They must have been fairly hardy individuals, I was under the impression that there was not enough oxygen to sustain life above eight thousand feet to sustain life, hence that is the altitude aircraft are pressurised at.
Also, an engineer once told me you could just about survive being in the unpressurised cargo hold of a 747 at thirty thousand feet if you wore a few warm jackets, but you would be struggling to breathe.
Remember that chap who survived a flight from India to London heathrow in the whell compartment of a 747?
