Guard Against Grain Dust Explosions

OMAHA (DTN) -- Farmers can keep grain storage facilities safe from potentially deadly dust explosions by utilizing the basics of good housekeeping and technology. That was the message speakers had for attendees of a workshop put on by Kansas State University after the Grain Elevator and Processing Society Exchange Expo held in Omaha, Neb., this week.

SCIENCE OF A GRAIN DUST EXPLOSION

Grain dust explosions still occur, but in the last decade injuries and deaths have been greatly reduced, Brandi Miller, KSU Department of Grain Science and Industry distance education coordinator, said during a presentation Wednesday. This decline in grain dust explosions comes at a time when the industry has seen grain-handling volume increase significantly.

Miller said KSU broke down the grain dust explosion incidents from 2006 to 2012 by month. A disproportionally higher number of incidents occurred in the month of August.

"Why is this?" Miller asked those in attendance. "Probably because bins are being emptied for fall harvest, and this tends to produce more dust."

Miller presented what she called the dust fire and explosion pentagon: Combustible dust, oxygen in the air and an ignition source contribute to a fire risk, while dispersion of dust particles and confinement of dust can lead to an explosion risk.

Grain facilities are subject to primary and secondary explosions. Grain dust settles on surfaces, and a primary explosion disturbs the settled dust into a cloud. This cloud is then ignited, causing a secondary explosion.

Miller said even though grain storage facilities are built from solid building materials, they are no match for the power of a grain dust explosion. The maximum pressure from a corn dust explosion is greater than 100 pounds per square inch (psi), while concrete storage structures can withstand only about 25 psi of pressure and grain-handling equipment will fail at pressures less than 6 psi.

CLEANLINESS NEXT TO GODLINESS

There are basic steps workers at grain facilities can do to limit dust explosion hazards. One of the first things is identify dust hazards. An example would be trying to limit the dust generated during grain transfers by making sure the bucket elevator belt is aligned properly and leaking conveyors and spouts are plugged correctly.

Practicing good housekeeping is key to preventing dust accumulation, Miller said. This would include vacuuming with proper equipment, using compressed air, dry sweeping with brooms and paying attention to hidden areas such as the top of beams, light fixtures and ledges.

This cleaning should also extend to dust collection or ventilation systems. These systems should be maintained and cleaned out at scheduled intervals.

"Establish a consistent housekeeping procedure and schedule and follow it," Miller said.

ADVANCED ENGINEERING CONTROLS

Modern technology also plays a key role in limiting grain dust explosions. R.P. Kingsly Ambrose, KSU Department of Grain Science and Industry assistant professor, said there are several devices that can detect possible explosions and suppress or isolate the explosion.

Ambrose told DTN the percentage of grain facilities using these newer technologies varies. Some facilities may have all these devices, some may not have any and some may utilize a selection of these newer technologies.

"I believe in general newer and larger facilities utilize these technologies more," Ambrose said.

There is a complete line of sensors that can detect possible problems in grain-moving equipment, which could be an ignition source for a fire or ignite a dust cloud.

Belt speed sensors will sound an alarm when there is a 10% change in belt speed, while a 20% change in speed will cause the senor to shut down the system, Ambrose said. Belt alignment sensors can sense when the belt is out of alignment. This sensor is not affected by dust or material buildup.

Sensors are also available that can read bearing temperature. A bearing that is out or in the process of going out can cause a spark, which can be disastrous.

"You need to be careful not to overload grain-handling equipment," Ambrose said. "It would be better to run less than full capacity than to overload the system."

Explosion suppression systems help to stop explosions as they begin. They can be divided into different categories and are in various locations within the grain storage facility, he said.

Depending on the industry and end use of the grain, there are different types of systems, Ambrose said. Oil suppression systems will apply roughly 1 gallon of food-grade mineral oil to 1,000 bushels of grain to limit dust.

Deflagration suppression systems can detect an ignition and/or explosion, apply the suppressant and contain the fire or explosion in as little as 80 milliseconds, he said.

Isolation equipment is used to interrupt or mitigate the flame, deflagration of pressure, pressure increase and ignition between enclosures interconnected by pipes or ducts. This can be accomplished by either chemical method or by mechanical valves.

Ambrose said chemical isolation methods will protect any size duct and can be triggered with a pressure sensor or vent burst sensor. It is the lowest-cost option, easy to retrofit or can be a new installation and is also available in flexible mounting options.

Mechanical isolation will prevent the propagation of flame through piping. The mechanical option utilizes a fast-acting valve that will stop the flow of the flame.

Because of the heavier construction, mechanical isolation is more expensive and is only available in round configurations. Ambrose said both systems are effective, and he does not promote one over the other.

Suppression and isolation systems can be mounted in bucket elevator systems in various positions to protect the head (top) and boot (bottom) as well as points in between. These systems can be mounted in single-leg as well as double-leg construction, he said.

Kansas State University offers education workshops on grain dust explosion prevention. For further information, Ambrose can be contacted at graindust@ksu.edu or by calling (785) 532-4091.

Russ Quinn can be reached at russ.quinn@dtn.com

(AG/CZ)

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