How can air volume shrink as you go deeper, when the tank itself doesn't shrink?

[CT-Rich]

So, what would happen if you went on a deep dive after a couple of your lunch burritos had time to ferment at depth and then you ascend?

I am questioning the wisdom of answering this…. Gas in your gut will also be compressed. If you form more, it will expand upon rising. I have never met anyone that had this as a problem, but I am sure there is a story out there…

 

[tursiops]

I am questioning the wisdom of answering this…. Gas in your gut will also be compressed. If you form more, it will expand upon rising. I have never met anyone that had this as a problem, but I am sure there is a story out there…

That gas has an escape route...an overpressure valve, as it were. Many of us use it all the time to make sure it will work when we need it for our next deep dive in Coz. Always good to test your gear.

 

[CT-Rich]

That gas has an escape route...an overpressure valve, as it were. Many of us use it all the time to make sure it will work when we need it for our next deep dive in Coz. Always good to test your gear.

The burrito barotrauma

 

[RXTdiver]

A very common question with some excellent responses so far. My take, FWIW:

4. Your lungs are only compressed when you descend while holding your breath. Because of the action of your regulator (#3), your lungs during normal respiration while diving contain the same gas volume as they do on the surface. There are just more gas molecules packed into that lung volume. The deeper you go, the higher the pressure will be in your lungs, therefore the more gas molecules your lungs contain.
This is why your tank is used up more quickly the deeper you go - deeper = more gas molecules in your lungs = using the available gas molecules in your tank more quickly.

As you progress in your diving, you'll learn to calculate approximately how long your tank will last at any given depth given your own personal air consumption rate.

Best regards,
DDM

Thank you for mentioning that. I always thought you lungs volume got smaller as you go deeper but after reading your post and everybody else's posts, now I understand why the lung volume at any depth would be the same as on the surface.

 

[RXTdiver]

Thank you everybody for your helpful replies.

 

[Dan]

I thought that the air in the tank would get compressed as you go down deeper.

No. The air in the tank would be compressed to whatever tank pressure gauge shows, regardless the depth. It will get decompressed as you let the air bled out by you breathing from it through your regulator or feed the air into your BCD.

 

[The Chairman]

In the picture below, at 50 meters the gas volume is only 17% of what it was at the surface. At that depth, surely the tank itself isn't 17% of what it was at the surface. Although the tank is exposed to much greater pressure at 50 meters than at the surface, how does the air in the tank actually get compressed into such a small volume? The tank is sealed with no openings so it's not like water can get in there to compress the air that is in the tank.

Here's another question. If you were to visualize the arrangement of the air particles when the air is compressed at any given depth, what would that arrangement of air particles look like? Would all of the air be concentrated at the bottom of the tank (due to gravity), concentrated at the top of the tank, spread out evenly throughout the tank, something else?


View attachment 794741

The whole point of this is to demonstrate that BOYLES Law is actually an acronym for
Breathe Or Your Lungs Explode Stupid.

The air in your tank remains the same.
The air in your lungs will create an air embolism if your try to hold your breath as you ascend!

 

[Dan]

how can the pressure in the tank change with depth?

Because you bleed it out by breathing through regulator. Take a spare tank with a pressure gauge on the tank that shows, say 3000 psig and don't breathe from it and see if that spare tank pressure would go down or not. I bet it'll stay the same at 3000 psig at depth.

 

[RXTdiver]

Because you bleed it out by breathing through regulator. Take a spare tank with a pressure gauge on the tank that shows, say 3000 psig and don't breathe from it and see if that spare tank pressure would go down or not. I bet it'll stay the same at 3000 psig at depth.

Looking back now I can't believe I posted that question.

 

[L13]

Looking back now I can't believe I posted that question.

The power of education.