[pdonis]

> A while back there were concerns (notably not from physicists) about the LHC forming black holes.

There were concerns, but they were not well founded in actual physics.

> I remember the response being that tiny black holes frequently form in the upper atmosphere due to high energy particle collisions

I'm not aware of any such response. The response I'm aware of was that events with higher energy than the LHC is capable of creating happen routinely in cosmic ray collisions, and no black hole formation has ever been observed in such collisions, so black hole formation is not going to happen at the LHC either. That is consistent with our best current theoretical prediction, which is that you would need an accelerator capable of reaching the Planck scale, many orders of magnitude higher energy than the LHC, for black hole production to be possible.