In this work, the behavior of exothermic chemical reactions conducted in a wall-cooled, semibatch stirred-tank reactor is studied, with particular attention to conditions that lead to a thermal accident. The dimensionless heat and mass conservation equations for a semicontinuous tank were solved using second-order irreversible kinetics and a number of selected dimensionless numbers, for both the feed period and the late batch stage. The criterion implemented is based on the nonaccumulation of the dosed reactant, and the safest operating mode is based on the values of the reactor parameters that lead to an instantaneous consumption of the dosed feed. The criterion is implemented into an algorithm that runs in parallel with the integration of the model equations. Its applicability is shown using a few examples that show that the computer implementation of our methods works well in hazard prediction. (c) 2006 American Institute of Chemical Engineers.