Fire control and self-extinguishment by blocking smoke flow with water spray in a tunnel fire

This study clarified the effect of water spray on fire control and extinguishment in a tunnel fire. A series of fire experiments were conducted using a 1:10 scale model tunnel to investigate the performance of water spray for suppressing the fire and blocking the smoke produced by the fire. The water spray trapped the smoke in the fire zone and prevented the inflow of fresh air from the tunnel portal. That is, the water spray sealed off the smoke and compartmentalized it in the tunnel. A calorimetry method was developed to estimate the chemical heat release rate (HRR) in the tunnel with the sealed-off descended smoke. Within the test conditions considered in this study, the following results were obtained. First, self-extinguishment occurred in 86% of the cases tested in the fire zone sealed off by the water spray. Second, the maximum HRR of the vitiated fire induced by the water spray was reduced to one-fifth compared to that during free burning. Finally, a ghosting flame and selfextinguishment by suffocation occurred when the smoke blocking rate exceeded about 60% and 80%, respectively.