## 3 Analysis of Simulation Results
### Visibility Analysis  
Visibility generally refers to the furthest distance at which a person can see an object clearly. SP-PE has obtained an acceptable visibility reference value of about 10 m for a person who can just see the safety exit through the experimental data statistics [30]. Visibility slices are shown in Figure 7. When a fire occurs, smoke mainly affects the floor where the source of the fire is located, and visibility in the vertical direction is much faster  
Figure 5: Temperature distributions of four points with time: (**a**) temperature distribution of point A with time; (**b**) temperature distribution of point B with time; (**c**) temperature distribution of point C with time; and (**d**) temperature distribution of point D with time. than the horizontal direction of the decline. The visibility of the upper floors of the fire is affected the most. The visibility of the fire room in the corresponding room on the fourth floor decreases fastest; the visibility of the stairwell is mainly affected above the third floor; and the closer to the fire, the greater the impact of the visibility of the stairwell. As can be seen from Figure 7, the visibility of the corridor outside the room on fire drops to below 10 m at a fire time of 100.8 s. The visibility of the stairwell on the fourth floor drops to below 10 m at 709.2 s. It is recommended that personnel escape from more than four floors within 709.2 s.  
It can be seen from Figure 7a that, due to the spread of smoke generated by the fire, the visibility of the fire room fell to less than 10 m in 20.4 s. At this time, the smoke in the fire room was in the high temperature role of upward floating to the room on the upper floors, and at the same time, in the four-floor room on top of the fire room, the visibility also fell to less than 10 m, so in the evacuation process of these two rooms, the personnel needed to evacuate within 20 s.  
It can be seen from Figure 7b that, at the time of the fire for 36.0 s, the visibility at the top of the third-floor corridor is extremely low, but in the third-floor corridor, 2 m below the location of the visibility does not affect the personnel escape. At this time, the visibility at the fourth-floor corridor has declined, but the visibility has not yet reached below the threshold, and the visibility of the fire room at the door has been reduced to less than 10 m.  
As can be seen from Figure 7c, at the time of fire for 100.8 s, the visibility of the fourth-floor corridor has been reduced to less than 10 m, and the visibility of the fourth  
Figure 6: CO concentration variation: (**a**) CO concentration variation of point A; (**b**) CO concentration variation of point B; (**c**) CO concentration variation of point C; and (**d**) CO concentration variation of point D.  
floor to the fifth floor of the right side of the stairwell has also been reduced to less than the critical value. At this time, the people who are in the stairwells of the fourth to fifth floors are in a dangerous state and are prone to stampede or congestion. Therefore, within 100 s, people who want to escape from the front stairwells on the fourth to sixth floors need to evacuate as soon as possible; otherwise, they are prone to stampede and other accidents due to insufficient visibility. From Figure 7d, when the fire occurred at 709.2 s, the smoke was covered with the fourth-floor vestibule and the fourth-floor left stairwell, and the visibility of the vestibule was reduced to less than 10 m. It is hard to escape. From the whole fire process visibility slice, it can be seen that, when a fire occurs, the smoke mainly affects the floor where the fire is located and the floors above. Visibility decreases much faster in the vertical direction than in the horizontal direction. On the floor where the fire started, visibility decreased gradually from the roof to the ground.