Attention! The nitrogen pipeline may not necessarily contain nitrogen! Illegal hot work ignited the nitrogen pipeline, causing an explosion in the benzene storage tank

Course of the accident and emergency response (1) Course of the accident: At the end of May 2016, while the tank farm facility was carrying out purging of the feed line for tank V181001, leaks were detected in the nitrogen valves on the nitrogen distribution panel in the pump room as well as in the main nitrogen pipeline leading to the tank farm. On August 15, Zhao Qiang, the deputy director of the tank farm facility, issued a maintenance task order to the maintenance team, requesting that the location of the nitrogen distribution panel be modified and that the valves on the main nitrogen pipelines be replaced. On that day, Jiang Tao, the dedicated safety officer for the facility, obtained a fire work permit (level 2). Welders from the maintenance company, including Ma Junsheng, cut the nitrogen distribution valve assembly off the nitrogen pipelines in the pump room; however, the ends of the cut nitrogen pipes were not sealed, leaving them fully connected to the atmosphere. On August 16 and 17, the maintenance staff prepared and replaced the nitrogen distribution panel for the valves, replaced the valve in the nitrogen main pipeline that was leaking internally, and closed the first main nitrogen valve. On the morning of August 18, it is planned to install the pre-fabricated nitrogen distribution panel on the nitrogen pipeline on the north side of the pump house (the same nitrogen pipeline that was cut using welding on the 15th). Cui Wenge, an employee of the tank farm facility, was responsible for obtaining the firework safety operation permit; the fire risk level was determined to be level two, and Zhang Qingwei served as the fire supervisor. After the ticket was signed off by Zhao Qiang, the person responsible for the initial review of hot work, Guo Lechun, who confirmed the safety measures, and Hu Zhiyu from the safety management department, it was approved by Chang Fangfang, the deputy director of the branch factory. Following confirmation by Li Guowei, the shift supervisor and ticket checker, it was handed over to Zheng Daiwen, the person in charge of the hot work. During the process of issuing permits, safety measures required by the operating procedures, such as using blind flanges for isolation and conducting combustible gas analysis, were not implemented; no on-site verification was carried out either. There were also serious cases of unauthorized signing – Cui Wenge signed in place of Zheng Daiwen, Zhang Qingwei, and Jiang Tao, as well as filled in the relevant information regarding fire safety measures. No hot work was carried out this morning as the company had visitors. At 14:30 on the 18th, Zheng Daiwen, Zhang Qingwei, and maintenance worker Ma Junsheng (the person in charge of performing hot work), along with others, moved the nitrogen distribution station to the north side of the pump room of tank group 1810 in order to get ready for the work. At 15:10, Ma Junsheng turned on the oxygen and lit the welding torch, getting ready to start cutting. During that time, the fire watcher, Zhang Qingwei, left the hot work area to conduct inspections between tank groups 1810 and 4810. At 15:11–15:12, Ma Junsheng, the welder at the site where work was being carried out, cut through the nitrogen pipeline, thereby igniting the flammable benzene gas inside it. At 15:13, an explosion and combustion occurred in the storage tank. When a deflagration occurs in a storage tank, it starts in the gaseous space at the top of the tank. The explosion pressure causes black smoke and liquid to be ejected from the oil discharge ports on the tank roof. Flames emerge from the crack at the junction of the ventilation port located in the southeast corner of the tank roof and the roof structure itself. The bottom of the tank is lifted about 3 meters on the north side and about 4 meters on the south side. Subsequently, the cleaning hole at the lower part of the tank was torn at the junction of the tank wall and the bottom plate, causing a large amount of crude benzene liquid to spray out rapidly. This led to a tear in the bottom of the tank on the southern side, and the rapid release of liquid triggered an even larger scale of deflagration. Eventually, the tank and the bottom plate were completely torn apart from each other; the entire tank was lifted about 7–8 meters into the air, resulting in the formation of a fireball and a mushroom cloud at the scene.

(2) Emergency response to the incident 1. Emergency response actions: Upon the occurrence of the incident, the company’s emergency response center promptly took action; fire trucks and ambulances arrived at the scene within 2 minutes to carry out emergency rescue efforts. Immediately, company leaders such as Wang Zhonggang and Han Ximin rushed to the scene to direct the rescue efforts and activate the emergency response plan. Wang Futai, the manager of the benzene processing plant, called 119 to alert the fire department at around 15:25. At 15:20, the company dispatched water trucks, foam trucks, and high-pressure spray trucks to the scene via Jing San Road, while dry powder trucks and emergency rescue vehicles remained on standby at Wei San Road. The water tanker immediately laid hoses to cool the tanks surrounding the fire, while the mobile foam truck was positioned to the south of the tank area, near the fire, to discharge foam for extinguishing the fire. The high-pressure spray truck was dispatched to the southeast of the tank area to extinguish the fire using two foam guns. Upon arriving at the scene, the personnel in charge of the tank farm activated the sprinkler systems there as well as the fixed foam station, directing a large volume of water to cool down tank V181001. At 16:35, thanks to the efforts of the firefighters, the flowing fire at the scene was largely extinguished. At 17:15, all remaining embers at the scene were extinguished. At 17:00, Wu Jinseng, deputy general manager of Yangmei Group, Yan Wenquan, chairman of Yangmei Chemical Industry Group, and others arrived at the accident site one after another. (3) Environmental pollution and monitoring status: Environmental monitoring showed that no characteristic pollutants were detected in the air surrounding the enterprise affected by the accident. The fire-fighting wastewater outside the tank farm cofferdam, as well as the rainwater in the facility during accidents, are discharged into the 10,000 m3 accident pond located within the facility. The fire-fighting wastewater inside the cofferdam of the tank farm (including rainwater during accidents), along with the wastewater generated from subsequent flushing outside the cofferdam, is collected in tanks V181009, V181013, and V181014, as well as in the sewage collection pond. The deflagration incident in the crude benzene storage tank did not cause any secondary environmental pollution.

Cause and nature of the accident: (1) Direct cause – After feeding into tank V181011 in the benzene processing plant, the level of crude benzene remained below the bottom position of the floating disk for an extended period, resulting in the formation of an explosive mixture inside the tank. This mixture then entered the nitrogen pipeline that was connected to the tank. The illegal instruction to carry out cutting operations on the nitrogen pipeline without taking safety measures such as using blind flanges for isolation, conducting combustible gas analysis, and conducting on-site inspections was the direct cause of the deflagration in the crude benzene storage tank. Cause analysis: 1. After feeding into tank v181011, the liquid level of the stored material was low; the floating disk remained in its lowest position for an extended period, resulting in a large amount of flammable gas within the tank that reached the explosive limit. 2. The shut-off valve located on the tank top of the nitrogen pipeline is open, the check valve is functioning properly, and the bypass valve of the control valve assembly is open; thus, the nitrogen pipeline forms a complete pathway for the dispersion of combustible gases. 3. Since the nitrogen pipe openings remaining after the nitrogen distribution panel was cut out in the pump room were not sealed, nitrogen from the pipes leaked out. The flammable gases in the storage tank could gradually spread along the nitrogen pipes to the open openings located in the pump room; the concentration of flammable gases decreased gradually as one moved from the storage tank to the nitrogen pipe openings in the pump room. 4. Before carrying out the hot work, no safety measures were taken to completely isolate the pipeline using blind flanges; when the nitrogen pipeline was cut, the heat from the welding flame ignited the combustible gases inside the pipeline. The flame spread gradually through the 246-meter-long main and branch nitrogen pipelines toward the storage tank. Once it reached the top of the tank, it ignited a large amount of combustible gas there, resulting in an explosion in the gaseous space above the floating roof of the tank.

(II) Indirect causes: 1. Yangmei Taohua New Materials Company failed to fulfill its responsibilities regarding safe production, and its safety management was inadequate. (1) The safety production responsibility system is not properly implemented. The company’s leadership and employees have not yet shifted their mindset from the infrastructure construction phase to the trial production phase, and their safety awareness is poor. Following the internal organizational restructuring, the job responsibility systems were not adjusted in a timely manner, resulting in unclear safety responsibilities and undefined job duties. The safety management capabilities are weak; there are no deputy positions responsible for production and safety, internal management is inefficient, and various levels fail to carry out their duties in a proactive and effective manner. After the accident occurred, it was not reported in a timely manner to the relevant **departments and superior authorities as required. (2) Trial production management is not strict. The relevant regulations regarding trial production for hazardous chemical construction projects and the principle of \"simultaneous implementation\" of safety facilities were not strictly followed; feeding operations were carried out in violation of these rules, despite the fact that the nitrogen system and oil and gas recovery facilities were not in proper operation, pressure monitoring devices for storage tanks were not installed, detection and alarm systems for flammable and toxic gases were not in use, and it was unclear whether the storage tanks met safety requirements. (3) The operating procedures and process control parameters are not strictly followed. Before feeding the tank farm unit, the crude benzene storage tanks were not purged and displaced with nitrogen as required by the commissioning plan. After the crude benzene was fed in, the prohibition against the floating tray reaching the bottom, as well as the process control requirement that the minimum liquid level must not be below 2000 mm, were not strictly enforced. (4) Poor management of hot work. In areas of this genus where work involving hot work at level 2 is required, work permits are issued as if it were hot work at level 2. Approvals are given in violation of regulations when gas analysis has not been conducted, when the nitrogen pipelines used for hot work are not properly isolated from the storage tanks, and when safety checks on site have not been carried out. There are also cases of someone signing approvals on behalf of another person, and the person responsible for monitoring the hot work leaves the site to carry out inspections. (5) The management of process and equipment changes is arbitrary. During the renovation of the oil and gas recovery system in the storage tank installations in the tank farm, no risk assessment was conducted for converting the internal floating roof tanks into those equipped with nitrogen seals; there was no proper design, no appropriate change management was carried out as required, and no corresponding measures were taken. The modification of the nitrogen pipeline distribution panel and the replacement of the storage tank level gauge were also not subject to the required change management procedures. (6) Safety education and training are inadequate. II. The content of the level 2 and level 3 safety training is incomplete and lacks specificity; employees do not study seriously, assessments are not strict, and specialized training for special operations prior to trial production is not properly organized. Employees are not familiar with safety knowledge and regulations such as job-related process technologies, operating procedures, rules and regulations, as well as existing safety risks. (7) Failure to conduct thorough inspections and rectifications of potential hazards. In the various inspections carried out, no hazards such as the floating pads touching the bottom as explicitly required by the ban, or the bypass valves of the nitrogen pipelines that should have been closed being in an open state, were detected. Some of the identified hazards, as well as those related to the gas detection and alarm systems that were not put into use as reported by the branch plant, remained unrepaired for a long time.

2. Before carrying out hot work, the maintenance personnel assigned to the Qingxu Baoyun project department of Taiyuan Chemical Industry Group Engineering Construction Co., Ltd. failed to properly identify the potential dangers and hazardous factors present at the work site and during the operation, in accordance with the safety regulations for special operations in chemical production facilities; they also failed to implement the necessary safety precautions that should be taken before performing hot work. The project department failed to provide adequate daily management, training and education, supervision and inspection, as well as follow-up oversight for the maintenance personnel working on the tank farm facilities. 3. Yangmei Chemical Group failed to provide adequate supervision and management over Yangmei Taohua New Materials Company. During the inspection of Yangmei Taihua New Materials Company, the identified potential risks were not followed up on promptly to ensure corrective actions were taken, resulting in a lack of closed-loop management ； Failures were made to detect issues at Yangmei Taihua New Materials Company, such as inadequate identification of potential hazards, insufficient safety training, lax management of trial production, and chaotic procedures for handling hot work. 4. The safety supervision authorities at the Taiyuan city and Qingxu county levels have different understandings regarding their powers and responsibilities in overseeing safety in hazardous chemical construction projects; they failed to refine the safety supervision powers and responsibilities related to Yangmei Taohua New Materials Company in accordance with the requirements set by their superiors. The local supervision responsibilities were not fulfilled properly; the special rectification efforts regarding hazardous chemicals and the special inspections related to specific types of operations were not promptly communicated and implemented to Yangmei Taihua New Materials Company. 5. Zhejiang Meiyang International Engineering Design Company failed to adopt a weak-roof structure design for the internal floating roof storage tanks in accordance with the \"Code for Fire Protection Design of Petrochemical Enterprises\" (GB50160-2008); as a result, when an accident occurred, the entire tank body and its bottom were completely torn apart, further exacerbating the situation. (III) Nature of the accident: The “8.18” explosion and combustion incident in the crude benzene storage tank at Yangmei Group Taiyuan Chemical New Materials Co., Ltd. was a routine production safety liability accident.

Hehe, a simple mistake led to big trouble. It’s hard to understand how such a chemical company could have such problems; this speaks volumes about the quality of its management.