In the absence of atmospheric
pressure water will spontaneously convert into vapor, which would cause
the moisture in a victim's mouth and eyes to quickly boil away. The
same effect would cause water in the muscles and soft tissues of the
body to evaporate, prompting some parts of the body to swell to twice
their usual size after a few moments. This bloating may result in some
superficial bruising due to broken capillaries, but it would not be
sufficient to break the skin.





Within seconds the reduced
pressure would cause the nitrogen which is dissolved in the blood to
form gaseous bubbles, a painful condition known to divers as "the
bends." Direct exposure to the sun's ultraviolet radiation would also
cause a severe sunburn to any unprotected skin. Heat does not transfer
out of the body very rapidly in the absence of a medium such as air or
water, so freezing to death is not an immediate risk in outer space
despite the extreme cold.





For about ten full seconds- a long
time to be loitering in space without protection- an average human would
be rather uncomfortable, but they would still have their wits about
them. Depending on the nature of the decompression, this may give a
victim sufficient time to take measures to save their own life. But this
period of "useful
consciousness" would wane as the effects of brain asphyxiation begin to
set in. In the absence of air pressure the gas exchange of the lungs
works in reverse, dumping oxygen out of the blood and accelerating the
oxygen-starved state known as hypoxia. After about ten seconds a victim
will experience loss of vision and impaired judgement, and the cooling
effect of evaporation will lower the temperature in the victim's mouth
and nose to near-freezing. Unconsciousness and convulsions would follow
several seconds later, and a blue discoloration of the skin called
cyanosis would become evident.





At this point the victim would
be floating in a blue, bloated, unresponsive stupor, but their brain
would remain undamaged and their heart would continue to beat. If
pressurized oxygen is administered within about one and a half minutes, a
person in such a state is likely make a complete recovery with only
minor injuries, though the hypoxia-induced blindness may not pass for
some time. Without intervention in those first ninety seconds, the blood
pressure would fall sufficiently that the blood itself would begin to
boil, and the heart would stop beating. There are no recorded instances
of successful resuscitation beyond that threshold.





Though an
unprotected human would not long survive in the clutches of outer space,
it is remarkable that survival times can be measured in minutes rather
than seconds, and that one could endure such an inhospitable environment
for almost two minutes without suffering any irreversible damage. The
human body is indeed a resilient machine.