"W. D. Allen Sr." wrote:

44,000 ft altitude means only about 1/7 of the atmospheric
pressure at sea level. So it's hard to believe a person
could maintain consciousness without oxygen pressure
equipment to get to 49,500 feet.

With half the atmosphere below 18,000 feet the U. S.
military requires oxygen masks above 15,000 feet. And if I
remember correctly they require full pressure suits above
50,000 feet altitude.

WDA


Well, I know for a fact that you can survive at 45,000 feet with
only a 'demand' oxygen regulator connected to a regular oxygen
mask as issued to the Canadian Military in the mid sixties in an
aircraft with a 25,000ft service ceiling. That puts the cabin at
~30,000ft. Hell, we did a bunch of high altitude trials in an
UNPRESSURIZED Fairchild C-119 at 25,000 for several hours at a
time. But, of course, back then, men were men... harrumph...
--

-Gord.