Metal Combustible Dust Particle Size

Information in Material Safety Data Sheets concerning fire hazards of most combustible particulate solids and the combustible dusts generated in the manufacturing process is absent in most instances. The definition of a combustible dust as defined by NFPA 654 is:

"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." The same definition is used for combustible metal dust in NFPA 484, Standard for Combustible Metals, Metal Powders, and Metal Dusts.

Additionally, OSHA's Safety and Health Information Bulletin (SHIB), "Combustible Dust in Industry: Preventing and Mitigating the Effects of Fire and Explosions," published in 2005 states:

"That one possible source for information on combustibility is the Material Safety Data Sheet (MSDS) for the material. In some cases, additional information such as test results will be available from chemical manufacturers."

But thats were the problem arises, MSDS's, don't have the vital fire and safety information concerning combustible dust and laboratory testing is very costly. It's highly advised to have testing conducted as soon as possible . Until the facility management completes testing there is one alternative that the Combustible Dust Policy Institute has found most helpful concerning metal combustible dusts in the fabricated metal product manufacturing industries when determining if finely divided solid material is 420 microns or smaller in diameter .

For example, Atlantic Equipment Engineers has provided on their website a metal product technical data reference for over 120 metal powders and compounds. While browsing the numerous metal powders its quite easy in determining the product size of many many powders used in industry. Any US Sieve Series and Tyler Mesh Size higher than 40 would rank the powder as a combustible dust .

For a helpful review of micron powder particle size in relation to mesh size, here is a helpful link:
ESPICorp Inc.

Hope that helps in clarifying particle size in determining if your metal dust is a combustible dust or not. Until then, as soon as possible schedule a testing of your process dust for ignition sensitivity and explosion severity.

Resources:
NFPA 484, Standard for Combustible Metals, Metal Powders, and Metal Dusts