At What Altitude Does Altitude Start Being a Problem?

That’s why I always carry a camera. I can always stop to compose photos. :slight_smile: Getting to the top of the pass in Nepal I was reduced to 25 steps then a pause, and I was very well acclimatized. The Nepali were walking as if they were on the sidewalk in Kathmandu, but a few Westerners were doing the same.

And someone typo’d the elevation of Everest, it’s 29,035’. Several westerners have summited it (and all the other 8000 meter peaks) without O2 but they are few and far between. The Sherpa are physiologically better suited to handle high altitude and have been able to operate at altitude much better.

If you stayed at 30,000’ you’d be unconscious in about 1.25 minutes. Down at 20,000’ you’ll be around for longer, more like 10 minutes. Depending on just how quickly you get down and how much tolerance you have for hypoxia, you may lose consciousness, you may not. You’d be very unlikely to suffer any long term health problems aside from a phobia of flying :).

A normal descent is done at a rate of (ground-speed kts x 5)+100 in feet per minute, this gives a 3 degree descent profile. For us in the Dash 8, we usually do about 300kts so our initial rate of descent is 1600 fpm. The ground speed slows as we get down in to the thicker, lower atmosphere, so the descent rate drops gradually.

For a commercial jet, they’d have a higher rate of descent as they are flying quite a bit faster than us.

An emergency descent is done at the maximum operating airspeed, assuming the aircraft is still structurally sound (if the descent is due to a big hole in the cabin, all bets are off.) I’ve never looked at the rate of descent while practicing one, but 4000 fpm would be close to the mark.

Forgot to mention. Most pressurisation problems involve a slow depressurisation. This means the cabin altitude will slowly rise. Once it gets to 10,000’ a WARNING light will come on, the pilots will then don oxygen masks and carry out an emergency descent. They will get down to 10,000’ before the cabin gets to a dangerous altitude. You, as a passenger, will probably suffer no more than popping ears, expanding stomach gasses, and associated smells.

During a visit to Xining in China (alt. 7500ft), I passed out after getting out of bed to answer the door, as a result of the elevation there.

At the time I was 22 and in good physical condition, but we’d come straight from Shanghai (alt. 50ft) with no time to adjust.

(I should add that I’ve spent most of my life living below sea level)

My Wife and I live at 11,200 feet. As everyone has said, altitude sickness varies from person to person. I have never had a problem, but once, when my (pre)Wife went to Alaska for 6 months, when she got back she got sick. My 10 year old nephews got sick but my 70 year old MIL was fine. My Dad doesn’t have a problem, but my cousin does.

It’s hard to predict.

Also very hard to predict. My Wife runs marathons and is training for a triatholon. No way, no how can I keep up with her. But Normal, day to day stuff, light hiking is no problem. ‘Course living up here has aclimated me.

I will agree with Bobotheoptimist. Lower elevation does feel heavy, though I think it mainly has to do with humidity. I had also thought that ‘extra’ oxygen near sea level would give me a boost. Doesn’t seem to be the case. My Wife, the athelete agrees.

I lived for quite some time at about 5200 feet. During my time as a medic there we did occasionaolly have someone fly in and become short of breath. Nothing too crazy, and it never resulted in any medical emergency. Granted, all of these people had pre-existing chronic conditions, but they all came from sea level or close there to. After figuring out the lack of any pulmonary embolis or other illness, we guessed it was the elevation.

But yes, in general, age and fitness does not make a major difference.

When we flew to Tibet last year from near sea level, my wife collapsed the moment we arrived - 3,200 metres (~10,000 feet). After about 5 days she was OK. My legs got very tired walking upstairs, but otherwise I had no other symptoms. We eventually ended up at 5,600 metres (~18,000 feet) and had dreadful insomnia, waking up freaked out and gasping at the lack of air, all night long.

When I went trekking in Nepal, I was fine until I crossed 4,500 metres (~15,000 feet) and then I got a headache and puked everywhere in front of lots of people. Most embarrassing.

[QUOTE=1920s Style “Death Ray”]
If you stayed at 30,000’ you’d be unconscious in about 1.25 minutes. Down at 20,000’ you’ll be around for longer, more like 10 minutes. [/Q]

There is far too much “depends on” to make blanket statements.

I’ve done some hang gliding sans O2 that put me above 20,000’ MSL for a half hour at a stretch. flying a hang glider in calm conditions is about like doing one pushup a minute…not very strenuous.

At the time I kept in decent shape bicycling, and and was in a prone harness that put my body at one level.

One rule of thumb the glider guiders used was every 3,000’ (1000m) above your home altitude equals about one beer worth of stupidity. Most adult males would be pretty stupid on a 6 pack, but somewhat short of passing out.

Another significant factor is temperature. Due to insolation, even on glaciated mountain slopes, the temperature near the ground is significantly warmer than encountered in an aircraft. Each 18F (10C) is worth about 1000’ density altitude.
This effects how hard you have to breath, but 02 absorbtion is mostly related to partial pressure.

The most significant after effect of long, high altitude flights was an extreme lack of motivation once I landed. The better the flight, the longer it took me to pack up my glider.

I was in Nepal in the Everest area. In Lobuche (16,200’) I felt alright. Lack of appetite and a slight headache was all. But the next day the hike to Kala Patar (18,000’+) kicked my ass. During the last 500 feet, it was 2 or 3 steps and sit down and rest. The view of Everest at the top was fantastic.

I walked in from Lamasangu (4000’) (where Hillary walked in from) not Jiri. And took over 3 weeks to reach Kala Patar so I was relatively acclimated. I also stayed one complete day at 12,000’ and another at 14,000’ as was recommended to me.

Before I left for Nepal, I was running 5 miles a day at a 7 minute a mile pace just to make sure I was in condition for the hike, but it didn’t help at all at 18,000’!

Quote:
Originally Posted by Telemark

I had no trouble in CO or CA with altitude sickness for the 14’ers. In Nepal at 18K I had a nasty headache but that was about it. But the lack of oxygen up there is a killer. I didn’t really notice it much at 14K but at 18K it felt like walking in a fog. It took us 6 attempts to get a successful two-person hackysack.

An altitude of 18,000 ft. is impressive, but is nowhere close to the “death zone,” which is imprecisely defined, but starts at 25,000 or so feet. :wink:

Since you asked about “problems”, in general, rather than full-blown altitude sickness: Whenever I visit the family, down at a few hundred feet above sea level, for a few weeks, when I get back here to nine-tenths of a mile, it generally takes me about three weeks to re-acclimate. In the meanwhile, it’s nothing painful or anything, but it feels like all the hills are steeper, and I sometimes can’t make my whole (uphill) commute on my bike. Contrary to what others have said about exercise not helping, I do find that if I maintain a regular exercise routine while visiting, the effects when I get back are less severe and don’t last as long (though of course this is all subjective, and I only go back once or twice a year, so I don’t have the greatest statistics). I also notice that even once I’m acclimated, if I’m short of sleep, it’s as if I weren’t, for that day (though this goes away with a single good night’s rest).

Note that it’s actually 29,035’.

I have a friend who use to fly 747s and who says that 10,000 fpm is possible.

I assumed KG was joking. :slight_smile: There was a guy running a tea shop at 18,000’.

Yeah, I know. On the desktop I’d have gotten it right, but I’m not used to number entry on a laptop keyboard. Sorry for any confusion created, especially in people who leaped up saying, “20,035 feet, that’s not so high! I’m booking a flight to Nepal.”

[QUOTE=Telemark]
I assumed KG was joking. :slight_smile: /QUOTE]

You’re right, I was, but forgot the damn smiley. :smack:

Former big jet driver …

Emergency descents from cruise altitude can easily exceed 12,000 feet per minute. Starting from the low 30s (thousands of feet) we won’t even get to max descent rate before it’s time to start pulling out of the dive to level at 10,000 (or higher if over mountains). So figure 1 or 2 minutes tops in the descent.

If we suspect structural problems, like an unexpected hole in the airplane letting out all the air, then we’ll gently descend, perhaps taking 10 minutes to get from the high 30s to around 10. If the problem is believed to be lack of air supply, rather than lack of hull integrity, well, we’re going downhill at speed right NOW.

Oxygen requirements for passengers are designed around keeping elderly & infirm people conscious until we can get to an altitude where they can remain conscious breathing ambient air. Imagine a cabin with 50 passengers per flight attendant and 2/3rds of the pax passed out; where do the F/As begin to help?

Oxygen requirements for the pilots are based on the need to be mentally in top form while processing a lot of adrenaline. So we get more, and better.

A portion of the need for haste to low altitude is to minimize the likelihood of decompression sickness in the pilots (and pax). It’d be a shame to have everybody survive the descent just fine and then have both pilots incapacitated with the bends a few minutes later. By reducing the time at low pressure as much as possible, that possiblity is reduced.

In altitude chamber training one time years ago I got some evolved gas problems in one wrist. Hurt like hell & I was pretty much one-handed for the rest of the day. I could have used the hand if my life depended on it, but it sure wasn’t fun.

I vaguely remember reading the book Mayday by Nelson DeMille, about an airliner that gets hit by a missile at high altitude. I may be misremembering but I thought that most of passengers and crew were severely brain damaged by the lack of oxygen or something. If someone remembers this book perhaps you could explain why the plane couldn’t descend fast enough to prevent this. From reading the above posts it would seem like it should have been able to do this.

Sure. My figures are just the times of useful consciousness from my ATPL text book. There will be people who last a lot longer. Also they are the time available for clear thought before confusion sets in. I was incorrect to say you’d be unconscious in that time, but you would be confused.

It’s worth noting that a lot of people don’t know they are hypoxic until they pass out, even when they are incapable of writing their own name. This is what it makes so dangerous.

Ring,

I read Mayday some time ago. I remember thinking it was a bunch of bollocks. If there’s anything in there that didn’t sound right it’s probably because the author has no idea what he’s talking about.