Re: Greek plane crash questions

On Fri, 19 Aug 2005 15:38:24 -0400, Derf wrote:
> The problem with a quick decompress at cruise altitude is that
> the drop in pressure will almost surely cause one to exhale. Now you
> have only the oxygen already in the bloodstream until you get that
> mask on, and that means you have about 10 seconds of useful
> consciousness.


I'm VERY confused about this 30-second consciousness thing.

I just exhaled and could still hold my breath for much more than ten
seconds. Maybe not thirty ... but I was conscious. I'd "guess" (no I have
no proof) then I'd be real panicky but I'd still be alive. Certainly if an
oxygen mask popped up in front of me after that 30 second period of no air,
I'd grab at it like Barry Bonds eying a bottle of steroids.

I am sure I must be wrong ... 'cause everyone is saying you have only ten
or fifteen seconds of consciousness ... but it seems to me you'd have a
minute or more (even BTK took three or four minutes of strangling to kill a
person although I don't know how long they were conscious without blood to
their brains).

Why would one only have 10 seconds, even with all the air pushed out of
their lungs by the decompression? I fundamentally don't understand this???

--------------------------------------------------------------------------
Aviation experts believe the Helios Airways plane that crashed in Greece,
killing all 121 people on board, may have suffered a catastrophic loss of
cabin pressure, exposing those on board to extreme cold and lack of oxygen.
Aviation commentator Mark Welsh explains how modern aircraft regulate air
pressure and temperature to allow safe flying.
Experts believe some Helios Airways passengers died before the crash

Modern commercial aircraft operate at altitudes which cannot sustain human
life.
To provide a comfortable environment, the cabin of the aircraft is sealed
and the flow of air in and out of this "metal tube" is carefully
controlled.
The flow of air out is regulated by several valves in the body of the
aircraft and the flow of air in is provided by compressed air taken from
the engines.
WARNING SIGNS

At high altitudes the concentration of oxygen in the atmosphere is much
lower
Starvation of the body's supply of oxygen is known as hypoxia. Early
symptoms may include headache, nausea and deeper breathing as the body
attempts to compensate
Breathing may become shallow as the person becomes weaker and the brain
realises it is expelling too much carbon dioxide and creating a harmful
imbalance of oxygen to CO2 in the body. They may lose consciousness.
Cyanosis - blue or purple discolouration of extremities such as the lips
and fingers - occurs as hypoxia progresses

This air has its temperature and pressure corrected before being fed into
the cabin. If the regulating valves fail or if the cabin structure is
breached (by a failure of a door or window for example) then the pressure
in the cabin would suddenly drop to match the outside air pressure.
If there was a failure in the air supply system then the pressure would
decrease more slowly but still eventually match the outside air pressure.
If an aircraft flying at an altitude of 35,000 feet were to lose its
pressurisation system completely, then the occupants would have 25-30
seconds to establish an alternative oxygen supply. If they were unable to
do so they would die within two minutes.
To combat this threat, aircraft have a warning system which alerts the crew
if the cabin altitude is approaching dangerous levels.
If this alert is received, the pilots should put on masks which will
provide them with oxygen while they rapidly descend the aircraft to an
altitude where the occupants can breathe without assistance.
While this is happening, the passengers will be provided with oxygen from
drop-down masks which will give them oxygen for 12 to 15 minutes, by which
time the aircraft should be at a lower level.
Oxygen supply
As well as air pressure, the aircraft's occupants must be protected from
the deadly outside air temperature. If the warmed flow of air into the
cabin were to fail, the temperature in the aircraft would decrease until it
approached the outside air temperature of -45C to -60C.
The emergency oxygen supply used by the pilots is independent of that used
by the passengers. Any malfunction in this system would leave the pilots
with very little time to recover the situation.
If they were unable to do this, it is possible that the pilots would lose
consciousness, the aircraft would continue on autopilot and the cabin crew
and passengers would face a situation where they were running out of
emergency oxygen and the air temperature in the cabin was rapidly dropping.
The cabin crew would have portable oxygen supplies and a means of opening
the locked cockpit door but would not be trained to fly the aircraft to a
safe altitude. With the cabin air exhausted and the temperature dropping to
-50C, the aircraft would fly until it ran out of fuel.
Crucial data
The "black box" flight data recorder stores a huge amount of data gathered
from sensors around the aircraft.
This includes cabin pressure, the position of the flying controls and
aircraft height and speed. There is also a cockpit voice recorder which
will record noises, such as cockpit warnings, and conversations within the
cockpit.
Older voice recorder systems record sound onto a constantly running
magnetic tape loop while newer systems use digital storage devices to hold
much more voice data.
In the event of a plane crash, depending on the model of the recorder and
whether the data can be recovered, experts will be able to analyse cockpit
voice recordings for either the last 30 minutes of the flight or for up to
two hours before it crashed.

GREECE AIR DISASTER

1. 0900 [0700GMT]: Helios Airways Flight ZU522 leaves Larnaca bound for
Prague via Athens
2. 0920 approx: Plane reaches cruising altitude of 35,000ft
3. 0937: Plane enters Greek airspace
4. 1007: Air traffic control unable to contact aircraft
5. 1030: Greek ATC issues "Renegade alert"
6. 1055: F16 fighter aircraft scramble
7. 1120: F16s intercept aircraft; pilots observed slumped over controls
8. 1205: Aircraft crashes near Grammatiko, 40km north of Athens
------------------------------------------------------------------------

"Harvey Deinst" wrote:

> I'm VERY confused about this 30-second consciousness thing.
>
> I just exhaled and could still hold my breath for much more than ten
> seconds. Maybe not thirty ... but I was conscious. I'd "guess" (no I have
> no proof) then I'd be real panicky but I'd still be alive. Certainly if an
> oxygen mask popped up in front of me after that 30 second period of no air,
> I'd grab at it like Barry Bonds eying a bottle of steroids.
>
> I am sure I must be wrong ... 'cause everyone is saying you have only ten
> or fifteen seconds of consciousness ... but it seems to me you'd have a
> minute or more (even BTK took three or four minutes of strangling to kill a
> person although I don't know how long they were conscious without blood to
> their brains).
>
> Why would one only have 10 seconds, even with all the air pushed out of
> their lungs by the decompression?

It's not because the air rushes out of the lungs; you can still breathe.
It's because the pressure at high altitude is so low, oxygen is actually
*removed from the blood* through the lungs. As a result, the brain is much
more rapidly deprived of oxygen than it is when you simply exhale and hold
your breath.

At very high altitude, even pure oxygen from the little drop-down masks is
useless because the pressure is too low to get it into the blood.

--
Dan
C-172RG at BFM

Thought we had gone through this before...must have been in another
newsgroup.

I have had the ineffable pleasure of being taken up to 25000 feet in a
pressure chamber and then having the pressure dumped to simulate an
explosive decompression. Your ability to hold your breath is
immaterial....when the cabin decompresses, all air in your lungs is expelled
forcefully. You have no control over it, so you have no breath to hold. Your
only chance is to put on supplemental oxygen and do it as quickly as
possible.

The masks that drop from the overhead must be activated by pulling/jerking
on the string to activate an oxygen generator...there are no little oxygen
tanks up there. The crew has a separate oxygen supply, and if all is in
order and everyone reacts properly, each pilot will reach over his shoulder,
grab a quick-donning mask, and have it place and operating in a matter of a
few seconds. I have no idea what happened in the case of the Helios
airplane, but I do know that when the pressure vessel (cabin plus flight
deck) decompresses, the noise is horrific, the atmosphere becomes foggy
instantly, and loose papers fly in all directions. Training has to take
over, because a calm, reasoned reaction is unlikely.

Bob Gardner


Bob Gardner
"Harvey Deinst" <hdeinster1234@sbcglobal.net> wrote in message
news:1usqdmp1axhvp$.r25032fqugz3$.dlg@40tude.net.. .
> On Fri, 19 Aug 2005 15:38:24 -0400, Derf wrote:
>> The problem with a quick decompress at cruise altitude is that
>> the drop in pressure will almost surely cause one to exhale. Now you
>> have only the oxygen already in the bloodstream until you get that
>> mask on, and that means you have about 10 seconds of useful
>> consciousness.
>
>
> I'm VERY confused about this 30-second consciousness thing.
>
> I just exhaled and could still hold my breath for much more than ten
> seconds. Maybe not thirty ... but I was conscious. I'd "guess" (no I have
> no proof) then I'd be real panicky but I'd still be alive. Certainly if an
> oxygen mask popped up in front of me after that 30 second period of no
> air,
> I'd grab at it like Barry Bonds eying a bottle of steroids.
>
> I am sure I must be wrong ... 'cause everyone is saying you have only ten
> or fifteen seconds of consciousness ... but it seems to me you'd have a
> minute or more (even BTK took three or four minutes of strangling to kill
> a
> person although I don't know how long they were conscious without blood to
> their brains).
>
> Why would one only have 10 seconds, even with all the air pushed out of
> their lungs by the decompression? I fundamentally don't understand this???
>
> --------------------------------------------------------------------------
> Aviation experts believe the Helios Airways plane that crashed in Greece,
> killing all 121 people on board, may have suffered a catastrophic loss of
> cabin pressure, exposing those on board to extreme cold and lack of
> oxygen.
> Aviation commentator Mark Welsh explains how modern aircraft regulate air
> pressure and temperature to allow safe flying.
> Experts believe some Helios Airways passengers died before the crash
>
> Modern commercial aircraft operate at altitudes which cannot sustain human
> life.
> To provide a comfortable environment, the cabin of the aircraft is sealed
> and the flow of air in and out of this "metal tube" is carefully
> controlled.
> The flow of air out is regulated by several valves in the body of the
> aircraft and the flow of air in is provided by compressed air taken from
> the engines.
> WARNING SIGNS
>
> At high altitudes the concentration of oxygen in the atmosphere is much
> lower
> Starvation of the body's supply of oxygen is known as hypoxia. Early
> symptoms may include headache, nausea and deeper breathing as the body
> attempts to compensate
> Breathing may become shallow as the person becomes weaker and the brain
> realises it is expelling too much carbon dioxide and creating a harmful
> imbalance of oxygen to CO2 in the body. They may lose consciousness.
> Cyanosis - blue or purple discolouration of extremities such as the lips
> and fingers - occurs as hypoxia progresses
>
> This air has its temperature and pressure corrected before being fed into
> the cabin. If the regulating valves fail or if the cabin structure is
> breached (by a failure of a door or window for example) then the pressure
> in the cabin would suddenly drop to match the outside air pressure.
> If there was a failure in the air supply system then the pressure would
> decrease more slowly but still eventually match the outside air pressure.
> If an aircraft flying at an altitude of 35,000 feet were to lose its
> pressurisation system completely, then the occupants would have 25-30
> seconds to establish an alternative oxygen supply. If they were unable to
> do so they would die within two minutes.
> To combat this threat, aircraft have a warning system which alerts the
> crew
> if the cabin altitude is approaching dangerous levels.
> If this alert is received, the pilots should put on masks which will
> provide them with oxygen while they rapidly descend the aircraft to an
> altitude where the occupants can breathe without assistance.
> While this is happening, the passengers will be provided with oxygen from
> drop-down masks which will give them oxygen for 12 to 15 minutes, by which
> time the aircraft should be at a lower level.
> Oxygen supply
> As well as air pressure, the aircraft's occupants must be protected from
> the deadly outside air temperature. If the warmed flow of air into the
> cabin were to fail, the temperature in the aircraft would decrease until
> it
> approached the outside air temperature of -45C to -60C.
> The emergency oxygen supply used by the pilots is independent of that used
> by the passengers. Any malfunction in this system would leave the pilots
> with very little time to recover the situation.
> If they were unable to do this, it is possible that the pilots would lose
> consciousness, the aircraft would continue on autopilot and the cabin crew
> and passengers would face a situation where they were running out of
> emergency oxygen and the air temperature in the cabin was rapidly
> dropping.
> The cabin crew would have portable oxygen supplies and a means of opening
> the locked cockpit door but would not be trained to fly the aircraft to a
> safe altitude. With the cabin air exhausted and the temperature dropping
> to
> -50C, the aircraft would fly until it ran out of fuel.
> Crucial data
> The "black box" flight data recorder stores a huge amount of data gathered
> from sensors around the aircraft.
> This includes cabin pressure, the position of the flying controls and
> aircraft height and speed. There is also a cockpit voice recorder which
> will record noises, such as cockpit warnings, and conversations within the
> cockpit.
> Older voice recorder systems record sound onto a constantly running
> magnetic tape loop while newer systems use digital storage devices to hold
> much more voice data.
> In the event of a plane crash, depending on the model of the recorder and
> whether the data can be recovered, experts will be able to analyse cockpit
> voice recordings for either the last 30 minutes of the flight or for up to
> two hours before it crashed.
>
> GREECE AIR DISASTER
>
> 1. 0900 [0700GMT]: Helios Airways Flight ZU522 leaves Larnaca bound for
> Prague via Athens
> 2. 0920 approx: Plane reaches cruising altitude of 35,000ft
> 3. 0937: Plane enters Greek airspace
> 4. 1007: Air traffic control unable to contact aircraft
> 5. 1030: Greek ATC issues "Renegade alert"
> 6. 1055: F16 fighter aircraft scramble
> 7. 1120: F16s intercept aircraft; pilots observed slumped over controls
> 8. 1205: Aircraft crashes near Grammatiko, 40km north of Athens
> ------------------------------------------------------------------------

What you are not understanding is the physics of it.

At that high of an altitude, the pressure in the air is very light.

When you don't have that pressure on your body, the oxygen molecules just
float out of your blood. You have no oxygen in your system (even if you
could hold your breath), so you go unconscious after it leaves your system.

Even when you breath 100% oxygen, and you are up too high, that oxygen
doesn't do you any good, since the exchange isn't taking place in your
system. The oxygen is just floating away. The pilots masks are supposed to
be pressurized, which pressurizes your lungs, and allows the exchange to
occur, but even thats not effective above a certain altitude when you need a
full pressure suit.

Its a lot more complex than I've explained as a lot of people can tell you,
I've just tried to simplify it.

Someone put a link up to a Navy Surgeon site that explained it perfectly.

Dave

"Harvey Deinst" <hdeinster1234@sbcglobal.net> wrote in message
news:1usqdmp1axhvp$.r25032fqugz3$.dlg@40tude.net.. .
> On Fri, 19 Aug 2005 15:38:24 -0400, Derf wrote:
>> The problem with a quick decompress at cruise altitude is that
>> the drop in pressure will almost surely cause one to exhale. Now you
>> have only the oxygen already in the bloodstream until you get that
>> mask on, and that means you have about 10 seconds of useful
>> consciousness.
>
>
> I'm VERY confused about this 30-second consciousness thing.
>
> I just exhaled and could still hold my breath for much more than ten
> seconds. Maybe not thirty ... but I was conscious. I'd "guess" (no I have
> no proof) then I'd be real panicky but I'd still be alive. Certainly if an
> oxygen mask popped up in front of me after that 30 second period of no
> air,
> I'd grab at it like Barry Bonds eying a bottle of steroids.
>
> I am sure I must be wrong ... 'cause everyone is saying you have only ten
> or fifteen seconds of consciousness ... but it seems to me you'd have a
> minute or more (even BTK took three or four minutes of strangling to kill
> a
> person although I don't know how long they were conscious without blood to
> their brains).
>
> Why would one only have 10 seconds, even with all the air pushed out of
> their lungs by the decompression? I fundamentally don't understand this???
>
> --------------------------------------------------------------------------
> Aviation experts believe the Helios Airways plane that crashed in Greece,
> killing all 121 people on board, may have suffered a catastrophic loss of
> cabin pressure, exposing those on board to extreme cold and lack of
> oxygen.
> Aviation commentator Mark Welsh explains how modern aircraft regulate air
> pressure and temperature to allow safe flying.
> Experts believe some Helios Airways passengers died before the crash
>
> Modern commercial aircraft operate at altitudes which cannot sustain human
> life.
> To provide a comfortable environment, the cabin of the aircraft is sealed
> and the flow of air in and out of this "metal tube" is carefully
> controlled.
> The flow of air out is regulated by several valves in the body of the
> aircraft and the flow of air in is provided by compressed air taken from
> the engines.
> WARNING SIGNS
>
> At high altitudes the concentration of oxygen in the atmosphere is much
> lower
> Starvation of the body's supply of oxygen is known as hypoxia. Early
> symptoms may include headache, nausea and deeper breathing as the body
> attempts to compensate
> Breathing may become shallow as the person becomes weaker and the brain
> realises it is expelling too much carbon dioxide and creating a harmful
> imbalance of oxygen to CO2 in the body. They may lose consciousness.
> Cyanosis - blue or purple discolouration of extremities such as the lips
> and fingers - occurs as hypoxia progresses
>
> This air has its temperature and pressure corrected before being fed into
> the cabin. If the regulating valves fail or if the cabin structure is
> breached (by a failure of a door or window for example) then the pressure
> in the cabin would suddenly drop to match the outside air pressure.
> If there was a failure in the air supply system then the pressure would
> decrease more slowly but still eventually match the outside air pressure.
> If an aircraft flying at an altitude of 35,000 feet were to lose its
> pressurisation system completely, then the occupants would have 25-30
> seconds to establish an alternative oxygen supply. If they were unable to
> do so they would die within two minutes.
> To combat this threat, aircraft have a warning system which alerts the
> crew
> if the cabin altitude is approaching dangerous levels.
> If this alert is received, the pilots should put on masks which will
> provide them with oxygen while they rapidly descend the aircraft to an
> altitude where the occupants can breathe without assistance.
> While this is happening, the passengers will be provided with oxygen from
> drop-down masks which will give them oxygen for 12 to 15 minutes, by which
> time the aircraft should be at a lower level.
> Oxygen supply
> As well as air pressure, the aircraft's occupants must be protected from
> the deadly outside air temperature. If the warmed flow of air into the
> cabin were to fail, the temperature in the aircraft would decrease until
> it
> approached the outside air temperature of -45C to -60C.
> The emergency oxygen supply used by the pilots is independent of that used
> by the passengers. Any malfunction in this system would leave the pilots
> with very little time to recover the situation.
> If they were unable to do this, it is possible that the pilots would lose
> consciousness, the aircraft would continue on autopilot and the cabin crew
> and passengers would face a situation where they were running out of
> emergency oxygen and the air temperature in the cabin was rapidly
> dropping.
> The cabin crew would have portable oxygen supplies and a means of opening
> the locked cockpit door but would not be trained to fly the aircraft to a
> safe altitude. With the cabin air exhausted and the temperature dropping
> to
> -50C, the aircraft would fly until it ran out of fuel.
> Crucial data
> The "black box" flight data recorder stores a huge amount of data gathered
> from sensors around the aircraft.
> This includes cabin pressure, the position of the flying controls and
> aircraft height and speed. There is also a cockpit voice recorder which
> will record noises, such as cockpit warnings, and conversations within the
> cockpit.
> Older voice recorder systems record sound onto a constantly running
> magnetic tape loop while newer systems use digital storage devices to hold
> much more voice data.
> In the event of a plane crash, depending on the model of the recorder and
> whether the data can be recovered, experts will be able to analyse cockpit
> voice recordings for either the last 30 minutes of the flight or for up to
> two hours before it crashed.
>
> GREECE AIR DISASTER
>
> 1. 0900 [0700GMT]: Helios Airways Flight ZU522 leaves Larnaca bound for
> Prague via Athens
> 2. 0920 approx: Plane reaches cruising altitude of 35,000ft
> 3. 0937: Plane enters Greek airspace
> 4. 1007: Air traffic control unable to contact aircraft
> 5. 1030: Greek ATC issues "Renegade alert"
> 6. 1055: F16 fighter aircraft scramble
> 7. 1120: F16s intercept aircraft; pilots observed slumped over controls
> 8. 1205: Aircraft crashes near Grammatiko, 40km north of Athens
> ------------------------------------------------------------------------

"Dave" <johndsykes@hotmail.com> wrote in message
news:Sy5Pe.12803$td5.5288102@news.sisna.com...
> What you are not understanding is the physics of it.
>
> At that high of an altitude, the pressure in the air is very light.
>
> When you don't have that pressure on your body, the oxygen molecules just
> float out of your blood. You have no oxygen in your system (even if you
> could hold your breath), so you go unconscious after it leaves your
> system.
>
> Even when you breath 100% oxygen, and you are up too high, that oxygen
> doesn't do you any good, since the exchange isn't taking place in your
> system. The oxygen is just floating away. The pilots masks are supposed
> to be pressurized, which pressurizes your lungs, and allows the exchange
> to occur, but even thats not effective above a certain altitude when you
> need a full pressure suit.
>
> Its a lot more complex than I've explained as a lot of people can tell
> you, I've just tried to simplify it.
>
> Someone put a link up to a Navy Surgeon site that explained it perfectly.
>
> Dave

Do you mean this one?

http://wwwsam.brooks.af.mil/af/files...hapter_02.html

Cross-posting is frowned on. You want to discuss it? Discuss it on your own.


"Harvey Deinst" <hdeinster1234@sbcglobal.net> wrote in message
news:1usqdmp1axhvp$.r25032fqugz3$.dlg@40tude.net.. .
> On Fri, 19 Aug 2005 15:38:24 -0400, Derf wrote:
> > The problem with a quick decompress at cruise altitude is that
> > the drop in pressure will almost surely cause one to exhale. Now you
> > have only the oxygen already in the bloodstream until you get that
> > mask on, and that means you have about 10 seconds of useful
> > consciousness.
>
>
> I'm VERY confused about this 30-second consciousness thing.
>
> I just exhaled and could still hold my breath for much more than ten
> seconds. Maybe not thirty ... but I was conscious. I'd "guess" (no I have
> no proof) then I'd be real panicky but I'd still be alive. Certainly if an
> oxygen mask popped up in front of me after that 30 second period of no
air,
> I'd grab at it like Barry Bonds eying a bottle of steroids.
>
> I am sure I must be wrong ... 'cause everyone is saying you have only ten
> or fifteen seconds of consciousness ... but it seems to me you'd have a
> minute or more (even BTK took three or four minutes of strangling to kill
a
> person although I don't know how long they were conscious without blood to
> their brains).
>
> Why would one only have 10 seconds, even with all the air pushed out of
> their lungs by the decompression? I fundamentally don't understand this???
>
> --------------------------------------------------------------------------
> Aviation experts believe the Helios Airways plane that crashed in Greece,
> killing all 121 people on board, may have suffered a catastrophic loss of
> cabin pressure, exposing those on board to extreme cold and lack of
oxygen.
> Aviation commentator Mark Welsh explains how modern aircraft regulate air
> pressure and temperature to allow safe flying.
> Experts believe some Helios Airways passengers died before the crash
>
> Modern commercial aircraft operate at altitudes which cannot sustain human
> life.
> To provide a comfortable environment, the cabin of the aircraft is sealed
> and the flow of air in and out of this "metal tube" is carefully
> controlled.
> The flow of air out is regulated by several valves in the body of the
> aircraft and the flow of air in is provided by compressed air taken from
> the engines.
> WARNING SIGNS
>
> At high altitudes the concentration of oxygen in the atmosphere is much
> lower
> Starvation of the body's supply of oxygen is known as hypoxia. Early
> symptoms may include headache, nausea and deeper breathing as the body
> attempts to compensate
> Breathing may become shallow as the person becomes weaker and the brain
> realises it is expelling too much carbon dioxide and creating a harmful
> imbalance of oxygen to CO2 in the body. They may lose consciousness.
> Cyanosis - blue or purple discolouration of extremities such as the lips
> and fingers - occurs as hypoxia progresses
>
> This air has its temperature and pressure corrected before being fed into
> the cabin. If the regulating valves fail or if the cabin structure is
> breached (by a failure of a door or window for example) then the pressure
> in the cabin would suddenly drop to match the outside air pressure.
> If there was a failure in the air supply system then the pressure would
> decrease more slowly but still eventually match the outside air pressure.
> If an aircraft flying at an altitude of 35,000 feet were to lose its
> pressurisation system completely, then the occupants would have 25-30
> seconds to establish an alternative oxygen supply. If they were unable to
> do so they would die within two minutes.
> To combat this threat, aircraft have a warning system which alerts the
crew
> if the cabin altitude is approaching dangerous levels.
> If this alert is received, the pilots should put on masks which will
> provide them with oxygen while they rapidly descend the aircraft to an
> altitude where the occupants can breathe without assistance.
> While this is happening, the passengers will be provided with oxygen from
> drop-down masks which will give them oxygen for 12 to 15 minutes, by which
> time the aircraft should be at a lower level.
> Oxygen supply
> As well as air pressure, the aircraft's occupants must be protected from
> the deadly outside air temperature. If the warmed flow of air into the
> cabin were to fail, the temperature in the aircraft would decrease until
it
> approached the outside air temperature of -45C to -60C.
> The emergency oxygen supply used by the pilots is independent of that used
> by the passengers. Any malfunction in this system would leave the pilots
> with very little time to recover the situation.
> If they were unable to do this, it is possible that the pilots would lose
> consciousness, the aircraft would continue on autopilot and the cabin crew
> and passengers would face a situation where they were running out of
> emergency oxygen and the air temperature in the cabin was rapidly
dropping.
> The cabin crew would have portable oxygen supplies and a means of opening
> the locked cockpit door but would not be trained to fly the aircraft to a
> safe altitude. With the cabin air exhausted and the temperature dropping
to
> -50C, the aircraft would fly until it ran out of fuel.
> Crucial data
> The "black box" flight data recorder stores a huge amount of data gathered
> from sensors around the aircraft.
> This includes cabin pressure, the position of the flying controls and
> aircraft height and speed. There is also a cockpit voice recorder which
> will record noises, such as cockpit warnings, and conversations within the
> cockpit.
> Older voice recorder systems record sound onto a constantly running
> magnetic tape loop while newer systems use digital storage devices to hold
> much more voice data.
> In the event of a plane crash, depending on the model of the recorder and
> whether the data can be recovered, experts will be able to analyse cockpit
> voice recordings for either the last 30 minutes of the flight or for up to
> two hours before it crashed.
>
> GREECE AIR DISASTER
>
> 1. 0900 [0700GMT]: Helios Airways Flight ZU522 leaves Larnaca bound for
> Prague via Athens
> 2. 0920 approx: Plane reaches cruising altitude of 35,000ft
> 3. 0937: Plane enters Greek airspace
> 4. 1007: Air traffic control unable to contact aircraft
> 5. 1030: Greek ATC issues "Renegade alert"
> 6. 1055: F16 fighter aircraft scramble
> 7. 1120: F16s intercept aircraft; pilots observed slumped over controls
> 8. 1205: Aircraft crashes near Grammatiko, 40km north of Athens
> ------------------------------------------------------------------------

Harvey Deinst <hdeinster1234@sbcglobal.net> wrote in
news:1usqdmp1axhvp$.r25032fqugz3$.dlg@40tude.net:

<snip>
>
> Why would one only have 10 seconds, even with all the air pushed out
> of their lungs by the decompression? I fundamentally don't understand
> this???
>

The difference between 35K foot pressure ordinary air and "holding your
breath" is almost entirely in the considerable reservoir of oxygen in
your lungs at sea level, 80% of which is missing at 35k feet.

In the decompression case, right from the start the blood leaving your
lungs, which came in as venous blood at quite low O2 saturation, leaves
the lungs at much lower than customary O2 saturation.

Worse, the much lower remaining stock oxygen is the more rapidly
depleted, so you go from little to very, very little fairly quickly.

The useful consciousness time as it reaches its high-altitude minimum is
mostly the transit time of the already oxygenated blood that just left
your lungs on the way to the brain at the "moment" of pressure loss--when
that low oxygen blood gets there, your conscious brain cells, which have
some of the most rapid replenishment rates of any tissue in the body, go
to sleep almost immediately. The times are a bit longer at less extreme
altitudes, as initially some oxygenation is taking place, and a modest
supply is still in the lungs.

The urge to breathe which makes you fight and eventually lose an attempt
to hold your breath is based on a carbon dioxide sensor, not an oxygen
sensor. Though I've not read on this specific point, I think it likely
that folks exposed to rapid pressure loss of atmospheric oxygen
concentration air _do not_ feel a sudden overwhelming urge to breathe
such as you and I feel after holding our breath for 1 minute and a half,
even though the oxygen saturation of their blood leaving the lungs (and
soon thereafter passing the sensor in the carotid body in the neck) is
actually _lower_ by quite a bit, because the blood leaving the lungs is
still quite low in carbon dioxide level in the high pressure altitude
case.

I'd love to hear actual experience on the "urge-to-breathe" point from
folks with altitude chamber experience.

Peter A. Stoll
(took a course in cardiovascular pathophysiology in college, and have
kept up a little on some physiology since).

With no warning that pressurization is going to be lost, it's kind of hard
to be prepared with any kind of gadgetry or procedure. When it feels like
someone has thrown a basketball at your gut and you have ooofed out every
last cubic inch of air, it is too late.

Bob

"Sbharris[atsign]ix.netcom.com" <sbharris@ix.netcom.com> wrote in message
news:1124925673.534126.237350@f14g2000cwb.googlegr oups.com...
> Bob Gardner wrote:
>> Thought we had gone through this before...must have been in another
>> newsgroup.
>>
>> I have had the ineffable pleasure of being taken up to 25000 feet in a
>> pressure chamber and then having the pressure dumped to simulate an
>> explosive decompression. Your ability to hold your breath is
>> immaterial....when the cabin decompresses, all air in your lungs is
>> expelled
>> forcefully. You have no control over it, so you have no breath to hold.
>> Your
>> only chance is to put on supplemental oxygen and do it as quickly as
>> possible.
>
>
> COMMENT:
>
> All this is more or less true, with a few caveats. You actually CAN
> hold up to about 2 psi differential against a closed glottis and with
> your chest muscles, but it's very dangerous to try it. This is enough
> to give you air embolism (anything over about half a psi can do that),
> and is why people are urged NOT to hold their breath on scuba ascent
> (where you breathe pressurized air at depth, which potentially can
> expand to "more than 2 lungsfull" as you rise).
>
> The rest of what has said about the lungs working just as well in
> reverse to DE-oxygenated your blood after decompression, is correct.
> That's why your consciousness time is lung to brain blood transit time,
> at very high altitude.
>
> I once talked to somebody working on a somewhat improbably system that
> used a sort of CPAP mask with chest constriction support and pure
> oxygen, to allow somebody to keep 1.5 PSI of O2 in their lungs, even in
> near-vacuum, after explosive decompression. In theory, this would give
> you a few minutes of conscious survival even without a full pressure
> suit--- enough to bail out of a very high altitude situation and fall
> down to a level where the pressure allowed you to survive on pure O2
> without the pressure support (40,000 feet or so). He said in tests the
> thing had actually worked. Of couse, you need to be all masked up
> BEFORE the blowout.
>
> SBH
>

"Harvey Deinst" <hdeinster1234@sbcglobal.net> wrote in message
news:1usqdmp1axhvp$.r25032fqugz3$.dlg@40tude.net.. .
> On Fri, 19 Aug 2005 15:38:24 -0400, Derf wrote:
> > The problem with a quick decompress at cruise altitude is that
> > the drop in pressure will almost surely cause one to exhale. Now you
> > have only the oxygen already in the bloodstream until you get that
> > mask on, and that means you have about 10 seconds of useful
> > consciousness.
>
>
> I'm VERY confused about this 30-second consciousness thing.
>
> I just exhaled and could still hold my breath for much more than ten
> seconds. Maybe not thirty ... but I was conscious. I'd "guess" (no I have
> no proof) then I'd be real panicky but I'd still be alive. Certainly if an
> oxygen mask popped up in front of me after that 30 second period of no
air,
> I'd grab at it like Barry Bonds eying a bottle of steroids.

<snip>

This might also be of interest:
http://www.sff.net/people/Geoffrey.Landis/vacuum.html

Paul Nixon

[snip]
Folks, comp.compression discusses data compression, not air pressure.

The wide cross-posting is probably not a good idea, but this is
*definitely* off-topic in comp.compression. Followups set.

--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.