O2 and Cypriot airliner crash

John Gaquin wrote:
"Bob Moore" wrote in message

My thoughts on yesterday's accident.


My thoughts were tending in the same direction, Bob. Speculation on the
availability of O2, or the system integrity, is fine, but the first and most
obvious question to me was as to why the airplane was still at altitude.
Job 1, superceding all others, is to get the craft to breathable air. What
was going on? All it takes is one body in the cockpit to initiate the
descent.

The news tonight said the airliner was on autopilot, in climb mode,which
it continued in until finally reaching it's service ceiling. My
understanding is Job 1 is to put on an oxygen mask, which, if it failed
to deliver oxygen, might mean they never get to Job 2 (descend).


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Eric Greenwell
Washington State
USA

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. 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


Sure pp is 6" at sea level, but at 35 k ft (using your numbers) the pp
O2 is 20% of 7" or 1.4" Hg. At that pressure only about 50% of the
hemoglobin in your blood is saturated, and it hangs on to that O2 pretty
strongly, so it's not available for use by your brain (or anywhere else).

Shawn

Also, many of the high-altitude climbers who do not
use oxygen have shown significant brain damage when
cat-scanned.



At 14:00 15 August 2005, Stefan wrote:
John Kirksey wrote:

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?

First, acclimatisation.

Second, walking (and climbing) is different from flying.
You don't need
much brain to walk. When piloting, however, everything
is about
thinking. And it's the brain which needs the most oxygen.

And maybe a third reason: There are exceptional people
who are just
better suited for such things than you and me.

Stefan

"Stewart Kissel" wrote in
message ...
Also, many of the high-altitude climbers who do not
use oxygen have shown significant brain damage when
cat-scanned.



Before or after climbing without O2?

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Stewart Kissel wrote:
Also, many of the high-altitude climbers who do not
use oxygen have shown significant brain damage when
cat-scanned.

Interesting! Do you have a reference?

Tony V.

On Mon, 15 Aug 2005 04:21:32 UTC, wrote:

: 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...

Oxygen is only part of it. The breathing reflex is triggered by the
carbon dioxide partial pressure in your lungs: when atmospheric
pressure falls below that you never get the trigger and your lungs
just stop working. This is a Bad Thing.


Ian


--

CO2 is generated by cellular respiration. This is essentially
independent of oxygen, as a matter of fact, anaerobic respiration can
occur in the absense of adequate oxygen, but it is VERY inefficient, and
makes LOTS of waste products.

Arterial CO2 concentration, having left the lungs, is around 35-45 torr
(mmHg). In mixed venous blood, returning to the lungs, it is around 50
torr/mmhg or so.

At sea level, atmospheric CO2 is in the high 20's/low 30's mmhg. The
body's buffer system in a healthy individual will RAPIDLY move the CO2
level back towards normal if it vary's too much from those values. So,
even at altitude, your venous blood gas values are pretty much normal
after one pass around the body. You hold your breath, and this blood
with "venous" levels of CO2 will make a second pass, and when it hits
the chemo and baro receptors in in your carotid (artery) bodies you will
start getting that URGE to breath.

All of this is independent of how oxygen is handled by the blood. Each
gas's function in the body is more or less independent of each other.
Even though your body uses oxygen to make CO2 as a waste product, your
body will continue to make CO2 for a short time without adequate oxygen.
As an example: the burn in your muscles after a sprint - lactic acid
generated along with CO2 when the oxygen requirement of the muscles
outstrips the oxygen supply.

To say "the lungs stop working" is at best, technically inaccurate. You
are just too hypoxic to make the muscles responsible for gas exchange to
work properly.

Dave

wrote:

Any thoughts or corrections to my reasoning?

The ATP is correct. While people do vary greatly, and some people have been able
to perform adequately without oxygen at 20,000' or more, most people can't go
much higher than 10,000' without suffering some ill effects. Because of this,
the FAA requires that a pilot use oxygen if they spend over 30 minutes above
12,500'.

In general, people can use a cranula or similar device to provide oxygen up to
about 20,000' (the FAA limits use of these to 18,000'). These simply bleed
oxygen into the air you breathe. Above that, you need a low-pressure mask. These
ensure that all you are breathing is oxygen and are good up to about 25,000'.
Above that, you need a pressure mask. Those increase the pressure of the oxygen
and work well up to about 35,000'. Above that, you need a pressure suit or a
pressurized aircraft.

The emergency drop-down masks for airline passengers are low-pressure. They
won't keep you conscious at 35,000', but they may keep you alive.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

George Patterson wrote:


In general, people can use a cranula or similar device to provide oxygen
up to about 20,000' (the FAA limits use of these to 18,000'). These
simply bleed oxygen into the air you breathe. Above that, you need a
low-pressure mask. These ensure that all you are breathing is oxygen and
are good up to about 25,000'.

My understanding is cannulas are still effective to at least 25,000',
and the FAA mask requirement is only to guard against pilots that might
inadvertently breathe through their mouth instead of their nose. The
masks I've used all allow ambient air into the mask; i.e., they are not
intended to supply only oxygen. They used staged valves for constant
flow systems, or just small holes in the sides of the mask for
pulse-delivery devices like Mountain High's EDS controller.



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Eric Greenwell
Washington State
USA

In article %N5Me.1542$yb.46@trndny01,
George Patterson wrote:

Because of this, the FAA requires that a pilot use oxygen if they
spend over 30 minutes above 12,500'.

My recollection of my O2 training is that the rule is 30 minutes over
10,000 ft, or if you go over 12,500 ft at *all*.

But I've only been to about 20,000 ft in a glider, unlike some people I
know who have been far higher.

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