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Scott:
Yesterday after reading parts of the extensive catfight on rec.scuba
over recreational tri mix,
I emailed the OTHER Scott at Hoodsports, esssentially asking who, what,
when, where, and how.
Scott replied he would contact a local blender and see if he could arrange a
try-dive for me.
I'm fortunate in that I'm actively mentored by a commercial diver with a lot
of mixed gas experience, but, all the same last night we were throwing about
various conditions and scenarios, including forced deco, bail out, extreme
cold (argon vs back gas for suits) emergency bounce dives past MOD, stage
bottles, travel mix, etc. In other words all those nasty real world things
that can screw up nice day.
Mentor Mikes experience has been with surface supplied heliair as taught
by Ocean Corp., who stressed the use of a travel mix even then, reserving
Hypoxic mixes for true saturation diving. The use of any trimix with out a
travel mix struck him as unusual, so if and when this try dive comes along,
he'll be there asking all those "how come" questions.
My point being - Ok Heliair, hotX, Normoxic trimix, Hotmix sounds like a
good thing. I narc easily so Nitrox is good,as I explained to Scott, being
able to keep that clear head past 110 would be better. Heliair seems ideal
for that purpose, with the understanding of possible longer deco, extra
bottles, etc.
But as you have noted there seems to be some arbitrary bottoming out on
depth limits. Ive heard MODs of 150, 180, 200, 230 fsw. Also alot of ranting
about various agencies forcing useless jumping thru hoops on what should be
a simple learning curve ( that I agree with- I still can't make heads or
tails of IANTD or TDI's "progression' other than charging a lot of money).
Maybe I'm just spoiled by having answers a phone call away.Our conclusion
was IF heliar is the best of all possible worlds for MOST diving, IF it can
be used on more extreme depths- then why not as an all purpose back gas?
Just looking to learn. We've some excellent diving here in the 100 to
250 ft range, and I'd like to take advantage of it.
Dive Safe
Brock
----- Original Message -----
From: <ScottBonis@ao*.co*>
To: <RDecker388@ao*.co*>; <mhkane@pr*.ne*>; <techdiver@aquanaut.com>
Sent: Friday, August 04, 2000 12:50 PM
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
>
> --
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