[net.space] 100% oxygen

gutfreund.umass-coins@UDel-Relay@sri-unix (11/16/82)

From:     Steven Gutfreund <gutfreund.umass-coins@UDel-Relay>
A couple questions about the EVAs:

1. Does anyone know why they use 100% oxygen in the suits?
  (is it merely so that they can hold more oxygen and stay out longer?)
  (does it make suit design easier?)

2. Are they really using 100% oxygen or is there 2% CO(2) so that they
   do not hyperventilate?

3. Are they running at sea-level pressure, or is it less?

4. What's the big advantage in the two piece suits, they look more rigid
   to me.

5. Why do they need complete suits? Why not just a helmet and 
   their thermal "spaghetti" suits? 16psi is not too much for the
   skin to handle (just look at our feet). <I have read an SF anthology
   that did have the characters running around in just thermal suits,
   the only problem was you had to fart first or you would feel very sick>

6. Why don't they use tubes from the ship to give oxy/nitrogen mix if
   self-contained suits can only use 100% oxygen.


		I guess the questions show I have a lot to learn
		can anyone give me a start.

				- Steven Gutfreund

CSvax:Physics:els (11/18/82)

    If there's no CO2, then the pressure of the oxygen is probably less.
At lower pressures, you don't hyperventilate (at least that's my understanding).
Also, carrying around the extra bottle for the N2 would constrain working time
even more.  As for feeding air from shuttle, I'll bet that freedom of movement
has something to do with that.


                                  Taking a stab,

                                    els[Eric Strobel]
                                    pur-ee!pur-phy!els

cjh@CCA-UNIX@sri-unix (11/18/82)

   re (2), I expect you mean hyp\o/ventilate; emergency oxygen for revival
(e.g., on football fields, at fires) is 5% CO2 because without that the
breathing reflex would shut down entirely.

karn (11/18/82)

The reason pure oxygen is used in the shuttle suits is as follows:

Suits are easier to design and offer less resistance to movement if the
pressure differential between inside and out is as low as possible.
Using pure oxygen allows the suit pressure to be minimized while
maintaining the same partial pressure of oxygen for breathing.

You certainly don't want to use pure oxygen at normal (1 bar) pressure;
it represents a serious fire hazard.  I'm curious if the fire hazard
of pure oxygen at low pressure is still greater than air at normal
pressure, assuming, of course, that the oxygen partial pressures are the
same.  Does anyone know?

Phil Karn

sjb (11/19/82)

They use 100% oxygen to reduce the chances of getting the bends
from the pressure changes.  If there's no nitrogen in your system
(they breath the stuff for three hours to get pure O2 in the blood
before going out), you can't get the bends.
(Can you?)

ark (11/19/82)

I do not think that breathing 100% oxygen could cause the breathing
reflex to shut down.  This reflex is triggered by blood CO2, so
not taking in any CO2 shouldn't make a difference. The reflex WOULD
shut down, though, if you were to breathe 100% nitrogen.
..

tomoc (11/19/82)

Wasn`t the use of 100% oxygen the main cause the fire that killed 3
U.S. astronauts in 1967 spread so quickly in the spacecraft that
nobody could get to them in time?  Not that familiar with chemistry,
I would think the use of pure oxygen is a mighty big risk, even
though there haven`t been any such accidents since then.

					Tom O`Connor
					ixlpc!tomoc