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> The deep dives for Deep Air have been conducted at 120-130 ft. and on air. > I've been narc'd in the water up here and it would of been real nice to be > on 28% mix. I'm not sure I understand exactly what you mean here, so forgive me if I missed the point.... but do mean that you think you would experience less narcosis at 120-130 fsw on nitrox than you would have on air? I know that all or at least most of the agencies still teach that nitrogen is the only part of nitrox that causes narcosis, but this concept is quickly being replaced by a smoewhat more elightened concept (backed up by at least one study and a hell of a lot of experience from certain individuals) that the oxygen component of the breathing gas also contributes to narcosis. The best and easiest rule of thumb is that oxygen contributes to narcosis about the same amount that nitrogen does. This means all nitrox mixtures should be thought of as causing the same level of narcosis at a given depth, regardless of the O2:N2 ratio. Truth is, there is some pretty convincing anecdotal evidence that, under certain conditions, nitrox causes MORE severe narcosis than air at a given depth. However, this seems to be most true when the PO2 exceeds about 1.8 or thereabouts, and only when the PN2 is pretty high also, so for most nitrox dives, it's reasonable to consider O2 and N2 equipotent for narcosis. > One of the recurring themes in the tech community, is self knowledge and > reliance. Would it not serve people better just to offer a set of skills > classes and not put standards out there? Just relie on the ability of > people to judge their own skills and offer training for where they are at. > That way the communtiy could adapt best practices as they are found. A lot of us wish it could be that way; this is the underlying point of my little banner message I frequently append to the bottom of my messages. For a few of us, this is reality as well. However, there a couple of reasons why this ideal does not always work in everyone's reality. Specifically, standards are important for issues that involve lawyers, and for people who are in some way responsible for the actions of others (dive team leaders, institutional diving safety officers, etc). For example, George has a set of very strict standards for people who dive under his auspices. Without such standards, written on paper, I suspect he would not have been granted permission to dive in the places that he dives from whatever governmental agency that has jurisdiction. However, I would argue that the safety record of his team is NOT because of the standards per se, but because he has, through his experience and the experience of those he works with and was trained by, figured out the "best" possible way to do the dives he does, and that the people who dive under his auspices are smart enough to dive this way. My personal beef with the whole "standards" concept is that it goes hand-in-hand with the attitude of "Do it this way because I said so, and it's the standard so don't argue." This stance does not help students *UNDERSTAND* the concept, it only forces them to memorize certain numbers and arithmetical formulae. I tend to prefer the attitude of "This is why I do it this way, and why I don't do it another way. If you're smart, you'll either agree, or provide me with convincing evidence that there is a better way." In other words, what I would like to see covered in courses is the rationale behind why certain limits (such as max PO2 of 1.4 ata/bar) and certain fomulae (such as equivalent narcotic depth in feet = (PO2+PN2-1)*33 ) have come to be the way they are, including references to the sudies that shed light on the specific issues. I was not trained by any agency; I learned how to do mixed gas dives by myself (before any agency taught it). Although I am very fortunate to have survived some very stupid mistakes (which is why I do not recommend that people try to learn this stuff by themselves), at least I learned it from the "bottom up", meaning I read all the original source publications on the hows and whys of where these "standards" came from. I believe I am a much better diver for it. I believe training agencies should always work hard to stay at the cutting edge of what information is available about hyperbaric physiology and successful and unsuccessful diving practices (as evidenced by accident analysis), and should constantly be updating their certification programs (through dissemination of frequent periodic reports to all of their instructors) in response to new insights. Also, I don't think agencies should feel pressured into chosing one method or another; or one side of a controversey or another. Instead, they should present both sides of the issue fairly. For example, take the methods by which decompression profiles are calculated. Instead of just saying "There are these theoretical compartments with such and such half times and...etc", I think their courses should say "Nobody really understands what's going on physiologically during decompression. Historically, neo-Haldanian models [and explain the compartment-based system] have been used in conjunction with empricle evidence to generate decompression schedules. More recently, a statistical approach to modeling....[and explain the statistical methods]. Another approach to decompression schedule generation involves a lot of bubble dissolution physics...[and explain doppler results, and the basic concept of bubble-based decompression schemes]. There are important differences in the schedules generated by these different models [and then explain how bubble-based models call for deeper initial stops and less tedious shallow stops, etc.]" Then, the instructors should say, "Well, this is why I prefer to do it this way, but you have to decide how you're going to do it, because if you die it's your own damn fault because you shouldn't be going underwater where you weren't designed to go in the first place, stupid!" There are a whole bunch of issues besides decompression physiology which do not have clear answers -- PO2 limits, narcosis limits, oxygen narcosis, HPNS, long term neurological damage, manifolds vs. independant twins, whether to run your primary under your armpit, around you neck, or between your legs....and so on (Before George asks me to lick his Ball Bag, let me clarify that I agree there are "best" ways to do things in a well-defined environment, such as clear, warm-water limestone caves in Florida, for example.) The fundamental flaw in my scheme is that not all people who want to do deep mixed gas dives in demanding evironments (and not even all instructors) are intelligent enough or disciplined enough to make the right choices about how to do certain things. This isn't a flame, or even a cynical reflection on society; this is cold, hard, scary fact. Such people will die, and those deaths will ultimately bring harm to a large sector of the people who ARE intelligently doing it. Oh, hell, this got awfully long, didn't it? Sorry...but this morning I made my first dive in almost a month, and conditions were excellent, so I'm a little bit pumped. 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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