## 2 Background and Related Work  
Most routing protocols for WSNs focus on energy efficiency and link node lifetime related explicitly to its energy resources, _i.e.,_ a node is assumed to fail when the battery is depleted. Some WSN applications require real-time communication, typically for timely surveillance or tracking. Real-time routing protocols in WSNs are not new. For example, SPEED [1], MM-SPEED [2], RPAR [3] and RTLD [4] were all designed for real-time applications with explicit delay requirements. [PERSON] _et al._[1] proposed an outstanding real-time communication protocol binding the end-to-end communication delay by enforcing a uniform delivery velocity. [PERSON] _et al._ proposed [2] a novel packet delivery mechanism called MMSPEED for probabilistic QoS guarantee. [PERSON] _et al._ proposed [3] a real-time power aware routing protocol by dynamically adapting transmission powerand routing decisions. But these routing protocols are not well suited for routing in emergency applications such as building fires, where critical and dynamic network scenarios are key factors. [PERSON] _et al._ proposed [4] a novel real-time routing protocol with load distribution that provides efficient power consumption and high packet delivery ratio in WSN. There are many robust routing protocols proposed for WSNs. [PERSON] _et al._[5] proposed a framework of constrained flooding protocols. The framework incorporates a reinforcement learning kernel, a differential delay mechanism, and a constrained and probabilistic retransmission policy. The protocol takes the advantages of robustness from flooding. [PERSON] _et al._[6] presented a light-weight, dependable routing mechanism for communication between sensor nodes and a base station in a wireless sensor networks. The mechanism tolerates failures of random individual nodes in the network or a small part of the network. [PERSON] _et al._[7] presented a fault tolerant and low latency algorithm, which refer to as periodic, event-driven and query-based protocol that meets sensor networks requirements for critical conditions surveillance applications. The algorithm uses a publish/subscribe paradigm to disseminate requests across the network and an ACK-based scheme to provide fault tolerance. In building fires, network topology changes rapidly because of hazard and node failure, so general robust protocols are not suitable for such scenarios. Here, we want to design protocols that can be adaptive to the occurrence of fire expanding, shrinking or diminishing, _etc._ So, \"robustness\" in this paper means \"adaptive to fire situations\". In this regard, the work by [PERSON] _et al._[8] is interesting as they propose a proactive routing method that is aware of the node's destruction threat and adapts the routes accordingly, before node failure results in broken routes, delay and power consuming route re-discovery. They pay attention to the aspect of node failures caused by the sensed phenomena themselves. However, in their work, they focus on disasters such as forest fire that are very different from design issues in building situations, fire emergencies using wireless sensor networks within buildings are more challenging because of the complex physical environment and critical factors of fire hazards. In [9], we proposed a fire emergency detection and response framework for building environments using wireless sensor networks. We presented an overview of recent research activity including fire detection and evacuation in addition to providing a testbed especially designed for building fire applications. Other researchers have worked on emergency guidance and navigation algorithms with WSNs to buildings. [PERSON] _et al._[10] proposed a distributed 2D navigation algorithm to direct evacuee to an exit while helping them avoid hazardous areas. Their design allows multiple exits and multiple emergency events in the sensing field. Sensors are used to establish escape paths leading to exits that are safe as possible.