At what altitude does unconsciousness occur due to hypoxia symptoms?

Unconsciousness due to hypoxia typically occurs at altitudes around 20,000 feet. At this altitude, the decrease in the partial pressure of oxygen significantly impairs the body's ability to absorb oxygen, leading to a lack of oxygen available to the brain and resulting in unconsciousness.

While some individuals may begin to experience hypoxia symptoms at lower altitudes, such as 15,000 or 18,000 feet, full unconsciousness is more commonly observed at or above 20,000 feet. The physiological response to reduced oxygen levels varies among individuals, but the onset of severe hypoxia and the risk of unconsciousness are well-documented at this altitude. Thus, the correct selection aligns with established aerospace medicine findings regarding altitude hypoxia effects on human physiology.