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1 Fire and explosion hazards 1.1 The main raw material used in ammonia synthesis is coal, which is a combustible solid. These materials do not easily catch fire at normal temperatures, but they can ignite when exposed to high temperatures. In coal storage areas, where large quantities of coal are piled up, if heat cannot be dissipated promptly, the coal may self-ignite and cause a fire. 1.2 In ammonia synthesis production systems, there are a large number of static equipment such as towers, tanks, and vessels. Since most of these devices are exposed to high temperatures and pressures, and these conditions often change, moreover, the media involved in the process are mostly flammable, explosive, corrosive, or toxic. As a result, operational errors, unauthorized use of fire, failures in sealing mechanisms, corrosion of equipment and pipelines, or defects in the manufacturing of such equipment and valves can all lead to leaks, the formation of explosive mixtures, and subsequent explosion accidents. 1.3 The ammonia synthesis production system contains a large number of heat exchangers; some of these require operation under high temperature and pressure conditions, while the working fluids involved are often flammable, explosive, toxic, or corrosive. If the heat exchanger is poorly designed, has manufacturing defects, inappropriate material selection, severe corrosion, improper operation, operational errors, or inadequate maintenance and management, accidents such as combustion and explosion, serious leaks, and loss of control over the tube bundle may occur. 1.4 The gas generator is a key device in the synthetic ammonia production system for generating the raw gas used in synthetic ammonia synthesis. Since the main components of semi-water gas are hydrogen, carbon monoxide, along with small amounts of hydrogen sulfide, methane, etc., these gases are not only highly flammable and explosive but some of them are also corrosive and toxic. Moreover, the gas generator operates under high temperatures, in harsh conditions, with short gas generation cycles; any carelessness or violation of operating procedures can lead to explosions in the gas generator. Upon analysis, the main reasons for the explosion in the gas generator are as follows: (1) Operation with excess oxygen led to the explosion of the gas generator. During the production of semi-water gas, to prevent a decrease in the catalytic activity of the conversion unit in subsequent processes, as well as to avoid damage to that unit and explosions in the gas generation system, the oxygen content must be kept below 0.5%. If the oxygen content in semi-water gas increases and reaches the explosive limit, it can cause an explosion when exposed to an open flame or other ignition sources. (2) Backflow of air and gas creates an explosive mixture. The main issues are as follows: a) During maintenance, no measures were taken to isolate the system using blind flanges, and the downstream valve was not closed; as a result, water accumulated in the main gas pipeline leading to the gas holder as well as in the gas holder’s water seal, causing pressure buildup. This led to the gas breaking through the water seal of the scrubber tower, or the blind flanges failing due to insufficient strength and allowing the gas to flow back into the furnace, thereby triggering an explosion. b. After the water seal is drained, or if the water supply valve on the gas cleaning box is damaged, the water seal is compromised allowing air to enter the furnace; or if there is a leak in the water seal of the gas cleaning box, gas flows back into the furnace. c. Gas is generated when the furnace is heated with coal, or gas remains inside the furnace; an explosion can occur if air enters the furnace accidentally. d. When servicing the automatic control valve, the bypass line was not opened, resulting in a steam interruption that caused gas to flow back. e. The overflow pipe of the gas scrubber is blocked by foreign objects. f. The furnace lid is not airtight, and the explosion-proof plate is cracked. g. Backflow of gas due to corrosion and perforation of equipment and pipelines. h. During maintenance, the gas valve was not closed or not closed properly, resulting in an explosion when work was carried out in the presence of a large amount of gas. (3) The sharp increase in water vapor pressure is causing overpressure and explosion in the water jacket of the gas generator. The water in the water jacket vaporizes rapidly under the radiation of the high-temperature gases inside the furnace; as a result, the pressure of the water vapor increases. If, for various reasons (such as increasing the production capacity of the gas generator by deliberately reducing the valves for water inlet and water vapor outlet in the water jacket), the temperature of the gas generator is raised to accelerate the reactions ； Due to reasons such as a lax shift-handover system and operational errors, the water jacket or steam drum becomes part of a closed system, causing its temperature and pressure to rise increasingly, until the material can no longer withstand the high pressure and undergoes a physical explosion. (4) An explosion of the gas generator was caused by illegal welding. (5) Equipment defects and poor maintenance lead to the explosion of the gas generator. (6) Poor fuel quality and improper operation cause explosions at the gas generator outlet. The main reasons are: a) the fuel has a high volatility content; when the furnace is shut down, the temperature at the furnace surface is low, causing the volatile components to accumulate in the upper part of the furnace. Alternatively, if the fuel temperature is too high, water gas is generated upon contact with the hot coal. b. The carbon layer inside the furnace is severely caked, with large pieces hanging suspended, and the residual gas inside cannot be completely expelled. c. The main steam valve and the top steam valve are leaking or not closed, allowing water gas to escape from the furnace outlet. d. Hot ash or coal falling into the water-filled ash hopper generates water vapor, which produces water gas through vaporization. e. When adding coal, the flames in the furnace are extinguished, resulting in the distillates and water gas not being completely burned. (7) An explosion at the furnace bottom occurred at the end of the secondary top blowing and the start of air blowing. The main reasons are: during the secondary top blowing, the steam valve for top blowing is not opened or is opened too slowly, resulting in the steam at the bottom of the furnace not being completely blown away ； There are large pieces of material in the furnace bottom ash hopper, and they cannot be completely removed during the second blow-in ； The blowdown valve is leaking, causing air to mix with the gas at the bottom of the furnace during downward blowing. 1.5 H2, CO, CH4, and H2S in semi-water gas are all flammable and explosive gases. In the desulfurization section, fires and explosions often occur due to leaks in equipment or pipelines ； Accidental operation or equipment defects can also cause the Roots blower to create a negative pressure, allowing air to enter the system and mix with semi-water gas to form an explosive mixture that can lead to explosions. On the surfaces of equipment and pipes in production systems, due to the effect of H2S gas, a layer of loose iron sulfides (FeS and Fe2S) often forms. When these sulfides come into contact with oxygen in the air, they undergo oxidation reactions that release large amounts of heat, causing their temperature to rise rapidly until it reaches their ignition point and leading to spontaneous combustion. Meanwhile, during maintenance, when the equipment pipes are opened, spontaneous combustion can also occur due to the rapid oxidation reactions between the sulfides of iron on their internal surfaces and coal tar, in combination with the air that enters. 1.6 The transformation process takes place under certain temperatures and pressures, posing both the risk of physical explosions and the risk of chemical explosions. During the production process, due to inherent defects in the equipment and pipelines during manufacturing, inspection, and maintenance, or as a result of prolonged exposure to gases, these components can experience thinning of their walls and fatigue as a result of corrosion, which in turn leads to the formation of cracks and other defects. If such issues are not detected and addressed in a timely manner, the equipment and pipelines may explode under normal operating pressures, with consequences that could include secondary fires and chemical explosions. After semi-water gas is converted into shift gas, the H2 content in the gas increases significantly. Once such high-temperature gas leaks out, it can form explosive mixtures when in contact with air, and it is prone to cause fires and explosions when exposed to fire or high temperatures ； If a device or production system develops negative pressure, air is drawn in and mixes with gas, forming an explosive mixture; under the influence of high temperatures, friction, static electricity, etc., a chemical explosion can also occur ； If the oxygen content in the semi-water gas from the production system exceeds the specified limits, it can lead to peroxide explosions. Illegal welding operations and unauthorized maintenance activities can also cause chemical explosions. 1.7 The nitrogen-hydrogen compressor is a key device in ammonia synthesis production; the medium being compressed is a flammable and explosive gas, and it is prone to leakage under high-pressure conditions. It can easily cause combustion and explosion accidents. The main causes include: (1) leakage of flammable gases through defects such as connections in the cylinder body, intake and exhaust valves, flanges on equipment and pipelines, welds, and seals ； Fatigue fracture of compressor components, with high-pressure gas escaping into the factory area ； Air enters the compressor system, forming an explosive mixture. If improper operations, maintenance, or repairs are carried out during these processes, the mixture of flammable gases at the explosive concentration with air can ignite violently upon contact with a source of fire, potentially leading to an explosion. (2) Mineral lubricating oil is used for cylinder lubrication; it is a flammable substance. When the temperature of the gas rises sharply and exceeds the flash point of the lubricating oil, intense oxidation occurs, posing a risk of combustion and explosion. Moreover, the lubricating oil molecules in suspension can easily react with oxygen in the air under high temperature and pressure. This oxidation is particularly intense on the oil films attached to the hot metal surfaces of exhaust valves and exhaust pipes, resulting in the formation of acids, asphalts, and other compounds. These compounds combine with dust in the gas and metal particles generated by mechanical friction, and deposit in the cylinder head, piston ring grooves, valves, exhaust pipes, buffer tanks, oil-water separators, and gas storage tanks, forming carbon deposits. Carbon buildup is a flammable substance, and it can catch fire on its own or even explode under conditions such as excessive heat, accidental mechanical impact, airflow shock, electrical short circuits, external fires, and static electricity sparks. (3) During the compressor startup process, it is started without the use of an inert gas for displacement or with incomplete displacement ； Overpressure occurred due to a lack of operational knowledge, as the compressor outlet valve and bypass valve were not opened ； During operation, failures in the instruments of the compressed gas control system, as well as excessive gas pressure, can all lead to combustion and explosion accidents. (4) Mechanical failures of the compressor, such as broken piston rods, cracked cylinders, ruptured cylinders and cylinder heads, broken crankshafts, broken and deformed connecting rods, broken connecting rod bolts, stuck or cracked pistons, broken compressor housings, and vibration in the compressor unit, can lead to catastrophic accidents; sometimes, such mechanical failures can trigger secondary explosions of flammable gases. 1.8 The pressure and H2 concentration in the copper washing section are very high. At the same time, there are many connections between high-pressure and low-pressure areas, which makes it easy for high pressure to leak into the low-pressure sections, thereby posing risks of physical explosions, chemical explosions, and fires. 1.9 The synthesis section operates under high temperature and high pressure conditions, with both high and low pressures present; this imposes higher requirements on the equipment and pipelines used for producing ammonia. If there are defects in the material itself, if the manufacturing quality is substandard, if the repair work is of poor quality, or if external pressures exceed the bearing capacity of the equipment and pipes, a physical explosion will occur, which can also lead to a chemical explosion. Under high temperature and pressure, H2 has a strong ability to penetrate carbon steel, leading to hydrogen corrosion that causes the steel to lose carbon and become brittle (i.e., hydrogen embrittlement) ； N2 can also cause nitriding of the equipment, thereby reducing its mechanical properties ； The material itself undergoes continuous plastic deformation under high temperature and pressure, which alters its microstructure; this leads to a decrease in mechanical properties such as strength and elongation, and causes the material to suffer from stretching, bubbling, cracking, and ultimately failure. The occurrence of hydrogen embrittlement, nitrogen erosion, and plastic deformation can also lead to explosion accidents. The synthesis section primarily uses H2 as a raw material, and ammonia is produced through the reaction. H2 and NH3 are flammable and explosive gases, and their explosion limits increase under high temperature and pressure; once they leak and mix with air, explosions can occur very easily. 1.10 The refrigerant for food carbon dioxide is liquid ammonia; in the event of a leak, liquid ammonia can form an explosive mixture of ammonia and air, which may cause an explosion when exposed to an open flame or high heat. 1.11 Methanol is a flammable liquid; during the methanol distillation process, if methanol or methanol vapor leaks, it can form an explosive mixture with air, and exposure to an open flame or high heat can lead to an explosion. 1.12 The causes of electrical fire accidents include defects in electrical equipment or wire overload, improper installation or use of electrical equipment, such as inaccurate classification of hazardous areas, inadequate explosion-proof performance of electrical equipment, short circuits, leakage currents, or overloads in electrical equipment, which lead to an increase in temperature to dangerous levels and result in the combustion or explosion of the equipment itself or surrounding objects. 2 Boiler explosion: Waste heat boilers are present in the ammonia synthesis production system, and boiler explosions can occur due to reasons such as severe water shortage, poor water quality, or equipment defects. The specific analysis is as follows: (1) Severe water shortage accidents can be caused by operator errors, malfunctions of water level gauges or automatic water supply systems, poorly sealed drain valves, or faulty check valves. Severe water shortage accidents may lead to overheating and damage of the heating surfaces, reduce the strength of the steel used in these surfaces, cause deterioration in the microstructure, and result in the rupture of the furnace tubes, thereby leading to a boiler explosion. (2) Full-water accident: Full-water accidents can occur due to operator errors or malfunctions in the water level gauge or automatic water feeding system. A large amount of water in the steam reduces its quality; in severe cases, water hammer can occur, damaging pipes and equipment that use steam. (3) If the water quality is unsatisfactory, the salt content in the boiler water reaches a critical level, or the boiler operates under overload conditions, a sudden increase in gas consumption or too rapid a drop in pressure can lead to azeotrope formation between steam and water. This disrupts the water circulation, deteriorates the quality of the steam, causes water hammer vibrations, and affects the safe operation of equipment that relies on steam. (4) The use of steel of poor quality or inferior welding in boilers, along with poor water quality that leads to severe corrosion and scaling, as well as problems with water circulation, can also cause explosions in the boiler. (5) When the operating pressure exceeds the boiler’s maximum allowable operating pressure, the stress on the steel plates (tubes) increases beyond its limit; at the same time, the failure of the safety valve and overpressure interlock systems can also lead to an overpressure explosion. 3 Container explosions: There are numerous high-pressure devices and pressure vessels in various production facilities; if there are defects in the design or installation of these devices and vessels, ； The safety accessories or protective devices are defective or incomplete ； In the course of use, if phenomena such as erosion, corrosion, fatigue, and creep occur ； It was not inspected by a qualified quality inspection unit as required, nor was a safety approval certificate obtained ； Container explosion accidents can occur due to reasons such as human error. 4 Poisoning and asphyxiation accidents 4.1 In the ammonia synthesis process, semi-water gas and ammonia present in the system are both toxic substances; if they leak in large quantities, it can lead to widespread poisoning incidents. 4.2 During the methanol production process, methanol is also a toxic substance; if it leaks and its vapors or liquid are inhaled or ingested by people, it can cause poisoning incidents. 4.3 Carbon dioxide is a asphyxiant gas; a leak of carbon dioxide during food carbon dioxide production can cause suffocation. 5 Burns 5.1 High-temperature steam, as one of the most common heat carriers, is present throughout the entire production system; its leakage can cause severe burns to personnel. 5.2 Ammonia (including ammonia gas and liquid ammonia) is present in systems after synthesis; it becomes liquid ammonia after compression and condensation. It is an important intermediate product and refrigerant in production. At normal pressure, liquid ammonia vaporizes into ammonia gas at -33.3°C, absorbing a large amount of heat in the process. Therefore, contact with liquid ammonia can cause severe frostbite to the skin. The pressure in liquid ammonia systems is generally between 1.6 MPa and 2.0 MPa, and a leak can cause serious harm. 6 Crane-related injuries: There are multiple cranes and electric hoists in the factory, and during lifting operations (including installation, use, and maintenance), accidents that can cause injury to personnel such as crushing, falling, being struck by lifting equipment or loads, and electric shock may occur. 7 Falls from height: The production facilities in this factory are mostly multi-story buildings. Working on floors above the second floor or on operating platforms at a height of more than 2 meters above the ground or floor surface can lead to falls from height, especially if the protective railings are not properly installed, are corroded or damaged, or if other safety measures are inadequate. 8 Mechanical injuries: At the moving parts of various mechanical devices, if protective covers or other safeguards are not in place, contact with these moving parts by human hands can lead to mechanical injury accidents. 9 Electric shock: If protective measures for various electrical devices are inadequate (such as unreliable electric shock protection, leakage protection, short-circuit protection, overload protection, insulation, electrical isolation, shielding, and proper electrical safety distances), it is possible for people to suffer electric shock. 10 Vehicle collisions: Vehicles moving around within a factory can easily collide with the factory’s facilities if the protective measures in place are insufficient; this can also result in injuries to people. 11 Noise hazards: The use of various types of production equipment during the manufacturing process – such as compressors of different kinds (especially the high-pressure compressors and circulators used in ammonia synthesis systems), pumps, blowers, cranes, crushers, and various material handling devices – generates noise to varying degrees while in operation. If noise reduction measures are lacking or ineffective, and if workers do not have adequate protection against noise, the resulting noise can cause damage to the hearing, cranial nerves, and other bodily systems of those who are exposed to it. 12 Dust hazards: During processes such as gas production in ammonia synthesis, this company generates industrial dust. If dust prevention and removal measures are inadequate and personal protective equipment is not used properly, it can lead to environmental pollution and harm to the health of employees. 13 Harmful effects of high temperatures: High-temperature operations are present in processes such as gas production and ammonia synthesis. Power distribution systems contain a large number of electrical devices, wiring, as well as large and medium-sized manufacturing equipment, which generate significant amounts of heat during operation, thereby raising the air temperature in the work area. If ventilation and air conditioning in the working environment are inadequate, and measures to prevent heat stress are insufficient, workers can be exposed to the harmful effects of high temperatures.