Request for the Standards for Dust Explosion Prevention Safety in Food Processing, Storage and Transportation Systems GB17440-1998

Safety Regulations for Dust Explosion Prevention in Grain Processing, Storage, and Transportation Systems 1 Scope These standards specify the classification and boundaries of hazardous areas with explosive dust in grain processing, storage, and transportation systems, as well as the safety requirements for dust explosion prevention related to processing equipment, electrical systems, building structures, ventilation, dust removal, cleaning up accumulated dust, pneumatic conveying, and related management practices. This standard applies to the design and construction of new and expanded projects in which explosive dust hazards associated with grains may arise during grain handling, transportation, storage, and processing, as well as to the entire process of grain production, storage, transportation, and management. This standard applies to grain processing and storage and transportation systems, but not to oil extraction workshops. 2 Referenced Standards The provisions contained in the following standards become part of this standard by being referenced herein. At the time of publication of this standard, all versions shown are valid. All standards will be revised, and those using this standard should consider the possibility of adopting the latest versions of the following standards. GB 50057—94 Code for Design of Lightning Protection of Buildings; GB 50058—92 Code for Design of Electrical Installations in Explosive and Flammable Environments; SBJ 03—89 Design Standards for Grain Silos; SBJ 06—93 Engineering Design Code for Wheat Milling Plants. 3 Definitions: This standard adopts the following definitions. 3.1 Grain: A general term for agricultural products consumed by humans. It mainly refers to wheat, corn, rice, soybeans, oilseeds, as well as their processed products, semi-finished products, and finished products. 3.2 Grain processing: The process of transforming raw grains into finished or semi-finished grains through specific techniques. 3.3 Grain storage & transportation: Grain is transported and stored using conveying machinery and vehicles, following specific processes, methods, and routes. 3.4 Grain dust refers to the tiny particles of grains that can remain suspended in the air; it is a non-conductive, flammable dust. 3.5 Explosion prevention of grain dust: Technologies for preventing the combustion and explosion of grain dust, as well as for reducing losses in the event of such combustion or explosion. 4 Classification and Scope of Hazardous Areas for Grain Dust Explosions 4.1 Principles for Classifying Hazardous Areas for Grain Dust Explosions 4.1.1 Hazardous areas due to grain dust explosions are classified according to the frequency and duration of the presence of explosive dust mixtures: a) Zone 10: Enclosed environments where explosive grain dust is present in large quantities and continuously, or for extended periods, during normal operations, with concentrations reaching the explosive limit. b) Zone 11: Areas that are not classified as Zone 10, but in which, under abnormal conditions, an explosive mixture of grain dust and air can occur in enclosed environments that reach explosive concentrations. c) Non-explosion hazardous areas: Areas other than Zones 10 and 11. 4.1.2 The classification of areas at risk of grain dust explosions shall be determined based on the amount of explosive dust, the explosion conditions, and the ventilation and dust removal conditions. 4.1.3 A area can be classified as a non-hazardous area if it meets one of the following conditions: —— It is equipped with a dust removal system with effective dust removal capabilities, and when this system stops operating, the production line can be shut down immediately through interlocking. ——An environment with good natural ventilation, such as open-plan buildings. ——Areas separated from Zones 10 and 11 by walls and spring doors. Note: Silo towers (including grain silos) are not included. 4.2 Classification of explosive hazard areas for grain dust The classification of explosive hazard areas for grain dust is shown in Table 1. Table 1 Classification of Areas at Risk of Grain Dust Explosions. Dust Environment: Zone 10, Zone 11; Non-explosion-risk areas: Grinding rooms √, Packaging rooms √, Cleaning rooms √, Rice mill husk rooms √, Flour mixing rooms √, Feed processing workshops √, Open flour storage bins √, Inside vertical silos＊＊ √, Working towers of vertical silos and the upper and lower layers of the silos √, (Conveyor tube layers √), Open conveyor tunnels √, Underground grain transport tunnels √, Above-ground enclosed grain transport tunnels √, Bulk grain storage bin-type warehouses √, Packaged grain storage bin-type warehouses √, Finished goods warehouses √, Corridors with walls＊＊＊, separated from Zones 10 and 11 by spring doors √, Open areas √, Ash rooms √, Inside enclosed equipment √, Control rooms with walls＊＊＊, separated from Zones 10 and 11 by spring doors √, Independent buildings √. Note: *This table uses the factory building as a unit to classify areas at risk of grain dust explosions. ＊＊Shallow circular silos shall be handled in accordance with vertical silo procedures. ＊＊＊Wall refers to brick walls, walls made of lightweight materials, etc. 5 Process Equipment 5.1 Process Design 5.1.1 The process design should outline the specific measures and methods to prevent dust explosions. 5.1.2 Magnetic separation devices should be installed at appropriate locations in the process design to remove metal substances contained in the grains. 5.1.3 According to the process flow, the following principles should be followed when arranging equipment on each floor: a) Mechanical equipment prone to dust explosions should be located at higher positions within the building, near the exterior walls. b) Equipment of the same category should be arranged together. c) Easy to use and maintain. d) The minimum width of various passages in the production workshop is as follows: 1) Non-operational passages: 500mm ； 2) Operation channel: 800mm ； 3) Main channel: 1000mm. 5.1.4 Each production line shall follow: ——Start up in reverse order of the process flow ； ——Shut down in accordance with the process flow ； ——In the event of a fault, the equipment located before the fault point stops operating instantly in accordance with the process flow, and feeding is halted ； The equipment downstream of the fault point shuts down sequentially in accordance with the process flow to drain all materials. 5.2 Mechanical Equipment 5.2.1 General Requirements 5.2.1.1 Mechanical equipment used in Zones 10 and 11 shall be equipped with reliable explosion venting devices. The observation windows made of materials such as 3mm thick plexiglass in the Zone 11 mechanical equipment can be considered as explosion vents. The observation window should be sealed to prevent dust from leaking out. 5.2.1.2 Mechanical equipment shall be made of non-flammable materials, and enclosed equipment must not leak dust outward. 5.2.1.3 Mechanical equipment and pipe connections shall be airtight to prevent dust leakage. 5.2.1.4 Inside buildings, no open chutes (tanks) or equipment that allow dust to disperse freely without effective dust removal and ventilation measures shall be used. 5.2.1.5 Belt drives shall have a sufficiently high friction coefficient and a reliable tensioning mechanism to ensure proper operation. 5.2.1.6 Mechanical equipment used in Zones 10 and 11 shall have the necessary operational condition monitoring functions. 5.2.1.7 The materials used for mechanical equipment shall have sufficient strength to prevent sparks from occurring during operation due to fractures, distortions, collisions, etc. 5.2.1.8 The bearings of the equipment and the slides of the control valves shall be separated from the grain flow. 5.2.2 Conveying Equipment 5.2.2.1 Bucket Elevators – The casing, head, base, and connecting chutes of bucket elevators shall not leak dust. ——Vent openings should be installed on the vertical section of the casing, and the vent area at the nose of the unit should be maximized as much as possible. ——An appropriate cleaning port should be provided at the frame, which can be used to inspect the frame, drive wheels, bucket, and belt. ——The head section should have an inspection access point, through which a thorough inspection of the head cover, the bucket belt, and the discharge opening of the elevator can be carried out. ——Each hoist should be driven by a separate motor, and the power of the motor must be sufficient to meet the requirements of the hoist when operating at full load. ——Each elevator should be equipped with devices such as speed monitoring, which can automatically cut off the power supply to the motor in case of a fault, thereby stopping the feeding of material into that elevator promptly, and issuing audible and visual alarm signals for the fault. ——There should be maximum contact area between the drive wheel and the bucket belt. 5.2.2.2 Screw conveyors and buried scraper conveyors — The entire structure shall be enclosed with metal material to prevent dust from leaking out. If the discharge outlet becomes blocked or the scraper chain breaks, the machine should be stopped immediately to halt feed intake. ——The discharge opening of the grain feeding equipment for vertical silos should be large enough to allow the dust-laden air inside the silo to be discharged smoothly outside. 5.2.2.3 Belt conveyors and other conveying equipment — Intake vents should be installed at the feeding and discharging ends of the equipment to prevent dust from escaping. ——It features reliable tensioning and belt alignment devices to prevent the conveyor belt from slipping or drifting. 5.2.3 Processing Equipment 5.2.3.1 Processing equipment mainly includes machinery for cleaning, hulling, grinding, crushing, threshing, rolling, measuring, packing, puffing, etc., but does not include drying equipment. 5.2.3.2 All equipment shall have maintenance holes, cleaning holes, and inspection holes that are easy to access. 5.2.3.3 When grains are fed into high-speed rotating equipment for processing such as grinding, crushing, milling, and hulling, magnetic separators and other cleaning devices must be installed in front of these equipment to remove metal impurities, inorganic impurities, and other contaminants. 5.2.4 Shut down inactive operation circuits (including branches) in a timely manner to prevent the spread of accidents in case of failures. 6 Electricity 6.1 General requirements 6.1.1 Grain processing, storage, and transportation systems shall be designed in accordance with the requirements for electrical engineering in explosive dust environments, and shall comply with the provisions of Chapter 3 of GB 50058—92. 6.1.2 The electrical design should be closely integrated with the process and civil engineering designs, ensuring safety and suitability, ease of maintenance, economic rationality, and technological advancement. Electrical design must strictly comply with the technical requirements for preventing dust explosions, adhering to the principle of overall protection. 6.1.3 The automatic control systems for food processing, storage, and transportation systems should be designed in accordance with the principles of safety, reliability, advancement, and suitability. 6.1.4 The production operations in food processing, storage, and transportation systems shall be equipped with electrical interlocks that meet the requirements of the manufacturing process and ensure safe production, so as to guarantee safety during failures. Electrical interlocks include: a) electrical interlocks between production lines ； b) Electrical interlocking between various electrical devices in the production line ； c) Emergency shutdown of the production line. 6.1.5 Electrical equipment and wiring should be installed and laid in environments with low dust explosivity or in non-explosion hazardous areas. 6.1.6 All electrical equipment shall be equipped with short-circuit and overload protection. 6.1.7 Dust-explosion-proof equipment and wiring as required in Chapter 3 of GB 50058—92 shall be used. For Zone 11, field switch buttons that are used only during maintenance, installation, and commissioning can be non-dust explosion-proof products, provided they have a robust dust-proof enclosure for protection. 6.1.8 The control room shall provide automatic control for all process operations, and it shall have the capability to monitor the operating conditions of on-site equipment in real time. 6.2 Electrical Equipment 6.2.1 Electrical equipment that may generate electric sparks during normal operation, such as sockets and lighting distribution boxes, should be located outside areas with explosive dust. 6.2.2 Mobile electrical equipment should not be used in Zones 10 and 11. When it is necessary to use mobile electrical equipment, YC or YCw rubber cables should be used, with the minimum cross-sectional area of their main conductors being no less than 2.5 mm2. 6.2.3 Distribution cabinets and control cabinets should be located centrally in non-hazardous areas. 6.2.4 Electrical equipment installed in areas with an explosive hazard from grain dust shall be selected in accordance with the provisions of Table 2. Table 2 Regulations for selecting the protection ratings of electrical equipment in environments with explosive dust hazards. Hazardous areas: Zone 10, Zone 11. Enclosure types: DT, DP. Explosion protection markings: DIP, DT, T11(T12); DIP, DP, T11(T12). Note: DT refers to a dust-tight enclosure, with an enclosure protection rating of IP6x ； DP is a dust-proof enclosure with an IP5x protection rating. 6.2.5 Electrical equipment installed in Zones 10 and 11 shall be capable of operating at full load without causing excessive temperatures that would lead to excessive dehydration or gradual carbonization of the grain dust accumulated on it. In actual operation, the maximum surface temperature of electrical equipment should not exceed that shown in Table 3. Table 3 Maximum surface temperature of electrical equipment. Temperature categories: no overload, permitted overload. T11: 215ºC, 195ºC; T12: 160ºC, 145ºC. 6.2.6 No electrical equipment that may generate electric sparks or raise the temperature in the grain storage beyond normal levels shall be used there. 6.2.7 Dust-proof lighting fixtures shall be used in Zones 10 and 11. The clear distance between lighting fixtures and grain should be no less than 500 mm. 6.3 Wiring 6.3.1 In Zones 10 and 11, copper-core insulated wires or cables should be used for the conductors; bare wires shall not be employed. The long-term allowable current capacity of the branch circuits leading to electrical equipment that is prone to overload at voltages below 1000V should not be less than 1.25 times the rated current of the motor ； The allowable current capacity of the branch leading to other electrical equipment shall not be less than the rated current of the electrical equipment. 6.3.2 In Zone 10 or Zone 11, electrical wiring shall be installed in metal conduits, either exposed or concealed, in accordance with the provisions of Table 4. The surface of the pipelines concealed in the floor slab should be no less than 40 mm above the ground level. Table 4 Technical Requirements for Steel Pipe Wiring in Environments with Explosive Hazards from Grain Dust | Item | Technical Requirements |
|---------------------------|--------------------------|-------------------------------------------------------------------------------------|
| Explosive hazard area | Minimum cross-section of insulated wires | Zone 10: Copper core of 2.5 mm2 or higher; Dust-tight type, with at least 5 screw turns. |
| | | Zone 11: Copper core of 1.5 mm2 or higher; Aluminum core of 2.5 mm2 or higher; Dust-tight type or dust-proof type is also acceptable; At least 5 screw turns. |
| 6.3.3 | Wires laid in cable trays and shafts | Copper-core cables shall be used, in compliance with the requirements in Table 5, and there shall be no joints in between. | Table 5 Technical requirements for cable wiring in environments with explosive hazards from grain dust Item Technical requirements Explosive hazard zone Minimum cross-sectional area of cable Mobile cables Zone 10: Copper core of 2.5 mm2 or more; Heavy-duty Zone 11: Copper core of 1.5 mm2 or more; Medium-duty 6.3.4 Electrical conduit shafts shall not be used as shafts for other types of pipelines. 6.3.5 When electrical conduits (cable trays) pass through walls and floor slabs, the openings must be tightly sealed with non-combustible filler. 6.4 Lightning Protection and Grounding 6.4.1 The lightning protection and grounding design for environments prone to grain dust explosions shall comply with the provisions of GB 50057. 6.4.2 It is permitted to use the structural steel bars of buildings to form a lightning protection system. The lightning protection system should preferably use a concealed cage type. Between the grounding electrode, down conductors, and lightning arresters, reliable and code-compliant welding from bottom to top should be employed to establish a proper electrical path, preventing dust explosions caused by lightning and ensuring the safety of people and facilities. 6.4.3 It is permitted for the working ground, protective ground, lightning induction protection ground, and anti-static ground systems in electrical engineering to be connected together, with the grounding resistance being the minimum value among them. 6.4.4 Copper sheets should be used for bonding between the metal enclosures of each section of the equipment, frames, and pipelines to establish a continuous electrical path without any interruptions. 6.4.5 In Zones 10 and 11, all equipment, racks, and pipelines shall be equipped with anti-static grounding, and shall be connected separately to the grounding electrode or grounding main line; they shall not be connected in series before being grounded. 7 Building Structures 7.1 General Requirements 7.1.1 In addition to complying with ** or industry standards SBJ03 and SBJM, all buildings (structures) must also meet the requirements specified in this standard. 7.1.2 Within a 10-m radius around the vertical silo storage area and the main workshop of the processing plant, buildings or structures belonging to Zones 10 and 11 should not be located there. Around the plants (warehouses) in Zones 10 and 11, fire access roads with a width of not less than 3 m should be provided. 7.1.3 Grain storage silos and processing plant buildings should be located separately, and it is advisable to use open or semi-open designs. 7.1.4 In environments where grain dust is explosive, fire and explosion-proof partition walls should be installed in appropriate locations to ensure operational safety and to facilitate the demarcation of hazardous areas with explosive dust. 7.2 Explosion Venting 7.2.1 Buildings in Zones 10 and 11 shall be equipped with necessary explosion vents. Glass doors, windows, lightweight walls, and lightweight roofs can be included in the calculation of the flood discharge area. 7.2.2 The mass of lightweight walls and lightweight roofs used as spillways should not exceed 120 kg/m2. 7.2.3 The ratio of the blast area to the volume of the building (m2/m3) should not be less than 0.03. However, the values for vertical silos, star-shaped silos, and the lower layers of vertical silos in vertical silo warehouses, raw material silos in processing plants, super-large grain silos, wheat moistening silos in flour mills, as well as bulk storage silos for flour and feed, can be reduced and are not subject to this restriction. 7.2.4 The main building shall have sufficient explosion resistance and shall not collapse or burst before the explosive pressure is safely discharged. 7.3 Floor 7.3.1 The floors of grain stores and processing plants should be made of materials that do not generate sparks, and they should be flat, smooth, and easy to clean. 7.3.2 When insulating materials are used as the overall surface layer, anti-static measures shall be taken. 7.4 Walls 7.4.1 The minimum fire resistance rating for the walls of the working towers, silo-type storage facilities, and the main workshops in vertical silo warehouses is 3 hours. 7.4.2 The inner surfaces of buildings and the surfaces of components should be smooth and flat to reduce dust accumulation. 7. Tunnels and basements for transporting grain with 5.5 channels should have exits leading to the surface at both ends. When the basement area is small and the number of workers is usually no more than 2 (such as in work towers for vertical silos), only one exit leading to the ground is allowed. 7.6 Manholes and explosion vents: All grain storage bins shall be equipped with manholes and explosion vents. Manholes and vent openings should be covered to prevent dust from leaking out. 7.7 Windows: To function as effective explosion vents, windows should be of the outward-opening type. 7.8 Doors 7.8.1 Doors used for separating different areas should have sufficient strength and be properly sealed to prevent dust from entering. The minimum fire resistance rating of the door is 1 hour. 7.8.2 Doors used for explosion venting shall open outward. 8 Ventilation and Dust Removal 8.1 Ventilation 8.1.1 To ensure the normal progress of production, a good and safe working environment, and the safety of stored grain, effective ventilation should be achieved through natural or mechanical means. 8.1.2 Recirculating ventilation should not be used in the production areas of grain warehouses and processing plants. If used, it should be equipped with a filtration system that can effectively remove dust from the air. 8.1.3 All grain storage silos should be equipped with ventilation holes at the roof, and rain caps should be installed on these ventilation openings to prevent rainwater from entering. 8.1.4 All grain storage rooms shall be airtight and shall not have holes connecting them. If exhaust ventilation between silos is indeed necessary, a separate ventilation system should be used ； Vents should be installed at the joints, and these vents must be properly sealed to prevent the spread of dust explosions. 8.1.5 The air ducts should be arranged reasonably to ensure uniform air distribution, with the air volume meeting the required standards. 8.2 Dust removal system 8.2.1 A dust removal system shall be installed in grain processing, storage, and transportation systems. The dust removal system should be efficient, reliable, and safe. 8.2.2 The dust removal system shall be designed with negative pressure to prevent dust from leaking outward, and its piping network shall have no loops. If a circulation circuit is indeed necessary, a filtration system capable of effectively removing dust from the air must be installed, along with an explosion venting device that has sufficient venting area. 8.2.3 The dust removal system shall be robust and safe, and no equipment or ventilation ducts in the system shall be damaged during explosion venting. 8.2.4 The radius of curvature of elbows in the ductwork should be 1–4 times the diameter of the air duct. 8.2.5 Regulating valves should be installed on each air distribution duct in the dust removal network to adjust the air volume and balance the system pressure. 8.2.6 Each air intake point shall be equipped with sufficient air volume and pressure, and dust accumulated in the pipes shall not be released outside. 8.2.7 The collected dust should be stored in a centralized location to prevent it from becoming airborne again. 8.2.8 All equipment and components of the dust removal system shall be made of non-combustible materials, although its pipes may be made of flame-retardant materials. 8.2.9 The dust collector should be equipped with explosion vents leading to the outside. 8.3 Dust Control 8.3.1 Dust extraction vents should be installed at all mechanical equipment where dust is generated, as well as at the points where grains are imported and exported, in order to prevent dust from escaping and to effectively collect it. 8.3.2 The buffer silos and metering funnels shall be sealed and equipped with air intake vents to collect and remove the dust generated when grain is loaded into or unloaded from the silos. 8.3.3 The collected dust should be stored separately and should not be reintroduced into the grain stream. 8.3.4 The dust collection system of grinding or pulverizing equipment shall not be connected to other dust collection systems; the collected dust can be returned to the same processing step. 8.3.5 Dust collection equipment shall be sealed and made of non-flammable materials. 8.3.6 The ash room and waste material storage area should have good airtightness; they should be located separately from other buildings or structures, and explosion relief facilities should be provided. l.3.7 When the air streams discharged from multiple dust removal systems enter a single wind shaft or dust collector at the same time, each dust removal system should be equipped with a stop valve that can effectively prevent dust and flames from passing between the different dust removal systems and spreading. 8.3.8 When a dust removal system is equipped with multiple air inlets in several grain storage bins, a shut-off valve should be installed at each air inlet. 8.3.9 Dust collection equipment should be placed outdoors. When it needs to be placed indoors, an explosion vent pipe leading directly outside should be installed, with a length not exceeding 3 meters. 9 Removal of Dust 9.1 Dust accumulated on surfaces such as the floor, walls, and equipment should be removed promptly. 9.2 Materials that spill from the equipment and ducts or become blocked there should be cleaned up promptly. 9.3 Blower-based dust removal devices should not be used for cleaning dust indoors; vacuum cleaners are preferred. 10 Pneumatic conveying 10.1 All pneumatic conveying equipment shall be made of non-flammable or flame-retardant materials. 10.2 When multiple pneumatic conveying systems are connected in parallel, each system should be equipped with a stop valve. 10.3. The pneumatic conveying systems between different grain silos shall not be interconnected. If connection is indeed necessary, a shut-off valve should be installed. 10.4 The dust removal system and dust control of the pneumatic conveying system shall comply with the provisions of Chapter 8. 10.5 Positive pressure pneumatic conveying equipment shall be of a sealed type to prevent dust leakage. 10.6 In negative pressure pneumatic conveying systems, the air leakage rate of the unloader shall not exceed 10%. 11 Management 11.1 Design and construction management 11.1 The engineering design of food processing, storage, and transportation systems should strictly comply with relevant laws, regulations, standards, and the provisions of this standard; relevant designers should carry out their work with a commitment to ensuring safe production. 11.1.2 The design documents shall include a dedicated section on dust explosion control, clearly specifying the classification of areas at risk of grain dust explosions in the design and the dust explosion prevention measures taken. 11.1.3 The superior competent authority shall review the design, particularly the safety design, to ensure the specific implementation of relevant standards and regulations. 11.1.4 The design of newly built or expanded grain processing, storage, and transportation systems shall undergo a safety assessment and be approved by the higher-level competent authorities. 11.1.5 The construction contractor shall construct in accordance with the approved design drawings and shall not make any unauthorized modifications. Practical problems encountered during construction should be resolved through consultation among the management, design, and construction departments. 11.1.6 Upon the completion of the project, the competent authority shall conduct an inspection in conjunction with relevant departments. Works that have not been inspected or have failed the inspection shall not be delivered for use. 11.2 Enterprise Management 11.2.1 The principal persons in charge of food processing, storage, and transportation enterprises should have a sufficient understanding of and be highly vigilant regarding the potential for dust explosions involving grain during the production process. They must be fully aware of all areas within their enterprises where there is a risk of grain dust explosions, and they should implement measures that can effectively control such explosions. 11.2.2 In line with the principle of giving equal emphasis to prevention and management, as well as to inspection and education, enterprises should establish specific and practical safety operating procedures, and assign dedicated personnel to be responsible for them. 11.2.3 A safety assessment of the food processing, storage, and transportation systems should be conducted annually. Safety assessments should be conducted by specialized agencies with relevant authority and experience. 11.2.4 Before starting work, employees should receive professional training and education on knowledge related to grain dust explosions, as well as information on fire and explosion prevention measures for grain dust and relevant safety regulations. Employees who have not received training or obtained the necessary certification are not allowed to operate the equipment. On-the-job employees receive training once a year to keep their knowledge up to date and remain prepared at all times. 11.2.5 Facilities for safety, ventilation and dust removal, explosion prevention, and explosion relief shall not be removed without the approval of the competent authorities. 11.3 Operations and On-site Management 11.3.1 Grain processing, storage, and transportation systems shall be operated in accordance with the relevant operating procedures. 11.3.2 Persons entering Zones 10 and 11 are prohibited from smoking, carrying kindling, or using open flames. 11.3.3 Staff in Zones 10 and 11 should not wear shoes with metal studs, nor should they wear fiber-based clothing or headgear. 11.3.4 Remove dust accumulation during production, and promptly address any leaks of dust outside as well as blockages in the grain flow. 11.3.5 Open-flame operations shall not be carried out in Zones 10 and 11. If electric spark cutting and welding are indeed necessary for work purposes, the following rules must be followed: ——The operating procedures and implementation plans must be approved by the higher-level supervising authority. ——The relevant personnel must wear work permits approved by the safety supervisor for that day. ——After the production line has been shut down for 4 hours, all valves are closed. ——Clean the area surrounding the work site **and remove dust from the ground, as well as from inside and outside equipment and pipes, and from walls, etc.; this area should extend at least 5 meters away from the work site. ——The work area is securely sealed from the connected pipes and equipment. ——There must be timely and reliable measures in place for the recovery of all cut-off components, to prevent hot components from falling into sealed chutes, bins, equipment, etc., and causing dust explosions. ——Be prepared for fire prevention at all times to prevent spark splashing. After the work is completed, fire monitoring should be carried out for at least 1 hour to ensure that the fire does not reignite. ——Painting and welding should not be carried out simultaneously. Painting should be carried out after the welding is completed and the workpiece has cooled down. ——The job approver should be present on site to direct operations, supervise the entire process, and sign the completion documents. 11.3.6 When performing cutting, welding, or repair work on bucket elevators, buried scraper conveyors, and screw conveyors, in addition to complying with the requirements of 11.3.5, it is also necessary to remove any dust accumulated inside the equipment before starting the work, and to operate the dust removal system for at least 10 minutes. 11.3.7 Fuel-powered motor vehicles and dust-proof electric motor vehicles are not permitted in Zone 10. When using Zone 11, the provisions of 11.3.5 shall be followed within the route taken by motor vehicles. 11.4 Equipment Maintenance and Management 11.4.1 The department responsible for safety inspects the dust removal system once a year, covering aspects such as system performance, the condition of the equipment, and the reliability of electrical operations and interlocks, and issues a certificate of compliance. For operational dust removal systems, inspections should be carried out at least twice a day to ensure their reliability and effectiveness. 11.4.2 Before the thunderstorm season each year, a comprehensive inspection of the lightning protection systems shall be carried out in accordance with relevant regulations to eliminate potential hazards. 11.4.3 Before each start-up of the production line, key components should be carefully inspected. Mechanical and electrical equipment that has been out of use for an extended period must be approved by the safety officer before it can be put back into operation. Before the equipment is put into use after maintenance, it should be inspected by the relevant departments, which shall issue a certificate of conformity. 11.4.4 All mechanical and electrical equipment should be regularly inspected, and production technical records should be maintained; the equipment put into operation within the system must be in good condition. 11.4.5 The bearing temperature of operating equipment should generally not exceed 50°C; if overheating is detected, it must be inspected immediately until the cause is eliminated. 11.4.6 For the magnetic magnets used in magnetic separation equipment, if their magnetic induction intensity is less than 160 mT, they should be replaced or re-magnetized immediately. 11.4.7 Strengthen the operational management of grinding mills and rice milling machines; during production, close attention should be paid to the following aspects: —— ensure uniform feeding to prevent interruptions in the supply of material. ——Ensure that the feed wheat is free of metal impurities or other bulky, hard contaminants; otherwise, the rotation of the feeding roller should be stopped immediately, the grinding roller released, and the contaminants removed. ——The air intake duct should be unobstructed. ——The transmission is stable; the belt should not be too tight or too loose. ——Adjust the outlet pressure of the rice mill in a timely manner to prevent overload. ——The fan used to draw in rice bran should be checked once a day to prevent the accumulation of bran residue. 11.4.8 Equipment should be started and stopped strictly in accordance with the procedures. The dust removal system should be turned on 10 minutes before the process equipment starts up, and turned off 5 minutes after operations cease. 11.5 Clearance 11.5.1 The grain dust accumulated in the silos should be removed promptly. 11.5.2 During inventory clearance, no harmful gases should remain in the warehouse; there must be sufficient oxygen as well as appropriate safety measures to protect the workers. 11.5.3 The cleaning tools should be flexible to prevent sparks from being generated inside the warehouse, which could trigger dust explosions. 11.5.4 The lighting fixtures used during inventory clearance should be dust-proof, with a voltage not exceeding 36V. Appendix A (Suggested Appendix) Table of Properties of Grain Dusts The table of properties of grain dusts is shown in Table A1. Table A1: Dust Names, Temperature Groups, Ignition Temperature of Dust Layers Accumulated on High-Temperature Surfaces (5 mm), Ignition Temperature of Dust Clouds (°C), Lower Explosive Limit Concentration (g/m3), Average Dust Particle Size (μm), and Hazardous Properties
- Raw wheat flour: 325, 415, 67–93, 20–50
- Raw wheat grain flour (untreated): 305, 430, 50–100
- Flammable non-conductive dust: Raw wheat sieve residue (ground): T11, 305, 415, 30–40
- Wheat flour (charred): 410, 20–40
- Wheat grain flour: 290, 420, 15–30
- Wheat sieve residue (ground): 290, 410, 3–5
- Rye and barley grain flour: 270, 440, 50–150
- Rice bran after screening: 270, 420, 50–100
- Corn starch: T12, charred, 410, 2–30
- Potato starch: charred, 430, 60–80
- Pudding powder: charred, 395, 10–20
- Starch syrup powder: charred, 400, 71–99, 20–30
- Sugar powder: melts at 360°C, 77–107, 20–40
- Lactose: melts at 450°C, 83–115

Appendix B (Suggested Appendix): Other Relevant Standards and References
1. GB/T 15604—1995: Terms for Dust Explosion Prevention
2. GB 15577—1995: Safety Regulations for Dust Explosion Prevention
3. SBJ 16—87: Code for Fire Protection in Building Design
4. IEC 1241—1—1(2): Electrical Equipment for Use in Environments with Combustible Dusts
5. NFPA.61B: Standards for Dust and Explosion Prevention in Warehouses and Facilities for Bulk Agricultural Products
6. NFPA.61C: Standards for Fire Protection and Dust Explosion Prevention in Feed Mills
7. NFPA.61D: Standards for Preventing Fires and Dust Explosions during the Grinding of Food-Grade Agricultural Products
8. NEC: U.S. Electrical Code

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