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On Mon, 2 May 1994, Carl G Heinzl wrote: > Each diver must *always* learn their own > limits. This is taught from day one in the basic openwater course. On the first sentence, I TOTALLY agree!!!! I've been trying to make this point for years. However, I'm not so sure the second sentence is true of many of the OWI courses I've seen & heard about. I think the idea of knowing one's own limitations should be the FIRST and MOST IMPORTANT concept taught in ANY diving course. > much more advanced diver. For those people that do get narc'ed easily, > Nitrox *will* help them dive deeper safer (bet many people never > thought of this one!). Actually, this is a misconception often perpetuated about nitrox. At first, it would seem that the reduction in nitrogen content of nitrox would reduce narcosis at a given depth. But the problem is, Oxygen ALSO appears to cause narcosis. A paper has been published on it (Hamilton was one of the authors) - I've misplaced my copy, but I sure somebody else on this forum knows the reference. Narcotic potency of gasses seems correlated with lipid solubility - Oxygen is about twice as lipid-soluble as nitrogen (I don't have the exact numbers with me now - again, I'm sure someone out there will post them). The complicating factor is that oxygen is metabolized and some of it is bound by hemoglobin, so that its dissolved partial pressure is somewhat lower in the tissues than the inspired partial pressure. "Oxygen narcosis" in itself is seldom a concern, because the PPO2 needed to cause it is WAY in the O2 toxicity red zone. However, the point is that because oxygen does seem to cause narcosis, nitrox is not a "less-narcotic" breathing mixture. The paper I mentioned earlier involves emperical evidence of this. Also, I've had an anecdotal experience which convinced me that nitrox is MORE narcotic at depth than air. Like many of my stories, it's a long one and I don't have time to write it all out now. Perhaps in a later posting, if anyone is interested. John Crea, who recently joined the forum, knows more about the concept of oxygen toxicity than I do....any comments, John? > There is some speculation going around that the body is more easily > able to take a "spike" in the PPO2 level if the gas being breathed > prior to the spike isn't near the limit (i.e. it's at 1.2 PPO2 or less). Yes, this does seem to be true, which is why the recommended PPO2 on a fully-closed rebreather is low (i.e. 1.0 - 1.2ATM) Just a few comments..... Aloha, Rich
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