The Armstrong Limit

Sometimes it takes a popular event to realise something about science. The recent skydive stunt (I say stunt but am still slightly scared getting in the lift where I work!) brought out a wonderful bit of science - the Armstrong Limit.

As most people are aware, the boiling point of water at 100 degrees is only actually true at sea level (and this is actually the definition of 100 degrees C like the freezing point of water is the definition of zero degrees). Thus, as you go higher, the boiling point of water decreases (as the pressure decreases, water finds it easier to evaporate and boil) to the point where water boils at 71C on the top of Everest). Extending this, it means that there will be a certain altitude where water boils at body temperature (37C). That point is the Armstrong Limit (or Armstrong line) and is found at about 19 km above sea level. If you were to get up to that height without any type of pressure suit, your tears, snot, saliva and lung fluids would start to boil spontaneously............ Despite not being a doctor, that does not sound good!!