## 1 Introduction  
Recent advances in MEMS (Micro Electro Mechanical Systems) and microprocessor and wireless communication technologies have enabled the deployment of large-scale sensor networks, where thousands or even tens of thousands of small sensors are distributed over a vast field to obtain sensing data. Sensor networks have attracted significant attention as important infrastructure for data collection in an environment for pervasive computing. In this field, wireless sensor networks play a special role in home automation, environmental monitoring, military, health, and other applications. In particular, wireless sensor networks have important applications in hazardous areas such as battle fields or disaster areas, where access by humans is difficult. However, in addition to being dangerous for humans, the hazards in these areas might also threaten sensor nodes, which are often physically fragile. Usually, sensor nodes are designed to be cheap, very small, and use very limited resources. Therefore, they should not be regarded as strong enough to resist a physical impact. This fragile characteristic of sensor nodes makes a wireless sensor network vulnerable to the hazards in such areas. If some of the sensor nodes in a wireless sensor network deployed in a hazardous area become damaged and can no longer work properly, the data from the area covered by these damaged sensor nodes cannot be collected properly. Therefore, these sensor nodes should be repaired or covered by other sensor nodes. Moreover, the damaged sensor nodes could also obstruct the sink node from collecting data from behind the area of the damaged sensor nodes because these sensor nodes are not only data sources but also routing (relaying) nodes for other source nodes. For example, in Figure 1, when a hazard (fire) occurs in the sensor network (Figure 1a), some sensor nodes (sensor nodes 11-13) fail, and thus, these nodes are no longer able to forward data from other sensor nodes (sensor nodes 15-24) in the lower part of the routing tree (Figure 1b). In this case, although only 3 sensor nodes (sensor nodes 11-13) fail and the child nodes (sensor nodes 15-24) of these sensor nodes are still working properly, packets from the child nodes (sensor nodes 15-24) are not able to arrive at the sink node because the parent nodes (sensor nodes 11-13) have failed. Data from the child nodes (sensor nodes 15-24) should be delivered to the sink nodes, and therefore, the routing paths should be reestablished using the available nodes connected to a sink node to recover from the failure (Figure 1c). Hence, for reliable data transfer, routing protocols should be aware of failures and have the ability to recover from them quickly. Figure 1: Node failure and routing recovery. Node failures in a large area can be regarded as a routing hall in the geographic routing protocol which works based on the geographic coordinates and thus be recovered fast since the geographic routing protocol usually has the ability to detour the routing hall. However, the geographic routing requires that sensor nodes have to know their location on the network field. Localization of a sensor node is in need of a special device to estimate the location such as GPS or Ultra Sound Emitter which is expensive or has the limited usage. On the other hand, the tree based routing protocols doesn't require any special device and thus can be used in any case without additional cost. As a consequence, the tree based routing protocol is still used in many area and the node failures in tree based routing can be a big problem. Therefore, we concentrate to the node failures in large area with tree based routing protocol. Usually, routing protocols for wireless sensor networks have the ability to recover from the failure of a sensor node. In these protocols, if a sensor node cannot receive messages from surrounding nodes for a specified period of time, the sensor node is classified as a failed node and thus excluded from the routing path.