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A team of researchers from the Institute of Science and Concrete Technology of the Universitat Politècnica de València (ICITECH-UPV) has developed a system consisting of optical fibre sensors and the methodology necessary for its distribution in tunnels, which aims to facilitate the detection of fire inside tunnels and indicate where and how to intervene more effectively.

This work, whose results have been published in the journal of Tunnelling and Underground Space Technology and in the Fire Safety Journal, is a significant improvement in the safety of tunnel infrastructures, in addition to reducing both the time they would remain closed and the resulting financial losses.

Monitoring by sections depending on the temperature

The method developed by UPV researchers is based on the monitoring of temperatures by sections in the tunnel. Ignacio Payá, ICITECH-UPV researcher, points out that "in this way, we are able to identify the evolution of the temperature at each point of the tunnel -information that is not provided by current methods- as well as exposure times to the highest temperature".

It reduces costs and streamlines a quick recovery and the reopening of traffic to the tunnel

In addition to offering relevant information to rescue teams, this methodology is especially important for a rapid "recovery" of the tunnels and their reopening to traffic.

Paula Rinaudo, also a researcher at the ICITECH-UPV, notes that "once the fire is extinguished, the system provides a comprehensive assessment of the residual resistance of the tunnel and limits the areas in which engineers must act so that the tunnel is operational as soon as possible.

"This way," she adds, "it reduces both investment and the time needed for repair and, ultimately, decreasing the number of days that the tunnel is closed".

A study validated in the Virgolo tunnel (Bolzano, Italy)

For the development of the system, UPV researchers have used computational fluid dynamics techniques and statistical and multi-objective optimisation methods.

The methodology was validated through its implementation in the Virgolo tunnel (Bolzano, Italy). Where, according to Rinaudo, "we recorded temperatures in 16,000 control points for 18 fire scenarios. Subsequently, we analysed up to 100 different configurations of sensors distribution."

During the study, the team analysed different types of fires, from one caused by a car crash to another generated by a tanker truck. From this analysis, they obtained a set of guidelines applicable to each case.

Specially designed optical fibre sensors

Different types of sensors capable of measuring high temperatures can be used for the system developed. However, researchers believe that optical fibre sensors are particularly suitable for this purpose.

In that sense, Pedro Calderon (ICITECH-UPV), explains that "optical sensors can be multiplexed, allowing multiple sensors in a single cable which simplifies and reduces the cost of the installation. In addition, optical sensors are immune to electromagnetic interference, which allows installing them in places where conventional (thermocouples) do not work, such as electrified railway tunnels".

Temperatures up to 1,230 ºC recorded

This type of device, which allows recording temperatures of up to 1,230 ºC, has been developed and patented by a multidisciplinary team of researchers from ICITECH-UPV -Paula Rinaudo, Benjamín Torres, Pedro Calderón and Ignacio Payá- and by the Institute of Telecommunications and Multimedia Applications (ITEAM-UPV) -Salvador Sales and David Barrera-.

The development of this work has been funded by the Ministry of Finance and Competitiveness.

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