Time of useful consciousness
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 supply.[1] 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. 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, 6–8 seconds of consciousness is expected.[2]
Medical analysis and variations
[edit]There are many individual variations of hypoxia, even within the same person. Generally, old age tends to reduce the efficiency of the pulmonary system, and can cause the onset of hypoxia symptoms sooner.[3] Smoking drastically reduces oxygen intake efficiency, and can have the effect of reducing tolerance by 1,000–2,000 metres (3,300–6,600 ft).[4] Hypoxia can be produced in a hypobaric chamber. 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; a rapid ascent results in a lower TUC.[5] The TUCs for any given individual may differ significantly from this. Aerobic exercise 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.[6]
| Altitude (measured barometrically) | TUC (normal ascent) | TUC (rapid decompression) |
|---|---|---|
| FL180 (18,000 ft; 5,500 m) | 20 to 30 minutes | 10 to 15 minutes |
| FL220 (22,000 ft; 6,700 m) | 10 minutes | 5 minutes |
| FL250 (25,000 ft; 7,600 m) | 3 to 5 minutes | 1.5 to 3.5 minutes |
| FL280 (28,000 ft; 8,550 m) | 2.5 to 3 minutes | 1.25 to 1.5 minutes |
| FL300 (30,000 ft; 9,150 m) | 1 to 2 minutes | 30 to 60 seconds |
| FL350 (35,000 ft; 10,650 m) | 30 to 60 seconds | 15 to 30 seconds |
| FL400 (40,000 ft; 12,200 m) | 15 to 20 seconds | 7 to 10 seconds |
| FL430 (43,000 ft; 13,100 m) | 9 to 12 seconds | 5 to 6 seconds |
| FL500 (50,000 ft; 15,250 m) | 8 to 10 seconds | 5 seconds |
Implications for Aviation Safety
[edit]- Importance of Immediate Oxygen Mask Use: The updated understanding of TUC underscores the critical need for pilots and crew members to don oxygen masks immediately following cabin depressurization. Delays in mask usage can significantly reduce the available TUC, increasing the risk of incapacitation before corrective actions can be taken[7]
- Training Programs Incorporating TUC Awareness: Many aviation training programs are now incorporating lessons on TUC to enhance awareness among pilots regarding the effects of altitude on cognitive function. These programs emphasize the importance of recognizing symptoms of hypoxia early and responding promptly to maintain safety during flights[8]
See also
[edit]- Armstrong limit maximum survivable altitude
- Cabin pressurization
- Pressure suit
- Uncontrolled decompression
References
[edit]- ^ Dehart, R. L.; J. R. Davis (2002). Fundamentals Of Aerospace Medicine: Translating Research Into Clinical Applications, 3rd Rev Ed. United States: Lippincott Williams And Wilkins. p. 720. ISBN 978-0-7817-2898-0.
- ^ Geoffrey A. Landis, Human Exposure to Vacuum web page
- ^ Yoneda I, Tomoda M, Tokumaru O, Sato T, Watanabe Y (January 2000). "Time of useful consciousness determination in aircrew members with reference to prior altitude chamber experience and age". Aviat Space Environ Med. 71 (1): 72–6. PMID 10632134.
- ^ Yoneda I, Watanabe Y (September 1997). "Comparisons of altitude tolerance and hypoxia symptoms between nonsmokers and habitual smokers". Aviat Space Environ Med. 68 (9): 807–11. PMID 9293349.
- ^ "AC 61-107A - Operations of aircraft at altitudes above 25,000 feet MSL and/or mach numbers (MMO) greater than .75" (PDF). Archived from the original (PDF) on 2015-02-13.
- ^ Mark Wolff (2006-01-06). "Cabin Decompression and Hypoxia". theairlinepilots.com. Retrieved 2008-09-01.
- ^ "Time of Useful Consciousness | SKYbrary Aviation Safety". skybrary.aero. Retrieved 2024-11-17.
- ^ "Time of Useful Consciousness | SKYbrary Aviation Safety". skybrary.aero. Retrieved 2024-11-17.