Is the LHC safe?
Various people have proposed scenarios in which the LHC could be dangerous,
even as far as destroying the Universe! These doomsday scenarios are completely
untrue, and you can see why at CERN's Q&A on the topic.
Whilst the LHC will be the most powerful particle accelerator ever built, it
is still dwarfed by the scale of natural events. Cosmic rays in our own
atmosphere produce much higher energy collisions and have been doing so since
long before mankind existed.
Safety considerations are taken very seriously at CERN and you can find
details of the various safety reports on the CERN website.