Analysis of thermal hazards of O,O-dimethylphosphoramidothioate by DSC, TG, VSP2, and GC/MS

Abstract O,O-dimethylphosphoramidothioate (DMPAT) is widely used as the vital intermediate in pesticides to synthesize acephate, chlorine methamidophos, and methamidophos. February, 2016, a serious explosion and fire occurred in Taichung, Taiwan, resulting from DMPAT decomposition, causing one death and injuring one employee. To explore the thermal hazard of DMPAT, we applied various instruments of thermal analysis. Combustion phenomena and decomposed products were identified by combustion test and gas chromatography-mass spectrometry. Differential scanning calorimetry and thermogravimetry were used to analyze the thermal stability parameters, and mass loss conditions under five heating rates illustrating decomposition. Vent sizing package 2 was used to simulate stirring or unstirring system failure in a practical process. The apparent activation energy of DMPAT and self-accelerating decomposition temperature were, respectively, 92.4 ± 3.2 kJ/mol calculated by Starink equation, and 66.0 °C by simulated approach. The findings of these results are vital for inherently safer measures during production, storage, and transportation.