[justinph]

Mythbusters tested this: https://en.wikipedia.org/wiki/MythBusters_%282003_season%29#...

You still die:

Dropping Buster with an internal accelerometer from a crane led to difficulty because the dummy continually lost parts on each control impact. Eventually, they managed consistent drops (mostly just below 300 g), finding that the hammer reduced the impact slightly, but the 150-foot (46 m) fall would still be lethal.

[slavik81]

It seems they tested whether a hammer could break the surface enough. Larger debris would create a significantly larger disturbance and would probably be more effective.

[nickpsecurity]

Did they test proper landings or drop it randomly? That's a critical thing left out of many analysis. You learn its importance to preventing injury in both martial arts (esp relaxing or break falls) and military, jump school. The methods for high falls should be tested on each of those techniques given prior effectiveness.