Tuesday, 29 March 2011 19:21

Grain, Grain Milling and Grain-based Consumer Products

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Grain goes through many steps and processes to be prepared for human consumption. The major steps are: collection, consolidation and storage at grain elevators; milling into an intermediate product such as starch or flour; and processing into finished products such as bread, cereal or snacks.

Grain Collection, Consolidation and Storage

Grains are grown on farms and moved to grain elevators. They are transported by truck, rail, barge or ship depending on the location of the farm and the size and type of elevator. Grain elevators are used to collect, classify and store agricultural products. Grains are separated according to their quality, protein content, moisture content and so on. Grain elevators consist of bins, tanks or silos with vertical and horizontal continuous belts. Vertical belts have cups on them to carry the grain up to weighing scales and horizontal belts for distribution of the grain into bins. Bins have discharges on the bottoms which deposit grain on a horizontal belt which conveys the product to a vertical belt for weighing and transportation or return to storage. Elevators can have capacities ranging from just a few thousand bushels at a country elevator to millions of bushels at a terminal elevator. As these products move towards processing, they may be handled many times through elevators of increasing size and capacity. When they are ready to be transported to another elevator or processing facility, they will be loaded into either truck, railcar, barge or ship.

Grain Milling

Milling is a series of operations involving the grinding of grains to produce starch or flour, most commonly from wheat, oats, corn, rye, barley or rice. The raw product is ground and sifted until the desired size is reached. Typically, milling involves the following steps: raw grain is delivered to a mill elevator; grain is cleaned and prepared for milling; grain is milled and separated by size and grain part; flour, starch and by-products are packaged for consumer distribution or bulk transported to be used in various industrial applications.

Grain-based Consumer Products Manufacturing

Bread, cereal and other baked goods are produced using a series of steps, including: combining raw ingredients, batter production and processing, product forming, baking or toasting, enrobing or frosting, packaging, casing, palletizing and final shipment.

Raw materials are often stored in bins and tanks. Some are handled in large bags or other containers. The materials are transported to processing areas using pneumatic conveyors, pumps or manual material-handling methods.

Dough production is a step where raw ingredients, including flour, sugar and fats or oils, and minor ingredients, such as flavorings, spices and vitamins, are combined in a cooking vessel. Any particulate ingredients are added along with puréed or pulped fruits. Nuts are usually husked and cut to size. Cookers (either continuous process or batch) are used. Processing of the dough into intermediate product stages can involve extruders, formers, pelletizers and shaping systems. Further processing can involve rolling systems, formers, heaters, dryers and fermentation systems.

Packaging systems take the finished product and encase it in a paper or plastic individual wrapping, place individual products in a box and then pack boxes on a pallet to prepare for shipment. Manual pallet stacking or product handling is used along with fork-lift trucks.

Mechanical Safety Issues

Equipment safety hazards include points of operation which can abrade, cut, bruise, crush, fracture and amputate. Workers can be protected by guarding or isolating the hazards, de-energizing all power sources prior to performing any maintenance or adjustment on the equipment and training workers in proper procedures to follow when working on the equipment.

The machines used to mill and convey products can be particularly dangerous. The pneumatic system and its rotary valves can cause severe finger or hand amputations. The equipment must be locked out while maintenance or clean-up is being performed. All equipment must be properly guarded and all workers need to be trained in proper operating procedures.

Processing systems have mechanical parts moving under automatic control which can cause severe injury, especially to fingers and hands. Cookers are hot and noisy, usually involving steam heating under pressure. Extrusion dies can have hazardous moving parts, including knives moving at high speed. Blenders and mixing machines can cause severe injuries and are particularly dangerous during clean-up between batches. Lockout and tagout procedures will minimize risk to workers. Slitter knives and water knives can cause severe lacerations and are especially dangerous during change-outs and adjustment procedures. Further processing can involve rolling systems, formers, heaters, dryers and fermentation systems, which present additional hazards to the extremities in the form of crushing and burn injuries. Manual handling and opening of bags can result in cuts and bruises.

Packaging systems have automated moving parts and can cause crushing or tearing injuries. Maintenance and adjustment procedures are particularly hazardous. Manual pallet stacking or product handling can cause repetitive strain injuries. Fork-lift trucks and hand pallet movers are also dangerous, and poorly stacked or secured loads can fall on nearby personnel.

Fire and Explosion

Fire and explosion can destroy grain-handling facilities and injure or kill workers and others who are in the facility or nearby at the time of explosion. Explosions require oxygen (air), fuel (grain dust), an ignition source of sufficient energy and duration (spark, flame or hot surface) and confinement (to allow pressure build-up). Typically, when an explosion occurs at a grain handling facility, it is not a single explosion but a series of explosions. The primary explosion, which can be quite small and localized, can suspend dust in the air throughout the facility in concentrations sufficient to sustain secondary explosions of great magnitude. The lower explosion limit for grain dust is approximately 20,000 mg/m3. Prevention of fire and explosion hazards can be accomplished by designing plants with minimal confinement (except for bins, tanks and silos); controlling dust emissions into air and accumulations on floors and equipment surfaces (enclosing product streams, LEV, housekeeping and grain additives such as food-grade mineral oil or water); and controlling the explosion (fire and explosion suppression systems, explosion venting). There should be adequate fire exits or means of escape. Firefighting equipment should be strategically located, and workers should be trained in emergency response; but only very small fires should be fought because of the explosion potential.

Health Hazards

Dust can be created when grain is moved or disturbed. Although most grain dusts are simple respiratory irritants, the dusts from unprocessed grain can contain moulds and other contaminants which can cause fever and allergic asthma reactions in sensitive persons. Employees tend not to work for prolonged times in dusty areas. Typically, a respirator is worn when needed. The highest dust exposures occur during loading/unloading operations or during major cleaning. Some research has indicated pulmonary function changes related to dust exposure. The current American Conference of Governmental Industrial Hygienists (ACGIH) TLVs for occupational exposure to grain dust are 4 mg/m3 for oat, wheat and barley and 10 mg/m3 for other grain dust (particulates, not otherwise classified).

Respiratory protection is often worn to minimize dust exposure. Approved dust respirators can be very effective if worn properly. Workers need to be trained in their proper use, maintenance and limitations. Housekeeping is essential.

Pesticides are used in the grain and grain-processing industries to control insects, rodents, birds, mould and so on. Some of the more common pesticides are phosphine, organophosphates and pyrethrins. Potential health effects can include dermatitis, dizziness, nausea and long-term problems with liver, kidney and nervous system functions. These effects occur only if employees are overexposed. Proper use of PPE and following safety procedures will prevent overexposure.

Most grain-processing facilities apply pesticides during shut-down times, when there are few employees in the buildings. Those workers present should be on the pesticide application team and receive special training. Re-entry rules should be followed to prevent overexposure. Many locations heat the entire structure to about 60 ºC for 24 to 48 hours in lieu of using chemical pesticides. Workers may also be exposed to pesticides on treated grain being brought to the truck cargo facility in trucks or rail cars.

Noise is a common problem in most grain-processing plants. The predominant noise levels range from 83 to 95 dBA, but can exceed 100 dBA in some areas. Relatively little acoustical absorption can be used due to the need for cleaning of equipment used in these facilities. Most floors and walls are made of cement, tile and stainless steel to allow easy cleaning and to prevent the facility from becoming a refuge for insects. Many employees move from area to area and spend little time working in the noisiest areas. This reduces personal exposure considerably, but hearing protection should be worn to reduce noise exposure to acceptable levels.

Working in a confined space such as a bin, tank or silo can present workers with health and physical hazards. The greatest concern is oxygen deficiency. Tightly sealed bins, tanks and silos can become oxygen deficient due to inert gases (nitrogen and carbon dioxide to prevent pest infestation) and biological action (insect infestation or mouldy grain). Prior to any entry into a bin, tank, silo or other confined space, the atmospheric conditions inside the confined space need to be checked for sufficient oxygen. If oxygen is less than 19.5%, the confined space must be ventilated. Confined spaces should also be checked for recent pesticide application or any other toxic material which may be present. Physical hazards in confined spaces include engulfment in the grain and entrapment in the space due to its configuration (inward sloping walls or entrapment in equipment inside the space). No worker should be in a confined space such as a grain silo, bin or tank while grain is being removed. Injury and death can be prevented by de-energizing and locking out all equipment associated with the confined space, ensuring that workers wear harnesses with lifelines while inside the confined space and maintaining a supply of breathable air. Prior to entry, the atmosphere inside a bin, silo or tank should be tested for the presence of combustible gases, vapours or toxic agents, and for the presence of sufficient oxygen. Employees must not enter bins, silos or tanks underneath a bridging condition, or where build-up of grain products on the sides could fall and bury them.

Medical Screening

Potential employees should be given a medical examination focusing on any pre-existing allergies and checking liver, kidney and lung function. Special examinations may be required for pesticide applicators and workers who use respiratory protection. Evaluations of hearing need to be made to assess any hearing loss. Periodic follow-up should seek to detect any changes.



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