KeelsonGraham
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But, why did you have a full mask at 16m?? What went wrong?
Panic!!!
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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.
Goonzodiver
Registered
About CESA:
en.wikipedia.org
"This procedure is recommended for ascents where there is no decompression obligation, a free surface with little risk of entanglement, and the diver has sufficient breath hold capacity to easily reach the surface conscious.
Advantages of this method, when applicable, are that no outside assistance or special equipment is required. Disadvantages are that it requires the diver to reach the surface in a limited time, which does not allow for staged decompression, possible delays due to entanglement or snags, or long distances to reach the surface. "
I read everywhere and also in my book that PADI limits CESA to 9 meters.
But maybe, now, I'm interested in your bibliographic sources...
Emergency ascent - Wikipedia
"This procedure is recommended for ascents where there is no decompression obligation, a free surface with little risk of entanglement, and the diver has sufficient breath hold capacity to easily reach the surface conscious.
Advantages of this method, when applicable, are that no outside assistance or special equipment is required. Disadvantages are that it requires the diver to reach the surface in a limited time, which does not allow for staged decompression, possible delays due to entanglement or snags, or long distances to reach the surface. "
I read everywhere and also in my book that PADI limits CESA to 9 meters.
But maybe, now, I'm interested in your bibliographic sources...
Goonzodiver
Registered
off topic, I know:
to be honest I doubt that it is possible to escape from a submarine at 100 meters of depth (300ft).
When the gases are compressed they heat up, it is true that the fugitive exhales all the air, but he is left with 1200 ml or more of residual volume, which are compressed instantly by a factor of 11, at 100m.
It makes me think of the possibility of burns on the internal walls of the lungs due to the heat developed in the instantaneous compression.
to be honest I doubt that it is possible to escape from a submarine at 100 meters of depth (300ft).
When the gases are compressed they heat up, it is true that the fugitive exhales all the air, but he is left with 1200 ml or more of residual volume, which are compressed instantly by a factor of 11, at 100m.
It makes me think of the possibility of burns on the internal walls of the lungs due to the heat developed in the instantaneous compression.
Goonzodiver
Registered
In this forum I can read:
"Fortunately in diving, the regular movement of a tank on and off the boat etc, would be sufficient to ensure a complete mix of the gases if they did stratify. So the only real reason for this question is when analysing, which is quite serious."
Stratification of Nitrox Mixes
Having just completed the DSAT Blenders course, thinking about this and applying some aeronautical engineering knowledge, and seeing a PADI Master Instructor shaking a tank prior to analysing the O2 content of a tank, I have a short question regarding the stratification of Nitrox mixes. I...
You are confusing stratification of a closed system of gases with stratification of introduced gases. Simple diffusion will eventually ensure that a mixture of gases in a closed system will become close to homogeneous. However, if you introduce gases into a system faster than they can diffuse - or be mixed if there any other sources of turbulence in the system - then you will have areas that have different concentrations of the gases.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):
If there had been no stratification, no one would have died ...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.
The Lake Nyos disaster was the latter. A vast amount of CO2 was suddenly introduced into the atmosphere and suffocated a bunch of people and livestock. But this volume of CO2 did not stratify. Molecular diffusion and the regular processes of atmospheric turbulence such as wind quickly mixed the CO2 into the atmosphere.
johndiver999
Contributor
Panic itself is not a constant.
At the very least, I have experienced two very distinct and different types of panic. In one type, the victim completely freezes and can perform no useful activity or life preserving action(s) - they are stuck motionless.
In the other, the person may "charge off", bolt for the surface or run away as they lose control of the situation and panic.
I have experienced, "mild panic" many times when ascending from a breathhold dive. You are supposed to ascend in a controlled and efficient manner and NOT try to swim up too fast (because it is inefficient) - no matter how bad you are feeling.
However, when you are coming up and begin to "lose it", it is so easy to just bolt for the surface and kick at near 100% of effort - when the pain of breathhold exceeds your mental ability to calmly withstand the pain - this type of panic (or near panic) ascent is something to be avoided and is something that the safety diver should be specifically watching for. It is not that unusual of an occurrence for less than skilled freedivers who are pushing things.
When freediving, you really don't want to be doing this - nor when scuba diving.
Hello
The gas in the tank is NOT a closed system !
If the temperature of the gas remains constant due to the heat transport through the wall of the tank, the gas pressure and thus the average velocity of the specific gas molegule will also remain constant.
A stratification by density can build up if the mean free path length of the molecules movements is small against the geometric dimensions of the room .
This happens, for example, in a wine cellar or in the sewer system.
With a helium-oxygen mix in the tank ? may be .
In the lungs of the diver at the smaller dimensions and the mixture through the breathing and short time I do not suspect a large stratification. However, there is still a rapid reaction of the CO2 with the water vapor.
I don't know of any research on these topics.
Thats not true !
The gas in the tank is NOT a closed system !
If the temperature of the gas remains constant due to the heat transport through the wall of the tank, the gas pressure and thus the average velocity of the specific gas molegule will also remain constant.
A stratification by density can build up if the mean free path length of the molecules movements is small against the geometric dimensions of the room .
This happens, for example, in a wine cellar or in the sewer system.
With a helium-oxygen mix in the tank ? may be .
In the lungs of the diver at the smaller dimensions and the mixture through the breathing and short time I do not suspect a large stratification. However, there is still a rapid reaction of the CO2 with the water vapor.
I don't know of any research on these topics.
Hello Goonzodiver
The escape from the sub was done was by a torpedo tube that was flooded with water. From a certain water level in the pipe, the air had to be held .
In the first part of the compression, the air was cooled considerably by the cold water.
The two German divers had a Dräger TR66 submarine rescuer, which could only have been used at a shallower depth because of 50% O2. That's all i know from memory 25 years ago .
Nevertheless, many accidents would be preventable by apnea skills.
If Padi or other schools were to demand apnea as a compulsory course for AOW they would lose customers
and certificates . And freediving itself, when you approach your own limits, is more dangerous than scuba.
The escape from the sub was done was by a torpedo tube that was flooded with water. From a certain water level in the pipe, the air had to be held .
In the first part of the compression, the air was cooled considerably by the cold water.
The two German divers had a Dräger TR66 submarine rescuer, which could only have been used at a shallower depth because of 50% O2. That's all i know from memory 25 years ago .
This is a significant security disadvantage that can only be reduced a little by a lot of effort and restrictions.
Nevertheless, many accidents would be preventable by apnea skills.
If Padi or other schools were to demand apnea as a compulsory course for AOW they would lose customers
and certificates . And freediving itself, when you approach your own limits, is more dangerous than scuba.
I am having a world of trouble understanding your point.
What follows comes from the current written version of the PADI OW course, page 161. It describes the 4 choices a low on air/out of air diver has. The first two options are a normal ascent and and alternative air source ascent. Here is what comes next.
Look at the second bullet on Option 4, and you will see that the two ascents are identical except for one thing--dropping weights. It is the same process otherwise.
See in bullet #1 that it is your judgment about when to do it.
I am absolutely baffled by your point here. What does this prove? If I remember correctly, I think you are trying to prove that free diving skills are necessary for cases when people run out of air, but I am totally lost as to how this proves anything about that.
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