The effect of traffic blockage on fire smoke spreading and safety escape in highway tunnel

When a traffic accident causes a fire in a highway tunnel, traffic congestion may hinder the spread of smoke and the ability to escape safely. In this paper, FDS and Pathfinder software are used to examine the impact of a vehicle blocking on critical wind speed, tunnel vault temperature, and safe tunnel egress. Using FDS software, the effect of different blocking vehicle sizes on the critical wind speed was analyzed when the surface area of the fire source was held constantly. It was discovered that the lower the critical wind speed is, the greater the tunnel's blocking area is. For a given fire scale, the higher the tunnel's blocking ratio is, the greater the critical wind speed reduction ratio is. The higher longitudinal ventilation velocity and the greater shielding effect of a higher vehicle on the fire source can reduce the vault's temperature, reduce the tunnel's heat accumulation, and safeguard the tunnel's structural integrity. Pathfinder was utilized to investigate the effects of stair pitch, resting platform, and stair spacing on evacuation time. The results indicate that the shortest evacuation time occurs when the stair slope is set to 30°. When compared with the original design of 80 m stair spacing, the 60 m spacing reduces evacuation times by more than 10%. It is more conducive to the safety of personnel. This paper enriched the research on tunnel smoke dispersion, which is useful in designing tunnel fire escape systems.