Thermal safety assessment for multiple exothermic reaction systems in multiphase reactors is challenging. One of the first step is to determine the presence or absence of secondary reactions producing non-condensable gaseous products. Then, a kinetic and thermal study should be performed to evaluate the value of the heat-flow rates due to chemical reactions. Epoxidation of a free fatty acid by a percarboxylic acid produced in-situ was studied. A classical approach by determining the adiabatic temperature rise (Delta T-ad) and the time to maximum rate under adiabatic conditions (TMRad) by microcalorimetry was used. Then, different cooling and stirring failure scenarii in a semi-batch lab-scale reactor under isoperibolic mode were performed. It was confirmed that the formation of peroxyformic acid governs the overall reaction kinetics and the reaction temperature. It was confirmed that in case of cooling failure, mechanical agitation should be maintained. (C) 2016 Elsevier Ltd. All rights reserved.