and do slow breathing and feel the effect.

Umm. Don't do that. The point at which you feel the effect may be beyond the point at which you are capable of removing the bag. Thanks.

 

[BlueTrin]

Mine said the same thing. But he added: Pray. And that’s not good enough for me. I don’t believe in God

Pretty sure pray is optional