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1. What are the components of waste gas? What percentage is it? The yellow, crude gas produced during coal coking in the carbonization chamber, which has not been purified, is called raw gas. The composition of raw coal gas is approximately (grams/m3): water vapor 250–450, coke oven gas 80–120, crude benzene 30–45, ammonia 8–16, hydrogen sulfide 6–30, cyanides 1.0–2.5, light pyridine bases 0.4–0.6, naphthalene 10, and others 2–2.5. 2. Why must raw coal gas be purified? The gas produced during coal coking in the carbonization chamber (raw coke oven gas) contains a large number of various chemical substances; among them, tar and naphthalene tend to condense and form deposits that can block the pipes, thereby affecting the transport of the gas. In addition, waste gas also contains toxic substances such as sulfides and cyanides, and it is corrosive to gas equipment. Therefore, this type of gas cannot be used as a gaseous fuel without being processed or refined. The purpose of gas purification is to remove tar mist, ammonia, benzene compounds, light oils, sulfides, cyanides, naphthalene, and the liquids present in the gas (i.e., condensed ammonia water), thereby obtaining refined coke oven gas that consists mainly of non-condensable gases such as hydrogen and methane. 3. What are the components of pure coke oven gas? The composition of net gas (gas after the recovery of chemical products, also known as recycled furnace gas) is approximately as follows (by volume %): hydrogen 54–59, methane 23–28, other hydrocarbons 2–3, carbon monoxide 5.5–7, carbon dioxide 1.5–2.5, oxygen 0.3–0.7, nitrogen 3–5. 4. What are the main products obtained after the purification of raw gas? What are the yields? After being condensed and recovered, waste gas is separated into gas, tar, crude benzene, and ammonia. The yield of coal from this process is as follows (expressed as a percentage of the weight of the dry coal used in coking): gas 15-19%, tar 3-4%, crude benzene 0.9-1.2%, ammonia 0.2-0.3%. 5. What are the requirements for city gas? Countries have strict requirements for the quality of city gas, with specific regulations set for the content of impurities. The indicators specified in China are basically similar to those of industrially developed countries. The specific requirements are as follows: (1) The low calorific value must be greater than 14,654 kJ/m3; (2) The allowable levels of impurities (in mg/m3) are: tar and dust at less than 10, hydrogen sulfide at less than 20, and ammonia at less than 50 in winter and less than 100 in summer; (3) The oxygen content must be less than 1% (by volume). 6. What are the properties of coke oven gas? The properties of coke oven gas are mainly as follows: (1) Coke oven gas is a colorless toxic gas (it appears yellow when no chemical products are recovered; it contains about 6% CO) ； (2) It has a high calorific value (16,720–18,810 kJ/m3), contains little inert gas (about 4% nitrogen), and has a high hydrogen content (near 60%); as a result, it burns rapidly with a short flame ； (3) Large explosion range (5–30%), and it easily forms explosive gases when in contact with air ； (4) Easy to catch fire, with a low ignition point (600°C) ； (5) When the gas is dirty, the pipes are prone to being clogged by tar and naphthalene, and the condensates in the gas can also corrode the pipes. 7. How is hydrogen sulfide formed in coke oven gas? During the coking process, part of the sulfur in the coaling coal, under high temperatures, primarily forms inorganic hydrogen sulfide, along with small amounts of organic sulfides (such as sulfur dioxide and thiophene). Organic sulfides continue to react at higher temperatures, being converted almost entirely into hydrogen sulfide; the sulfur contained in hydrogen sulfide within the gas accounts for over 90% of the total sulfur content in the gas. 8. What are the main physical properties of hydrogen sulfide? At room temperature, hydrogen sulfide is a gas with a pungent odor; its density is 1.539 kilograms per cubic meter. When burned, it produces sulfur dioxide and water; it is toxic, and even a concentration of 0.1% in the air can be fatal to humans. At the same time, hydrogen sulfide is highly corrosive to steel equipment. 9. What is the content of hydrogen sulfide in gas? The content of hydrogen sulfide in coke oven gas mainly depends on the sulfur content of the blended coal. During high-temperature coking, about 25–30% of the sulfur in coal is transferred into the coal gas. The sulfur content in coal in our country is low; the hydrogen sulfide content in coke oven gas is generally 4.5–6.0 grams per cubic meter before the benzene washing tower, and 4–4.5 grams per cubic meter after it. 10. Why is it necessary to remove hydrogen sulfide from coke oven gas? Hydrogen sulfide in coke oven gas is a harmful substance that corrodes equipment used for the recovery of chemical products as well as equipment for the storage and transportation of gas. Using coke oven gas with a high hydrogen sulfide content in steelmaking reduces the quality of the steel ； Used in ammonia synthesis; it can poison catalysts and corrode equipment ； When used as city gas, sulfur dioxide produced by the combustion of hydrogen sulfide is toxic, thereby damaging environmental hygiene and affecting human health. Therefore, it is very important to remove hydrogen sulfide during the coke oven gas purification process. 11. Why is ammonia removed during the purification of coke oven gas? Therefore, there are three main reasons for removing ammonia from coal gas in industrial production: (1) Ammonia is a good agricultural fertilizer. (2) Ammonia has a serious impact on the quality of washing oil used to absorb crude benzene from coal gas; it easily causes the washing oil to emulsify and deteriorate. (3) Ammonia has a severe corrosive effect on equipment used in crude benzene production as well as on gas pipelines. 12. What conditions are required for gas combustion? Gas combustion requires three conditions: (1) an oxidizer, namely air or oxygen. (2) Fire source. Coke oven gas can be ignited at 600–650°C. (3) Flammable gases. That is, the combustible gas components contained in gas. 13. What is an explosion? What are the conditions for an explosion to occur? When combustibles (gas, coal dust, benzene) mix with air, they ignite and burn rapidly within a small area. This process releases a large amount of heat in an instant, causing a sharp rise in temperature and pressure. The flame propagates at speeds of several hundred or even thousands of meters per second; this phenomenon is known as an explosion. The following conditions must be met for an explosion to occur: (1) Air (or oxygen) and combustible material are mixed within the explosive limits. (2) Explosive gases turn into red-hot gases when exposed to a heat source. 14. What is the explosion limit? The range of proportions in which a combustible material mixes with air (or oxygen) and can explode is known as the explosive limit. 15. What is the explosive limit of coke oven gas? Why do the regulations stipulate that the oxygen content in coal gas should not exceed 2%? The explosive limits of coke oven gas are 5.5-30%. It refers to the volume percentage of coal gas in the air ； Simple mathematical calculations show that for an explosion to occur, the proportion of air mixed into the gas must be 70–94.5%. Below 70% or above 94.5%, no explosion will happen. In other words, an explosion can only occur when the oxygen content in the gas is between 14.7% and 19.85%. For safety reasons, gas regulations stipulate that the oxygen content must not exceed 2%. 16. What is the autoignition point? What are the two types of spontaneous combustion? Autoignition point: It refers to the lowest temperature at which a combustible material can catch fire when heated in air or oxygen, without the presence of a flame, electric spark, or other ignition source; this temperature is known as the autoignition point (or ignition temperature). There are two types of spontaneous combustion: spontaneous combustion due to heating: combustible materials experience an increase in temperature as a result of an external heat source, reaching their ignition point and thus burning on their own. Spontaneous heating and combustion: A phenomenon in which a combustible material generates heat through physical, chemical, or biochemical processes occurring within it, without any external heat source; over time, this accumulated heat reaches the material’s autoignition point, causing it to burn on its own. 17. What are the causes of natural heating of substances? The reasons for the natural heating of substances include decomposition heat (such as celluloid), oxidation heat (such as unsaturated fats), adsorption heat (such as activated carbon), polymerization heat (such as liquid hydrogen cyanide), fermentation heat (such as hay), etc. Spontaneous heating and combustion are common phenomena in the storage and transportation of chemical products, and they pose a great threat. 18. How to prevent spontaneous combustion in coke oven gas equipment and pipelines during maintenance? (1) Before dismantling coke oven gas equipment and pipelines, they shall be purged and displaced with steam, nitrogen, or flue gas ； After disassembly, moisten with water and remove the combustible residues. (2) When maintaining equipment kept under negative pressure by the blower’s negative pressure system, it is necessary to block the pipeline leading to the blower with a blind flange in advance. (3) For closed equipment whose maintenance operation temperature is equal to or higher than the auto-ignition point of the material, the main cover or manhole cover must not be opened immediately after production stops. (4) After cleaning the tower, which may contain sulfides, with steam, it must be cooled to room temperature before it can be opened ； Before opening the access hole at the bottom of the tower, the oil and vapor pipes as well as the vent pipe at the top of the tower must be closed. 19. Why must components made of copper not be used in the shut-off devices for coke oven gas pipelines? Since gas contains components such as hydrogen sulfide and ammonia that are corrosive to copper components, especially ammonia can form complexes with copper; this reaction occurs rapidly, and the resulting complex ions are soluble in water. Therefore, copper components are generally not suitable for use in such gas pipelines. In other words, because hydrogen sulfide, ammonia, and similar substances are corrosive to copper components and cause rust, it can lead to leaks in the sealing devices. 20. What color should coke oven gas pipelines be? How should it be labeled? Coke oven gas pipelines should be painted black ； The main gas pipelines in the plant area should be marked with clear signs indicating the direction and type of gas flow. 21. What are the steps for systematically stopping the use of coke oven gas for heating in coke ovens? (1) Start the switch to turn off the switching cock (manual switching is performed during power outages). (2) Close the addition/subtraction cock and vent pipe valves. (3) Shut off the gas pressure regulator and fix the flap in the fully open position. (4) A dedicated person in the control room monitors pressure changes; if the pressure drops rapidly and a warning is issued (below 300 Pa), steam should be supplied immediately, while the valves before and after the preheater should be closed to maintain positive pressure in the pipes. (5) Disconnect the flue gate plates on the machine side and the coke side from the control mechanism, close them slightly, and secure them with pins. (6) If the stoppage time exceeds half an hour, a reversing operation should be performed. (7) If the heating is stopped for an extended period, the air cover that rises due to the exhaust gases as well as the exhaust gas damper that descends should be lowered, and the shutters on the machine side, coke side, and main flue should be closed. (8) Maintain the normal water level of the water seal during the heating shutdown period. 22. What are the steps to restore coke oven gas heating in coke ovens? (1) Open the dispersion pipe. (2) If the gas supply is interrupted for an extended period and the pressure in the gas pipeline drops to zero, it should first be purged with steam; steam supply should be stopped 5 minutes after steam appears in the vent pipe and the explosion-proof pipe. (3) Open the valves before and after the preheater, then introduce gas to displace the steam. After 5 minutes from the moment gas appears at the vent pipe and explosion-proof pipe, take samples from the outlet of the explosion-proof pipe and conduct three consecutive explosion tests; if all tests are successful, close the vent pipe. Maintain the pressure in the main pipeline at no less than 2 KPa. If the gas supply has been interrupted for a short period and the pressure in the gas pipeline has not dropped to zero, there is no need to purge it with steam; instead, gas can be directly supplied to the main gas pipeline. (4) Return the small iron wrench of the air intake door for the waste gas exhaust from the machine and furnace to its original working position. (5) Connect the flue dampers for the machine and furnace to the controller, and adjust the flue gates to achieve a suction level corresponding to the normal heating parameters. (6) After the commutation system passes the inspection, the gas flow control flap is connected to the controller. (7) Gradually open the make-up and drain cocks in batches, while a dedicated person monitors to ensure that the main pipe pressure remains above 1000 Pa. (8) The heating shutdown time is long; when the temperature in the vertical flue drops below the ignition point of the gas, an ignition source must first be introduced into the vertical flue before the gas can be supplied. 23. What operations should be prohibited when delivering coke oven gas to the coke oven basement? (1) Feed into several coke ovens simultaneously ； (2) Other coke ovens are undergoing direction reversal ； (3) Coke pushing or coal charging operations ； (4) Welding operations at the furnace area, between furnaces, and in the basement. 24. What is carbon monoxide poisoning? Coke oven gas contains about 6% CO. If this gas spreads into the air and raises its CO concentration to above 0.06%, it becomes harmful to human health; a CO concentration of 0.4% in the air can be fatal immediately. When CO is inhaled by the human body, it reacts with the blood, causing a lack of oxygen, which is known as carbon monoxide poisoning. 25. What precautions should be taken to prevent gas poisoning accidents? (1) Gas equipment that is newly installed, renovated, or overhauled must undergo inspection, acceptance, and leak testing by the relevant safety authorities before it can be put into use. (2) In the event of a gas leak from gas equipment, it must be addressed immediately, and indoor gas equipment should be regularly inspected. (3) Whenever working with gas, such as removing or installing blind flanges, sealing leaks, or drilling holes, it is essential to wear a gas mask; one must not act recklessly out of enthusiasm. (4) Whenever working inside gas equipment, it is necessary to reliably cut off the gas supply, thoroughly remove any remaining gas, and only proceed with the work after testing. (5) The use of gas for heating is strictly prohibited, and it is not allowed to connect gas pipelines illegally. (6) Utility facilities for daily use, such as water supply and drainage pipes and steam pipes, must not be connected to gas equipment. (7) It is strictly prohibited to establish any living quarters or rest rooms near gas equipment. (8) When working with or handling gas, proper supervision must be provided to prevent unauthorized persons from entering. (9) Regularly disseminate knowledge about gas safety; it is strictly prohibited to rest near gas equipment. Warning signs stating things like “Gas hazard – staying is strictly forbidden” should be installed on all gas equipment in factories. (10) When working in gas areas, at least two people must be present to supervise each other and pay attention to the wind direction. (11) Regularly monitor the CO level in the working environment; wherever work is carried out in areas with gas, the CO level must not exceed the **health standards. 26. What requirements must gas gate valves meet? (1) Single supports should be installed on both sides of larger gate valves. (2) An operating platform and ladder are required. (3) Gate valves with exposed stems should be preferred, and the direction of operation should be indicated on the handwheel. (4) The first gate valve should be installed within 0.5 meters of the main pipe at the distribution branch; double gate valves should be used for the pipes in front of the furnace, with a vent pipe installed between them. (5) Gate valves not designed for use with gas shall not be used on gas equipment. 27. What are the two main safety indicators for gas drainers? One is the height of the water seal, which should be determined based on its effective sealing pressure; for gas, this pressure is set at 500 mm ； Another measure is to install check valves or water seals in both the water supply and drainage systems, to prevent gas from entering the water pipes in case of a water outage. Meanwhile, disconnecting the drain from the underground drainage pipes prevents gas from entering the sewers in case the drain leaks gas. 28. How many types are there for gas vent pipes? What is its main function? Vent pipes are divided into three types: excess vent pipes, emergency vent pipes, and purge vent pipes. The vent pipes used by various gas customers are all purge vent pipes. Generally speaking, the vent pipe serves the purposes of excess venting, emergency venting, and purging venting. 29. What is the main purpose of installing steam pipes or nitrogen pipes on gas equipment and pipelines? Installing steam pipes or nitrogen pipes on gas equipment and pipelines serves three main purposes: displacement, cleaning, and pressure maintenance. 30. What safety checks should be performed before carrying out hot work on gas equipment? (1) Whenever work involving open flames is to be carried out on gas equipment, an application for such work must be submitted two days in advance; the time and location of the work must be specified in detail, along with sketches and safety measures, and work may only commence after approval from the relevant authorities. Before starting hot work, it is necessary to carefully check for flammable materials in the vicinity, as well as flanges, welds, and valve cores that are prone to gas leakage. (2) Before carrying out hot work, necessary fire-fighting equipment should be prepared, such as foam extinguishers, dry powder extinguishers, carbon dioxide extinguishers, fire trucks, as well as yellow mud, wet straw bags, steam pipes, etc. Work involving open flames is not permitted unless safety measures are implemented, and safety training must be provided to the workers. (3) If there are any gas leaks at the location where work will be carried out, those issues must be resolved first; any flammable materials should be removed or covered up. (4) Perform hot work at the designated time and place; in case of any changes, a new hot work permit must be obtained, and the permit should be returned after the work is completed. (Generally refers to maintenance work on main pipelines or systems.) (5) Depending on the specific circumstances, the safety station should conduct on-site inspections to check for leaks in the gas pipelines and the desiccators located below them, as well as to verify whether there are any combustible gas pipelines in the area where welding is being carried out. 31. What precautions should be taken when working with gas equipment that is in use? (1) The pressure of gas equipment should be kept normal and stable. Low-pressure gas equipment, whose gas pressure should be above 500 Pa (50 mmH2O) ； High-pressure gas equipment should have a pressure of over 2 kPa (200 mmH2O). If the gas pressure is below the specified level or if there are large fluctuations in the gas pressure, with a pressure difference of 0.5 kPa–1 kPa (50–100 mmH2O), welding operations must be stopped immediately to prevent negative pressure from causing a backflow explosion of the gas. Welding can resume only once the pressure returns to normal levels. (2) A pressure gauge should be installed near the hot work area, steam pipes should be prepared, and a dedicated person should be assigned to monitor them. (3) When welding directly on gas equipment or pipelines, only electric welding is permitted; oxygen welding is not allowed. (4) When working with fire near a gas pipe blind flange or on equipment where gas does not flow, it is necessary to conduct gas analysis to confirm that it is pure gas; however, it is best to carry out the work when gas is flowing. (5) Welding work may be carried out on negative-pressure gas pipelines and equipment only when the gas supply is continuous, the compressors and extractors are operating properly, the pipelines and equipment are airtight, and the gas is pure; this applies to items such as the gas extractors in coking plants that lead to the main coke oven gas pipeline, as well as the pipelines and equipment ahead of the gas compressors. However, it is not allowed to puncture the pipe lining and allow air to enter; it is best to introduce an appropriate amount of steam into the equipment where heating is applied. (6) Under special circumstances, when working on gas equipment and pipelines involving welding (i.e., when the pressure in the gas production system is abnormally low below the specified level), strict organizational measures as well as appropriate safety measures must be taken. The gas pressure should be maintained at 50–100 Pa (5–10 mmH2O) or higher, or an appropriate amount of steam should be introduced to assist in maintaining the pressure. The wiring switches of the welding machine should be placed near the pressure gauge, so that power can be cut off immediately in case of an emergency, thereby stopping the welding work. (7) Electrical equipment must meet the specified requirements, have good insulation, and be properly grounded to prevent electric sparks from causing fires. 32. What precautions should be taken when working with fire near gas equipment and pipelines that are no longer in use? (1) A reliable cutting device must be used to cut off the gas supply. Blind plates are usually used, along with sealed plug valves, cocks, and check valves. When using a water seal to cut off gas, it must be used in conjunction with a gate valve to ensure that the water seal overflows; moreover, a dedicated person should monitor this overflow to prevent the effective height of the water seal from decreasing, which could allow gas to enter the rear area during pressure fluctuations and mix with air to form explosive gases. (2) Before carrying out hot work, the equipment should be purged with steam or nitrogen to completely remove any residual gas; hot work may only proceed after a hot work analysis shows satisfactory results. (3) When working on coke oven gas equipment and pipelines, a small amount of steam should be introduced, and flammable substances such as tar and naphthalene residues that are accumulated inside the area where work is being done must be removed. Sand should be spread over an area of 1.5–2 meters on either side of the area where work is being carried out. (4) Whenever steam is used for welding, the gas supply must be reliable and continuous throughout the welding process. (5) Gas equipment and pipelines that have been left unused for an extended period must be re-ventilated before any work is carried out on them; work may only commence after tests confirm that the ventilation is satisfactory. (6) During maintenance work involving open flames, a re-analysis must be conducted every two hours; additionally, a re-analysis is required half an hour before resuming work after an interruption. 33. What should be done if gas ignites inside a gas pipeline due to maintenance work on the pipeline? When maintenance work on gas pipelines causes the gas inside the pipelines to catch fire, or when deposits within the gas equipment (such as naphthalene, tar, etc.) ignite, all access holes in the equipment, such as manholes and vent valves that allow communication with the atmosphere, can be closed to isolate the area from air and allow the fire to extinguish naturally. Alternatively, large amounts of nitrogen or steam can be introduced to put out the fire. Only after the fire has been extinguished and the source of gas has been cut off or the deposits in the equipment have been removed can maintenance work resume. 34. What are the ways to prevent gas fires? (1) All sources of fire are prohibited in the vicinity of gas equipment or within 40 meters of areas where gas work is being carried out. (2) Special electrical equipment that is not related to gas equipment shall not be installed on top of gas equipment. (3) Whenever working with gas, it is necessary to prevent the emergence of sparks. Especially when working with coke oven gas, copper tools must be used; in special cases, if iron tools are used, butter should be applied to them, and great care must still be taken. (4) During blind plate operations, the blind plates should be oiled, and all lifting equipment must have measures to prevent friction-induced sparks; the blind plates used for connecting and disconnecting coke oven gas should be grounded. (5) When working with gas, high temperatures, open flames, and exposed hot pipes in the vicinity should be insulated. (6) Whenever work involving open flames is to be carried out on gas equipment, the necessary procedures for obtaining permission must be strictly followed, and fire prevention and extinguishing measures must be put in place; the work must be conducted at the designated time and location as specified. (7) The grounding device of gas equipment should be inspected regularly, and its grounding resistance should not exceed 4 ohms. 35. How should gas leaks be handled? (1) Upon detecting a leak, initiate the emergency procedures; if the leak occurs indoors, activate the exhaust system immediately. Wear a valid positive-pressure air respirator and a portable alarm device before going to the site to locate the source of the leak. (2) Once the leak location is identified, quickly seal the crack using asbestos rope, clay, lead paint, etc. If the blockage cannot be resolved, the pressure of the pipeline gas can be reduced to 500 Pa; if this does not work, a large amount of steam is introduced into the pipeline, after which the gas pressure is lowered to 100–200 Pa before attempting to remove the blockage. (3) Immediately halt the work of other personnel in that area, and set up barriers at the leakage site to prevent unauthorized persons from entering the affected zone. 36. How to handle fires caused by coke oven gas? (1) In the event of a gas fire, it is necessary to immediately notify the gas dispatch center, the gas safety station, and the fire department, so that they can work together with the unit where the incident occurred to quickly handle the fire. (2) Activate emergency procedures while controlling factors to prevent the accident from spreading. (3) In the event of a fire in a pipe with a diameter of less than 100 mm, the valve can be closed directly to cut off the gas supply and extinguish the fire. (4) When a pipe with a diameter greater than 100 mm is on fire but the fire is small, methods such as using foam, spraying water, or blocking the pipe can be employed to extinguish the fire. If the fire becomes larger, the users connected to that pipe should be stopped from using gas, and the fire must be extinguished. Reduce the gas pressure appropriately; a pressure gauge should be used, or the valve should be closed gradually by observing the size of the flame. At the same time, a large amount of steam should be introduced into both sides of the pipe where the fire is occurring in order to extinguish it. However, the gas pressure must not be lower than 100 Pa, and sudden closing of the valve is strictly prohibited to prevent backfire explosions. After extinguishing the fire, the gas supply must be completely cut off, and attention should be paid to the risk of poisoning. (5) Locate the leak point and quickly seal the crack using asbestos rope, yellow clay, lead paint, etc. Stop heating or treat the leak with gas as appropriate. (6) Immediately after a fire breaks out, spray water on the gas equipment and flanges to prevent the equipment and flanges from being damaged or deformed. When the equipment is red-hot, it must not be suddenly cooled with water to prevent cracking or deformation. (7) In case of people suffering from suffocation or burns, proper medical assistance must be provided. 37. How should gas explosion accidents be handled? Whenever there is a gas explosion accident. Generally, it is caused by damage to gas equipment, gas leaks, or fires and poisoning resulting from those leaks. Therefore, after a gas explosion occurs, fires or poisoning incidents usually follow, or a second explosion might happen. As such, dealing with gas explosion incidents can be divided into the following five steps: (1) When an explosion occurs but no fire has started yet, the relevant valves should be closed immediately, or water seals should be used to prevent leakage; meanwhile, blind flanges should be installed to cut off the gas supply. Before the gas supply is completely severed, the users involved must put out any fires and stop using the gas. (2) At the same time, a large amount of nitrogen, steam, or natural ventilation should be introduced into the pipeline to dilute the residual gas and prevent another explosion. (3) When a large amount of toxic gas generated by the explosion cannot be removed immediately, all personnel should be directed to evacuate the site to prevent poisoning. (4) In cases where a gas equipment explosion results in fire or poisoning, it shall be handled as a fire or poisoning incident. Find out the cause of the explosion. The cause has not been identified, and the equipment cannot resume production. 38. How should an explosion caused by negative-pressure coke oven gas be handled? In the event of an explosion in the equipment or pipelines prior to the main valve through which the gas pipeline enters the fan room, the fan should be stopped immediately and the coke oven’s exhaust system should be activated. Users downstream should be informed to cease gas supply in order to prevent the introduction of air, which could lead to an expansion of the accident. If a fire breaks out after the machine is stopped, it should be dealt with in accordance with the emergency procedures for fires. 39. How to prevent gas explosion accidents? To prevent gas explosion accidents, it is essential to prevent the formation of a gas-air mixture, as well as to prevent it from coming into contact with any open flames, electrical sparks, or temperatures exceeding the ignition point of the gas. Therefore, the requirements regarding the tightness of gas equipment and its operation are particularly strict. (1) The gas equipment and pipelines to be repaired must be reliably isolated using blind flanges; isolation solely through valves is not permitted. Only after purging and passing the inspection can ignition be carried out ； When working on a gas pipeline that is in operation, it is necessary to maintain positive pressure. (2) When purging residual gas from containers and pipes, the top or end discharge must be opened, and the other end should be purged with steam; if possible, nitrogen can be used for purging. (3) When gas users ignite the burner, it is necessary to ensure that the gas pressure is normal. Before ignition, check whether all burner valves are tightly closed and conduct an explosion test. Open the flue and furnace door; the suction force in the flue should be greater than -5 Pa. When igniting from the burner at the far end of the furnace, it is necessary to supply a flame first and then open the gas valve. If the first ignition fails, the residual gases in the furnace should be dealt with again and removed through the flue. After identifying the cause, restart ignition. For furnaces with forced air supply, the fan should be started before ignition, and automatic shut-off interlock devices must be installed on both the air ducts and the gas pipelines. (4) For gas equipment that has been left unused for a long time, the residual gas must be reprocessed before any welding or firing can be carried out; only after re-sampling and testing confirm that the gas meets specifications is it permissible to proceed with such operations. For equipment involving steam and hot work, the gas supply must not be interrupted during operation. (5) After a power outage at a gas station, it is necessary to ensure that the pipeline network remains sealed to prevent air from entering and mixing with the gas. After power is restored, water should be supplied first, followed by air supply; finally, the gas compressor can be started. (6) In the event of a short-term gas shutdown, when it is impossible to maintain a pressure of 19.8 Pa in the pipeline, steam may be introduced into the pipeline to assist in maintaining the pressure. 40. What aspects are mainly checked during the inspection of gas pipelines? (1) For gas pipelines and auxiliary equipment, check for any leaks of gas or oil. Upon detection, such issues must be addressed promptly according to the division of responsibilities. (2) Integrity of overhead pipelines, inter-span deflection, inclination of supports, foundation settlement, and other facilities; conditions of metal corrosion and concrete damage. (3) Check whether any electrical wires, cables, additional pipes, or other equipment have been installed on the gas pipeline; whether any flammable or explosive materials are stored beneath the pipeline; and whether there is any excavation or soil removal near the pipeline, as well as whether there are any warehouses or buildings in the vicinity. (4) Whether open-flame operations on and around gas pipelines comply with safety regulations; whether fire prevention measures are adequate; and whether they pose any threat to the safety of the gas pipelines. (5) Can the water seal of the dehydrator and water seal function properly? Is drainage normal? Is there any leakage or overflow from the sump? Is there any removal of accumulated water? Are the drain pipes blocked? Is there any connection between them and the domestic sewage pipes? (6) In winter, how is the insulation of pipeline auxiliary equipment? Are there any freezing or blockages? Is there any water accumulation or ice buildup? What is the degree of harm caused by these issues? (7) Check whether construction near the pipeline network involves using the pipes as supports for lifting or pulling; ensure that the objects being lifted do not pose a threat to the safety of the pipes, and such activities must be stopped immediately if detected. (8) Condition of pipeline grounding points and lines. (9) Blockages in fire and emergency evacuation routes throughout the area, as well as the impact of customers with gas supply disruptions and new gas projects on the existing pipeline network. (10) Are there any illegal constructions beneath and around the pipeline? (11) Keep records of any abnormal phenomena that occur on a daily basis as well as the operation status of the pipeline network, and address them promptly. 41. What are the main tasks for maintaining gas pipelines? (1) Apply anti-corrosion paint to the metal surfaces of gas pipelines and associated equipment every five years. (2) Conduct a pipeline wall thickness inspection once a year. (3) Conduct an inspection of the pressure drop in the gas supply line once a year, as well as an inspection of the sediment thickness in the flow channels, pipes, and main pipelines. (4) Check for leaks once before the onset of winter and after thawing each year, keep records, and address any issues within a specified time frame; inspect the valve packing quarterly. (5) The grounding resistance should be tested once a year, the lightning protection, rain protection, and wind protection systems should be inspected once a year, and the water collection tanks and drainage channels should be cleared once a year. (6) Lubrication checks and replenishments are generally carried out in the first and third quarters of each year, with lubricant applied to all valves. (7) Clean the drainers twice a year. (8) Conduct anti-freezing assurance inspections before sending steam each year, and complete the work before winter arrives. (9) Conduct a test on the opening and closing of the vent pipe valve once a year at the onset of winter, drain the water accumulated in the vent pipe, and check the condition of the compensator. (10) The pipeline network and operation platform are cleaned and organized once every spring.