# Breathe Air from a source without any pressure compensation?

I just thought about what I'd do if I was on a sinking ship and of course breathing was the first thing that came into my consideration.

Now imagine the ship's front going up and the room you are in being filled with water. An upper edge of the room (where 2 side-walls and the ceiling meet) will be - at one point - the only one containing air (as the rest of it is filled with water). I could swim there and grab some air before trying to escape. But regarding the fact that water doesn't compress very well this will get harder the less volume is taken by the air.

When I think about 100l of air at the described edge of the room I suppose this won't affect breathing too much as I guess there is enough space to compensate the pressure. But let's say there is only 2 liters of air surrounded by said water, do you have a chance? Your lungs won't be able to push the air that much that the water level somewhere else at the ship will rise (maybe at the edge of the room next to you) right?

To eliminate any sources of error let's just assume the room is built out of one piece of steel without any holes, also there is no waves at al.

Inhale first and exhale second. Since you are removing a volume of air no problem. It will only matter as you rise to the surface and the air in your lungs expand. That could be a problem.

• "Since you are removing the volume" what do you mean by that? Btw. I kind of found the answer on my own now Commented Sep 10, 2015 at 21:01
• When you inhale you will be taking in a volume of the air remaining, pressure will be going into your lungs not so much into the surrounding room. Negative pressure will be created. Commented Sep 10, 2015 at 21:06
• Already answered this one on my own with the exact same solution, will tick yours tho for the effort. You might wanna expand for others maybe. Commented Sep 10, 2015 at 21:08

Almost panicking about the thought of not being able to breathe I noticed my stomach moving - which made me that my stomach which is still in the water will roughly move as much (and therefore make room) as the air I am inhaling/exhaling which should roughly compensate the compression/release of pressure.

Looking forward to surviving a few more minutes :D

But regarding the fact that water doesn't compress very well this will get harder the less volume is taken by the air.

If water is flooding the room, the room must have a breach where water can enter. As such exhaling will just push the water out. The incompressibility of water is not a factor. Only the pressure of the water at the breach.

• But try to blow water through a 1m hose. It is incredibly hard already Commented Sep 10, 2015 at 21:46
• In this scenario though, the air in the room is already compressed. So it is much easier to breathe in than from a hose to the surface. There might not be much left due to compression, but at equilibrium, it won't be hard to breathe. Commented Sep 10, 2015 at 21:49