You don't normally use a pressure O2 system in anything except jets (for
emergencies) and some high altitude gliders and you don't want to anyway.
Pressure O2 systems are very uncomfortable.

Mike
MU-2

"O. Sami Saydjari" wrote in message
...
OK, very helpful answers. But, how does one get a "pressurized mask"? Is
this a matter of buying a pressurized mask and hooking it to a built-in O2
system (such as might be found on a Cessna Turbo 310), or is there
something special about the 02 system itself that is needed. It sounds
like one needs a special pressure regulator like one might find in Scuba
equipment. I ask this because I want to know what to ask for when I am
looking at Turbo Cessna 310s in terms of an adequate O2 system to make it
up to its 28,000 ft service ceiling.

-Sami


john smith wrote:

Very good answer Ben!
The partial pressure of O2 at FL180 is 50% that of sea level.
As you go higher, the rate of partial pressure change decreases more
rapidly, so that by FL270 it is into single digits.
A pressurized mask is necessary to force the air into your lungs and into
your blood.

Ben Hallert wrote:

I think the other posters have it right. The specific concept behind
it, if I remember my science fiction books correctly, is 'partial
pressure'. With the open cycle (the one that hooks to your nose),
there's an open path direct to the low pressure area through your
mouth. The oxygen enters your lungs through osmosis, and if the
pressure on the inside of the hemoglobin in your pulmonary capillary is
greater then the pressure of the O2 against it, it just won't enter.
Another part of the problem may be that at high enough altitudes, CO2
may no longer be effective at triggering the breathing impulse.
I think the partial pressure issue is probably more relevant.