At what oxygen level will a person typically begin to feel disoriented?

• A. 16%
• B. 12%
• C. 8%
• D. 20%

Answer: (A)

When the brain isn’t getting enough oxygen, cognitive function starts to degrade. The onset of disorientation tends to occur when inspired oxygen drops into the mid-teens, around sixteen percent. That level is lower than normal air, but not so low as to cause immediate collapse; it’s enough to impair thinking and balance, leading to confusion or disorientation.

At higher levels, close to normal air (about twenty percent), most people don’t notice disorientation. As oxygen drops further—to around twelve percent or even lower around eight percent—the effects become much more severe, with marked confusion, dizziness, and potential loss of consciousness.