Implementation of a complex monitoring system to track people in the ATLAS detector

ATLAS is one of the four large experiments at the Large Hadron Collider at CERN. The detector itself and the surrounding structures in the cavern of the experiment are accessible for people during maintenance periods. People can easily be isolated and difficult to localize in which case their safety may be compromised in this very complex environment. Therefore a dedicated system called ¿Finding Persons Inside ATLAS Areas¿ has been designed and implemented to track persons in the experimental cavern. It is based on a network of passive infrared sensors which are read out by specific front-end electronics. A complex software architecture provides active tracking of people in the cavern with the possibility to detect abnormal situations where people are possibly in danger. This paper describes the technological choices which have been made for this monitoring system and explains the implementation of the software components. This provides a tool for the operation in the control room of ATLAS to actively follow people in the cavern underground. As the system is data-driven, it can be easily adapted to other environments where similar safety problems exist.