Space Forum / Space Flight / September 2003

Various places use 5PSI pure O2 as a second choice to sea-level mix.
This corresponds quite well to the 4.6 PSI you need to get the
same partial pressure of oxygen at the lung wall (there is water
vapour and CO2 there too).

In the article with message-ID:
<1018565841.10667.0.nnrp-01.9e98d142@news.demon.co.uk>
posted in april 2002, I posted the results of some sums.
At 1.8PSI you'r groggy and weak, even if acclimitised.
At 2.1PSI, more or less OK.
<snip>

<snip>

Yes.
Fluid will rapidly pool in the limbs causing them to become swolen
and useless.

You need something to provide a pressure in the flesh that's high enough to
squeeze the blood back from the extremeties to the heart.

The skin usually does this, with the help of the lymphatic system.
However, in space this won't work nearly well enough.

However, do some searching on "skin suit".
Basically, you use a tight elasticated suit to maintain a pressure over
the body, hope the lymphatic system can iron out any minor inconsistancies,
and don't pressurise the suit, only having a pressurised helmet.
Gloves are a big problem, owing to the complex geometry.
The torso is another problem, leading some to suggest just doing the
limbs, and using a hard torso.

moughanj@tcd.ie (James Moughan) :

You just re-invented the skinsuit.  Check out:

http://yarchive.net/space/science/skinsuits.html

http://www.google.com/search?&q=skinsuit+vacuum

Skinsuits have been posited by SF writers for some time.  Niven I think did a
riff on them once or twice. A skin-tight membrane similar to a wetsuit contains
the body under pressure, in some versions, it is semi-permeable to allow sweat
cooling of the body. Usually in the stories a thermal and micrometeroid
overgarment still is worn over it. It would make a fascinating experiment in
materials science. Once you can make a suit so form-fitting as to become usable
as pressure garment, how do you get into and out of it? Maybe it is painted on
you? ;-) A tear in such a garment would probably make for an ugly wound,
looking like what happens when you boil a kielbasa too long...

Nope.  The breath will rush from your lungs, but you can't *inhale* if you body
is under vacuum.  The water vapor and CO2 produced in the lungs has  a partial
pressure of 1psi; this will distend the thorax and make breathing movements
impossible, besides which 1psi of oxygen is insufficient for human life.

Bear in mind, oxygen masks deliver gas at *ambient* pressure.  For Everest
climbers this is 29,000 ft; in space, it is zero.

Besides which, most of a body is water at 37C, and above 63,000 ft, water
*boils* at 37C.  Even if you could somehow get your breath, your blood vessels
would fill with steam bubbles in a very nasty way.

Not necessarily.  What you care about is the partial pressure at the lung
wall, not in the surrounding air.  They differ because air going into the
lungs is diluted by CO2 and water vapor coming out.  That dilution is by
roughly an absolute amount, *not* proportional to total pressure, so it
affects thinner atmospheres more.  So you need more than just a similar
partial pressure.

The Apollo suits -- which would have run at a lower pressure if they
possibly could, for greater flexibility -- ran pure oxygen at 3.85psi.

Plausible reasoning, but the details don't work out.  As little as 1.5psi
excess pressure in your lungs, relative to your skin, involves serious
risk of lung rupture.  This is not just theory; scuba divers deal with
this operationally.  If you take dive training, you will get it hammered
into you that you MUST NOT hold your breath even momentarily during
ascent, because as little as 1 meter of ascent with a closed airway can
become a life-threatening medical emergency.

Two things.  Partial pressure at 2psi is not enough.  I believe you really
need almost the full partial pressure of oxygen to make this work.

In any case, google for skinsuit and you should find a bunch of research on
this very subject.

(note, the skin itself can handle even higher pressure differentials than
2psi.  But there are other issues thta come up.

There are other factors to consider.  The sunlight in space is ~7 times
brighter than on the surface of the earth, and completely unfiltered.
Anyone lounging around in a tank top will get the worst sunburn of their
life not to mention a raging case of leukemia or worse.  this coupled with
subdural hematommas over every exposed surface will make for a rather
unhappy afternoon.

See dick
see dick go EVA without his pressure suit
see dick go blind as his inner-ocular pressure blows his optic nerve out the
back of his eyeball.
see dick get a bad bad sun burn and funny lumps on all his major organs
see dick get one REALLY BIG BRUISE over his entire body
see dick gasp for air as his blood tries to take the path of least
resistance out of his lungs
dont be a dick, wear your space suit.

Interesting thoughts. As a mixed-gas diving instructor I have some
thoughts regarding your post:

First, please excuse my use of metric units instead of imperial.
(For reference: 1 ATM = 14.7 psi ~= 1 bar)

Normal ppO2 (partial pressure of oxygen) in sea-level atmosphere is
0.21 bar. A normal human can survive, without training, with 0.16 bar ppO2.
With some training, this can be reduced to about 0.13-0.11 for a short
periods, but this reduces also physical and mental performance. So, let's
keep it in 0.16 bar, what is also the minimum accepted level in mixed-gas
diving (while in rest).

So, if you use pure oxygen instead of air, you can drop the ambient pressure
to 0.16 bar, which is 1/6 of sea-level ambient pressure (1 bar, 1 ATM).
But you can't drop the pressure suddenly. See: Decompression (Google etc.)
Anyway, with proper decompression time you can be exposed to one sixth of
sea level pressure, if you're breathing pure oxygen. And for short periods
and some acclimation, you can reach even one tenth of sea-level pressure.
But this is the limit, no matter what you do, without pressure suit.

The vacuum conditions:
If you are exposed to vacuum, there are some lethal aspects:
1) If exposed suddenly, you do need to exhale your lungs *fast*, otherwise
your lungs will explode. Not like in horror-movies (cheast open), but you'll
rip your lung tissue and get an embolia/emphysema.
2) If you survive above, then you'll have few seconds before black-out due
to the lack of oxygen.
3) Keep your eyes shut. They are moist, and water evaporates (boils...) from
the surface of your eyes. This happens also to your tongue and mouth.

You won't freeze, even in cold space, for some time. Human body is water,
and water has large heat capacity, and freezing to icycle takes some time.
And you won't explode due to the internal blood pressure. Your lungs might,
in worst conditions, if you don't exhale.

Anyway, with some kind of "belt" in your chest, you still can't survive.
While human propably can be exposed to vacuum for some seconds without
"exploding", the pain due to the internal pressure could be awful. You
do need full protection. And in space, you have to take the thermal aspects
into account also. And possible radiation issue etc.

So, in my opinion, the minimum space suit would be a suit that can take the
one sixth of sea level pressure, and the suit would have a rebreather
system to provide you oxygen and get rid of the carbondioxiode.

Matti Anttila
www.antti.la