  The safety of collisions at the Large Hadron Collider (LHC) was studied in
2003 by the LHC Safety Study Group, who concluded that they presented no
danger. Here we review their 2003 analysis in light of additional experimental
results and theoretical understanding, which enable us to confirm, update and
extend the conclusions of the LHC Safety Study Group. The LHC reproduces in the
laboratory, under controlled conditions, collisions at centre-of-mass energies
less than those reached in the atmosphere by some of the cosmic rays that have
been bombarding the Earth for billions of years. We recall the rates for the
collisions of cosmic rays with the Earth, Sun, neutron stars, white dwarfs and
other astronomical bodies at energies higher than the LHC. The stability of
astronomical bodies indicates that such collisions cannot be dangerous.
Specifically, we study the possible production at the LHC of hypothetical
objects such as vacuum bubbles, magnetic monopoles, microscopic black holes and
strangelets, and find no associated risks. Any microscopic black holes produced
at the LHC are expected to decay by Hawking radiation before they reach the
detector walls. If some microscopic black holes were stable, those produced by
cosmic rays would be stopped inside the Earth or other astronomical bodies. The
stability of astronomical bodies constrains strongly the possible rate of
accretion by any such microscopic black holes, so that they present no
conceivable danger. In the case of strangelets, the good agreement of
measurements of particle production at RHIC with simple thermodynamic models
constrains severely the production of strangelets in heavy-ion collisions at
the LHC, which also present no danger.
