The machine will probably create hundreds or thousands of mini black holes. However, a black hole only has the mass of that which created it, and since they're using subatomic particles, the black hole won't have enough mass to do anything, and will simply collapse on itself within a few nanoseconds. Plus, the Moon and Earth are hit with mini black holes made of subatomic particles all the time, the only difference is they are actually traveling at light speed (or faster), and, they're much bigger and more energetic.
The other hazard is, the LHC will create strangelets, which convert matter to anti-matter (or something equally devastating, anyway). Strangelets are only theory though, so who knows.
P.S. I'm what you can consider very poor at astrology/cosmology/particle physics, so, take what I say with a grain of salt and Google