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On Thu, 4 May 1995, Robert Laird wrote: > Granted the show was a little dated, but they made several > remarks that indicated heliox was a much better gas mix for > deep diving than trimix... i.e., ANY nitrogen in the gas mix > was bad. > > Not having read through my book on Mixed Gases, I thought I'd > ask the experts here. Is NO nitrogen better than a tiny bit? The word "better" in this context is too broad for a simple answer (besides, I NEVER give simple answers....;-) ) Helium is "good" for the following reasons: - No narcosis - Very light molecule; easier to breathe at depth - Very low solubility, so the total volume of dissolved gas is less - Exits the body much faster than N2, which is important for longer, deeper dives (like commercial saturation dives) Nitrogen is "good" for the following reasons: - Enters the body much slower than He, which is good for shorter, "shallower" dives and for decompression from Heliox dives - Narcosis can (might?) counteract the effects of HPNS on very deep, quick-descent dives - Lower heat conductance, if in the surrounding atmosphere - Cheap, plentiful, and easy to put in a cylinder at high pressures Commercial divers and other saturation divers are usually better-off with heliox than trimix, because it works out to be less decompression on sat. dives, and because they can take all the time they want to do a slow descent to minimize the risk of HPNS. Technical divers are usually better-off with trimix 'cause it's easier and cheaper to fill a cylinder with, and depths and times of dives are generally such that decompression time is less with trimix than with heliox. How's that? 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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