Explosion incident occurs at the MDI storage tank in the Yantai Industrial Park of Wanhua Chemical Group Co., Ltd

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An explosion occurred in an MDI storage tank at the Yantai Industrial Park of Wanhua Chemical Group Co., Ltd. At around 17:22 on September 20, 2016, during a shutdown and material removal process at the diphenylmethane diisocyanate (hereinafter referred to as MDI) production facility located in Yantai City, Shandong Province, a 12 m3 MDI buffer tank exploded, resulting in 4 deaths and 4 injuries. Preliminary analysis indicates that during the shutdown and material removal process of the affected unit, improper operations caused diaminodiphenylmethane – a raw material used in MDI synthesis (referred to as DAM; DAM reacts with phosgene to produce MDI) – to enter the MDI buffer tank. There, it reacted with the MDI already present in the tank to form urea-based polymers, which blocked the filter on the outlet pipeline of the MDI buffer tank as well as the pressure balance pipeline above the tank. Meanwhile, the heat generated by these reactions caused the temperature inside the buffer tank to rise continuously, leading to the autopolymerization of MDI and the production of carbon dioxide. This increased the pressure inside the tank, eventually resulting in an explosion due to overpressure and thus the accident. The accident revealed issues such as inadequate risk assessment by the company, insufficient hazard analysis and control measures for the manufacturing processes, poor management during plant shutdowns, and improper operations. All regions and relevant enterprises should draw lessons from this incident, thoroughly learn from its consequences, strengthen the management of plant start-up and shutdown processes, detect and address any abnormalities promptly, carry out hazard and operability analyses in strict accordance with relevant requirements, earnestly implement various measures to prevent serious accidents, enhance risk identification and control, eliminate all potential hazards in a timely manner, and further ensure safe production during the National Day holiday and in the fourth quarter.