From: gee@dciem.dciem.dnd.ca (Thomas Gee)
Newsgroups: rec.aviation.military
Subject: Re: Aurora
Date: 29 Dec 92 17:15:39 GMT
Organization: Defence and Civil Institute of Environmental Medicine

In article <BzsnLz.F8q@acsu.buffalo.edu> v111qheg@ubvmsb.cc.buffalo.edu (P.VASILION) writes:

>To wit I respond:
>
>Ascent ----> Reduction in  -------> Decompression Sickness
>         |   total pressure   |

It takes at least a couple of minutes of exposure to these altitudes to 
cause DCS (well, more or less.  DCS is complex and not well-understood).
However, DCS due to altitude exposure has the very unusual property that
the symptoms generally do not appear until 8-12 hours _after_ exposure,
which gives you plenty of time to get to a hyperbaric chamber.  So, if
you have to eject at altitude, DCS is the least of your immediate worries.

>         |                    |---> Ebullism

To be honest, this doesn't appear to happen (significantly) in human beings.
Bottles of water, yes.  Guinea pigs (animal-kind :), yes.  Monkeys, no.
People, no.  The internal pressure change in the human system is quite small
even with a large ambient change.

>         |                    |---> Effects of gas contained w/in
>         |                          body cavities                   <-|

Not particularly life-threating.  A few belches and you should be fine.  
Can be acutely uncomfortable, I admit, but not particularly dangerous.
(It will, however, blow your ear drums.  Again, a painful condition but
not a dangerous one.)

>         |-> Reduction of  -------> Hypoxia                           |
>         |   part'l O2 prssr                                          |

This is the biggy, and this is the issue what my rather longish post
addressed.  PPB solves this problem, especially if we are only talking about
a few minutes of exposure.  Are there PPB-equipped ejection seats currently?
Not to my knowledge.  But I know of no particularly complex technical
problems in building such things.

>         |-> Reduction in  -------> Cold injury                       | 
>	  |   temperature                                              |

Frostbite could be a problem.  But we are only talking 3-4 minutes of
exposure at most, so, once again this is (probably) not life threatening.

>Descent  --> Increase in total O2 pressure  --------------------------|

This is what saves your life, not endangers it.

>     Hypoxia symptoms increase rapidly over 45,000'. Consciousness is lost in
>abt. 20 seconds, and death occures abt 4 minutes later.... Gases obey Boyles'
>law,

Granted.  And that is the problem that PPB addresses very well.  Ask the USAF
who are currently installing the COMBAT EDGE system in their F-16's.

>and as such cause such trouble as the bends and the like. As pressure is
>lost, boiling points fall and at 100,000 feet the lack of pressure combined 
>with lack of moisture will cause liquids to boil and evaporate instantly. 
>(In Antarctica, if you take a cup of coffee outdoors, it will evaporate
>immediately leaving a dry cup.)

I suspect that you didn't really read my post.  Again, the heart provides
80 to 120 mmHg of pressure above ambient at altitude, and this is quite
sufficient to maintain blood pressure and internal pressures above the (I
think it's 47mmHg?) pressure threshold that would cause your blood to boil
at altitude.  I've been there.  We have fourteen others who have been there.
Repeatedly.  And we haven't blown up anyone.  (Not yet, at least.)

Tom Gee
S/W Development
Aerospace Physiology Section

---
Thomas Gee  -=-  S/W Development  -=-   gee@dretor.dciem.dnd.ca
Aerospace/Biosciences, DCIEM, CFB Toronto, DND, Canada
Disclaimer: the previous is solely the opinion of the author.
Newsgroups: rec.aviation.military