Re: Passenger cabin pressurization

Date:         16 Sep 97 02:37:13 
From:         jf mezei <"[non-spam]jfmezei"@videotron.ca>
Organization: VTL
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rdd@netcom.nospam.com wrote:
> But lest your memory has suffered, a typical pressurization system maintains
> a pressure differential of 8.5 psi, or whatever is closest to the landing
> altitude.

Can someone tell me where I am making a mistake ?

8.5 PSI -> 8.5*6.98 kPa = 59.33 kPa  ->  59.33/101 atm = 0.58 atm.

Sea level is 1 atm. If at cruise, plane has 8.5psi difference with
sea level, this mean that it has 0.59 atm difference with sea level.

Hence, at cruise, plane would have 1 - 0.58 atm = 0.42 atm cabin
pressure.

0.42 is less than half the pressure at sea level. When travelling by bike,
I always carry my plastic water bottle on board and make a point of
emptying it and closing the lid just prior to start of descent. And at
times, the bottle does appear almost half squeezed by the time we are on
the ground. So, I cannot dismiss this 0.42 value so easily.

Now, a poster in a different newsgroup posted this:

>If this were true then the partial pressure of O2 in the cabin
>would be .08 atmospheres, only half of the .16 atmospheres required
>to sustain life.

Am I right in my calculations and the above paragraph wrong, or did I
totally err in my understanding/calculations ?

OR: is the 8.5psi related to cabin pressure versus outdoor pressure at
cruise?

  If that is the case, I saw a news release from Bombardier concerning
  tests of its new Global Express which saw cabin pressure of 25.4psi.

  If cabin pressure differential with exterior at cruise is usually 8.5,
  why would they have to test an aircraft to 3 times that value ?