I've been experimenting with this in the PbP Humanspace games and I'm thinking of writing it into the rules to handle unplanned WTF kind of situations.
Currently, in the Ancient Astronauts campaign, the party was on the run from a group of cold blooded Shen assassins. migellito came up with this plan:
"Quickly scanning above and around the shen as they step out of the dust, Sungam looks for a structural element to hit with his old disruptor. Will he find a way to bring down a bit of the Old Quarter on top of their pursuers? Perhaps he can at least put some rubble between them, buying the impromptu group some time to lose the shen in the bazaar."
I was a bit skeptical of this plan and wasn't clear on what Martian architectural elements might be overhanging the street so I left it up to the Professor's "roll percentile dice and let's see what you get" mechanic.
The roll was "02" so I decided something pretty favorable should happen. It turns out the Shen were standing next to a parked standard utility marked "Abuzek's Best Liquid Oxygen."
Too much fiat? Does anyone use this or a similar method in their games? What about building this into the Humanspace rules for certain situations?