This paper deals with the management of operational crisis situations in a large unified Automated Material Handling System (AMHS) of a semiconductor wafer fabrication facility (fab). We propose an original approach to handle crisis situations, i.e. when a vehicle stops (due to a breakdown) on a rail and thus prevents other vehicles to use the same portion of the rail. This kind of crisis may lead to the blocking of many vehicles, thus impacting the fab productivity. To manage such situations, two Decision Support Systems (DSS) have been designed. The proposed DSS helped the fab to improve the reliability of lot deliveries.