The theory goes, that tiny black holes are created by "super massive" matter, and don't have enough gravity to pull more matter in (unless they occur very close to other matter - the tunnel lining for example), so collapse in milliseconds.
Apparently, the hadron collider has a 48% chance of creating a black hole of some size. No idea who worked that figure out, or how though.
Personally, I reckon the guys at CERN will turn it on, and they'll hear it power up, then nothing.
Then they'll say "Aha! Just as we predicted, a miniture black hole! Shame it didn't last long enough for us to capture on one of the 2 giant telescopes."
