Pressure underwater

[StringJunky]

When you measure pressure as you go down, when you say it's "1 atmosphere", are you treating the atmospheric pressure above as 0 pressure and it's relative to that?

Edited August 5, 2018 by StringJunky

[Moontanman]

30 minutes ago, StringJunky said:

When you measure pressure as you go down, when you say it's "1 atmosphere", are you treating the atmospheric pressure above as 0 pressure and it's relative to that?

I am an open water certified diver, the pressure increases by one bar every 33 feet you go down. Looking at it from that perspective then at 33 feet you would be under 2 bars of pressure but one bar more than at the surface...  I am going to say from the perspective of decompression tables you do not consider the surface pressure to be 0 bar. Traveling in an airplane after a deep dive can be fatal even though you are fine at the surface... 

[StringJunky]

30 minutes ago, Moontanman said:

I am an open water certified diver, the pressure increases by one bar every 33 feet you go down. Looking at it from that perspective then at 33 feet you would be under 2 bars of pressure but one bar more than at the surface...  I am going to say from the perspective of decompression tables you do not consider the surface pressure to be 0 bar. Traveling in an airplane after a deep dive can be fatal even though you are fine at the surface... 

Cheers. Sorted.

[Endy0816]

Da. Likewise 1 atm ~= 14.7 psi.

[mistermack]

Going below 1 atmosphere becomes more and more risky. At the top of Everest, it's about 1/3 of a bar, and will kill most people pretty quickly.

I think the highest permanent settlement on Earth is roughly half the height of Everest, but the local people have evolved tolerance to those conditions, so most visitors would get sick living there.