【Accident Case Analysis】Case Study of the Dimethyl Sulfoxide Plant Explosion at a Company in 07

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I. Accident details: At 8:30 on August 4, 2005, Sun, the operator on duty at a certain company, noticed that the signal indicating the sulfur ether feed flow rate in Tower A# was abnormal in the control room. He immediately reported this to Zhang, the technical supervisor of the device’s technology provider (the legal representative of Benxi Qinghua Applied Technology Institute), and they went to the site together to investigate; it was confirmed that there was a problem with the flow meter. At 8:35, they returned to the control room; under Zhang’s instructions, the operators stopped feeding in sulfide and notified the maintenance staff to inspect the sulfide flow meter. At 9:39, the on-site maintenance was completed and the system passed the testing, after which Zhang was informed immediately. At 9:44, Zhang instructed the operators to sequentially open the thioether feed control valve and the solenoid valve in order to feed material into Tower A#. Upon detecting a low oxygen flow rate, Zhang ordered an increase in the oxygen flow. At 9:46, an explosion occurred in the exhaust gas recovery pipeline on the second-floor platform; debris penetrated the shells of equipment such as the sulfide distillation tower, the sulfide distillation condenser, and the oxidation tower, resulting in a leak of flammable materials and a fire. Large amounts of yellow smoke emerged from the roof. The explosion killed 2 people and injured 11. At 9:50, the emergency rescue team arrived at the scene to carry out emergency rescue efforts, and the injured were taken to the staff hospital for thorough treatment. All types of hazardous materials at the accident site were promptly shut off, allowing the vehicle to be brought to a safe stop. 30 minutes later, the flames at the scene were extinguished, and the production equipment continued to be cooled by spraying water, allowing the situation to be brought under control. II. Analysis of the accident causes (I) Direct causes 1. The technology transfer party violated the operating procedures during the guidance of the testing process by giving incorrect instructions: Due to abnormalities in the sulfide flow meter, following Zhang’s instructions, adjustments were made to increase the sulfide flow rate, which resulted in a large amount of unreacted sulfide entering the exhaust pipeline. During the restart trial run, Zhang gave the incorrect instruction to introduce sulfur ether first and then increase the oxygen supply, which resulted in a considerable accumulation of sulfur ether at the site of the explosion. This led to a violent exothermic chemical reaction in the exhaust pipeline, thereby causing the explosion. 2. Defects in process design: The nitrogen dioxide recovery device in the exhaust pipeline is poorly designed; an excessive amount of sulfides in the exhaust pipeline leads to intense chemical reactions, which cause the dinitrogen tetroxide condenser to become clogged by the reaction products, resulting in overheating and overpressure in the exhaust pipeline. 3. Defects in the instrument control design: The device lacks a reliable safety interlock mechanism to prevent an excessive amount of sulfide from entering the oxidation tower. (II) Indirect causes: 1. The low professional competence of technical personnel and operators, as well as their weak safety awareness; their insufficient understanding of the device’s technology and excessive reliance on the technology transfer party led to their inability to make correct judgments when the transfer party issued incorrect instructions, thereby violating operating procedures. 2. The project review failed to identify any design defects in the process or instrument control systems. 3. Safety management is inadequate; potential safety hazards within the equipment have not been effectively identified or rectified. III. Preventive Measures: (1) Carry out process modifications and on-site protection for the dimethyl sulfoxide facility; develop detailed technical plans. All materials such as sulfide liquids, dinitrogen tetroxide, and sulfoxides stored in the on-site tanks, along with finished products and semi-finished products, must be sold or subjected to harmless treatment, in order to completely eliminate any potential hazards present within the facility. Additionally, each step of the treatment process must be inspected and verified. (II) Strictly implement the work safety responsibility system. Comprehensively establish and improve various safety production regulations and systems, strengthen safety responsibilities at all levels, and focus on identifying potential hazards as well as advancing the standardization of safety and quality. By implementing quasi-** management, we enhance the execution capability of staff and employees, ensuring that all safety measures are properly put into practice. (III) Strengthen safety education and training for all employees to enhance safety awareness and improve safety skills. (IV) Improve the supervision mechanisms of factories over private enterprises, step up safety inspection and management of such enterprises, eliminate instances of violations at the work site, take decisive actions against those activities that pose risks to safe production and personal safety, and order them to suspend operations for rectification. (5) For new construction, renovation, and expansion projects, all relevant approval procedures must be carried out in strict accordance with applicable laws, regulations, and rules, and all safety responsibilities related to project construction, commissioning, and operation must be properly implemented. (VI) Order all private chemical production facilities to suspend operations and carry out comprehensive safety rectifications.