Investigation of the Performance of Emergency Ventilation Strategies in the Event of Fires in a Road Tunnel — A Case Study

Abstract

A study has been conducted at the National Research Council of Canada to evaluate the effectiveness of in-place emergency ventilation strategies to control smoke spread in the event of a fire in the Louis-Hippolyte-La Fontaine road tunnel. Some of these strategies date back to the design of the tunnel in 1964. Following a recent fire, the operating instructions have been revised. A scientific-based numerical and experimental evaluation of these operating instructions is the main objective of this paper. The numerical evaluation uses the fire dynamics simulator (FDS) model to investigate smoke ventilation in tunnels. The experimental evaluation is used to provide the necessary initial and boundary conditions for the numerical solutions. A parametric study is performed, using the FDS model, assuming a heat source of 20 MW in the tunnel. Two fire scenarios, deemed to cover the two main situations likely to occur in the tunnel, are simulated. The parameters examined are the capacity of ventilation fans and the percentage opening of the vent dampers. The results of the numerical analyses indicate that the phenomenon of `backlayering' does not occur in all simulated cases. Backlayering is the situation in which smoke moves against the provided ventilation upstream of the fire creating an environment that poses a danger to both tunnel users and emergency responders. While the existing ventilation strategies are, in general, deemed acceptable, this article proposes recommendations to further improve the performance of tunnel ventilation. These recommendations have inspired the tunnel authorities to conduct a series of feasibility studies to re-engineer the ventilation system and refit the service galleries to improve the safety level for means of evacuation of the tunnel.