Abstract
For the transportation of dangerous substances, several modes of transportation are possible. If there are multiple possibilities, it is relevant to compare the safety of the transportation alternatives.
TNO has developed a consistent method to compare the different transportation modes, using standard risk criteria like cumulated Individual Risk (Locational Risk) and Societal Risk.
An evaluation of the method was done for two typical cases: transport of 100,000 t/y ammonia and 100,000 t/y propane. By using a standard QRA (Quantitative Risk Assessment) tool, the individual risk contours, the societal risk (FN) curve, and additional societal risk maps were generated and compared for 4 modes of transportation: railway, road, ship and pipeline. When using the Individual Risk contour as a criteria, the “distance to 10-6/y risk value” is often used to compare risks of transport. Because of the important contribution of loading and unloading activities at the beginning and endpoints of the route, one should evaluate the cumulated contours for interference with vulnerable objects.
For Societal Risk, the Dutch prescribed approach would be to consider the FN-curve for the kilometre segment of the route with the highest risk. The paper demonstrates that this approach may give misleading results when comparing different route tracks. Furthermore, because stationary equipment is subjected to stricter allowance rules (a lower guide value of societal risk curve), comparison of the combined effect of the transport and stationary loading & unloading activities is ambiguous. By applying societal risk maps, where (cumulated) risk is observed from the point of view of the receiver, this ambiguity can be taken away. The usage of these maps can hence be considered a very valuable addition in ranking risks of different alternatives.
