Thermal decomposition of pure dimethyl sulfoxide (DMSO) and DMSO in the presence of different incompatible substances including N,N-dimethyl formylamine, NaOH, KBr and FeCl3 were investigated using accelerating rate calorimeter. Hazard indicators such as onset temperature T-onset, adiabatic temperature rise Delta T-ad, maximum pressure P-max at T-final residual pressure P-residual at 50 degrees C, maximum rate of pressure-rise (dP/dt)(max) and self-heating rate (dT/dt)(max) have been determined directly. Activation energy E-a of decomposition reaction and time to maximum rate TMRad of pure and impure DMSO have been studied from the measured self-heating rate data by assuming a zero-order reaction. Moreover, the decomposition mechanisms of pure and impure DMSO have also been discussed. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.