The Time of Useful Conciousness (TUC) or Effective Performance Time is the period of elapsed time from the interruption of normal air supply or exposure to an oxygen-poor environment until the time when the ability to function usefully is likely to be lost at which point an affected individual would no longer be capable of taking normal corrective or protective action.
Time of useful consciousness (TUC) is not the time to total unconsciousness.
source: Carlyle, L. High altitude breathing. Approach. January, 1963. Pp. 30-35.
The physical condition of individuals influences the TUC. The TUC will be less for people with existing health conditions.
The TUC is less if the person is engaged in any kind of physical exercise, such as moving around the cabin.
In the case of explosive decompression, the TUC may be halved because of the effects of the sudden outflow of oxygen from the body's tissues.