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Incident overview of the water seal failure in the gas holder of the hydrogen production plant: Around 17:00 on March 29, 2004, the water seal in the 10,000 cubic meter gas holder failed, resulting in the leakage of gas. The liquid level in the gas holder dropped rapidly from 60% to 30%, and the large amount of gas that leaked was carried by the north wind to the vicinity of the heavy aromatic hydrocarbon heater, where it encountered an open flame and caused an explosion. The fire truck arrived and put out the fire. At the same time, the operator at the gas tank station contacted the company’s dispatch team; the gas was directed to the flare instead of being fed into the gas tank. The compressor was stopped, and efforts were made to determine the cause of the break in the water seal of the gas tank. After the second gas tank fell, it was found that the level of the water seal between the first and second layers of the tank was low, and gas was escaping from the tank in the northern part. The workshop’s technical staff immediately connected hoses to add water to the water seals on the first and second layers of the tank, restoring the water seals and preventing further gas leakage. The workshop technicians went to the air receiver to inspect the overall appearance as well as the idler wheels and guide rails; no abnormalities were observed visually. After consultation among the company’s relevant leaders and the workshop, it was decided to maintain production by controlling the liquid level in the gas tank at 50%. At 23:00, the large screw compressor began to operate normally. Cause of the accident: a. There were certain issues with the gas holder itself; under the force of strong winds, this could prevent the third layer of the gas holder from rising, leading to an increase in internal pressure and consequently the breaking of the water seals in the first and second layers of the gas holder. b. There was insufficient assessment of whether issues could arise if the gas holder’s liquid level is maintained within the 57%–58% range and the system operates for four and a half hours. c. There are few parameters that can ensure the normal operation of the gas holder. Lessons learned from the accident and measures taken: a. The curve used to control the liquid level in the gas holder should not remain unchanged for an extended period; it is necessary to adjust the operations accordingly in order to detect any issues promptly. b. Strengthen the inspection of gas cylinders; conduct thorough inspections of them at the end of each shift (including checking for any abnormal changes in their appearance, idler wheels, and guide rails). Check it once especially when lifting and lowering at the junction of the two towers. c. Ensure that the gas holder liquid level is not controlled between levels. Managers should enhance their sense of responsibility, gain a better understanding of gas tanks, and ensure that supervision and inspection are carried out properly.