Analysis of the Silicon Tetrachloride Leak and Poisoning Incident in the Silica Workshop – Case Study Sharing

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On October 23 of a certain year at 13:00, 14 people working at the silicon tetrachloride distillation station in the silica gel production workshop of a chemical company suffered poisoning due to a silicon tetrachloride leak while attempting to resolve a malfunction in Distillation Vessel No. 2; this resulted in 2 deaths and 4 cases of minor injuries, constituting an industrial accident resulting from negligence. 1. Incident details: During the night shift on October 22, it was discovered that the No. 2 distillation system was blocked while feeding material into the No. 2 distillation vessel; therefore, the No. 1 distillation system was used, with the issue to be addressed during the day shift on October 23. After lunch on the 23rd, Deputy Supervisor Liu, together with shift leader Li, operators Hou and Gao, along with three others, went to the second floor of the distillation area to address the abnormal situation. Upon arriving at the scene, Li asked Liu, “Has it been dealt with?” (Referring to pressure relief and discharge), Liu replied, “Don’t worry; it’s taken care of.” Then Liu asked Hou, who wasn’t wearing a mask, to go find the rebar used for clearing the pipes. After placing the iron drums and wooden planks for elevation, Li and Gao, who were wearing masks, removed the sight glass located 2 meters above the ground at the lower part of the blocked main pipe. They opened the stop valve on top of the sight glass; seeing that no material or pressure was escaping, they replaced the stop valve with a ball valve in order to make it easier to clear the pipeline using rebar, and then opened the valve to create a direct connection with the blocked pipe. Li and Gao took turns using rebar to clear the pipeline three times; after about 10 minutes, Liu, who was not wearing a mask, took over from Li and Gao to continue clearing the pipeline. After a while, suddenly a large amount of a mixture of gases, solids, and liquids containing HCl, SiO2, and SiCl4 leaked out from the bottom of the valve. Instantly, white smoke filled the interior space, and it spread downward and outside through the open windows, doors, and holes in the floor used for equipment installation. Upon seeing the incident, Li and Gao, who were located to the southeast of the leak site, immediately ran away from the scene using the stairwell on the southeast side of the building. After quickly washing their faces, they went to the north side outside the first floor of the building. After the accident, Liu suffered facial injuries and struggled to run away from the scene; after reaching the ground on the lower floor, he collapsed and was rushed to the hospital. Hou, who was not far to the southwest of the leakage site, was also taken to the hospital for emergency treatment after running out of the building. After the accident, shift leader Shen and team leader Li wore masks and carried wrenches to remove the rebar and close the valve, thereby stopping the leak. After being taken to the hospital, Liu died on the same day despite attempts to save him, while Hou died on the 24th after treatment proved ineffective. Four other workers were performing electrical work on the first floor; they suffered facial injuries of varying degrees due to leaks of materials from above. 2. Accident cause analysis 2.1 Direct causes 2.1.1 Upon examining the condenser of the silicon tetrachloride No. 2 distillation system, it was found that there were leaks in the welds of the tubes inside the condenser. The silicon tetrachloride material reacted rapidly with the cooling water leaking from these welds to form hydrolysis products, which led to the blockage of the discharge pipe of the condenser. During the process organized by Liu to handle the abnormal situation, reverse vaporization and pressure relief were not carried out in accordance with the technical requirements; instead, rebar was used to force the flow of materials, which constituted reckless handling. This violated the production process regulations and safety rules for that product, resulting in the leakage of materials and serving as the direct cause of the accident. 2.1.2 The deceased workers failed to wear protective equipment as required by safety regulations and lacked awareness of personal protection; when there was a material leak, they had no form of protection, which led to poisoning and death, and this was also the direct cause of the accident. 2.2 Indirect causes 2.2.1 The factory management fails to provide adequate safety training for employees; workers pay attention to the toxicity of chlorine but lack awareness of the toxicity of silicon tetrachloride. As a result, their awareness of safety precautions is weak, their ability to handle unexpected failures during production is poor, and their overall safety competence is low – all of which are indirect causes of accidents. 2.2.2 There is no awareness of the potential risks in equipment management, and there are no means for the inspection and maintenance of equipment ； The lack of a work order system for dealing with abnormal phenomena in production is also an indirect cause of accidents. 3. Accident remediation measures 3.1 Drawing lessons from this serious accident, the entire plant carried out a major discussion campaign themed “Combating violations and eliminating hidden dangers,” with employees taking the initiative to identify unsafe issues around them. Conduct a thorough safety education program for leaders and employees at all levels to improve their safety awareness and firmly establish the principle that safety comes first. 3.2 Conduct a thorough equipment inspection of this production system to eliminate the root causes of accidents and prevent similar incidents from occurring in the first place. 3.3 Strengthen daily safety management efforts, formulate practical work orders, and strictly implement the maintenance system for abnormal conditions during production. Strengthen the management of process equipment, ensure that everyone fulfills their responsibilities, strictly prohibit the three types of violations, and eliminate any instances of reckless operation. 3.4 All employees in the plant should undergo training on production processes, equipment, and safety regulations, so that each employee is aware of the dangers associated with working in violation of these rules, and thus develops a work attitude that views compliance with regulations as honorable while considering violations to be shameful.