Peroxyacids are commonly used in chemical processing, synthesis and bleaching. Recently, they have been demonstrated to be very versatile for the epoxidation of unsaturated oil, aiming at the synthesis of polyepoxides (plasticizer, resins and adhesives). These processes are characterized by high yields and selectivity. However, due to their hazard and instability, the peroxy reactants are often obtained from the corresponding organic acid in situ by combination with Hydrogen Peroxide, in the presence of a mineral (Sulphuric or Phosphoric) acid as catalyst. The aim of this study is to analyse the thermal stability of the catalytic system used for vegetable oil per oxidation with the purpose of operating under safety conditions and then identify the safety parameters necessary to prevent the runaway reaction. This paper presents the study of the decomposition of peroxyacetic acid in aqueous phase by using a Thermal Screening Unit. Also, the effect of the presence of the acid catalysts was analysed. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.