This paper deals with the thermal runaway of exothermic dichromate catalysed hydrogen peroxide decomposition. This reaction is characterized by a kinetic law which presents two limiting cases: zeroth and second apparent kinetic order in peroxide so that classical stability conditions could not be directly applied. A thermal stability criterion is proposed and applied to performed and simulated batch experiments. Some classical runaway boundaries are compared, and a condition, based on the Morbidelli's condition is proposed. The characteristics of zeroth order reactions, whose stability conditions have to be verified not only for initial conditions, but also throughout the reaction, are also illustrated. (c) 2006 Elsevier B.V. All rights reserved.