Air Pressure half as mile underground

[samsara15]

Years ago, I went to an Iron mine in Minnesota, and we took an elevator half a mile underground. Why wasn’t the air pressure down there stiffling?

 

[H=Leo]

To keep everything safe, pressure regulators are displaced in mines. It is used to regulate the air pressure there so that miners working extended hours won't feel sick. ( There are quite a number of cases before where miners fell ill because of this.) The principle behind this is just like the cabin pressurization in airplanes, just the opposite of that.

 

[sophiecentaur]

1/2 mile (only 800m) above ground is hardly a big deal so why would 1/2 mile under the ground be?