breathing compressed air at depth

[waterishome]

I know this might sound like a dumb question to most of you, and I should know the answer becuase I am a certified diver, but its just slipping my mind and I would like a little more explanation on the subject. A friend showed me the video of Audrey Mestre’s last dive on youtube (which I will never watch again, it is a terrible video) and we were wondering why she could not just breath off of the saftey divers gas. Im sure there is a perfectly good explanation why you cant breath compressed air at depth but I guess Im just having a brain fart. Thanks for your time and I look forward to learning more on this.
-waterishome

[sanso]

Decompression is the word You're looking for, I think.

[BennyB]

Like Sanso said, once you take a breath off a reg you in effect become a scuba diver and have to deco the same as they do. I don't scuba so I can't say for sure, but I doubt the safety person would be carrying enough gas for 2 people to breath, and at those depths you're talking hours of deco.

There is also probably an issue of a diver not realising how much trouble they're in and trying to make it to the surface without assistance. The scuba guys may also have not been close to her while she was still conscious.

There may also be some issues of gas toxicity at depth but a scuba person would be better to answer that.

In general, it is much better for a scuba safety person to send the athlete in trouble back up to the surface then it is for them to try and maintain the athlete's consciousness or revive them underwater. A scuba underwater rescue would put the scuba diver in danger as well as the athlete, instead they can easily attach an airbag to the athlete and send them up, an airbag at about 100m would take around 1 minute to reach the surface, maybe less. After this the surface team can start a more robust rescue procedure.

Cheers,
Ben

[sheepeck]

Can actually freediver take a breath from reg at that depth? Doesn't he/she have lungs full of plasma at that time?

[alexrom1207]

I read the story by her husband online. Here's the link CDNN :: Death for Sale - Audrey Mestre's Last Dive by Francisco Ferreras Terrible Story. Anyway the rescue diver at the bottom (170 meters) was wearing 5 tanks of mixed gas. When the bag failed to inflate he tried to inflate it using his air. So it seems having her breathe from his tanks wasn't their first idea (probably as Benny said because if it took him 5 tanks to get there and back, he wouldn't have enough air to get them both back to the surface). She was still conscious when she started moving toward the surface but lost consciousness along the way. And by the time the diver got to her she had stopped breathing, so breathing through a regulator wasn't possible. I know that doesn't answer the question of breathing air at depth (which like sheepeck said with lungs full of blood/plasma that may be an issue?) but it does explain why she didn't immediately start breathing with the diver: not enough air + they thought they could still recover the dive and didn't have to abort.

[sanso]

Originally Posted by sheepeck

... Doesn't he/she have lungs full of plasma at that time?

That's a common misunderstanding, it seems. One would think that all freediving courses take care of that.
It is the lung tissue that swells. Liquid entering the lung airspace qualifies as a squeeze - and that would be a different problem.

[sheepeck]

Oh, thanks for explanation.
But still - even if the tissue itself is swolen, would there be a space for air then?

[rbsub]

The more and more I'm thinking about breathing compressed air in the deep, the more I ask myself why it's not possible.

The pressure in your lung and the pressure of the air from the regulator is nearly the same. And if you have the air supply under water for your ascent, you normaly have enough time for it. So decompression shouldn't be an issue.

But at every course you hear that you even never should try it. But what is the reason for that? Does anybody has a physical or medical anser to that issue?

[sanso]

Originally Posted by sheepeck

Oh, thanks for explanation.
But still - even if the tissue itself is swolen, would there be a space for air then?

Here's my theory - anyone who really knows this, please correct me!

The air You get from a SCUBA comes at ambient pressure. Likely the pressure in Your lungs will be slightly less than that because ribcage and diaphragm will absorb some of the force exerted by the surrounding water (reduce pressure) for You. So there will be a slight pressure drop from the air from the regulator to the air in the lungs. Breathing in is also an active process. In order to breathe in You flex the intercostal muscles to increase the volume Your ribcage encloses, thus lowering the pressure of the air still enclosed in Your lungs. ATM I can't see why this shouldn't work at higher pressure.
Also, having Your lungs pressurized would nullify the passive part of the blood shift, pushing some of the blood in the lung tissue back where it came from - thus further increasing the total lung volume.

[osusim]

Originally Posted by rbsub

The pressure in your lung and the pressure of the air from the regulator is nearly the same. And if you have the air supply under water for your ascent, you normaly have enough time for it. So decompression shouldn't be an issue.

Even in a case of pure freeding decompression is big issue.
http://www.aida-international.org/as...d%20diving.pdf

Originally Posted by rbsub

But what is the reason for that? Does anybody has a physical or medical answer to that issue?

The reason - no one wonna spent rest of the life in a wheel cheer or be dead.

[sanso]

Originally Posted by osusim

Even in a case of pure freeding decompression is big issue.

Yes, we know that, but how do You weigh a slight DCS against losing conciousness at depth?

The reason - no one wonna spent rest of the life in a wheel cheer or be dead.

Can You back that statement up with a little more substance? Sadly, it's not much use as is.

[Erik]

One can easily breath off a regulater at depth during freediving. Youre diaphragm still works in concert with the lungs, it would just be a biiiig breath! Not that it's the safest thing to do, but I have done it in an earlier incarnation, and I wouldn't recommend it of course. The greatest danger is that the freediver, especially a panicked/incoherent/stoned on nitrogen freediver, might burts a lung as the gas expanded on ascent.
That's part of the reason to have a better retrieval system, a topic well-discussed here on DB. Herbert Nietsch seems to be doing it right IMO.

[rbsub]

Originally Posted by Erik

One can easily breath off a regulater at depth during freediving. Youre diaphragm still works in concert with the lungs, it would just be a biiiig breath!

Are you sure about that? I'm sure that it will be ok for the first 30-40m.

But what will happen if you dive deeper (60, 80,100 m) and your lung capacity is reduced to the RC? Then there will be not place for the incoming air, or?
Does anybody had really try it? I'm in doubt. If it would work, why Non Limit divers don't have a spare bottle?

Any more comments about that?

[trux]

Originally Posted by rbsub

Are you sure about that? I'm sure that it will be ok for the first 30-40m.

Of course, there is no problem at all. It is a simple physical principle. Your claim that you could not inhale when lungs are reduced, is the same as if you told you cannot inflate a balloon when it is empty - that's nonsense, of course.

First, the lungs will be never 100% collapsed - the inner pressure of the air in lungs is always (practically) equal to the ambient pressure. The body compensates the inner lung air pressure by reducing the volume - first by the flexibility of the rib cage and diaphragm, and the by filling the capillaries in the alveoli. The alveoli won't collapse - that would likely have fatal consequences. The inner volume simply shrinks, keeping the air in them under the same pressure as the ambient water pressure.

Second, the air pressure from the regulator is (practically) equal to the ambient water pressure - so you are in exactly the same situation as if you tried to inhale on the surface.

If there is some air you can inhale, what do you think could prevent the diaphragm and the ribcage to start inhaling? Nothing of course - there is equilibrium of pressures, so if you start the natural inhalation (with your diaphragm and rib cage muscles), you create a pressure gradient sucking in the air from the regulator.

The problems of inhaling compressed air in great depth are definitely not coming from not being able to inhale physically. There may be problems with the right gas exchange, or a shock, considering you dove with natural air, and inhale suddenly trimix or other mixture, when already in hypoxia and hypercapnia.

[trux]

Originally Posted by osusim

Even in a case of pure freeding decompression is big issue.

Yes, that's well known, but what rsub meant here is that the DCS would not be an issue, because once breathing air (or a mixture) from tanks, you can do the decompression properly as if you were a scuba diver. The fact that the safety diver had gas only for himself is no issue, because there is time enough to send down more tanks as needed.

Well, that all assumes that the involved people were properly trained for hadling such situation, which was apparently not the case. And Carlos Serra even susggests in his book that it was a pre-mediated criminal intention, and that the failures were no accident. I cannot judge, but reading his book may be worth of it - just to see it also from another angle.