From Tue Apr 29 20:40:02 2003
Date: Thu, 10 Apr 2003 15:34:54 +0100 (BST)
From: Gordon Henderson 
Subject: Greetings from planet Zorg...

Here on Zorg, we abducted some humans to test your resistance to CO2 and
the efficiency of our patented CO2 grabbing demon chamber.

We took a human and connected a hose to them. The hose supplies gas and
has one-way valves. The exit of the hose goes into a box.  Inside this box
are 1000s of little demons. These demons adore CO2. They will grab a
passing molecule of CO2 and hang onto it for the rest of their lives. They
can only hold one each. After the CO2 demon box there is another box with
different demons inside - these count the number of O2 molecules you have
used and replaces them.

We observed that humans when in a steady state consume the same amount of
O2 per breath, regardless of the pressure we subjected them to. When given
100 molecules of our gas, they would use 4 molecules of our oxygen and
turn this into 3 molecules of CO2 and 1 molecule of water vapour.

So in the test, with 100 molecules of gas in the loop. The human
push/pulled this through the box with the CO2 demons in it. Every breath,
3 lucky demons grab a CO2 molecule each and are happy for the rest of
their lives. We repeated this for many of your earth hours, pushing 100
molecules of gas through the CO2 box at a nice steady rate - the happy
demon front line progressed linearly through the CO2 demon box until
eventually they are all happy. At that point, the loop gas has some CO2 in
it and we observed that the humans started to show signs of unease, panic
and general ill-feeling. They eventually died a rather uncomfortable

To continue our experiments, we abducted more humans and carried on, this
time we subjected them to a pressure of 2 bar. This is the same as being
under 10 metres of your water. There is now 200 molecules of gas in the
loop, but the human still only uses 4 molecules of O2 and turns these
into 3 molecules of CO2 and 1 water vapour. Each breathe pushes 200
molecules through the CO2 demon chamber, so the demons have to work faster
to grab the CO2 molecules and die happy. Sometimes a front-line demon
misses, but the 2nd line catches it OK. This carries on and eventually all
the demons are happy, then as above, the human dies painfully and horribly
from CO2 poisoning.

We needed to do more experiments, so we continued with our abduction
programme. Now we're testing to 90m. There are now 1000 molecules of gas
in the loop, but as observed before, then humans still only take 4
molecules of O2 out and metabolises these into 3 of CO2 and one of water
with each breath, However, the poor CO2 demons now have 1000 molecules of
gas going through their chamber like a hurricane, and in those 1000
molecules there are still only 3 molecules of CO2! It's now very hard for
the demons to catch a CO2 molecule and hang on to it! The front-line
demons have a real hard time catching the CO2 molecules and a lot more
pass further down the line to be caught by the latter ones. Eventually,
the front-line demons are full, but still the latter ones need to work to
catch the CO2 and there will come a stage where there aren't enough latter
ones who can catch the CO2 fast enough, so some will get through.
Eventually so many will get through that the human starts to notice it and
dies horribly as before - even when there are still some unhappy and empty
CO2 demons left.

Continuing our experiments with more abducted humans, we test again at
90m, but then we decide to ascend the human to some depth where the number
of molecules in the loop is much less, so each breath the CO2 demons have
more of a chance to catch the CO2 molecules left.

Eventually, after 100's of trials, killing a great many humans every time,
(And you should have seen our abduction budget! Off the scale!) we have
come up with some rules for keeping humans alive and maximising the
happiness of the CO2 demons. Our rules are many, long and complex but to
simplify them for you humans we have reduced them to 3 simple rules..

Rule 1: You have 3 hours maximum.

Rule 2: For subsequent dives deeper than 20m: You must leave the bottom
when the _total_time_ breathed through the system reaches 140 minutes.

Rule 3: For subsequent dives deeper than 50m: You must leave the bottom
when the _total_time_ breathed from the system reaches 100 minutes.

I'm glad the Inspiration was machine tested at DERA. Glad I wasn't the
human being killed every time. I wonder what other rebreathers would show
given the same tests? I wonder why others don't bother with these tests,
and instead resort to cycling in the garage with a unit on their backs.
It's fairly obvious from reading above that things happen differently at
depth. The deeper you go, the wider the reaction front becomes and
eventually you'll run out of scrubber before the reaction front reaches
the end.

On my first hit, I was on my 2nd 60m dive with the same scrubber. First
had been 60m for 30 minutes and about 60 minutes of deco. Second was 60m
for 30 minutes... Thats 20 minutes at depth too many. (3rd rule) Combine
that with an increase in breathing rate and workload and bingo, I got a
hit. You can not do 2 x 30 minute, 60m dives on the same scrubber without
violating the rules.