Oxygen above 20,000 feet

I seem to recall that my portable 02 system said something about not
being about to go above 20,000 feet with it. This does not present a
problem with my Turbo Arrow since that represents its service ceiling.
Now, I am contemplating a Cessna Turbo 310 R and I am wondering whether
the 02 will be the limiting factor on how high I fly?

-Sami

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.

If someone here is a doctor or actually KNOWS the answer, feel free to
tell me where I pooched it up. My education comes from the likes of
Del Rey Publishing and Baen Books, not John Hopkins.

Ben Hallert
PP-ASEL

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.

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.

O. Sami Saydjari wrote:
OK, very helpful answers. But, how does one get a "pressurized mask"?

Here's a low pressure model.
http://www.mhoxygen.com/index.phtml?...product_id=373

Here's this retailer's entire offering.
http://www.mhoxygen.com/index.phtml?...prd_group_id=9

George Patterson
"Naked" means you ain't got no clothes on; "nekkid" means you ain't got
no clothes on - and are up to somethin'.

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.

"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

Some information!

http://www.mhoxygen.com/index.phtml?...prd_group_id=4

http://www.aerox.com/Pages/masks.html

On 26-May-2005, john smith wrote:

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.

Actually, you nailed the main issue -- oxygen partial pressure -- but missed
the precise reason for the pressure mask.

As altitude increases, partial pressure of O2 decreases, as you correctly
state. The O2 PP at sea level is way more than we need, and healthy
individuals can tolerate the air at up to about 14000 ft without much loss
of mental capacity (physical capacity, including visual acuity, is another
matter.) Above that (actually, above 12500 ft), in an unpressurized
airplane, we increase the PP of the O2 we breath by adding supplemental
oxygen. The cannulas and/or masks typically used in light aircraft mix pure
O2 from the bottle with atmospheric air at a ratio that can be somewhat
adjusted (by the flow adjustment) to result in roughly the desired O2 PP.
But these systems are not designed to deliver anything close to pure O2 to
the user. The maximum O2 concentration they CAN deliver will provide
sufficient O2 PP at about 18000 ft for cannulas and about 26000 ft (if I
recall correctly) for masks. Above that, you need a system that can deliver
higher O2 concentrations, up to and including pure O2, which is where the
pressure mask comes in. What it does is provide O2 at slight positive
pressure relative to the outside air to prevent uncontrolled mixing in the
mask. Such masks also cover both nose and mouth to prevent leakage/mixing
that way. It doesn't really "force" the O2 into the user's lungs, nor does
it need to.

Above about 35000 ft even pure O2 will not have sufficient PP for adequate
breathing, so unpressurized aircraft cannot safely operate at anything close
to that level (unless the occupants are equipped with pressure suits).

This also explains why cabin depressurization above 30000 feet is an
emergency requiring (a) the immediate donning by the pilot(s) of a pressure
mask and (b) emergency descent to an altitude where the conventional
emergency masks used by passengers will be sufficient.

--
-Elliott Drucker

wrote:
This also explains why cabin depressurization above 30000 feet is an
emergency requiring (a) the immediate donning by the pilot(s) of a pressure
mask and (b) emergency descent to an altitude where the conventional
emergency masks used by passengers will be sufficient.

I believe that emergency descent capability is one of the factors that
limits allowable operating ceilings. Some aircraft could get higher than
their certified ceilings, but are not allowed to do so because getting down
to breathable air before the pax suffocated would involve tearing the wings
off (or some other overspeed disaster).

("Roy Smith" wrote)
[snip]
I believe that emergency descent capability is one of the factors that
limits allowable operating ceilings. Some aircraft could get higher than
their certified ceilings, but are not allowed to do so because getting
down
to breathable air before the pax suffocated would involve tearing the
wings
off (or some other overspeed disaster).


What is the time limit - 3 minutes? Tell me it's not 4 minutes.

What are planes/jets doing (ft/min) in emergency descents - and how low must
they go to get to "breathable air?" What's the reg for breathable air out of
an emergency descent - 18,000 ft?


Montblack