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Division of Occupational Safety and Health
Combustible Dust: Agricultural Related Fires
and Explosions Increasing, but Preventable
Many different types of dust are found in the agrieultural
industry. Sources include grain, cotton and Hour. One of the
largest agrieultural catastrophes in U.S. history took place at
the DeBruce grain elevator in Wichita, Kan., in 1998 when a
20-million-bushel grain elevator caught fire and exploded.
Seven people died in the explosion.
Since then, agrieultural explosions have steadily declined in
the United States from eight in 2002 to seven in 2003 and six
in 2004. Despite this decline, four fires broke out in grain
handling facilities during one week in October 2006. The
fires broke out in Nebraska, South Dakota, Indiana and
Maryland. In December 2005, two North Carolina work¬
places experienced dust explosions resulting in one fatal
injury and three nonfatal injuries.
The recent fires serve as a reminder to the industry that
although agrieultural explosions recently have declined, the
hazard remains. Dust fires and explosions are preventable.
Operators can prevent these fires by knowing what
conditions spark these catastrophic explosions.
Five factors contribute to a volatile environment that can lead
to an explosion — oxygen, a fuel, ignition source, dust dispersion
and confinement.
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
teim health effects such as pneumoconiosis. The variety of
combustible dusts creates difficulty for a brief discussion.
Industries with this hazard are classified as a Class II location
based on the National Electrical Code Article “Class II
locations.” Class II locations are those that are hazardous
because of the presence of combustible dust. Many different
dusts are recognized as a combustion and explosion hazard.
Dust Hazards Can Be Found in N.C.
North Carolina is home to many industries and locations
where the hazard of combustible dust can be commonly
found. These include:
• 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
• Pharmaceutical plants
• Dust collection bins or bags
• Shelves, nooks, crannies, inside of equipment and above
false ceilings in all facilities.
These dusts are generated in various parts of the production
processes. Explosions can occur within any process where a
combustible dust accumulates, is produced or stored, or is
airborne. A variety of energy sources can trigger a dust
explosion. 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
Hazard Assessment
A thorough hazard assessment is essential in identifying and
eliminating factors contributing to dust fires and explosions.
Ask yourself questions such as the following when you
are considering your facility and process.
• Is vacuuming used whenever possible rather than blowing
or sweeping combustible dust?
• Do I have electrical installations in hazardous dust or
vapor areas? If so, do they meet the National Electrical
Code (NEC) Chapter 5 for hazardous locations (i.e.,
installation of intrinsically safe (I.S.) apparatus, wiring and
systems for Class I, II and III locations)?
• Are accumulations of combustible dust routinely removed
from elevated surfaces including the overhead structure
of buildings, false ceiling, shelves, etc.?
