I
n the 'World of Hypoxia' the Time of Useful
Consciousness (TUC) is a very important parameter. For low ambient pressure
conditions it indicates the time available to perform purposeful activities,
such as oxygen mask donning or aircraft control. Beyond this time frame mental
and physical capabilities are dangerously impaired and finally result in
unconsciousness and potentially death.TIME
USEFUL
Time of useful consciousness
|
|
20000 ft
|
less than 10 mts
|
25000 ft
|
2.5 mts or less
|
30000 ft
|
Appx 30 sec
|
37000 ft
|
Appx 18 sec
|
45000 ft
|
Appx 15 sec
|
As shown in the table, TUC is negatively
correlated with altitude. It is important to note that even if activities are
performed within the TUC time frame there is a significant deterioration of
work rate and mental capability, which is correlated with the time spent at low
pressure conditions (at the end of the TUC time frame, performance is much
lower than at the beginning). The TUC is the 'Window of Opportunity' for
donning an oxygen mask and can be very limited so must take overriding
precedence over any other activities.
Time of
Safe Unconsciousness
Some experts believe that for passengers – in
contradiction to the flight crew - a short period of unconsciousness during
cabin depressurization can be tolerated since they are not performing an
operational task. Unconsciousness is a clear sign of insufficient oxygen supply
to the brain and it is obvious that this time can only be very short before
permanent brain damage occurs. So far, it has not been possible to associate a
specific time frame for the safe time of unconsciousness.
The uncertainties in extrapolation of animal
data and the wide variability in individual tolerances have so far prevented
determination of a commonly agreed value for Time of Safe Unconsciousness (TSU)
among human physiology experts. It is believed that a safe time of
unconsciousness is somewhere between 90 seconds and 4 minutes.(Adapted from safety first)
Interesting post. I think... know... that anytime the brain lacks oxygen, there is some damage. How much? That's the question.
ReplyDeleteThanks for sharing this information.
Now you know why the pilots are bonkers. Half their life they spend at 6-8000 ft cabin alt and it is likely to take a toll. While it falls under the "indifferent stage" of Hypoxia, nevertheless the brain Oxy concentration drops from about 98 % to 93 % by 10000 ft where an increase in breathing rate compnesates the drop somewhat.
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