Survival without oxygen at high altitude
Jim Morris
the movie, I have seen several comments about the crew of the Memphis
Belle removing their oxygen masks at high (i.e., about 25000 feet of)
altitude. I saw the movie and I don't remember anybody having their
oxygen masks off for very long.
Now, I am not an expert in human physiology, nor do I advocate anyone
violating FAA regulations concerning oxygen use at altitude. However,
I have always thought the danger of anoxia in aircraft is generally
overstated.
Myth: Mountaineers climbing Mt Everest (29000 feet high) must breathe
supplementary oxygen for the last several thousand feet of the climb
because they would die of anoxia (i.e. suffocation) if they relied only
on the oxygen at 29000 feet to breathe.
Reality: Mt Everest has been climbed several times without the use of
supplementary oxygen. The climbers who achieved this were at altitudes
of 27000-29000 feet for quite a while. It takes several hours to make
the last two thousand feet, and this with a very heavy bodily demand
for oxygen. The primary reason mountaineers climbing Mt Everest
breathe supplementary oxygen at altitude is not because of the danger
of anoxia, but because the human body needs oxygen to produce heat for
the body. Without supplementary oxygen at these altitudes the real fear
is frostbite, not anoxia.
It is not correct to say that mountaineers climbing Mt Everest are all
young supermen. Mt Everest has been climbed by a 50-year old
businessman (see the book "Seven Summits"). He did use oxygen, but not
until he got well above 20000 feet. In fact, I climbed a 20000 foot
volcano in Mexico at the age of 30. I was in relatively good physical
condition, but I was no superman by a long shot. I stayed at the
summit for about an hour. While sitting at the summit I had no more
difficulty breathing than I am having right now.
One of the main reasons I am saying all this is that during my training
for flying the C414A at a well known national training establishment, I
couldn't believe I was told things like "if a decompression occurs at
high altitude you have only minutes to live". I can believe this for
45000 feet, but I just don't believe it for 30000 or below. In fact,
for the average person, I believe there is very little danger of anoxia
at 25000 feet or below. Just as in mountaineering, I believe one might
suffer frostbite or hypothermia before one would succumb to anoxia.
In training to fly the C414A I was taught that following a rapid
decompression at high altitude (25000 is high altitude for the C414A),
one should IMMEDIATELY dive for lower altitude. When we practiced this
in the simulator, there were definitely overtones indicating this was a
situation that required reflexive response rather than thoughtful
response.
My concern is that overstating the danger of anoxia might result in
panic after a rapid decompression that could pose a greater danger to
the passengers and the aircraft than the danger of anoxia.
--
Jim Morris ...!sequent,ogicse!verdix!simsol!jimm
Systems Simulation Solutions, 15455 NW Greenbrier Parkway #210
Beaverton, OR 97006 (503) 295-7658
Cessna 414A (N2689U)
Lars-Henrik Eriksson
> One of the main reasons I am saying all this is that during my training
> for flying the C414A at a well known national training establishment, I
> couldn't believe I was told things like "if a decompression occurs at
> high altitude you have only minutes to live". I can believe this for
> 45000 feet, but I just don't believe it for 30000 or below. In fact,
> for the average person, I believe there is very little danger of anoxia
> at 25000 feet or below. Just as in mountaineering, I believe one might
> suffer frostbite or hypothermia before one would succumb to anoxia.
Some years ago, there was a training accident over England involving loss of
oxygen. A jet aircraft flying at (I believe) FL 290 had requested and was
cleared for a simulated emergency descent after cabin decompression. The crew
said on radio that they would commence the exercise shortly. That was their
last transmission. The aircraft continued to fly at FL290 (apparently on
autopilot with altitude hold) in very wide circles, drifting with the wind,
not responding to any radio calls. RAF, and later French air force fighters
were sent up to intercept the aircraft. They reported that apart from the
crew not moving and some warning lights being lit on the instrument panel,
everything looked completely normal. The aircraft eventually ran out of fuel,
stalled as the autopilot attempted to maintain altitude by raising the nose,
and crashed in France. It was determined that both crew members had died from
hypoxia shortly after their final radio call. It was also determined that the
oxygen masks had likely been inoperative.
So. Here are two pilots flying at FL290 all mentally set to make this
exercise. They get their descent clearance, they dump cabin pressure, don
oxygen masks, and become unconscious either before they realise the problem
with the masks or have time to initiate a real emergency descent.
Lars-Henrik Eriksson Internet: l...@sics.se
Swedish Institute of Computer Science Phone (intn'l): +46 8 752 15 09
Box 1263 Telefon (nat'l): 08 - 752 15 09
S-164 28 KISTA, SWEDEN
Tony Verhulst
>for the average person, I believe there is very little danger of anoxia
>at 25000 feet or below. Just as in mountaineering, I believe one might
>suffer frostbite or hypothermia before one would succumb to anoxia.
Jim, I think that you'd benefit greatly by taking a "ride" in an altitude
chamber. They take you up to a simulated altitude of 25000 ft and have you
take off your mask. After a few minutes you take a written test that
has some simple aritmetic problems and a maze for you to figure out. Now,
This maze is simple and I had no trouble finding my way through it AFTER
getting back down to sea level pressure. But, after 5 minutes sans
supplemental oxygen at 25000, I simply could not do the problem.
One thing that they teach you is that people react differently to anoxia,
and it's important that you learn to recognize your individual reaction.
This alone made the "ride" worthwhile for me.
Anoxia is real!!!
Tony V.
P.S. Another thing they do on the "ride" is a rapid decompression. From
25000 they drop you to 8000 in about 5 seconds. It really wasn't a big deal.
I expected my ears to hurt and who knows what else..... but there was nothing.
Of course, if you're next to an airplane window when it blows out, you're
history.
PP - ASEL, Glider
to anoxia
Gregory TRAVIS
>In article <1...@simsol.UUCP> ji...@simsol.UUCP (Jim Morris) writes:
>> One of the main reasons I am saying all this is that during my training
>> for flying the C414A at a well known national training establishment, I
>> couldn't believe I was told things like "if a decompression occurs at
>> high altitude you have only minutes to live". I can believe this for
>> 45000 feet, but I just don't believe it for 30000 or below. In fact,
>> for the average person, I believe there is very little danger of anoxia
>> at 25000 feet or below. Just as in mountaineering, I believe one might
>> suffer frostbite or hypothermia before one would succumb to anoxia.
[ Story about crew in jet w/o Oxygen passing out deleted ]
>So. Here are two pilots flying at FL290 all mentally set to make this
>exercise. They get their descent clearance, they dump cabin pressure, don
>oxygen masks, and become unconscious either before they realise the problem
>with the masks or have time to initiate a real emergency descent.
I was told a story by an FAA examiner about a year ago. We were chatting
and he asked me how I had if I lost oxygen at 30,000 feet. At the time
I thought it was simply a function of how long one could hold one's
breath so I said, "Oh, at least four or five minutes."
He then pointed to one of the EVERGREEN (yes, EVERGREEN) aircraft outside
and said "Let me tell you a story..."
Seems that an EVERGREEN DC-9 had left HUF (Terre Haute) field on a "cargo"
flight one night about five years ago. They either lost or could not
maintain pressurization at 25,000 feet. Both the Captain and Co-Pilot were
on cockpit oxygen and radioed their troubles to the ground. As they were the
only souls on board they were not particularly concerned. The captain told
the co-pilot he was going to go back and see if the door was open or something
and donned a portable oxygen mask and bottle.
("Door is ajar...Door is ajar" - Sorry, I got to play in a Malibu this
weekend. I couldn't find the "Empennage has separated" annunciator)
Well, the captain never came back. The co-pilot became concerned and
immediately landed at the closest adequate airport. They found the captain
collapsed and dead on the cabin floor about half way back, apparently
on his way back to the cabin. The regulator on the portable bottle had
failed.
This story may be apocryphal, but it was told by an FAA examiner and
corporate King Air pilot in all seriousness.
--
Gregory R. Travis Indiana University, Bloomington IN 47405
gr...@cica.cica.indiana.edu Center for Innovative Computer Applications
SLAPPY,ASHLEY L.
>
>P.S. Another thing they do on the "ride" is a rapid decompression. From
>25000 they drop you to 8000 in about 5 seconds.
How about going from cabin pressure (8000 ft) to outside pressure (25000 ft).
You aren't decompressing if you're going from a higher altitude to a lower
one. I think you just transposed the numbers 8-).
>I expected my ears to hurt and who knows what else..... but there was nothing.
>Of course, if you're next to an airplane window when it blows out, you're
>history.
Why ? If you don't get sucked out why would you be history ?
I saw a film at an FAA seminar at our local flying club meeting (Yellow
Jacket Flying Club). It was test with military pilots in an altitude chamber
done by Lockheed for the Air Force (I think). They were showing the effects
as well as testing quick don oxygen masks. They would go from 10000 ft to
45000 ft in about 5-10 seconds. The pilots had to fly a mock yoke with lights
on it telling them which way to turn while trying to get the mask on. It
was pretty amazing. Most of the pilots were unable to get the mask on before
they went wacko. If they got the mask on they couldn't execute the commands
given by the lights on the yoke for a while.
I think that the key term here is RAPID DECOMPRESSION. In the Mount Everest
article, the climbers were very very slowly decompressing as they went up
and their bodieswere able to adjust to the lower amounts of oxygen.
In the aircraft, the oxygen levels drop in 5 to 10 seconds. Probably your
body can't adjust that quickly and goes into shock and you become unconcious
and if you aren't revived quickly you don't revive.
But I must say that I don't think this is the same thing as the bends which
is what divers can experience if they decompress too quickly and nitrogen
gas is precipitated from their blood (ultra bad news). They go from multiple
atmospheres of pressure to one atmosphere at the surface. Pilots can only
go from a large fraction of one atmosphere to a smaller fraction of one
atmosphere - not nearly as big of a change.
Ashley
Tony Verhulst
<>25000 they drop you to 8000 in about 5 seconds.
<
<How about going from cabin pressure (8000 ft) to outside pressure (25000 ft).
<You aren't decompressing if you're going from a higher altitude to a lower
OK, you caught me. Sure, in rapid decompressions you go from 8000 to 25000
in about 5 seconds. And I was at sea level pressure when I made that typo.
Sheesh!
Tony V.
c...@ifi.unizh.ch
>
>I have always thought the danger of anoxia in aircraft is generally
>overstated.
>
>Myth: Mountaineers climbing Mt Everest (29000 feet high) must breathe
>supplementary oxygen for the last several thousand feet of the climb
>because they would die of anoxia (i.e. suffocation) if they relied only
>on the oxygen at 29000 feet to breathe.
>
>Reality: Mt Everest has been climbed several times without the use of
>supplementary oxygen. The climbers who achieved this were at altitudes
>of 27000-29000 feet for quite a while. It takes several hours to make
>the last two thousand feet, and this with a very heavy bodily demand
>for oxygen. The primary reason mountaineers climbing Mt Everest
>breathe supplementary oxygen at altitude is not because of the danger
>of anoxia, but because the human body needs oxygen to produce heat for
>the body. Without supplementary oxygen at these altitudes the real fear
>is frostbite, not anoxia.
>
>for flying the C414A at a well known national training establishment, I
>couldn't believe I was told things like "if a decompression occurs at
>high altitude you have only minutes to live". I can believe this for
>45000 feet, but I just don't believe it for 30000 or below. In fact,
>for the average person, I believe there is very little danger of anoxia
>at 25000 feet or below. Just as in mountaineering, I believe one might
>suffer frostbite or hypothermia before one would succumb to anoxia.
>
>In training to fly the C414A I was taught that following a rapid
>decompression at high altitude (25000 is high altitude for the C414A),
>one should IMMEDIATELY dive for lower altitude. When we practiced this
>in the simulator, there were definitely overtones indicating this was a
>situation that required reflexive response rather than thoughtful
>response.
>
Sorry, but this prompts my VERY SHARP protest. The problem with not breathing
enough oxygen at altitude is loosing your immediate attentiveness and wakeness
of your mind. Those mountaineers do climb the Everest VERY slowly. If you read
their books, eg of R. Messner who climbed the Everest and others several times
without supplemental oxygen, you will notice that they do desribe a lot
of halluzination, illusions like speaking to distant relatives that visit
them during their climb etc.
As a pilot your life depends on the ability to be able to immediately
react (eg. to engine fire, one-engine-out etc. ) to be fully attentive
( non-auto-pilot IFR (;>) ) and to keep up a critical mind. And it's just
that, what you loose on lack of oxygen. Additionally, a lack of oxygen puts
you mind in a state underestimating every danger (including that of lack of
oxygen). There are several interesting (:-( accident histories.
However I also draw this opinion from my experiences as skydiver and jump pilot,
that gave me quite some time of flying and free-fall at 17.000 feet. When you do
larger relative-work formation in skydiving, this is a quite complicated exercise
requireing MUCH concentration. However in loads going up 15 grand or higher
you will notice a remarkable tendency to make even the most trivial errors.
Freefall technique you are able to manage perfectly at 12 grand does pose it's
problems at 15 or 18 grand !! And the skydivers and jump-pilots at my club do
recognize and respect that fact.
So, please do youself and your passengers a favour, and do take this danger for
real. Even better: Try to get a high-altitude-chamber experience at an air-force
base. You'll understand my opinion then ...
--
* Enjoy yourself ... try 'rm -rf' or try grep flame * > /dev/null
* Dr. Clemens H. CAP c...@ifi.unizh.ch
* Dept. of Computer Science Phone 05 - 01 - 257 / 4326
* University of Zurich All opinions expressed are my own
Mark Rowe
> I have always thought the danger of anoxia in aircraft is generally
> ... In fact, I climbed a 20000 foot
> volcano in Mexico at the age of 30. I was in relatively good physical
> condition, but I was no superman by a long shot. I stayed at the
> summit for about an hour. While sitting at the summit I had no more
> difficulty breathing than I am having right now.
> ... I was told things like "if a decompression occurs at
> high altitude you have only minutes to live". I can believe this for
> 45000 feet, but I just don't believe it for 30000 or below. In fact,
> for the average person, I believe there is very little danger of anoxia
> at 25000 feet or below.
> Jim Morris ...!sequent,ogicse!verdix!simsol!jimm
WARNING, WARNING, WARNING. The preceding is a very dangerous point of view.
Hypoxia is a real danger at high altitude. If you would like to have this
confirmed I believe you can still enroll in a flight physiology program
which is open to civilians (at no charge) through FAA sponsorship. I went
through this 1 day program about 10 years ago (I will describe the experience
below). Yes, there are a number of myths about hypoxia, but the danger is
very real. All of the examples given to counter hypoxia danger involved
heavily acclimated individuals who had spent considerable time adjusting to
high altitudes prior to arriving at 20,000+ ft elevations. You cannot go
immediately from a life near sea level to 30,000 ft and function for more
than moments before passing out.
MYTH: At high altitudes, you will be unable to breathe, gasping for breath,
etc.
FACT: When being suddenly introduced to high altitudes (say 25,000 ft higher
than your typical altitude, you will feel fine, you will be breathing
normally, and you will continue to breath normally and think every-
thing is fine right up to the moment (a few minutes later) when you
pass out.
I can only speak personally from my own experiences in the flight physiology
program (see below). Here I was part of a dozen or so people who were
suddenly introduced (in an altitude chamber) to a 25,000 ft. environment.
The results were interesting, entertaining, and very educational. I do not
know for certain what the results would have been had it been only 20,000 ft
or 15,000 ft. But from what I experienced at 25,000 ft., I am a believer.
If you fly high, you fly on oxygen.
FLIGHT PHYSIOLOGY PROGRAM:
My local soaring club (long since defunct) enrolled a group of us in the
program. A session was being held at the Whidbey Island Naval Air Station
near Seattle and we flew up to participate in the one day program. The
program began with a half day of classroom lecture. There were about 12
people in the course; about 6 of us (us = civilians) and about 6 of them
(them = navy personnel). The lecture was pretty intense and very dry. It
consisted mostly of the same material you could get out of any decent text
on high altitude flight. The real education (fun) began after lunch.
After lecture and lunch, we entered an altitude chamber and were instructed
in the use of the oxygen equipment. They then put us all on oxygen and ran
the chamber up to 25,000 ft. At this point we got to both observe and
experience the effects of hypoxia. One or two at a time we would take off
our masks and spend a few minutes performing some task while the rest of
the group observed. The tasks included such things as touching finger-to-
nose repetitively, testing peripheral vision, reading, etc.
When a person first took off the mask they experienced no ill effects and
continued to announce no problems as they went through the exercises. Those
of us observing would notice coordination problems quickly appear and often
the person would start slurring speech. After a few minutes the person would
just stop in mid-task and stare off into space. Sometimes they would then
respond to instructions to put their masks back on (often requiring help), and
sometimes the mask would have to be put on them by one of the attendants.
After the mask was put on they would breath oxygen for a few minutes and
then either snap out of it with a slightly embarrassed look or possibly
continue their task without ever recognizing the lapse. Not one person in
that chamber would have lived for more than 5 minutes+decent time had they
been piloting a plane.
My own experiment was particularly interesting (to me anyway). Two of us
(myself and the person sitting across from me) removed our masks. I was
given a deck of cards and a wooden box (little bigger than a shoebox). The
top of the box had four slots labeled with spades, hearts, diamonds, and
clubs. My task was to take cards one at a time, look at them, show them to
the rest of the group, announce what the card was, and stick it in the
appropriate slot. So I began going through the cards, breathing fine, having
no difficulty what-so-ever. I had only gone through maybe a dozen cards
when I noticed the guy across from me was just sitting there staring blankly
ahead. I remember thinking that hey that guy is completely out of it and it
isn't affecting me at all. Well anyway, after I had gone through about
twenty cards (no problem) the instructor told me to put my mask on. So I
stopped, put the cards down and put my mask on. I had a little trouble with
the straps so one of the attendants helped me out a little. The guy opposite
me did not respond and had to have his mask put on for him. After a few
minutes on oxygen the instructor turned to the guy opposite me and asked him
how I did. He announced that I had performed flawlessly and gotten every
card right (to which I thought yeh how would you know).
The instructor then turned to me and asked me how I thought I did. I was
about to respond when I noticed that there were only about 10 cards
remaining in the deck I had started with. I responded that I thought that
I had done fine but did not remember going through that many cards. This
elicited a bit of a chuckle from the rest of the group and I knew that I
too would have bought the farm.
I really wished they had video taped the session. It appears that after I
had gone through about twenty cards I had hit the three of clubs and got
stuck. I had held up the 3 of clubs, announced 3 of clubs, and put the card
in the clubs slot. I then picked up the next card, looked at it, showed it
to the group, announced 3 of clubs, and put it in the clubs slot. I then
proceeded for another dozen or so cards. Picking each one up, looking at it,
showing it to the group, announcing that it was the 3 of clubs, and putting
it in the clubs slot. Apparently I stopped when instructed to do so, but
was told three times to put my mask back on before I responded and I seem to
have required more assistance in getting my mask back on than I recall. The
whole episode seems a little spooky looking back on it. At no time did I
feel any effects from the altitude. At no time did I have any hint (except
from the behavior of the guy opposite me) that I might be experiencing
hypoxia. At no time did I have any difficulty breathing or have any shortness
of breath. The only observable phenomena I have to clue me that I might be in
danger of hypoxia is the altimeter reading, and you can believe that I'm
not going above 14000 without oxygen and even then wondering if the FAA is
actually being stringent enough.
Mark Rowe
Corvallis, OR
Richard J. Miller
>Now, I am not an expert in human physiology, nor do I advocate anyone
>violating FAA regulations concerning oxygen use at altitude. However,
>I have always thought the danger of anoxia in aircraft is generally
>overstated.
>
>Myth: Mountaineers climbing Mt Everest (29000 feet high) must breathe
>supplementary oxygen for the last several thousand feet of the climb
>because they would die of anoxia (i.e. suffocation) if they relied only
>on the oxygen at 29000 feet to breathe.
>
>Reality: Mt Everest has been climbed several times without the use of
>supplementary oxygen. The climbers who achieved this were at altitudes
>of 27000-29000 feet for quite a while. It takes several hours to make
>the last two thousand feet, and this with a very heavy bodily demand
>for oxygen.
>Jim Morris ...!sequent,ogicse!verdix!simsol!jimm
they spend DAYS doing those last few thousand feet (to say nothing of
the weeks just before that) giving them lots of time to breathe and
ACCLIMATE to it. and although wind chill can be pretty bad in 50 mph
gusts, that's nothing compared to 200 knots or more.
a story is in order, one i heard while taking a chamber ride at
Peterson AFB in Colorado Springs. we spent the first 30 minutes at
ground level breathing 100% Oxygen to purge Nitrogen from our
bloodstreams to avoid the bends on the descent (something else that
climbers don't have to worry about!). they ran a tape of a test pilot
flying a F-4 in Florida while we were doing this.
in short, he had a problem with his canopy on the taxiway that got him
out of sequence on his checklist. the item he left out was turning on
the O2 system. we then heard him, his chase, and the tower as he took
off, climbed to 24K, and then descended straight into the ocean. he had
realized at 20K that he didn't have working oxygen, but he was beyond
useful consciousness. the chase figured he passed out around 22 or 23.
the aircraft was destroyed. he was in the air no more than 20 minutes.
all he had to do was give a single switch a quick uppercut. he was a
experienced pilot with plenty of fighter time. the Air Force and the
Navy work on use of Oxygen all the time, take a chamber ride if you
want to see how serious they are about it and why.
i've been in the chamber to 25K and know all of my hypoxia symptoms
from taking my mask off for 3 minutes. i also saw what happens to
night vision at 18K. it's VERY scary to see what can happen in that
short a period of time. i then went to 32.5K in a glider 2 days after
that, with O2 from takeoff and 100% O2 from 20K. the chamber ride was a
requirement for the flight. i wouldn't have it any other way.
Rich Miller
Schempp-Hirth Discus JBX
rmi...@i88.isc.com
{sun, amdahl, att (maybe)}!laidbak!rmiller
Robert Herndon
>I have always thought the danger of anoxia in aircraft is
>generally overstated.
I must vehemently disagree with the premise of this article.
Anoxia is very sneaky, and I hope never to run into it again.
Approximately ten years ago, when I was living in Phoenix, AZ,
(about 1000' MSL) a private pilot friend came out to visit.
He wanted to fly up to the Grand Canyon, and so we did. I
was not a pilot then, nor learning to be, as I am now.
Apparently, the authorities are fairly strict about low
overflights of the Grand Canyon, and we flew over it at
12.5K'. As he was working on learning instruments, he asked
me to take over the controls and just keep the plane level.
On attempting to do this, and him starting to play with the
VOR indicators (?) we both noticed that we were "not all
there". What was most distressing is that there was absolutely
no warning, no feeling of being "high", or "out of it" -- we
both felt fine until something of difficulty demanded our
concentration.
One does not breathe faster (the breathing reflex is
triggered by excess C02, not lack of 02), one isn't short
of breath, ... there really is very little to clue one in
on it.
It was quite easy to see how we could have lost consciousness
completely, and never even been aware of it happening.
Note that this altitude was substantially below 15K', and
at this time we were both in our (very) early 20s, and in
normal (not to say great) shape.
I now live at over 6K' MSL. Hiking at 14K' does not seem
to cause me trouble, but there was definitely a significant
period of adjustment -- a matter of weeks. Several friends of
mine have been hiking on the Himalayan plateau -- over 16K'.
Again, they take a long period (> 1 week) acclimating to the
altitude gradually, drinking lots of fluids and eating iron
rich foods, and even so, some got "altitude sick" (quite
unpleasant). Serious altitude sickness HAS been a problem
on numerous Everest climbs.
So, in conclusion: IF ONE IS ADAPTED TO HIGH ALTITUDES,
flying or performing other complex tasks at over 15K' is
not a problem; HOWEVER, for the rest of the world, EXTREME
CAUTION SHOULD BE EXERCISED in going above altitudes one
KNOWS she/he can function at.
Please excuse the length of this article.
Robert Herndon
------
--
Robert Herndon -- not speaking officially for Cray Computer.
Cray Computer Corporation 719/540-4240
1110 Bayfield Dr. r...@craycos.com
Colorado Springs, CO 80906 "Ignore these three words."
Jordan Brown
>violating FAA regulations concerning oxygen use at altitude. However,
>I have always thought the danger of anoxia in aircraft is generally
>overstated.
Some of what you say is true. Much is inadequate and dangerous,
though.
>Reality: Mt Everest has been climbed several times without the use of
>supplementary oxygen.
One of the factors in hypoxia is how fast you ascend. Rapid loss
of O2, as from an O2 failure, increases the effect. Rapid decompression,
as from a pressurization failure, increases it more.
> While sitting at the summit [20,000 ft] I had no more difficulty
> breathing than I am having right now.
Nor did I, at 25,000 in the Edwards altitude chamber. My ability to
do mental arithmetic deteriorated substantially within 3 or 4 minutes,
though. Being at high altitude does not make breathing difficult.
>One of the main reasons I am saying all this is that during my training
>for flying the C414A at a well known national training establishment, I
>couldn't believe I was told things like "if a decompression occurs at
>high altitude you have only minutes to live". I can believe this for
>45000 feet, but I just don't believe it for 30000 or below. In fact,
>for the average person, I believe there is very little danger of anoxia
>at 25000 feet or below. Just as in mountaineering, I believe one might
>suffer frostbite or hypothermia before one would succumb to anoxia.
Of our group of about 10 people in the chamber, one did not detect
any effects after about 10 minutes at 25,000, and one needed help to
get his oxygen mask back on and O2 flowing. It varies from person to
person. That first guy would have been OK, probably. The second
guy would have been dead, perhaps not from lack of O2, but from the
impact when the out-of-control airplane hit the ground, perhaps after
breaking up. He was not able to respond to simple instructions and
questions. Right up to the point where he was unable to respond to
questions, he was (groggily) claiming that he wasn't feeling any
hypoxia symptoms.
>In training to fly the C414A I was taught that following a rapid
>decompression at high altitude (25000 is high altitude for the C414A),
>one should IMMEDIATELY dive for lower altitude. When we practiced this
>in the simulator, there were definitely overtones indicating this was a
>situation that required reflexive response rather than thoughtful
>response.
Here's a paragraph or two from the Physological Training book I got
at Edwards...
---
EFFECTIVE PERFORMANCE TIME (EPT) OR TIME OF USEFUL CONSCIOUSNESS (TUC)
This is the amount of time in which a person is able to effectively or
adequately perform flight duties with an insufficient supply of oxygen.
At altitudes below 30,000 feet the EPT may differ considerably from the
time of total consciousness (the time it takes to pass out). Above
35,000 feet the times become shorter and eventually coincide for all
practical purposes, with the time it takes for blood to circulate from
the lungs to the head.
_Average_ Effective Performance Time for flying personnel without
supplemental oxygen:
20,000 feet......30 minutes or more
22,000 feet......5 to 10 minutes
25,000 feet......3 to 5 minutes
28,000 feet......2 1/2 to 3 minutes
30,000 feet......1 to 2 minutes
35,000 feet......30 to 60 seconds
* 40,000 feet......15 to 20 seconds
* 45,000 feet......9 to 15 seconds
NOTE: Based on interruption of O2 supplement after being at altitude
rather than ascending.
* Representative of a sudden decompression to these indicated altitudes
(reverse diffusion).
There are a variety of factors which will determine EPT, some of which
are:
1. Altitude. EPT decreases at higher altitudes.
2. Rate of Ascent. In general, the faster the rate, the shorter the
EPT.
3. Physical Activity. Exercise decreases EPT considerably.
4. Day-to-Day Factors. Physical fitness, diet, rest, drugs, smoking,
illness, and other factors may change your ability to tolerate
hypoxia from day to day, therefore, changing your EPT.
---
(I believe all the grammar mistakes are theirs... :-)
Hypoxia is insidious. If you're at 25,000 and you lose your O2 system
without noticing it, you may be in big time trouble. You may well be
incapacitated before you notice any symptoms. If you're at 30,000+ and
lose pressurization, get that O2 mask on and O2 flowing RIGHT NOW.
If you stop to try to do something else, you might never get around to
the mask.
I heartily recommend the Aviation Physiology courses that the FAA and
the Air Force give. They're cheap ($20 when I took it) and they're
interesting. If you're a low-altitude pilot, like I generally am,
they're merely an interesting way to spend a day. (I came out of
it with a substantial respect for oxygen-free atmospheres and a
terror of carbon monoxide, and later realized that I start to get
(slightly) hypoxic around 10,000 feet.) If you're a high-altitude
pilot, in a pressurized airplane or snorting O2 all the time, you
should probably consider it a required course.
The courses are given at Air Force bases everywhere in the country.
In the Los Angeles area, they're at Edwards. A 3rd class medical is
required, and no beards are allowed in the chamber.
The contact info I have might not be the right place to apply for a
spot in a course, but it'll probably lead to the right people
eventually...
Mike Monroney Aeronautical Center
Civil Aeromedical Institute
Airman Education Section, AAM-142
PO Box 25082
Oklahoma City, OK 73125
Geoff Brown
concerning the use of Oxygen at altitude.
Remember that a mountaineer ascends in stages, acclimatising his body to
the reduced Oxygen level. Stopping at various camps for some days. When your
aircraft becomes unpressurised it is relatively instanteous.
The initial effect of anoxia is to affect the brain, giving symptons similar to
being drunk. Whilst this is not too much of a problem to a landlubber, it is
not ideal for a pilot. This will occur at a much lower altitude than it takes
to kill you.
ASK6E
Geoff Brown Tel: (Home) +44 279 506927
(Work) +44 279 429531 Ext 2716
e-mail G.B.D...@stl.stc.co.uk
Bob Sutterfield
light pressurized aircraft (e.g. Piper Malibu) or those that often
operate with supplemental oxygen (e.g. Mooney TLS) is its descent rate
capability to get down to denser, more hospitable air. If the pilot
can be expected to be sentient for N minutes in thin air, and the
maximum emergency descent rate is X feet per minute, then the ceiling
is set at 12500+(N*X), even if the aircraft has the performance margin
to maintain the usual required climb rate above that altitude. (Of
course, there's an integral involved because the pilot can manage a
larger N as altitude decreases, but that's the short form.) If this
is the case, then an aircraft's certification ceiling should increase
with the installation of spoilers, drag brakes, or other such draggy
devices.
But then again, I may be smoking my socks. Can anyone comment
knowledgeably?
Jim Morris
- As a side note to this discussion, I believe there is an altitude
- above which the average person, even with adequate warmth, food and
- rest, NEVER acclimates to the reduced oxygen pressure, but only
- deteriorates physiologically; and I believe this altitude is well
- below 25,000 feet, maybe in the 15,000 to 20,000 range.
Correct. I believe the highest altitude at which people live permanently is
around 17000 feet, in Peru, Tibet, Nepal, etc.
Dennis Hurvitz
> the movie, I have seen several comments about the crew of the Memphis
> Belle removing their oxygen masks at high (i.e., about 25000 feet of)
> altitude. I saw the movie and I don't remember anybody having their
> oxygen masks off for very long.
>
> Now, I am not an expert in human physiology, nor do I advocate anyone
> violating FAA regulations concerning oxygen use at altitude. However,
> I have always thought the danger of anoxia in aircraft is generally
> overstated.
jim,
i'm worried about you in that 414.
i'm sure you'll know how to work all the controls, but your O2 comment
is really scarey.
i took the faa chamber ride at fightertown (miramar) in 1980. hypoxia is
frightening. it is insidious for just like the affect of alcohol, the
unsuspecting pilot thinks they're 5x5.
things start to grey out in the peripheral of ones vision. your night
vision is also severely hampered, judgement becomes fantasy, then good
night.
there is a well publicized story of 2 guys in a turbo charged twin who
violated the atlantic adiz around the carolinas i believe. the air
forced scrambled 2 f-16's to investigate. the f-16 pilot reported no one
visible in cockpit. the twin continued on its ghostly climb to about
33,000 or 36,000 ft, until to the horror of the chase f-16 pilot, the
bird probably stalled, and spin in.
the two general aviation pilots obviously perished. failure of their
O2 system or cabin pressure failure was the suspected cause.
gee, the 414 is pressurized, but hey, you're scared to death of hypoxia
now aren't you...
> Reality: Mt Everest has been climbed several times without the use of
> supplementary oxygen.
mountain climbers don't need to think, for if they did, they wouldn't be
hanging all that way up, on a simple carabeener.
>
> One of the main reasons I am saying all this is that during my training
> for flying the C414A at a well known national training establishment, I
> couldn't believe I was told things like "if a decompression occurs at
> high altitude you have only minutes to live". I can believe this for
you bet your ass ! why would they say something like that if it were not
true ?
>
> My concern is that overstating the danger of anoxia might result in
> panic after a rapid decompression that could pose a greater danger to
> the passengers and the aircraft than the danger of anoxia.
> --
> Jim Morris ...!sequent,ogicse!verdix!simsol!jimm
> Systems Simulation Solutions, 15455 NW Greenbrier Parkway #210
> Beaverton, OR 97006 (503) 295-7658
> Cessna 414A (N2689U)
at 28,000' your judgement is all but gone within 4 minutes followed by
loss of physical coordination shortly after. if you descend at 2,000
feet per minute in your 414 (assuming you know how to do that
IMMEDIATELY) you will be without your full mental capacity at 20,000',
hypoxic, without O2, descending, trying to figure out what went wrong,
where to land, reestimating fuel burn at the lower altitude and cruise
speed, re-adjusting power, things are grey now, on your way to statistics...
yeah, you're right. relax, you'll be on the ground in a few minutes.
dennis hurvitz
Dave Novotny
In article / ji...@simsol.UUCP (Jim Morris) / 12:48 pm Oct 14, 1990 /
Jim Morris writes:
>One of the main reasons I am saying all this is that during my training
>for flying the C414A at a well known national training establishment, I
>couldn't believe I was told things like "if a decompression occurs at
>high altitude you have only minutes to live". I can believe this for
>45000 feet, but I just don't believe it for 30000 or below. In fact,
>for the average person, I believe there is very little danger of anoxia
>at 25000 feet or below. Just as in mountaineering, I believe one might
>suffer frostbite or hypothermia before one would succumb to anoxia.
>
>In training to fly the C414A I was taught that following a rapid
>decompression at high altitude (25000 is high altitude for the C414A),
>one should IMMEDIATELY dive for lower altitude. When we practiced this
>in the simulator, there were definitely overtones indicating this was a
>situation that required reflexive response rather than thoughtful
>response.
>
>My concern is that overstating the danger of anoxia might result in
>panic after a rapid decompression that could pose a greater danger to
>the passengers and the aircraft than the danger of anoxia
Jim,
It sounds like you have never "taken a ride" in an altitude chamber. I took
one several years ago, and the memories are still vivid. The course takes one
day, usually taught by the Air Force, and covers physiological effects of
altitude on the body. My course included 2 rides in the chamber. The first
was a slow assent (on oxygen) to 29,000 feet where we took off our mask while
our "buddy" observed our actions as we did some simple math and nav problems.
Hypoxia set in on me after about 2-3 minutes (I am healthy, non-smoker, etc.).
The second ride was an "explosive decompression" from 10,000 feet to 29,000
feet. The effects here were dramatic!! It felt like I was kicked in the
stomach and hypoxia set in after 10-15 seconds max.
I suggest you inquire at your local GADO or FSDO about Physiological Training
classes in your area. It is well worth the day and money ($25, I think)
invested. After this, I sure you will agree that frostbite will be the last
thing on your mind when a cabin window blows.
Dave Novotny
CAP Mission Pilot
d...@hpctdlb.col.hp.com
719-531-4494
WA6IFI
Jordan Brown
>They would go from 10000 ft to 45000 ft in about 5-10 seconds.
>I think that the key term here is RAPID DECOMPRESSION. [...]
>In the aircraft, the oxygen levels drop in 5 to 10 seconds. Probably your
>body can't adjust that quickly and goes into shock and you become unconcious
>and if you aren't revived quickly you don't revive.
One of the things that's involved once you get up into the 40k+ arena is
that the partial pressure of O2 in the air is substantially lower than
the partial pressure in your blood, and so the O2 plays the "Henry's Law"
game and attempts to equalize the partial pressures by jumping *out*
of the blood and into the air. As it said in my excerpt from the
physiology book, the time of usefull consciousness starts to be
determined by how long it takes for the blood to get from the lungs to
the brain.
Incidentally, this is true if the partial pressure of O2 is low, no
matter what the total air pressure is. If you walk into a room full
of N2, close the door, and continue to breathe normally, you'll fall
over in not much more than 10 seconds. (I used to work in a lab with
a big tank of liquid N2. If I were to work there again, I'd be a *lot*
more careful...)
>But I must say that I don't think this is the same thing as the bends which
>is what divers can experience if they decompress too quickly and nitrogen
>gas is precipitated from their blood (ultra bad news). They go from multiple
>atmospheres of pressure to one atmosphere at the surface. Pilots can only
>go from a large fraction of one atmosphere to a smaller fraction of one
>atmosphere - not nearly as big of a change.
The bends can be an issue. The most well known case is where a diver
is fine having decompressed to sea level, but gets the bends when further
decompressed by an airplane ride. However, it's possible to get the
bends starting at SL, without having been at high pressure. In the
altitude chamber ride, as others have mentioned, you breathe pure O2
for a while before starting the ascent, in order to clean most of the
N2 out of your blood.
Jim Morris
> jim,
>
> i'm worried about you in that 414.
hypoxia) is not the fact that you are AT high altitude, but that you
GOT THERE RAPIDLY. I had not considered that subtle difference and I
had never had the difference explained to me. Thanks to everyone who
replied.
I now understand more clearly the necessity for a rapid descent in case
of a loss of pressurization. More importantly, I also perceive the need
to REGULARLY include the cabin pressure gauge in the instrument scan in
case of a loss of pressurization that otherwise goes undetected. I have
been scanning the cabin pressure gauge, but probably not as often as I
should.
I read a crash story several months ago about a twin that was being
flown by the writer's friend, whom he described as meticulous about
flying safety. The plane was found somewhere in Kansas. It had hit the
ground in an extreme vertical position and had buried itself several
feet into the ground. Inside were the pilot and his wife. There were no
clues as to how the accident occurred. The writer could not understand
what could have happened to cause this.
Perhaps there was a loss of pressurization that was not detected by
either passenger and they passed out. This is extremely scary to me.
Bret A. Marquis
>> I have always thought the danger of anoxia in aircraft is generally
>> overstated. ...
>
>
> etc.
>FACT: When being suddenly introduced to high altitudes (say 25,000 ft higher
> than your typical altitude, you will feel fine, you will be breathing
> normally, and you will continue to breath normally and think every-
> thing is fine right up to the moment (a few minutes later) when you
> pass out.
>
You don't really need to be that high for the effects to be dramatic.
I was flying a rented Mooney 231 back from Santa Barbara to San Diego,
shortly after levelling off at 17,500 ft, my passenger decided that
he was chilly and wanted his sweater. To reach his sweater, he
needed to remove his oxygen mask and reach into the very back of the
plane. It was a bit of a strain for him since it was hard to
reach. In the process, he passed out, hanging over the seat.
He revived immediately when I put his mask back on him. He did not
remember reaching for his sweater..
Bret Marquis
john reece
altitude, and probably more, check out "Going Higher", by Charles Houston.
He is an MD and climber, who has been involved with many high altitude research
experiments since WWII. You may have to go to REI or some other store
catering to climbers/trekkers, since it is written with the climber in mind.
John Reece
Not an Intel spokesman
jre...@yoyodyne.intel.com
Herbert Kanner
years ago, I decided to take my wife on a flight over an area of
Yosemite in which we had previously travelled on foot and horseback.
The regulations at the time were, that at the proposed flight altitude
(13,500), flight without oxygen was permissible for 20 min. I was
flying along with the firm resolve that if my fingernails turned blue,
I would execute the classic maneuver called "get the hell out of here."
The highest terrain immediately under us was 12,000, so our terrain
clearance was more than adequate. However, the nearby peaks appeared
to be reaching up to grab us; this made my wife quite nervous, and
after about ten minutes we decided that we had seen all we wanted to
see. At that moment, I looked at my altimeter, and absolutely did not
have the intelligence to decide whether it was saying "13,500" or
"10,350". So, I headed toward lower country and by the time we got
down to 9000 I enough the brains to read the altimeter correctly. Of course,
this is not solid evidence of mental recovery, because it takes less
brains to interpret altimeter readings that are below 10,000 :-)
--
Herb Kanner
Apple Computer, Inc.
{idi,nsc}!apple!kanner
kan...@apple.com
Brent Callaghan
explosive decompression procedures. I remember they
mentioned something about "trim for descent first *then*
don oxygen".
I think the rationale was that if for some reason they can't
get the emergency oxygen going then the aircraft will
eventually descend under control to an altitide at which
they revive. The alternative is to have an incapacitated
crew and an aircraft that continues straight and level on
autopilot until it runs out of fuel.
A better scheme would seem to be to designate one crewmember
to don emergency oxygen while the other trims for descent.
Does any of this make sense - or did I just hear it all wrong ?
--
Made in New Zealand --> Brent Callaghan @ Sun Microsystems
uucp: sun!bcallaghan
phone: (415) 336 1051
Andy Stadler
bad airplane disaster book I once read. When shopping in airport gift shops
I always try to buy really bad airplane disaster books. It's my favorite
reading while sitting in cattle class.
Here's the premise: There's a somewhat futuristic airliner making a supersonic
run from LA to Tokyo. Meanwhile the Navy is out messing around with a new
air-to-air missile. The missile locks on to this airliner (oops) and puts
two missile-shaped holes in the fuselage (no warhead). Besides killing all
the passengers in rows 18 through 27, it creates explosive decompression.
Now the airplane is at FL 650 or so, and the air is pretty darn thin. The
pilot manages to trim for descent and hit the AP before passing out. According
to the author, anyone who didn't get a mask on is dead. Even worse, however,
the O2 system is somehow screwed up and delivers not enough air. So all the
folks who DO get their masks on suffer major brain damage. And of course,
there are 4 or 5 passengers who somehow get enough O2 and wake up with only
a bad headache.
Which leads up to the best part of the book - the classic "passenger must over-
come fears to land stricken airliner" story, combined with "Night Of The
Living Dead" zombies milling around the cabin.... There's even a liability
angle, as the airline office considers routing them into a "water landing"
figuring it will be cheaper to pay one-time death settlements than the cost of
lifetime care in old zombie homes.
I told you it was bad! I can't remember the title otherwise I'd warn you
away it.... But think about it next time you go over 12,500 !!
--Andy sta...@apple.com
JDG1@lehigh
Lower altitudes are perhaps an even greater concern!
In my altitude chamber ride for the Air Force last spring, I
learned that vision in poor lighting can be noticably effected at
8000ft! For example, we were handed a card with fine print and asked
to read it with our masks on. No problem. After removing the mask for
5 minutes, not one of us could make out the other side!! I realize some
pilots are acclimated to higher altitudes, but a majority of us
are not!!!
While physical survival at lower altitudes may not be directly
threatened, what if you read your fuel gauge incorrectly? Or can't
make out the sectional chart? You could wind up in a dangerous
situation.
Also, the onset of hypoxia is slower at lower alititudes. The
effects may be too gradual to detect until it is too late.
Hypoxia is a serious matter. Education will lead to better
understanding and safer flying.
- Jonathan Goldstein
Lehigh University
Robert Charles Monsen
The last story I read had to do with someone passing out while reaching
into the back of a plane to get a sweater at altitude. Does the lower partial
pressure of oxygen actually take oxygen from the blood? It seems like I can
hold my breath long enough to get a sweater. Inquiring minds...
Bob Monsen
Orion Network Systems
Berkeley, California
Wiley M Sanders
Several books and articles I've read about Everest and other mountain
ascents made it plain that doing without supplemental oxygen for a period
of a few days made these people very prone to sicknees and injury - the
slightest glitch had seriuous consequences. One hard cough and you were
coughing up blood for days.
Also, many mountaineering deaths and injuries at high atitudes are
attributable to simple mistakes - mistied knots, for example - that may not
have occurred at lower altitudes.
I've taken al alitude chamber ride and don't doubt that I'd be able,
at 25000, to keep the wings level for the first few seconds. But after the
first 45 degree bank induced by reaching over to twiddle some knob, I'd
probably be history. I still have somewhere the written math exam I was
given while my mask was off at 25000. I knew my name and home town, but came
to a dead halt when I was supposed to write down the reciprocal heading
of some number.
Another technical error in Memphis Belle, by the way: You can't believe
how noisy it is in a B17. I had the good fortune to fly in one a few years
ago and it was the noisiest a/c I've ever been in. If you sit in front
of the wings where the navigator's station is, you can put your hand on the
wall and feel the pounding as the inside prop tips blast by about a foot away.
Memphis Belle's crew chats quietly like they were buzzing along in some
pressurized bizjet. Bunk. It was cold, noisy, grimy, nasty, bloody business.
I have a feeling "Catch-22" gives a better idea of what miltitary aviation in
WWII was really about. (or still is.)
In spite of the blandness of the movie it was still fun to see those
pretty planes roaring about, though...
-w
JDG1@lehigh
In response to "I can hold my breath long enough to get a sweater":
Lower partial pressure does not "take" oxygen from the blood.
Blood in oxygenated in the lungs. This occurs because the air
pressure in the lungs (assume sea level) is sufficient to disolve the
oxygen into the blood. The greater the air pressure, the more oxygen
can be disolved into the blood. The same principle keeps the gas in
carbonated beverages when they are bottled. When you open a bottle,
the air pressure is relieved, and the gas can be seen bubbling out of
solution. At higher altitudes, sufficient pressure may not exist to
disolve enough oxygen into the blood. It is very possible that even if
you were breathing PURE oxygen through a mask, you could pass out
because of insufficient air pressure to get the oxygen to the blood.
Holding your breath wouldn't help. Jonathan Goldstein
Lehigh Univerity
Don Elton
Whether you lose pressure to the environment would depend on the altitude.
This would be most likely to happen when your alveolar pressure were to become
less than your mixed venous oxygen partial pressure.
UUCP: [ ucsd nosc ] !crash!pro-carolina!delton
ARPA: crash!pro-carolina!del...@nosc.mil CIS: 72010,37
INET: del...@pro-carolina.cts.com MCI, AOL, GEnie: delton
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John Stanley
JDG1@Lehigh writes:
>
> In response to "I can hold my breath long enough to get a sweater":
>
> Lower partial pressure does not "take" oxygen from the blood.
> Blood in oxygenated in the lungs. This occurs because the air
> pressure in the lungs (assume sea level) is sufficient to disolve the
> oxygen into the blood. The greater the air pressure, the more oxygen
> can be disolved into the blood. The same principle keeps the gas in
Sorry. The greater the pressure of Oxygen, the more Oxygen can be
dissolved. This is a technical nit, but important when you start trying
to understand low pressure/mixed gas breathing.
Using rough numbers, air is 1/3 oxygen. At sea level, the 15 psi air
is 5 psi oxygen. The 5 psi is called the partial pressure of the oxygen.
If you breath pure oxygen, you can go to whatever altitude has a total
pressure of 5 psi.
This is how the astronauts survive. Not by breathing pure O2 (not
after the burned Apollo), but by having a mix that has a good partial
pressure of O2 with a low total pressure. I seem to recall the EVA suits
were about 4 psi pure O2.
> carbonated beverages when they are bottled. When you open a bottle,
> the air pressure is relieved, and the gas can be seen bubbling out of
> solution.
THe CO2 pressure is relieved. And that is why the liquid continues to
bubble for a short period after the top is replaced: the CO2 pressure is
increasing in the headspace. That is also why bottled fizzy drinks go
flat even when the top is on.
> At higher altitudes, sufficient pressure may not exist to
> disolve enough oxygen into the blood.
That is why you breath pure O2 at higher altitudes, so there WILL be
enough pressure to dissolve the O2. However, even on a mask, I would
guess there is enough leakage that you do no get pure stuff. Sort of like
the time I was on nitrous oxide at the dentist and started to mouth
breath. You DO NOT want to start feeling the guy drilling while his hands
are still in your mouth. He certainly was not a painless dentist. WHen I
bit him, he screamed.
> It is very possible that even if
> you were breathing PURE oxygen through a mask, you could pass out
> because of insufficient air pressure to get the oxygen to the blood.
> Holding your breath wouldn't help.
It might be enough to handle sedentary actions, like sitting in a chair
and thinking about flying. Once you start moving around your muscles will
make a hefty demand on what O2 is in the blood. Passing out is sort of
the brain's way of telling your muscles to "stop figiting, I'm trying to
think." ;-)
This is my signature. It doesn't contain my name at all!
David V. Phillips
Although I don't have any experience with low gas pressures, I do have
a fair amount of experience with high pressures, and various mixtures of
O2 and various combinations of inert gases. (Mostly N2 and He2) While
in the US Navy, I was a qualified Deep Sea (HeO2) Diver, meaning I was
trained in diving with Helium Oxygen gas mixes.
The body needs a minimum of .16 ATM of O2 to survive. You cannot do
much useful (at least strenous) work with this partial pressure of O2.
(That's another story I'll save for those interested enough to ask for it.)
If you are breathing less than .16 ATM of O2, you will develop anoxia.
I suspect it would take a rather high altitude to cause 100% O2 to drop
to .16 ATM. I've been at 40,000 ft with an O2 mask on, in a TA-4.
Since I can easily hold my breath for 45 seconds, and assuming there was
room to move, I could easily 'hold my breath long enough to get a
sweater.'
Is there a formula to determine the atmospheric pressure based on
altitude?
--
David Phillips sas...@dev.sas.com
"They that can give up an essential liberty to obtain a little temporary
safety deserve neither liberty nor safety". -- Benjamin Franklin (1759)
"Gun control is being able to hit your target." -- Me.
Jack Pines
...
>> In response to "I can hold my breath long enough to get a sweater":
>>
>The body needs a minimum of .16 ATM of O2 to survive. You cannot do
>much useful (at least strenous) work with this partial pressure of O2.
>(That's another story I'll save for those interested enough to ask for it.)
>If you are breathing less than .16 ATM of O2, you will develop anoxia.
>I suspect it would take a rather high altitude to cause 100% O2 to drop
>to .16 ATM. I've been at 40,000 ft with an O2 mask on, in a TA-4.
>Since I can easily hold my breath for 45 seconds, and assuming there was
>room to move, I could easily 'hold my breath long enough to get a
>sweater.'
>
>Is there a formula to determine the atmospheric pressure based on
>altitude?
from AOPA handbook:
Pressure Approx Alt
(millibars) (feet)
1000 400
850 5,000
700 10,000
500 18,000
300 30,000
200 39,000
100 53,000
Since we can legally fly at 12,499 feet as long as our bladders hold out,
I would assume that the FAA has deemed that the partial pressure of O2 in
normal air at 12,499 feet is sufficient for survival at a minimum. The
military wants the brains of their pilots to be fed with O2 from 10,000'.
700 millibars times 21 percent O2 gives O2 partial pressure of 147 mb.
Since 1 ATM is about 1013 millibars, military is implying that O2 pressure
of .145 ATM is adequate for pilots.
Note that somewhere around 45,000 the ambient pressure drops below 147 mb.
This implies that one can still get adequate O2 into the blood by
breathing pure O2 below this altitude. Since the concentration of O2
inside the lungs is less than that outside, I wouldn't try it
above 35,000. Above this altitude it is necessary to breathe O2 under
pressure so that the pressure in the lungs will be higher than ambient.
This means unlike normal breathing, our muscles must work to exhale. I
did a simple experiment with a length of pipe in a swimming pool and
found that with great effort I could exhale once against a pressure of
about 90 mb max. If I had to actually breathe that way, 30 or 40 mb
would be the most I might be able to sustain. The world record altitude
for gliders was reached by Bob Harris who had trained to be able to sustain
pressure breathing. He reached 49,000 feet.
In email Jordan Brown raised the issue of these overpressures damaging
the lungs. I asked a pulmunary specialist about this and he said the
lungs would be damaged above "50-60 cm water". Since a cm of water is
about the same as a millibar, I am guessing that this number is for an
unconscious person with relaxed chest muscles. I don't believe that I
damaged my lungs at 90 mb but in any case, I would be quickly asphixiated
if required to breathe against 60 mb of pressure.
If the vapor pressure of O2 in your blood is higher than the partial
pressure of O2 in your lungs, you will indeed lose O2 from your blood.
You will be in trouble before that point however. While holding your
breath, the concentration of O2 will decrease if you are adding it to
the blood on its way to your brain. This means that the partial pressure
of O2 will decrease. Even if you started with pure O2 in your lungs, you
would rapidly approach the point where you could not add sufficient O2 to
the blood going through your lungs. Any tobacco addict can tell you that
it doesn't take the blood in your lungs long to get to your brain. It is
an interesting question whether holding your breath has a positive or
negative effect on time of useful consciousness!
I heartily agree with the other posters that have recommended the FAA
sponsored flight physiology courses. If you are going to fly above 10,000
feet, you should take it.
Jack Pines ASELSG + USHGA III
Per Lindberg
>Is there a formula to determine the atmospheric pressure based on altitude?
From my HP-35 instruction book:
a = 8040 * ln(p0/p1) ; disregarding things like temperatures etc
where
a = altitude
8040 = a formula constant
ln () = the natural logarithm (base e)
p0 = pressure at sea level
p1 = pressure at altitude a
All measurements are in SI ("the metric system");
altitude in m (meters)
pressure in hPa (hecto Pascal) == mb (milli bar)
Example:
p0 = 1015 hPa, p1 = 337 hPa => a = 8865 m
(which probably means that you're on top of Mount Everest,
8882 m MSL).
Now, take a deep breath and extract p1 from the formula above:
p1 = p0 / exp(a / 8040)
--
Per Lindberg (p...@front.se) ! __!__
Front Capital Systems, Box 5727, ! _____(_)_____ Ceci n'est pas une Piper
11487 Stockholm, Sweden. 8-6611510 ! ! ! !