Richard, the answer is , as you point out, a function of what we have to
work with. I disagree with you on the deco worries with helium, as we
have in fact found that decompressing on helium based gases works better
than on nitrox, and is generally easier and has a better result the
higher the helium percentages that we use. 

I do use the highest possible helium percentage I can muster in my
bottom gas, no matter what depth I am diving at, shallow reef to deep
cave.

We get so much more pleasure from our ocean dives with helium, as we see
so much more, no matter how shallow.

BTW, your concerns with the KISS priciple are based on not having
confidence in the fact that you can dive helium with any percent oxygen
that you please, and this only requires a special series of deco gasses
depending on depth and exposure, not because it is helium. For instance,
if I dive 30% heliox, I do not need to do anything special in the way of
deco gases any more than I would with 30% nitrox.I am not saying this
for your benefit , Richie, as I now you understand this well, I am
saying it for the benefit of the cc list.  

The mixing may be more difficult than air, but then let's go back to the
fact that this is an IANTD cc lsit, and the T stand for technical, not
for air or KISS. If you want to talk KISS to IANTD, tell them to mark
their bottles properly. If I were forced to dive the IANTD bottle
markings, as Mouth has "dictated", I would dive air myself under the
KISS priciple, but then I do not have that problem, since I am just an
amateur, and these people are all pros. To tell you the truth, if I had
to do anything the way they do it, I would have quit diving a long time
ago, and would have had nothing to show for it at this time.

Richard Pyle wrote:
> 
> There is also the fact that people screw up when blending and analyzing
> Nitrox. I belive air has a purpose in diving, for both practical reasons,
> and for overall KISS reasons. Nitrogen causes narcosis at all depths -
> even at the surface.  We don't require all drivers on freeways to breathe
> heliox to have that little bit of extra edge of sharpness, despite the
> fact that drivers on freeways kill themselves and others much more
> frequently than divers do. The question is, to what extent does the
> increased impairment from increased nitrogen exposure at depth cause the
> increase in probability of diver error leading to diver accident outweigh
> the costs of using nitrox or heliox on all dives to all depths.
> 
> First, we have to ask ourselves whether nitrox really does reduce narcosis
> as compared to air.  We know that O2 does have some narcotic potency, and
> the best published controlled data we have seems to suggest that it is
> essentially equipotent for narcosis as nitrogen is.  That being the case,
> the only alternative to air at any depth from a narcosis perspective is
> heliox; with nitrox conferring essentially the same narcosis as air. There
> are anecdotal accounts that nitrox leads to less narcosis than air for low
> PO2 values, and more narcosis than air at high PO2 values.  But as these
> accounts are anecdotal and subjective, they don't do us much good when you
> consider that the anecdotal/subjective experience of most divers is that
> there is no narcosis effect at all at 40 feet, where apparently
> chess-playing ability is, in fact, affected when examined under controlled
> conditions.
> 
> Given this, we basically have two choices:
> 
> 1) Use heliox on all dives to all depths.
> 2) Choose a maximum narcosis level which we feel is acceptable.
> 
> Option 1 seems awfully impractical, and potentially dangerous from a
> decompression perspective, given that most of our knowledge about
> decompression characteristics of helium involve deep diving, without much
> knowledge on deco limits for heliox on shallow non-saturation dives.
> 
> For option number 2, if we select "zero" as the maximum narcosis level,
> then both air and nitrox are out as diving gases.  In fact, even heliox
> with an inspired PO2 greater than 0.21 atm is also out.  Again, it seems
> impractical (and potentially dangerous) to go with "zero" narcosis.
> 
> That leaves us with the question of "how much narcosis" is acceptable.  We
> also have the issue of defining how we measure narcosis.  The best (and
> only practical) way to do that is by gas content.  And, given our current
> best knowledge of O2 and its narcotic potency, the best measure to use is
> combined PN2 plus PO2. Thus, if you want to establish a standard for
> maximum narcosis exposure, you should invent the term "Pnarc", and define
> it as equal to PN2 + PO2.
> 
> If the maximum air/EAN depth is 165fsw, then maximum Pnarc = 6.0.
> 
> If this is viewed as an absolute maximum depth to which any dive made
> under IANTD auspices can ever be conducted, then I tend to think it is an
> appropriate value.
> 
> However, perhaps a more conservative alternative would be to follow the
> lead of other recreational agencies, and establish 130 fsw as the maximum
> non-helium depth, in which max Pnarc would be 5.0 atm.
> 
> If you really wanted to be conservative, then you might drop maximum Pnarc
> to 4.0 atm, and require helium on all dives deeper than 100 fsw.  I might
> be in favor of that, as it is more or less the route I have taken on my
> own dives.
> 
> Now, a question for the people in favor of eliminating air as a diving
> breathing gas (Bill, George, Rober, etc).  For each of the depths listed
> below, can you tell me what gas you would breathe, and explain why you
> feel such a gas would be better than air at each of the depths:
> 
> 20 fsw
> 40 fsw
> 60 fsw
> 80 fsw
> 100 fsw
> 120 fsw
> 
> Looking forward to the replies.
> 
> Aloha,
> Rich
> 
> O


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