Re: Cabin Depressurization

Date:         08 Jan 2000 13:39:05 
From:         "Hugo 'NOx' Tyson" <hmt@cygnus.co.ukx>
Organization: Cygnus Solutions, Cambridge, UK
References:   1 2
Followups:    1 2
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glpilotsrv@aol.com (GLPILOTSRV) writes:
> I would not doubt the statement. Drop down oxygen systems do not supply
> oxygen under pressure. Above approximately 25,000 feet, oxygen needs to
> be supplied under pressure, otherwise the hemoglobin will not absorb the
> oxygen present.

I think you misunderstand partial pressure: the body is quite happy with
100% O2 @ 0.21 Bar  or  50% O2 @ 0.42 Bar  or  21% O2 at 1 Bar  - it really
makes no difference.

I thought the point of passenger O2 systems is they let you breath a higher
%age of O2 at ambient pressure, thus giving enough partial pressure to stay
alive (even if not conscious).

According to the www ;-)
"To convert from pressure to height, just remember two rules:
    1.Sea level pressure is about 1000 mb;
    2.For every 5.5 km increase in height, the air pressure decreases by a
      factor of two."

So at a typical cruise of 11km (36,300ft) you get 0.250 Bar ambient, so you
need about 80 %O2 or better to stay conscious.

Your statement would be OK if it said "above 50,000 feet" where even 100%
O2 at ambient isn't enough.

	- Huge

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