# oxygen at 21,000 feet

Hello Everyone,

I’m reading Fighter Pilot, an autobiography written by a WWI fighter pills. He treks of making flights at 21,000 feet in orb cockpit planes with no supplemental oxygen. I have no doubt one could aran that height workout oxygen, but how long could one maintain that altitude before hypoxia set in?

Wikipedia gives a “time of useful consciousness” of 20 to 30 minutes at 18,000 feet, but only 5 to 10 minutes a 22,000 feet.

There’s a chart here:

It would depend on the pilot and their training, wouldn’t it? For me myself, I guess I’d last about 30 seconds, while a Sherpa probably could fly until they ran out of fuel…

It varies a lot from person to person.

I’ve been in a pressure chamber where one exercise was removing oxygen masks at the pressure equivalent of 25000 ft. Some of the folks were doing poorly after a couple of minutes; others were only slightly goofy after 5 minutes (the max time allowed without supplemental oxygen).

Exertion or stress will seriously shorten this time.

But note that Mt Everest (29028’) has been climbed without supplemental oxygen - and that requires some very serious exertion.

Overall air pressure at 21,000ft is approximately 46% of sea level pressure which corresponds to a partial pressure of Oxygen of 0.097atm. Such low partial pressure of oxygen would require a higher than normal respiratory rate and/or deeper breaths to meet basic metabolic needs for an active adult. But how much higher?

You can play around with the oxygen level calculator at Altitude.org and tweka the variables…

At 21,000ft and with a constant tidal volume of 0.65 liters the minimum necessary respiratory rate* is between 10 and 11 breaths per minute. Lower and, per its calculations, it is not enough to support the body’s oxygen requirements.

Similarly, at 21,000ft and with a constant respiratory rate of 14 of would need a minimal tidal volume** of 0.519 liters. That is a little bit deeper breath than normal, but not very noticeable. Lower and, per its calculations, it is not enough to support the body’s oxygen requirements.

So a healthy adult male at rest should be ok with relatively normal respiratory rate and tidal volume. A slight increase in respiratory rate, but staying within normal range, should negate the need for slightly deeper breaths.

But start having him do stuff and the oxygen demand goes up. How vigorous flying a plane is as it relates to oxygen demand is a bit tricky to put a number on.

*Average respiratory rate is 12 to 20 in a healthy adult.
** Average tidal volume is about 500ml (0.6 liters) in a healthy adult male at rest.

Yes, some people have unusual physiologies either naturally, through conditioning or a combination of the two. It is not impossible at all for some well-trained people to stay functional well above the altitudes that would kill or incapacitate the average person quickly. Fighter pilots are selected from an elite group of very physically healthy candidates so they are much more likely to be able to survive it than the average person.

There are also some very unusual freaks of nature like Wim Hof (“The Iceman”) who not only climbed up to 22,000 feet on Mt. Everest, he did it while wearing nothing but shorts and sandals and no supplemental oxygen. He planned to climb to the top but was forced to turn back due to a foot injury (not extreme temperature related; his body temperature does not drop due to exposure even to extreme cold for reasons doctors cannot explain).

I have read the biographies of other fighter pilots like Chuck Yeager that mention similar things. Any given story might be an exaggeration but I am confident that at least some of them are true because it really is possible for some highly selected and conditioned people to function just fine at those altitudes without supplemental oxygen.

The big difference between 21,000 ft altitude in an airplane as opposed to 21,000 ft altitude on a mountain is that there is no time to get acclimated. There are some exceptional individuals who can climb Everest without supplemental oxygen, but if one of them were to be plucked up from sea level and suddenly dropped onto the summit, he would be in trouble.

If a fighter or test pilot is flying a lot of missions consistently, even an average one (among the already elite) will develop tolerance for a low oxygen environment and not blacking out during high g-forces. That ability starts to fade fairly quickly when you don’t use it regularly but it also can be built back up fairly quickly through repetition. I am not saying that very many pilots can fly safely for very long at 22,000 feet without oxygen but a few can. Of those that can, it is most likely the ones that have a much higher than average baseline and have used it consistently and recently.

There is a small city in Peru that is at 16,700 feet and there are individuals that live even higher than that. They seem to do just fine and they would be good candidates for flying planes at high altitudes with no oxygen because they already live higher than the altitude where it is required.

However, it is extremely dangerous in any circumstances. Hypoxia because it isn’t painful (quite the opposite) but it is insidious and one of its main effects is to remove the ability to make ratyional judgements about the impending situation at all until it is too late.

Many folks in Peru and Nepal have genetic physiological differences that allow them to operate at high elevations that folks without those mutations simply cannot match.

Right but a few fighter pilots do too and they they get better at it with practice. They can also withstand g-forces that will cause a normal person to black out. I read Patty Wagstaff’s (the former aviation aerobatic champ) columns in aviation magazines. She can withstand much higher g-forces than a normal person but she has to build up to it at the start of every show season. It is the same thing with fighter and test pilots. If they practice and have some innate ability (almost all of them do by selection) then they can also pull off things that would disable or kill regular people that aren’t acclimated to that environment.

We are only talking about one person here and the possibility that the story is true. Without knowing who the OP is referring to, it is impossible to know but such feats have been demonstrated by many other people before. Chuck Yeager had many close calls as a test/fighter/maintenance pilot including several with a failure with supplemental oxygen. I will have to look it up but I believe some were much higher than that and he still made it back home one way or another at least eventually.

In short, I am not saying that I could do it and live through the experience but it is completely possible that a few people could with little ill effect. We aren’t talking about 40,000 feet here.

I wasn’t implying that the Nepalese and Andeans were the only people with this mutation. There are some high altitude mountaineers such as Reinhold Messner and Ed Viesturs who likely have the same adaptation, having pioneered climbing 8000 meter peaks without supplemental oxygen.

I am a flat lander but have oversize lungs. It is hard for the XRAY folks to get all of them in one shot.

I have been flying all my life and up until 1998, I worked 18k for an hour without oxygen many times.

I can no way do that now, heck, it is hard just to climb stairs and I quit smoking in 1996.

I could swim hard underwater for over 4 minutes since I was 10.

I was a weird one.

Now I am just an old one.

What is said up thread and without practice and being lucky in the physical department, doing that stuff on purpose is a quick way to die.

One mapping job back in PA, we had been at 23K + a little bit for almost right at 4 hours and I was about 15-20 minutes from being done when the oxygen ran out… The Wx was supposed to go down and we needed to finish.

I though out what symptoms would make me pull the power and descend no matter if we were through or not. And then we went for it. About 10 minutes from the end of the line I told ATC that I would need to get to 14K quickly when we hit the end of the line.

At that point I told them I was starting down and they requested a couple of turns at different altitudes and I said, “Unable, need straight ahead, been out of oxygen for 20 minutes and am not able to follow directions.”

Well, they had been working with us for several days so they did not turn me in as there was no real conflicting traffic. I could think OK by 16K, told ATC I was functional and we headed for the nearest airport. I did not mention that I had to go there because we were running on fumes. Bawahahahahaha

Of course all this did not happen, just an amusing story about flying back before 9-11.

One other concern with high-altitude flying is the effects it has on aircraft performance. Just as a pilot needs oxygen, so does the plane. Even during WWII, many aircraft weren’t able to operate competitively at 20,000 feet due to the engines struggling.

I’m curious about the context of a WWI fighter pilot operating at such altitude, and can only come up with a handful of reasons why any would bother. Off the top of my head is that he might have been hunting or defending airships, which used altitude as a big part of their strategy to avoid enemy air defenses. Similarly, he may have been seeking a high perch to spot an enemy and pounce on them from above, at which point the combat would quickly move to lower altitudes.

I suspect it’s also much more efficient for cruising, the same reason modern passenger jets cruise at ~35K feet. Not only is there less aero drag, but the engine will be operating with a wider throttle setting, reducing pumping losses and making it more efficient.

Also, IANAFP, but as I understand it, energy management is a critically important aspect of ACM engagements. Starting an aerial chess match from 20K feet gives you a good bit of extra energy compared to starting things at 5K feet. Need more speed? nose down, and suddenly you’re accelerating at 1 g, something your engine can’t do for you by itself at lower altitude.