Effects of the Ventilation System by Using Jet Fans during a Fire in Road Tunnels

People inside a road tunnel may be in grave danger if there is a fire. When a fire is developing, mechanical ventilation can be crucial in protecting occupants and facilitating the arrival of emergency crews. In this paper, a new calculation method that can analyze the evolution of the fire and of the airflow is illustrated. An assumed fire inside an 800 m long one-way road tunnel in Northern Italy was dealt with using the developed method. Subsequently, the acquired results were successfully compared to those of numerical modeling. By varying the position of the fire inside the studied tunnel, it was then possible to detect situations of high risk for the people when the fire is located at a limited distance from the upstream entrance. The newly developed calculation procedure was then able to verify how a simple different positioning of the pairs of jet fans inside the tunnel can eliminate the risks that people intent on escaping towards the upstream entrance can be reached by the fire fumes (back-layering phenomenon). It can therefore be a useful tool to improve the jet fan design in one-way road tunnels in accordance with safety principles.