It may be fairly obvious but oxygen is a critical factor when establishing our limitations,
and the higher you go the less oxygen there is. At high altitudes the air pressure is
lower, which means there’s less oxygen in the air you’re breathing, and the body can
be pretty sensitive when it comes to oxygen levels. In this scenario it expresses its
displeasure in the form of hypoxia and altitude sickness.
This will usually start to affect you when you pass 5,000 feet (1500 meters) above sea
level. Your breathing rate increases as your body tries to acquire more oxygen (BREATH
SFX) . Despite this, your muscles still won’t be receiving sufficient oxygen, making simple
exercises like walking more difficult. You'll start to feel tired, but you'll actually find
it harder to sleep, because the sleep centers of the brain won’t be getting enough oxygen.
These conditions just get worse the higher you go.
At around 8,000 ft (2500m) these symptoms can progress to dizziness and headaches leading
to nausea or vomiting.
These early forms of altitude sickness dubbed ‘Acute Mountain Sickness’ (AMS) are not
usually life threatening and will normally disappear as soon as you descend to a lower
altitude.
However if you continue up above 10,000 feet (around 3000m) leaving what’s termed the
‘Physiological-Efficient Zone’, then you run the risk of developing High Altitude Cerebral
(HACE) and/or Pulmonary Edema (HAPE), where fluid accumulates around your brain and in
your lungs. Without treatment fast, this can be fatal.
If you don’t suffer Acute Mountain Sickness, then from this height upwards the temperature
will typically drop below zero and then continue to decrease the higher you go, meaning you’re
also more likely to suffer frostbite as your blood is diverted from your extremities and
towards your core.
At 16,000ft you’ll be trying to survive in temperatures of -17ºC/2ºF. Now these
temperatures will vary according to the Lapse Rate which is dictated by the humidity of
the air, but it might surprise you to find out that not only do people survive at this
height but just above this at 16,700ft (5,100 m) you’ll find the highest permanent human
settlement. La Rinconada is a gold mining settlement of 50 - 70,000 people in the Andean
Mountains of Peru.
At this height each breath you take contains only half the amount of oxygen of the air
at sea level.
So how on Earth do the residents survive in such a harsh environment? Well there’s some
debate about whether the tolerance of high-altitude natives is genetic or a result of long term
exposure, but either way they tend to have larger lung capacities, and their bodies are
able to make more efficient use of the oxygen available, resulting in both better sleep
and exercise performance.
However, these traits aren’t a given among high-altitude natives, with a syndrome called
Chronic Mountain Sickness affecting nearly a quarter of the La Rinconada population and
6-20% of all residents living over 8,000ft/2500 meters above sea level worldwide.
This condition sees an excessive increase in the body's red blood cells, which among
other symptoms can result in heart failure and death. The only cure is to descend to
a lower altitude, but in some cases the symptoms will be irreversible.
While La Rinconada is the world’s highest permanent settlement, if we push on up further
to 19,520 ft (5,950 m) you’ll be at the highest recorded height that humans can permanently
tolerate.
A scientific expedition in 1935 found that Chilean miner Justo Copa lived at this altitude
for 2 years. With all miners from the temporary settlement suffering unsustainable side effects
if they went any higher for extended periods of time.
The expedition team led by Physiologist David Bruce Dill, concluded that residing at an
altitude any higher was impossible.
The occupants of this mine in Aucanquilcha, Chile have since been dubbed 'The Highest
Inhabitants Of The World’.
But how long could you survive above this altitude?
Well, push on above 26,000 feet (8000 meters) and you’re entering the ‘Death Zone’,
so called because the oxygen deficit is so great that the human body starts to break
down and die with each minute you spend here
So, with the ascent from this altitude to Everest’s summit at 29,029 ft / 8848M taking
around 7 hours how do climbers manage to stay in the Death Zone for so many hours?
For those that conquer the likes of Everest, two big factors come into play. Acclimatization
and supplemental oxygen. Most people can adapt to altitudes if they acclimatize first.
If you were suddenly transported from your home city to the top of Everest, you’d likely
be dead inside 2 minutes.
Acclimatizing or acclimating allows your body, among other things, to increase its haemoglobin,
the red protein in your blood responsible for transporting oxygen around your body.
This can then absorb more oxygen. This doesn’t necessarily negate all of the previous symptoms
we’ve talked about, it just gives you a better chance of making it to the top.
Most that suffer from altitude sickness ascend too quickly, the key is to climb slowly, with
progressional stops at different altitudes for days at a time. The climb to summit Everest
usually takes 2 months.
But even with the most comprehensive acclimatization route, at 23,000feet most climbers will begin
to tackle Everest with the assistance of oxygen bottles,
and when you’ve entered the Death Zone at 26,000 feet, acclimation becomes impossible
and nearly everyone uses auxiliary oxygen.
"EVEN IF YOU’RE ON OXYGEN AT EXTREME ALTITUDE, YOU CAN’T GET NEARLY ENOUGH OXYGEN TO FEEL
GOOD OR BE COMPLETELY SAFE," "WITHOUT OXYGEN, YOUR BODY IS SLOWLY DYING."
While needing a consistent supply of oxygen bottles doesn’t exactly fit the bill for
a survivable height, there are an elite group of climbers who have pushed past 26,000 ft
and summited the highest point on our planet without the assistance of extra oxygen.
At these heights each breath of air that you took would only contain about a third of the
oxygen you would normally be inhaling back at sea level.
“UP THERE, YOU DO SOMETHING THAT’S TOO AEROBIC ALL OF A SUDDEN AND YOU LAY THERE
FOR 10 MINUTES TRYING TO CATCH YOUR BREATH."
Ed Viesturs who has climbed all 14 of the world’s highest mountains above the Death
Zone mark,
is 1 of only 200 people to have ever summited Everest without supplemental oxygen.
This elite club accounts for only 3 percent of the total Everest summits, but 22 percent
of the 111 deaths that have occurred above 26,000 feet.
Understandably, most people tend to take in the view, get a selfie and start heading back
down out of the Death Zone, but Babu Chiri Sherpa decided to settle in
for a while longer,
remaining at the top for an incredible 21 hours! Unsurprisingly this is the longest
recorded time anyone has spent at the summit.
But is there a limit beyond the world’s highest peak of 29,000 feet (29,029 ft / 8848M)
without extra oxygen?
Well Professor Mike Grocott, an expert on the physiological effects of altitude, estimates
that the top of Everest is actually pretty close to our limit…
“I’D GUESS THE LIMIT WOULD BE ABOUT 9,000 METERS.”
However, for obvious reasons we can’t physically try to climb any higher than the Earth’s
highest summit, but what if we weren’t climbing,
what if we hopped on a passing balloon and travelled up toward the stratosphere, what’s
the absolute height we could survive to? Well with oxygen continuing to decrease you’d
need to get up there pretty quickly.
As we established earlier, the reduced amount of oxygen within each breathe is due to the
decrease in pressure- something that also continues to decrease the higher up we go.
Above 49,000ft or 15,000m the pressure is so low that even supplemental oxygen won’t
help you.
“...AT THIS ALTITUDE THE PRESSURE IS SO LOW THAT THE CARBON DIOXIDE IS REMOVED FROM
THE BLOOD FASTER THAN IT IS PRODUCED BY THE BODY. THIS LEADS TO THE BLOOD BECOMING TOO
ALKALINE [CAUSING] ALKALOSIS, DAMAGING THE DELICATE STRUCTURE OF PROTEINS, WITH FATAL
RESULTS.
This decrease in pressure also lowers the boiling point of fluids. You may be familiar
with the concept that on top of Everest instead of boiling at 100ºC/212°F water will boil
at around 68°C/154 °F. Well head up a little further to above 60,000ft, around 18,000 meters,
and the average body temperature of 37ºC / XXºF will become the new boiling point,
causing the surface fluids in your mouth, on your eyes, as well as the air sacs in our
lungs to vaporize and rapidly escape our bodies.
The common misconception that blood contained within your circulatory system will also boil
however is not true, as your internal blood pressure is still higher than the external
pressure.
Nonetheless, survival here will be extremely short lived unless you are urgently repressurized.
Humans are only able to survive above these heights with the use of specialized pressure
suits or pressurized cockpits.
Named after Harry G. Armstrong (Founder of the US Army's Department of Space Medicine),
the 60,000ft or 18,000 meter Armstrong Limit or Armstrong Line is considered the absolute
limit of human survival. Despite the name however, it is not actually a hard line, due
to variations in the human body temperature, effects could occur as low as 55,000 ft/17,000
meters, so you might want to take a thermometer with you to be sure.
This video is part of our human survival series, with another video out soon!
But in the meantime thank you to our The Great Courses Plus who have made this video possible.