physics question, air pressure in cave

[pisoiu]

That actually happened in an accident, not too far ago, when a ship sunked to the bottom (approx. 30 meters) and one crew member remained trapped alive in a bubble. Following the rescue, he had to be decompressed properly from that depth. He staid more than a day at that depth, if I remember correctly, and such interval may have put him into saturation.

 

[boulderjohn]

That actually happened in an accident, not too far ago, when a ship sunked to the bottom (approx. 30 meters) and one crew member remained trapped alive in a bubble. Following the rescue, he had to be decompressed properly from that depth. He staid more than a day at that depth, if I remember correctly, and such interval may have put him into saturation.

It was actually 3 days. This explanation of the incident will be helpful in this thread.

 

[marcushall]

Ignoring any potential air quality issues, isn't breathing from the bubble just like breathing from the "bubble" of air in the 2nd stage at the same depth as the water line? So breathing in the bubble is like breathing on scuba at the same depth.. One hour is certainly well beyond the NDL at 30m, but well under the limit at 10m. Is there any reason that it would be different?

 

[Subcooled]

It is possible to damage or compromise the pressure transducer on a dive computer by exposing to elevated ambient air pressure.

Liquid has cohesion (surface tension) and big molecules, and is generally bigger, so it does not get through narrow cracks as easily. If the seal is not perfect, then gas can get in easier than water, but what can get in can get out... Or is there some sort of one-way seal (the-wrong-way)? I guess it is possible...

I have been in a decompression habitat at 60 feet several times and it did not break my Suunto. If it did, I would be pretty angry. I have been to a diving bell at 90 feet several times and it did not break my Suunto.

My backup pressure gauge is a mechanical Bourdon tube pressure gauge. It works even if it floods with gas/liquid. My backup timer is 1.6bar/min SPG, also a bourdon tube. Flooding is not an issue. And hey, my backup diving light is designed to work properly even when flooded. I will submerge, after all.

 

[pisoiu]

It would be almost the same thing. In normal horizontal diving position, the only effort you have to do with your lungs is to overcome the cracking pressure of the 2nd stage. If you are in vertical position, it will be a bit more difficult. You have to 'suck' a bit harder, because to the cracking pressure of the 2nd stage, the hydrostatic pressure of the water column between your mouth level and your (approx) median lungs level will be added. Now, in the air bubble, if you remove your 2nd stage, the cracking pressure comes out from the equation, the hydrostatic pressure remains.

LE: Subcooled, the statement is a bit on the wrong side in my opinion. It is not the pressure transducer which gets damaged, but the sealings around it and around the other case components (buttons if any, screen, etc) which may be compromised by air leaking inside. Pressure transducer is designed to work under pressure but some other components are most certainly not. Some components such as quartz crystals may have small pockets of air inside. This issue will certainly not affect computers filled with oil such as alladin pro. But again, I have tested this on 2 computers with air and no problems arised...
I was also puzzled about this at the beginning, you can find some answers here: http://www.scubaboard.com/forums/advanced-scuba-discussions/500619-simulated-dive-chamber-3.html , at page 3

 

[Subcooled]

isn't breathing from the bubble just like breathing from the "bubble" of air in the 2nd stage at the same depth as the water line?

Yes it is,

and DO notice that if the air pocket is 30 feet tall, then there is NOT a 1 bar pressure difference within the bubble. The pressure at the water level is equal to the water pressure, but as you climb up within the bubble, the pressure lessens (by the weight of the air and that is not much). The pressure difference between the top (+30m) and the water surface is probably 0.001 bar. Air happens to be 1000 times thinner and weigh 1000 times less...

 

[RaceBannon]

And thanks for all the info, deffinatly have a better understanding of it now and also learned more on other aspects of it, expecially that since it is pressurized and if someone were to breath it in, considering it was just air of course that it could cause the bends going up something I didn't consider at all but makes sense.

---------- Post added March 7th, 2015 at 11:31 AM ----------

tried to post picture in first post but no luck, so if it's possible could someone do it for me?

 

[DandyDon]

It's late in the thread but here...

 

[BRT]

Ignoring any potential air quality issues, isn't breathing from the bubble just like breathing from the "bubble" of air in the 2nd stage at the same depth as the water line? So breathing in the bubble is like breathing on scuba at the same depth.. One hour is certainly well beyond the NDL at 30m, but well under the limit at 10m. Is there any reason that it would be different?

You are correct. No difference.

 

[RaceBannon]

any way to insert picture if its not at a url but from hd ?