*4.1. Optimum Number of Cross Passages Open*

*4.1. Optimum Number of Cross Passages Open*  When a fire occurs in the main tunnel, 2 m/s longitudinal ventilation will be provided, and 1.3 m/s pressurized wind speed will be applied at both ends of the service tunnel. With the number of cross passages open increasing from one to four, the variation of airflow is detected in Figure 3. When only one cross passage is open, the upstream ventilation velocity in the accident tunnel is stable at about 2 m/s, while airflow speed at the intersection of the cross passage and accident tunnel reaches 12 m/s. In addition, the longitudinal ventilation velocity of the main tunnel downstream maintains at 4.7 m/s. As shown in Figure 3a,b–d, the longitudinal wind speed from the tunnel entrance to the first cross passage is basically stable, as the number of cross passages increases. However, velocity is unstable at the intersection of channels, due to chaotic turbulence, gradually sta-When a fire occurs in the main tunnel, 2 m/s longitudinal ventilation will be provided, and 1.3 m/s pressurized wind speed will be applied at both ends of the service tunnel. With the number of cross passages open increasing from one to four, the variation of airflow is detected in Figure 3. When only one cross passage is open, the upstream ventilation velocity in the accident tunnel is stable at about 2 m/s, while airflow speed at the intersection of the cross passage and accident tunnel reaches 12 m/s. In addition, the longitudinal ventilation velocity of the main tunnel downstream maintains at 4.7 m/s. As shown in Figure 3a,b–d, the longitudinal wind speed from the tunnel entrance to the first cross passage is basically stable, as the number of cross passages increases. However, velocity is unstable at the intersection of channels, due to chaotic turbulence, gradually stabilizing at 4.5~4.7 m/s when reaching downstream.

bilizing at 4.5~4.7 m/s when reaching downstream. In this paper, cross passages are used for the evacuation of people, as well as ventilation. In order to prevent fire smoke from spreading into cross passages, the wind speed in passages has been stipulated to be between 1.5 m/s to 8 m/s by TB 10068-2010 [28]. In fact, as airflow velocity in the cross passage exceeds 5 m/s, evacuation efficiency will be negatively affected; therefore, it is necessary to optimize the number of cross passages open when addressing the issue of smoke control. After simulation, when one cross passage is open, velocity exceeded 8 m/s. When two cross passages are open, the velocity was between 4 m/s and 7 m/s. Average wind speed reached from 1.5 m/s to 5 m/s when CP1, CP2 and CP3 were open. With all four cross passages open, average wind speed in CP3 and CP4 are less than 1.5 m/s, which does not satisfy the safety evacuation requirement. In this paper, cross passages are used for the evacuation of people, as well as ventilation. In order to prevent fire smoke from spreading into cross passages, the wind speed in passages has been stipulated to be between 1.5 m/s to 8 m/s by TB 10068-2010 [28]. In fact, as airflow velocity in the cross passage exceeds 5 m/s, evacuation efficiency will be negatively affected; therefore, it is necessary to optimize the number of cross passages open when addressing the issue of smoke control. After simulation, when one cross passage is open, velocity exceeded 8 m/s. When two cross passages are open, the velocity was between 4 m/s and 7 m/s. Average wind speed reached from 1.5 m/s to 5 m/s when CP1, CP2 and CP3 were open. With all four cross passages open, average wind speed in CP3 and CP4 are less than 1.5 m/s, which does not satisfy the safety evacuation requirement. Therefore, when a fire occurs in a tunnel, the three cross passages closest to upstream of the fire source should be open for smoke control.

Therefore, when a fire occurs in a tunnel, the three cross passages closest to upstream of

the fire source should be open for smoke control.

**Figure 3***.* Velocity distribution with different numbers of cross passages open: (**a**) One cross passage open; (**b**) Two cross passages open; (**c**) Three cross passages open; (**d**) Four cross passages open. **Figure 3.** Velocity distribution with different numbers of cross passages open: (**a**) One cross passage open; (**b**) Two cross passages open; (**c**) Three cross passages open; (**d**) Four cross passages open.

### *4.2. Optimum Ventilation Quantity of Service Channel 4.2. Optimum Ventilation Quantity of Service Channel*

The distribution of smoke movement and airflow velocity, with three cross passages open, were analyzed at ventilation velocities of 0.7 m/s, 0.75 m/s, 0.85 m/s, 1.0 m/s and 1.3 m/s, at both ends of the service tunnel. Figure 4 compares the accident tunnel velocities at a height of 2 m, under a service tunnel wind speed from 0.7 m/s to 1.3 m/s. As reflected in the figures, velocities near the fire source increased with service tunnel wind speed; velocities in the cross passages were all less than 8 m/s, under different working conditions. Of note, the average wind speed in some cross passages was less than 1.5 m/s in airflow velocity conditions of 0.7 m/s, 0.75 m/s and 0.85 m/s; therefore, it is necessary to reconsider tunnel ventilation design systems, in order to ensure the effectiveness of fire smoke control in tunnel ventilation. The distribution of smoke movement and airflow velocity, with three cross passages open, were analyzed at ventilation velocities of 0.7 m/s, 0.75 m/s, 0.85 m/s, 1.0 m/s and 1.3 m/s, at both ends of the service tunnel. Figure 4 compares the accident tunnel velocities at a height of 2 m, under a service tunnel wind speed from 0.7 m/s to 1.3 m/s. As reflected in the figures, velocities near the fire source increased with service tunnel wind speed; velocities in the cross passages were all less than 8 m/s, under different working conditions. Of note, the average wind speed in some cross passages was less than 1.5 m/s in airflow velocity conditions of 0.7 m/s, 0.75 m/s and 0.85 m/s; therefore, it is necessary to reconsider tunnel ventilation design systems, in order to ensure the effectiveness of fire smoke control in tunnel ventilation.
