The “9·14” naphthalene storage tank explosion incident at Shaoxing Huayuan Chemical Co., Ltd

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Source: China Chemical Safety Association I. Accident Investigation and Analysis (I) Overview of the Accident 1. Brief Introduction to the Accident At 8:50 on September 14, 2013, an explosion occurred in a naphthalene storage tank at Shaoxing Huayuan Chemical Co., Ltd. (hereinafter referred to as Huayuan Company), which is located in the industrial zone of Daoxu Town, Shangyu District; this accident resulted in 3 deaths. 2. Cause analysis: (1) Direct cause – Yan Jiangqiang, an employee of Huayuan Company, used oxygen and acetylene cutting guns along with an open flame to heat the crystalline naphthalene pipes, which caused the molten naphthalene to spill out and catch fire upon contact with the open flame. The liquid naphthalene in the transfer pipe continued to flow out and burned near the manhole cover on top of Tank 1. The manhole cover, which had no insulating material, was directly exposed to the flames, which in turn ignited the crystalline naphthalene inside the manhole cover. This caused the liquid naphthalene in Tank 1 to vaporize further, reaching the explosive limit and resulting in an explosion followed by combustion. (2) Indirect cause ① Huayuan Company proceeded with production on its own during the period of suspension for rectification. On February 4, 2013, the company was subject to an administrative penalty in the form of a suspension of operations for rectification by the safety regulatory authorities; yet Huayuan Company continued to carry out production activities, and even resorted to deception during inspections by those authorities in order to pass off as compliant. ②Huayuan Company fails to fulfill its primary responsibilities for safe production. The company’s management has a severe lack of awareness regarding safe production practices, and fails to properly implement relevant laws and regulations. During the operation to clear blockages of crystalline naphthalene in the naphthalene transport pipeline, the regulations regarding hot work were severely violated, and improper procedures were used. ③Huayuan Company has chaotic safety management. The company adopts a family-style management model, resulting in unclear responsibilities for safety production management. Huayuan Company has two full-time safety officers, one of whom is not engaged in work related to safety management and has failed to fulfill the duties of a safety officer ； The other person is the actual person in charge of safety production at Huayuan Company; however, his safety officer certificate has expired. He also serves as a warehouse manager and holds a certificate for operating motor vehicles in warehouse areas. ④The management and operators at Huayuan Company lack the necessary professional knowledge and are not qualified for the requirements of their positions. Most of the company’s management staff are relatives of the company’s owners. Both managers and employees generally have a education level below junior high school; they lack knowledge and skills in chemical engineering as well as production techniques. They start working without receiving proper safety training ； Yan Jiangqiang, who was involved in the sulfonation process, operated welding equipment without a license and improperly used gas cutting tools with an open flame to clear the flammable and explosive crystalline naphthalene from the pipes. This caused the crystalline naphthalene to melt and flow onto the roof of Tank No. 1, leading to a fire; his improper handling of the situation further resulted in the explosion of the storage tank. ⑤While fulfilling their responsibilities for local safety management in Daoxu Town, the local people have done a great deal of work – issuing relevant documents in a timely manner and organizing comprehensive inspections and rectification efforts related to safety – yet there are still issues such as a shortage of safety supervisors and insufficient professional skills. As a result, it was not possible to detect in time that Huayuan Company had started production on its own during the period when it should have been shut down for rectification. ⑥The relevant regulatory authorities in Shangyu District had weaknesses in their oversight of Huayuan Company during the period when it was shut down for rectification; the on-site inspections were not thorough enough, and they failed to detect the illegal act of the company proceeding with the production of water-reducing agents without authorization during that time. (II) Basic Information 1. Information on the units involved in the accident: Huayuan Company is located in the industrial zone of Daoxu Town, Shangyu District. It was established and put into operation in July 2000. The legal representative is Mr. Hang, with a registered capital of 8 million yuan. The company currently has 35 employees, covers an area of 20,000 m2, and has a building area of 8,000 m2. Its business scope includes the production and manufacturing of chemical additives other than hazardous chemicals, as well as water reducers of type N. It offers more than seventy different products, including fluorescent brightener series, silicone series, leveling agents series, thickeners series, waterproofing agents series, dispersants series, emulsifiers series, post-treatment agents series, and cleaning agents series. The accident occurred at an industrial naphthalene warehouse, which is a single-story wooden structure with a pitched roof and was built in 1999. The warehouse has an area of 162 m2 (18m × 9m). Three fixed-roof storage tanks for industrial naphthalene are located there from east to west; Tank No. 1 (V60 m3, Ф3.7m, H5.8m) contains 2.4 tons of liquid naphthalene ； Tank No. 2 (V30m3, Ф3.7m, H3m) contains 27 tons of liquid naphthalene ； Tank No. 3 (V60m3, Ф3.7m, H5.8m) contains 57 tons of liquid naphthalene. The three storage tanks are equipped with steam tracing, and Ф110mm plastic vent pipes are installed for centralized discharge. Purchased liquid naphthalene is pumped into Tank 3, and then from the bottom of Tank 3 it is pumped to the top of Tank 1. Tank 1 is directly connected to Tank 2; Tank 2 is a naphthalene melting tank, and liquid naphthalene is pumped via the discharge port at the bottom of Tank 1 to the reaction vessels in the workshop for use as a reactant. The substance involved in the accident is industrial naphthalene; Huayuan Company uses 680 tons of it per year for the production of the water-reducing agent N. Liquid naphthalene is used, through a series of chemical reactions with other chemicals, to produce the water-reducing agent N, with an annual production volume of 1,000 tons. Huayuan Company uses a certain amount of hazardous chemicals in its production process, but it does not need to obtain any permits related to hazardous chemicals. (III) Timeline of the incident: Date and time – At 8:30 on September 14, Yan Jiangqiang, an employee of Huayuan Company (working in the sulfonate chemicals department), discovered while unloading purchased liquid naphthalene at the liquid naphthalene warehouse that the Ф45mm delivery pipeline running from Tank No. 3 to Tank No. 1 in the liquid naphthalene storage area was blocked by crystallized naphthalene. The company assigned Yan Jiangqiang and Zhang (a mechanic) to clear the blockage. Yan removed the Ф45mm pipe flange at the lower end of the Ф500mm manhole cover on Tank No. 1; he tried to clear the pipeline using steel bars first, and then by heating it with steam, but neither method worked. He then suggested using oxygen and acetylene cutters to burn away the crystallized naphthalene in the pipeline. Hang A (the warehouse manager, and sister of Hang Fu) asked Zhang to fetch oxygen cylinders and other cutting tools, but Zhang objected. Nevertheless, he still brought the oxygen cylinders and other cutting tools to the work site; after unsuccessful attempts to persuade him otherwise, he left the site. Yan picked up the oxy-acetylene torch to carry out welding work, heating the blocked pipeline, which caused molten naphthalene to spill out; upon coming into contact with the open flame at the tip of the torch, a fire broke out. Hang A and Chen (who had come to see Hang A) at the work site quickly called for help. Dong and Xu, company employees who were near the warehouse, heard the cries and rushed to the top of the tank to use woven bags to smother the open flames. At 8:50 on September 14, Tank No. 1 exploded. The explosion caused the wooden roof of the liquid naphthalene warehouse to be ripped off, leading to a massive fire; the roof of the tank was thrown by the force of the explosion 30 meters away onto a highway bridge. At 9:20 on September 14, the emergency vehicle arrived, and subsequently other employees from the factory found the 3 injured workers. The \"120\" ambulances transported all three to Shangyu District People’s Hospital for treatment, but they died despite efforts to save them. (IV) Accident losses: The explosion resulted in 3 deaths and direct economic losses of approximately 1.05 million yuan. http://www.chemicalsafety.org.cn/uploads/allimg/161209/7-1612091I105V1.jpg Figure 1: The naphthalene tank that exploded. http://www.chemicalsafety.org.cn/uploads/allimg/161209/7-1612091I116221.jpg Figure 2: The building in which the naphthalene storage tank is located. (V) Analysis of the cause of the accident: On-site investigations revealed that the horizontal distance between the transfer pipe connecting Tank No. 3 to Tank No. 1 was 10 meters, and the pipe was insulated with insulating material. At the explosion site, the fixed roof of Tank No. 1 was blown away, while the other two storage tanks remained intact. The roof of Tank No. 1, which exploded, was made of iron plates 5 mm thick, fabricated locally. The inner wall is relatively rough, with blackened marks within about 50 cm of the feed inlet; the areas that have not been smoked are covered in rust. The tank top is equipped with a manhole cover and a vent; there is no insulation material near the manhole cover, and there are obvious signs of burning on the outer wall. The welding patches at the original welds between the manhole cover and the tank top have fallen off, indicating that the outer wall of the tank top was on fire for some time. The blockage caused by crystalline naphthalene is located approximately 40 cm horizontally and 40 cm vertically from the feed inlet at the top of Tank No. 1; the flange connecting the blockage site to the feed inlet has been removed ； Tools such as gas cutters were left at the scene. An analysis of the materials in the three storage tanks on site showed that all of these tanks were used to store liquid industrial naphthalene. The chemical properties of liquid industrial naphthalene remain unchanged; at normal temperature and pressure, it is classified as a flammable solid of Category 4.1. Its explosion limits are 2.5 g/m2 for dust and 0.9–5.9% for vapor. Melting point: 80.2°C, boiling point: 217.76°C, flash point: 80°C, auto-ignition temperature: 526.1°C. Soluble in benzene, ethanol, and ethers; insoluble in water. 1. Analysis of the direct cause: Employee Yan Jiangqiang used oxygen and acetylene cutting guns along with an open flame to heat the crystalline naphthalene tubes, causing the molten naphthalene to spill over and catch fire upon contact with the open flame. The liquid naphthalene in the transfer pipe continued to flow out and burned near the manhole cover on top of Tank 1. The manhole cover, which had no insulating material, was directly exposed to the flames, which in turn ignited the crystalline naphthalene inside the manhole cover. This caused the liquid naphthalene in Tank 1 to vaporize further, reaching the explosive limit and resulting in an explosion followed by combustion. 2. Analysis of indirect causes: ① During the period of suspension for rectification, Huayuan Company proceeded with production without authorization. On February 4, 2013, the company was subject to an administrative penalty in the form of a suspension of operations for rectification by the safety regulatory authorities; yet Huayuan Company continued to carry out production activities, and even resorted to deception during inspections by those authorities in order to pass off as compliant. ②Huayuan Company fails to fulfill its primary responsibilities for safe production. The company’s management has a severe lack of awareness regarding safe production practices, and fails to properly implement relevant laws and regulations. During the operation to clear blockages of crystalline naphthalene in the naphthalene transport pipeline, the regulations regarding hot work were severely violated, and improper procedures were used. ③Huayuan Company has chaotic safety management. The company adopts a family-style management model, resulting in unclear responsibilities for safety production management. Huayuan Company has two full-time safety officers, one of whom is not engaged in work related to safety management and has failed to fulfill the duties of a safety officer ； The other person is the actual person in charge of safety production at Huayuan Company; however, his safety officer certificate has expired. He also serves as a warehouse manager and holds a certificate for operating motor vehicles in warehouse areas. ④The management and operators at Huayuan Company lack the necessary professional knowledge and are not qualified for the requirements of their positions. Most of the company’s management staff are relatives of the company’s owners. Both managers and employees generally have a education level below junior high school; they lack knowledge and skills in chemical engineering as well as production techniques. They start working without receiving proper safety training ； Yan, who was involved in the sulfonation process, operated welding equipment without a license and used gas cutting tools with an open flame to clear the flammable and explosive crystalline naphthalene from the pipes. This caused the crystalline naphthalene to melt and flow onto the roof of Tank No. 1, resulting in a fire; furthermore, his improper handling of the situation led directly to the explosion of the storage tank. ⑤While fulfilling their responsibilities for local safety management in Daoxu Town, the local people have done a great deal of work – issuing relevant documents in a timely manner and organizing comprehensive inspections and rectification efforts related to safety – yet there are still issues such as a shortage of safety supervisors and insufficient professional skills. As a result, it was not possible to detect in time that Huayuan Company had started production on its own during the period when it should have been shut down for rectification. ⑥The relevant regulatory authorities in Shangyu District had weaknesses in their oversight of Huayuan Company during the period when it was shut down for rectification; the on-site inspections were not thorough enough, and they failed to detect the illegal act of the company proceeding with the production of water-reducing agents without authorization during that time. II. Emergency Response to the Incident At 9:01 a.m. on September 14, 2013, the command center of the Shangyu District Fire Brigade received an alarm. Upon receiving the call, the dispatch center of the Shangyu District Fire Brigade quickly dispatched 4 fire trucks and 22 firefighters to the scene to handle the situation. The Shangyu District Public Security Bureau, the Shaoxing Branch of the High-Speed Traffic Police, the Emergency Management Office, the Quality Supervision Bureau, the Health Bureau, the Meteorological Bureau, the Environmental Protection Bureau, the Work Safety Supervision Bureau, and the Daoxu Town government, among other agencies, also rushed to the scene immediately to provide assistance. Upon arriving at the scene, the firefighters immediately organized efforts to extinguish the fire. The first injured person was brought to the hospital at 9:40, the second at 9:53, and the third at 10:45. At 10:50, the fire at the scene was completely extinguished. After the accident, the Shaoxing Municipal Party Committee and the municipal authorities attached great importance to it; Vice Mayor Yang rushed to the accident site immediately to oversee the rescue efforts on site ； The Shaoxing Work Safety Supervision Bureau also immediately participated in the on-site handling ； Immediately after the accident, the Shangyu District Party Committee and the municipal authorities activated their emergency response plans. Vice Mayor Wu of Shangyu District served as the overall commander of the emergency rescue efforts, with 7 rescue teams established to handle tasks such as rescuing victims at the scene, carrying out disaster relief operations, controlling hazardous sources, establishing safety barriers and organizing evacuations, providing logistical support, conducting environmental monitoring, and managing public relations. An accident handling team was established to actively carry out the follow-up work related to the accident. On that day, the People’s ** of Shaoxing City promptly established an accident investigation team to carry out investigations and gather evidence related to the accident. Thanks to the rapid actions and appropriate measures taken by the municipal and county (city) levels **as well as the relevant departments, the investigation and evidence collection related to the accident, along with the follow-up handling, have progressed smoothly. III. Reflections and Recommendations (1) Huayuan Company has poor safety conditions; its equipment, facilities, and production processes are outdated and do not comply with safety regulations. It is recommended that the people’s government of Shangyu District order it to cease the production of chemical products and pursue a transformation. (II) The people of Daoxu Town must earnestly learn from the lessons of this accident, use it as a warning to fulfill their responsibilities for ensuring safe production at the local level. They need to have a thorough understanding of the production and operation conditions of the enterprises under their jurisdiction, and conduct safety inspections of all these enterprises to ensure that no gaps or blind spots remain. Experts should be organized to conduct a comprehensive inspection of the implementation in hazardous chemical production and operation units, including the layout of production workshops, production process technologies, the safety and reliability of equipment and facilities, the establishment of safety management organizations, the staffing of safety management personnel, the competence of employees, safety management practices, responsibility systems, and operating procedures. Strengthen supervision over high-risk processes involving flammable, explosive, toxic, and harmful substances; firms that do not meet the requirements must be ordered to suspend operations for rectification. Those that still fail to meet safety standards after such rectifications should be advised to close down promptly, in order to effectively prevent similar accidents from occurring. To address the issues of a large number of chemical enterprises along with outdated facilities, equipment, and processes, it is necessary to further strengthen the regulatory capacity in the chemical sector and enhance supervision over the safe production of these enterprises. (III) The people of Shangyu District must draw inferences from this incident and take concrete steps to strengthen work related to safety production. It is necessary to further strengthen safety supervision and carry out comprehensive inspections for potential hazards in production safety, with a focus on small and old chemical product manufacturing enterprises. For those enterprises with low levels of technological capability, control systems, and safety conditions, those that should be shut down must be shut down, and those that should be closed down must be closed down. In accordance with the relevant documents from Zhejiang Province and Shaoxing City, as well as the requirements set out in the supervision letters issued by Zhejiang Province’s Safety Committee, efforts must be accelerated to close down and relocate those small chemical enterprises that have poor safety conditions within the jurisdiction. It is necessary to study and formulate specific measures to strengthen safety management in the chemical industry, taking into account the characteristics of this major industrial sector. In particular, the number of specialized safety supervisors in the chemical industry should be increased, and safety supervision over chemical enterprises should be enhanced to ensure a steady improvement in the situation regarding safe production.