## 3 Proposed Fires Monitoring and Detection Framework
### The Proposed Sensor Deployment Scheme
We assume that sensor nodes are in the initialization phase after powering on. In this phase, common nodes set up the connections with the cluster head. The selection and formation of clusters are described in Section 3.2. After the completion of clustering, each common node sends its Node ID and time slot information to the cluster head. The time slot of each common node is a dynamic parameter that is controlled by a cluster head depending on the current FOD. The current FOD value indicates the risk degree of fire at the moment and the location. A higher FOD will cause common node sensing and sending data to cluster more frequently. Additionally, a cluster head sends the FOD to each common node. By using this information, common nodes can determine if it should go to the non-fire phase or fire threat phase. The non-fire phase indicates that the FOD is low. At this time, the network self-adapts to decrease its activity level by putting common nodes into sleep mode for a while, so that it can improve energy efficiency without compromising the fire reaction time. In sleep mode, the frequency of sensing and sending data to the cluster head is set to be very low. However, when the FOD value exceeds the configured threshold, the network will go to the fire threat phase. In this phase, common nodes immediately and aggressively send warning messages to its cluster head. After the cluster head hears the warming message from one of its common nodes, it assigns more time slots to the node that has sent warming message. Additionally, besides temperature, more information such as humidity, solar radiation and wind power is sent by the cluster head to the sink station for further analysis. The damage phase indicates that there are some sensor nodes already destroyed by fires. When a common node is destroyed by the fire, it can be detected by the cluster head and appropriate action can be taken. However, if the death of the cluster head happens, the network topology will handle this situation. There are two cases that should be considered: (1) a cluster head enables the pre-sensing of the fire threat and takes actions to avoid becoming a non-functional cluster head; (2) a cluster head suddenly becomes non-functional due to the fire. In the first case, while the cluster head discerns the potential threat from fires, it will select the most suitable candidate cluster head based on Suitable Index (SI) which can be calculated by using below Formula (4):

\[\text{SI}_{i}=\frac{T_{max}-T_{c}}{\Delta T_{change}}\times e_{r} \tag{4}\]

where, \(\text{SI}_{i}\) is the suitable level of candidate node \(i\) to become a cluster head. \(T_{max}\) is the maximum temperature that a node can withstand. \(T_{c}\) is the current temperature of the node. \(\Delta T_{change}\) is the changes in the temperature of the node in the last period. \(e_{r}\) is the remaining energy of the node. In the second phase, to cope with the cluster head suddenly dying, at the beginning of the fire threat phase, the cluster head will send the information about the cluster to its common nodes so that this information will be replicated by common node. When the cluster head suddenly dies, the node first detects the death of the cluster head and will inform all the other members in the cluster and exchange some parameters among to decide on the next cluster head based on Formula (4). After that, the new cluster head informs the other nodes of the result of the selection. In the aspect of the proposed inter-cluster protocol, the inter-cluster protocol provides the communication among cluster heads and delivers the data gathered by the cluster head to the sink station via multi-hop forwarding. According to the requirement of forest fire monitoring and detection, the proposed inter-cluster protocol has two main goals: balancing the energy consumption among the cluster heads and forwarding the fire information to the sink station as soon as possible.