Panic!!!

[boulderjohn]

I think there have been some misunderstandings and maybe I can better clarify my position which I think is similar to that of the already mentioned Dulio Marcante, as I understand it.
It may be that the following reasoning is wrong and that the discussion is off topic (but not completely).
When I spoke about the freediver's best chances, I was not referring to the possibility of doing a free ascent after a "blow and go", after having emptied the lungs (to avoid over-distension). Although it may be sufficient for small depths, if we do a calculation and assume a "blow and go" from 30 meters, even if we empty the lungs, there are 1.2~1.5 liters of residual lung volume filled with air at 4 atmospheres that can be dangerous if brought to the surface.
And we all agree that in order to save your skin you must have a speed that is not excessive, let's say <18m/minute, but I would even say that the last 10 meters should be done at 10m/minute.

I went to get my PADI "open water diver" manual, 2013 edition and CESA is not taken into consideration for depths >9m.
This in my opinion leaves my question from a few days ago without an acceptable answer.
The reason I gave myself 5 years ago, when I got my certification is that, at the (not small) ascent rate of 18m/minute, 9m meters can be covered in 30 seconds.
Why 30 seconds? I note that the majority of people, who certainly have not had freediver training, have such an ability to tolerate CO2 that after only 30 seconds they feel the need to breathe. It is true that during the CESA you exhale weakly [the manual talks about actively exhaling air by vocalizing the sound "aaaah" to remove the compressed gas that is expanding], but the CO2 is continuing to accumulate in the lower part of the lungs and we know that it is the CO2 that triggers air hunger.
This means that if a CESA lasts much longer, on the order of more than a minute, if the diver does not have the ability to tolerate the CO2 that is accumulating, he will probably have a panic attack, far from the surface and there will be a failure, with probable death.
In essence this makes me consider a 20 or 30 meter CESA implausible for a scuba diver who does not also have freediving training.
This seems to me to be a problem (I would say not the only one, the other being the complete dependence on the BCD) for a modern scuba diver, while an "old diver" with freediving training should have a better chance in this context.

You do realize, don't you, that when you are exhaling all the way to the surface, you are also exhaling CO2?

 

[Goonzodiver]

You do realize, don't you, that when you are exhaling all the way to the surface, you are also exhaling CO2?

Yes but I think the amount of CO2 that manages to escape (diffusing from the lung walls) is negligible, most of it is compressed air in expansion that will tend to escape more copiously.
CO2 is heavier than air, I would expect it to start to occupy the lungs from the bottom up, before exiting in sufficient quantities. Let's remember that we are exhaling very weakly without making a real respiratory movement.

 

[boulderjohn]

Yes but I think the amount of CO2 that manages to escape (diffusing from the lung walls) is negligible, most of it is compressed air in expansion that will tend to escape more copiously.
CO2 is heavier than air, I would expect it to start to occupy the lungs from the bottom up, before exiting in sufficient quantities. Let's remember that we are exhaling very weakly without making a real respiratory movement.

Perhaps you should cite a source.

 

[Goonzodiver]

Perhaps you should cite a source.

I'll try to find some medical references, but in the meantime let's take a look at the molecular masses:
CO2 44,
molecular Oxygen O2 has 32,
Air on average ~29 (in fact it is a mix of oxygen and nitrogen that is even lighter than oxygen).
However, I am still interested in knowing why PADI does not recommend the CESA (or at least the version that we all know) from depths of over 9 meters.

 

[boulderjohn]

However, I am still interested in knowing why PADI does not recommend the CESA (or at least the version that we all know) from depths of over 9 meters.

The depth is arbitrary. They feel on deeper depths you should use a buoyant ascent. In a buoyant ascent, you drop your weights to be sure of getting to the surface. Other than that, it is exactly the same as a CESA. You exhale all the way to the surface. Buoyant ascents have been done from 100 meters.

 

[CG43]

Hello Mantaray 95616

Thank you for your kind explanation.
This is the way divers should talk to each other all the time .

Greetings Rainer

 

[CG43]

Hello

The gas molecules in the lungs move so fast that I assume complete mixing for the practice.
And CO2 is exhaled during exhalation.
Nevertheless, the free ascent is not quite as comfortable as one might assume.
Long time ago for a very advanced german VDST certificate a free ascent from 30 m had to be made.
This exercise was cancelled again because there were accidents.
Even for me with a max. freediving depth of 30 m, this exercise was demanding with a slow ascent speed and a short stop in 3 to 6 m.
I didn't really expect that. If you want to try it out, you should start with shallow depths.
Important : no deco preload and short scuba dive time .
High-speed ascents , for example from submarines , are another topic . A scubadiver with deco load should not orient itself to it .

 

[CG43]

Hello boulderjohn

The depth is arbitrary. They feel on deeper depths you should use a buoyant ascent. In a buoyant ascent, you drop your weights to be sure of getting to the surface. Other than that, it is exactly the same as a CESA. You exhale all the way to the surface. Buoyant ascents have been done from 100 meters.

All you say is true !

I have an acquaintance, he was a diving doctor in the German navy, who together with his commander had the opportunity to make a 100m free ascent from a US submarine.
However, these people are also very strictly screened out.
You should take this into account when you read a ascent depth of 100 m.
The doctor was freediving down to 35 m , scuba with air 96 m and experimented in his pressure chamber how many breaths you take at 6 bar pure oxygen (PPO2 6 bar) before the convulsions began.
But he only told me that after we had dived together and I had told him about the slightly less crazy things I had done.

 

[boulderjohn]

I'll try to find some medical references, but in the meantime let's take a look at the molecular masses:
CO2 44,
molecular Oxygen O2 has 32,
Air on average ~29 (in fact it is a mix of oxygen and nitrogen that is even lighter than oxygen).
However, I am still interested in knowing why PADI does not recommend the CESA (or at least the version that we all know) from depths of over 9 meters.

Is it your opinion that in a tank of trimix, the gases quickly separate by molecular weight, so that when the diver starts the dive, nothing but helium is being breathed?

 

[CG43]

Hello

Let's do some quick and rough calculations.
1.) the diver needs a purge air volume of 15 L/min to hold his PCO2 costant
2.) The purge air volume required for constant PPCO2 is independent of the ambient pressure
3.) the lungs of the divers should contain 5 L of air and be exhaled during the ascent in such a way that this volume remains constant.

Now I'm doing a simplification. Since most of the volume has to be exhaled at a shallow depth and the PPCO2 of the divers also rises slowly, I calculate as if the entire volume of purge air is only released shortly before the surface. This makes the calculation inaccurate but still accurate enough for a rough estimate of the effects.

1.) Example
Depth 30 m
Ascent Rate 30 m/min
ascent time 1 min
Exhaled air volume
(4-1)bar/1 bar * 5 L = 15 L
15 L are needed for 1 min CO2 reduction
(ascent time 1 min) - (1 min CO2 reduction time) corresponds to no breathhold time

2.) Example
Depth 30 m
Ascent Rate 15 m/min
ascent time 2 min
Exhaled air volume
(4-1)bar/1 bar * 5 L = 15 L
15 L are needed for 1 min CO2 reduction
(ascent time 2 min) - (1 min CO2 reduction time) corresponds to 1min breathhold time

3.) Example
Depth 30 m
Ascent Rate 10 m/min
ascent time 3 min
Exhaled air volume
(4-1)bar/1 bar * 5 L = 15 L
15 L are needed for 1 min CO2 reduction
(ascent time 3 min) - (1 min CO2 reduction time) corresponds to 2min breathhold time

4.) Example
Depth 100 m
Ascent Rate 30 m/min
ascent time 3,3333 min
Exhaled air volume
(11-1)bar/1 bar * 5 L = 50 L
50 L cause 3,3333 min CO2 reduction
(ascent time 3,33333 min) - (3,33333 min CO2 reduction time) corresponds to zero min breathhold time

5.) Example
Depth 100 m
Ascent Rate 23 m/min
ascent time 4,33333 min
Exhaled air volume
(11-1)bar/1 bar * 5 L = 50 L
50 L cause 3,3333 min CO2 reduction
(ascent time 4,33333 min) - (3,33333 min CO2 reduction time) corresponds to 1 min breathhold time

6.) Example
Depth 100 m
Ascent Rate 18,8 m/min
ascent time 5,33333 min
Exhaled air volume
(11-1)bar/1 bar * 5 L = 50 L
50 L cause 3,3333 min CO2 reduction
(ascent time 5,33333 min) - (3,33333 min CO2 reduction time) corresponds to 2 min breathhold time

For examples 5 and 6, the approximate calculation is questionable.
Nevertheless, the examples show that both a slow ascent from medium depth and a fast ascent of 100 m without a scuba are possible.
This requires comparatively freedive times of up to 2 minutes. Under the condition of no sufficient mental and physical preparation time, this is very not comfortable, but possible.