【Haichuan Chemical Accident Updates】An accident occurred in a sewage tank in Ankang, Shaanxi, resulting in six people being injured accidentally

“The incident occurred at the wastewater treatment plant of Hengxiang Biochemical Co., Ltd., where one worker accidentally fell into a chemical tank while handling wastewater; it is suspected that methane was present in the tank. ”On the afternoon of the 11th, an informed source said that after a worker fell into the chemical tank, five people went in to rescue him, but due to the high concentration of gases, six workers were injured. According to officials from the Hengkou Demonstration Zone in Ankang City, at around 1:10 p.m. that day, they were informed that six workers had suffered an accident, and relevant leaders rushed to the scene to handle the situation. At present, the 6 rescued individuals show no signs of life, and the person in charge of the factory involved as well as other relevant personnel have been taken into custody by the police. The cause of the incident is still under further investigation.

At around 16:30 on July 22, 2019, Great Wall Biochemistry Engineering Co., Ltd. in Huailai County, Hebei Province (which is not a chemical manufacturing company), suffered an accident involving exposure to harmful gases while carrying out operations to clean the wastewater sedimentation tanks on its premises. Great Wall Biochemical Engineering: As of 22:42 on July 22, the accident resulted in 5 deaths and 4 injuries. The injured were promptly taken to hospitals for treatment, and their vital signs are stable. The company has ceased production at present, and the cause of the accident is under investigation. Based on the author’s many years of work experience, it is inferred that the cause of the poisoning incident was intense anaerobic digestion of the sludge accumulated in the sewage sedimentation tanks during the hot summer months, which produced toxic and harmful gases such as H2S. These gases were released when the sludge was cleaned, stirred, and settled, thereby leading to the poisoning incident!

How to clean a septic tank properly? 1. Steps and precautions for cleaning sewage tanks: Before cleaning a sewage tank, the inlet valve for sewage should be closed, and the sewage inside the tank should be emptied as much as possible; natural ventilation should be allowed to occur for more than 24 hours. Whenever mechanical cleaning is possible, manual cleaning should be avoided as much as possible. 2. Workers entering the pool must be in good health and fully conscious. Persons under the age of eighteen, those with respiratory, cardiovascular, allergic, or skin allergy conditions, as well as women, are not allowed to engage in this type of work. 3. A \"Sewage Tank Cleaning Work Order\" must be filled out for sewage tank cleaning operations. On-site safety personnel are designated by the safety officer. The site safety officer must provide technical and safety instructions to the personnel carrying out the cleaning work, and both parties involved in these instructions should sign the \"Sewage Tank Cleaning Work Order\". 4. When working in the pool, a site safety officer must be present to supervise the implementation of safety measures throughout the process, and at least two supervisors should be designated. 5. Personnel entering the pool must wear appropriate protective equipment (gloves, safety helmets, safety belts, safety ropes), and oxygen tanks as well as toxic gas detectors must be carried; a site safety officer shall inspect the safety measures before starting work. 6. Before entering the pool, a multi-functional gas detector must be used to detect harmful gases. The oxygen content in the air of the work area should be between 19.5% and 23%; if the oxygen level is below 19.5%, an alarm signal should be generated. The concentration of toxic substances shall comply with the requirements of GBZ 2.1 and GBZ 2.2. If it is confirmed that there is no alarm due to excessive levels of hazardous gases, the safety officer shall supervise the operation on site; furthermore, approval from the primary safety officer is required before work can proceed in the pool. 7. When gas detection using a multi-functional gas detector indicates that dangerous gas levels are above the limit and an alarm is triggered, forced ventilation using a blower should be carried out for 15 minutes before conducting another test with the multi-functional gas detector. If the test shows that the dangerous gas levels are no longer above the limit, proceed according to point 6. 8. After mechanical ventilation is implemented using a blower, if the readings still exceed the specified limits as indicated by the multi-functional detector, the safety department should be notified immediately so that personnel can be sent to the site to check the safety measures. Only after approval is given by the plant manager in charge of production, and after wearing gloves, safety helmets, safety belts, safety ropes, and isolation respirators, can work be carried out in the pool. Records of such work must be kept, and the duration of work in the pool shall not exceed 30 minutes. 9. After entering the pool, tools and accessories must be lifted using tool bags; throwing them is strictly prohibited. There should be no stones, bricks, or other objects that could cause injury by impact within one meter around the work well. The personnel on the pool surface ensure all safety measures for those entering the pool. 10. A no-entry zone should be marked on the ground of the construction area, and construction signs should be installed to prevent unauthorized persons from entering; a safety ladder should be provided beside the pool. 11. The use of fire is strictly prohibited when working in the pool; flammable and explosive items are not allowed to be taken into the pool. If welding work is necessary and the conditions for such work are met, ventilation equipment must be used, fire-fighting equipment must be available, and a welding permit issued by the relevant safety authorities must be obtained before working in the pool. 12. Open flames and non-explosion-proof equipment are not allowed in areas where flammable gases are present. 13. If a production and operation entity does not possess the conditions necessary for carrying out cleaning operations, it shall assign such tasks to a construction unit with the appropriate qualifications, and enter into a contract for assignment as well as a safety production agreement. 14. If the cleaning operation takes a long time, workers should take turns entering the pool. If those working underwater experience symptoms such as dizziness, weakness in the legs, shortness of breath, or nausea, they must leave the pool immediately to rest. 15. During cleaning operations, the on-site safety officers and supervisors must remain at their posts, stay focused, and avoid engaging in any other tasks. They should maintain contact with the workers underground, pay close attention to their condition, identify any issues promptly, and prevent safety accidents from occurring. 16. In the event of an operational hazard, workers should be immediately rescued and taken away from the site for treatment, while the safety management department and relevant supervisors should be notified.

2. Accident rescue measures: The personnel responsible for rescuing in case of an accident should put on personal protective equipment and take necessary preventive measures before rushing to carry out risk mitigation work. Unrelated persons within the danger zone should be quickly evacuated from the site. Emergency responders must follow instructions, be aware of the toxic substance and the situation at the scene, and wear complete protective equipment. Emergency responders must provide assistance while ensuring their own safety. Emergency responders entering areas with toxic gases must do so in groups of at least two. Transport the injured to a safe area promptly. 3. First aid measures in case of accidents: 1. First aid for hydrogen sulfide poisoning: Quickly move the victim away from the area where exposure occurred to a place with fresh air; remove any objects in the mouth and contaminated clothing. Administer oxygen immediately, loosen the tie and belt to keep the airways unobstructed, and at the same time call emergency services at 120 for help. For those with stopped heartbeat and breathing, artificial respiration should be administered immediately (chest compressions are preferred over mouth-to-mouth respiration; if that is the only option, use several layers of wet gauze between the rescuer and the patient) as well as external chest compressions to enhance breathing, until they reach the hospital. 2. First aid for ammonia poisoning: Quickly move the patient away from the site of exposure to an area with fresh air, remove any objects in the mouth and contaminated clothing, thoroughly rinse the affected eyes and skin, and at the same time call emergency services at 120 for help. Also, loosen the tie and belt to keep the airways unobstructed.

Types of septic tanks and their common toxic substances I. Types of septic tanks 1. By location: indoor, semi-outdoor, and outdoor 2. By installation location: above ground as standalone units, or below ground. 3. Classified by the sewage cleaning device: fully automatic mechanical cleaning, semi-automatic mechanical assistance with manual cleaning, and manual cleaning. 4. By type of wastewater: wastewater from electroplating and circuit board manufacturing enterprises, wastewater from leather and papermaking industries, wastewater from printing and dyeing enterprises, domestic wastewater, septic tank wastewater, etc.

II. Common toxic substances in various types of sewage tanks 1. In the wastewater from electroplating and circuit board manufacturing enterprises, the main substances include heavy metal compounds such as chromium, cadmium, nickel, zinc, copper, gold, and silver, cyanides (derived from cyanide-based electroplating agents and substances like galangal), arsenic compounds (arsenic), as well as corrosive acids and bases (used for precipitating and neutralizing heavy metals in wastewater). 2. In the wastewater from leather and paper manufacturing industries, as well as dyeing and printing businesses, the main substances include heavy metals and non-metallic compounds such as chromium, cadmium, and barium (used in leather tanning and dye production), hydrogen sulfide, methane, ammonia, and carbon dioxide (generated by the decomposition of organic materials such as leather, paper, and natural fibers), along with corrosive acids and bases (used for precipitating and neutralizing heavy metals in wastewater). 3. Domestic wastewater and wastewater from septic tanks mainly contains hydrogen sulfide, methane, carbon dioxide, and ammonia (all generated by the decomposition of various organic materials). Additionally, in sewage tanks located underground, carbon dioxide naturally accumulates in the air at the bottom due to natural processes.