Boyle's law incorrectly used throughout the freediving literature

[VincentMicah]

Boyle's law states that at constant temperature, the volume of a given amount of gas is inversely proportional to its pressure. If you've taken a freediving class you've probably been taught that if you dive to 90m you will experience a 10-fold increase in pressure, and therefore the air in your lungs will get compressed to a 10th of the volume it occupied at the surface.

Well, no, not quite, because if we're talking about the air inside your lungs, then to apply Boyle's law we have to use the pressure inside your lungs too, and having 10 atmospheres of environment pressure does not mean there's 10 atmospheres also in your lungs. It's certainly not the case for a submarine: if a U-boat goes down to 90m, the pressure inside the vessel does not increase 10-fold, so why would it be for your lungs? True, your thoracic cage is more flexible than a sub, but your ribs will still oppose those 10 atmospheres quite stubbornly.

 

[Nathan Vinski]

Realistically speaking, there will be a tiny difference as the ribs, and tissues will exert some outward force. However, the body isn't that strong compared to water, so the vast majority (it's probably not been tested, but I'd assume somewhere near 99%) of outward force is created by the air-pressure in the lungs.

According to boyle's law, air needs to be compressed to 1/x the absolute external pressure to exert outward force that's equal to the inward force.

of you consider that the ribs may provide some tiny amount resistance, realistically we're probably looking at a ratio of something like 0.99/x

--

Of course, you can mechanically exert more outward force with the muscles, but in freediving we call this 'Tension'.

Tension in the breathing muscles is the #1 factor in causing shallow (less than ~50m) Lung-squeeze (pulmonary oedema) or the inability to equalize. (if internal pressure is less than external pressure, you can't equalize: Equalize means = pressure on both sides.)

--

Now what about at great depths (deeper than 50m), below the point where the ribs can no longer be mechanically compressed.

again, the body isn't that strong. If nothing happened and the internal pressure stopped increasing, they would probably crack or dislocate due to the enormous external inward force.

At this point the blood vessels on the alveoli become swollen, and this swelling displaces the air further, to the point where the internal pressure is nearly equal to the external pressure: Probably something like 99% or 0.99/x volume.

Again, if it wasn't near-equal, the body would be destroyed & equalization of the ears would be impossible..

 

[VincentMicah]

Boyle's law states that at constant temperature, the volume of a given amount of gas is inversely proportional to its pressure. If you've taken a freediving class you've probably been taught that if you dive to 90m you will experience a 10-fold increase in pressure, and therefore the air in your lungs will get compressed to a 10th of the volume it occupied at the surface.

Well, no, not quite, because if we're talking about the air inside your lun
appvalley tutuapp tweakboxgs, then to apply Boyle's law we have to use the pressure inside your lungs too, and having 10 atmospheres of environment pressure does not mean there's 10 atmospheres also in your lungs. It's certainly not the case for a submarine: if a U-boat goes down to 90m, the pressure inside the vessel does not increase 10-fold, so why would it be for your lungs? True, your thoracic cage is more flexible than a sub, but your ribs will still oppose those 10 atmospheres quite stubbornly.

issue solved!!