<s>[INST] How high in the atmosphere is it dangerous for humans to stay? [/INST] Most people will need supplemental oxygen to avoid hypoxia at an altitude above 4500m (15000ft). At altitudes above 11900m (39000ft), the oxygen must be delivered through a sealed mask with increased pressure to avoid hypoxia, and the user also needs a pressure suit or a counter-pressure garment to avoid possible lung damage caused by the extra pressure. At around 15000 m (49000 ft), a well-conditioned and experienced pilot also needs a pressure suit to safely operate the aircraft. At the Armstrong limit, which is around 18000-19000m (59000–62000ft), water will boil at the normal temperature of the human body. Without a full-body pressure suit or pressurized cockpit/cabin, any exposed body fluids will boil away, including the liquids wetting the alveoli in the lungs. This results in a rapid loss of consciousness and eventually death if pressure can't be restored within 60–90 seconds. </s>