Quantification of influencing parameters on plug-holing and smoke extraction efficiency for multi-point lateral vents in tunnel fires

In tunnel smoke extraction systems, the multi-point lateral vent configuration is critical for fire emergencies. However, variations in the fire heat release rate and the vent layout often cause non-uniform plug-holing at individual vents, which reduces the smoke extraction efficiency. To address this challenge, a theoretical method was developed to identify and quantify plug-holing. Using the Fire Dynamics Simulator (FDS), plug-holing during the fire stable stage was investigated in a three-lane submerged tunnel with multi-point lateral vents. The analysis reveals how the smoke extraction rate, the vent aspect ratio (width-to-height), the vent spacing, and the vent installation height together govern the plug-holing magnitude under different vehicle fire scenarios. Furthermore, a mathematical correlation between the plug-holing magnitude and the smoke extraction efficiency was established. The results show that the vent installation height and aspect ratio influence plug-holing more strongly than the smoke extraction rate. The plug-holing magnitude follows a multivariate power-law relationship with the governing parameters and is inversely correlated with the smoke extraction efficiency. Keeping the plug-holing magnitude below 0.4 is essential for maintaining a high smoke extraction efficiency. The proposed criteria, quantification method, and mathematical correlation provide a theoretical basis for optimizing tunnel smoke extraction systems and offer practical guidance for enhancing fire safety.