Cumene hydroperoxide (CHP) has been used in producing phenol and acetone by catalytic cleavage and as an initiator in polymerization. However, many severe fires and explosions have occurred because of its thermal instability and incompatibility,In fact, CHP has been given a hazard classification of flammable type or Class III by the National Fire Protection Association (NFPA). To date, however, its reactive and incompatible hazards have not yet been-clearly identified. In this study, the thermal decomposition and runaway behaviors of CHP with about 1 wt % incompatibilities such as H2SO4, KCI, NaOH KOH, Fe2O3, FeCl3, and Fe-2(SO4)(3) were analyzed by DSC thermal analysis and VSP2 adiabatic calorimetry. The thermokinetic data obtained via calorimetry, such as onset temperature, heat of decomposition, adiabatic temperature rise, and self-heat rate, were also compared with those df CHP in cumene. Hydroxide ion and ferric ion were found to be quite incompatible with CHP. The worst case of thermal runaway of CHP was observed when it was mixed with hydroxides tin the production or storage of CHP). The adiabatic self-heat rate,of 15 wt % CHP was 9 degreesC min(-1) in VSP2, which increased quite dramatically to a value of 100 degreesC min(-1). This study reveals that thermal hazards of CHP influenced by incompatibilities should not be overlooked. The different thermokinetic data affected by the incompatibilities are the key issues for ERS (Emergency Relief System) design in,CHP-related processes using DIERS technology. The decomposition pathway of CHP in various impurities was proposed by use of chromatography in product analyses.