The occurrence of a rapid phase transition, or so-called explosive boiling, when a cold volatile liquid comes into contact with a hot liquid or hot surface is a potential hazard in industry. This study was focused on the explosive boiling potential of thermally stratified liquid-liquid systems that result from a runaway reaction. The experimental runs were performed on both a non-reacting and a reacting system. The experimental results showed that under the analysed conditions, the cold phase was superheated but did not evaporate explosively, as the limits of superheat of the phase were not achieved. The response of the cold phase appeared to be completely controlled by the interface temperature between the hot and the cold phase. In general, based on the order of magnitude of temperature differences that result from a runaway reaction in a multi-phasic system and the fact that the system is pressurised by its own vapour pressure, the occurrence of explosive boiling under runaway conditions appears unlikely for these type of systems. (C) 2002 Elsevier Science B.V. All rights reserved.