Quantitative Transport Risk Analysis on a Regional Scale: an application of TRAT-GIS to East Sicily

Sicily has a very high concentration of chemical plants, mainly petrochemical and refineries, and thus is an area with a great risk of industrial accidents; in addition to this there are several natural risk sources such as earthquakes, volcanic eruptions and land decay, as well as deficiencies in the infrastructure, such as the transport networks and facilities. Large petrochemical and refinery plants (Priolo, Gela and Milazzo) are located on the east side of the island in the vicinity of highly populated areas of great environmental, artistic and tourist importance. The quantity of oil and other chemical products which are processed in Sicily is about 50·106 t/yr. This causes an over-production compared to the regional needs, and therefore a large part of these substances is exported; thus the region is characterised by an inflow of raw materials and an outflow of final products. Unfortunately the transport infrastructure is inadequate to cope with such a high level of traffic; the rail network, for instance, is still mostly single track, while important parts of the highway network are incomplete. As a consequence there are urban areas subject to an intense traffic of hazardous materials and safety cannot be ensured. In this paper an extensive quantitative risk assessment applied to the land transport of dangerous goods through the a wide territory of Sicily is outlined. A complete inventory of dangerous substances, detailed in the paper, was the basis of a complete risk analysis. From both individual risk distribution and societal risk curves the importance of parameters has been obtained and this has suggested measures to reduce the risk in Sicily. Calculations will be done with the software code named TRAT (implemented on a GIS platform) which has been developed to evaluate the risk to human health and to the environment due to the transportation of dangerous goods. The case study focuses attention on the application of the analysis to a very large area which can be managed by TRAT-GIS without loss of accuracy in calculations compared to previous application of the code to more restricted areas, such as the crossing of the Straits of Messina. Looking at the fundamentals of the code, it has to be noted that the prediction of individual and societal risk measures can make use of some different wind vectors, each of them referring to a meteorological station and its surrounding district. Of course a discontinuity will arise on the border between two districts, but the results will still be more accurate rather than those obtained by considering the same wind vector over the whole area. This is especially true for toxic gases such as Chlorine and Ammonia (both transported in the region): for the first one, which is heavier than air, an important role is played, besides the direction of the wind, by the atmospheric stability class (e.g Pasquill class) too, while for Ammonia, lighter than air if ambient conditions are considered, the transport is mainly dominated by the wind velocity. To take account of all the atmospheric conditions, in terms of stability classes and wind direction and velocity, and of their distribution in the seasons and on the territory this new feature has been implemented in the software with the help of a GIS platform. The table shows the fluxes of the main kinds of hazardous substances transported by road and rail in Sicily. A large amount of vehicles carrying dangerous goods has to be managed in the region. The discussion on results involves a comparison between different means of transport, useful to establish an order of priority, and the comparison with different tolerability criteria in order to outline considerations based on the absolute measures of risk introduced. The transport of hazardous materials through Sicily is characterised by some critical areas. The crossing of the Straits of Messina represents a very critical situation. The critical point of the road transportati...