## 7 Results and Discussion
Furthermore, it can form channels for different kinds of evacuees and reduce the  
Figure 8: The average energy consumption for each electric powered wheelchair of ten iterations in energy units. The error bars represent the min/max values found in the 10 simulations. Figure 7: The average health value of survivors in ten iterations. The error bars represent the min/max values found in the 10 simulations. total evacuation time. Compared with scenarios with homogeneous evacuees, less congestion occurs in [PERSON]'s algorithm and CPN with the distance metric owing to the effect of different speeds, which is similar to the \"faster-is-slower effect\" [52]. This slightly improves the performance of [PERSON]'s algorithm and CPN with the distance metric. CPN with the time metric guides evacuees to the quickest path at the cost of displacing a longer distance. Hence, some aged people or wheelchairs that originate on the second floor may deplete their physical strength or energy and, therefore, causing fatalities. Figures 10-14 show the number of visits of each edge in a scenario with 120 homogeneous evacuees. The thickness of the solid line is proportional to the number of visits. The edges that have not been traversed are shown as dotted lines. Figures 10 and 11, which use the shortest path routing metric, show that the shortest egress path on the ground floor is overused by evacuees. Most evacuees select the identical main channel to egress and cause continuous congestion. In both [PERSON]'s algorithm and CPN with a distance metric, 96% of the evacuees use the main exit in the middle, and only 4% of the evacuees escape from the alternative exit. Figure 12, which employs the shortest time routing metric, shows that several channels are formed on the ground floor to transmit evacuees. This phenomenon does not appear on the other floors, because the corridors on the first and second storey are narrow. Meanwhile, the distribution of evacuees is more balanced between the two exits, with 79% of the evacuees departing from the main exits and 21% of the civilians choosing the alternate exit. Therefore, the probability of congestion is reduced, and the latency in the evacuation process is decreased. Figure 13 shows that CPN with the safety metric initially directs most evacuees on the first and second floors to the central staircases, which are part of the future safest route, because the fire starts near the eastern staircase on the ground floor. The safety metric also adapts the safest path with the spread of the hazard. As can be seen from the ground floor, the main channel is gradually pushed away from the fire source as the fire propagates. Figure 14 confirms that although CPN with the energy metric also employs the congestion ease algorithm, it does not switch routes as frequently as CPN with the time metric. This is because  
Figure 9: The percentage of survivors for scenarios with heterogeneous evacuees. The results are the average of 10 randomized simulation runs, and the error bars show the min/max result in any of the 10 simulations. “CPN with four metrics” depicts the CPN-based algorithm to route four kinds of evacuees with the related metric.