An explosion that occurred during a nitromethane rectification process is investigated. Experiments were performed in an effort to elucidate the cause of the explosion. All test samples analyzed, including reaction product, crude product, 99% pure product and raffinate, were collected from the accident site. Gas chromatography was used to analyze the components of the samples, thermal analysis determined the exothermic character of the samples and the sample evaporating experiment recorded the reaction phenomena occurring at low liquid level. Based on the experimental results, the excess heat released by the decomposition of overheated raffinate is pinpointed as the root cause of the explosion. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.