# Integrating Decentralized Indoor Evacuation with Information Depositories in the Field
## 4 Evacuation Simulation Model
### Evacuation Simulation  
There are mainly four components in the evacuation simulation (Figure 5): the route graph, the emergency event, the mobile agents and the depositories. The route graph represents the indoor space  
Figure 4: Layout of each level from the ground floor (at the bottom) to the roof (at the top). Red points represent the locations of information depositories for DepotSt. Green points represent the locations of the information depositories for DepotCr. of the building. All the edges are unblocked before the emergency. The emergency event acts as a stimulus that changes the states of the edges in the route graph. The emergency event and the route graph together create a route graph with changing states over time, which forms the ground truth of the dynamic indoor environment in the simulation. Each mobile agent senses the dynamic changes by visiting certain part of the environment, and keeps a partially out-of-date version of this graph, which forms their local knowledge. Their local knowledge can also be updated by the short-range communication with encountered peer mobile agents and depositories. Information depositories also save a local version of the dynamic graph, but they cannot sense the blocked edges and are immobile. Information depositories are considered to be set up before any event, as a fix part of the infrastructure of a building. In contrast to any centralized communication infrastructure, local depositories are robust towards any type of event and capacity. In this simulation, mobile agents are only blocked by blocked edges. Since this paper assumes that the density of evacuees is low, the effect of congestions between mobile agents will not be considered. The route graph, the simulated emergency events, the locations of mobile agents, and the locations of depositories have been predefined and saved to files, so that each pair of comparison simulations refer to identical experiment conditions. The agent-based simulation tool Repast Simphony has been used. Figure 6 shows a flow chart of the simulation process. Before an emergency, the states of edges in the (global) route graph are unblocked, and the mobile agents are placed at predefined locations. All the mobile agents are initialized with the complete graph of the building as their prior knowledge. Evacuees are assumed to start evacuation simultaneously and immediately after the emergency alarm. The emergency event expands every two steps, and affects certain edges of the (global) graph, making them blocked. Also the information depositories will be destroyed if the emergency event expands to where the depository locates. The independence of each depository contributes to the robustness of the \"system\". Figure 5: Evacuation simulation model. A square with a capital letter M represents a mobile agent. A circle with a capital letter D represents a depository. The flow in Figure 6 describes necessarily a simplified model of human behavior. In a real evacuation scenario, people may not evacuate immediately after they hear the emergency alarm, which causes pre-evacuation delays. The start time of evacuation for each evacuee is uncertain, and can be affected by physiological and psychological factors. For example, some people may insist on gathering family members (known as kin behavior [71]) before they start evacuation. Such human behavior aspects are not modeled in this paper since they would add some noise to the results, conflicting with a desire to control the parameters of a simulation for comparison purposes. Figure 7 describes the subprocess of how a mobile agent acts in each step. Each mobile agent who has not finished the evacuation tries to compute a shortest path from the current local knowledge. Figure 6: The process of evacuation simulation for all the mobile agents. If no path is available, evacuation of this mobile agent is considered to be failing, otherwise this mobile agent tries to move along the evacuation path for 1.5 m unless it encounters blocked edges.