Experimental and numerical investigation of longitudinal ventilation velocity and heat release rate on temperature distribution in highway tunnel fires

Abstract Although tunnel fires are relatively infrequent, the unique, elongated, and nearly enclosed structure of tunnels exacerbates fire hazards, and their occurrence can result in catastrophic losses, necessitating effective fire safety management. This study examines the characteristics of smoke spread and temperature attenuation in highway tunnel fires under varying heat release rates and longitudinal ventilation velocities, specifically focusing on conditions of traffic congestion. By utilizing a combination of scaled-model experiments and analytical modeling, the research highlights that smoke generated in tunnel fires travels along the tunnel length, with its dispersion heavily influenced by both heat release rates and the presence of congested vehicles. In scenarios without ventilation, smoke ascends to the tunnel crown and propagates symmetrically toward both ends, while the movement of congested vehicles does not significantly affect smoke transport. The introduction of longitudinal ventilation significantly mitigates upstream smoke movement, leading to reduced maximum temperatures near the fire source and preventing smoke recirculation, especially critical during traffic congestion when evacuation routes may be limited. The study identifies critical wind speeds necessary for effective smoke management, revealing that these speeds increase with higher heat release rates. Initial increases in ventilation velocity may temporarily elevate temperatures due to enhanced combustion; however, further increases result in a predominant cooling effect that lowers overall tunnel temperatures. Additionally, the temperature distribution is asymmetrical, with downstream temperatures rising as heat release rates increase. A temperature decay model for tunnel crowns was developed, demonstrating a strong correlation with experimental data and underscoring the effectiveness of longitudinal ventilation in managing high temperatures and controlling smoke flow during tunnel fire incidents, particularly in congested traffic conditions.