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Sunday, 27 February 2011 06:40

Ergonomics

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Ergonomics is the science of assessing the relationship between workers and their work environment. This science includes not only an assessment of musculoskeletal risk due to the design of the work, but also includes a consideration of the cognitive processes involved in work that may lead to human errors.

Jobs in the rubber and tyre industry have been identified with an increased risk of particular types of musculoskeletal disorders. In particular, back injuries appear to be prominent. A sample of materials-handling jobs in the tyre and rubber industry has indicated that the high-risk jobs result in low-back disorder injury rates that are approximately 50% higher than that of general industry. An assessment of jobs indicates that these problems typically arise from jobs requiring the manual transport of rubber products. These jobs include rubber processing (Banbury) operations, tyre builders, tyre finishers and tyre transporters both in the factory and warehouse environment. Wrist problems such as carpal tunnel syndrome and tenosynovitis also appear to be prominent in tyre construction. An examination of tyre manufacturing operations suggests that shoulder problems would be expected. However, as expected, injury records tend to under-report the risk of shoulder injuries due to a lack of sensitivity to the problem. Finally, there appear to be some cognitive processing issues involved in the tyre industry. These are apparent in the inspection tasks and are often exacerbated by poor lighting.

There are several workplace-related risk factors believed to be responsible for these musculoskeletal problems in the tyre and rubber industry. Risk factors consist of static, awkward postures in the back, shoulders and wrists, rapid motions in the wrist and back, and large weights handled, as well as large forces applied to the trunk while handling large pieces of rubber during tyre building. A study of factors associated with low-back disorder risk indicates that greater weight is handled by workers in the tyre building industry than in other fields and these loads are handled at greater than average distances from the body. Furthermore, these forces and weights are often imposed on the body during asymmetric motions of the trunk, such as bending. The duration of the force applications in this type of work is also problematic. Often in a tyre-building operation, lengthy applications of force are required which diminish the worker’s available force over time. Finally, tyre and rubber workplaces are often warm and exposed to dirt and dust. The heat within the workplace will tend to increase the caloric demands of the job, thus increasing the energy demands. Resin and dust within the workplace increase the likelihood that workers will be wearing gloves while performing their tasks. This glove use will increase the required tension in the forearm muscles that control the fingers. In addition, when workers wear gloves they will increase their grip force since they cannot perceive when an object is about to slip out of their hands. Solutions to these ergonomic-related problems include the simple rearrangement of the workplace (e.g., raising or lowering of the work or moving the workstations in order to eliminate large twisting or lateral bending motions of the trunk; the latter can often be accomplished by reorienting origins and destinations of lifting tasks from 180º twists to 90º turns). Often more significant changes are needed. These may range from incorporating adjustable workstations such as scissors jacks or lift tables, to incorporating lifting assistance devices such as lifts and cranes, to fully automating the workstation. There is obviously a large cost associated with some of these solutions to the problem. Therefore the key to proper ergonomic design is to make only the changes that are necessary and to determine the effect of the change in terms of the change in musculoskeletal risk. Fortunately, new methods for quantifying the extent of the risk associated with a given design of the workplace are becoming available. For example, a risk model has been reported that assesses the risk of occupationally related low-back disorder given the demands of the job (Marras et al. 1993; 1995). Models have also been developed that assess the loading of the spine due to dynamic trunk activities (Marras and Sommerich 1991; Granata and Marras 1993). Thus, models are becoming available for the assessment of workplace designs in the industry that are capable of addressing the issue of how much exposure to a workplace is too much.

 

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