# Integrating Decentralized Indoor Evacuation with Information Depositories in the Field
## 1 Introduction  
When disasters strike, such as a fire, a gas leak, a chemical spill, an earthquake, a flooding, or a roaming sniper, the first and foremost action is to get people out of the disaster area. This paper focuses on those evacuees who find themselves without organized help when the alarm goes off. For them, environmental knowledge, knowledge about the dynamically changing event, and thus some risk awareness in their decision making is essential [1]. For these situations, decentralized evacuation has been embraced by recent research due to its robustness and scalability [2; 3]. In decentralized evacuations evacuees are guided by their smartphones that are acquiring environmental knowledge and risk information as the evacuees explore the environment. These smartphones are sharing their collected knowledge by peer-to-peer communication with other smartphones within communication range. Decentralized evacuation has the advantage that no further infrastructure is required, i.e., it is applicable in any environment. In simulation, it has proven to work well where there are good chances that evacuees come into communication range with each other. In reality, however, the chance that evacuees encounter may be low due to the following facts. * Encounters happen when two people walk in opposite directions; however, in evacuation situations people tend to move in similar directions, i.e., from their current positions to where they guess the closest exit is. * Even when people move towards each other, for example, trying to get to the same staircase from opposite directions, they may still miss each other if one person reaches the staircase earlier than the other. More formally, even if their two trajectories have a joint point in space, they still can miss each other by time. * High density of evacuees, although desirable in the context of exchanging knowledge, is also leading to congestions and panic situations [4], and thus risk-aware evacuees might actively avoid crowded spaces. The success of a single evacuee depends on up-to-date knowledge of the dynamics in the environment. A recently proposed 'fading memory' method, distrusting older knowledge, introduces some aspects of risk awareness, and generally improves evacuation success [2]. However, the fading memory method produces can even decrease evacuation success when older information is discarded that is still valid. The research question of this paper is how to effectively maintain the spatial and temporal information of the dynamic environment within the environment, and how to robustly keep evacuees updated. To bridge the spatial and temporal gaps in the communication of single evacuees in decentralized evacuations, and inspired by ants that communicate by pheromone traces that keep being updated by passers-by, this paper suggests information depositories in the field for decentralized evacuation. Information depositories enable the environment to maintain information and interact with passing-by evacuees. They record and update the environmental and risk information deposited by passing-by evacuees, and provide this information to later passers-by. They are sharing points in the environment for evacuees passing the same location at different times, enabling asynchronous communication [5; 6]. Thus information depositories add to peer-to-peer communication, can address all three challenges listed above, and therefore are expected to produce better evacuation outcomes. The hypothesis is that even a small number of information depositories will enhance risk awareness of evacuees and improve the evacuation results. The hypothesis will be verified through agent-based simulation by adding information depositories to a decentralized evacuation of an indoor environment. Simulation results will be evaluated with the success rates of evacuees, the number of steps required to exits, and the amount of knowledge that has been updated. The contributions of this paper are as follows.