SUGAR CANE CULTIVATION AND PROCESSING
R.A. Munoz, E.A. Suchman, J.M. Baztarrica, Carol J. Lehtola*
* Adapted from 3rd edition, “Encyclopaedia of Occupational Health and Safety”.
Sugar cane is a hardy crop that is cultivated in tropical and sub-tropical regions for its sucrose content and by-products such as molasses and bagasse (the waste fibrous residue). The plant grows in clumps of cylindrical stalks measuring from 1.25 to 7.25 cm in diameter and reaching 6 to 7 m in height. The cane stalks grow straight upward until the stalk becomes too heavy to hold itself up. It then lies on its side and continues to grow upward. This results in a mature cane field lying on top of itself in a mesh pattern. The sugar cane stalks contain a sap from which sugar is processed. Sugar cane is grown throughout the Caribbean, Central and South America, India, the Pacific Islands, Australia, Central and South Africa, Mauritius and the southern United States. Sugar cane’s main use is for sugar; however, it can be fermented and distilled to produce rum. Bagasse, the cellulose material that remains after pressing, may be used in the production of paper and other products or as a fuel source.
Under favourable conditions and the appropriate use of pesticides and fertilizers, cane grows rapidly. To ensure the maximum sugar content of 1 to 17% of total weight, the cane must be harvested immediately after it reaches its final growth period. The cane fields are burned prior to harvest, to eliminate weeds (without destroying the crop) and to destroy snakes, dangerous insects and other pests that live in the dense growth of the cane fields. Harvesting is done either by hand (machetes are used to cut the cane) or by a sugar cane harvesting machine. Mechanization of sugar cane harvesting has become more prevalent during the 1990s. However, hand harvesting still occurs in many parts of the world, as well as in field locations that are not conducive for harvesting equipment. Large numbers of seasonal or migrant labourers are employed during cane harvesting, especially in areas of hand harvesting.
To retain the sugar content, the cane has to be processed as soon as possible after harvesting; therefore the processing plants (mills) are located near the major areas of sugar cane production. The crop is transported to the mills by tractors, semi trucks or, in some areas, by internal rail systems.
Hazards and their prevention
In areas where hand harvesting prevails, many of the injuries are machete related. These injuries can range from minor cuts to the severing of body parts. Also, the machete is the tool that is most commonly used by the less skilled workers on the farm or plantation. Keeping the machete sharp aids in reducing injuries, since with a sharp machete the worker does not have to swing as hard and can maintain better control over the machete. There are also instances of workers getting into fights with machetes. Safety gloves armoured with chain mesh have been developed to provide protection for the hand from machete-related injuries. The use of steel-toed boots and arm and leg guards will also reduce these types of injuries. Boots will also provide some protection from snake bites. Working with cane also can very easily produce injuries and cuts to the eyes. Eye protection is recommended during hand harvesting, where workers are exposed to the cane stalks. Since cane is grown in tropical and sub-tropical locations, workers also need to be concerned about heat-related health problems. This can be exacerbated due to use of the necessary protective clothing. These regions are also areas of high levels of sun exposure, which can result in various types of skin cancer conditions. Precautions need to be taken to limit or protect against sun exposure.
Manual harvesting with machetes can also result in musculoskeletal injuries from the repetitive motions and physical effort. The size of the machete, sharpness and frequency of cutting strokes are factors that affect this. See also the article “Manual operations in farming” in this chapter.
Precautions need to be taken to prevent infection when cuts and abrasions occur. Where the harvesting has become mechanized, hazards exist that are associated with the particular machine being used. These are similar to those of other agricultural harvesting equipment.
Pesticides and other chemicals may involve toxic risks that can lead to poisoning through skin absorption or inhalation. People who apply the pesticides need to be instructed on the hazards of the operation and provided with protective clothing and adequate washing facilities. Their equipment needs to be maintained and repaired as needed in order to prevent spills. Back-pack sprayers are particularly prone to develop leaks that will cause spillage onto the person. Aerial applications of pesticides can affect other people that are in the area of the application. Also, when pesticides are applied, the product label provides both legal and practical requirements for handling and disposal after use, as well as listing time intervals after which it is safe for people to re-enter the field.
Sugar Cane Mills (Processing Plants)
The sugar cane industry is concerned with more than the production of food for human consumption. Certain kinds of sugar and sugar residues provide nutritious supplementary food for animals, and various products of commercial significance are obtained from the raw material and its by-products.
Principal by-products are saccharose, glucose, levulose, raffinose, pectin, waxes and betaines. Subproducts are stalks (used for fodder), bagasse, rum and molasses. Among products manufactured on an industrial scale are saccharose octacetate, ethyl alcohol and acetic, citric, glutamic, oxalic, formic and saccharic acids. Paper and hardboard are produced industrially from bagasse. Bagasse can also, when dried, be used as a biogas source or as fuel in the sugar mill.
In the sugar mill, the cane is crushed and the juice extracted by heavy rollers. The juice contains saccharose, glucose, levulose, organic salts and acids in solution, and is mixed with bagasse fibres, grit, clay, colouring matter, albumin and pectin in suspension. Because of the properties of albumin and the pectin, the juice cannot be filtered cold. Heat and chemicals are required to eliminate the impurities and to obtain saccharose.
The mixture is clarified by heating and the addition of lime-based precipitants. Once clarified, the juice is concentrated by vacuum evaporation until it precipitates in the form of grayish crystals. The concentrated juice, or molasses, is 45% water. Centrifugal treatment produces granulated sugar of a grayish hue (brown sugar), for which there is a market. White sugar is obtained by a refining process. In this process, the brown sugar is dissolved with various chemicals (sulphuric anhydride, phosphoric acid) and filtered with or without bone black, according to the purity desired. The filtered syrup evaporates under a vacuum until it crystallizes. It is then centrifuged until a white crystalline powder is obtained.
Hazards and their prevention
Worker conditions will vary according to geographical locale. Seasonal workers are especially vulnerable to living in substandard conditions. Health risks will vary in relation to the environmental factors, working conditions, living conditions and the socioeconomic class of the worker.
Due to the high temperatures in the areas where cane is produced, workers need to consume large quantities of liquid.
Fumes and gases such as carbon dioxide, sulphur dioxide, carbon monoxide and hydrochloric acid may be given off at various stages of the refining process. The high temperatures of processing can also result in fumes and steam that are not only irritating or hot, but sometimes can be toxic as well.
In some areas of the mill, there are excessive noise levels.
Bagassosis is an occupational lung disease of the extrinsic allergic alveolitis type, caused by breathing dusts containing spores of thermophilic actinomycetes which grow in stored, mouldy bagasse. Hypersensitivity pneumonitis can also result from this exposure.
In developing countries, workers may be unskilled, with no safety training. Also there may be a high turnover rate for employees, which can lead to problems in keeping up with training and increasing skill levels. Although statistical data do not show a high incidence of occupational disease, this can be due in part to reporting and calculating problems, such as the fact that the mills and refining plants are not open year-round, but only for 5 to 6 months of the year. Thus annual accident rates may appear low. During the remainder of the year, seasonal workers will be employed in entirely different jobs, while permanent employees will be maintaining and working with the machinery, equipment and facilities.
Occupational accidents, such as falls, strains, sprains and so on, differ little from those in other industrial and agricultural activities. With increasing mechanization, the occupational accidents are fewer but are often more serious. The more frequent injuries include diseases related to heat stroke or heat stress, dermatitis, conjunctivitis, burns and falls.
In order to plan and put into effect a health and safety programme for a specific sugar mill, it is necessary to conduct a qualitative and quantitative assessment of the risks and hazards involved, including identification of corrective measures, such as the use of local exhaust systems for dust, gas and fumes where appropriate. Dust control can be used effectively for controlling bagasse dust. The facility should be properly aired and ventilated to reduce excessive heat, and adequate lighting should be provided. Machinery should be properly guarded, and proper protective clothing should be provided and easily accessible to workers. Health and safety standards and regulations must be complied with. A proper safety programme, for which trained staff are responsible, to ensure the safety of the workers should be in place.
Noise is a widespread hazard. Noisy machines should be soundproofed, and, in areas where the noise level cannot be reduced adequately, hearing protection must be provided and a hearing conservation programme instituted. That programme should include audiometric testing and worker training.