Mitigating the presence of grain dust is a crucial part of any housekeeping program to comply with Occupational Safety and Health Administration (OSHA) standards and risk management practices, such as loss control.
OSHA can levy grain dust citations at a grain handling facility under three separate standards for housekeeping violations.
OSHA’s grain handling standard (29 CFR 1910.272) directly addresses grain dust hazards. Further, in 1910.22(a)(1), which applies to walking-working surfaces, OSHA contends that it continues to interpret combustible dust (which has not been formally defined) as a walking-working surfaces hazard since excessive accumulation is considered a slip, trip, or fall hazard. OSHA’s general duty clause, 5 (a)(1), requires employers to provide a safe work environment.
In addition, National Fire Prevention Association (NFPA) 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities, is the primary voluntary consensus standard focused on the grain handling industry.
Compliance with NFPA standards is not required under the OSHA grain handling facilities standard. Instead, NFPA standards are voluntary and only apply to facilities if local authorities have adopted the standards within their jurisdiction (e.g., fire marshals may adopt the standards and rely on them for enforcement purposes.) The NFPA standard specifically focuses on mitigation and prevention and management systems.
Oils for Dust Suppression
The grain industry primarily uses white mineral oil to reduce the concentrations of dust near potential ignition sources. Food-grade soybean oil also is an effective dust suppressant, but its use may be limited by its potential rancidity, flow characteristics in cold weather, and cost.
White mineral oil meeting U.S. Food and Drug Administration-established specifications may be used safely in food applications as a dust-control agent for wheat, corn, soybeans, barley, rice, rye, oats, and sorghum at a level of no more than 0.02% by weight of grain (200 parts per million [ppm]). In addition, white mineral oil meeting the established specifications and with ISO 100 oil viscosity may be applied as a dust-control agent for rice at a level of no more than 0.08% by weight of the rice grain (800 ppm), per 21 CFR 172.878.
Dust suppression oil usually is applied to grain at receiving and shipping legs, as well as at loadout spouts. In some cases, it will cause the dust particulates to stick to whole kernels within the grain stream. Normally, white mineral oil is applied at a rate of 1/2 to 1 gallon per 1,000 bushels (approximately 60 to 110 ppm). The use of dust suppression oil requires that a dust control system draw the oil from a supply tank to an internal pump, which in turn, supplies oil to the system’s pressure controls and then directly to the spray assemblies.
Dust Collection Systems
Dust collection systems capture the particulates and store them until they can be disposed of or reintroduced to the commodity. These systems operate very much like a large-scale vacuum cleaner. Powerful fans create suction to transport dust particles through duct work to a collector.
There are several types of dust-collector systems, such as:
• Cyclone collectors will push air through the top of the collector that then pushes the dust downward. The dust will hit the sides of the collector while the clean air is forced out into another filtration system to collect the finer particles. The larger dust collected by the cyclone then is moved away from the system via gravity or any other engineered system to a storage receptacle.
• Baghouse collectors have many different sizes and designs but all operate in the same basic way. The dust-laden or particle-laden air stream enters the baghouse through the dirty air inlet. It then travels along the surfaces of multiple fabric tubes (bags), then passes outward or inward through the fabric. The larger particles fall into a hopper, while the smaller particles accumulate on the fabric tube surfaces.
A cleaning mechanism occasionally cleans the particles from the tube, which then also fall into the hopper. This cleaning mechanism typically is a compressed air solenoid device set to fire in sequence as the dust suppression system operates. The clean air then exits from the top of the baghouse.
• Point-of-use collectors have increased in popularity in the past decade. They work similarly to other collectors, with airflow being the means of transport for the dust. These systems are installed where the bulk of the dust is created, such as dump pits, legs, shakers, and distributor floors.
The manufacturer or engineer will help in an on-site assessment of a facility’s best installation locations. Improvements have been made to the filtration medium allowing for maximum airflow. Options for a point-of-use system may limit duct work. Some systems will have the exhaust system flow to another centralized baghouse to reclaim the particulates. Others simply have an agitator or compressor in place to knock the product from the filter and back into the grain stream.
Choosing a Suppression Method
As part of OSHA’s grain handling standard, every grain handling facility is required to develop and implement a written housekeeping program. An effective housekeeping program may not only help to reduce safety risks, but also may control expenses that could affect a firm’s ability to compete in the marketplace. However, it may not be feasible to collect all dust using manual housekeeping methods; therefore, it may be necessary in some circumstances to utilize a dust collection system.
Prior to installing a new dust suppression system or overhauling an existing one, the source(s) of dust needs to be identified. Next, the amount of dust created through internal practices, such as unnecessary bin transfers or drying temperatures, should be mitigated.
This article is one in a series of Safety Tips published by the National Grain and Feed Association (NGFA), Arlington, VA (202-289-0873). To view more NGFA Safety Tips, go to ngfa.org and click on Issues.