Many commercial skydiving facilities offer jumps at 15,000 ft. However, when I took my ground theory exams, it was reiterated many times that hypoxia starts at 10,000 feet.
How does this work? Is it because of the short time spent at that altitude?
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12$\begingroup$ At 15k, unless you're a smoker, you won't really get hypoxic symptoms at 15k ft. Your night vision will be degraded mostly. 10000 ft is used to provide lots of fudge factor to account for variations in people, and those with poor lung capacity. La Paz is almost 13000 ft and you can acclimatize to that. Pilots in WW1 would patrol at 20000 ft w/o oxygen. Crazy mountain climbers go higher than that, with the really crazy ones scaling Everest w/o oxy, after years of special training. When you are at high alt just sitting, you can't tell the difference unless you are exerting yourself. $\endgroup$– John KAug 2 at 18:09
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7$\begingroup$ Climbers living at sea level routinely climb Mt Rainier at 14,410' without oxygen or any significant high elevation acclimatization other than normal conditioning hikes in the lower mountains averaging 3000' to 7000'ish... I've had cabin pressure bleed off slowly to 17-18k and started feeling symptoms, but they were mild enough that I recognized them and caught it. $\endgroup$– Michael HallAug 3 at 1:45
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1$\begingroup$ People routinely climb 14,000'+ mountains without oxygen. Even when excluding Alaska, the U.S. has more than 60 such peaks. $\endgroup$– reirabAug 3 at 21:43
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2$\begingroup$ You wouldn't use oxygen to climb Mont Blanc at 15,780ft, but I know from personal experience that people will experience the oxygen deprivation in a number of ways. In my case it was just physical (making very slow progress) but others in the party were affected mentally, e.g. making poor decisions and losing their temper. $\endgroup$– Michael KayAug 4 at 10:35
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$\begingroup$ @JohnK, at 15k, you'll make mistakes at about five times the rate you would at sea level. $\endgroup$– MarkAug 5 at 1:09
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4 Answers
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They don't. Hypoxia is an actual concern in medium and high altitude skydiving.
It has been specifically researched as a possible safety risk. Skydivers jumping from over 10,000 ft do begin to exhibit mild symptoms of hypoxia - reduced ability to concentrate, less situational awareness, etc - even after a short time at that altitude. It's usually not a problem on its own, but can increase the risk of human error.
To reduce this concern, skydivers use supplemental oxygen onboard the aircraft to keep their blood oxygen-saturated as long as possible. But once it's disconnected, the symptoms start to build up.
Hypoxia starts subtle, somewhat similar to light inebriation, and takes a while (or a very low ppO2) to reach full blackout. Still, in rare cases, loss of consciousness does happen in skydiving.
A full blackout incident has been recorded in this video. You can see the use of the supplementary oxygen system until right before the jump, but two of the skydivers had to share one oxygen mask. One of them passes out from hypoxia in freefall, and is rescued by his buddies. This is a 22K jump - the higher the altitude and the longer the exposure, the worse the symptoms.
However, there are permanent human settlements above 15,000 ft. When living at low pressure for a while, the human body will acclimatize to lower oxygen pressure. Virtually anyone can do it, but individual tolerance varies. A healthy lifestyle (mostly no smoking), good fitness (lung capacity, aerobic exercise), and specific training regimens can greatly accelerate this acclimatization.
The risk of blackouts from hypoxia is mitigated in just a couple days of training close to the target altitude. Long-term acclimatization goes on to also eliminate the mental symptoms, so after weeks or months a person can function continuously at training altitude at nearly full capacity.
Experienced skydivers acclimatize and develop tolerance to hypoxia. Just one jump a day over a few weeks does the same work as the couple days of conditioning hikes for mountain climbers. Doing any of your first (or first few dozen) jumps from 15,000 ft might not be a good idea, unless you've lived in the mountains. It's not so much the blackout risk as the secondary risks from the mental effects of hypoxia.
Acclimatization requires time; it doesn't happen during one flight. Multiple jumps in one day, or prolonged loitering before the jump will make the symptoms worse, as shown in linked research. Jumps spread over consecutive days will let the body adapt and reduce the symptoms.
answered Aug 2 at 12:04
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$\begingroup$ Something is up. I do not easily get hypoxia above 14,000 feet. I will eventually have problems that high up, but it develops over hours of exertion. I'm having a hard time reconciling the 15,000 feet extreme hypoxia with my 14,400 I can exert myself and feel nothing wrong for the first hour. $\endgroup$– JoshuaAug 4 at 2:35
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$\begingroup$ @Joshua If you've done multiple sessions of multiple hours of exerting exercise at 14,000 ft, you've probably already acclimatized. That's the LLTH training regimen from the linked article. $\endgroup$ Aug 4 at 4:57
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3$\begingroup$ When I went tandem skydiving the professional skydivers would have little tubes of oxygen they could stick in their mouths until about 30 seconds before they jumped. Since their passengers didn't need to be so alert, we were allowed to be mildly hypoxic (probably helped calm some of the more nervous ones!) $\endgroup$ Aug 4 at 11:02
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You're right that we're taught that hypoxia might become an issue above 10,000ft but there is no magic line. It's not like at 9,999ft you're fine then BAM 10,000ft you're in trouble. Hypoxia affects different people differently, often affected by general health, smoking and other physiological factors.
That said, you're assumption is almost certainly right, it's the lack of time spent in that zone that makes it relatively safe.
A quick calculation shows that at terminal velocity, a human will fall from 15,000ft to 10,000ft in roughly 30 seconds. According to SKYbrary:
Hypoxia occurs within a few minutes if the cabin pressure altitude rises to between 5,000-6,000 m (about 16,000 - 20,000 ft).
So with 30seconds in the "Hypoxia zone" (as it were) it's not really a problem. Any higher than 15,000ft there is good guidance that supplementary oxygen is an option:
For intermediate-altitude jumps (15,000-20,000 feet MSL), participants should hold at least a USPA B license and have made 100 jumps.
For high-altitude jumps (20,000-40,000 feet MSL), participants should:
- hold a USPA C license
- have made at least one jump from 15,000 feet MSL or below using the same functioning bailout oxygen system
For extreme-altitude jumps (40,000 feet MSL and higher), participants should:
- hold a USPA D license
- have made at least two jumps from below 35,000 feet MSL using the same functioning bailout oxygen and pressure systems
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8$\begingroup$ Unless you skydive on the way up, you're going to be spending a bit more than 30s in the low oxygen environment ;) $\endgroup$ Aug 2 at 12:46
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3$\begingroup$ @Sanchises It's a good point, but even the climb from under 10K to 15K isn't particularly long. $\endgroup$– Jamiec ♦Aug 2 at 13:15
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5$\begingroup$ One could be breathing o2 on the way up, too, @Sanchises. $\endgroup$– FreeManAug 2 at 18:29
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1$\begingroup$ 10k to 15k , lineup, preparations is an easy 5 minute time. $\endgroup$– Jpe61Aug 3 at 8:43
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I think the danger here is being overblown quite a bit.
About a million people a year visit the top of Pikes Peak, at 14,112 feet, so not quite 15,000, but well over 10,000. They do keep oxygen bottles at the top of the peak, but mostly to sell to tourists at hugely inflated prices, not because a significant number of people really need them as medical treatment.
It is fairly common for visitors to suffer from altitude sickness--feeling somewhat lightheaded and sometimes a bit nauseous. Quite a few have a little trouble sleeping the first few days as well. But that's rarely any sort of acute episode where their life is in any danger. Typically it's more like their plans change from getting up at 4 AM and being on the hiking trail by 5, into something like going to the hotel restaurant for brunch around 10 or 11. They mostly just lose ambition, not their lives.
FAA requirements aren't based so much on the idea that at 12 or 15 thousand feet you will suffer from hypoxia and die, so much as that a problem is possible, and easy to prevent, so they might as well require that you take precautions if you go that high.
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3$\begingroup$ Upvoted for "They mostly just lose ambition, not their lives." $\endgroup$ Aug 3 at 22:57
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As many people have noted here, skydivers can start to suffer from hypoxia during the climb to jump altitude. As per the requirements of §91.211(a)(3) all occupants aboard an aircraft at cabin altitudes above 15,000 ft MSL are required to have supplemental oxygen AVAILABLE to them, though they are not required to use it, except for the required minimum flight crew. They are required to use supplemental oxygen at cabin altitudes above 14,000 ft MSL (see §91.211(a)(2)).
And many larger skydiving aircraft are so equipped to provide jumpers with supplemental oxygen during the ascent. Below was a publicity stunt Tom Cruise did for James Corden's late night TV show for the release of one of his Mission Impossible movies. Here he takes James skydiving and they make the jump above 15,000 ft. You can see small, clear tubes hanging down along the jumper seat planks in the interior of the Shorts Skyvan they use for the drop. These are supplemental oxygen tubes which a jumper can place in their mouth and suck on to get oxygen during the ascent. This is only approved to limited altitudes; anything above FL180 is going to require a full face mask for delivery of oxygen to the jumper.
