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TUC (Time of Useful Consciousness) is..
  • A
    the length of time during which an individual can act with both mental and physical efficiency after pressure loss.
  • B
    the time after pressure loss until decompression sickness sets in.
  • C
    measured from the moment at which an individual starts being exposed to hypoxia and death.
  • D
    the time before becoming unconscious at a sudden pressure loss.


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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