O2 question - No

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Posted by Kevin on February 02, 2001 at 17:00:55:

In Reply to: Some O2 questions posted by mattschechter on February 02, 2001 at 15:23:22:

Dear Matt:

The human body needs to a minimum of 0.16 ATA of Oxygen to live. Some may argue a little less, some may argue more, but the approximate figure is 0.16 ATA.

The human body starts having problems with a CNS exposure around 1.4 ATA or 1.6 ATA. Like I said some may argue more, such as U S Diver Exceptional Exposure tables, but those are the rough upper limit numbers. ( For this question forget about Pulmonary Oxygen Toxicity ( the chokes ) when you uptake too many Oxygen Toxicity Units )

Remembering that the pressure that a gas exerts is equal to the percentage of gas in the mixture multiplied by the overall pressure, your scenario is not possible.

For instance at sea level ( or one ATM ) we are breathing air, and that means roughly 20.9% is oxygen, rounded up to 21% for discussion. That means that you are breathing .21 ATA of oxygen.

A diver breathing pure oxygen at 20 FSW would be exposing himself ( or herself ) to 1.61 ATA times 100% or 1.61 ATM of oxygen, the upper limit. A mountain climber high up in the Andes can easily climb so high, that the reduced atmospheric pressure causes his 21% air to be no longer able to sustain life, hence the reliance upon 100% oxygen at elevated climbing altitudes.

There is no way to be at both the maximum exposure ( 1.4 or 1.6 ATA ) and also be at the minimum ( 0.16 ATA ) at the same time !!

Does this make sense ? Its been a long Friday at work, email me if you need additional info or want to borrow some basic nitrox textbooks.

I will be at Redondo Beach this Sat morning, experience some 1.4 ATM O2 myself !


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