Copyright © 2002, Thomas J. Armstrong
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Previous studies demonstrate associations between certain physical work stresses, localized fatigue and chronic musculoskeletal disorders of the upper limb (see Figure 6.1) (see: Kuorinka et al. 1994; Bernard et al. 1997). These work stresses are referred to here as ergonomic stresses. This section is intended to show the reader how to look for these stresses and some of the things that can be done to control them. The procedures for identifying these factors range from qualitative observations to quantitative measurements using electromyography and goniometry. Even if quantitative measurements are desired, it is recommended that an observational approach be used first to determine those aspects of the job that are to be quantified. While some instrumental methods are described, this section focuses on observational methods.
Many examples are used to help the reader begin to recognize them when they see similar situations in the work place. In many cases the examples also show how the stresses are controlled. This is to help the reader understand the relationship between work design and ergonomic stresses to help them not only recognize, but to anticipate situations that are more stressful than necessary. This also lays the ground work for the discussion of work design in Section IV. In many cases, interventions for control of stresses will be obvious, but thorough analysis is necessary before control measures or interventions are attempted. It may be found that the same intervention addresses several stresses. The following section offers a more systematic approach to job design and presents additional examples.
Ergonomic stresses or Generic Risk Factors are common attributes of different industries and occupations and are associated with discomfort, impaired work performance and chronic muscle, tendon and nerve disorders. Examples include repetitive exertions, static exertions, forceful exertions, localized mechanical stresses, posture stresses, low temperatures, and vibration --- see Table 6.1. These factors may be found alone or in combination with one another. They are distinguished from job specific factors, such as a particular tool that exposes workers to vibration and posture stress or an incentive work standard that results in excessive work rates in given situations.
Table 6.1: Physical ergonomic stresses or generic risk factors.
|Repeated exertions:||Exertions or movements that are repeated in the same manner||Static exertions:||Forces or positions of the body that are maintained throughout each work cycle or for prolonged periods|
|Forceful exertions:||An exertion performed to overcome weight, resistance, or inertia of the body or a work object|
|Contact stresses:||Mechanical tissue stresses in the area of contact with external objects|
|Posture stresses:||Positions of the body that require more effort than others or result in compression or stretching of tissues in or around the joints, e.g. nerves or tendons|
|Low temperature:||Contact of the hand with air or work objects below 20°C or exposure of the worker to low ambient temperatures that result in reduced peripheral circulation|
|Vibration:||Contact of the hands with vibrating objects|
2. Job Documentation
|Job Title/Objective||The name of the job. The job title should be descriptive of what the operator does or the process. For example, the job title "clerical worker" suggests that this job involves clerical work, but does not indicate whether this position involves use of the telephone, copy machine, computer or all of them. The titles "transcriptionist," "receptionist" or "word processor" are more descriptive of what the worker does.|
|Production Standard||The amount and quality of work that is to be completed in a given period. The production standard may be explicitly stated as a standard time, production quota or line speed. It may also be implicitly stated as the completion of certain tasks or goals.|
|Location||The department, line position and/or building location.|
|Tasks||Groups of work elements or steps performed to accomplish
a common objective or sub-objective. Tasks are usually somewhat
independent of each other and may be performed in varying order,
while steps usually must happen in a prescribed order. Examples of tasks are:
|Methods||The sequence of steps or elements required to complete a task.
For example the steps required to load and activate a apress might be:
|Tools and Equipment||A list of tools, machines, and personal protective devices
used to perform the job. The list should include:
|Materials||Materials, sub-assemblies, assemblies, or scrap that is handled or used by the worker.|
|Environment||Temperature, vibration, noise, lighting, inside/outside|
See: Work sampling example.
See: McCormick (1982) for guidelines on conducting interviews
Detailed written documentation of each job is not necessary for the inspection; however, a cursory attention to each factor will help to assure that the inspection is systematic and that major factors have not been overlooked. The documentation information is used to identify and quantify the ergonomic stresses identified in the next step of the job assessment and to assist with the design of possible interventions. Additional information can be added as necessary to support the ergonomic assessment.