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Ted and others,
We (WKPP) feel that the only true gas related risk in the kind of
diving we do lies in breathing the wrong gas. I will leave it to you
guys to argue the filling, explosions, cleaning , etc . Suffice it to
say that I do not count these questions amont the real risks, since they
are both redundent subjects and subject to obvious influences). We know
how to care for and fill tanks.
Death comes with breathing the wrong gas. To avoid this, we mark
our tanks with the max operating depth of the gas according to our
standards. Most of this involves deco gas, and we have found the optimal
set of deco gases to be 190 (air) 120 (35%) 70 ( 50%) and 20 (100%.
Bottom gas in stages get the depth marking ( most of our stuff is 300 ,
so we only occassionally have to tape over the three hundred for a
shallower depth). Back qas gets tagged if it is in doubles.
There is a lot to bve said for uniformity and simplicity,
including easy handling of on the fly deco situations.
The markings we use are three inch high letters ( for the oxygen)
and three inch high numbers for the depth painted on ( or taped over the
paint for odd depth bottoms) horizontally in the orientation of the tank
on both sides. The divers name is also painted on the tank and on the
doubles. The diver can see his own tank marking, and his buddies can see
it regardless of which side the tank is on.
For filling, we use two tapes: one for the non-air contents and
date. This information is filled out before the tank is removed from the
whip. The second is for the post fill analysis, done before the first
piece is removed and put over the tank opening to signify it is full.
The analyis can be left on the tank, but is merely confirmation,
and with its date prevents any question. We dive nothing without an
analysis, unless it is taped over and still has the original analysis.
If the pressure reading is full, the gas is the same as it was.
The real key to tech diving is to identify and handle the real
risks - this is the biggest real risk in tech diving, and as an accident
cause, has the body count to prove it. - G
* we do not dive air at 190, but we will use it or a normoxic trimix
in the 190 bottle with gas on our backs. Any other choice of bottles or
gas follow the usual logic: 130 aed, 1.4 ppo2 max , with a 1.6 deco max
for the first stop of a bottle, like 35% at the 120 stop with
appropriate back gas breaks to prevent spike reactions, all dependent on
the cumulative exposure. In some cases the bottles are brought up a stop
or two first. This is not a likely problem in ocean diving, but is in
long cave bottom times where delays are possible.
--
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