If you will have noticed, LHC at CERN near Geneva may have dimmed half the lights in France, Switzerland, and Italy, and yes, it DID create black holes. But oddly enough, we didn't collapse into them. That is because a bh must be at least .25 Solar Mass to last more than a the short while the HHC experiment is on. Put your fears to rest, we're not going to collapse into a black hole. But if you want to know what can go wrong, rest assured that Murphy's Law still applies: anything that can go wrong has already gone wrong, but you simply didn't detect it before the whole machine turns into scrap.