Reflections on the November 28th accident

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More than a week has passed since the accident on 11.28, and it will take some time before an accident report is ready. Adhering to the principle of treating minor accidents as if they were major ones, attempted accidents as if they had already occurred, and others’ accidents as one’s own, we are now analyzing the accident based on the information available so far. We aim to determine how such accidents can be prevented and what actions should be taken in case of similar incidents; we hope everyone will actively participate in the discussion. A leak occurred in the gas tank; the substance leaking was gaseous vinyl chloride, with a boiling point of -13 degrees Celsius. In its gaseous state, its density is twice that of air. After the leak, the gas drifted across the ground with the wind, and upon coming into contact with an open flame outside the factory area, it exploded, triggering subsequent accidents. As is well known, gas phase leaks should be much safer than liquid phase leaks, as the proportion of vaporization in the liquid phase can reach 300 times or even higher. The accident at Linyi Jinyu 6’5 occurred as a result of an explosion 2 minutes and 10 seconds after a liquid phase leak of liquefied gas. Then why did a tank leak lead to such a serious accident? Setting aside the apparent reasons related to the vehicle doors, as production personnel, we should focus more on analyzing the causes of the gas tank leakage and determining how to address it. Gas tanks are usually installed in the flare network. To save energy and reduce consumption, the leaked gases or the fluids discharged as a result of safety valve operation are recovered and reused; therefore, a bypass line is generally provided. When the discharge volume through the main network is too high or the gas tank malfunctions and cannot recover these fluids, they are sent through the bypass line to be burned in the flare. As for how Shenghua Company handles such situations and what causes the leaks, we are not aware at present. Let me tell you about an accident we experienced firsthand. In 2014, our previous workplace also had a dry gas holder used to collect the liquefied gas emitted by the processing units. When the liquid level in the gas holder rose to a certain level, the control room would inform the operators to start the compressor in order to lower the liquid level. Once it reached a certain level again, the compressor was turned off, and this process repeated itself. On one occasion, when the personnel in the control room notified the operators that the liquid level was low and that the compressor should be shut down, the operators failed to do so in a timely manner, which resulted in the gas tank collapsing. Fortunately, no other secondary accidents occurred. After the collapse, cracks appeared in the tank itself, and the vapor phase of the liquefied gas leaked out. Due to the low pressure of the gas inside the tank and the low liquid level at that time, the amount of leakage was not particularly large. The valve leading to the flare was opened, the valve connecting to the tank was closed, and steam was used to protect the area; as a result, the accident was brought under control, with no casualties resulting from it. At the same time, to prevent similar accidents from occurring again, we have set up high and low level alarms for the gas holder’s liquid level, as well as interlocks for extreme high and extreme low levels; in case of an emergency, the gas holder can automatically cut off the air supply and stop the compressor. After the gas holder at Shenghua Company leaked, both the duration of the leak and its magnitude had a direct impact on the progression of the incident. Even if the personnel on site failed to conduct proper inspections or did so at an inappropriate time, the combustible gas detectors on site should have issued alarms. It is necessary to determine whether the control room staff and those on site carried out inspections, analyses, and corrective actions after the alarms were triggered, as well as whether those actions were appropriate. Based on the current situation, it appears that the leak persisted for a long time, and the personnel failed to cut off the pipelines connected to the gas holder, which led to the continuation of the leak and ultimately caused the accident. The causes of accidents are often multifaceted; the analysis above is merely one perspective, and a more detailed assessment can only be made after the accident report is prepared. Treat others’ accidents as one’s own, analyze and understand them carefully, apply what has been learned, and turn it into one’s own experience. Only in this way can we handle similar potential hazards promptly and effectively, and eliminate them.