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I think this private mail from George can benefit us on the ppO2 issue around deep diving. For me, I'd like to see at least 3 main streams of discussion that would benefit me the most: * ppO2 tolerance/seizures * ppO2 and narcosis * ppN2 and narcosis Anyone care to add on these? >> Hello George >> >>This is a private mail. I have followed the argument on deep air .x. mixed >>diving with a lot of interest and my perception is that ppO2 and ppO2 time >>exposure are the 2 central points for understanding the issues around deep >>diving and decompression diving. As you have a strong position on this, >>wouldn't you concede to write an article to the list and/or to some of the >>technical magazines so most of us could benefit from your access to information >>that goes beyond NOAA and the tech training agencies? >>Mauricio Henriques > > Mauicio, you are exactly correct in your assumptions. Without >being too speciific, I will answer this, and you can forward it >out to the list. > While is is true that there is a time/PPO2 tolerance expectation, >commercial diving has discovered that seizures can occure within >these bondaries, but that below certain PPO2's, the incidence of >seizures lessens dramaticly. This level appears to be 1.4 PPO2. >Miltitary (U.S.) goes even lower, like 1.2. Events like stress and >heavy workload can potentiate the mechanism that causes seizure, >either through depletion of the associated brain chemistry, as >in anything that blocks the reuptake of epinephrine, the action >of free radicals in depletion of chemistry, or something as simple >as the vasodilating effect of a buildup in CO2 partial pressure, >or something as complex as glutamate increases, or increased >levels of certain hormones, like estrogen. There are many others >who can elaborate on this a lot better than I can. > Whatever the case, my thinking is to avoid the boundary >as much as possible, and to that end I observe commercial >diving experience and standards. So, maintaining a lower >PPO2 is one objective of mixed gas diving. The other objective >is to plan a mix that will allow you some room for time error >in your dive. For ways to alleviate a buildup in oxygen exposure, >you must work with more sopisticated models, and for that we >use commercial sources. > The other benefit of mixed gas diving is to set the "depth" >by means of the helium percentage as a means of reducing the >nitrogen partial pressure to reduce the effects of narcosis and >to avoid the microcirculatory damage associated with high pressures >of nitrogen. > Additional benefits accrue in the form of reduced decompression >requirements for mixed gas over air. > In general mixed gas is a useful tool for most types >of diving. > - George Irvine Enjoy! --- Mauricio Henriques Network Consultant Phone: +[55](21)297-1122 x.4715 Digital Equipment Co. FAX: +[55](21)220-3324 Brazil mauricio@va*.en*.de*.co* ---
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