## 3 Results and Discussion
Figure 21: CO contours (ppm)—cross section through the door of the PSD system near the fire outbreak (minutes 5–20). Figure 13:0 CO\({}_{2}\) contours (ppm)—cross section through the door of the PSD system near the fire outbreak (minutes 1–4). As can be seen, the frame of the PSD system (at the top of the door to the ceiling) has a role as important as the part between the two consecutive doors. It represents a physical barrier that blocks the access of smoke generated by fire to the platform. Figure 13:1 CO\({}_{2}\) contours (ppm)—cross section through the door of the PSD system near the fire outbreak (minutes 5–20). On the other hand, it is worth mentioning that the buoyancy effect of the smoke generated by the fire is well represented by the results from this section, located at 2 m from the fire outbreak. In addition, although no UPE device is in this section, the contribution of the UPE system to limiting the spread of smoke toward the platform can be clearly noticed. Additional analyzes were performed to verify that air flow occurs entirely from the station to the tunnel to prevent smoke from entering the platform. Therefore, air velocity vectors are studied in a horizontal plane through the top of the PSD system, in the center of the station (Figure 24). It can be seen that the velocity vectors are oriented everywhere from the platform in the direction of the tunnel. In addition, air velocity vectors are analyzed in the cross section through the door of the PSD system near the fire outbreak (the same section from Figures 18-23)--Figure 13:2 The direction of air flow through the open door is clear: from the platform towards the tunnel and further to the evacuation above the train and under the platform. Finally, in order to have a complete image of the situation in the subway station during the considered emergency situation, 3D representations (Figures 26-28) are considered that capture the distribution of hot air and pollutants from the fire outbreak towards the ventilation devices. Based on the results concerning all three monitored parameters (temperature--Figure 26; CO concentration--Figure 27; CO concentration--Figure 28), it can be seen that the hot and polluted air near the fire outbreak is directed to the left due to the air flow entering the station from the connecting tunnels and not towards the ventilation devices located above the fire outbreak. Despite this asymmetrical spread, the efficiency of emergency ventilation remains very good, as the smoke does not reach the  
Figure 13:3 Air velocity vectors (m/s)—longitudinal section at the top of the PSD system (minute 20). Figure 13:4 Air velocity vectors (m/s)—cross section through the door of the PSD system near the fire outbreak (minute 20). evacuation area. Moreover, air velocity vectors are presented in Figure 29, in a horizontal plane between the subway train and the ceiling. It can be noted that there is a correlation between the air flow in this area and the tendency of hot air and pollutants to move towards the ventilation devices located up high, on the left-side of the fire outbreak. Figure 13:5 Temperature distribution (\({}^{\circ}\)C)—area above the fire outbreak. Figure 13:6 CO distribution (ppm)—area above the fire outbreak. Figure 13:7 CO\({}_{2}\) distribution (ppm)—area above the fire outbreak.