In scuba, why does the diver’s air get more compressed with depth? Does the tank not protect the air from outside forces?


In scuba, why does the diver’s air get more compressed with depth? Does the tank not protect the air from outside forces?

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The air in the tank is already pressurized (compressed). The diver breathes through a regulator that lowers the tank air to the same pressure as the “outside forces”. That is why a tank of air will get used up faster the deeper the diver goes.

I don’t think the air in the tank gets more compressed as the diver goes deeper. When people talk about pressure increasing with depth, they are talking about the effect of the pressure on the diver’s body, and on the air from the tank once it has left the tank.

The air in the tank doesn’t get more compressed, it’s unaffected unless maybe your corpse falls down the Marian’s trench.

The regulator drops the air pressure from that in the tank to match ambient for you to breathe. If you’re above water, it lets out normal atmosphere pressure air. If you’re 10m under water where water pressure is two atmospheres, it lets out air at two atmospheres to breathe.

Why does it do this? So you’re lungs and chest don’t collapse. If you were still breathing in surface one atmosphere pressure air but had two atmosphere pressure water on the outside of your chest, it would be like trying to breathe with someone sitting on your chest.

The tanks do not get compressed when you dive

If you look at [Diving_cylinder]( a bar approximately an atmosphere and the pressure increase by 1 bar per 10 meters of depth. So the low-pressure take will have higher pressure on the inside down to 1650meters depth. The tanks will not be compressed to any significant degree for the depth you dive at

* low pressure (2400 to 2640 psi — 165 to 182 bar)
* standard (3000 psi — 207 bar)
* high pressure (3300 to 3500 psi — 227 to 241 bar).

You breathe in the air at higher pressure at lower depth because you like to have the pressure in the lungs the same as the pressure of the water so there is not net compression on your lungs and ribcage.

It would be had/impossible to breathe anything in if the pressure is a lot slower than the water pressure because you need to push against the water to expand the lungs and get air in.

No because the tank is really only providing you with air, and the wetsuit/drysuit doesn’t protect you from water pressure. If you want protection from the pressure you would need to be in atmospheric pressure suits.

The pressure inside a SCUBA tank is much greater than the outside water pressure – even when a couple hundred feet deep.

The air coming from the SCUBA tank is always moving from high pressure to lower pressure, it does not “get more compressed” with depth. It just does not drop in pressure as much as it would if you were breathing at the surface.

The air inside the tank can be over 3,000 psi. The first stage of the regulator (the part that clamps onto the tank) reduces the tank pressure to about 150 psi. That is 150 psi above ambient pressure. The deeper you go the higher the absolute pressure, but the first stage always provides 150 psi above whatever pressure you are in. *150 psi is an example from memory, the exact values may be different.

That means that there is always 150 psi of air in the hose that connects to the second stage (the part that goes in your mouth).

When you are at depth the ambient pressure is greater. When you breathe in air from the 2nd stage regulator at 33 feet depth, the air in your lungs is almost 30 psi (absolute pressure) or about 15 psi greater than when at the surface.

For every 33 feet of depth the pressure increases by about 15 psi.

At some point, when the tank is nearly out of air, the first stage will no longer supply the 150 psi of pressure – because the tank itself is less than 150 psi. You might find that you have to “suck” the air out of the regulator. Of course if you are doing this then you have failed to be a good diver.

Source: I’m a PADI Divemaster and I used to service and repair SCUBA equipment.