-=> Quoting Jay Hanig to Don Burke <=-
 JH> 14 Sep 97 15:09, Don Burke wrote to Jay Hanig:
 
JH>> Whereas 1.5 psi of O2 may not be adequate for clear thinking, 7.5 psi
is more than enough.  You need to use O2, not compressed air in a
decompression incident.
 
DB> One of the hot items in SCUBA diving is enriched oxygen mixtures,
generally called NITROX.  Do you suppose carrying a 50/50 O2/N2
mix would be signifigantly safer than 100% O2?
JH> I'm operating under the limitation of not knowing what the total
atmospheric pressure is at altitude.  I know that sea level is roughly
15 psi, and that the pressure drops to half that value at 18,000 feet. 
The 50/50 nitrox mixture you suggested would have a partial pressure of
oxygen of 3.75% at 18,000 feet.... more than enough.  The problem is
what happens at normal cruising altitudes for the average airliner:  I
know it'll be less, but I don't know how much less. 
Maybe some of our airline buddies might favor us with with some
figures of altitude vs atmospheric pressure?
I can do that.  "Pocket Ref" by Thomas J Glover lists the following:
  FEET    PSIA
   820   14.26
  1640   13.85
  2461   13.44
  3281   13.03
  4101   12.64
  4921   12.26
  5742   11.89
  6562   11.53
  8202   10.83
  9843   10.17
 11483    9.54
 13123    8.94
 14764    8.38
 16404    7.84
 18045    7.33
 19685    6.85
 21325    6.39
 22966    5.96
 24606    5.56
 26247    5.17
 27887    4.81
 29528    4.47
 31168    4.15
 32808    3.84
 36089    3.29
 39370    2.81
 42651    2.41
 45932    2.06
 49212    1.74
 52493    1.50
 55774    1.28
 59055    1.10
 62336     .94
 65617     .80
 82021     .37
 98425     .17
 104986    .13
The table is in even meters so the English values look a bit strange.
I guess we now know why SR-71 drivers wear full suits. :)
It looks like pure oxygen is the only way at 35,000 or so.  
Nitrox 50 wouldn't hack it above about 23,000.
... The checksum is in the e-mail.
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