A simple model for predicting the smoke spread length during a fire in a shallow urban road tunnel with roof openings under natural ventilation. (March 2021) - Tanaka, Futoshi
Abstract: When a fire occurs in a road tunnel with roof openings, smoke generated by the fire is exhausted through the roof openings in the ceiling by natural buoyancy of the hot smoke, and as a result, the smoke spread length in the tunnel is limited. In this study, we conduct fire experiments using a 1:10 scale model tunnel with roof openings of a 10% opening ratio, and propose a simple model for predicting the smoke spread length in the tunnel based on the results of the experiments. A constant smoke spread length is both observed in the fire experiments and predicted by the simple model. Sensitivity analysis on the effects of the parameters used in the simple model on smoke spread length clarifies the dominant parameters. Furthermore, we clarify that the smoke spread length is decided by a balance between inertia and buoyancy in the hot smoke flow and the inertia of fresh cold air flow induced by the fire. Highlights: A simple model is developed for estimating the smoke spread length in tunnel fires. The effectiveness of the model is validated by scale model tunnel fire experiments. Constant smoke spread is obtained regardless of the heat release rate of fire. Sensitivity analysis clarifies the parameters governing the smoke spread length.