Re: I dont have a choice right now ... but thanks ..., the first place to look for a dive instructor

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Posted by Kendall Raine on May 28, 2002 at 15:10:57:

In Reply to: I dont have a choice right now ... but thanks ... posted by Karl on May 28, 2002 at 14:28:00:

As you like. The going onto Nitrox as soon as possible sounds a bit like the old "get off the He as soon as possible" school of deco. If so, please consider what you're going on to. If you're choosing, He is a lot easier to deco from than N2. This presupposes correct use of deep stops. People like Shreeves focus on the diffusivity of the inert gas and ignore the lipid solubility, which is the real Boogey Man. If you want to get off back gas, consider something like 35/35 trimix at 120 then 50 at 70 and 100 at 20.

I'm afraid I couldn't disagree more on your statement that the use of 50 and 100 are dive plan dependant (I'm paraphrasing, I know). Using a deeper deco mix is fine as long as you can manage the gasses and keep the FN2 low enough on the deeper mixes, but not at the expense of not using 50 and 100.

That's why I said Low Ox is out the Window. That's a pun on the Oxygen Window which is the key to the whole topic. Low Ox Nitrox mixes are not utilizing the Oxygen Window efficiently.

When you've had a chance to look into this concept a bit more, you might ask your instructor how he defends 36 and 80, particularly 80, in terms of the Oxygen Window. If he says, "well, you're at 1.6 ata at 30 fsw on 80%" he's totally missed the point of the Oxygen Window and really should look into additional training himself. If he says "80% costs you only a few more minutes of deco but substantially reduces the CNS clock" he's diving by the numbers and doesn't know how to do deco.

Trust me on this one, Karl, I've done it both ways and I know what I'm talking about.

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