【Haichuan Instrumentation and Control Accident Case】The \"11·2\" fire at Beihai LNG Company: lack of pipeline isolation and engineers activating interlocks blindly

Sequence of the incident: On the morning of November 2, 2020, Sinopec 10th Construction Company assigned workers to carry out work on the branch pipe for loading liquid into tank TK-02 with a DN300 diameter (in other words, welding work was performed on the LNG export pipeline located on the second-level platform in front of tank TK-02; a section of 500 mm in length was cut from the existing DN300 low-pressure pump outlet pipe, and a tee was added). At around 8 o’clock, Tang Xiaohua, a laboratory technician from the Metrology and Testing Center of Beihai LNG Company, arrived at the platform in front of tank TK-02 to carry out combustible gas sampling. At 8:15, personnel from the Beihai LNG Company’s receiving station and those from the construction party arrived at the work site one after another. The personnel from Beihai LNG Company who arrived at the construction site included Song Zongjie, deputy director of the Production and Operation Department; Liang Chi, a process engineer from the receiving station’s operation team and also the leader of the daily work safety analysis; equipment engineers Yang Junjie and Lu Yongfei. Three firefighters, Shu Dengyue, Zhou Fuqiang, and Zhang Xingzhuang, were responsible for monitoring the fire. The personnel from the construction party include Sun Jianjun, the deputy manager of the general contracting project; plumbers Chen Haiqin and Guo Zongyan; welders Chen Shuaijie and Cheng Zhenyu; general workers Xie Yong and Chen Yang; and construction supervisor Pang Xiaoli. Except for Sun Jianjun, who is a member of Sinopec 10th Construction Company, the rest are all employees of the installation subcontractor, Henan Hongyu. There is also Wu Xianwen from Sichuan Yitong Safety Supervision. Liang Chi and Yang Junjie determined the combustible gas sampling points, while Lu Yongfei assisted Tang Xiaohua with the sampling. At around 9:30, Yuan Yongjun, the head of the operation department at Beihai LNG Company’s receiving station, and Chen Xueyan, the company’s safety director, arrived at the site where the work was being carried out. Sun Jianjun left the site after checking the construction preparations. The gas sampling results are satisfactory (a level below 10% LEL is considered acceptable); the LEL value was 9.36%. Liang signed the fire operation permit. At around 9:45, Yuan Yongjun and Chen Xueyan signed the fire operation permit in turn, after which the two left the site to attend the regular scheduling meeting scheduled for 10:00. Before leaving, they instructed that another purging process be carried out to reduce the level of combustible gases and to report on the results. At 10 o’clock, a dispatch meeting for the reception station was held, with participants including Chen Xueyan, Yuan Yongjun, Song Pengyuan, the deputy director of the operation department at the reception station, and Zhang Shuhao, the dispatch officer at the reception station (who served as the chief dispatcher on that day), among others. At around 10 o’clock, Song Zongjie left tank TK-02 due to other tasks and returned to the office area. At around 11 o’clock, the acceptable value for gas sampling was LEL 3.82%. At 11:14, Tang Xiaohua filled in the sampling and analysis results on the spot, signed them, and left. Pang Xiaoli left a little earlier. A few minutes later, Lu Yongfei also left the platform; upon reaching the ground, he saw that the construction workers had started working. After about 50% of the work on the pipeline’s first section had been completed, Chen Haiqin told Chen Shuaijie, Cheng Zhenyu, Xie Yong, and Chen Yang to go back and eat first, and the four of them left together. At around 11:20, Song Zongjie returned to the work platform and found that the section of the pipeline near the tank had been cut. At around 11 o’clock, the coordination meeting came to an end, and Yuan Yongjun, Song Pengyuan, Zhang Shuhao, and others returned to their offices respectively. At around 11:30, Song Pengyuan received a call via walkie-talkie from Liang Chi, asking about the progress of completing the work order for the instrument interlock related to the forced shutdown of the valve. Song Pengyuan then took the instrument interlock work order to the control room to hand it over to Zhang Shuhao for processing, before returning to his own office. At 11:37, Zhang Shuhao contacted Cui Qiang, an instrumentation engineer at the station’s maintenance center, by phone and asked him to take the form to Lei Jiangkai, the head of the maintenance center, for signing. At 11:40, Song Pengyuan called to urge Cui Qiang to handle the instrument interlock work order as soon as possible. Since Cui Qiang was eating at that time, he asked Lai Xiaolin, who was nearby, to go to the control room to get the form. Lai Xiaolin arrived at the control room, obtained the instrument interlock work order from Zhang Shuhao, and encountered Song Pengyuan in the corridor after leaving. Song Pengyuan urged Lai Xiaolin to handle it quickly. Lai Xiaolin failed to carry out a series of subsequent procedures such as review, approval, and signature for the instrument interlock work order; without the supervision of any other instrument engineers, he entered the engineer station (with Song Pengyuan entering as well) and performed the operations alone. At around 11:44, Song Zongjie left the scene on his bicycle. At 11:44:48 (all subsequent event times are based on the clock of the tank farm SIS system), Lai Xiaolin used the SIS system to force the closure of valve 0301-XV-2001; immediately thereafter, valve 0301-XV-2001 opened and LNG began to be discharged. At 11:45:00, the valve was fully opened. About 10 seconds after the LNG was ejected, a fire broke out on the platform in front of the TK-02 tank. At 11:51:59, valve 0301-XV-2001 closed due to a power loss (subsequent investigations revealed that there was a short circuit from the positive terminal of the valve control circuit cable to ground, and the fuse for the corresponding circuit inside the cabinet blew, resulting in the power loss). The open flame in front of the TK-02 storage tank was extinguished as the valve was closed. When the LNG started to spray and catch fire, there were 8 people on the platform in front of Tank TK-02, namely Liang Chi, Yang Junjie, Chen Haiqin, Guo Zongyan, Wu Xianwen, Shu Dengyue, Zhang Xingzhuang, and Zhou Fuqiang; there was 1 person on the tank top, named Tian Wen.

Post-incident site inspection: Upon inspection, it was found that the work platform in front of tank TK-02 had been damaged to varying degrees; the structure of the second-level platform remained relatively stable； The upper three platforms of the tank were severely damaged by fire. The facilities on the tank top platform were severely damaged by fire ； 0301-XV-2001 valve: the actuator fails to determine the valve status ； Approximately 2,600 meters of various cables were damaged, 40 pressure gauges were damaged, 3 detectors were damaged, and 42 other measuring instruments were damaged. The process pipelines on the tank front platform suffered minimal damage due to the protection provided by the insulation layer (see Figures 7, 8, and 9 for details).

Analysis of the accident cause: (I) Direct cause: Upon investigation, it was determined that the direct cause of the accident was as follows: During the welding work carried out on the main outlet pipe of the low-pressure pump on the second floor platform of tank TK-02 as part of the project to load both rich and lean liquids in phase two, isolation valve 0301-XV-2001 was opened. LNG from the low-pressure transmission pipeline sprayed out through the cut opening, and the mixture of LNG mist and air ignited upon encountering some form of ignition source. Analysis shows that the source of the fire was the ignition energy that could be generated by cables whose insulating protective layers became brittle and detached as a result of the impact from the low-temperature LNG spray. (II) Indirect causes: 1.0301-XV-2001 – Improper isolation method of the valve. In accordance with the provisions of Sinopec Natural Gas Branch’s “Notice on the Issuance of Relevant Regulations” (Shareholding Natural Gas Safety [2018] No. 14), this hot work falls under the category of “high-risk hot work,” and “reliable sealing and isolation must be carried out.” The valve of tank TK-02 0301-XV-2001 utilizes instrument-based logical isolation rather than physical isolation through the separation of power sources, which led to isolation failure during operation and consequently an accident. 2. Instrument engineer Lai Xiaolin failed to follow the prescribed approval procedures and operating procedures for instrument interlocks during the instrument interlock operation. Without the instrument interlock work order yet being approved and without a supervisor present, forced operation of the SIS interlock was initiated, and an operational error caused valve 0301-XV-2001 to open. After the task was completed, the forced output result of the SIS interlock was not verified. 3. The conditions for carrying out hot work were not adequately verified. The pipe cutting operation was started without confirming that the SIS forced interlock for valve 0301-XV-2001 had been activated in accordance with the provisions of the \"Isolation Plan for Leak Testing of Valves and Hot Work Procedures in Storage Tank Liquid-Laden Pipelines,\" which led to LNG spraying out from the cut pipe opening when the valve opened abnormally and resulting in a fire.

4. Insufficient awareness of safety risks and inadequate risk control. (1) Beihai LNG Company failed to properly implement the safety production requirements during the transition period of the oil and gas pipeline network reform, and had an insufficient awareness of safety risks. (2) The \"Construction Technical Plan for Connecting the Rich and Lean Liquid Pipelines in the Second Phase of Guangxi LNG Project\" prepared by the contractor does not require Beihai LNG Company to provide explanations regarding the process flow, as well as safety risk control plans and measures ； There are no clear definitions of the job responsibilities and scope of work for personnel at the construction site, no identification of the specific individuals who are authorized to issue construction orders, and no clear indication of the emergency evacuation routes in the event of a fire ； On November 2, project manager Hu Shaosen failed to arrive at the site as required by the plan regarding the allocation of construction workers, and failed to fulfill his supervision duties properly. The \"Plan for Leak Testing of Valves Installed on the Liquid-Laden Lines of Storage Tanks and for Isolating Processes Involving Hot Work\" developed by Beihai LNG Company is inadequate; it does not specify the person responsible for organizing and carrying out the leak testing of valves on those lines as well as the isolation procedures for hot work, nor does it define the roles of other personnel involved in this work ； There is insufficient hazard analysis and identification of safety risks for high-risk operations such as production while construction is in progress; furthermore, no discussions are held with the contractors prior to such operations regarding the process procedures, as well as safety risk control plans and measures. Due to the fact that the approval processes for the instrument interlock work order and the (special-grade) fire use permit are separate from each other, and neither the contractor’s plan nor North Sea LNG Company’s plan specifies any particular individuals responsible for confirming the handover of tasks, the construction organization is not thorough enough. 5. The labor production organization model of \"small owners, large contractors\" results in inadequate implementation of responsibilities for safe production management. 6. Inadequate contractor management. Without the consent of the employer, Sinopec 10th Construction Company subcontracted the installation work for Phase 2 of the LNG project to Henan Hongyu, which does not possess the necessary qualifications.