I think I read somewhere that most direct falls from 30 ft. or more onto a hard surface are fatal, perhaps not immediately (which might be worse...)
“I read somewhere that most direct falls from 30 ft. or more onto a hard surface are fatal”
Essentially true.
There is a very detailed paper from NASA (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930020462.pdf), from which figure 5 (p. 36) is most useful.
The summary is:
It does depends on where and which way up you land - feet-first onto a soft surface is best (pretty obvious).
For a hard surface, assuming you don’t land on your head, up to about 12m/s impact velocity, you are almost certain to survive (corresponding to a fall from a height of about 23 feet). Though “survive” is likely to involve life-changing injuries at the top of this range.
Between 12 and 17m/s, you may or may not survive (corresponding to a fall from between 23 and 39 feet).
Over 17m/s, you are almost certain not to survive (corresponding to a fall from over 39 feet).
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.