Adapted from 3rd edition, “Encyclopaedia of Occupational Health and Safety”.
The term oils and fats is generally applied to the triglycerides of fatty acids in plant seeds and animal tissues. Oils and fats constitute one of the three main types of organic materials regarded as the building materials of living organisms, the other two being proteins and carbohydrates.
More than 100 varieties of oil-bearing plants and animals are exploited as sources of oils and fats. The most important vegetable sources are: the olive, coconut, peanut, cotton seed, soya bean, rapeseed (canola oil), mustard seed, flax or linseed, palmfruit, sesame, sunflower, palm kernel, castor bean, hemp seed, tung, cocoa, mowrah, corn and babassu.
The main animal sources are beef cattle, pigs and sheep, the whale, cod and halibut.
Edible oils and fats provide a concentrated source of food energy, serve as carriers of fat-soluble vitamins and also furnish the essential fatty acids which are of vital importance to metabolism. Oils and fats constitute the major raw materials for soaps and detergents, paints, lacquers and varnishes, lubricants and illuminants such as candles. They are also used in the manufacture of linoleum and oiled fabrics, in the manufacture of fixatives and mordants in the tanning of leather, and as feedstock for chemical synthesis.
Initial processing depends upon the raw material; for example, animal fats are rendered in steam-jacketted vessels, seeds are cleaned, milled and separated and nut-meats are flaked. The fats or oils are extracted by pressing or treatment by solvents, and further processing depends upon the end use. Olives may be pressed several times, but no further treatment is usually required. For other edible oils and fats, processing may comprise a number of different stages, including refining, deodorization, hydrogenation, solidification or emulsification.
Raw oils and fats contain impurities, some of which are objectionable because they darken the oil, cause it to foam and smoke on heating, impart an undesirable flavour or odour or affect processing. Refining, which consists of neutralization and bleaching, removes most of these impurities. Neutralization removes fatty acids and gummy phosphatides by alkali and degumming treatments. The raw materials are bleached by absorption on natural or activated bleaching earths; however, heat bleaching may be employed. Oil temperature does not normally exceed 100 °C during refining.
Deodorization removes the odoriferous compounds by steam distillation at high temperature and low absolute pressure.
Liquid oils and soft fats are converted into firm plastic fats by hydrogenation, which also helps prevent rancidity due to oxidation. In this process, the oil is reacted with hydrogen at a temperature of 180 ºC or more in the presence of a catalyst, usually finely divided nickel. The hydrogen is fed in at a pressure of between 2 and 30 atmospheres, depending upon the desired end-product.
If the oil or fat is to be marketed in plastic or emulsion form, further processing is required. Many proprietary brand oils and fats are blended, and shortenings are solidified to yield granules by controlled gradual cooling (fractionation) and separation of crystallized fractions at various temperatures based on their melting points. An alternative method produces a texturized product by rapid chilling in special equipment called a votator.
Hazards and Their Prevention
Hydrogen presents a high risk of explosion and fire in the hydrogenation process. Burning oils and fats may emit highly irritant fumes such as acrolein. The solvents, such as hexane, used for the extraction of oils are highly flammable, although they are commonly used in closed systems. Precautions against fire and explosion include:
- elimination of all sources of ignition
- use of explosion-proof equipment and spark-proof tools
- prohibition of smoking
- ensuring fire exits are not blocked and are well maintained
- provision of appropriate fire extinguishers
- development of procedures for spills and leaks of hydrogen and flammable solvents
- training of staff in firefighting procedures.
Electrical installations present a risk of electrical shock in damp and steamy conditions. All equipment, conductors and so on should be suitably protected with special attention to any portable equipment or lights. Ground fault circuit interrupters should be installed on electrical equipment in wet or steamy areas.
Injuries from moving machinery parts can be prevented by efficient and well maintained machinery guarding. Particular attention should be given to crushing machinery, filling and drum-seaming machines and nips between belts, drums and pulleys of conveyors. Lockout/tagout procedures should be used when maintaining and repairing equipment. Risks of explosion and leakage in steam plant should be prevented by regular inspection and maintenance procedures.
Excessive noise from equipment should be minimized by engineering controls if possible. Employees exposed to excessive noise should wear appropriate hearing protectors, and there should be a hearing conservation programme.
Manual handling of drums may cause musculoskeletal strains and injuries to hands and toes. Mechanical handling equipment should be used when possible. There should be training in correct methods of handling and lifting, foot and hand protection, and checking of containers for sharp edges. Badly stacked drums may fall and cause serious injury; supervision and training in stacking and destacking will reduce the risk involved.
Falls may occur on slippery floors and staircases, and can be prevented by well maintained non-slip floor surfaces, regular cleaning and good housekeeping, and wearing of non-slip footwear.
Burns may be caused by sodium hydroxide during handling of drums for refining and from spurts of liquid caustic when drums are opened; by hot oil or spent catalyst during cleaning of filter presses; from acids; and from steamlines and steam leaks. Protective clothing, boots, aprons and gloves will prevent many injuries; face shields are necessary to protect the eyes from splashes of corrosive or hot material.
Oils are processed at high temperatures, and physical discomfort can result, especially in the tropics, unless effective measures are taken. Muscle cramps, exhaustion and heat strokes may occur. Radiant heat should be reduced by lagging or insulating the vessels and steam pipes. Efficient mechanical ventilation should provide frequent changes of air. Workers should have frequent access to liquids and frequent breaks in cool areas.
Entering bulk tanks for repair or cleaning can be a confined space hazard. Employees should be trained in confined space procedures, such as testing of the confined space air and emergency rescue procedures. A minimum of two workers should be present.
Solvents used for the extraction of fats and oils may present toxic risks. Benzene should not be used, and the least toxic solvent practicable should be substituted (e.g., substitution of heptane for hexane). LEV is required to remove solvent vapours at the point of origin, or closed systems should be used.
Dermatitis may be caused by handling of oils, fats and solvents. Provision and use of adequate washing and sanitary facilities is essential; barrier creams and protective clothing also aid in prevention.
In peanut oil processing plants, under suitable conditions of moisture and temperature, press-cakes can be contaminated by moulds of Aspergillus flavus, which contain aflatoxins. Workers exposed to heavy aflatoxin contamination in workroom air have been found to develop acute or subacute liver damage and to present an increased prevalence of tumours.
Rendering of animals to produce animal fats and animal feed can also involve biological hazards. Although most animals and animal materials used as a source for rendering are healthy or from healthy animals, a small percentage comes from animals that have been road-killed or have died of unknown causes and perhaps are diseased. Some animal diseases, such as anthrax and brucellosis, can also affect humans. Workers in slaughterhouses and rendering plants may be at risk. In the United Kingdom, people called knackers make their living going around the countryside picking up dead animals and rendering them in their backyards. They could be at greater risk because of the greater likelihood of their exposure to diseased animals and the crude conditions they work under.
The past rendering of sheep organs, including brains, as a source for cattle feed has resulted in bovine spongiform encephalopathy (“mad cow disease”) in some British cows where the sheep had a brain disease called scrapie. It appears that some humans have developed this disease from eating beef from cows with mad cow disease.
Periodic medical examination of workers, selection, training and supervision are aids in prevention of both accidents and occupational diseases.