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At 04:07 PM 3/23/00 -0800, Walter Jaccard wrote: Hello Walter, >100% at 20 ft. However, for some reason that noone can really explain, 100% >at any depth works better for decompression than anything else The short explanation: the higher the PO2 is over the total gas tension in the body, the faster the off-gassing of bubbles. This is because of the oxygen-window, which by definition is the difference between the hydrostatic pressure and the total dissolved gas tension. The oxygen-window phenomenon doesn't have anything directly to do with the presence of an inert gas in the decompression mix... it has to do with the hydrostatic pressure and the dissolved gas tension only. It's not an intuitive concept, and I think that's why people have so much trouble with it. Breathing 100% achieves the highest PO2 (therefore the largest oxygen-window and the fastest off-gassing of bubbles) during the *longest stops*, 10 and 20 feet. (Note the emphasis on *longest stops*.) The PO2 on 80% at 30 feet is 1.53 - a fairly large oxygen-window, yes, but you're only at 30 feet a short time compared to the time you spend at the 20 and 10 foot stop. The benefit of the large oxygen-window is brief. At 20 feet the PO2 is only 1.28, (a much smaller oxygen-window) and at 10 feet (your longest stop) it's only 1.04 (a tiny oxygen-window). Even at the 30 foot stop, the PO2 of 1.53 is ~4% smaller than 100% O2. With 80%, you benefit from a large oxygen-window for only a short time at 30 feet and gain very little from the oxygen-window during the comparatively long time you spend at 20 and 10 feet. You still off-gas, yes, but you don't get any benefit from the oxygen-window. I am working on a more comprehensive explanation of the oxygen-window, but it's a technical subject and takes time to write about clearly and concisely... and I have a life outside this list. :-) Hope this helps for now... -Mike Rodriguez <mikey@ma*.co*> Pn(x) = (1/(2^n)n!)[d/dx]^n(x^2 - 1)^n -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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