Not to be too gross, but what happened to the human beings on the lower floors of the WTC towers on 9-11. Did they just get squished into water and powdered bone? Was anything at all left after the upper floors pancaked on top of them? Did what was left of their bodies dry up and evaporate over time?
In the the CBS documentary on 9/11, one of the firefighters says after the collapse, “We’re not finding anything. Not a desk, or a computer, or even a phone. The only thing I found was part of a keypad from a desk phone.”
My guess, they were pulverized. 
The kinetic energy imparted in the high-speed pancaked collapse of a 110-story building is staggering, resulting in the occupants being smashed, then pulverized, then atomized, and finally absorbed by the surrounding mountain of micronized debris.
You have probably never seen shredded people. The remains are much more like muscle, skin, fat, gut fragments (particularly serosa), and bone after being put through a wood chipper. Soft viscera tend to become goo, but it is a pulpy and bloodlike goo with mucoid elements. It isn’t at all like water.
And the shreds begin to change color from red to brown, then green, then black, with hours and heat (number of hours depending on amount of heat). And as they change they stink.
I bow to my knees and deeply salute the Office of the Chief Medical Examiner of the City of New York for the incredible number of identifications achieved through DNA analysis on these decomposing, goo-covered human fragments.
Forgot to mention, but much less of a concern than evaporation is insect and rodent activity. Decaying protein and fat is very attractive to small predators and very difficult to stop. Which is why so many fragments of flesh were carefully packaged up and delivered to the NY OCME for the indefatigable forensic anthropologists and DNA analysts to work on for the next several years.
Twenty people who were on the lower floors or underground survived the collapse.
Actually, the people on the lower floors were nearly all evacuated and survived the day. This was due to the delay between the impact and the collapse of the buildings. It was the people on the upper floors (above the planes impact location) who were trapped by the damage to elevators & stairwells who died. Those on the lower floors were mostly rescuers trying to help those trapped.
But this doesn’t change the answer much. The effect on a human body is largely the same whether it’s all 110 floors collapsing onto you or just the top few floors.
Also (and how scary is this?) well over 100 people trapped in elevators.