Analysis of the cooling tower accident at Fengcheng Power Plant in Jiangxi (reprinted)

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Analysis of the cooling tower accident at Fengcheng Power Plant in Jiangxi. On around 7 a.m. on November 24, 2016, a severe accident occurred at a cooling tower under construction at a power plant in Fengcheng, Jiangxi; to date, it has resulted in 74 deaths and 2 injuries. The search and rescue operations at the scene have been largely completed, while the cause of the accident is still under investigation. No one knows what exactly caused such a serious accident until the investigation report is released, but we can still conduct some analysis based on the available information. Since this article is merely a compilation and analysis based on existing online materials, there may be inaccuracies; the future accident reports shall take precedence. The incident occurred in Fengcheng, Jiangxi, where a cooling tower was under construction to support a thermal power generation unit with an installed capacity of 2×1000 megawatts. According to news reports, the cooling tower is designed to be 165 meters tall, and more than 70 meters of it has already been built. What does a design height of 165 meters mean? According to the \"Code for Design of Industrial Circulating Water Cooling Systems (GB/T 50102-2014)\\", a cooling tower with a height of 165 meters is already the largest model of cooling towers in China! http://ww3.sinaimg.cn/large/6b48e3e4jw1fa4qsdd1szj21kw0r647v.jpg The bottom of the 165-meter-high cooling tower has a diameter of 124 meters; its base area is 12,000 square meters, with a perimeter of nearly 400 meters ； The air inlet of the inclined support at the bottom of the cooling tower is 11.6 meters high. It is truly regrettable that such an accident occurred in a project of this scale. What exactly was the cause of the accident? Based on my personal analysis, there may be the following 3 reasons: 1. Insufficient cement strength led to the collapse of the operating platform ； 2. Failure of the operation platform’s own anchoring facilities ； 3. The collapse of the tower crane triggered a chain reaction. 1. Insufficient cement strength leading to the collapse of the operating platform: I believe this is the most likely cause, so I will devote most of the discussion to it. 「There are two possibilities for \"insufficient cement strength\": one is the use of cement that does not meet the required standards ； Secondly, the curing time for the cement was insufficient, which led to the formwork being removed before the design strength was achieved. After being poured into concrete, it needs to be \"cured\" for a certain period of time; only once it has set and reached a sufficient strength can the formwork be removed. If the quality of the concrete used in on-site pouring is substandard, and the on-site technicians fail to test the concrete’s strength but instead rely on past experience regarding curing times, the concrete will not have sufficient strength after the formwork is removed, which will naturally lead to collapse. Requirements for concrete strength in the \"Code for Design of Industrial Circulating Water Cooling Systems\": http://ww1.sinaimg.cn/large/6b48e3e4gw1fa4qxqno5xj21930nxdmw.jpg Even when the quality of the concrete is satisfactory, too short a curing time can also lead to problems. Since the curing time of concrete is greatly affected by temperature, concrete requires more time to reach its design strength in low-temperature conditions. According to many reports, the construction site where the incident occurred was under a tight deadline, with the slogan \"Work together for 100 days\" being used; therefore, it is highly likely that the accident was caused by the pressure to meet this deadline. The \"Code for Construction and Quality Acceptance of Hyperbolic Cooling Towers (GB 50573-2010)\") also contains relevant regulations on this topic: http://ww3.sinaimg.cn/large/6b48e3e4gw1fa4qyfk65gj212x0i4gsp.jpg A report in the Beijing News cited sources who said, \"The accident occurred during the final stage of construction; workers from Hebei were removing the wooden scaffolding surrounding the condensing tower, but the concrete, which had not yet dried completely, began to crumble, leading to the collapse.\" 」This claim is highly credible. Let’s take a look at a schematic diagram: http://ww3.sinaimg.cn/large/6b48e3e4gw1fa4rgzpiykj21kw1vqwxa.jpg. The common construction method for cooling towers these days involves using the already poured reinforced concrete tower walls as a support, on which working platforms and formwork are erected. Once the poured concrete has reached its strength, remove formwork A from below and install it on top of formwork B to proceed with the next round of pouring. However, when formwork A was removed, the concrete at formwork B had not yet reached its design strength and was not strong enough to support the entire operating platform, resulting in a collapse. As construction was carried out simultaneously around the entire upper part of the cooling tower, the connected work platforms collapsed, causing workers to fall from a height of over 70 meters. http://ww1.sinaimg.cn/large/6b48e3e4gw1fa4r0util1g20dc0a04qv.gif In fact, there have been precedents for such cooling tower accidents, and they are very similar to this one! In 1978, an accident involving the collapse of an operating platform occurred at a power plant under construction on Willow Island in West Virginia, USA, resulting in 51 deaths and making it one of the worst accidents in U.S. construction history. The cause of the accident was the removal of the formwork before the poured concrete had dried, resulting in severe casualties. People did not learn from the accident; it is heartbreaking that a similar incident occurred in China decades later. http://ww1.sinaimg.cn/large/6b48e3e4gw1fa4r28m3i0g20dc0a07wp.gif Since there are no detailed photos of the top of the cooling tower, the true cause of the accident remains unknown. Here, I’d like to complain about the news media in general: there are so many photos online taken right above the site of the cooling tower accident – a ** circular shape – and the photos taken by different media outlets are astonishingly identical. But people can hardly get any information from such photos! http://ww1.sinaimg.cn/large/6b48e3e4gw1fa4r3ac40dj20pu0hmq69.jpg Since a drone was already used for aerial photography, why not get closer? Why not shoot some details of the areas where the operating platforms collapsed? If it were possible to capture traces of the tension on bolts and rebar, as well as the pattern of cracks in the concrete, the analysis of the accident could be much more detailed. 2. Failure of the platform’s own anchoring facilities: It is possible for the platform to collapse due to the failure or aging of its anchoring equipment, or because not all bolts have been tightened as required, which can trigger a chain reaction. The \"Code for Construction and Quality Inspection of Hyperbolic Cooling Towers (GB 50573-2010)\") also addresses this issue: http://ww3.sinaimg.cn/large/6b48e3e4jw1fa4r5wvtyoj20zp0ctn4s.jpg Section 6.3.7, highlighted in bold, constitutes mandatory provisions that must be strictly followed; however, due to insufficient information available at present, it is not possible to determine the cause in this case. 3. The collapse of the tower crane triggered a chain reaction: It was CCTV and The Paper that claimed the collapse of the tower crane caused the operation platform to fall, and The Paper even created a 3D simulation animation to illustrate the scene of the accident. But I think the current data is not sufficient to draw such a conclusion. http://ww3.sinaimg.cn/large/6b48e3e4gw1fa4r7lwoq8j20xc18ggq9.jpg The tower crane located inside the cooling tower serves as a passage for pumping concrete, as well as a route for workers to go up and down. In such accidents, since workers have only one escape route, they often have nowhere to go once an accident occurs. There is no exact figure regarding the proportion of casualties among the workers on the ground and in the cooling towers. However, according to reports from Xinhua News Agency, \"Apart from the workers on the ground floor, everyone above fell and were crushed by materials such as rebar.\" Wang Yaolong, a worker who managed to escape from the ground floor, said that all the workers on that floor escaped safely, with only two sustaining minor injuries. This news suggests that all the workers in the towers died, while only two people on the ground were injured. Due to the unique design of cooling tower structures, the safety equipment for workers is still inadequate. It is hoped that manufacturers will pay attention to workers’ safety and develop new safety mechanisms to enable them to escape in the event of an accident. Furthermore, I believe that workers’ blind reliance on experience rather than science during construction could also be a cause of accidents; if they had used instruments to test the strength of the concrete as required before removing the formwork, this accident could likely have been avoided. Construction workers have very tough jobs. It is said that most of those who died were carpenters from Hebei; they came all the way to Jiangxi to work, only to suffer such a tragedy. These workers were likely the breadwinners of their families, and it’s hard to imagine the situation of wives losing their husbands and children losing their fathers. The occurrence of accidents is truly heartbreaking; every accident serves as a bloody lesson. I only hope that the safety of workers can be better protected day by day……