A simple model for predicting the smoke spread length during a fire in a shallow urban road tunnel with roof openings under natural ventilation

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.

Automated summary

This study investigates the mechanism of smoke spread length during tunnel fires with roof openings, revealing a constant smoke spread length observed in experiments and predicted by a simple model. A sensitivity analysis clarifies the dominant parameters affecting smoke spread length, showing that it is determined by a balance between inertia and buoyancy in the hot smoke flow and the inertia of fresh cold air flow induced by the fire.