Simulation of an Evacuation into an Escape Buildings during a Tsunami Event
4. Experimental Results and Discussion
The results of the simulations indicated that the entrance of the shelter affect the rate of the evacuees entering the shelter (rate of survival) when the rate of the incoming evacuees at the shelter is more than the capacity of the entrance. This can be seen from the comparison between the rates of survival with the rate of the evacuees that passed an imaginary line 20 m in front of the entrance (unaffected by the entrance) as is indicated by Figure 2.
Figure 1. Lay out of the simulation
Obstacle
Figure 2. The effect of narrow entrance of a shelter on the flow of evacuees
Figure 2 indicates that the flow of evacuee that was unaffected by the entrancewas higher than that at the entrance which consequently prolong the evacuation process. The wider entrance (2.5 m) provides significantly higher survival rates when compare with the 1.5 m width of entrance. The constant rate of the 1.5 m entrance width starting from 50 seconds was due to the congestion in front of the entrance which resulted in an almost constant supply of evacuees. From Figure 1 it can be deduced that the 2.5 m and 1.5 m entrances have delayed the evacuation process by 51% and 130%
respectively. An example of simulation where the rate of arrival at the shelter was higher than the entrance capacity was given by Triatmadja and Benazir (2015). They showed that the escape building at GampongPie, is capable of catering 500 evacuees as designed. However when more than 1000 people were evacuating into the shelter, a traffic jam in front of the shelter should be anticipated. This situation may happen in real evacuation condition when people arrive at the shelter almost at the same time.
The flocking of the people near the entrance affects the survival rate significantly especially when the center of the flock was relatively close to the entrance.
Indeed there can be various pattern of flocking and that more simulations should be carried out to find out the statistics of such effect. Other possibilities such as the random placement of evacuees within the shelter seems only slightly hinder the survival rate.
This was due to the size of the simulated shelter which actually can accommodate more than twice of the total evacuees. Placing the final positions of the evacuees near the walls away from the entrance gave the quickest entrance process and should be an ideal situation. Figure 3 shows the final positions of the evacuees inside the shelter after 440 seconds.The random final positions of evacuees somehow hinder the flow of the evacuees into the shelter. The flock of the evacuees near the entrance clearly obstructs the flow through the entrance whilst the final positions away from the entrance clearly the best situation with regard to the flow of the evacuees. As indicated by Figure 4 that the flocking of evacuees near the entrance reduced the survival rate especially after most of the evacuees (700 out of 1000) have entered the shelter.
Figure 3. Final positions of the evacuees. (a) Fifty percent of the evacuees prefer to stop near the entrance, and (b) random, (c) away from the entrance.
Figure 4. Example of the effect of final destinations of the evacuees inside the shelter on the number of survivals. Number of evacuees 1000, size of shelter 34 x 34 m2.
The flocking of the evacuees near the entrance made the survival rate even worst if the size of the shelter was relatively smaller. When the evacuation was simulated using a smaller shelter area (24 by 24 m) the flocking behavior proved to be very damaging in term of survival rate as can be seen in Figure 5. In addition, the effect of the random final destinations on the survival rate was more significant for relatively smaller shelter area. As expected, the behavior of stopping near the wall away from the entrance was not affected by the smaller size of the shelter. As can be seen in both Figure 4 and Figure 5, all of the evacuees have survived after approximately 240 seconds.
(c) (b)
(a)
Flocking start to hinder evacuation
Figure 5. Example of the effect of final destinations of the evacuees inside the shelter on the number of survivals. Number of evacuees 1000, size of shelter 24 x 24 m2
5. Conclusion
We have simulated the effect of shelter’s entrance on the rate of survival, the effect of evacuees’
final positions within the shelter, and the effect of flocking behavior near the entrance. Although the results of the simulation depend on a number of variables that were not taken into account or were assumed in the simulations such as the rate of incoming evacuees at the shelter, the simulations suggested that the size of the entrance and the final positions chosen by the evacuees clearly affect the survival rate.
6. Recommendations
1. The size of the shelter should be designed much larger than the size of the floor packed by the expected number of evacuees.
2. The entrance capacity should be made wide enough to reduce the possibility of traffic jams at the entrance
3. A sufficiently large area near the entrance should be freed from evacuees. This area should be marked with different alarming color such as red (no stop), yellow (may slow down) and green (recommended for stopping and rest).
4. Automatic guidance within the shelter should be provided. This guidance (loud speaker announcing that people should stay near the walls away from the entrance and not to occupy the red zone or the red floor) may be set on if a number of people stand near the entrance.
5. Education on evacuation related to entering and stopping in the shelter should be provided to the people.
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