About this chapter: Chapter 22 provides requirements that seek to reduce the likelihood of dust explosions by managing the hazards of ignitable suspensions of combustible dusts associated with a variety of operations including woodworking, mining, food processing, agricultural commodity storage and handling and pharmaceutical manufacturing, among others. This chapter provides various requirements to control ignition sources, use properly listed and designed dust collection systems, maintain good housekeeping practices and provide proper training to those involved in these processes. Appropriate standards are referenced to deal with the specific dust hazards.
CRITICAL DEPTH LAYER
|TYPE OF DUST||CRITICAL DEPTH LAYER (INCHES)|
|All other dusts||1/32|
For SI: 1 inch = 25.4 mm.
MINIMUM CONVEYING VELOCITIES
|TYPE OF PRODUCT||FEET PER MINUTE|
|Fine light dust such as cotton, lint and wood flour (100 mesh and under)||2,000|
|Dry dust such as fine rubber molding powder||2,500|
|Average dust such as sawdust, grinding dust and coal dust||3,500|
|Heavy dust such as metal turnings, including aluminum and magnesium powder||4,000|
For SI: ;1 foot per minute = 0.00508 m/s.
Exception: Drying apparatus listed for the intended use and installed in accordance with the manufacturer's instructions.
Exception: Forced-air or similar methods shall be permitted to remove dust in accordance with NFPA 652, NFPA 654 or NFPA 664.
EXPLOSION PROTECTION STANDARDS
|NFPA 61||Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities|
|NFPA 68||Standard on Explosion Protection by Deflagration Venting|
|NFPA 69||Standard on Explosion Prevention Systems|
|NFPA 70||National Electrical Code|
|NFPA 77||Recommended Practice on Static Electricity|
|NFPA 85||Boiler and Combustion System Hazards Code|
|NFPA 120||Standard for Fire Prevention and Control in Coal Mines|
|NFPA 484||Standard for Combustible Metals|
|NFPA 654||Standard for Prevention of Fire and Dust Explosions from the Manufacturing, Processing and Handling of Combustible Particulate Solids|
|NFPA 655||Standard for the Prevention of Sulfur Fires and Explosions|
|NFPA 664||Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities|