When diving underwater, oxygen is typically considered toxic at a partial pressure of 1.4. However, hyperbaric chamber treatment tables regularly require taking patients up to 60fsw on 100% O2, which translates to a partial pressure of 2.81. Why is the same amount of oxygen more toxic underwater than in the chamber, if the pressure exerted on both the body and the gas are the same in both scenarios? What variable when we’re “dry” allows us to tolerate more than double the amount of oxygen than when we’re “wet”?
In: Biology
You will definitely run into oxygen toxicity/seizure territory in a chamber in the low-mid 2atm range. Safety guidelines basically disallow you being above 2.5atm on pure oxygen for longer than 30 minutes. Generally if you’re getting a treatment at those pressures, you will be given “oxygen breaks” where the gas is occasionally switched to normal air instead of oxygen. There’s a whole bunch of science, partial pressures, exchange rates under pressures with different gas mixtures, etc. that I’ve forgotten since taking a hyperbaric operator course, but in general the answer is it’s not really that different, you just have a lot more control of a chamber than under water.
There might also be some confusion on terminology, as 33′ of water is 1 ATM of water but it is 2 ATA because of the 1 atmosphere of air above it. I generally calculated a dive with atm, but the chamber I ran also showed in PSI which I felt was a bit easier to read and adjust for.
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