Reactors for carrying out exothermal reactions are amongst others equipped with trip systems. These are normally active systems requiring a number of components, for example sensors, pumps or valves to function for a successful trip. They may, for example, be based on the fast injection of a reaction inhibitor or the fast 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 a increasing 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 and by accompanying simulations using a computer model for the process and the trip system.