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Hi Kent, Thanks for the answer to my questions. In a message dated 8/5/00 10:53:16 AM, klind@al*.ne* writes: << Scott: First, Can you point to a single depth for with a heli-air mix is the ideal mix? How about planning a typical trimix wreck dive that is 220' on the sand. What is your target END for such a dive and what is your max PP02? Cutting way back on your oxygen just means more deco and it puts you in much more of a world of hurt if you have to bail out and/or lose some or all of your deco gas. If an emergency forces you to surface without any deco at all, you'll be in much better shape if you have been breathing higher PP02 bottom gas during the dive. >> I have to agree with you here. << Second, if you are afraid of handling and mixing Oxygen, how are you going to fill your deco bottles and what are you going to fill them with? If you're going to do any deco then you need oxygen clean equipment and you need to know how to handle oxygen anyway. Playing with Heli-air won't get you out of handling oxygen. And if you're going to be handling oxygen anyway, there's no conceivable reason not to put the correct amount of oxygen in your bottom gas at the same time. >> This is not a problem for me. << Third, if you don't have confidence in how your tanks are being mixed run screaming from that shop and don't look back. If you're going to be mixing heli-air you're going to need an accurage pressure gauge and an accurate O2 analyzer anyway. How does adding a third gas make any difference? You still need to closely monitor the amount of each gas you put in and you still need to analyze your final mix. >> You can't believe, well maybe you can, some of the stuff I've seen going on when filling tanks. As an example when mixing nitrox, I put in oxygen and ask for a 3000 psi fill of air. I watch as the compressor pumps the tank up to 3700 and then the fill station operator shows up, says "Oh sh*t" and bleeds the tank back down to 3000. Great for mixing, huh? It's stuff like this that I'm worried about. << Fourth. what's with this "topping off with helium?" What shop do you know of that has helium in 3500 psi banks? >> I don't really need 3500 psi helium. For example, say I'm diving 40% heli-air and I come back with 1300 psi of gas in a pair of Al 80's. If they're topped off up to 1980 psi with helium and then pumped to 3000 with air, then I'm ready to go again. And if I don't need too much, I can usually get 2000 psi helium. << This is not a sport that lends itself to cutting corners. The people who survive and thrive in this sport are those who are obsessive about every aspect of the sport; gear, technique, planning, fitness, etc. Getting mentally sloppy or lazy about what you are doing is a recipe for disaster. -Kent- >> I agree that cutting corners is not the thing to do. In fact it was my being obsessive with measuring what I was breathing that led me to heli-air in the first place. But I understand Bob's (and your) arguments and I need to agree. Heli-air is indeed a compromise that may well not be the wisest choice. Again, thanks a lot for answering my questions. Take care and dive safe, Scott -----Original Message----- From: ScottBonis@ao*.co* [mailto:ScottBonis@ao*.co*] Sent: Friday, August 04, 2000 9:50 AM To: RDecker388@ao*.co*; mhkane@pr*.ne*; techdiver@aquanaut.com Subject: Heli-air 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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