The effect of Air Flow Rate on Smoke Stratification in Longitudinal Tunnel Ventilation

The construction of tunnels is associated with mining. For safety and suitable working conditions, it is necessary to ensure that there is suitable ventilation during construction. During operation, tunnels form the infrastructure of the area, which has a number of characteristics. Tunnel ventilation is designed with regards to many different factors. Longitudinal ventilation is especially used in one-way, extra-urban tunnels but in some cases also in urban or two-way tunnels. The article describes the purpose and types of tunnel ventilation, focusing on longitudinal ventilation and ventilation design strategy. Longitudinal tunnel ventilation is the cause of significant turbulence that affects the smoke stratification. The article compares different tunnel ventilation options in terms of selected strategies and the different values of applied airflow rates. A case study was conducted on the Klimkovice road tunnel in the Czech Republic using the fire model from the Fire Dynamics Simulator. The study compares the effect of airflow rate on smoke stratification. The study was conducted with air flow rate values of 0 to 5 m.s(-1). The results of the study show that even with lower airflow rates, the smoke build-up is so significant that the safety of individuals in the tunnel cannot be ensured. The dynamicity of fire is also an important factor. Opting for a lower airflow rate strategy because of higher expected congestion or other factors is a questionable practice. Greater airflow rates, however, create better conditions for evacuating individuals, although it is also necessary to combine smoke stratification options with the selected ventilation strategy.