Space Freefall and Boiling Blood

News coverage of Felix Baumgartner and his crazy idea to be the first person to break the sound barrier by free falling 23 miles from THE EDGE OF SPACE always seems to mention that should he fail...his skin will boil.  Well this sounds incredibly dangerous and as a curious scientist I wanted to find out more about his jump and the risks involved.

For his jump, Felix will wear  pressure suit manufactured by David Clark Co., the makers of suits worn by astronauts and high altitude pilots.  The biggest risk seems to come from Felix ripping his suit as he makes the jump.  He would be exposed to the harshest of conditions; 120,000 feet up, -23 degrees celsius and an air pressure of 1LB per square inch.  The lack of oxygen and low temperatures could cause lethal bubbles to form in his bodily fluids.

This phenomenon caused by exposure to near vacuum is known as the Armstrong Limit and represents the altitude at which atmospheric pressure reaches 0.0618 atmosphere units.  At this altitude water boils at around 37°C due to the direct relationship between saturation temperature and saturation pressure.  In simpler terms, at normal pressure (say in London) water boils at 100°C because this is the temperature that saturates how much thermal energy the liquid water can take on before boiling or turning into a gas.  In comparison, at low pressure (say at the top of Mt. Everest) the same water will boil at 71°C.  So if Felix rips his suit he will be exposed to pressures so low that the water in his body will begin to boil...not ideal.

It sounds like the makings of an 80's horror film death but exposure to vacuum is not as damaging as it sounds.  The containing effect of your skin and circulatory system protects your blood from boiling.  No instant freeze as heat does not dissipate that rapidly from the body.  Loss of consciousness occurs only after sufficient oxygen deprivation from the brain.  NASA reported that in 1965 a test subject was accidentally exposed to near vacuum and simply went unconscious after 14 seconds.  He regained consciousness after re-pressurisation to around 15,000 feet and reported that the last thing he remembers is the water on his tongue beginning to boil.