In this paper an intrinsic runaway criterion is applied to the early detection of hazardous states in batch, semibatch and continuous chemical reactors. The new criterion is based on parametric sensitivity. The evaluation of the criterion is done by means of a model-based measuring technique, namely a Kalman filter. After a comparison with runaway criteria known from literature, the power of the early warning system is shown for the example of a continuous oxidation of ethanol with hydrogen peroxide.