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What is the Time of Useful Consciousness?
  • A
    The period of time between the start of exposure to hypoxia and the moment that the pilot becomes aware of its symptoms.
  • B
    The time taken to become aware of hypoxia due to gradual decompression.
  • C
    The period during which an individual can act with both mental and physical efficiency, measured from when an adequate oxygen supply is no longer available.
  • D
    The pilot’s reaction time when faced with hypoxia.


The time of useful consciousness refers to the time available to individuals to perform their tasks, after they have been deprived of oxygen, but are still aware of their environment and capable of controlling their actions.
It is important for the cabin crew to realize that the time of useful consciousness is different for each individual, and depends on the:
  • Altitude;
  • Individual’s state of health;
  • Amount of activity.

Relationship between Altitude and TUC:
Altitude TUC
40 000 ft 15 – 20 s
35 000 ft 30 – 90 s
30 000 ft 1 – 2 min
25 000 ft 2 – 3 min
20 000 ft 30 min

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