# Smart Disaster Response in Vehicular Tunnels: Technologies for Search and Rescue Applications
## 5 Discussion  
The proposed search and rescue system introduced various technologies to cope with tunnel fires. In general, disaster response can be divided into two processes, initial detection and rescue. The most important factor is the accurate detection of accidents. This is also important in securing the golden time for recovery. For this purpose, the proposed system can monitor the whole accident situation through the use of heat, smoke, and flame sensors, camera-based image processing technology, and radar to detect the location of burning vehicles when a fire occurs. If the initial response fails, a fire brigade is dispatched. Thereafter, a robot capable of gathering data to assess the internal situation can be used while securing the safety of fire fighters. Finally, to support fire fighters' efficient activities, a location-tracking device and an area search monitoring technology were proposed. However, to make these proposed technologies more useful in the field, it is necessary to consider some of the following challenges:  
* Monitoring range and the number of sensors. Various kinds of sensors can be used to monitor fires and various algorithms are used to process the data gathered by them. However, when applied to a tunnel longer than 1 km, dozens of sensors must be arranged according to a certain pattern and rules. Typically, they should be installed at minimum intervals according to the sensor's sensing range and wireless communication distance. The installation should not interfere with the traffic of the vehicles, and the detection performance should not be impaired by external factors, such as weather conditions. In particular, the degree of robustness against rain, snow, wind, and temperature changes may affect overall performance. Additionally, battery and power supply issues should be considered for long-term use. Regarding CCTV and radar, it is also important to secure the optimal detection distance and LOS visibility. Although recent performance improvements have been made with the introduction of signal filtering and pan-tilt-zoom (PTZ) technologies, it is still necessary to review the installation height, angle, and software calibration for optimal performance. * Communication and networking. The data obtained from various disaster-detection sensors must be transmitted accurately and quickly to the correct administrator or control server. Various communication solutions based on IoT (e.g., WiFi, Bluetooth, ZigBee, long-term evolution (LTE), etc.) can be applied for this purpose. The proposed system basically adopts a fiber optical cable built into the tunnel as a backbone and mainly uses WiFi for the backbone network connection. The most reliable communication method is to deploy APs at certain intervals to ensure the traffic distribution and network connectivity. However, if there is an infrastructure failure, such as a power outage or building collapse due to a fire, a mobile ad hoc network can be established to ensure network connectivity. To this end, routing protocols, such as ad hoc on-demand distance vector (AODV) [44], dynamic source routing (DSR) [45], and optimized link state routing (OLSR) [46], have already been proposed as international standards, and recent open-source-based BATMAN [47] algorithms are also applicable. However, when constructing a wireless network, physical errors due to unstable channel conditions (e.g., distortion, attenuation, interference), the hidden-terminal problem, and the exposed-terminal problem should be considered. In addition, since mobile devices employed by a fire brigade have mobility, the signal disconnecting problem due to delayed reconnection and routing failures are potential degradation factors. To cope with these problems, various solutions, such as active route maintenance, error control, and congestion control, can be considered. * Robot operation. Recently, since types of tunnels and buildings have diversified and the length of tunnels is increasing, the damage caused by fires is also increasing rapidly.