**7. System requirements**

228 Environmental Monitoring

ENs were located, regularly positioned around the plant to detect any VOC emission generated by the plant itself. Two WSD sensors provide information about wind intensity/direction in form of a blue arrow (see Fig. 2). Taking into account for the fact that the wind is turbulent within the plant, the WSD information turns out to be very useful to

establish a proper correlation between wind distribution and VOC concentration.

Fig. 2. Lay-out of the installation featuring the SN units (grey) and the EN units (rose)

**6. System architecture** 

In the pipeline area two ENs were located in close proximity of the possible sources of fugitive, while three ENs were located along the perimeter. The installation on top of the benzene tank requires ATEX certification which was not yet completed at the time this paper was edited. The units deployed so far consist of a total of seven SNs and ten ENs; owing to the high degree of modularity of the WSN architecture, however, the system is fully scalable by simply deploying additional ENs, with self-configuration capability.

Various WSN architectures, including mesh and cluster three, have been investigated as potential candidates, each exhibiting advantages and drawbacks; in this application, as it will be explained below, the VOC detectors have to be continuously powered-on and the wireless node has to transmit data at minute data-rate. VOC detector cost, in terms of power consumption, is thus predominant with respect to transmission cost; in that context, the mesh configuration turned-out to be unnecessarily complicate in terms of protocols and less efficient in terms of energy budget; consequently, the much simpler and effective cluster For hazardous and complex industrial sites, it is very important to have a monitoring tool with a whole range of features in an economically feasible way. In particular, when designing a monitoring network is necessary to take into account the following issues:

