What is The Time of Useful Consciousness at 40,000 feet?

• A. 12 seconds
• B. 18 seconds
• C. 30 seconds
• D. 45 seconds

Answer: (B)

Time of Useful Consciousness is how long you can stay conscious and think clearly after a loss of breathable oxygen at altitude. At 40,000 feet, the air is so thin that the brain takes on hypoxia very quickly. Without supplemental oxygen, typical people will lose consciousness in about 18 seconds. This is why pilots are trained to don oxygen immediately after a sudden decompression—to keep oxygen levels high and extend conscious time. The longer times in the other options would not fit the rapid onset of hypoxia at that altitude.