Subject: hi alt oxygen
From: (WaltBJ)
Date: 3/10/04 9:12 PM Pacific Standard Time
Message-id:

Here's some quick and dirty info on oxygen - normally about 1/5 of
'air'. So the 'partial pressure' is 1/5 of 29.92 inches/760 mm Hg
equalling 152mm O2. The ambient air pressure drops by 1/2 every 18,000
feet (roughly). So at sea level you get 1/5 of 760mm; at 18,000 you
get 1/5 of 380mm. At about 34000 you get the equivalent of sea level
oxygen partial pressure breathing 100% oxygen. If you keep going on up
pretty soon you reach a dangerously low level of partial pressure -
that's at about 41,000. So modern diluter-demand O2 regulators start
feeding you oxygen under pressure. Easy to inhale - you have to work
to exhale. This gets worse as you keep going up. At 50,000 cabin
pressure it is physically demanding to exhale and the mask has to be
very tightly strapped on your face. Not to mention painful. Note that
so far we don't have any 'cabin pressure' - air bled from the
engine(s) to remedy the situation. Also as you keep climbing into
areas of lesser pressure water boils at progrssively lower
temperatures. At 63,000 ambient pressure water boils at 98.6F/37C -
body temp. That means your lungs are now filled with water vapor and
you can no longer absorb oxygen. Hence pressure cabins and pressure
suits over 50,000 feet. Breathing pure oxygen for extended periods of
time is a hassle. First, there is no water in Aviator's oxygen - can't
take the chance of water freezing in the lines. Therefore every breath
you're becoming more and more dehydrated. Second, oxygen can flood the
inner ears (through the eustachian tubes) and late at night in bed
that oxygen gets absorbed by the blood and you wake up with giant
earaches. Third, if you're breathing pure O2 and pulling lots of G -
the lower airsacs in your lungs tend to stick together because with
pure O2 you're not breathing as deeply. Back on the ground when you
take a deep breath it feels as if someone just knifed you. This is
termed 'atelactasis'.
Now, oxygen is used to keep pilots crew and passengers functioning at
more or less an efficient level. Rule of thumb - O2 over 10,000 feet.
There is a 'cheat' where one can got to 12 for 30 minutes. But the
brain needs O2 to function properly. With hard training one can
function adequately at higher altitudes. But even the best can screw
up - read 'Into Thin Air'. FWIW I used to teach this stuff.
Walt BJ


I was just glad to get rid of the high pressure system with the spitbag to the
low pressure demand mask. It doesn't take much to make me happy.


Arthur Kramer
344th BG 494th BS
England, France, Belgium, Holland, Germany
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer