Re[2]: 42,000 feet

Date:         20 Mar 97 02:34:55 
From:         "Peter Mchugh" <PMCHUGH@mail.hq.faa.gov>
References:   1 2 3
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>I suspect the size has more to do with stress on both the fuselage
>and the window, including heat stress on the latter.  At the sort of
>pressures involved, even a relatively small aperture will vent a lot
>of air very quickly.  I'm not sure how quickly Concorde can dive in
>an emergency, but 10,000 fpm seems pretty fast and even at that, it
>would take two minutes to get down to FL 400, never mind down to
>breathable levels.

I've forgotten much of my flight physiology training...but many of you
will remember those enjoyable (tho potentially noxious) flights in the
hi altitude/low pressure chamber...which provided opportunity to
experience rapid decompression, cyanosis, and hypoxia.

Training never included a decompression at pressures equivalent to
FL600...but did at 35,000' equivalents...where time of useful
consciousness (TUC) was something like 30 seconds or less...depending
on personal physiology.

TUC varies with individuals and is the period during which normal
(near normal) mental and physical activity can be sustained...followed
by euphoria, diminished mental and motor function.  Most individuals
gradually pass through the euphoric stage to unconsciousness...but
death takes a little (lots) longer.

Most high level flights (above FL400) can get down quickly enough
that, while passengers and unaided crewmembers may suffer one or both
of the first phases of hypoxia, none will incur any permanent
effects...but will quickly revive when oxygen becomes available.  My
recollection is that of surprise at the quickness with which full
performance capability returns after oxygen is supplied (either by
mask, or because ambient conditions return to normal.

Obviously, TUC is greatly reduced at altitudes above which pressure
breathing is required...because oxygen begins to leave the body at
such heights...

Most passengers, and many crewmembers, are probably less prepared for
the other effects of rapid decompression at very high altitudes...the
immediate loss of visual conditions (condensation) and debris,
initiation of rapid descent by the cockpit, noise, possible onset of
extreme cold, etc...at that moment, oxygen possibly isn't the first
thing on one's mind!

Cheers