He was an internationally recognized expert on the subject and his work resulted in a sharp decline in the number of explosions annually. That work included annual reports from to McKinney : The highest frequency of grain dust explosions occurred in the late s and early s. A lot of fact finding went on at that time. McKinney: All grain dust can be explosive given the conditions described earlier are met. Other kinds of dust can be explosive. I believe it was in , there was a sugar mill that exploded in Georgia.
Q: Is there more danger of an explosion in one type of construction — wood, steel or concrete — compared to others? McKinney: No, there is no evidence to support that the type of construction makes a difference in grain dust explosions. Q: Could this kind of accident happen in smaller, on-farm grain handling facilities? With a focus on industry applications and research, the online program is designed with maximum flexibility for today's working professionals.
Skip to main content. Share Tweet Email. Within the silos, there is always air and, the stored grain, forms deposited layers of dust. During the operations of loading and unloading, such layers, because of the motion due to the circulation of air, always generate a permanent cloud.
The dispersed combustible dust clouds in the air form an explosive atmosphere. The clouds, if triggered, are able to oxidize so fast as to generate an explosion. The reactivity of the dust is as greater as smaller are the particles that compose it. L Lower Explosive Limit and the U.
This Standard will help you performing the classification considering all the hazards due to the presence of dust clouds or dust layers. Inside the volume of the silo, the storage layer of grain must be considered Source of Emission of continuous degree able to originate a Zone 20 extended to the entire internal volume of the silo.
In this case, the interior of the transport system is classified as Zone During the phases of loading and unloading, a certain amount of dust is normally emitted from the doors that communicate with the outside. So, if a dust explosion is limited to a primary explosion because of good housekeeping and sanitation, far less damage is done than if secondary explosions occur.
Once initiated, a continuous series of explosions occurs as long as adequate fuel and confinement are present. The result is a chain reaction of secondary explosions that move with destructive force throughout an elevator wherever grain dust levels are above the MEC , causing major structural damage.
This is why empty silos are blown out of an annex in some explosions, while full silos may not be directly affected. Dust explosions usually occur at grain transfer points — in bucket elevators or enclosed conveyors — where small dust particles become dislodged from kernels due to tumbling, agitation, and kernel impacts, as fast-flowing grain hits bucket elevator cups or changes direction in drag or belt conveyors.
This turbulent grain movement causes high levels of suspended dust particles two to 20 microns in diameter in the airspace, often close to a hot leg boot section bearing or a spark from tramp metal in a dump pit or drag conveyor.
According to national survey data, of reported grain dust explosions in the U. Schoeff, Many primary explosions originate in elevator legs. Stored grain typically contains 2 to 10 pounds of grain dust per ton Parnell, If a 12,bushel per hour leg handles wheat at tons per hour, at the lower level of two pounds of dust per ton, pounds per hour of grain dust is moving with the grain. If this leg is feet high, the leg trunk casing volume is about cubic feet. At the MEC level of 0. So, when only 0.
Belt speeds for a 12,bushel per hour leg typically run between and feet per minute, or about 10 to 13 feet per second. The belt in a foot leg makes one revolution in about 20 seconds. Part of the airborne dust tends to circulate continuously as the air is dragged along by the cups in the leg casing.
Continuous housekeeping and sanitation regular cleaning of the elevator , and regularly scheduled bearing service should be top priorities at all grain elevators and at flour and feed mills.
Many insurance companies insist on strict housekeeping, sanitation, and preventive maintenance at insured elevators. Grain, broken kernels and grain dust accumulate in the leg boots and should be cleaned out periodically. Some elevators install easily removable doors on leg boot side panels for quick, easy cleanout. Listed below are a number of grain dust control and prevention procedures. All elevators and mills should be doing item number one, housekeeping and sanitation, for elevator safety and worker health, as well as for integrated pest management IPM purposes.
It is the most important safety practice in any elevator or mill. Buss, Kenneth L. Gillis, Joseph P.
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