What is Dust?

The breaking down (i.e. crushing, grinding, rapid impact etc.) of organic or inorganic materials such as rock, ore, metal, coal, wood and grain, generates solid particles, otherwise known as dust.  Depending on the size of these dust particles, they may settle onto surfaces or remain airborne.

The size of dust particles is measured in micrometers (μm). One micrometer is equivalent to 10-6 meters (or 0.00001 meters). To get a better feeling for how small a micrometer is, red blood cells are 8 μm and the diameter of a strand of human hair is about 50-75 μm.

What distinguishes a Combustible Dust from Other Dusts?

According to the National Fire Protection Association (NFPA), combustible dust is “a combustible particulate solid that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle shape or size.”

A particle is considered to be combustible if it measures at most 420 μm in diameter, as determined by passing through a U.S No. 40 Standard Sieve. However, there are particles whose lengths are much greater than their diameter and do not pass through a standard sieve, thus they are also hazardous. Therefore, any particle with a surface area to volume ratio greater than that of a 420 μm diameter sphere is considered to be combustible dust.

Combustible dust can be formed from the majority of natural and synthetic organic materials and inorganic metals. The NFPA’s Industrial Fire Hazards Handbook states “any industrial process that reduces a combustible material and some normally non-combustible material to a finely divided state presents a potential for a serious fire explosion.”

Natural and Synthetic Organic Materials

Inorganic Materials


  • Food products (grains, sugar, powdered milk, flour, cocoa)
  • Pharmaceuticals (vitamins)
  • Wood (wood dust, wood flour)
  • Textiles (cotton and nylon dust)
  • Plastics (polypropylene, phenolic)
  • Resins (phenol-formaldehyde)
  • Bio-solids
  • Coal and other carbon dusts



  • Aluminum
  • Iron
  • Magnesium powder
  • Manganese
  • Sulphur

Which Industries are at High Risk?

Combustible dust explosion hazards exist in multiple industries including, but not limited to:

  • Agriculture
  • Chemicals
  • Fertilizer
  • Food ( candy, sugar, spice, flour)
  • Furniture
  • Metal Processing
  • Pharmaceuticals
  • Rubber Manufacturing
  • Tobacco