To improve fire detection methods in the underground railway link passing through Milan, Metropolitan Milanese Spa (MMS) has installed two Distributed Temperature Sensing (DTS) systems from York Sensors. The systems monitor temperature in an extension to Milan’s current underground transport complex, providing a rail link which will connect the north-west of the city to the city centre.
Phase one includes four underground stations connected with the surface public railway stations and over 6km of two way train tunnels.
MMS which has overall responsibility for the project, decided to employ fibre optic distributed temperature monitoring for continuous temperature profiling all the way along the underground link, for fire detection and ventilation control purposes.
Two DTS800 units, one placed in Lancetti station and the other in Repubblica, have been supplied to monitor the temperature of 18km of optical fibres. Each unit is connected to three loops of optical fibre.
Standard telecommunication grade optical fibre cables, low smoke and zero halogen type, are installed on the ceiling of the tunnels and inside the stations.
Using optical fibres as a continuous temperature sensor results in immunity from high EMI that usually affects underground railway tunnels.
Temperature data from the stations and tunnels are arranged into zones: there is a zone for each railway in each tunnel and in each station. For each zone the relevant DTS800 system gives the maximum temperature and its position, as well as the average zone temperature. Temperature alarms are currently set at a threshold of 308 degrees C (warning) and 508 degrees C (alarm). Other alarms are set to signal a sensor cable break, and monitoring system faults.
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