Why are we not crushed by atmospheric pressure?

Answer 1

The pressure of the atmosphere is countered by the pressure inside our own bodies.

It's like when a pressurized submarine goes under water, it doesn't get crushed up to its limit because of the equal force being exerted from inside.

Hope this helps. :)

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The first sentence is correct: the air pressure in our bodies is equalised automatically to that outside. The comment about submarines is wrong. Submarine interiors are not pressurised. They rely on hull strength to survive and if they dive much too deeply the hull will be crushed.

Answer 2

Because we are used to it. Humans can get used to almost anything. Deep-sea divers have lived for weeks at pressures 20 times the atmospheric pressure at sea level; they live quite nicely on the sides of mountains where the air pressure is one half the pressure that we flatlanders are used to.

Standard air pressure is 14.7 pounds per square inch, or PSI. Of that, about 20 percent is oxygen, the rest nitrogen. Too much of ANYTHING will kill you. Above about 100 PSI, the nitrogen in the air will make you drunk and foolish; divers call it "nitrogen narcosis". Too much oxygen will cause seizures and blindness. Deep sea divers breathe a specially-balanced mixture of helium and oxygen that provide the proper "partial pressure" of oxygen. Divers with such equipment have been down more than 1,000 feet below the surface of the water, and survived.

If you lived in a pure oxygen environment in a spacecraft, you would only need 3 PSI of pressure to give you the "normal" amount of oxygen pressure.