Medical Analysis and Variations
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. Smoking drastically reduces oxygen intake efficiency, and can have the effect of reducing tolerance by 1,000-2,000 meters (approx. 3,000-6,000 feet). Hypoxia can be simulated in an altitude 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. Although the times in the table below are often called average TUCs, an average failure is meaningless to a person who has a shorter TUC.
The table below reflects various altitudes with the corresponding average TUC:
| Altitude in Flight level | Time of Useful Consciousness | Altitude in meters | Altitude in feet |
|---|---|---|---|
| FL 150 | 30 min or more | 4,572 m | 15,000 |
| FL 180 | 20 to 30 min | 5,486 m | 18,000 |
| FL 220 | 5-10 min | 6,705 m | 22,000 |
| FL 250 | 3 to 6 min | 7,620 m | 25,000 |
| FL 280 | 2.5 to 3 mins | 8,534 m | 28,000 |
| FL 300 | 1 to 3 mins | 9,144 m | 30,000 |
| FL 350 | 30 sec to 60 sec | 10,668 m | 35,000 |
| FL 400 | 15 to 20 sec | 12,192 m | 40,000 |
| FL 430 | 9 to 15 sec | 13,106 m | 43,000 |
| FL 500 and above | 6 to 9 sec | 15,240 m | 50,000 |
These times have been established from observations over a period of years and are for an individual at rest. Any exercise will reduce the time considerably. For example, usually upon exposure to hypoxia at FL 250, an average individual has a TUC of 3 to 5 minutes. The same individual, after performing 10 deep knee bends, will have a TUC in the range of 1 to 1.5 minutes.
A rapid decompression can reduce the TUC by up to 50 percent caused by the forced exhalation of the lungs during decompression and the extremely rapid rate of ascent.
For orbital altitudes and above, that is, direct exposure to space, 6-9 seconds of consciousness is expected.
Read more about this topic: Time Of Useful Consciousness
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