Extreme hypoxia occurs at which altitude?

• A. 10,000 ft
• B. 14,000 ft
• C. 20,000 ft
• D. 37,000 ft

Answer: (C)

As altitude climbs, the pressure of oxygen in the air drops, so the amount of oxygen that reaches your lungs and is available to the blood falls. By around 20,000 feet, that drop is enough that the oxygen your bloodstream can carry is far below what your brain and other organs need to function normally. That leads to severe impairment in thinking, coordination, and judgment, and without supplemental oxygen or pressurization, consciousness can be lost rapidly—seconds to a minute or two. So 20,000 feet is the point where hypoxia becomes extreme because the body's tissues simply aren’t getting the oxygen they require to operate, even with casual breathing. At lower altitudes you’d notice symptoms, but not the extreme level, and at much higher altitudes the onset would be even more rapid and dangerous.