The networks-of-zones model has been used to analyse the mixing behaviour in three dimensions when a cold slug of quenchant material is injected into a batch of reactants. In this way, it is possible to make predictions of the conditions required for achieving a safe quench when a reaction is close to a runaway condition. Some illustrations are presented typical of styrene polymerization using O(10(4)) zones in a stirred autoclave. The dynamic responses of sets of thermocouples arranged within the reacting fluid form a convenient basis for validation of the model. The complexities of compositional and temperature changes, together with the consequent reaction rates, are conveniently predicted from integration of sets of ordinary differential equations. The model fluid flow parameters can be easily deduced from simple tracer visualization tests.