So I was coding the scale-height-based density calculations and to verify some of the calculations I ran it at 60km and ended up with an atmospheric density equal to that of Earth’s.
However, I ran it again at 50km and the density is twice as much already! At 35km (where we parked the first extractor) it is almost 7 times the density as it is at sea level on Earth.
It looks like we are at the 100 PSI level at 35km. As long as there is an inert gas like Helium making up 95% of the volume it is survivable. You would have to carry an oxygen breather which exhausts the CO to the atmosphere.
Long-term exposure to that pressure will cause aseptic bone necrosis similar to underwater exploration here on Earth. The deep-dive record is above 30 atmospheres, we are only talking about 7 atmospheres here.