World Grain - January 2012 - 78

GRAINOPERATIONS

Explosive issue
Grain dust and ignition sources must be controlled to prevent grain dust explosions
by Paul F. Stevenson

People in the grain industry know the causes and effects of grain dust explosions and how deadly they can be. But for a variety of reasons, namely operations tempo and the thought that “it will never happen to us,” some grain operators and management do not spend the time and devote resources to prevention and reducing the risk. Most grain dust explosions in grain elevators happen within the bucket elevator or leg. Grain is ﬂowing into the facility by truck or railcar. A heated bearing or a spark is produced inside the leg and a primary explosion rocks the facility. Usually a primary explosion is not the explosion that causes the most damage or kills elevator employees. The secondary explosion is the deadly killer and produces the most damage to the facility. There are three elements to a grain dust explosion. First, there must be grain dust. Grain dust in a leg casing and throughout the facility is managed by keeping grain dust in suspension to a minimum. Second, there must be a conﬁned space. Leg casings and even certain parts of an upright concrete elevator can be considered conﬁned spaces. Third, there must be a spark or heat source to ignite the fuel. How does an explosion happen? First, there is a heat source inside the leg casing, perhaps a dry and heated bearing. Grain dust builds in the leg casing until the heat source or spark ignites the dust inside the leg casing. The primary explosion in the leg casing rocks the facility but is mainly controlled inside the casing. In most cases, buckets elevators were built with “blast” panels installed to relieve explosions. Now that the facility has been rocked by the primary explosion, fugitive grain dust on ledges, equipment, spouts, ﬂoors, etc., is shaken loose and put into suspension inside the upright concrete. Once the “blast” panels blow, heat and ﬁre escape into headhouses, basement tunnels and gallery ﬂoors. Since dust is already in suspension and there is heat/ﬁre, the secondary explosions start and do not stop until all fugitive grain dust has been utilized. How do you stop an explosion from happening? The simple answer is we need to remove one of the three elements mentioned above.
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Seven people died in this June 1998 grain dust explosion at the DeBruce Grain Company elevator in Haysville, Kansas, U.S. Photo courtesy of Battalion Chief Michael R. Steele and the Wichita Fire Department, Wichita, Kansas, U.S.

CONTROLLING GRAIN DUST If you control grain dust, you eliminate the fuel source. There are several methods to reduce the fuel source. However, elevator operators must be motivated to clean and maintain effective controls and management must be committed to installing effective controls and eliminating the risk of an explosion. Remember that any method to control the dust costs time and money. Effective use of food grade mineral oil is a great example of controlling grain dust. Food grade mineral oil is approved for use in commodity grain. It is applied to grain at the receiving pit (chute to leg). Grain dust is attracted to the grain, thus removing suspended grain dust. Mineral oil systems are installed and are monthly/annually calibrated to ensure proper application rates. Application rates vary with the type of upright concrete storage. However, a good rule of thumb would be 1 gallon to 1,000 bushels. In many cases, companies are applying food grade mineral oil at in-house belts or enclosed conveyors for the frequent turning of grain. This is strongly recommended
January 2012 / World Grain / www.World-Grain.com

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World Grain - January 2012

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