How do we determine if we have combustible dust in our facility?

The NFPA’s Industrial Fire Hazards Handbook states that “any industrial process that reduces a combustible material and some normally noncombustible materials to a finely divided state presents a potential for a serious fire or explosion.” Examples of potential combustible dust materials include (but are not limited to):

• Plastics
• Coal
• Epoxy resin
• Corn
• Fertilizer
• Flour
• Metals
• Sugar
• Sulfur

The primary factor in an assessment of these hazards is whether the dust is, in fact, combustible. Any material that will burn in air in a solid form can be explosive when in a finely divided form; however, combustible dust is defined by NFPA 654 as “any finely divided solid material that is 420 microns or smaller in diameter (material passing a U.S. No. 40 Standard Sieve) and presents a fire or explosion hazard when dispersed and ignited in air.” One possible source for information on combustibility is the Safety Data Sheet for the material. In some cases, additional information such as test results will be available from chemical manufacturers.

Different dusts of the same chemical material will have different ignitability and explosibility characteristics, depending upon many variables such as particle size, shape, and moisture content. Additionally, these variables can change while the material is passing through process equipment. For this reason, published tables of dust explosibility data may be of limited practical value. In some cases, dusts will be combustible even if the particle size is larger than that specified in the NFPA definition, especially if the material is fibrous.