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A little grim this but I was discussing free soloing with a non-climber in work and I said
"Well once you get over a certain height you're not going to survive a fall anyway so anything over this doesn't really make much of a difference."
... which got me thinking, how high is too high?
I'd guess it's reasonably low. So does anyone have any empirical evidence of how high a fall a human being can fall and survive (though not necessarily walk away from)?
It's not the fall that gets you, it's the sudden stop at the end. The most detailed data on the effects of large accelerations (or equivalently, decelerations) on the human body comes from research into spaceflight and aircraft ejection systems. There is a very detailed paper from NASA here, from which figure 5 (p. 36) is most useful.
The summary is:
There is no specific distance from which a person can fall and have it said they will survive or not survive. There are simply too many variables that will dominate the factor of "distance."
In 1971, flight attendant Vesna Vulović fell 10,160 meters (~33,300 ft) and survived without a parachute. On the other hand 556,000 people died in 2013 from slip-and-fall accidents from essentially 0 meters.
Any studies I could find cite too many variables such as your physical condition, what you land on, the orientation of how you land, any obstacles that may have changed the way you fell, how fast; even what you are wearing can change survivability.
Anecdotally, pole workmen and tree arborists seem to cite 9 meters (~30 ft) as the "cutoff" for fatality in a fall — that is, most who fall from thirty feet or higher die. Figure that after only 27 meter (~90 feet) of free fall, you are traveling over 80 km/h (~50 mph). Survivability at those speeds is just not that high.
When rock climbing, you're pretty much guranteed to be landing on rock if you fall. When I trained in CSPS and EMP III, the magic number was 16ft (~5m). If someone fell from upright with their feet above that height or higher onto a solid surface, then they were an instant bag and drag, aka: strapped to a spine-board and rushed to the hospital.
Unless you land on your feet, and you have the leg strength to soak up the force of the landing or you have the skills to tuck and roll, then you're either going to break bones or suffer internal injuries. You won't die instantly from this height (unless you land on your head or neck) but you will be at risk of dying from shock if you can't get help.
So, according to emergency first-aid responders (in Canada), the answer to your question would be; a fall from any height above 16ft or 5m can result in serious injury that could lead to death.
This doctor's blog claims that:
The median height leading to death is about 49 feet (15 meters), or about 4 to 5 storeys. 100% of victims die after falling 85 feet (25 meters), or about 8 storeys.
Obviously, the 100% figure is incorrect as there have been individual people who survived higher falls.
In any case, the height alone is not decisive. It makes a huge difference what surface you fall on and in what position. You'd have a pretty good chance to survive a 20 meter fall legs-first onto half a meter of snow on top of grassy ground, while a 5 meter drop head first onto concrete or rock is almost certainly fatal.
There is no such thing as this certain height.
You can fall from a chair, hit your head badly and be right dead. On the other hand, a couple of people fell thousands of meters (without parachutes...) and survived.
Some things affecting the outcome of the fall are: Your posture (head/feet first), the surface (water, rock, snow, trees or bushes...) and protective gear. And, of course, there is always a lot of luck involved.
Some facts:
Wikipedia cites that 50% of children who fall from 4 to 5 storeys (12 to 15 meters) high die. On the other hand, after falling approximately 450 meters you have reached terminal velocity, which means you don´t get faster. So after that, your survival chances should be - more or less - unaltered.
I knew a guy who was a medical examiner for the State Coroner. He dealt with a lot of people who had jumped from things. His rule was "Jump from seven, straight to heaven" ie 7th floor or more if you wanted to go right now rather than after a very painful interval.
The extract from a report linked below might be of assistance, and the report is well worth the read and should be quite accessible to those without a medical background.
The American College of Surgeons' Committee on Trauma (ACS-COT) defines a critical threshold for a fall height in adults as > 20 feet (6 meters), as part of the field triage decision scheme for transport to a designated trauma center [3]. A retrospective analysis of 101 patients who survived vertical deceleration injuries revealed an average fall height of 23 feet and 7 inches (7.2 meters), confirming the notion that survivable injuries occur below the critical threshold of a falling height around 20-25 feet [1]. A more recent study on 287 vertical fall victims revealed that falls from height of 8 stories (i.e. around 90-100 feet) and higher, are associated with a 100% mortality [4]. Thus, a vertical falling height of more than 100 feet is generally considered to constitute a "non-survivable" injury.
Generally a fall of 50-60 ft will kill almost anyone. However, I had a friend fall of the back of a motorcycle that was not moving, and he died because he hit his head on a rock, so go figure. A number of people have survived falls of 100-200 ft without substantial injury. There are three people who have survived falls of 10,000 feet:
As other answers have mentioned, there are too many factors to determine a fatal fall height. However, the rule of thumb for determining if there's a likely mechanism of injury for a spinal injury is whether there's a fall from more than 3x the person's height.
