Flow Resistance of Fires in Road Tunnels

The ventilation of longitudinally ventilated road tunnels must be designed in such a way that the smoke gases resulting from a fire can be discharged to one side in such a way that people can escape to safety. There is growing evidence that design guidelines do not take into account all the effects of a tunnel fire. In particular, this is the case for the so-called "throttling effect." This effect describes the accelerated flow at the tunnel ceiling due to smoke and temperature stratification, which increases the pressure loss and thus the ventilation encounters more resistance. With the help of CFD simulations and large-scale fire tests in a 600-meter test tunnel in Spain, this effect is to be tracked down and, based on the results, the guidelines are to be reviewed and adapted if necessary. The project is funded by the Swiss Federal Roads Office (FEDRO), runs until the end of 2026 and is being carried out in collaboration with Riess Ingenieur-GmbH.