Taking precautions with grain dust - a hazard
ARLINGTON - The grain handling industry is a high hazard industry where workers can be exposed to numerous serious and life-threatening hazards. These hazards include: fires and explosions from grain dust accumulation, suffocation from engulfment and entrapment in grain bins, falls from heights and crushing injuries and amputations from grain handling equipment.
The Wisconsin Agri-Business Association works with grain facilities around the state to help them address safety issues at their facilities. Jim Nolte is the safety director for that organization.
He points out that grain dust explosions are often severe, involving loss of life and substantial property damage. Over the last 35 years, there have been over 500 explosions in grain handling facilities across the United States, which have killed more than 180 people and injured more than 675.
Grain dust is the main source of fuel for explosions in grain handling. Grain dust is highly combustible and can burn or explode if enough becomes airborne or accumulates on a surface and finds an ignition source (such as hot bearing, overheated motor, misaligned conveyor belt, welding, cutting, and brazing).
OSHA standards require that both grain dust and ignition sources must be controlled in grain elevators to prevent these often deadly explosions.
To prevent dust explosions and fires, employers must develop and implement a written housekeeping program with instructions to reduce dust accumulations on ledges, floors, equipment and other exposed surfaces.
Nolte points out, “Dust doesn’t just accumulate on floors and conveyors but it is on beams, rafters and fan blades, too. You need to identify "priority" housekeeping areas in grain elevators.”
He defines priority areas as floor areas within 35 feet of inside bucket elevators, floors of enclosed areas containing grinding equipment and floors of enclosed areas containing grain dryers located inside the facility.
Dust accumulations in these priority housekeeping areas shall not exceed 1/8th inch. Employers should make every effort to minimize dust accumulations on exposed surfaces since dust is the fuel for a fire or explosion, and it is recognized that a 1/8 inch dust accumulation is more than enough to fuel such occurrences.
He identified five things that need to be present for an explosion to occur. These include a heat source, grain dust that provides the fuel, oxygen, confined space and dust suspended in the air. While there is no control over three of them, he says it is possible to eliminate the ignition sources by minimizing the potential for spark and dust control.
Temperature sensors help. Magnets can help catch metal in grain that could cause a spark as it flows. Built-in alignment sensors detect belt rubbing and proper grounding prevents sparks from static electricity.
Also, it is important to make sure any electrical equipment used at the facility is rated for use in dusty areas. Tools and vehicles can cause sparks.
Bearings must be mounted externally to the leg casing or the employer must provide vibration, temperature, or other monitoring of the conditions of the bearings if the bearings are mounted inside or partially inside the leg casing.
These bucket elevators must be equipped with a motion detection device which will shut-down the elevator when the belt speed is reduced by no more than 20 percent of the normal operating speed.
Implement a preventative maintenance program with regularly scheduled inspections for mechanical and safety control equipment, which may include heat producing equipment such as motors, bearings, belts etc. Preventive maintenance is critical to controlling ignition sources. The use of vibration detection methods, heat sensitive tape or other heat detection methods can help in the implementation of the program.
Minimize ignition sources through controlling hot work (electric or gas welding, cutting, brazing or similar flame producing operations).
Nolte says continuous cleaning and removal of dust is an important preventive measure.
While shop vacs are commonly used for cleaning up dust, he cautions that it must be rated for this type of use or it can put dust into suspension and that is one of the contributing factors to explosions.
Nolte demonstrated the difference suspended dust makes by creating a mock-explosion in a specially designed box. As soon as he released dust into the air inside the box an explosion occurred.
Design and properly locate dust collection systems to minimize explosion hazards. All filter collectors installed after March 1988 shall be located outside the facility or located in an area inside the facility protected by an explosion suppression system or located in an area that is separated from other areas by construction having at least a one hour fire resistance rating and which is located next to an exterior wall vented to the outside.
Finally, he suggests installing an effective means of removing ferrous material from grain streams so that such material does not enter equipment such as hammer mills, grinders and pulverizers.
While dust accumulation and the potential of explosion primarily occurs at feed mills where grain is mixed and moved around inside, he says any grain storage facility has the potential for explosions and it is important to be aware of the dangers and the ways to prevent a problem.
“Explosions occur in just a split second and without any warning,” Nolte cautions. “Make sure to eliminate anything that contributes to the potential of an explosion or fire.”