Anywhere around the accelerator you are going to have massive cyclotron radiation ( ie. the photons emitted when you coerce of near light speed proton out of a straight line).

In addition, at the detectors themselves, you have all sorts of radiation from the collisions. Muon, gamma, etc.

The author does pass on a good point, the biggest danger is oxygen deprivation from liquid helium, argon, and I assume Nitrogen ( though not mentioned ).