# Radio Wave Propagation and WSN Deployment in Complex Utility Tunnel Environments +
## 4 WSN Deployment
### Infrastructure and Work Safety Monitoring Application  
In order to guarantee the security and protection of the infrastructure against unauthorized access, vandalism or sabotage, as well as to ensure occupational safety at work, a surveillance and monitoring system prototype was developed to allow infrastructure and work safety remote monitoring. In general, these types of systems usually include WSN, closed-circuit television (CCTV) and an antifire system, each of them with its own independent communication network. Although they could share the same communication network, for security and fault tolerance reasons, normally, three different communication networks are deployed, both wired and wireless. Adequate precautions, such as the use of shielded cables or fiber optics, should be incorporated when installing the complete wiring system to ensure the immunity to the effects of electromagnetic interference. However, sometimes, due to cost or deployment reasons, a wired network is not available, requiring a wireless communication network. In the analyzed real case, a fiber-optic network was available for the city's security cameras, although no cameras were included inside the underground utility tunnel systems. If they were included, they could be connected to the fiber-optic network without further complications. Nevertheless, either special infrared cameras or visible spectrum cameras, in conjunction with presence sensors that activate the lighting system, should be included as well. This second option is more efficient in terms of infrastructure installation costs due to the difference in price of the cameras, but it has a higher probability of failure because it involves more elements (sensors and actuators). While, currently, no CCTV cameras are available in the galleries of the underground utility tunnel system, a wireless infrastructure and work safety monitoring application is proposed. Regarding infrastructure security and work safety monitoring, WSN are devoted to monitoring possible leaks, zones or areas and personnel. When monitoring leaks (mainly water and gases), sensors should be installed as close as possible of the possible leakage in order to facilitate that the detection of the leak, if any, be as quick as possible. When monitoring zones/areas, detectors are regularly distributed throughout the area according to the potential risk (and its assessment) of leakage. On the  
Figure 17: Schematic view of the proposed ZigBee 868-MHz WSN deployment. one hand, some combustible gases, such as hydrogen or methane, are lighter than air, so the detector should be placed above the possible leak origin point or on the ceiling, where there is a high probability of accumulations of these gases. On the other hand, other gases such as propane or butane tend to move through the lower parts and can cover large areas. Therefore, in order to detect this type of gas in the fastest possible way, it is necessary to place the detectors in the lower parts of the installation, avoiding the contact with water. Finally, personnel monitoring is pivotal in order to provide work safety conditions, especially in underground environments. By means of a wireless network, surveillance and maintenance teamwork can be controlled and monitored along the galleries using wearables or worn body sensors, allowing free mobility and work service. The development of an infrastructure-monitoring tool implies an adequate analysis and design of the whole system but, also, an adequate choice of the types of sensors, their locations, their configurations and their communication frequencies. In addition, the tool must allow the definition of alarm levels and the processes and procedures to be activated in case of alarm confirmation. Infrastructure monitoring will focus on both temperature and humidity control to prevent mold and bacteria buildup and to control potential sources of contamination. To do this, the humidity must be kept below 50% (desired values 30-50%).