Performance validation of a hybrid ventilation strategy comprising longitudinal and point ventilation by a fire experiment using a model-scale tunnel

•We conducted tunnel fire experiments using a model-scale tunnel.•We examined the exhaust performance of a hybrid strategy in a tunnel fire.•The hybrid strategy maintained a safe environment on both sides of the fire.•The smoke height remained constant even when the smoke extraction rate was varied.•We derived the correlation for predicting the smoke height.

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire.