"Am I susceptible to hypoxia at 10-12,000 feet? I regularly fly at these altitudes but am not required by regulation to use oxygen." - Chris O.
“Hypoxia is a state of oxygen deficiency in the body sufficient to impair functions of the brain and other organs. Hypoxia from exposure to altitude is due only to the reduced barometric pressures encountered at altitude, for the ratio of oxygen to other gases in the atmosphere remains about 21 percent from the ground out to space. As altitude increases, the number of oxygen molecules per breath is reduced. At 12,000 feet there are roughly 40% fewer oxygen molecules per breath than at sea level.
If you regularly fly at altitudes above 8-10,000 feet, you should invest in a pulse oximeter. These relatively inexpensive devices clip onto a fingertip and read out blood oxygen levels.
The minimum blood oxygen level you should see is 90%, anything less than that means you need to either use oxygen or descend to a lower altitude.
The problem with hypoxia is that by the time you are experiencing it; your cognitive ability may be so impaired that you can’t recognize the symptoms and take the appropriate action.
The FARs for Part 91 pilots only require that supplemental oxygen be used after 30 minutes of exposure to altitudes between 12,500 and 14,000 feet. But consider that pilots for hire (Part 135 and 121) are required to use oxygen above 10,000 feet. I would favor the conservative approach that professional pilots are required to adhere to and use supplemental oxygen anytime above 10,000 feet.”