"Chris" wrote in message
...
snip


Upto 10,000 ft air only
10,000 - 33,700 ft Oxygen/air mix
33,700 - 40,000 ft 100% oxygen
40,000 + 100% Oxygen under pressure



I flew fighters for the Air Force (F-4E) and I recal going to pressure
breathing at about 25,000 feet cabin altitude. This was an emergency only
because the cabin pressure never got this high. I also recall a rule to not
go over 50,000 feet because of blood boiling (bends) IF the cabin pressure
was lost at greater than 50,000 feet.


Danny Dot