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On 9 May 1996, Billy Deans (FL) wrote: > Since 1989 certain phases of our dive operations have called for multiple mixed > gas dives on a daily basis. The secret is plenty of helium- I completely agree with Billy on this - that you should lean heavily towards more helium-rich gas mixtures on dives where you do multiple deep dives in a day. I think it's more important on the first dive than it is on the second dive. The reasons are: 1) More helium means deeper inital deco stops when you run your tables on a compartment-based model. And Y'all know how I feel about deeper initial deep stops.... 2) Helium is a "faster" molecule, so it comes out of you more quickly during the interval. This applies both to dissolved helium leaving your blood via the lungs, and helium molecules migrating out of bubbles and into your blood. In other words, your body "resets" more quickly during the interval. The offset to the helium leaving the bubble faster is that helium is less soluble in blood than N2, so the blood surrounding the bubble is apt to more quickly approach equilibrium with the PHe inside the bubble. 3) Over and above the fact that helium is faster, most people breathe air on the surface interval, and thus the *gradients* (both across alveolar membranes and across bubble membranes) will be steeper, thus enhancing the speed of offgasing between dives. I'm not as certain whether it is equally important to go heavy on the helium for the second dive of the day. Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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