Panic!!!

[Goonzodiver]

About CESA:

Emergency ascent - Wikipedia

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. "

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.

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]

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.

 

[Goonzodiver]

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?

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...

scubaboard.com

 

[lowwall]

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):

Lake Nyos disaster - Wikipedia

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.

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.

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]

I personally don't believe that there is such a thing as "mild panic". I think there are varying levels of "extreme concern" and maybe even varying stages of approaching panic. But actual panic is a "switch" that is either ON or OFF.

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.

 

[CG43]

Hello

Unlike a fluid, the gases have a continual motion, so are constantly mixing, but over time, this motion slows due to molecular friction with the tank walls

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.

 

[CG43]

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 .

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).

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.

 

[boulderjohn]

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...

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.

Option3. Make a controlled emergency swimming ascent sometimes called a CESA).​

• This is the best choice if you are completely out of ari, no deeper than 6 to 9 metres/20 to 30 feet, the surface is closer than your buddy(ies) or another diver, and you have no other alternative air source.
• Simply look up and swim to the surface making a continuous ahhhhh sound into your regulator.The ahhhhh sound assures that you exhale expanding gas, which is necessary to avoid lung overexpansion injury.
• Leave all your gear in place and keep the regulator in your mouth. Do not drop your weights to start the ascent.
• Ascend at a safe rate. The ascent gets easier as you ascend because air expanding in your BCD increases your buoyancy. Vent air as needed to maintain a safe rate.

Option 4: Make a buoyant emergency ascent.​

• Use this option when you are too far from your buddy(ies) or another diver, have no alternate air source, and are so deep that you doubt you can reach the surface any other way.
• You make a buoyant emergency ascent exactly like a controlled emergency swimming ascent, except you ditech you weights and exceed a safe rate.
• Again, look up and make the ahhhhh sound as you ascend.
• Because you exceed a safe rate, this method has more risk than the other options (which is why it is your last choice), but it is obviously better than staying on the bottom without air.
• As you near the surface, you can flare out your arms and legs to create drag and slow your ascent.

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.

 

[boulderjohn]

Stratification of gases in a scuba tank

First of all, it is impossible for me to guess how many times I have mixed gases. I have also taught gas blending courses.

When your first mix gases through partial pressure blending, you get stratification, with the stuff you put in last sitting on top of what as there first. When mixing nitrox or (especially) trimix), I don't even think of analyzing the gases until time has passed. If I need to analyze sooner, I agitate the tank by laying it on its side, picking it up, laying it down, etc. many times. With trimix, whenever possible I prefer to leave it for a day.

Please note: over time it becomes less stratified, not more stratified.

Right now I have a bunch of nitrox and trimix tanks in my garage that have been there for many moths because I have been laid up for health reasons. I guarantee you that if I were to go out analyze them right now, I would get the same results that are on the analysis sticker I put on many months (in some cases over a year) ago.

 

[lowwall]

Every time I see the title of this thread...