Oxygen Deficiency Hazard (ODH) Monitoring System in the LHC Tunnel

The Large Hadron Collider (LHC) presently under construction at CERN, will contain about 100 tons of helium mostly located in equipment in the underground tunnel and in caverns. Potential failure modes of the accelerator, which may be followed by helium discharge to the tunnel, have been identified and the corresponding helium flows calculated [1, 2, 3]. In case of helium discharge in the tunnel causing oxygen deficiency, personnel working in the tunnel shall be warned and evacuate safely. This paper describes oxygen deficiency monitoring system based on the parameter of limited visibility due to the LHC tunnel curvature and acceptable delay time between the failure and the system activation.