Reactors for carrying out exothermic reactions are amongst others equipped with trip systems. Normally these are active systems requiring a number of components such as sensors, pumps or valves to function for a successful trip. They may, for example, use the injection of a reaction inhibitor or the dumping of the reactor contents into a knock-out tank. The availability of such systems, i.e. their probability of functioning on demand, largely depends on their degree of redundancy. However, the possibility of common cause failures places a limit on increasing their availability by raising their degree of redundancy. Nevertheless, a trip system may reach a high availability if instead of stepping up its redundancy a passive system is used. The design of such a passive trip system for batch reactors is described and its feasibility is demonstrated by experimental investigations of three different types of reactions. (C) 2009 Elsevier B.V. All rights reserved.