O2 and Cypriot airliner crash

In accounts of the crash of the Cypriot airliner in Greece, all I've
read say that loss of cabin pressure could not, by itself, incapacitate
the pilot. Yet, I was once told by an ATP that at 40k feet (admittedly
this plane was at 35k) O2 supply by itself will not suffice to keep you
conscious and that the drop down masks only give a false sense of
security. He said that the ambient pressure is so low that even 100% O2
does not provide enough to keep you conscious without a pressure
breathing mask. If he's right, that could explain the crash, especially
given that all it would take is 20 seconds of distraction (i.e., not
donning the mask) to knock out the pilot as indicated in the table
below. On the other hand, I checked and a standard atmosphere at 35k
feet is 7.0 in of Hg, which is more than the partial pressure of O2 at
sea level (6 in = 20% of 30 inches), which would seem to contradict the
info given by the ATP. Any thoughts or corrections to my reasoning?


Tlme of useful
consciousness
Altitude (ft) without oxygen

40,000 15 seconds
35.000 20 seconds
30,000 30 seconds
28,000 1 minute
26,000 2 minutes
24,000 3 minutes
22,000 6 minutes
20,000 10 minutes
15.000 Indefinite

wrote:
40,000 15 seconds
35.000 20 seconds
30,000 30 seconds

I don't get it. Can't a person stay conscious for longer than 30
seconds without breathing? Most people can hold their breath for over
a minute.

The "partial pressure of O2" has nothing to do with it.

Your premise is wrong. Loss of cabin pressure IS what incapacitates
pilots. The lungs need atmospheric pressure to exchange gasses with
hemoglobin in the alveoli. It doesn't matter what gas it is - without
the pressure, respiration stops happening. As altitude increases and
pressure decreases, respiration becomes less effective. Below a
certain pressure, you can suffocate on 100% oxygen.

In article .com,
wrote:

In accounts of the crash of the Cypriot airliner in Greece, all I've
read say that loss of cabin pressure could not, by itself, incapacitate
the pilot. Yet, I was once told by an ATP that at 40k feet (admittedly
this plane was at 35k) O2 supply by itself will not suffice to keep you
conscious and that the drop down masks only give a false sense of
security. He said that the ambient pressure is so low that even 100% O2
does not provide enough to keep you conscious without a pressure
breathing mask.

I personally know glider pilots here in New Zealand who have flown to
betweeen 35,000 and 37,000 ft with only an ordinary oxygen mask, not a
pressure system.

The glider world record of 49,000 ft used a pressure system.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

"Bucky" wrote in message
oups.com...
I don't get it. Can't a person stay conscious for longer than 30
seconds without breathing? Most people can hold their breath for over
a minute.

When they do that, they are using up a small reserve of oxygen-filled air
contained in their lungs. Exhale as much air from your lungs as you can,
and THEN see how long you can hold your breath.

Peter Duniho wrote:

When they do that, they are using up a small reserve of oxygen-filled air
contained in their lungs. Exhale as much air from your lungs as you can,
and THEN see how long you can hold your breath.

Even then, there's still a lot of oxygen in the lungs, the human lung is
pretty inefficient. What happens at altitude is that you don't feel the
absence of oxygen, hence just continue to breath normally. This empties
your oxygen reserves rather quickly.

On airliners, though, there are instruments which alarm the pilot of
pressure loss and drop the mask immediately. So there must have been
another problem.

Stefan

"Peter Duniho" wrote in message
"Bucky" wrote in message
oups.com...
I don't get it. Can't a person stay conscious for longer than 30
seconds without breathing? Most people can hold their breath for over
a minute.

When they do that, they are using up a small reserve of oxygen-filled air
contained in their lungs. Exhale as much air from your lungs as you can,
and THEN see how long you can hold your breath.

Partially crap. Learn how lungs work.

moo

"Bruce Hoult" wrote in message news:bruce-566936.
wrote:

In accounts of the crash of the Cypriot airliner in Greece, all I've
read say that loss of cabin pressure could not, by itself, incapacitate
the pilot. Yet, I was once told by an ATP that at 40k feet (admittedly
this plane was at 35k) O2 supply by itself will not suffice to keep you
conscious and that the drop down masks only give a false sense of
security. He said that the ambient pressure is so low that even 100% O2
does not provide enough to keep you conscious without a pressure
breathing mask.

I personally know glider pilots here in New Zealand who have flown to
betweeen 35,000 and 37,000 ft with only an ordinary oxygen mask, not a
pressure system.

It's OK at 34,000 ft and above 38,000 ft. And all other altitudes,
partialy. You were asleep or missed this class, right?

moo

Brien K. Meehan opined

The "partial pressure of O2" has nothing to do with it.

Your premise is wrong. Loss of cabin pressure IS what incapacitates
pilots. The lungs need atmospheric pressure to exchange gasses with
hemoglobin in the alveoli. It doesn't matter what gas it is - without
the pressure, respiration stops happening. As altitude increases and
pressure decreases, respiration becomes less effective. Below a
certain pressure, you can suffocate on 100% oxygen.

Seems to me that astronauts use 3psi of pure O2 during EVAs.


-ash
Cthulhu in 2005!
Why wait for nature?

Tlme of useful
consciousness
Altitude (ft) without oxygen

40,000 15 seconds
35.000 20 seconds
30,000 30 seconds
28,000 1 minute


How, then, can someone like Ed Viesturs repeatedly climb the tallest
mountain peaks in the world without supplemental oxygen? Is it because of
the slower ascent and the time spent acclimating to the higher altitudes?

John K.