CESA theory

[rhwestfall]

substitute "hope for the best" then....

 

[BlueTrin]

bring a pony

At least that’s not controversial here

 

[lowwall]

I assume that's a forceful, complete exhale? That's the point. As you ascend, your lungs inflate -- just as if you breathed. Further, the urge to breath is less because the partial pressure of CO2 drops as you ascend.

Why not simulate this sitting in your chair? Normal tidal volume is 0.5 liters. The expansion from 30 ft is another liter (doubling of the residual volume). Exhale and start a stopwatch. Can you make it 30 seconds on two normal breaths? I'm pretty sure you can.

ETA: you may be able make 30 seconds without breathing at all after the exhale. This is harder on the surface because of the CO2 buildup. When ascending, that partial pressure is reduced by about 50% compared to sitting in your chair. Can you exhale and not inhale for 15 seconds? A real ascent from 30 ft would be easier.

Again, the issue will be avoiding barotrauma, not blacking out from O2 deprevation or fighting the urge to take a breath.

Exactly. I just did a 40 second exhale with no problem. My normal exhale when diving is longer than 15 seconds. I kind of just dribble the air out through the reg. I was a competitive swimmer and trumpet player, both of which require short inhales and relatively long exhales so it's a breathing pattern I'm used to. It also conserves gas.

 

[NW Dive Dawg]

Ok.... so I just read this entire thread....and most importantly the original question from the OP... I think the simple answer is that there is no real answer as to what "might" happen or what it might "feel" like. Since we all absorb 02 at different rates, we all typically exhale at different rates, we all typically have different SAC rates and MOST importantly, we all manage stress differently which will most definitely affect all of the above.

In general any gas left is going to expand upon ascent and more exaggeratedly as you approach the surface.

I also very much agree with the previous post from Tursiops regarding "humming" rather than "exhaling". The entire point is to conserve, utilize and maximize any expanding gas during the CESA. By even just slightly and "barely" "humming" you are keeping your airway open the bare minimum necessary to avoid an over expansion injury.......while maximizing any remining air.. Just slightly hum and the expansion fairies will take care of the rest for you.

Last but not least.... and even at the risk of segueing off of the OP's original question...... I don't worry too much about ever having to do a CESA from any depth.......because I always have Silent Bob with me!

 

[David Novo]

@Dody probably understanding how those people ended in a situation that required a CESA would be more productive for your future diving career.

 

[David Novo]

Just so that you understand my behaviour (or questions). I hate not being in control. I know control can be an illusion but like most human I happily accept this illusion. When I don’t feel something that I might have to do someday, I feel vulnerable like a baby.
I have a good and old friend. Very experienced diver certified in France, GUE Instructor (the only one who accepts diving with a cigar smoker ), over 1000 dives. We plan to go diving together for the first time in Thailand in a couple of weeks. I was drinking his words talking about the plan but when he told me about a story where he was alone at 30 m, had first stage failure, closed his valve and quietly did a CESA, I was like: I could not do it if I don’t understand the physics. Not only the theory. He told me: don’t worry, it’s easy, you will see. Well, I don’t want to see. I want to understand. Beyond simple explanation we get in diving training.

For example, where was the buddy of this GUE instructor, an agency that focus on diving as a team? (And why did he close is valve before doing a CESA?!)

 

[BlueTrin]

@Dody probably understanding how those people ended in a situation that required a CESA would be more productive for your future diving career.

The case in the article I linked was a group of two people wanted to try a quarry dive.

This quarry has had a few close calls because it’s cold and dark at depth. Also the owners put the entrance on the deep end and it is like a pit to 33m.

Many people come here thinking this is gonna be an easy dive because it’s a closed water body.

From what I heard from the buddy of the guy who did the CESA. This person claimed that the first stage closed shut and he couldn’t get any breath. He tried to reach his buddy but he couldn’t see the octo. They kicked some silt and in zero vis, he panicked and decided to go to the surface and did a CESA from about 32m.

 

[Dody]

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?

10 m is just a number. It happens that I have done easily several times from 10. And I stick to this number. I would not say that I fully understand the DC algorithms but I try in the limited time I can dedicate to it. I don’t think that most DMs that you believe are better than me have the time or knowledge to study Buhlmann algorithm but we are digressing .
It was a simple question. That I don’t want to test because I am afraid. I wanted the to give me comfort or to tell me to forget about it.

 

[tursiops]

10 m is just a number. It happens that I have done easily several times from 10. And I stick to this number. I would not say that I fully understand the DC algorithms but I try in the limited time I can dedicate to it. I don’t think that most DMs that you believe are better than me have the time or knowledge to study Buhlmann algorithm but we are digressing .
It was a simple question. That I don’t want to test because I am afraid. I wanted the to give me comfort or to tell me to forget about it.

Try it from 11m. then try it from 12m. Expand your comfort zone.
Of course thinking about 30m is scary! But even scarier is the thought of needing to do it from 30m and NOT doing it because you don't understand the physiology completely. Sometime you have to make choices between two evils...choose the lesser one. When you get to the surface after that necessary 30m CESA, you can then say, "That Was Really Scary!"

 

[Dody]

For example, where was the buddy of this GUE instructor, an agency that focus on diving as a team? (And why did he close is valve before doing a CESA?!)

Once again, you are off topic. It’s not about buddies.
But for your sake, I asked him the same question about closing the valve and his answer was priceless: I am a Professionnal and I don’t want to scare the customers at the surface with my bubbles. This shows that he was completely in control. I wish I could do the same.