Dynamics of harmful factors in inclined road tunnels according to the results of numerical modeling of up to 50 MW fires in terms of natural ventilation

The present paper explores the change of the harmful factors by means of full-scale numerical models. In the numerical models, the tunnel length is 400 m; the slope gradient varies within 0-9%, with a 2% step; and the heat release rate is within 5-50 MW. The outdoor air temperature on the models was assumed to be 20℃, while the pressure difference between the portals on different models varied depending on the slope, and the variation range was 50-400 Pa. The modeling results show that the propagation of the harmful factors is characterized by stabilization as demonstrated by the fact that the distance of descending propagation of the harmful factors decreases for each specific tunnel gradient and eventually shows a pronounced asymmetry with respect to the seat of fire. This confirms the preferential and pronounced ascending movement of the ventilation flow with toxic products of combustion. Thus, the worst results during the natural ventilation are expected for ascending flows. Based on the isolines of temperature, as well as the concentrations of carbon monoxide and oxygen, the gradient factor can be calculated, which can be used to design ventilation systems for engine tunnels, ensure their safe operation and save human lives during the fire.