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Division of Occupational Safety and Health
Combustible Dust Poses a Dangerous,
Explosive Threat in the Workplace
In North Carolina, an explosion of fine plastic powder used
in the manufacture of polyethylene products killed six people
and injured 38. Wood dust in a particleboard manufacturing
plant explosion killed three and injured 10 in Pennsylvania.
In Mississippi, rubber dust exploded in a rubber manufacturing
plant, killing five and injuring 1 1 . And in Kansas, a series of
wheat-dust explosions in a large grain storage facility resulted
in the deaths of seven people. Accident investigators in each
of these facilities, although different industries, found similar
conditions that resulted in a massive, tragic dust explosions.
They are quite different one from another. In the stories men¬
tioned above, however, they all met the five conditions
necessary for a dust explosion: oxygen, fuel, igni¬
tion source, dispersion of dust, and confinement.
Your facility may have the same hazard!
Dust Is a Hazard
Dusts pose a range of hazards from
simple nuisance to explosion hazards.
Minor hazards may include reduced visibility
and slippery surface conditions. Some dusts
such as asbestos and silica pose serious respiratory
hazards and long tenn health effects such as pneumo¬
coniosis. Many different dusts are recognized as a combustion
and explosion hazard. The variety of combustible dusts creates
difficulty for a brief discussion. Industries with this hazard
are classified as a Class II locations. This classification is
based on the National Electrical Code article “Class II
Locations”, those that are hazardous because of the presence
of combustible dust.
North Carolina is home to many industries where the hazard
of combustible and explosive dust can be commonly found
such as the following:
• Wood processing and storage
• Grain elevators, bins and silos
• Flour and feed mills
• Manufacture or storage of metal powders such as
magnesium and aluminum
• Chemical production
• Plastic production
• Starch or candy producers
• Spice, sugar and cocoa production or storage
• Coal handling or processing areas
• Phannaceutical plants
• Dust collection bins or bags
• Shelves, nooks, crannies, inside of equipment and
above false ceilings in all facilities
Hazard Assessment
A thorough hazard assessment is essential in identifying and
eliminating factors contributing to an explosion. Dusts are
generated in various parts of any production process.
Explosions can occur within any process where a com¬
bustible dust accumulates, is produced or stored, is airborne,
and can be triggered by a variety of energy sources. The
severity of the resulting explosions is related to the heat
released in the combustion of these materials. Only a couple
of these dust types spontaneously ignite in air; the majority of
them need another source of ignition. Possible ignition
sources include:
• Open flames (welding, cutting, matches, etc.)
• Hot surfaces (dryers, bearings, heaters, etc.)
• Heat from mechanical impacts
• Electrical discharges (switch and outlet activation)
• Electrostatic discharges
• Smoldering or burning dust
• Cigars, pipes and cigarettes
Look for this hazard in your facility and try to eliminate
it. Ask yourself questions such as the following when
considering your facility or process.
• Is vacuuming used whenever possible rather than blowing
or sweeping combustible dust?
• Do you have electrical installations in hazardous dust or
vapor areas? If so, do they meet the National
Electrical Code (NEC) Chapter 5 for hazardous locations?
• Are accumulations of combustible dust routinely removed
from elevated surfaces including the overhead structure
of buildings, false ceiling, shelves, etc.?
• Is metallic or conductive dust prevented from entering or
accumulating on or around electrical enclosures or
equipment?
• Where may dust accumulate that we have not considered
in this production process?
• Wood dusts can decay and create their own heat as a
possible source of ignition. Has this possibility been
addressed?
Prevention
Investigators at the accidents mentioned determined that the
explosions, like most accidents, resulted from a chain of
events or factors. Training employees to recognize this hazard
