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At 06:40 AM 6/6/97 -0700, you wrote: >Frankly, I thought Nigel�s comments raised some interesting questions >not only about the use of oxidizers but the use of low percentage >helium trimixes for conventional shallow diving. > Bob, Nigel's comments do raise a question about the use of high fO2 breathing gasses such as nitrox. The problem is that he has confused oxidants with Oxygen. Free radicals (the little buggers antioxidant destroy) are NOT Oxygen. They are molecules that have one or more extra electron. They readily "give up" that extra electron in a chemical reaction known as "oxidation". There is a second part to the "oxidation" equation, that is "Reduction". This type of reaction results in a covalent bond between two or more atoms. There is no need for Oxygen to be present for "oxidation" to take place. For example NaCL (salt) is formed when one atom of Sodium (Na) is "oxidized" by one atom of Chlorine (Cl) which is "reduced". Again this has nothing to do with Oxygen! Nigel is right on target about the effects of antioxidant vitamins and current medical thinking with regard to cancer and other disease. However he was unable to differentiate between Oxygen, an element, and oxidation, a chemical reaction. I don�t believe Nigel fully understands nitrox, He wouldn�t use the expression "ultra hyperoxic" for a nitrox mix if he understood. Here is a little different twist on the "Nitrox vs. Tri-Mix" debate. For a moderately deep dive say 160� why not use a Tri-Mix with a 24% fO2 and 15-25% He. Or for a 120� dive how about a 30% fO2 and 10-20% He. If you run tables using many (if not all) of the available deco software, you will find a very similar profile to Air if you use nitrox for decompression. These are EXAMPLES ONLY!! I DO NOT SUGGEST USING ANY GAS MIX WITHOUT PROPER TRAINING AND UNDERSTANDING. I know there are still many misconceptions with regard to nitrox. And many more with regard to Tri-Mix. If nitrox and Tri-Mix scare you, don�t use them. But whatever your choice for a breathing gas is, understand your choice and why you made it. Because "my instructor said so" is not understanding! >>A quote from Nigel, >>I was in the chemist yesterday and I couldn�t help but notice that almost one entire aisle of the store was devoted to antioxidant vitamins. Let�s see: there were all sorts of vitamin Cs, vitamin Es, vitamin A , B complexes, pynxogenol, mineral supplements and to top it all off hormones like melatonin which spposedly has mega antioxidant powers. In fact the whole thrust of the anti cancer and anti aging crusade seems to be oriented around the power of antioxidants in preventing free radicals from damaging connective tissue and DNA. Many physicians now agree that colon cancer as well as arteriosclerosis are preventable through a proper diet, high in antioxidants.<< >>When this as a backdrop why on earth would anyone in their right mind voluntarily expose themselves to a ultra hyperoxic breathing mix unless it was absolutely necessary. I would love one of you Yank diving rocket scientists out there to tell me that oxygen is not an oxidizer if you breath it (while you busily oxygen clean tanks and replace buna o-rings with Viton). Instead of boosting the oxygen content of the breathing gas I would lower it and replace it instead with an inert gas such as helium. Nitrox I should really be 12 - 14% helium and 19% oxygen. Nitrox II should be slightly higher helium and lower oxygen still. I am not advocating this for deep diving either (Deep diving for me is another whole subject). This is strictly my suggestion for a physiologically more healthy mix. Helium is a very rapid diffusing gas and transits the tissue rather quickly for low to moderate exposure dives. Weigh the advantages: reduced ppo2, reduced ppn2 (bad for those red blood cells and capillaries) and reduced deco (if you don�t have a pfo). << >>Helium is bloody expensive in the UK and Oz, but when you keep the mix to 10 -14% on an 80cf tank you can get as many as 30 dives out of a 290-300cf cylinder of helium when you cascade several. Even at $200 U.S. per cylinder this works out to 6 - $10 additional cost per dive. Big deal! Look what dive charters cost these days and with the weather in the UK being typically bad all of the time, how many weekends of diving do you actually get anyway. We spend more on petrol driving to the port of embarkation.<< Bill (aquadart) Bott -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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