Say an average person, in average health, was helicoptered to the top of Everest in warm clothing (in the death zone) and got to walk around on the summit for a while. How long could they last before the low pressure, lack of oxygen, etc. became a serious danger? Half an hour?
If they did have supplemental oxygen, could they stay for as long as the O2 lasted?
Aside from the fact that it would not be possible to safely land a helicopter on the summit of Everest (helicopter altitude flight records have exceeded 40 kft but not under fine control or stability), even with supplemental oxygen there would be the problem with adequate perfusion of oxygen into the bloodstream and tissues due to the low atmospheric pressure (less than 38% of sea level atmospheric pressure). A person would have to pre-breathe oxygen to purge excess nitrogen and hyperload the bloodstream with oxygen, and even then without an elevated hemoglobin count that is part of the adaptation to high altitudes they would probably not last very long. They would likely also suffer from high altitude pulmonary edema (HAPE) and/or high altitude cerebral edema (HACE), and while it is not possible to accurately predict who this will happen to the rapid unprepared ascent will very likely cause these syndromes to occur in someone who is not well-adapted to high altitude regardness of overall fitness and supplemental oxygen.
Stranger
Actually, it’s already been done.
In aviation they talk about the “Time of Useful Consciousness” for how long a person will be able to keep flying the plane after pressure is lost.
For Everest altitudes they list 2.5-3 minutes. It will vary a lot by individual fitness and other factors.
Helicopters can (just barely) land on Everest: Eurocopter AS350 B3 Everest summit landing - YouTube
I also disagree with Stranger on how well people could function with supplementary oxygen. Back before pressurized cockpits fighter pilots used to do max performance climbs to 30kft+ to intercept bombers. No pre-breathing aside from what they got during the climb up (10-15 minutes or so for WWII fighters). They then had to fight when they got there. Most pilots seem to have handled this just fine.
A number of people have climbed Everest without supplemental oxygen, but how long they can stay there is debatable. I would hazard anyone climbing to that elevation would spend several hours in the death zone, even if they only spend a few minutes on top. If someone was taken from sea level to the top and dropped off, without any acclimatization, I would think they would pass-out in less than 5 minutes.
Military Student pilots who undergo testing in hypobaric chambers are pretty stupefied after this much time. That’s the point at which the instructor in the chamber with them will tell them to put their O2 mask back on, and a lot of times they are too inebriated to follow the instruction and require help.
Here’s Destin Sandlin, of the SmarterEveryDay channel, in a hypobaric chamber at a simulated 25,000 feet. The video is cued to the moment he takes his O2 mask off:
Within a couple of minutes his pulse ox is down in the 60s. A couple of minutes longer, and he’s having serious problems with cognition and dexterity. 30 seconds later he’s unable to comprehend and follow instructions to put his O2 mask back on, at which point the attendant takes care of this for him.
So yeah, a few minutes on the summit of Everest should leave a non-acclimated helicopter passenger in pretty rough shape.
Relating the Payne Stewart accident to this question:
Research has shown that a period of as little as 8 seconds without supplemental oxygen following rapid depressurization to about 30,000 feet (9,100 m) may cause a drop in oxygen saturation that can significantly impair cognitive functioning and increase the amount of time required to complete complex tasks.
I stand corrected about helicoptering to Everest Peak. The ability to step out of the helicopter and remain functional while undertaking any physical effort, however, still remains.
Stranger
In the video I shared, at 8:19, there’s a chart showing time of useful consciousness at different altitudes and for “slow” and “rapid” decompression. For rapid decompression at 30K feet, he shows 30-60 seconds, although I suppose that does leave plenty of room for being sluggish long before you pass out.
The TUC numbers mentioned by @ThisOneGuy is probably the most relevant. There’s a big difference between a sudden decompression as described by @snowthx versus a gradual multi-minute transition from sea level to high altitude.
The TUC at 25,000 feet as commonly used in military altitude chambers and at 30,000 feet = Everest is significantly different. I can recall as an in-shape 22yo being semi-sensible for a good 4 minutes at 25,000. I outlasted a few other folks and was outlasted in turn by a couple. But after that I was pretty listless / stupid. And that’s sitting in a chair, having been breathing pure oxygen until we took off our masks.
In the airline biz we’re told to expect any flight attendants or passengers standing up when we blow a cabin to be found unconscious on the floor every time. Standing or walking is far more oxygen consumptive than is sitting.
As to supplemental oxygen …
25,000 is as high as you can go and still attain normal blood perfusion passively breathing pure oxygen. Said another way, the partial pressure of oxygen in the atmosphere at sea level is the same as the “partial” pressure of pure oxygen breathed at the ambient pressure found at 25,000 feet. At 30,000 ft breathing pure oxygen at ambient pressure will quickly give you low spO2 and you’ll be weak and a bit stupid, but can probably wander around on a nice day without hurting yourself for at least a few minutes.
The oxygen systems in high altitude aircraft include a tight fitting mask and the provision, above 25,000 feet, to ram the oxygen into your lungs at above ambient pressure. So called “pressure breathing”. In effect it’s a mini pressurized compartment consisting of just your lungs, pharynx, nose, mouth, and the mask interior. It’s hard work to breath against the pressure, and the higher you go the higher the pressure has to be to keep you adequately perfused. At about 50K feet it’s impossible to force oxygen into you at a high enough pressure to keep perfusion up to a safe level without tearing up your lungs. Above there you need a space suit to survive.
In normal breathing your diaphragm does work to inhale and relaxes to exhale, letting the stretched chest and ribs spring back to their normal relaxed size. Under pressure breathing it’s the opposite; you relax and the system fills your lungs then you need to push like mad to exhale against its constant shoving. It gets old real quick and talking is a right bitch.
I’m not aware of any portable pressure breathing systems, but I’m not a mountaineer.
LSLGuy - everything you say in your post makes sense and you have more expertise and knowledge in this area. However, I don’t understand this partial pressure part :
Partial pressure of oxygen at Seal Level = 0.21 x 14.7 = 3.1 psi (0.21 is the fraction of oxygen in air)
To get an air pressure of 3.1psi, you have to be about 37,000 ft in altitude. (Per this calculator Air Pressure at Altitude Calculator)
You’re quite right. I’m guilty of repeating something I was taught.
The physics numbers I gave are obviously wrong in detail, but the concept remains that above a certain altitude, even 100% oxygen at ambient pressure just doesn’t have enough O2 molecules per lungful to keep you going.
I suspect the difference is down to something in the biomechanics of lung gas exchange. When it come to biology there’s always more going on than simply physics.
Thanks, @LSLGuy, for the informative post!
My experience of going to the summit of Mt Fuji from sea level (Tokyo) to 3,776 m in a few hours was that it was unpleasant. In Japan I noticed the thinner air from about 2,500 m (around 9,000 ft, which AFAIK is airliner cabin pressure) and from 3,000 m it got harder. In Nepal I went over the Thorong La pass at 5,416 m, having acclimatized by gaining 300 m of altitude a day after 3,000 m, and after getting some tablets to help with the altitude. Everest is an order of magnitude greater. Climbers use supplemental oxygen, but not pressurized - it would be way too heavy t carry that much. It is just enough to keep you functional and compos mentis.
Since the helicopter would get you to altitude very quickly, you would not acclimatize. I have heard of travelers getting altitude sickness when traveling up the new high altitude roads in Pakistan, at about 15,000 ft. I think you would be feeling none good even before the landing. Once there, my guess is that you would be gasping hard and probably very nauseous.
My guess is that you could last out as long as your supplemental oxygen, but you would be really glad when you got back into the 'copter and started down again. And from my experience of (very mild) altitude sickness, I would not volunteer to take the ride.
Dangerous? You won’t get the lethal forms of altitude sickness during a short stay, but there is a good reason why altitudes of 8,000 m and above are regarded as the death zone.