Self-reactive decompositions associated with the exothermic behavior of tert-butyl hydroperoxide (TBHP) solutions with three diluents of H2O, tertbutanol, and nonane were investigated. We used two calorimeters, Differential Scanning Calorimeter and Vent Sizing Package 2, to characterize the inherent thermal hazards of TBHP solutions. By thermal analysis, various beats of decomposition of TBHP in water, in nonane, and in tert-butanol solutions were determined to be 1622.4, 1438.8, and 753.2 J/g of TBHP, respectively. Adiabatic runaway data, such as exothermic onset temperature, maximum self-heat rate, maximum pressure rate, adiabatic time to maximum rate, and noncondensable pressure, were obtained using a VSP2.