Five Key Measures to Prevent Dust Explosions

2. Preventive Measures for Dust Explosions

(1) Control the Generation and Concentration of Combustible Dust

1. Prevent Leaks of Materials and Dust: Regularly maintain equipment that leaks materials. Sealing inspection holes in process equipment can help prevent dust dispersion.
2. Reduce Dust Concentration: Dust collectors play a key role in lowering combustible dust concentrations. Approximately 40% of dust explosion accidents are linked to dust collection systems. Therefore, it is critical to focus on the design, installation, and maintenance of dust collection systems.
   • Design of Dust Collection Systems: Prevent dust accumulation in ducts by ensuring the air velocity is appropriate. The wind speed should remain constant or slightly increase from the suction point to the dust collector. Additionally, the duct design should minimize resistance losses and reduce the length of horizontal ducts.
   • Dust Collector Explosion Prevention: Incorporate anti-static filter bags and explosion-proof fans in the design.
   • Regular Maintenance: Frequently check air velocity, pipe blockages, and filter condition. Install pressure monitoring devices to detect filter clogging or damage.
   • Wet Dust Collectors: For wet-type collectors, ensure that the water flow and speed can completely filter dust and set up continuous monitoring systems to track water flow and speed.
   • Dry-Type Collectors: For dry-type systems, install explosion venting devices at air intake points and monitor pressure differences at the intake and exhaust points. Implement a pneumatic system for cleaning filter bags.

(2) Eliminate Ignition Sources

1. Ban Electrical Heating Elements: In explosive environments, do not use electrical heating elements such as electric heating plates, induction heating devices, and electric cables.
2. Explosion-Proof Electrical Equipment: Select and install electrical equipment according to national standards. Use overload protection and short-circuit protection for electrical circuits. Equipment should be properly grounded, with insulated connections bridged to form a continuous path.
3. Avoid Open Flames: Avoid open flames in dust-prone areas. If hot work is required, ensure an appropriate permit is obtained and follow fire protection guidelines. Ensure that equipment surfaces in direct contact with dust (such as motor casings and drive shafts) do not exceed the dust’s minimum ignition temperature.

(3) Static Electricity Protection

1. Minimize Friction: When transferring dust, consider using conductive belts instead of traditional non-conductive ones. Control the flow speed of materials in pipes. Also, use smooth pipes and appropriate materials for reduced static accumulation.
2. Static Grounding: Proper grounding of static electricity is necessary. The resistance should be between 10 and 1000 ohms. Materials like plastic should be grounded with even lower resistance. Small particle size dust (less than 100µm) poses a higher static risk. In pneumatic systems, ensure the pipe walls are smooth, and the dust collection bags are made from cotton or conductive fabric.
   • Humidity Control: If possible, increase the humidity level to over 65% to reduce static buildup.
   • Conducive Equipment: All conveyor equipment must be reliably grounded, and pneumatic pipelines should be made from conductive materials.

(4) Explosion Isolation and Containment

1. Mechanical Isolation: Use physical barriers to isolate dust from potential ignition sources. For instance, employ protective covers, local exhaust hoods, or dust extraction systems to enclose dust-producing equipment.
2. Chemical Isolation: Inject inert gases like nitrogen or carbon dioxide to reduce oxygen content in systems, which helps suppress explosions.
3. Automatic Explosion Isolation Devices: Install automatic devices that detect and contain explosions, such as by releasing extinguishing agents or closing valves to prevent the explosion from spreading.
4. Explosion Suppression Systems: In some cases, increasing the equipment’s structural strength can prevent explosions from propagating. Although this method is expensive, it helps to control the explosion.
5. Dust Collection System Sealing: Ensure dust collection hoods are tightly connected to dust-producing equipment to prevent dust leakage. Seal all entry and exit points of dust collectors to avoid dust escape.

(5) Explosion Relief and Pressure Venting

1. Explosion Venting: Explosion relief panels (rupture discs) are commonly used to release pressure from dust collectors before they reach dangerous levels. These panels direct hot gases and particles safely to prevent damage.
2. Explosion-Proof Doors and Plates: Explosion-proof doors are used to protect powder-handling equipment in outdoor environments, while explosion-proof plates protect indoor equipment like dust collectors and cyclone separators.
3. Flame-Free Venting: For indoor equipment, use a flame-free venting system to release material safely when flames or explosive events occur.
4. Explosion Suppression: Suppression systems can detect early signs of an explosion and rapidly release suppression agents, preventing secondary explosions and damage to equipment.