From: "Kevin R. Hardwick" <[k r hrdw c k] at [wam.umd.edu]>
Newsgroups: rec.games.frp.advocacy
Subject: Vacuum--What the Doctor Says
Date: Fri, 7 Feb 1997 14:56:14 -0500

Well, given the disagreements concerning the basic question "How long can
you stay conscious in a vacuum," I went ahead and took the step I've been
advocating--I asked our group's expert on the question, who is an MD
specializing in internal medicine.

Here's what he said:

First--is there any reliable information out there?  Yes--NASA did do some
research into the question during the Apollo 13 program.  The physical
effects of being in a vacuum are reasonably well known, although the
specific question "how long can you stay active" is not especially well
addressed in the research.  However, quite a bit is known about oxygen in
the bloodstream, which can be used to supplement the NASA studies.

The result is a guess, however.  Such research as exists does not answer
the question definitively.

Question:  Can you hold your breath in a vacuum?  Yes, but doing so will
cause embolisms in your lungs.  Do it for very long and you will cause
permanent damage (of course, dying is rather permanent too.)  Moreover,
you will really have to make an effort to hold your breath (that vacuum
really wants to be filled :)

Question:  Does hyperventilation help?  Not much.  Why?  Well, your body
has a reflex which causes you to breathe.  It is based on carbon gas
levels in your blood--when they reach a certain level, you
breathe--whether you want to or not.  This happens *before* the oxygen
levels in your blood are depleted, naturally--you have something of a
reserve at the time that your body forces you to breathe.
Hyperventilation lowers the carbon gas levels in your blood, which lets
you cut into that reserve further before you breath.  It also increases
the oxygen levels in your blood, but not by a very large amount--for game
purposes, its an afterthought.  So--hyperventilation lets you stay longer
underwater, since you have a greater interval in which you get by on the
oxygen in your blood before you breath water and convulsively and
involuntarily choke.  But in a vacuum, in which you are best advised to
release the air in your lungs immediately and in which breathing
reflexively will not have catastrophic consequences, it helps you very
little (only the fractional increase in blood-oxygen matters, in the
vacuum case).

OK.  Suppose you hyperventilate with pure oxygen--does that matter? Well,
no.  Hyperventilation doesn't help you much at all (see above) whether
with oxygen or not.  However, simply breathing oxygen for a while *does*
raise your blood oxygen level, by a rather large margin.

A margin on the order of 400%?  No--that's utterly unrealistic.  Maybe
50%-100%--he said he would have to look it up to give a more precise
figure.

So--how long can someone survive in a vacuum before passing out?  Well, he
thought that the GURPS mechanic for slight activity captured things pretty
well--that is, HT*4 seconds, + a margin for FAT.  The figures for vigorous
activity, he thought, were way too low (ie, HT*1 seconds, + FAT).  While
he accepted the principle that inactivity would prolong consciousness, he
rejected the notion that HT*10, + FAT was realistic.  Inactivity buys you
more time, but not 250% more.  (I didn't ask him what a realistic
figure would be, but I'm sure he could give an educated guess as to what
it is.)

He suggested that all of these numbers be treated as *maximums*, under
ideal circumstances.  In general, there are numerous other icky things
happening to you in a vacuum (he had no quarrel with the
textual charcteriztion of those things provided in GURPS Space), which
normally will cut down your ability to remain conscious.  He predicted
bleeding from eyes, ears, nose, and mouth very rapdily after exposure,
followed by "bend" like symptoms--which would occur shortly after exposure
to the vacuum, regardless of whether you breathed oxygen or normal air
beforehand.  These would tend to lower you ability to remain conscious and
functional.  Thus, being inactive or breating oxygen helps some, but not
all that much, since the bends and other nasty things kick in very quickly
anyway.

What about those Ainu and Fiji divers, who (as Psychohist has reported
to us) can swim under water for such long periods of time?  Well, they do
that by rigorous exercise and training, to increase their lung capacity.
They also hyperventilate (which, as I report above, does help you under
water).  Could they survive longer in a vacuum?  Probably not much, if at
all.

*****

So--the outcome here is that HT*4 provides a realistic maximum figure,
while HT*6 (or possibly 7) for someone who has breathed oxygen beforehand.
Likely, however, true figures would be less than maximum--say HT*3 and
HT*4 (or maybe 5) respectively, to take into account the other physiologic
ills of being in a vacuum.

The major point of this, however, is that the GURPS mechanic was, in a
number of important ways, purely made up, out of whole cloth.  The error
regarding the function of hyperventilation is particularly
egregious--clearly the author was not writing from an informed background.
Likewise the flat out statement that you cannot hold your breath in a
vacuum was incorrect (although it is not clear that you would want to,
save in a dire circumstance).

Yes, there really is NASA research, as David S. has mentioned repeatedly.
But that was never in dispute.  The real queastion is "was the GURPS
mechanic in any way based on it?"  And the answer to that clearly is
"loosely, at best."

My best,
Kevin