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As part of the modular approach to rebreather systems,
the normally pure-oxygen IDA-71 is also used as a Nitrox rebreather
using a solid-chemical means of replacing metabolized oxygen. This
relied on an offboard cylinder connected by a quick-disconnect to
carry the Nitrox.
WARNING: It
is VERY important to understand that once the Nitrox system
becomes active that there is NO access to the internal 02 supply, as
it is TOTALLY isolated once the Nitrox system becomes active at about
40 feet. Once passing the depth where the system switches over to
Nitrox, the ONLY additional oxygen available comes from the chemical
reaction taking place when using the special (and unavailable)
Russian scrubber chemical. PAY ATTENTION! I'll say it again: The
system relies ONLY on the 02 produced by the Russian chemical carried
in one of the two scrubbers. Failure to understand this WILL result
in your death if you dive one of these without knowing this.
Here's how the system works:
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1: Diver starts the dive on 02, as fed from the
internal 02 bottle. Only pure 02 is available. You had better have
purged all of the nitrogen out of your lungs like with any pure 02
rebreather, otherwise you'll use up all of the 02 in the mix and then
pass out. But up until now it's just like any other 02 rig.
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2: At about 40 feet, the regulator on the offboard
bottle is triggered by a hydrostatic valve, and initiates a 30-second
purge cycle that blows all of the pure 02 out of the loop, and
replaces it with the 50% Nitrox in the offboard bottle.
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3: Here's the scary part: From that point on, there is
NO 02 makeup other than the 02 produced by the special scrubber agent
that's in one of the two scrubbers installed. Plus, since there is no
PP02 measurement on an unmodified rig, you are simply trusting the
Russian chemical to do it's job. But it's even worse than that: Once
the system switches over to the offboard bottle, there is NO way to
manually add 02 from the internal bottle! At this point, the auto add
valve is supplied only by the offboard bottle. Not my idea of the way
to do this. In fact, it's damned dangerous.
A word about this Russian 02 producing chemical: This
is a nasty exothermic stuff that is very caustic when exposed to
water. Trust me, it's REALLY bad stuff. Actually, not only will it
KILL you if you breathe in a bit of it after it gets wet, the
cannister that it's contained it will get hot enough to MELT its way
right through a steel ships-deck if it becomes water-saturated, and
lastly it contains Asbestos, so you are playing with lung damage even
on a good day. I TOLD YOU that it was bad stuff, so now do you
believe me? Trust me on this: Don't even think of trying to use any
of this stuff.
To make this TRIPLY Clear: Even
though you have an on-board 02 bottle, there is NO WAY to use it to
replace the 02 into the loop once the system activates as you
descend. You must either A: Use the Russian Chemical, B:
Manually flush the loop every few minutes to replace the Nitrox, or
C: Modify the system with an 02 bottle that can be used to replace
the 02 that you metabolize. If you do none of these things you will
die. Got it? DEAD, as in you'll be lucky to float back up to the
surface so your family will be able to have a nice funeral for you.
This isn't a game. It's played for keeps.
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4: On ascent, back at about 40 feet, the hydrostat
triggers again, and the system again runs a 30 second purge cycle,
blowing out all of the Nitrox and replacing it with pure 02 from the
internal bottle. From that point on, the system acts again as a pure
02 rebreather. BUT: You better have been breathing in and out fully
during the purge-cycle, otherwise the nitrogen in your lungs will
prevent the rig from being on pure 02. You'll then metabolize the 02
from the mixture, pass out, and drown! So, PURGE YOUR LUNGS while
this cycle is happening otherwise you will not be a happy camper. See?
I told you it was easy to kill yourself with stuff like this!
Also, don't soil your shorts the first time the cycle occurs: It
happens without warning, and the first time it occurs you'll swear
that the counterlung just exploded. You'll get used to this, trust me.
You've just been warned about all
of the bad stuff that can trap
the unwary diver. What about the good news? The good news is that
there are ways to modify the rig to provide a safe tool for the
thinking diver. I just want to make sure you realize that you need to
KNOW what you are doing with this type of system. |
