Designing your dust collection system to meet NFPA standards — Part I
About 40 percent of combustible dust explosions reported in the US and Europe over the last 25 years have involved dust collectors. Dust collection systems are now a primary focus of inspections required by OSHA's National Emphasis Program on safely handling combustible dusts. OSHA also has the authority to enforce National Fire Protection Association (NFPA) standards for preventing or protecting against dust explosions. This two-part article focuses on how you can design your dust collection system's dust collector, ductwork, and exhaust fan to meet the intent of these NFPA requirements.
The explosion hazards posed by dusts commonly handled in bulk solids plants can be surprising. In fact, most natural or synthetic organic dusts and some metal dusts can explode under the right conditions. You can find a limited list of combustible dusts and their explosion data in the appendix to the NFPA standard focusing on dust explosion hazards, NFPA 68: Standard on Explosion Protection by Deflagration Venting (2007), and in Rolf K. Eckhoff's book Dust Explosions in the Process Industries. While such published data can give you some idea of your dust's explosion hazards, using this data for designing explosion prevention or protection equipment for your dust isn't recommended. Your processing conditions and your dust's characteristics -- such as its particle size distribution -- differ from those for the published data for the same material, producing different combustible dust results.