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I'd like to propose a self-test for someone who is interested in trimix. Sorry that it's a bit long... First, is your gear adequate for a nontrivial 200+ fsw dive (e.g., 20 minutes bottom time)? If you don't know, then it probably isn't. Second, are you comfortable in a double tank setup with two stage bottles? By "comfortable" I mean: Can you swim, maintain trim, and manage your bouyancy, even in a current, or when low on air, with two stage bottles? Can you reach a piece of gear without looking, or thinking hard about where it is? Can you reach all your valves and emergency equipment? Can you execute a gas switch while ascending or descending a line? Third, have you thought through contingency plans for failure of any single piece of equipment? Have you ever practiced a valve drill, emergency ascent line deployment, stage bottle removal and recovery, and air sharing through a wreck/cave restriction? Fourth, are you familiar with gas & decompression planning for deep dives (and overhead environments, if appropriate), and do you have the maturity and discipline to stick by your plan? If the answers to all are yes, then you should have little trouble with trimix (in fact, you can probably read a trimix book and skip the course). On the other hand, if you can't do these things at 100 fsw on air, you will not be able to do them on trimix at 250 fsw. I believe these criteria are relatively independent of how many dives you have. An often-proposed criterion for trimix readiness is experience at 160, 180, or even 200+ fsw on air before doing gas. This requirement should have nothing to do with physiological tolerance for narcosis. What it should mean is that you are sufficiently comfortable with the technical skills described here so that you can accomplish them even when somewhat impaired by narcosis. If a skill isn't well-enough learned as to be semi-automatic, then it will disappear under the influence of nitrogen. To comfortably dive deep on air, one must have mastered his equipment and diving skills to the point where he can focus (what is left of) his mind on his environment. All these things will be presented to you in a deep air or technical nitrox course, but the few dives you will do in these courses aren't nearly enough to give you the experience you need to master these skills in an emergency situation at depth. If deep ar/tech nitrox are the first time you are exposed to doubles, stage diving, or decompression diving, then consider spending a year or two and 50-100 dives getting used to the equipment and procedures before moving on to trimix. John Heimannj@ma*.nd*.gt*.co*
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