Partial Pressures and Depth Question

[pelagic_one]

Thank you all. The pop bottle opening is a perfect example.

 

[rjack321]

Are the lungs capable of rapid degassing? I guess so? Is there a study about this?

It's not really possible (or necessary or in people ethical) to study individual tissues. In theory, any tissue can get bent. In practical terms, if your lung tissues are over their maximum tolerable dissolved gas pressures the rest of your body is probably already dead or fizzing so badly you'll be dead shortly.

 

[gmerick]

Take an unopened clear plastic bottle of soda underwater with you on your next fun dive.
When you get to 30 feet or so, the bottle will loose it's firmness. Shake it well, it should still be squishy. Hold it upside down, and take off the cap.
The soda in the bottle is a liquid supersaturated with CO2. The ambient pressure of lake water at 30 feet is greater than the ambient pressure of CO2 in the soda.
As you ascend, the two pressures will reach equilibrium, and soon (about 9 feet) gas bubbles will form in the soda, and collect at the upper end of the bottle.
Think of the soda as your tissues, the surface of the soda at the upper end of the bottle as your lungs.

 

[pelagic_one]

gmerick, that'll be a good demo, I'll use a clear soda.

 

[gage_patton]

I conceptualize it (probably over simplified): that the ascent (i.e., decreasing ambient pressure) is what stimulates bubbles, but once they form, you want the highest partial pressure differential practical to start eliminating them.

This is a good way to conceptualize it!

 

[gage_patton]

A carbonated beverage has no bubbles when it is sitting in your refrigerator, but it suddenly gets bubbles when it is opened and exposed to ambient pressure.

This is really helpful for a mental picture

 

[dmaziuk]

Now the question is, if you switch to Nitrox as the gas on ascent, are you making a greater partial pressure gradient, as you would by ascending too fast, leading to the bends?

I think it probably could if you didn't oxtox first. At least that's what seems to happen to divers who switch to deco gas at depth and make it to the A&I forum.

 

[L13]

Easy summary:

• Gas transport (in/out of tissues/bubbles/lungs) is driven by partial pressure gradient - Dalton's law
• Bubble formation driven by ambient pressure vs supersaturation.
• Bubble expansion is driven by change in ambient pressure - Boyle's law

Three different but related phenomenon.

 

[lowwall]

If you want to observe gas bubble formation firsthand without getting soda all over your arm, all you need to do is heat up a pot of water. A fluid's ability to hold dissolved gas diminishes as its temperature increases. At a high enough temperature, but still short of the boiling point, the gases will start to come out of the water in the form of bubbles that spontaneously appear at scratches or pits at the bottom of the pot.

Edit: I went ahead and did this myself. It's kind of fascinating.

 

[rjack321]

If you want to observe gas bubble formation firsthand without getting soda all over your arm, all you need to do is heat up a pot of water. A fluid's ability to hold dissolved gas diminishes as its temperature increases. At a high enough temperature, but still short of the boiling point, the gases will start to come out of the water in the form of bubbles that spontaneously appear at scratches or pits at the bottom of the pot.

View attachment 897791

And the higher the altitude (with lower atmospheric pressure) the lower the temperature it takes to reach a boil