Safety production technology

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Chapter 1 Mechanical and Electrical Safety Technologies Section 1 Basic Knowledge of Mechanical Safety A machine is a device composed of various interconnected components assembled according to certain rules, capable of performing specific functions. During operation, mechanical equipment has at least some parts that move relative to each other in a certain pattern. A complete mechanical system consists of a prime mover, a control and operation system, a transmission mechanism, a support device, and an actuator. Machinery is essential equipment in modern production and daily life. While machinery provides people with efficiency, speed, and convenience, it can also cause mechanical injuries such as impacts, crushes, and cuts, as well as non-mechanical hazards like electric shocks, noise, and high temperatures during its manufacturing, operation, and use. The task of mechanical safety is to take systematic measures to ensure the safety and health of workers throughout the entire process of manufacturing and using machinery, protecting them from various hazardous factors. Mechanical safety encompasses two main aspects: the safety in the manufacturing of mechanical products and the safety in the use of mechanical equipment. I. Safety in the Manufacturing of Mechanical Products (1) Main Categories of Mechanical Products There are a great variety of mechanical products. The main products of the machinery industry are as follows: (1) Agricultural machinery: tractors, internal combustion engines, seeders, harvesting equipment, etc. (2) Heavy mining machinery: metallurgical machinery, mining machinery, lifting machinery, loading and unloading machinery, industrial and mining vehicles, cement equipment, etc. (3) Construction machinery: forklifts, earth-moving and transportation machinery, compaction machinery, concrete machinery, etc. (4) General petrochemical machinery: oil drilling and production equipment, refining machinery, chemical processing machinery, pumps, fans, valves, gas compressors, refrigeration and air conditioning equipment, papermaking machinery, printing machinery, plastic processing machinery, pharmaceutical machinery, etc. (5) Electrical machinery: power generation machinery, transformers, motors, high and low voltage switches, wires and cables, batteries, welding machines, household appliances, etc. (6) Machine tools: metal cutting machine tools, forging machinery, casting machinery, woodworking machinery, etc. (7) Vehicles: trucks, road buses, sedans, modified vehicles, motorcycles, etc. (8) Instruments and meters: automated instruments, electrical instruments and meters, optical instruments, composition analyzers, automotive instruments and meters, electrical equipment, audio-visual teaching equipment, cameras, etc. (9) Basic machinery: bearings, hydraulic components, seals, powder metallurgy products, standard fasteners, industrial chains, gears, molds, etc. (10) Packaging machinery: packaging machinery, metal-packaged items, metal containers, etc. (11) Environmental protection machinery: equipment for water pollution control, equipment for air pollution control, solid waste treatment equipment, etc. (12) Other machinery. 2) The main products in industries other than the machinery sector include railway machinery, construction machinery, textile machinery, light industrial machinery, and shipbuilding machinery, etc. (II) Mechanical safety design and machine safety devices Mechanical safety encompasses the safety at all stages, including design, manufacturing, installation, adjustment, use, maintenance, and disassembly. Safe design can minimize risks. Mechanical safety design refers to the use of various measures during the mechanical design phase – ranging from the materials used for components to the appropriate shape and relative positioning of these components, from limiting the force required for operation as well as the mass and speed of moving parts to reducing noise and vibration. It involves the application of intrinsically safe technologies and power sources, as well as the use of principles related to mechanical interactions between components. In addition, ergonomic principles are taken into account, and by selecting appropriate design structures, it is possible to avoid or minimize hazards as much as possible ； Dangers can also be avoided or reduced by improving the reliability of equipment, mechanizing or automating operations, and carrying out adjustments and maintenance outside hazardous areas. 　　1. Intrinsic Safety Intrinsic safety is a method of mechanical safety in which the designer of the machine takes measures during the design phase to eliminate mechanical hazards. 　　1) Use of intrinsically safe technology Intrinsically safe technology refers to the use of such technology in the design and manufacturing of machinery, so that the machinery can meet its own safety requirements when performing its intended functions under specified conditions, without the need for any additional safety measures. Including: avoiding sharp edges, points, and protrusions ； Ensure an adequate safety distance ； Determine the limits for the relevant physical quantities ； Use intrinsically safe process systems and power sources. 　　2) Limit mechanical stress The mechanical stress on mechanical components shall not exceed the allowable value, with a sufficient safety factor ensured. 　　3) Safety of materials and substances The materials, fuels, and processing materials used in manufacturing machinery must not pose a threat to the safety or health of people during their use. The mechanical properties of the material, such as tensile strength, shear strength, impact toughness, yield limit, etc., should meet the requirements imposed by the loads acting to perform its intended function ； The material should be able to withstand the intended environmental conditions, such as having corrosion resistance, aging resistance, and wear resistance ； The material should be uniform, to prevent residual stresses from arising due to an uneven microstructure of the material resulting from improper process design ； At the same time, toxic materials or substances should be avoided, and it is necessary to prevent fire and explosion hazards caused by the machinery itself or by gases, liquids, dusts, vapors, or other substances resulting from the use of certain materials. 　　4) Implementing safety ergonomics principles In mechanical design, safety ergonomics principles are applied through the rational allocation of human and machine functions, adaptation to human characteristics, user interface design, and the arrangement of the working space. This improves the operability and reliability of mechanical equipment, reduces the physical strain and psychological stress on operators, and thereby minimizes operational errors. 　　5) Safety principles for designing control systems During operation, typical hazardous conditions in machinery include: accidental startup, uncontrolled speed changes, inability to stop movement, detachment and flight of moving mechanical parts or workpieces, and malfunctioning of safety devices. The design of the control system should take into account the operating modes of various tasks or employ fault indication devices to enable operators to handle them safely. 　　6) Preventing hazards in pneumatic and hydraulic systems Machinery that uses pneumatic, hydraulic, thermal energy, and other such systems must be designed to avoid various potential dangers resulting from the accidental release of these energies. 　　7) Prevention of electrical hazards Electrical safety is an important part of mechanical safety; the electrical components in machinery must meet the requirements of relevant electrical safety standards. To prevent electrical hazards, it is necessary to guard against electric shock, short circuits, overloads, and static electricity. 　　In the design, it is also necessary to consider improving the reliability of the equipment and reducing the failure rate, in order to decrease the likelihood of operators having to locate faults and repair the equipment ； Mechanization and automation technologies should also be employed to keep operators as far away as possible from dangerous areas ； The safety of adjustments and maintenance should also be considered to reduce the need for operators to enter dangerous areas. 　　2) Fail-safe design The designer should ensure that no danger arises in the event of a machine failure. Relevant devices include operation limit switches, preset braking devices to prevent shocks and movements that should not occur, devices for installing handles and to prevent falling, and fail-safe power cut-off switches. 　　3) Positioning for safety 　　Place the machine’s components in locations that cannot be accessed, thereby ensuring safety through proper positioning. However, the designer must take into account those dangerous components that are not normally accessible, but may become accessible under certain circumstances, such as when repairing the machine using a ladder. 　　4) Machine layout A reasonable and safe arrangement of machines in the workshop can significantly reduce accidents. When planning a safe layout, the following factors should be considered: (1) Space: to facilitate operation, management, maintenance, debugging, and cleaning. 　　(2) Lighting: Includes general lighting in the workplace (natural and artificial light, with attention to avoiding glare) and lighting specifically required for operating machinery. 　　(3) Pipe and cable layout: It should not obstruct safe access around the machine, prevent tripping, and provide sufficient headroom. 　　(4) Safety for entry and exit during maintenance. 　　5. Machine safety devices 　　1) Fixed safety devices 　　Where possible, fixed safety devices should be incorporated into the design to prevent contact with dangerous parts of the machine. The device should be able to automatically meet the environmental and operational conditions required for the machine to function. The effectiveness of the device depends on its fixing method and the size of the opening, as well as the appropriate distance from the hazard point once it is opened. Safety devices should be designed to be removable only with specialized tools such as screwdrivers or wrenches. 　　2) Interlock safety device The basic principle of the interlock safety device: The machine can only operate when the safety device is in the closed position ； And the safety device can only be activated when the dangerous parts of the machine stop moving. Chain safety devices can take mechanical, electrical, hydraulic, pneumatic, or combined forms. When designing interlocking devices, it is necessary to ensure that they do not expose personnel to danger in the event of any failure. 　　3) Safety control devices 　The machine is required to be able to stop moving quickly, and control devices can be used for this purpose. Principle of the control device: The machine can only start when the control device is fully closed. Only when the operator activates the control device does the machine’s operating program start to function ； If the control device is disconnected, the machine’s movement will stop quickly or reverse. Typically, in a control system, the control device does not remain locked in the closed state while the machine is running. 　　4) Automatic safety device The mechanism of an automatic safety device is to remove the human body that is in danger from that hazardous area. It can only be used in environments where there is sufficient time to perform such actions without causing harm; therefore, it is only applicable to machines moving at low speeds. 　　5) Isolation safety devices 　Isolation safety devices are mechanisms that prevent any part of the body from approaching dangerous areas, such as fixed fences and the like. 　　6) Adjustable safety devices 　　When it is not possible to isolate the hazardous area, partially adjustable fixed safety devices can be used. The protective effect that these safety devices can provide depends to a large extent on the operator’s use of them, as well as their proper adjustment and regular maintenance. 　　7) Automatic adjustment safety device 　　The automatic adjustment device activates automatically due to the movement of the workpiece, and returns to its closed state once the operation is complete. 　　8) Trip safety device The function of the trip safety device is to automatically stop or reverse the movement of the machine before it reaches a dangerous position. Such devices rely on sensitive trip mechanisms, as well as on the machine’s ability to stop quickly (this can be achieved using braking devices). 　　9) Two-hand control safety device This type of device forces the operator to use both hands to operate the controller. However, it can only protect the operator, not other people who might approach the dangerous area. Therefore, safety devices that can provide protection for everyone must also be installed. When using such devices, there should be an appropriate distance between the two controls, and the machine should only start operating when both control switches are turned on; furthermore, the control system needs to be restarted after the machine stops operating each time. 　　【Example Question】Which of the following statements about interlock safety devices is correct: ▃__. ( ) 　　A. The machine can only operate when the safety device is in place. 　　B. The machine cannot operate when the safety device is in place. 　　C. The safety device can only be activated when the dangerous parts of the machine have stopped moving. 　　D. The safety device cannot be activated when the dangerous parts of the machine have stopped moving. 　　【Answer】 A C (III) Hazardous points in mechanical production power facilities and general safety technology management 　　Facilities that provide power for the mechanical production process are referred to as power stations. The main components include: boilers and auxiliary equipment, gas stations, oxygen production stations, air compression stations, acetylene stations, substation stations, etc. Information on the safety technologies for boilers and auxiliary equipment can be found in the relevant sections on special equipment; the following text discusses the potential hazards and safety technologies related to other mechanical power facilities. 　　1. Safety technology for gas stations This content is applicable to gas stations within industrial enterprises, as well as natural gas and gas storage and distribution stations. 　　1) Overview of hazard points A gas station is a facility where gas is produced. Since gas is a toxic and flammable, explosive gas, it can easily lead to poisoning incidents as well as fire and explosion accidents. 　　2) Requirements for safety technology management 　　(1) Gas stations and gas generators: 　　① The design of gas station buildings must comply with **specified requirements. 　　②Gas production equipment should be products manufactured by specialized manufacturers, which are safe and reliable and come with complete technical documentation. 　　③The viewing port cover of the gas generator should be airtight, and the viewing port as well as the coal feeding mechanism must be perfectly airtight. 　　④The water quality used in gas generators with water jackets must meet the specified requirements. 　　⑤A control valve and a check valve must be installed on the air inlet pipe of the gas generator, and they must be flexible and reliable ； An explosion-proof valve and a vent valve should be installed at the end of the pipeline. 　　⑥The water seals at all levels of the gas generator (such as the maximum relief valve, dual vertical pipes, furnace bottom, etc.) must maintain an effective water level, with normal overflow. 　　⑦Gas purification facilities should be maintained in a good state of purification, and reliable isolation devices should be installed at the inlet and outlet of the electrostatic precipitator. 　　⑧The furnace must be shut down when the oxygen content in water gas and semi-water gas reaches 1%. 　　⑨The safety devices of the steam collector shall be complete and functional. 　　⑩An automatic water supply device should be installed in the steam collector. 　　(2) Instrument signals and safety devices: ① All kinds of instruments, signals, and interlock devices shall be in good condition and functional. 　　②An acoustic and optical alarm device should be installed at the outlet of the generator furnace. The conveyor and blower should be interlocked. 　　(3) Electrical: ① The electrical equipment in the gas conveying machine room and coal hopper room must meet explosion-proof requirements. 　　②When the blower and exhaust fan are installed in the same room, all electrical equipment must meet explosion-proof requirements. 　　③The gas station should be supplied with power from two separate sources. When it is difficult to supply power from two sources, safety measures should be taken to prevent power outages, and emergency lighting should be installed. 　　(4) The production and delivery systems of gas stations shall be equipped with vent pipes as required; these vent pipes must be at least 4 meters above the roof of the building, and they shall have rain protection as well as reliable measures to prevent them from toppling over. 　　2. Safety Technology for Oxygen Production Stations This content applies to oxygen production stations (facilities) that use the air liquefaction and separation method for the production, storage, and cylinder filling of oxygen. 　　1) Overview of hazard points Oxygen has highly reactive chemical properties and can act as an oxidizer. Its strong oxidizing property can also promote the spontaneous combustion of certain substances, making it one of the fundamental elements involved in the combustion and explosion of materials. There are considerable dangers involved in the production, storage, and packaging of oxygen. 　　2) Requirements for safety technology management 　　(1) The layout of station (building) structures shall meet the following requirements: 　　① The air intake of air separation equipment shall be more than 1 m above the eaves of the oxygen production (station) building, and its vertical distance from the ground must be greater than 10 m. The air should be clean, with its hydrocarbon impurities kept within acceptable limits. 　　②Independent rooms (warehouses), bottling rooms, bottle storage rooms, and air tank storage rooms should have insulation measures as well as measures to prevent direct sunlight from reaching inside the premises. 　　③The storage bottle room should be a single-story building with a floor that is flat, non-slippery, wear-resistant, and does not generate sparking from impacts. 　　(2) Equipment and facilities: All process equipment should be in good condition ； The equipment’s cooling system and lubrication system are operating normally ； There should be no carbon buildup in the air separation system, and regular inspections are required ； The safety devices are complete and reliable, and the indicating instruments are sensitive ； The levels of acetylene, hydrocarbons, and oil in air separation units should be regularly monitored and analyzed, with proper records kept ； Any tools or materials in contact with pure oxygen must not have grease adhered to them ； The piping system shall comply with relevant regulations ； The gas exhaust pipe should be led to a safe outdoor location and equipped with warning signs ； The oxygen exhaust pipe should be kept away from heat sources and equipped with lightning protection measures ； The nitrogen exhaust pipe should have measures to prevent suffocation of personnel ； Pressure vessels shall meet the requirements of the regulations ； Vertical floating roof tanks should be free from severe corrosion, the lifting mechanism should be flexible, and the water seal should be reliable, with interlocks at the maximum and minimum levels ； The water seal and overpressure protection devices of the rubber storage bladder must be in good condition and reliable. 　　(3) Bottle warehouse: ① The actual inventory of bottles should not exceed 2,400. 　　②When empty and full bottles are stored together, they should be kept separate, with a distance of at least 1.5 meters between them, along with clear markings and reliable measures to prevent them from toppling over. 　　(4) Fire protection facilities: ① Fire protection facilities should be complete and properly equipped. 　　②A fence or barrier with a height of not less than 2 m should be installed around the station area. 　　③There are no accumulations of flammable or toxic materials within the fire separation distance. 　　④The fire exits are unobstructed. 　　⑤Arrange prominent safety signs in a logical manner. 　　3. Safety Technology for Air Compressor Stations 　　1) Overview of Hazardous Points 　　An air compressor station is a facility in a company that supplies air at a certain pressure to various areas that require it. Inside the air compression station, the compressor compresses air into gas at a certain pressure and stores it in the air storage tank; at this point, the air storage tank becomes a container with an explosion hazard. In pressure vessel explosion accidents, a considerable number involve compressed air tanks. If the air reservoir is of poor quality and operates under faulty conditions due to inadequate inspection and maintenance, there is a significant risk involved. 　　2) Requirements for safety technology management 　　(1) Complete technical documents: 　　① The factory documents for air compressors and air storage tanks include: product manufacturing license, quality certificate, strength calculation reports for pressure-bearing components, discharge capacity calculation reports for safety valves, installation and operation manuals, etc. 　　②In accordance with the requirements of the \"Regulations on the Safety Supervision of Pressure Vessels\", archives and management cards for pressure vessels must be established, regular inspections shall be carried out, and the vessels shall be used within the inspection period, with complete inspection report documentation. 　　(2) Safety valves and pressure gauges: The safety valves and pressure gauges are sensitive and reliable, and are calibrated regularly. The safety valves and pressure gauges on the gas storage tank are prone to rusting due to exposure to wind and rain, which can undermine their reliability; therefore, they need to be inspected once a year and sealed with lead, along with proper recording and signing. 　　(3) Safety protection: 　　① The protective cover for the air compressor pulley is reliable. In air compressors, power transmission is mostly achieved through belts. The speed during transmission is high, and the belts are long with a large range of movement; the area where the belt meets the drive pulley is particularly dangerous. In the absence of protective covers, there is a risk that operators may be caught by the pulleys. It is required to enclose the movement range of the pulley to ensure that the operator’s sleeves are not caught in during inspections. 　　②The noise level in the operation room should be below 85 dB, and there must be a test report from the noise monitoring department. 　　(4) Gas storage tank: ① The gas storage tank shows no severe corrosion. Gas storage tanks are mostly installed outdoors, in an environment with poor conditions, making them prone to corrosion. Corrosion reduces the wall thickness, thereby decreasing its pressure-bearing capacity ； Severe corrosion can lead to the explosion of the gas storage tank. It is required to perform rust removal and painting maintenance on the gas storage tank once a year, to measure the thickness and keep records, paying special attention to the lower part of the tank. 　　②The gas storage tank is supported stably, there are no cracks at the welds, and it does not experience severe shaking during operation. The compressed air stream at the compressor outlet is pulsatory; it undergoes buffering upon entering the air storage tank, and is then delivered to the points of use once it becomes stable. The gas storage tank vibrates due to the pulse pressure acting on it ； If the support is not secure, it will exacerbate the shaking of the tank. The shaking caused the weld between the tank and its support to crack due to fatigue. 　　4. Safety Technology for Acetylene Generation Stations This content applies to acetylene generation stations (rooms) that produce acetylene gas using calcium carbide as raw material. 　　1) Overview of hazard points Acetylene generation stations are widely used in enterprises that do not have the facilities to use acetylene cylinders, in order to supply acetylene gas centrally to the production areas. However, due to the hazardous properties of acetylene gas, such as a wide explosive range, a low lower explosive limit, and low ignition energy, it can easily lead to fire and explosion accidents. 　　2) Requirements for safety technology management 　　(1) The design of acetylene stations (rooms) shall meet the specified requirements. 　　(2) Establish sound safety management rules and regulations: ① Registration is required for entering and leaving the station (building); fire sources must be handed in, and clothing must meet the specified requirements. 　　②Strictly implement the routine inspection system, with complete and reliable records. 　　(3) Various corresponding safety technical documentation files should be established. 　　(4) Pipeline system: 　　① Pipelines and valves should be tight and reliable. For components in long-term contact with acetylene, the material should be a copper alloy with a copper content of not less than 70%. 　　②Pipelines should have effective measures to discharge static electricity, and there should be records of regular tests. 　　③The piping system must be equipped with tempering arrestors in a proper manner to ensure their reliability and effectiveness. 　　(5) Calcium carbide storage area and crushing system: ① The storage area shall meet the specified requirements, have good ventilation, and remain dry; water accumulation, leaks, and humidity are strictly prohibited. 　　②Calcium carbide drums must be kept airtight to prevent air from coming into prolonged contact with the calcium carbide inside them. 　　③When manually crushing calcium carbide, proper personal protective equipment must be worn ； When mechanically crushing calcium carbide, a dust removal device should be used, and the powdered calcium carbide must be removed promptly; it should also be properly disposed of using the method of adding calcium carbide to water as specified. 　　④When setting up the intermediate calcium carbide storage area and crushing room, moisture-proof measures should be taken. 　　(6) Safety measures: ① Before maintaining the acetylene generation system, it must be thoroughly purged with an inert gas; maintenance can only proceed after sampling and testing show satisfactory results. 　　②The balance valve of the low-pressure acetylene generator should be in good condition, clearly labeled, and equipped with measures to prevent incorrect operation. 　　③Float-type gas tanks should be equipped with alarm devices linked to the extreme position limits, and sprinkler systems should be installed depending on the environmental conditions. 　　④The electrical equipment and instruments (meters) inside the station building must meet explosion-proof requirements. 　　⑤All safety devices shall be sensitive, reliable, in good condition and functional, and shall undergo regular inspections and tests as specified, with records kept. 　　⑥Lightning protection measures should meet the requirements. 　　(7) Fire protection facilities: ① Fire-fighting equipment should be properly installed, with prominent warning signs. 　　②Fire exits should be unobstructed, and it is best to arrange them in a circular pattern. 　　③It is strictly prohibited to use water or foam extinguishers to put out fires involving calcium carbide, and it is strictly forbidden for halogenated substances such as carbon tetrachloride to enter the station (building). 　　【Example question】The vent pipe of a gas station should be at least ▃□ m above the roof of the building, and it must have rain protection as well as reliable measures to prevent it from toppling over. （ ） 　　A. 2 　　B. 3 　　C. 4 　　D. 5 　 【Answer】 C