CESA Training

[oly5050user]

I’ve seen the video. I also talked with a guy who said he had to, as a result of his own carelessness, perform a CESA from 70 feet. Having just exhaled when he discovered he was out of air, he said he did not experience any benefit from air expanding in his lungs, but he did get one small extra breath on the way up as the air in his tank/reg/hose expanded enough to give one sip of air that he thinks made the difference in getting to the surface alive.

Air did not expand in tank/ reg/hose. What did happen is surrounding ambient pressure decreased allowing him to access a breath from remaking air in tank

 

[Scraps]

Air did not expand in tank/ reg/hose. What did happen is surrounding ambient pressure decreased allowing him to access a breath from remaking air in tank

Thanks.
This is something I've wondered about.
I know that under normal circumstances, the pressure in the tank is unrelated to the ambient pressure, but I wondered what happens when the tank pressure gets below, say, the intermediate pressure that your first stage is supposed to reduce it to.
At some point of emptiness, I assumed you would get free exchange of air between the tank, the first stage, and the second stage (unless the tank becomes a vacuum, which I don't think could happen). And at that point, ambient pressure would expand whatever is in that system. I've never been exactly clear on the location of the air that might become available for that extra breath on the way up.

 

[johndiver999]

The regulator will continue to deliver air, even as the supply (tank) pressure drops below the intermediate pressure. If you don't believe me, just vent your tank down low before a fill. If you have a digital pressure gage you can confirm that.

 

[Coztick]

So basically you estimate your consumption in any situation based on your "steady state" SAC?

P.S.: According to PADI tables, between 30m and 40m the safety stop is mandatory.

So far I have been limited to 30m on vacation but I do think a 19cuft would suffice to 40m for most.
I am only claiming a SAFE alternative to ever needing to CESA in the same context as it being SAFE to be at depth in the first place.
I don't care if I do a 3 min. stop if I've gone ooa. All I NEED is time to get to surface. My rule is that immediate access to gas will not be compromised.
Personally, if I feel I should take more gas for any reason, the pony is replaced with a second tank as I sidemount regardless.
My estimate of consumption was not for any situation. Just for an ooa for any reason. I can see a bit of a temporary increase, but triple for the duration is over the top.
I appreciate your concern for my safety though!

 

[David Novo]

I appreciate your concern for my safety though!

While I hope everyone dives safely, my goal was to try to understand what was the basis for your recommendation.

So far I have been limited to 30m on vacation but I do think a 19cuft would suffice to 40m for most.

What SAC are you considering for this? Does it include planning with one decompression strategy and then following something else?

I am only claiming a SAFE alternative to ever needing to CESA in the same context as it being SAFE to be at depth in the first place.

If CESA is the benchmark to determine a safe plan, almost anything is safe. The same argument could be used to promote a SpareAir.

I don't care if I do a 3 min. stop if I've gone ooa. All I NEED is time to get to surface. My rule is that immediate access to gas will not be compromised.

This is not an issue if you take an appropriate amount of gas: you can get to the surface with enough gas and follow the decompression strategy as it was designed.

My estimate of consumption was not for any situation. Just for an ooa for any reason. I can see a bit of a temporary increase, but triple for the duration is over the top.

The OP considered an increase from 9L/min to 15L/min: that is not even twice.

 

[Coztick]

The OP considered an increase from 9L/min to 15L/min: that is not even twice.

Wrong, he went with 15 L/min. AND tripled it as recommended.

 

[David Novo]

Wrong, he went with 15 L/min. AND tripled it as recommended.

Ascending from 40m, you have an average pressure of 3 bar, so a SAC of 15L/min leads to an actual consumption of 45L/min.

The OP consciously or not considered a SAC of 15L/min.

P.S.: I am aware that it can be lower with a safety stop but the error is on the conservative side.

 

[Coztick]

While I hope everyone dives safely, my goal was to try to understand what was the basis for your recommendation.



What SAC are you considering for this? Does it include planning with one decompression strategy and then following something else?



If CESA is the benchmark to determine a safe plan, almost anything is safe. The same argument could be used to promote a SpareAir.



This is not an issue if you take an appropriate amount of gas: you can get to the surface with enough gas and follow the decompression strategy as it was designed.



The OP considered an increase from 9L/min to 15L/min: that is not even twice.

Hi David.
If you took anything I wrote as professional instruction then you got what you paid for. I was offering my point of view.
Does a guide check your SAC before telling you to start your ascent with no less than 1000psi?

 

[David Novo]

Hi David.
If you took anything I wrote as professional instruction then you got what you paid for. I was offering my point of view.
Does a guide check your SAC before telling you to start your ascent with no less than 1000psi?

No idea. I do not do trust me dives so I do not rely on the guide for gas management.

 

[David Novo]

Hi David.
If you took anything I wrote as professional instruction then you got what you paid for. I was offering my point of view.

Do not take it personally. I was just trying for you to give a bit more color to the reasoning underlaying your opinion.

This is a forum for new divers. For you it may be just something you said from the top of your head, but some may take it at face value.