Precautions for construction of chemical plants during the winter rainy season

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1 When constructing in winter and the rainy season, it is essential to pay close attention to nine types of prevention (prevention of freezing, fire, violence, slipping, poisoning, falling, collapse, burns, and electric shock). 2. Arrange the construction schedule reasonably; for those sub-projects that are particularly difficult to construct in winter, efforts should be concentrated on completing them as soon as possible. 3. For projects that must proceed during the winter construction period, it is also necessary to arrange work in an order of working on the interior first and then the exterior. Proper material and technical preparations should be made, and labor conditions should be improved as much as possible. For projects where conditions permit, the work should be completed as soon as possible. 4. In rainy, snowy, or freezing weather, assign dedicated personnel to clean the construction roads, scaffolds, and work platforms promptly, to ensure that the roads remain unobstructed and that any water accumulation is removed. Anti-slip measures should be taken on slopes, such as laying slag or installing strips on them. 5. Working at heights must only be carried out after the ice and snow on the scaffolding and work platforms have been cleared or melted. In addition to wearing a safety helmet and seat belt, soft-soled shoes should also be worn, and the work area must be equipped with reliable fences and safety nets. Objects falling should be tied with a rope, and tools should be placed in bags. Wearing cotton clothes in winter makes movement difficult, so special attention should be paid to safety. 6. Before construction in winter, a comprehensive inspection should be carried out on the site’s fire-fighting facilities, safety protection equipment, temporary structures that do not comply with safety and fire prevention regulations, containers (tool rooms), vehicles, construction machinery, and other facilities used for production and daily activities. This inspection should focus on aspects such as stability, fire resistance, and proper grounding. Technical measures must be put in place, and necessary safety equipment and supplies should be purchased promptly. 7. Stoves, electric heaters, and other open flames are not allowed to be used for heating at the construction site or in the offices without permission. To use a stove, it is necessary to apply to the security department in advance, go through the necessary procedures, and assign a person responsible for its use. The stove must have an exhaust chimney that extends outside, and no flammable materials should be piled up around it. 8. Maintain existing roads by proper design of road arches and by constructing drainage ditches along the roads to ensure effective drainage, so that there is no water accumulation, sinking, or slipping after rain. 9. All mechanical sheds must be constructed securely to prevent water leakage; mechanical and electrical equipment should have measures in place to protect them from rain and flooding, and grounding safety devices must be installed. The leakage protection device of the motorized switch box must be reliable. 10. During pipeline pressure testing, the ambient temperature should not be lower than 5°C; when it is below 5°C, anti-freezing measures must be taken during the testing. After the hydraulic testing of the pipes, the water supply should be cut off, any water remaining inside the pipes should be drained, and the pipes should be dried out. 11. Before installing the equipment, check its connections to ensure that they are in good condition; all water accumulated inside should also be drained. After installation, any open inlets and outlets must be sealed to prevent rain and snow from entering the equipment. 12. During the installation of the storage tank, proper protective measures must be in place to prevent safety accidents among welders while they are welding. When working on the top of the tank, safety belts must be worn as required to ensure the safety of the workers. 13. Precautions for welding during the winter rainy season 13.1 The secondary storage area for welding rods must maintain a certain temperature and humidity level, as well as good ventilation; the welding rods should be stored at a certain distance from the ground and walls to prevent them from becoming damp and deteriorating. 13.2 Welding must not be carried out in rainy weather; welding operations should be performed in areas equipped with protection against rain, snow, and wind ； When welding workpieces with high temperatures during the winter rainy season, it is necessary to preheat the area around 100 mm on each side of the weld to 40–50°C in order to remove moisture and water. 13.3 When spot-welding workpieces with high rigidity in winter, the weld metal should be 1.5 times thicker than at normal temperatures to prevent cracking due to low temperatures. 13.4 During the winter rainy season, special attention must be paid to keeping the welding rod insulation containers sealed to prevent moisture absorption. 13.5 Welding shall not be carried out when the surface of the workpiece is damp or covered with ice and snow, or during rain, snow, or windy conditions, without appropriate protection for the welder and the workpiece. 13.6 During construction, arcing on the equipment is strictly prohibited when welding; the welder’s neutral wire must not be connected to the equipment. 14. Material Management: 14.1 Materials should be stored in available warehouse space, or temporary warehouses with roofs and pads should be constructed; the roads leading to the warehouses must be smooth and unobstructed. Materials should be handled with care during loading and unloading; rough handling is strictly prohibited. Rain protection measures must be in place during transportation. 14.2 When materials arrive at the warehouse, they should be stacked separately according to their category, model, specification, and order of use, with markers placed to prevent confusion, and transportation pathways should be reserved. 14.3 Materials that need to be stored in a sealed condition should only be opened when in use. 14.4 Materials that have become damp and frozen, as well as frozen water, must not be used. 14.5 The clay mixture should be used immediately after preparation and should not be left standing for an extended period of time. If cementation occurs during construction, it should not be used any further. 14.6 If there is ice on the acid-resistant bricks, it must be removed completely; otherwise, they must not be used. 15. Concrete works: For concrete poured in winter, in order to shorten the curing time, portland cement or ordinary portland cement should generally be used. The cement grade should not be lower than 425; the amount of cement used per m3 of concrete should not be less than 300 kg, and the water-cement ratio should not exceed 0.6. And an early-strength agent is added. Early-strength agents can be used in concrete projects that require early strength or frost resistance, and where construction takes place at normal temperatures, low temperatures, or even negative temperatures (with the minimum temperature not falling below -5°C). The dosage of various early-strength agents should not exceed the values specified in the table below: Type of early-strength agent, Dosage (% of cement weight): Chlorides – 1; Sodium sulfate – 2; Triethanolamine – 0.05. Chloride salts, crystalline sodium sulfate, and organic amines-based early-strength agents can be used in solution form; hot water at 40–70°C can be used to accelerate their dissolution. The solutes must be fully dissolved, and the solution must remain homogeneous. Sodium sulfate solution should be prepared and used immediately; its concentration must not exceed 20%. If crystalline precipitates form before use, it should be heated and stirred to ensure complete dissolution. For concrete containing early-strength agents, when cured naturally, it should be covered with plastic film; in low-temperature conditions, insulating materials should be used for coverage. The amount of antifreeze to be used should be determined according to the product instructions or based on the construction temperature through testing. The amount of the antifreezing component required shall comply with the provisions in the following table:

**Antifreeze Category** | **Amount of Antifreezing Component**
--- | ---
Chloride-based antifreezes | The amount of chlorides shall not exceed 7% of the weight of the mixing water.
Chloride-rust-inhibiting antifreezes | The total amount shall not exceed 15% of the weight of the mixing water. When the amount of chlorides is between 0.5% and 1.5% of the cement weight, the ratio of sodium nitrite to chlorides shall be greater than 1; when the amount of chlorides is between 1.5% and 3% of the cement weight, this ratio shall be greater than 1.3.
Chloride-free antifreezes | The total amount shall not exceed 20% of the weight of the mixing water. Among these, the amounts of sodium nitrite, calcium nitrite, sodium nitrate, and calcium nitrate shall not exceed 8% of the cement weight, urea shall not exceed 4% of the cement weight, and potassium carbonate shall not exceed 10% of the cement weight.

When the daily minimum temperature is -5°C and the concrete is covered with one layer of plastic film and two layers of straw bags or other substitutes for curing, an early-strength agent or an early-strength water-reducing agent can be used in place of an antifreeze. When the minimum temperature during the day is -10°C or lower, antifreeze at specified temperatures can be used respectively. When preparing the composite antifreeze, it should be stirred thoroughly; if crystallization or precipitation occurs, separate solutions should be prepared and added to the mixer separately. When the temperature is below -5°C, hot water can be used to mix the concrete; when the water temperature is above 65°C, the hot water should first be mixed with the aggregates before adding cement for mixing. 16. Masonry work: The water used for mixing mortar should be pre-heated, and both sand and lime paste should also be kept at a suitable temperature before mixing, so that the mortar retains a temperature of over 5°C after mixing and transportation, at the time of construction. By adding chlorides (table salt or calcium chloride) to the mixing water, the mortar can harden under negative temperatures after being laid, thus eliminating the need for measures to prevent settlement and deformation of the masonry. Due to the corrosive effect of chlorides on steel rebar, rebar and steel embedments placed in masonry should be pre-treated to prevent corrosion. The amount of chlorides in the mortar (as a percentage of the weight of the mixing water) is specified in the table below. Item: Type of chloride; Daily minimum temperature (°C): Equal to or above -10, -11 to -15. 1: Sodium chloride; 3, 5, 17. For decorative work, the mortar used for plastering should be kept at a temperature of above 5°C. When sodium nitrite is added to the mortar as an antifreeze, its amount (as a percentage of the water content) is given in the table below. Outdoor temperature (°C): 0 to -3, -4 to -9, -10 to -15; Amount (%): 1, 3, 5. The antifreeze should be prepared and used by a qualified person. A 20% concentration standard solution is first prepared, and then a solution with the appropriate concentration is made based on the outdoor temperature. If there is frost or snow on the surface of the plastering substrate, it can be rinsed with a hot water solution of antifreeze at the same concentration as the plastering mortar, so as to remove any debris from the surface before proceeding with plastering. Salts should be dissolved in water first, and then added while stirring. 18. Requirements for construction during the winter rainy season in underground projects 18.1 The excavated soil should be sloped in accordance with regulations, and regular inspections should be carried out to prevent landslides. Special attention must be paid to preventing freeze-thaw collapse during excavation; the backfill soil should be compacted before freezing occurs, and proper drainage on the surface should be ensured promptly. When backfilling, the content of small frozen soil clumps shall not exceed 15% of the fill material. 18.2 The construction of valve chambers should be carried out at temperatures above zero degrees; if necessary, the grade of the mortar can be increased to ensure the strength of the chamber. Frozen mortar must not be used, and the chamber should be covered with straw after it has been built. 19. Requirements for traffic vehicles and construction machinery during winter and rainy seasons 19.1 Before entering the winter construction period, a thorough inspection of all traffic vehicles and construction machinery should be carried out; it is necessary to ensure that insulation covers, anti-skid chains, and antifreeze are available. The quality of the antifreeze must meet the required standards, and deteriorated or low-quality products must not be used. 19.2 During winter construction, all traffic vehicles and construction machinery shall drain their cooling water promptly after finishing work for the day. 19.3 All vehicles operating on icy or snowy roads must be equipped with anti-skid chains, and drivers should drive at reduced speeds. 20. Requirements for temporary electricity use during the winter rainy season 20.1 Electricity used in construction must comply with relevant regulations on electricity usage; a temporary electricity installation plan should be prepared in advance, with complete technical documents available. At the construction site, an electrician shall be responsible for overseeing electrical work, and it is strictly prohibited for persons who are not electricians to carry out electrical installation or maintenance tasks. 20.2 The installation of overhead lines at the construction site and indoor distribution lines shall comply with regulatory requirements; they must not be laid haphazardly, nor wrapped around scaffolding or buildings, and should be secured using porcelain insulators. 20.3 Distribution boxes and switch boxes shall have doors and locks, and shall be installed in dry, well-ventilated locations that are easy to operate; in outdoor areas, they shall be equipped with rain protection devices, and their enclosures shall be connected to the protective ground system. The box should be equipped with automatic switches and leakage protection switches, and the outgoing wires should indicate the circuit and capacity. 20.4 All non-live metal parts of electrical equipment and power tools shall be properly grounded or connected to the neutral wire.