Monitoring stations are sets of dedicated probes, specific electronics and communication systems that automatically send data of the predefined relevant parameters to a supervisory system for on-line display, archiving and analysis. For each monitored parameter, specific alarm thresholds are set to trigger the intervention of the HSE Unit and in some cases the intervention of the CERN Fire and Rescue Service.

At present, 149 monitoring stations supply the remote supervisory system with the data provided by 464 on-line channels, which monitor the environmental relevant parameters of the following domains:

  • stray radiation (gamma and neutron);
  • effluent water (temperature, pH, conductivity, turbidity, hydrocarbon and gamma emitters);
  • ventilation and ambient air (alpha/beta);
  • meteorological data (precipitation, wind speed, azimuth...).

monitoring stations

Stray radiation

Stray-radiation results from high energy particle beams that can generate secondary particles such as photons, muons and neutrons, which can potentially reach the environment. This stray radiation, that ceases when CERN's accelerators are stopped, is added to the omnipresent natural radiation. CERN has 42 on-line stray radiation monitoring stations that are spread over the CERN sites. In addition, this monitoring network is completed by about 100 passive dosimeters (Thermo Luminescent Detector - TLD) that are exchanged and measured on a quarterly basis to check the level of stray radiation.

Configuration of a new stray radiation monitoring station

Thermoluminescent detector dosimeter (TLD)

Air monitoring

Accelerator installations, which also include experimental halls, transfer tunnels, etc., need continuous ventilation and air renewal especially in closed areas like tunnels. Atmospheric releases of the ventilations are continuously monitored by on-line gases monitors. The controlled parameters are short-lived radioactive gases (i.e. 11C, 41Ar, etc.).  The on-line monitoring system collects a sample of air from the ventilation exhaust through a sampling line, for which the flow rate is regulated in order to control the volume of the gases.

A Ventilation monitoring station situated on a roof near the ventilation exhaust

Supervision synoptic of the south part of the Prévessin site

Effluent water

Water is mainly used on the CERN sites for cooling purposes, but also for more common sanitary and industrial usages. Two discrete networks are in place at CERN to release water, the site drainage network, which receives cooling, meteoric and infiltration water and the sewage drainage network, which receives sanitary and industrial process water. The effluents flowing into the site drainage network are discharged from the CERN sites into watercourses in a controlled way, since the water-quality monitoring programme at CERN includes the continuous monitoring of gamma emitting radionuclides and conventional parameters such as temperature, pH, turbidity, conductivity and presence of hydrocarbons.

Water monitoring station


The weather conditions are monitored by means of several meteorological stations which record temperatures, heat fluxes, wind speeds and directions. Recorded parameters are used to calculate the dispersion coefficients of atmospheric releases by means of widely recognised standards.