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Topic: General Question About Gas and Diving  (Read 3664 times)

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Offline nepenthean

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General Question About Gas and Diving
« on: August 31, 2008, 03:34:14 AM »
Accepting no change in temperature, if I take a breath and hold it while I descend to 2 atms and then ascend fast, will the gas in my body expand beyond what it formerly was at 1 atm? If so, why should it? The gas I inhaled at 1atm will diminish in volume by 1/2 while its density increases 2x; therefore, the same pressure increase bringing these to bear must also bring the same volume at sea level upon pressure decrease.

From what I have read, it seems if I take a breath of mixed air at that depth, hold it, and then ascend fast, the volume will expand greater than it was at 1 atm.

Thanks again.


Offline Borek

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Re: General Question About Gas and Diving
« Reply #1 on: August 31, 2008, 04:14:22 AM »
From what I have read, it seems if I take a breath of mixed air at that depth, hold it, and then ascend fast, the volume will expand greater than it was at 1 atm.

You have misread it most likely.
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Offline nepenthean

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Re: General Question About Gas and Diving
« Reply #2 on: August 31, 2008, 05:53:35 PM »
Thanks for your reply. Please forgive me if I seem a bit obtuse this morning...well, 3 pm is morning for me these days in view of my brimmed schedule.

From Chang's 9th edition, p 198:

What would happen if a diver rose to the surface from a depth of 20feet rather quickly without breathing? At the surface, the volume of air trapped int he lungs would have increased by a factor or 1.6. This sudden expansion of air can fatally rupture the membranes of the lungs.

 


Offline Borek

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Re: General Question About Gas and Diving
« Reply #3 on: August 31, 2008, 06:14:44 PM »
All depends on the amount of air that was present originally in lungs. If you are diving just with snorkel, no rupture is possible, as amount of the air on teh surface won't be higher than the lung volume. If you are scuba diving, with compressed air, you may have more air in the lungs - so when you rose expansion is dangerous.
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Offline nj_bartel

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Re: General Question About Gas and Diving
« Reply #4 on: August 31, 2008, 09:58:50 PM »
What Chang is saying is that if you took a breath from a scuba tank at that depth and held it while you returned to the surface.

Offline pantone159

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Re: General Question About Gas and Diving
« Reply #5 on: August 31, 2008, 11:30:55 PM »
Using SCUBA is the key point.

If you breathe in a full breath of air at c. 10 m depth, which is at c. 2 atm, hold it, then rise to the surface suddenly, this will want to double in volume and will cause severe lung damage.  This is why divers always keep breathing, never hold your breath.

OTOH, if you fill up at the surface, then dive to 10 m, the air compresses by x2, then if you surface quick, it is back to 1x volume, and everything is ok.  There is no concern when not breathing pressurized air.

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