These things come up and are always amusing (my favorite was the &quot;video&quot; of the LHC starting up). I wonder though, assuming no supernatural world-ending phenomenon, what is the worst that could happen given the energy involved? This is high-energy particle physics, using magnets to guide collisions? How high is the energy?  Can we put a value on the intensity of a complete and 100% efficient conversion of the particle collider energy to kinetic energy? Would it be like a 1 megaton nuclear bomb? Not even that? 1000x that? Do all concerns involve some unknown-maybe phenomenon like a runaway black hole? If we assume conservation of energy, what is the worst? Anyone know?