CESA theory

[VikingDives]

I know that this subject has been discussed ad nauseam on SB (I have probably read all the related threads) but not in the way that I am searching. Out of all the diving skills that I have learnt, this is the one that worries me the most. Let me explain. We learn the skill no deeper than 9 meters or so because it is dangerous. I would then assume that it should not be considered below that depth. But some people claim that they practise it at 20 meters and other than they did it in real life from 30 meters. A « controlled » ascent from this depth would take at least 90 seconds following the old rule of 18m/ min and the double with the 9m/ min. No way would I be able to exhale during 90 minutes starting with my lungs empty. My question is: can someone explain step by step what happens during a deep CESA? At what depth should the air in the lungs expand so that you could inhale or continue to exhale? Can you do it only once? Is this whole thing true or should you be prepared to die if you can’t reach the surface with whatever air you already have in your body? I am not talking about OOA due to lack of air in the cylinder but more a 1st stage failure. Thank you.

In general, the training for CESA is that you shouldn't do one below 30 feet, deeper than that you should ditch your weights and perform a buoyant ascent (this depends a little on agency).

The principle dangers of a deep emergency ascent are the same as those of a shallow ascent, but the risk is somewhat increased.

As for your questions, the answer is it depends on your depth at the start of the ascent, how deeply you exhaled before realizing your were out of air, your rate of ascent.

If you go back to your training, at 30 meters, you are at 4 BAR/ATA so your trip from 40 to 30 will result in an expansion of the volume of the air in your lungs that isn't significant. As you get closer to the surface the volume changes are more pronounced. In your last 10 meters to the surface, that volume will double.

 

[James79]

So, you consider that the risk of death is higher in a CESA from 30 m than breathing out of BCD? So all those stories about CESA from 30 m are just from exceptional i dividuals?

You're hyperbole makes you sound like you're trolling. Nobody has said successful CESAs are only from exceptional individuals. A CESA done correctly from a recreational NDL dive is safe. Emphasis on correctly. If you are in the scenario you listed, CESA done wrong is drowning. Low to moderate likelihood, but catastrophic consequences. Breathing off BCD is suboptimal, but unlikely to cause infection or major CO2 problems in the time you're doing it. Less good at it's best, but less catastrophic at it's worst.
In response to your original question, at 30m the air in your lungs is at 4 ATM.... At 20 meters it's at 3 ATM (30% increase in volume). At 10 meters it's at 2 ATM (double the volume it started at 30m). At the surface it will have doubled in volume again. And while exhaling all the way up you are flushing CO2 reducing the perceived need to inhale.
Respectfully,

James

 

[Dody]

Have you missed the part in your training on how gasses respond to changes in pressure? Do you understand why you don't hold your breath? You are asking questions that are basic principals...

You list your credentials as a DM....

If you are capable of precisely telling me how much air you have in your body after a normal exhale at 30 m and exactly how and in which quantity it expands (blood and lungs) during the ascent and how much is available to exhale, I will stop thinking you are a world champion… and you will have answered my initial question.

 

[Dody]

You are Einstein, yet you ask this question??? You should be the expert to answer the question. Perhaps you were out sick of a hangover when they discussed this in your physics course??

Read the thread carefully. At least try to understand. Obviously you have not.

 

[BoltSnap]

Read the thread carefully. At least try to understand. Obviously you have not.

I am not an Einstein like you.

 

[Dody]

You're hyperbole makes you sound like you're trolling. Nobody has said successful CESAs are only from exceptional individuals. A CESA done correctly from a recreational NDL dive is safe. Emphasis on correctly. If you are in the scenario you listed, CESA done wrong is drowning. Low to moderate likelihood, but catastrophic consequences. Breathing off BCD is suboptimal, but unlikely to cause infection or major CO2 problems in the time you're doing it. Less good at it's best, but less catastrophic at it's worst.
In response to your original question, at 30m the air in your lungs is at 4 ATM.... At 20 meters it's at 3 ATM (30% increase in volume). At 10 meters it's at 2 ATM (double the volume it started at 30m). At the surface it will have doubled in volume again. And while exhaling all the way up you are flushing CO2 reducing the perceived need to inhale.
Respectfully,

James

Totally agree with the theory. However, it does not help the calculation if you don’t know how much air you have in your body from the start. So we know that it is possible if it is done right but I still miss one data in the equation. But thank you for answer.

 

[boulderjohn]

Totally agree with the theory. However, it does not help the calculation if you don’t know how much air you have in your body from the start. So we know that it is possible if it is done right but I still miss one data in the equation.

My earlier post seems to have been completely ignored, so I will repeat the main point.

The navy procedure for submarine escapes is to exhale fully before beginning a submarine escape and then continue to exhale all the way to the surface. This has been done at depths to 300 feet.

 

[CuzzA]

I will add that per your original post, if your first stage fails to deliver gas, there will not be any extra breaths coming from your tank. But when they do fail, which is rare in above freezing temps, they usually vent the tank which means you have breaths to take on your ascent.

As for out of gas, you might get a breath or two. The biggest consideration is trying to stay calm and letting your bc do the work instead of you kicking and burning oxygen on the way up. Though I would probably begin kicking up quickly to get off the bottom and try to slow my ascent at 20 meters and control it from there. Taking gas from the bc if necessary.

The goal is simple. Try to balance not passing out with not exceeding 20 meters per minute. At 30 meters this is physically possible for most people. 1:30 breath hold is not instant death. Breath hold training is good practice as you learn to keep your head clear with the build up of co2.

 

[James79]

If you are capable of precisely telling me how much air you have in your body after a normal exhale at 30 m and exactly how and in which quantity it expands (blood and lungs) during the ascent and how much is available to exhale, I will stop thinking you are a world champion… and you will have answered my initial question.

While you insult regulars on the forum who go out of their way to help you and others, I spent 15 seconds on Google to find an average residual lung volume in adult males is 1.2 liters. See earlier answer to your question, do basic math and come up with at 20m expansion will allow a .4 liter exhale.. by 10m another .8liters will be available to exhale. By the surface another 1.2 liters of exhale. Regards nitrogen dissolved into your blood, if you are within NDL it won't be supersaturated and will remain in solution (as in not get bent).
People are concerned that you don't know this, not to be mean... But because as a DM you are in a position of authority and responsibility where you should already have a thorough grasp of this. So please don't attack .. listen.
Respectfully,
James

 

[CuzzA]

Here's an example from our old friend dumpsterdiver at 60 meters. Though he had a pony and switched to it on his ascent.

This type of failure has happened to two people I know.