Time of useful consciousness (TUC), also effective performance time (EPT), is defined as the amount of time an individual is able to function effectively (e.g. perform flying duties) in an environment of inadequate

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

supply. It is the period of time from the interruption of the oxygen supply or exposure to an oxygen-poor environment to the time when useful function is lost, and the individual is no longer capable of taking proper corrective and protective action. It is not the time to total

unconsciousness Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an awareness of self and environment or to respond to any human or environmental stimulus. Unconsciousness may occur as the r ...

. At the higher altitudes, the TUC becomes very short; considering this danger, the emphasis is on prevention rather than cure. For orbital altitudes and above, that is, direct exposure to space, 6–9 seconds of consciousness is expected.

Medical analysis and variations

There are many individual variations of hypoxia, even within the same person. Generally,

old age Old age refers to ages nearing or surpassing the life expectancy of human beings, and is thus the end of the human life cycle. Terms and euphemisms for people at this age include old people, the elderly (worldwide usage), OAPs (British usa ...

tends to reduce the efficiency of the pulmonary system, and can cause the onset of hypoxia symptoms sooner.

Smoking Smoking is a practice in which a substance is burned and the resulting smoke is typically breathed in to be tasted and absorbed into the bloodstream. Most commonly, the substance used is the dried leaves of the tobacco plant, which have b ...

drastically reduces oxygen intake efficiency, and can have the effect of reducing tolerance by . Hypoxia can be produced in a

hypobaric chamber A hypobaric chamber, or altitude chamber, is a chamber used during aerospace or high terrestrial altitude research or training to simulate the effects of high altitude on the human body, especially hypoxia (low oxygen) and hypobaria (low ambien ...

. This can be useful for identifying individual symptoms of hypoxia, along with rough estimates of the altitude that causes problems for each person. Identifying symptoms is often helpful for self-diagnosis in order to realize when altitude should be reduced. The table below shows average TUCs as documented by the

Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic ...

; a rapid ascent results in a lower TUC. The TUCs for any given individual may differ significantly from this.

Aerobic exercise Aerobic exercise (also known as endurance activities, cardio or cardio-respiratory exercise) is physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process. "Aerobic" is defined as "relating to, inv ...

during the TUC period will reduce the TUCs considerably; so will exercise immediately prior to the TUC as this induces an oxygen debt prior to exposure.

References

{{Reflist Aviation medicine Pulmonology Aviation accidents and incidents

Medical analysis and variations

See also

References