Analysis of possible development of runaway at production, storage and use of a chemical product, and subsequent choice of measures that can prevent an accident or mitigate its consequences are the important tasks of reaction hazards assessment. A kinetic model evaluated from calorimetric data gives a reliable basis for implementing the analysis by means of numerical simulation. The purpose of this paper is to discuss some features of the approach as applied to such typical problems as determination of critical conditions of thermal explosion and the self accelerating decomposition temperature (SADT) for solid and liquid reactive chemicals. First a brief survey of some popular simplified theories is discussed to reveal their main limitations. Second the mathematical models of thermal explosion in solid and liquid reacting systems are presented followed by a basic sketch of the numerical methods chosen to solve the problems. Finally the practical usefulness of the kinetics-based simulation approach for analysing the influence of various factors on explosion development is illustrated with several examples. The discussed models and methods were included in the ThermEx and ConvEx program packages developed by CISP. All the presented results were obtained by means of this software.