I can’t recall any air accidents where survival depended on the air masks, but that may be because non-lethal accidents are under-reported.
There have been depressurization incidents where the masks deployed. Don’t know how you would prove a life was saved.
Well, have the masks deployed due to complete and non-recoverable depressurization at 35K feet for example? And if so, would it be impossible for the airliner to safely descend to 10K feet before the passengers froze/asphyxiated?
I suspect the passsengers would survive without them. Climbers have scaled Mt. Everest (29,029 feet) without supplemental oxygen before. Granted, these were fit, acclimated people, but there are some people capable of doing great exertion for days at a time at greater than 20,000 foot elevations.
The passengers only need sit quietly in a chair for the time it takes the plane to descend. Many would pass out, and some people with respiratory or cardiac issues might die, but the vast majority of people would take hours rather than minutes to die of hypoxia at the altitude that commercial planes fly, and in a depressurized emergency descent you’d come down around 4000 feet per minute or so, at least until the air thickened up enough so that breathing wouldn’t be an issue.
I love the standard instruction during the preflight briefing: “put the mask over your nose and mouth*** and continue to breathe normally***”. Oh, sure. A major system has visibly failed in this this glorified beer can traveling at 500 knots and I’m supposed to just chill out? You’re going like this: :eek: and are supposed to sit there all like .
But yes, it’s essentially a supplemental oxygen flow right into your nose and mouth for a few minutes until a still-flyable plane descends to safe altitude “just in case” but the procedures for such a descent are for a matter of minutes so that a reasonably healthy person should not suffer major hypoxic injury.
In the notorious Aloha Airlines accident in the late 80s the roof blew off at 24,000 feet. Half the plane had no ceiling from where masks could fall down yet the only fatality was one FA who got blown away.
There is always Aloha Airlines flight 243*, the poster child for explosive decompression.
*AKA the sunroof flight.
ETA. That’s what I get for reading the entire Wiki article before posting.
Radid descents due to pressurization problems are roughly a once-a-month thing industry wide in the US. In most cases it isn’t as dramatic as a big hole in the fuselage. And as such most events never make it into the newspapers. Most rapid descents begin where a problem is detected before it gets critical and we race to descend fast enough to get down before the cabin gets high enough to trigger mask deployment. Sometimes we win; sometimes the masks win. I’ve done one in my 20+ years. We beat the masks. We also started out fairly low; we were still climbing when the problem surfaced.
Per http://en.wikipedia.org/wiki/Uncontrolled_decompression we see that full-on hole-in-the-airplane events occur roughly once a year worldwide. FYI, I know of two events which meet the criteria and are not on that list, so it’s something less than complete.
Survivability vs. altitude is very non-linear. Humans can live and work a full lifetime at 15,000 ft. At 25,000 ft a healthy 30 year old could sit in a chair for maybe 30 minutes & remain conscious, although they’ll be stupid, lethargic, & useless after about 5 minutes. At 35,000 the numbers might be 10 minutes & 2 minutes. At 40,000 the numbers are more like 1 minute & 15 seconds.
Airliners fly as high as 43,000 ft, while some bizjets get up to 50,000. Mountaineers consider anything above 26,000 to be unsurvivable without oxygen http://en.wikipedia.org/wiki/Death_zone#Death_zone .
For situations involving a malfunction of pressurization supply or control we can descend very rapidly, getting down to no-oxygen-required altitudes in 3-5 minutes. If passenger masks were never deployed during that scenario we’d probably have a bunch of unconscious heavy smokers & elderly folks & maybe a heart attack or two. But a young healthy person who never got oxygen would be awake the whole time & OK. Maybe a little stupid, but they’d recover in another few minutes sitting there at low altitude.
Conversely, for a situation with a big hole in the airplane, we have to balance hurrying down to breathable air pressure with the risk of breaking the airplane completely. And there’s no good way for us to rapidly assess whether we’ve got a well-contained 2’ square hole or something more dramatic like Aloha 243.
So procedure calls for a fairly gingerly descent, more like what you experience on a normal flight. Which might take 15+ minutes to get down. To be sure, each minute we’re lower & hence the ambient pressure is getting more and more compatible with healthy life.
But for a descent started real high and done gingerly, we’d expect most of the people who don’t get on oxygen to be unconscious for a time.
Also, it’s important to think about *why *they’re unconscious. After all, each of us spends 7+ hours a day unconscious. So that doesn’t sound so bad at first glance. The reason they’re unconscious is their brain is getting too little oxygen to operate. We know that when a brain is deprived of *all *oxygen (e.g. after a sea-level heart attack) for as little as 3 minutes permanent damage is assured. And after 5 minutes it’s likely they’re brain dead for good.
So for somebody at very high altitude who’s deprived of 90+% of all oxygen, some damage is going to happen pretty soon. Probably soon enough that it’ll happen before we gingerly get down to lower altitudes. And once the whole body becomes oxygen-starved, what will happen to their breathing or heartbeat? Those bodily functions need oxygen too.
IANA medical guy, but I’d bet that pretty soon after they become unconscious they’ll also stop breathing or stop heartbeating. And then they are in the same situation as a sea-level heart attack; 3 minutes to damage, 5 minutes to dead. Getting them going again would require an oxygen mask supplying oxygen, plus somebody to do chest compressions & heart compressions to get that oxygen moving into their body until they started breathing & beating on their own.
In other words, simply descending to a breathable altitude will not, in and of itself, revive somebody who’s stopped breathing/beating. Paramedics work in crews of 2 or 3 per patient. We have one flight attendant per 50 passengers. And they’re in the same low-oxygen situation you are. Statistically speaking, you’re on your own.
Bottomline: The passenger oxygen masks, rinky-dink though they appear, are sufficient to deal with the worst case of a maximum altitude rapid decompression & ginger descent to survivable altitudes. *Provided *you put it on properly within the time available before you become stupid & lethargic. Which can be shorter than you might have thought.
I don’t know that you can point to a specific named individual on a specific date & say “*This *mask saved *that *person.” But it’s pretty clear to me that absent passenger oxygen systems we’d be killing or maiming a few people on many of these high altitude loss-of-pressurization events.
Thanks for your awesome response.
I guess what I was looking for is, for example: plane loses complete pressurization (“complete” I think would be the difference between, say, a 2" hole in the fuselage vs a 12" hole – I’ve read that the aircraft’s pressurization systems can compensate pretty well for small holes, so that the pressure drops, but not dramatically) at 40K feet, and takes 20 minutes to descend to 30K feet. In this case people were exposed to 20 full minutes of > 30K atmosphere and would have died without supplemental oxygen. I was looking for at least one clear case where lives would definitely have been saved.
I’ve experienced one of these as a passenger. It was… interesting. The pilots did the 25000 foot dive, then told us why. It was due to a failure in the cabin pressurization unit, which is redundant, but, according to our pilot, they can fly with only one operating. The remainder, about 1/3, of our flight from JFK to Miami was at 10,000 feet or so. It was very, very quiet. Until we hit a big air pocket and a few people kind of lost it. Then you heard some sobbing and praying.
Correct. The valves which control the flow of air overboard are a lot bigger than 2" across. Unless we’re at the very max altitude for the airplane the valves can certainly close enough to offset a small hole. On a really big airplane, e.g. 747, even losing a single cabin window wouldn’t result in immediate total depressurization. I’d bet they have to descend to a more moderate altitude (WAG 25,000). But once there they’d be able to maintain normal cabin pressure despite missing a single window.
Even a careful descent from 40,000 to 30,000 isn’t going to take that long, assuming no other control problems.
We could pick through the various events listed on that wiki page & find at least one where it’s a good bet somebody would have died but for the emergency oxygen supplies. I don’t think we’re going to find a “smoking gun” event where we can safely say “But for passenger oxygen, all the passengers would have died.”
Passenger oxygen systems typically operate for ~15 minutes total before being exhausted. Their goal is to sustain you well enough for long enough for us to get lower enough. There are corner cases, such as failures over the Andes, the Himalayas, or a hurricane, where the standard assumptions don’t hold and we could find ourselves needing to descend but being unable to do as much descending as the normal profile assumes.
The answer in that case is to get as low as possible & navigate to areas of lower terrain or better weather as quickly as possible. Once below 25,000 (and certainly below 20,000) all but the most infirm will survive indefinitely. They might not be happy, but they’ll be alive.
Prove that, had I not gotten out of the way of that semi-truck yesterday, that I would have died.
They weren’t saved, but the victims of the Helios Ariways crashat least were alive right up to the end.
And no one’s mentioned Payne Stewartyet, although that was a Learject and not a commerical airliner.
C’mon now. The point of my OP is obviously not to prove someone was saved for arguments sake. I am simply curious about whether these oxygen masks are really all that necessary (though of course I’m not complaining – I don’t mind that they are there!). It seems like except for exceptionally rare circumstances (that may not have ever occurred), the aircraft will always descend to breathable atmosphere long before any normally healthy individual should die or have brain damage. Sure, maybe someone who is very unhealthy might die, but they also might just die from getting a scare on a bumpy ride. Let’s ignore that grey area.
The oxygen masks that keep the passengers alive in a depressurisation event are the pilot’s. The oxygen masks given to the passengers keep them relatively alert and comfortable. Whether or not that makes them necessary is debatable. The authorities who make the rules have decided they are.
Maybe this is getting into the realm of so unlikely it’s not worth considering, but survival of a plan crash could depend on how alert you are when the plane comes down. My mother-in-law-in-law was a survivor of United 232 that crashed in Sioux City. She said a major factor in determining who lived was if you were able to get out of the plane and run after it crashed.
Of course, there probably hasn’t been a incident of depressurization followed by a crash like that one, so not much of an argument for oxygen masks.
If those climbers were transported from seal level to 29,000’ without time to acclimatize, they would pass out nearly immediately and soon die. It takes a while to acclimatize to those elevations.
If there were a situation in which some masks deployed, but some didn’t, or some worked properly and some didn’t, and the people who got the (working) masks lived while others died, that’d be pretty strong evidence in favor of the masks. I don’t know if such a situation has ever occurred.