Collection of accidents and their handling in various chemical plants

Once, in the compression workshop of a fertilizer plant, a leak occurred at the flange connection of the pipeline in the factory’s system at the exit of the fifth stage of the compressor, which led to a fire. The pressure was 15 MPa. The incident was detected in time; the employees first used dry powder fire extinguishers. After using two cans of extinguishing agent without success, they quickly connected the fire hoses and combined those with the fire extinguishers to put out the fire. It took over ten minutes to finally extinguish the fire. The entire system’s pressure was reduced as a result, which almost caused the whole plant to stop operating, resulting in certain economic losses.

In 2006, when our plant was replacing the desulfurization agent in the desulfurization tower, we first used nitrogen to purge the tower and then air, ensuring that a slight positive pressure was maintained within the tower (0.01 MP). Due to the poor sealing of the nitrogen valve, the pressure inside the tower became extremely high during the time when the manhole was opened (it was later found to have reached 0.3 MP). At the moment the manhole was opened, the desulfurization agent, along with the ceramic balls, was ejected from it to a height of around 20 meters. Several people suffered minor injuries (wearing safety helmets). According to the accident analysis, the main cause of the incident was the failure to seal the nitrogen pipeline with a blind flange, despite ensuring that the tower was under slightly positive pressure. The DCS operator’s lack of careful monitoring, which failed to detect the abnormally high pressure in the desulfurization tower in a timely manner, was a secondary cause of the accident.

[Incident unit]: A chemical plant in Shaanxi – an internal explosion occurred in the methanol regeneration tower of the low-temperature methanol washing unit during maintenance work. During the maintenance work carried out after the methanol replacement was confirmed to be successful, an explosion occurred inside the methanol regeneration tower once its manhole was opened, resulting in all the trays of the tower being destroyed. : Due to the large amount of ferrous sulfide present in the methanol regeneration tower, when the manhole was opened, a large amount of oxygen entered, causing the ferrous sulfide to catch fire spontaneously and resulting in an internal explosion. : Precautions to take during maintenance: The tower should be washed with water (chemical cleaning is preferred). If only water washing is available, the manholes should be opened for maintenance under a slight positive nitrogen pressure. When removing the manholes, it is crucial not to open all of them at once, as this would increase air convection; the usual approach is to check one manhole at a time, close it immediately after inspection, and then proceed to the next one.

[Incident-affected unit]: Lutianhua. This incident occurred on the morning of December 10: the seal of the outlet valve of the high-pressure ammonia pump at Lutianhua failed, resulting in 1 death and 3 injuries during emergency repairs. : Online maintenance and repair of equipment: Unknown. This post is a repost from Master’s post in the Production Technology Exchange section

Unit involved in the accident: A factory in Hebei. Accident details: Explosion of the condensate tank. Cause of the accident: This condensate tank was used to collect steam condensate and the waste steam from steam reciprocating pumps. During production, the heat-supply steam was not properly controlled; meanwhile, the reciprocating pumps needed to be switched over, and both pumps were operating at the same time, which resulted in an excessive load on the condensate tank. The overpressure led to the explosion. This was due to design and operational issues.

Explosion incident in the PVC and sodium hypochlorite storage tank 1. Course of the incident At 11:44 a.m. on January 15, 2008, after the wastewater containing acetylene and sodium hypochlorite from the PVC workshop of the electrochemical plant passed through the sodium hypochlorite reuse unit, a certain amount of acetylene gas evolved from this wastewater and entered the sodium hypochlorite storage tank. It accumulated at the top of the tank and then entered Reactors No. 1 and No. 2 via the pipes connecting the tank to the venturi reactors. Inside these venturi reactors, the acetylene gas reacted with chlorine gas to form chloroacetylene, resulting in an instantaneous explosion. This explosion in turn triggered an explosion of the mixed explosive gases present in the sodium hypochlorite storage tank, causing direct economic losses of 48,000 yuan. 2. Accident cause analysis: (1) Acetylene gas, which precipitated from the waste sodium hypochlorite wastewater, entered the waste sodium hypochlorite storage tank and then proceeded to the Venturi reactor. There, the acetylene gas reacted with the chlorine remaining in the chlorine gas pipeline to form chloroacetylene, which was the direct cause of this accident. (2) In the process technologies for recycling waste sodium hypochlorite, the design does not take into account the fact that even after wastewater with a low acetylene content is prepared using a Venturi tube, acetylene gas can still accumulate above the sodium hypochlorite storage tank due to changes in weather conditions ； The safety risk posed by the dead corners remaining in the original #1 and #2 Venturi chlorine pipes was not taken into account; this led to the reaction between chlorine gas and acetylene gas to form chloroacetylene, which was the main cause of this accident.

: A refinery in Hebei: Compressor accident. The compressor is designed to use hydrogen as its working medium, but since it is currently in the airtightness testing phase and there is a shortage of hydrogen, purified air has to be used for pressurizing the system during this process. After the compressor had been running for about 4 hours, smoke started to come out of the intermediate cylinder, and the compressor’s connecting rod bent. : The compressor has an excessive compression ratio, and there are pressure fluctuations during operation. : Afterwards, the connecting rod is corrected to prevent excessive compression ratio.

:A refinery in Hebei: The compressor for coking off-gas stopped operating suddenly, resulting in an emergency shutdown of the subsequent hydrogen production equipment. Compressor pressure and temperature interlocks were in operation; during production, one of the thermocouples failed. The instrumentation staff carried out repairs, and during this process, the remote data from the control room reached its full scale, which triggered the interlocks and caused the compressor to stop operating. The other compressor could not be put into use in time. : In the case of interlocked operation, to prevent malfunction of the equipment, as in the situation mentioned above, it is necessary to disconnect the interlock before performing instrument maintenance.

:A surfactant factory in Jiangsu: During maintenance work on a methanol storage tank, a fire broke out due to the failure to replace the medium inside the tank. Fortunately, prompt action was taken, and no major accident occurred. : Before performing hot work in a container, it is necessary to carry out gas displacement, and hot work analysis as well as oxygen level testing must be conducted in strict accordance with the requirements specified in the hot work permit.

: A synthetic ammonia plant in Jiangsu: explosion in the scrubber tower, resulting in the shutdown of the entire plant. During the furnace conditioning period in the gas generation furnace, it was not detected that the furnace had stopped operating; the operator continued to feed materials without following the procedural requirements of conducting analysis and sampling or releasing air before restarting the furnace, which led to an oxygen explosion in the system. : Prevent accidental operation of the equipment, strengthen inspections before feeding materials, ensure that the system is ready for feeding, and follow the operating procedures strictly.

Unit involved in the accident: A certain factory. Nature of the accident: Flash explosion in the carbon washing tower. Cause of the accident: After feeding material into the gasifier, the return line of the coal slurry pump was connected to the inlet by mistake; this was a result of improper operation. Fortunately, no casualties were reported

1. Last year, during the ignition process of a tubular furnace in a plant’s coking crude benzene section, the first attempt at ignition failed. An attempt at ignition was made again without purging the tubular furnace first; as explosive gases were present inside the furnace, this led to an explosion that completely destroyed the tubular furnace. One person suffered serious injuries and another suffered minor injuries! The tubular furnace must be purged again when reignited! ! ! ! ! ! 2. In 2005, a coking plant experienced an explosion of concentrated ammonia gas while carrying out welding repairs on pipes containing concentrated ammonia; improper measures taken led to one person falling from a high-mounted pipe rack and sustaining serious injuries! It is recommended that the following measures be taken when performing hot work on pipelines containing concentrated ammonia solution or concentrated ammonia gas: (1) Implement a strict hot work permit system and on-site supervision ； (2) Steam purge the pipeline to be worked on until it meets the requirements ； (3) Plug blind flanges on both sides of the pipeline!

[Company involved in the accident]: Hebei Cangzhou Chemical Co., Ltd. and Cangzhou Hongji Chemical Co., Ltd. ceased operations. While removing the chlorosulfonic acid equipment from these companies, the operators simply processed the small amount of chlorosulfonic acid residue remaining in the equipment and poured it into wet waste tanks. Upon contact with water, this substance decomposed into sulfur trioxide and hydrogen chloride, resulting in the formation of acid mist (white smoke). 16 people were taken to the hospital for treatment, and fortunately no deaths occurred. : Caused by improper operation by the operator. :

:A chemical plant in Henan: In the ammonia synthesis section, a fracture in the weld of a pressure gauge pipe connected to a circulation pump caused a fire. The flames penetrated a DN15 high-pressure pipeline, which in turn led to leaks at the flanges of other pipelines. The fire destroyed power distribution cabinets, control rooms, and other facilities; it was impossible for people to approach the area, and multiple pipelines were affected. Eventually, the fire was extinguished when the oxygen supply was exhausted. : The equipment pipelines are in service beyond their intended lifespan, with inadequate inspection. : Strengthen equipment management and improve the alarm system and safe discharge system.

“Course of the “June 11, 2008 explosion accident”: At noon on June 11, the entire production line came to a stop due to a malfunction in the acid synthesis system of the resin factory; the chlor-alkali plant and the electrical plant carried out maintenance on the equipment that could not be serviced during normal operation. The chlor-alkali plant’s hydrogen chloride processing unit plans to inspect the nozzles in the hydrogen spray tower. Since the water flow rate from this tower has remained low after the spring maintenance, and the temperature at the hydrogen outlet is high due to rising temperatures, this affects subsequent operations. It is planned to adjust the spacing between the nozzles in order to increase the water flow rate and reduce the hydrogen temperature. At around 13:14, Section Chief Li consulted Lin, the deputy director of the chlor-alkali plant, regarding this issue. Since the equipment in question was a tower with a diameter of φ1200, there was a manhole with a diameter of φ500 located 3.8 meters above the top of the tower. Above this manhole were four layers of spray pipes, with 4 nozzles on each layer; adjusting these nozzles required entering the equipment through the manhole for manual adjustment. Before entering the equipment, it was necessary to replace the air inside with nitrogen. After giving verbal approval, Lin asked Li to contact the production department to prepare for replacing the hydrogen system with nitrogen. Subsequently, Section Chief Li explained the situation to Production Department Head Wang and waited for instructions. After returning to the work area, Li received a call from the shift supervisor Zhang, who informed him that it would still take about 2 hours before nitrogen could be supplied. Li was concerned about it affecting driving time; without conducting any replacements, he took the risk of organizing maintenance based on faulty experience, assigning Yang and Sun to monitor the pumps, while he himself together with Liu and Yang inspected the hydrogen spray tower, unscrewing one screw out of every two at the manholes of the tower. At around 13:30, Li asked Sun to go to the plant’s safety officer to obtain a permit for working in confined spaces. At the same time, he ordered the main water supply valve for the spray tower to be closed. Liu and Yang were assigned to check whether there were any blockages in the secondary water valves; after several rounds of inspection and testing, no issues were found. Around 14:05, Li closed all the water supply valves on the spray tower and instructed Liu and Yang to open the manholes. After Sun returned with the confirmation document, he instructed Yang to enter the tower for an inspection. After checking the sprinklers on the first and second floors and finding no problems, Yang felt short of breath while examining the third floor and informed the personnel outside the tower. Li ordered Yang to stop working and planned to use nitrogen to fill the tower. At that time, Wang, the safety officer from the chlor-alkali plant who was present, suggested using a fan to blow air inside the tower. Without thinking further, Li and Liu fetched a fan and its power cord, placed the fan upright at the manhole so that the air could flow upward. Once it was set up, Yang held onto the fan inside the tower; about 20 seconds after Li turned on the power, an explosion occurred, around 14:30. At that time, Li and Liu suffered burns to their faces, while Yang quickly emerged from an access hole after the explosion and ran more than 100 meters to the safety and quality control department. A company car was there, so he got into it and headed to the city people’s hospital. Upon arriving at the hospital, he went to the burn unit on the fourth floor to wait for treatment; the other two injured persons were also taken to the hospital shortly after. Cause analysis: Based on the conditions at the scene after the explosion, and taking into account the results of the accident analysis meeting held on June 24, the causes of the accident were identified as follows: 1. Prolonged stable production led to severe complacency among most employees, including managers; failure to strictly follow safety procedures was the main cause of this accident ； 2. Section leader Li Haiping had a weak safety awareness; he ordered employees to work in confined spaces in violation of safety rules, as the system had not been replaced, and he also used non-explosion-proof electric fans inside the containers in violation of regulations. These actions were the direct causes of this accident ； 3. Wang Jingcheng, the safety officer at the chlor-alkali plant, failed to fulfill his duties as a safety manager. Knowing that safety measures had not been implemented, he still issued permits in violation of regulations, and he also instructed maintenance workers to use non-explosion-proof fans – actions that constituted serious violations and were the direct cause of this accident ； 4. Operator Yang Yunfang had a weak safety awareness; she failed to wear protective equipment as required, and did not promptly stop the violations that posed a risk to her own safety. She is primarily responsible for the occurrence of this accident. Given that she has passed away, no further liability will be pursued against her ； 5. The Safety and Quality Control Department failed to exercise proper supervision and was grossly negligent; it only implemented safety measures verbally, and signed off on the relevant documents without actually ensuring that those measures were put into practice on site, which was a key cause of this accident ； 6. The inadequate safety management in the chlor-alkali plant, along with a lack of emphasis on safety measures, and the failure to implement and monitor safety protocols during maintenance tasks, were also important factors that contributed to this accident. Precautionary measures: 1. Re-filter the entire production system to identify any areas where *inherent errors in operation still exist, and address those areas with particular focus ； 2. Refine the safety operating procedures further to ensure a one-to-one correspondence between key equipment and relevant regulations, and strictly adhere to these procedures in all operations. In particular, strict review and supervision processes must be implemented for safety work permits and safety prevention measures at all levels ； 3. To address the issue of weak safety awareness among employees, the company will increase its efforts in safety training in the future, providing targeted safety training for factories, work sections, and teams to enhance employees’ safety awareness. 4. Carry out extensive publicity throughout the company to raise safety awareness among all employees, so that they can fully understand the implications of this accident and prevent similar incidents from occurring again. 5. Clarify responsibilities and strengthen management; regarding violations of safety production regulations, improper command, or inadequate safety measures within the work area, the company will adhere to a zero-tolerance policy and impose stricter penalties.