It is found that the results such as observed in the differential scanning calorimeter (DSC), which show the major thermal decomposition (TD) of a self-reactive material, lack the detail to reveal what happens at the initial stage of a reaction. The reaction at this stage is corresponding to the handling condition of storage or transportation, often possibly having the potential to be developed to a runaway reaction. This paper examined and compared the thermal behaviors of AIBN at various working conditions in calorimeters and Dewar vessels. The mechanism that affects the initial reaction and self-heating behavior of the given material was clarified. Near its onset decomposition temperature, physical processes, such as sublimation or melting interfered the initial reaction of AIBN. The mutuality of the physical effect and the chemical reaction made AIBN behave differently under different measuring conditions, and as the result, quasi-autocatalysis or TD possibly occurs in the same sample at the handling temperature range. The heat accumulation storage tests in two Dewar vessels presented completely different self-heating behaviors due to this mechanism and heat transfer capability of the vessels.