Effects of Ventilation and Water Spray in a Model-Scale Tunnel Fire

At the present time, eight new long tunnels are currently being constructed in Taiwan and plan to utilize sidewall sprinkler nozzles to conduct fire protection. To explore the effect of ventilation and water spray on tunnel fires, this research used a 1/5.5 model scale tunnel to perform experiments, while using a heptane oil pan of 0.45 m diameter as the fire source. Under five different ventilation velocities, the cooling effects of water spray on tunnel fires was discussed while controlling the water density at 2.3 mm/min. The critical velocity without water spray was 1.24 m/s, which fits empirical equations by past research. Under a ventilation velocity of 0.87 m/s, the smoke backlayering would be 2 m without water spray, while none was present with water spray. Overall quantitative analysis shows the significance of water spray in affecting backlayering, and it can be acknowledged that water spray can prevent backlayering from larger fires under the same velocity. This research used visual and temperature measurement methods to determine the location of backlayering, and it is recommended that maximum temperature gradient be used in future research as the basis for smoke backlayering location.