Effects of vacuum on humans and animals

The environment of space is highly dangerous without appropriate protection. The greatest threat is from the lack of pressure in the vacuum environment, while temperature and radiation effects also have an influence.
Vacuum is primarily an asphyxiant. Humans exposed to vacuum will lose consciousness after a few seconds and die within minutes.
 
Blood and other body fluids do boil (the medical term for this condition is ebullism), and the
 vapour pressure may bloat the body to twice its normal size and slow circulation, but tissues
are elastic and porous enough to prevent rupture. Ebullism is slowed by the pressure
containment of blood vessels, so some blood remains liquid. Swelling and ebullism can be
reduced by containment in a flight suit. Shuttle astronauts wear a fitted elastic garment called
the Crew Altitude Protection Suit (CAPS) which prevents ebullism at pressures as low as
15 Torr (2 kPa). However, even if ebullism is prevented, simple evaporation of blood can
cause decompression sickness and gas embolisms. Rapid evaporative cooling of the skin will
create frost, particularly in the mouth, but this is not a significant hazard.

Animal experiments show that rapid and complete recovery is the norm for exposures of
fewer than 90 seconds, while longer full-body exposures are fatal and resuscitation has never
been successful. There is only a limited amount of data available from human accidents, but
it is consistent with animal data. Limbs may be exposed for much longer if breathing is not
impaired.

In 1942, in one of a series of experiments on human subjects for the Luftwaffe, the Nazi
regime tortured Dachau concentration camp prisoners by exposing them to vacuum in order
to determine the human body's capacity to survive high-altitude conditions.

Some extremophile microorganisms, such as Tardigrades, can survive vacuum for a period of years.

Liquids inside the body - including water - will not boil. At body temperature the vapour pressure of water is 47mm Hg, or 1/16 of normal atmospheric pressure. Skin is a very strong substance well able to exert a much higher pressure on expanding body contents. Exposed liquids will boil.

Dissolved gases in the blood may come out of solution, and after 10 seconds or so, decompression sickness (the bends) may result.

In a vacuum there is no medium for removing heat from the body by conduction or convection.




However, the primary threat is of asphyxiation. In the low pressure environment, gas exchange in the lungs would continue as normal but would result in the removal of all gases, including oxygen, from the bloodstream. After up to 15 seconds, the deoxygenated blood would reach the brain, and loss of consciousness would result. Death would gradually follow after two minutes of exposure - though the limits are uncertain. If actions are taken quickly, and normal pressure restored within around 90 seconds, the victim may well make a full recovery.

As well as experimentation with humans and monkeys, a few cases of loss of pressure have occurred in the past, especially in experimentation on spaceflight projects.

There has been one recorded incident of death from decompression in spaceflight, the Soyuz 11 decompression accident.
On June 30, 1971, after an apparently normal re-entry of the capsule of the Soyuz 11 mission, the recovery team opened the capsule to find the crew dead.
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