Perhaps you should cite a source.
Panic!!!
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Goonzodiver
Registered
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.
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
Contributor
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 .
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
Contributor
Hello boulderjohn
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.
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.
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
Contributor
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.
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.
KeelsonGraham
Registered
But, why did you have a full mask at 16m?? What went wrong?
Goonzodiver
Registered
I haven't found the time to do bibliographic research yet.
This forum is fun but there can't be much time to dedicate to it.
However, it is false to think that gases mix homogeneously. The speed of the molecules will tend to make stratification faster towards the bottom.
Just think of the disaster (not related with diving):
en.wikipedia.org
If there had been no stratification, no one would have died ...
This is just an example. There are other testimonies in the history of diving, for example in the first full face masks the CO2 collected at the bottom, where the mouth is. To avoid intoxication many (I think everyone in the Royal Navy) mounted a mouthpiece inside the face mask, to avoid breathing in stale air.
Also here there is an aggravating factor: an expanding gas in the central part of the lungs that exerts higher pressure on the walls where the CO2 is forming and will tend to create a "gas wall", even if not perfect.
I note that just on this forum you can read about divers who after a CESA of 25 feet [that is ~8m] at the surface had lungs that were burning: CO2, without a doubt.
What happens if it is not 8m but 40m and the diver does not have the skills and self-control of a freediver?
@CG43 you say that it is possible to make an ascent from high depths...
I have never questioned it, but you talk about 1 minute 2 minutes of breathhold... But look, a normal diver does not hold his/her breath for more than 30 seconds (like my wife).
So with good reason and very responsibly PADI does not suggest a CESA of more than 9 meters, because most divers are NOT capable of doing much more without getting into trouble.
And you can't give a recipe that not everyone is capable of following.
Doing so would be deceptive, it only serves to provide an illusion of safety, and presumably a death sentence for the unaware inexperienced diver.
I read that George Bond made ascents from 100 meters (but from a submarine or with scuba?, we know very well that they are very different things. And then 100m? or 100ft?). But George Bond, the "papa topside" in SEALAB I project, was an old diver, a true pioneer, with the nose-clip (it is even documented that he was a big supporter of it) and all the rest. And obviously he also had a freediver training.
There is a mention to leave the weights (but in the true CESA you have not to do it, really). A modern diver often dives with 10kg of weights. Without a functioning BCD I see it as hard for a diver without freediver training to get out without damage, I see it as hard to be able to control the descent.
And let's leave aside the rope [I didn't have it in the sea trial] and the truth is that it is difficult to have any kind of similar help when disaster strikes...
Instead an old diver, without a BCD, rarely used more than 2 or 3kg, from what I read and with a freediver training he could be able to keep calm, tolerate CO2, and swim actively at the speed required at the given depth.
Let's see if I can find some interesting documentation and not anecdotes.
But in the meantime I just read, on:
www.scuba.com
"Some experienced divers have experienced success with this skill at depths beyond 30 feet, but as a general rule (and following PADI guidelines) this skill should not be attempted from deeper than 30 feet."
He is saying that a normal diver is not capable of making a 20 or 30 meter CESA. And that has always been the point.
This forum is fun but there can't be much time to dedicate to it.
However, it is false to think that gases mix homogeneously. The speed of the molecules will tend to make stratification faster towards the bottom.
Just think of the disaster (not related with diving):
Lake Nyos disaster - Wikipedia
This is just an example. There are other testimonies in the history of diving, for example in the first full face masks the CO2 collected at the bottom, where the mouth is. To avoid intoxication many (I think everyone in the Royal Navy) mounted a mouthpiece inside the face mask, to avoid breathing in stale air.
Also here there is an aggravating factor: an expanding gas in the central part of the lungs that exerts higher pressure on the walls where the CO2 is forming and will tend to create a "gas wall", even if not perfect.
I note that just on this forum you can read about divers who after a CESA of 25 feet [that is ~8m] at the surface had lungs that were burning: CO2, without a doubt.
What happens if it is not 8m but 40m and the diver does not have the skills and self-control of a freediver?
@CG43 you say that it is possible to make an ascent from high depths...
I have never questioned it, but you talk about 1 minute 2 minutes of breathhold... But look, a normal diver does not hold his/her breath for more than 30 seconds (like my wife).
So with good reason and very responsibly PADI does not suggest a CESA of more than 9 meters, because most divers are NOT capable of doing much more without getting into trouble.
And you can't give a recipe that not everyone is capable of following.
Doing so would be deceptive, it only serves to provide an illusion of safety, and presumably a death sentence for the unaware inexperienced diver.
I read that George Bond made ascents from 100 meters (but from a submarine or with scuba?, we know very well that they are very different things. And then 100m? or 100ft?). But George Bond, the "papa topside" in SEALAB I project, was an old diver, a true pioneer, with the nose-clip (it is even documented that he was a big supporter of it) and all the rest. And obviously he also had a freediver training.
There is a mention to leave the weights (but in the true CESA you have not to do it, really). A modern diver often dives with 10kg of weights. Without a functioning BCD I see it as hard for a diver without freediver training to get out without damage, I see it as hard to be able to control the descent.
And let's leave aside the rope [I didn't have it in the sea trial] and the truth is that it is difficult to have any kind of similar help when disaster strikes...
Instead an old diver, without a BCD, rarely used more than 2 or 3kg, from what I read and with a freediver training he could be able to keep calm, tolerate CO2, and swim actively at the speed required at the given depth.
Let's see if I can find some interesting documentation and not anecdotes.
But in the meantime I just read, on:
Controlled Emergency Swimming Ascent Guide
The Controlled Emergency Swimming Ascent (CESA) shouldn't be used except in emergencies. Learn more about what it is and when to use it.
www.scuba.com
"Some experienced divers have experienced success with this skill at depths beyond 30 feet, but as a general rule (and following PADI guidelines) this skill should not be attempted from deeper than 30 feet."
He is saying that a normal diver is not capable of making a 20 or 30 meter CESA. And that has always been the point.
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