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Richard Pyle answers:
>The less-simple answer is that CNS O2 toxicity may be *GREATER* for air than
>almost any other technical diver's breathing mixture at a given PO2. The
>reason for this is that a deep air dive combines high PO2 with high gas
>density, which means exertion of breathing is greater, which means CO2
>levels may be higher, and increased CO2 levels appears to increase the
>probability of a CNS O2 toxicity problem. Enriched-air nitrox mixtures
>achieve a given PO2 at depths shallower than the same PO2 for air, and O2
>is a lighter molecule than N2, so enriched air will always have a lower
>density than air at any given PO2. Almost any practical mixture with helium
>in it will similarly have a lower gas density than air at any given PO2.
>
>Not to mention the added complexities if there is truth to the trend that
>CNS O2 toxicity is more likely for gas mixtures than for 100% O2 (i.e.,
>which gases affect toxicty problems and how)......
>
The relationship between CO2 fraction and oxygen toxicity sounds
interesting, but O2 is NOT a lighter molecule than N2. O2 has a molecular
weight of 32; N2 has a molecular weight of 28. I thought he might have
meant viscosity, so I looked that up, and viscosity for oxygen is higher
than air which is higher than nitrogen. What have I missed?
-----------------------------------------------
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Gene Hubbard | logo under |
ghubbard@at*.ti*.co* | construction |
San Diego CA +--------------+
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