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Hi Mike and Bob, On the Scuba Chat on AOL last evening, we had just started to talk about the concept of using the heli-air trimix blends as possible bottom mixes instead of other blends of trimix, when time ran out. Now previously you had written... RDecker388@ao*.co* or mhkane@pr*.ne* (I'm not sure which) wrote: << I often have these discussions, and generally what I do is focus on a few simple concepts. In that I suggest that at least we [DIR] are presenting something. Many seem to want to just argue the anti- *anything* approach. I always suggest let's go line by line. What do you believe in your system is better than what we believe in the DIR system and why??? I have little, if any, tolerance for someone who just wants to argue for the sake of agrguing. If you have a position, put it forward and let's discuss the merits. >> I am not arguing against anything. I have learned a great deal from studying about, analyzing and adopting various DIR techniques. I would like to understand why the apparent objection to using heli-air. I see one important (to me extremely significant) advantage for heli-air and one other nice feature. The significant advantage is that at any time, I can use an oxygen sensor and determine exactly what is in my tanks. This is not true with other trimix blends. And the nice feature is that because I can analyze my blend, I can have confidence in topping off my half filled tanks after each dive, with Helium and then air to optimize the mix for my next dive. In both of these cases I am not dependent on the accuracy of any compressor pressure gauges or the conscientiousness of fill station operators or any other personnel, in determining exactly what I will be breathing. And when I need a bunch of tanks for a dive team, this becomes IMHO, particularly important. I teach my students that it is real risky to dive using any tank (nitrox or trimix) that they haven't personally analyzed with an instrument that they have personally calibrated. As far as the use of heli-air as a bottom mix is concerned, I don't understand the objections. It's just like other trimix blends but with a somewhat lower oxygen content. I pick an acceptable END and that then defines the mix. Typically the PP(O2) comes out to a little below 1 ATA at depth and remembering that we are talking here about bottom mixes and not deco mixes, a slightly lower PP(O2) would not necessarily seem to be such a bad thing. And of course for any mix for a dive of less than say, 400 feet, once I am down to 20 or 30 feet, the mix is no longer hypoxic, so I don't "need" a travel mix. So could you please explain, in slow and simple terms, what problems are being created? Have I missed something? Since I obviously would have deco gasses available for any required surface swimming, why is 18/50/32 so much better of a mix than 10/50/40 for a say, 250 foot dive? I'm not trying to start any kind of argument here, but I would like to understand the rationale for precluding the use of these heli-air mixes. I have attempted to explain "What do you believe in your system is better than what we believe in the DIR system and why???" Although I would not use the word "better" but rather "different." I understand that this subject has been discussed previously on this list, but I have not been able to find the answers to my questions. The previous discussions seems to concentrate on Richard Pyle and Sheck Exley using heli-air, calling heli-air "poor man's trimix" (which as an aside, I had thought only referred specifically to the 17/17 blend obtained from putting 500 psi of Helium in an Al 80 tank), saying that oxygen should be available for mixing, and arguing that if you can mix heli-air then you should be able to mix trimix. But I cannot find any discussion of why heli-air should not be used. Thank you very much for your time in answering my question. Take care and safe diving, Scott -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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