On safety measures for entering towers and tanks as well as performing hot work in chemical enterprises

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The production processes in chemical enterprises are complex, and the facilities contain many flammable, explosive, toxic, harmful, and corrosive substances. Additionally, chemical plants are subject to hazardous conditions such as high temperatures, high pressures, and deep cold. One of the risks associated with equipment maintenance is the presence of numerous special types of operations. Since special operations often involve multiple types of work carried out in conjunction, the working conditions are complex, it is difficult to implement safety measures, and accidents occur frequently; therefore, high attention must be paid to this issue. Among these, operations such as entering towers and tanks as well as hot work must be carried out with due care. I. Work inside towers and tanks: Work carried out inside towers and tanks is also known as work in equipment (including tasks that take place in tanks, vats, towers, kettles, tank trucks, underground storage tanks, furnaces, channels, exhaust ducts, etc., where there is a risk of oxygen deficiency). Due to the limited internal space of the equipment, air circulation is poor, and dangerous substances are stored there ； It is very likely that harmful gases as well as flammable and explosive substances have accumulated there; working inside such an environment can lead to accidents such as poisoning, suffocation, burns, fires, and explosions with the slightest carelessness. Therefore, during operations involving entry into tanks and vessels, it is essential to strictly adhere to the “eight musts” for entering containers and equipment as stipulated in the former Ministry of Chemical Industry’s “41 Prohibitions on Work Safety”. 1. An application for a permit must be submitted and approved. Reliable safety measures must be taken and approved by the relevant authorities before implementation. The safety measures listed in the work order must be implemented one by one without any changes; if issues arise during implementation, any modifications can only be made with the approval of the chief supervisor. 2. Safety isolation must be implemented. Insert blind flanges into all pipes on the equipment that are connected to the outside, or remove a section of pipe, to ensure complete isolation from the system. 3. The power supply must be disconnected, and safety lighting must be used. Cut off the power supply, remove the fuse, and verify that the removed fuse corresponds to the circuit that has been shut down. Then attach a sign stating “Under maintenance; do not start.” The lighting used must be explosion-proof safety lamps with a voltage of 12V; they must have good insulation, and the lamps should be securely fastened. 4. Replacement and ventilation must be carried out. Cleaning and displacement must be carried out prior to maintenance, and two requirements must be met simultaneously: (1) the rinsing solution must be neutral. (2) There are no flammable or explosive gases at concentrations exceeding the specified limits. During cleaning and purging, it is necessary to remove any deposits inside the equipment. Since these deposits continue to evaporate and decompose, they must be thoroughly removed using steam or hot water. 5. Safety analysis must be conducted in accordance with the time requirements. Sampling and analysis must be carried out 30 minutes before entering the equipment; the levels of toxic and harmful gases as well as oxygen in the air inside the equipment must comply with the requirements of the \"Hygienic Standards for Industrial Enterprise Design\" (GBZ1-2002) and the \"Safety Regulations for Operations in Low-Oxygen Environments\" (GB8958-88). The oxygen content must be between 18% and 22% to allow entry into the equipment for work. If the duration of work inside the equipment is relatively long, analyses should be conducted every 2 hours. Should any values exceed the limits, work must be immediately halted and personnel evacuated. 6. Specified protective equipment must be worn. In case of special circumstances, in oxygen-deficient and toxic environments, a self-contained or mechanically ventilated long-tube gas mask or an oxygen respirator should be worn. In an environment contaminated by corrosive media, full-body protective equipment such as corrosion-resistant helmets, gloves, rubber boots, face shields, and clothing should be worn from head to toe. Work inside the tank while wearing a gas mask, with rotations every half hour. 7. Someone must be stationed outside the container to monitor and stay at their post. Guardians should be selected from individuals with work experience who are familiar with the duties of their position. Guardians must remain at their posts and must not leave the monitoring area. When necessary, they should secure a rope to the safety harness worn by the maintenance worker to facilitate construction. Outside the equipment, first-aid supplies such as rescue and fire-fighting equipment as well as clean water must be readily available. In the event of an abnormal situation inside the tank, the supervisor must not enter without any protective measures. 8. There must be backup measures for emergency rescue. When working inside large equipment, safety ladders or platforms must be erected according to the equipment’s depth and height, and rescue equipment must be provided to ensure emergency evacuation. II. Hot work
Hot work is a common task carried out during maintenance in chemical enterprises. However, it is a high-risk activity and one in which accidents occur frequently. To ensure safe maintenance and prevent fires and explosion accidents, it is essential to pay close attention to the safety of hot work, and to strictly comply with HG23011-1999 \"Safety Regulations for Hot Work in Industrial Areas\". Hot work refers to welding and cutting operations carried out in areas where such activities are prohibited, as well as temporary tasks using blowtorches, electric drills, grinding wheels, etc. in flammable and explosive environments that may generate flames, sparks, or hot surfaces. Hot work must strictly comply with the six prohibitions regarding hot work outlined in the former Ministry of Chemical Industry’s \"41 Prohibitions for Safe Production\". 1. Welding is prohibited without an approved welding permit. Hot work is divided into three categories: hot work with special hazards, category 1 hot work, and category 2 hot work. Special hazardous hot work refers to hot work carried out on production units, transfer systems, storage tanks, containers and other such facilities that contain flammable and explosive materials while they are in operation, as well as in other sites with special hazards ； Class 1 hot work refers to hot work carried out in flammable and explosive areas ； Level 2 hot work refers to hot work other than specially hazardous hot work and Level 1 hot work. Before carrying out hot work, it is necessary to apply for a \"Hot Work Safety Permit.\" For Category 1 and Category 2 hot work, the application must be submitted by the supervisor of the workshop where the work will be carried out; it is then reviewed and approved by the company’s safety and technology department ； For special hazardous hot work, an application must be submitted by the supervisor of the workshop where the work will be carried out; it is then reviewed by the safety and fire protection departments, and approved by the plant manager (director) or chief engineer. Firing is prohibited without approval. 2. Welding is prohibited as it cannot be reliably isolated from the production system. Except for operations involving particularly hazardous welding, Category 1 and Category 2 welding tasks must be reliably isolated from the production system; the components involved in the welding process must be removed before welding can proceed, in order to meet the requirements for such work as well as those related to fire safety. 3. No cleaning; if the replacement is unsatisfactory, welding is prohibited. Any containers, equipment, pipes, or other production and storage devices that have been used to hold **chemical substances must be cleaned and purged before any welding work can be carried out; welding is only permitted after tests confirm that the area is free of such substances. 4. Do not eliminate surrounding flammable materials; welding is prohibited. A dedicated person should be assigned to supervise the welding work. Before carrying out any hot work, flammable materials in the area where the work will be done and its surroundings must be removed, or other effective fire safety measures must be taken, along with the provision of sufficient and appropriate firefighting equipment; otherwise, hot work is prohibited. 5. Hot work is prohibited if a hot work analysis is not conducted on time. The sampling for hot work analysis must be representative; the sampling points are determined by the full-time or part-time safety officer of the unit where the hot work is carried out, or by the shift supervisor. The analysis samples for special types of hot work should be retained until the hot work is completed. The interval between sampling and hot work must not exceed 30 minutes; if this interval is exceeded or the hot work is interrupted for more than 30 minutes, sampling and analysis must be carried out again. 6. Without fire protection measures, welding is prohibited. For work involving special hazardous welding operations, both level 1 and level 2 welding tasks require reliable fire suppression measures; welding is strictly prohibited in the absence of such measures. In addition to meeting the conditions for level 1 and level 2 hot work, special hazardous hot work requires that a dedicated person be assigned to monitor pressure changes within the production system, ensuring that the system maintains a positive pressure of at least 980.665 Pa (100 mm water column). Hot work must be stopped when the pressure is below positive levels; hot work under negative pressure is strictly prohibited.