The objective of the study reported herein is to simulate various physical and chemical phenomena accompanying fuel-rich n-butane-oxygen mixture preparation, ignition, preflame oxidation, and combustion in the standard 20-1 explosion vessel, by applying mathematical models. Based on the computational fluid dynamics (CFD) simulations of the mixing process and natural convection of the ignition kernel, as well as on the analysis of the detailed reaction mechanism of n-butane oxidation, laminar flame propagation, and self-ignition, possible explanations for the phenomena observed experimentally have been suggested. The results of the study indicate that seemingly inflammable mixtures can become hazardous depending on the mixture preparation procedure and forced ignition timing, (C) 2007 Elsevier Ltd. All rights reserved.