Patrolling the PS tunnel

The main PS magnets are installed on a large concrete foundations. Outside the ring, next to these foundations, is a very small underground passageway where cables and cooling water circulate. At the start of the beam run, these corridors must be patrolled to ensure that no one is present. This passageway is so small that sometimes the person doing the patrol has to walk sideways to pass. Access to these gangways is through metal hatches which are locked afterwards. This is why on the last photo one can see someone with a metal chain in their hands.