Defective design; pumping operations were carried out under power in violation of regulations

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On May 7, 1998, an explosion occurred in an oil separation tank in the water supply and drainage workshop of the refinery at a petrochemical complex in Xinjiang, resulting in 5 deaths and 1 person being burned. I. Accident course and hazards On May 7, 1998, in the water supply and drainage workshop of the refinery at a petrochemical complex in Xinjiang, the sewage in the oil separator tank of the secondary circulating water section pump room was pumped into the collection tank in accordance with the plant’s maintenance plan. The workshop requested that the electrical maintenance team send an electrician to the oil separator to install a submersible pump and connect it to the power supply, and to handle the relevant electrical invoices as required. On May 8, the electrical maintenance team sent electricians to the oil separator tank to connect power to the submersible pumps. The deputy director of the water supply and drainage workshop, along with the workers, lowered the 3 pumps that were functional into the inlet trough at the western end of the oil separator tank, as well as into Tank No. 1 and Tank No. 5. Those pumps were started up that same night to pump water. On May 9, the workshop supervisor went to the oil separator site to repair the faulty pump and install a new one; they also wrapped the cracked sections of the old cables with waterproof tape. After completing these repairs, the pump was powered on for a test run, and once it was operating properly, it was placed in Tank No. 3 to start pumping water. At 12:50, the on-duty female worker discovered during her inspection that no water was flowing from the outlet pipelines of the submersible pumps in tanks 3 and 5. After consulting with the shift supervisor, she turned off the power switches for these two pumps. After having lunch in the cafeteria, 6 people including the shift supervisor and the crew members went to the oil separator to continue the water pumping work. At 14:10, the shift supervisor and six other workers were about to check the operation of the submersible pump again; as soon as they stepped outside, they heard an explosion and saw a fire break out in the oil separator tank. Immediately return to the control room to report to the refinery dispatch room. The burned section manager then ran to the control room to report that there were 5 people still at the accident site, and the section manager was taken to the hospital for emergency treatment. At 17:30, the firefighters put out the fire. Upon on-site inspection, 2 bodies were found on the ground to the east of the oil separator, while 3 bodies were recovered from the oil separator. The accident resulted in 5 deaths and 1 person suffering burns. II. Analysis of the accident causes 1. The wastewater in the oil separator contains oil and a high proportion of light components; as the external temperature rises, the amount of flammable gases that evaporate increases. Furthermore, due to continuous water pumping on the 8th and 9th, the water level in the tank dropped, allowing air to enter and increasing the amount of explosive mixture present. 2. The operators violated safety procedures by performing pump operations while the equipment was under voltage, which put the cable under significant stress; this caused one phase of the cable to break and start sparking, breaking down the insulation and sheath and thereby igniting the flammable gases. 3. The water supply and drainage workshop has not developed specific cleaning and maintenance plans for the oil separation tanks, nor have it put forward specific preventive measures for safety issues in the key operational steps. 4. From workshop supervisors to operators, there is insufficient awareness of the special hazards in flammable and explosive environments; non-explosion-proof load switches, open switches, and exposed wiring are used in such areas. 5. Since the installation of the oil separator, the relevant functional departments at the refinery have not established comprehensive safety standards and operating procedures for its operation and maintenance. 6. There are defects in the design and acceptance process of the sewage lift pump room. If instrument panels and control panels that are not explosion-proof are installed in the control room located in an area prone to fire and explosions ； The oil separator does not have steam fire suppression facilities designed in accordance with specifications ； For the discharge of wastewater from the outlet overflow weir, only pipelines leading to the open-channel drain have been designed; there are no pipelines for direct discharge into the collection tank, which increases the difficulty and risk of maintenance work.