FAQs About Combustible Dust

The Combustible Dust explosion at Imperial Sugar began the discussion about the hazards

The fatal combustible dust explosion at Imperial Sugar created a discussion about dust hazards.

OSHA has compiled a list of industry SIC codes and NAICS codes for industries that are at risk for Combustible Dust.


View a list of the industry codes to find out if your company is at risk.




What NFPA publications are relevant to Combustible Dust?

NFPA Number Title
61 Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities
68 Guide for Venting of Deflagrations
69 Standard on Explosion Prevention Systems
70 National Electrical Code
77 Recommended Practice on Static Electricity
85 Boiler and Combustion Systems Hazards Code
86 Standard for Ovens and Furnaces
91 Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids
484 Standard for Combustible Metals
499 Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
655 Standard for Prevention of Sulfur Fires and Explosions
664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities

How does the NFPA define Combustible Dust?

According to NFPA 654 “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 size or shape.”


According to NFPA 654, 3.3.7 “Propagation of combustion zone at a volictiy that is less than the speed of sound in the un-reacted medium.”

What are the necessary conditions for Dust Deflagration?

Combustible particulate solid small enough to be deflagrable.
Deflagrable particle suspended in air.
Deflagrable particulate of high enough concentration.
Adequate igniter.

What are Combustible Particulate Solids (CPS)?

Any combustible solid material with a distinct particles or pieces. They can include fibers, chips, fines, dusts, and flakes.

How small does a particulate need to be for a dust explosion?

The smaller the particle size the more dangerous the particulate and greater likelihood of explosion.

Where do you generally find the finest, which are more hazardous, accumulations of particulate in a building?

Typically in the Highest compartments of buildings, such as rafters, top of ductwork, top of lights, etc.

When does ignition occur?

When sufficient energy per unit (temperature) of time and volume is applied to a suspended deflagrable particle.

What is the one most important factor to mitigate the risk of a dust explosion?

Limiting, or eliminating accumulated fugitive dust in the workplace.

How much of the Floor Area in a typical Industrial Plant does the Surface area of Top of Ductwork, Conduit, Rafters, and all high surfaces account for?

Rough calculations show that the available surface area of bar joists is approximately 5 % of the floor area and the equivalent surface area for steel beams can be as high as 10%.

What is the Minimum Explosible Concentration (MEC)?

The minimum concentration that will propagate a flame front through a suspension of the particulate in air or other medium of concern.”