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On Thu, 9 Jun 1994, Wrolf Courtney wrote: > Rich (and others) wrote: > >> > All this talk of dissimilar tanks, doubles w/o manifolds and newbie > >> > technical divers makes me want to remind everyone: > >> > > >> > We all know of many "near-misses" and a couple of fatalities that > >> > could have been avoided had a dual-outlet manifold been > >> > properly used. > >> > > > > >I have two different mixtures in my main doubles, so obviously I have a > >reason to use independant tanks. > > Rich: > >From the published descriptions, your rig is not fully redundant. > I am comparing with for instance a typical deep air diver, with either > fully independent doubles, or doubles with an isolating manifold. I've never actually claimed that my rig was "Fully" redundant. Yes, it is "fully" self-contained, and yes, it has partial redundancy of certain critical equipment elements, but "Fully Redundant" it is not. > You seem to have bought off on the theory that a Y-valve plus completely > independent first and second stages, all off a given tank, makes for > an acceptable level of redundancy. Is this a fair statement? For the nitrox supply, yes I think it is a fair statement, the active phrase being "ACCEPTABLE level of redundancy". For my Bottom mix, I have two independant cylinders, which seems to meet your definition of "Fully Redundant". Designing an "ideal" rig for a particular application requires a trmendous amount of thought, and goes beyond simply providing multiples of each piece of equipment. Some considerations need to be given towards other aspects of the dive like being streamlined, not too much task loading, etc. > Or do you > have bailout procedures with the gas mixes that you carry so that you > have redundancy? Yes I do - bailout proceedures involve extra cylinders hanging from the boat, which are there only as an extra buffer. However, I do not consider these as part of a redundant system, because it requires that a diver be able to return to the staged cylinders when they are needed. I could go on and on about the philosophy of why I designed my rig the way I did, but I won't, because I lack the time right now, and I pretty much covered it in the article I wrote for aquaCorps:MIX. Bottom line is, you've achieved full redundancy when a minimum of two problems have to occur before a "system failure" results (i.e., seriously life-threatening) My rig is NOT fully redundant because it has two bottle-necks; the Y-valve on my nitrox cylinder (mostly the neck o-ring & the over-pressure burst disk), as you've already pointed out; and my mouth. If a major problem occurs with either one of these components (the valve or my mouth), then I have a very serious problem. Aloha, Rich
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