The big risk in gas
diving is breathing the wrong gas. The WKPP
developed as part of its overall system a simple methodolgy for preventing
this.
Bottles are marked
horizontally on either side in the orientation of the diver as to the
maximum operating depth of the bottle in three inch high numbers. It's
that simple.
Since "20"
can look like "70" the 20 foot bottle is also marked "OXYGEN"
horizontally under the "20" (not necessary in the metric system).
The diver's name is also on the bottles.
With thousands of
man dives of decompression results in the field, we settled on standard
decompresion gasses: oxygen from 20 feet, 50% oxygen from 70 feet, 35%
oxygen from 120 feet, and 18% oxygen from 240 feet for deco, with all
gases conforming to a minimum standard of 120 feet AED and 1.6 maximum
ppo2 for deco ( with 100 AED and 1.4 maximum ppo2 for diving ). Bottom
tanks are labeled for maximum operating depth as well.
There is no excuse
for not permanently and properly marking bottles no matter what gas is
used. It is your life we are betting. Painted numbers can be knocked off
with a swipe of PVC cleaner, and new ones painted on instantly. Tape can
be used also, but nothing should be on the tank as to the contents other
than the MOD and the dated analysis. Clean, uncluttered tanks are safer.
They say a lot about the person diving them.
With the tanks correctly
marked, we fill them according to the following regimen. Two pieces of
tape are placed on the empty tank.
After adding one gas,
but before disconnecting it from the whip, one tape is marked with the
date and the gas psi just added. The whip is removed and the next gas
added. The same proceedure is followed, marking the addition of the gas.
The tank can then
be analyzed if heliox or to see what the helium percent is by getting
the oxygen percent, or the tank is topped with air. At that point the
tank is analyzed and the analysis is written on the other piece of tape
along with the date, the first piece of tape is then used to cover the
tank valve mouth indicating a full tank.
For all tanks the
analysis is left on until ready to dive, but can be removed at that point
since the identification is by MOD only. Doubles whether used or not and
unused stages must re-taped and dated as to analysis for travelling and
storage. More smart people have been killed by failing to observe this
rule than any other. To keep it simple, don't dive anything that does
not have a current analysis. When in doubt, check it out.
With MOD it makes
no difference where the bottles are located on the diver, but there should
be no effort to identify a gas by its position - this leads to error.
Both the diver and his buddies whould be able to clearly see the MOD of
the gas being breathed as a check on each other. The correct procedure
when ready to breathe a gas is to locate the correct bottle by the MOD,
remove the reg, place that reg around the neck and into the mouth, then
go back and re-locate the correct bottle, and turn it on. IF YOU CAN BREATHE,
YOU ARE BREATHING THE RIGHT GAS.
All bottles are turned
off and the regs parked on the bottle when not in use - ALWAYS. This also
makes buddy idenfication of your breathing gas easier in wreck diving
where all bottles are carried. In cave, we NEVER carry a bottle past its
MOD. Trying to maximize PPO2 past a detph for purposes of fear of decompresion
is too stupid to comtemplate given the risk assumed in the process.
If you can not see
the bottle, and can not identify the gas, you DON'T breathe it. You stick
with what you know is ok until you can make a positive id. Missing a litle
deco gas is better than dying. Betting on a system where any error cound
have been made (like putting the wrong cover on a reg) is inadequate for
life bets.
All of our regs look
the same - we do not take the chance of trying to code regs for gases.
This allows putting the wrong reg on the wrong bottle, or the wrong cover
on the wrong reg, among other things. It is akin to loading one gun with
blanks and one with real bullets, and then trying to identify them in
a dark closet before putting one to your head and pulling the trigger.
Sound preposterous? This is exactly what you are doing if you code regs
in any way. Oxygen kills you as dead as any gun.
On a more practical
note, we leave our second stages hand tight on the hoses so we can change
them out if one starts freeflowing. This way the main regs can be replaced
with the stage regs ( which bottles are turned off anyway until used),
and then the stage regs switched around to provide something that works
without killing the dive. This is SOP on long dives. This identical reg
business also prevents any problem of switching seconds before a dive
and then forgetting about it.
With the back gas
, ALWAYS our deepest gas, we can always identify those regs. The backup
is hung around the neck in the DIR system, and the other is attached to
the long hose - both easy to identify. In cave diving, we do not carry
a gas through or past it rated depth. You can see that for ocean diving
, keeping the bottles turned off is the next best thing .
You can see that in teaching gas diving of any kind, the convenience
of the MOD check on each other becomes paramount. Trying to id a student's
gas by little labels, stickers, or a plethora of "nitrox " banners
or little markings everywhere with reg jackets and colors and bands is
not going to make it safer - it is going to make it a mess. I know that
Jarrod Jablonski, in his trainging agency, Global
Underwater Explorers, uses the WKPP method, as he should, he helped
develop it and uses it in all of his diving.
Part of what makes
a great system like this work is the ease of working it, and the perceived
benefits thereof. The GUE/WKPP method requires doing nothing that takes
you out of your way at all - it is just there, and provides so many solutions.
Long drawn out convoluted sytems break down in action and never work underwater,
and in the end get discarded or poorly observed. This one is not only
easy to do right, it is self-correcting in that it only falls together
one way - you either do it or you do not know what you've got.
Efforts to complicate
and "technify" diving make it more dangerous.
Try a little simple logic.
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