World Grain - August 2018 - 68


Preventing grain
dust explosions
Installing dust suppression systems and not
allowing excessive accumulation are critical
by Gretchen Mosher, Dirk Maier, Kingsly Ambrose,
and Samuel Cook

Moving and handling grain creates grain dust, which when
combined with other components typically found in a grain
handling environment, can result in grain dust explosions.
Grain dust explosions are high impact events that can result
in human fatalities and injuries, loss of facilities, and sigQL¿FDQWRSHUDWLRQDOGRZQWLPH
The May 2018 explosion in South Sioux City, Nebraska,
U.S., damaged the structure, injured two workers, and interrupted business operations. A second explosion in eastern France in June 2018 injured six and destroyed the facility. Like many grain dust explosions, the cause of the
blasts in both incidents is still unknown, but given what we
know about previous grain dust explosions a likely suspect
is the ignition of combustible grain dust. Because a grain
dust explosion has far-reaching effects, preventing these
events is critical. Since 2015, Purdue University in West
Lafayette, Indiana, U.S., has gathered information on grain
dust explosions in the United States. The table on page 72
summarizes the explosions and known sources recorded in
2015, 2016 and 2017.
EH LQ SODFH R[\JHQ FRQ¿QHG VSDFH LJQLWLRQ VRXUFH GLVpersion, and a fuel source (grain dust). The elements make
up the dust explosion pentagon, shown in Figure 1 (page
70). Grain handling creates an environment that can result
in combustion and explosion of dust. The three elements
prevent an explosion, but elimination of these hazards is not
handling grain and cannot be eliminated. Therefore, managing housekeeping related to grain dust and appropriate
maintenance of equipment to prevent ignition sources from

sparking and dispersing is a critical challenge. Managing
grain dust and maintaining equipment is not a once-a-year
task, rather, these tasks should be approached as an ongoing,
scheduled, continuous improvement process.
Because of the operating environment in grain handling
facilities, the potential hazard of combustible dust can never
be completely eliminated. Moving grain generates dry dust
and that grain dust is highly combustible. Sparks from friction, static electricity, rubbing pulleys, and hot work are just
a few of the ignition sources potentially present within the
grain handling environment. Most grain handling and processing systems that include bucket elevators, transfer bins,
hammermills, baghouses, and headhouses provide the con¿QHGVSDFHQHHGHGIRUGXVWWRUHPDLQLQVXVSHQVLRQDQGIRU
pressure to build, increasing the potential for explosion.
The 1987 implementation of the OSHA Grain Handling
Facilities Standard reduced the number of grain dust exploVLRQV E\  WKH ¿UVW \HDU EHFDXVH RI LQFUHDVHG DWWHQWLRQ
hazards associated with entry into bins, silos and tanks. Yet,
several grain dust explosions still occur every year.
A key to preventing large-scale damage and injury is understanding the difference between the primary explosion
and a secondary explosion. The primary explosion is frequently the result of ignition sources such as welding sparks
or overheated bearings causing fuel sources such as corn or
wheat dust to combust. The primary explosion may not be
large, but it often results in a dispersion of dust that can then
combust, leading to a larger and more damaging secondary
explosion that carries further into the facility.
A common question is: How much dust is needed to cause
a grain dust explosion? The simple answer is "no amount of
cannot see the color of the surface (about the thickness of a
piece of paper), enough dust is present to lead to an exploAugust 2018 / World Grain /

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