When thinking about possible effects of repetitive trauma disorders (RTDs), consider ergonomics. Ergonomics is the study of proper work designs and environments for human characteristics. Researchers are constantly striving to learn more about human limitations and capabilities. This information is being used in workstations, tool and equipment development, and work task applications.
While there is no evidence that following the guidelines presented here will eliminate the development of cumulative trauma symptoms in susceptible people, there are indications that the probability of their occurrence will be reduced. General and specific guidelines are given for the prevention and management of repetitive trauma disorders in the workplace.
- Engineer products to allow machinery to do highly repetitive tasks; leave more variable tasks to human operators.
- Spread the load over as many muscle groups as possible to avoid over-loading the smaller muscle groups.
- Design tasks to permit gripping with the fingers and palm instead of pinching.
- Avoid extreme flexion or extension of the wrist. Design work surface heights, orientations, and reach length to permit the joints to remain as close a possible to their neutral positions for maximum muscle strength. Keep forces low during rotation or flexion of the joint. Use power assists if forces are high. Avoid repetitive gripping actions.
- Provide fixtures to hold parts during assembly so that awkward holding postures can be minimized.
- If possible, provide a variety of tasks over a work shift.
- Minimize time or pace pressures.
- Give people time to break into a new repetitive task.
Specific Design Guidelines:
- Keep the work surface height low enough to permit operator to work with elbows to the side and wrists near neutral position. Avoid sharp edges on workplace parts bins that may irritate the wrists when the parts are procured.
- Keep reaches within 20 inches of the front of the work surface so elbow is not fully extended when forces are applied.
- Keep motions within 20 to 30 degrees of the wrist’s neutral point.
- Avoid operations that require more than 90 degrees of rotation around the wrist.
- Avoid gripping requirements in repetitive operations that spread the fingers and thumb apart more than 2.5 inches. Cylindrical grips should not exceed a diameter of 2 inches with 1.5 inches as the preferable diameter. Hand tools that produce vibrations, require wide grip spans, or repetitively abrade the wrist area during use are of particular concern.
- For continuous, highly-repetitive operations, design a five-minute break into each hour for another activity.
- If hand protection is needed for a repetitive task, select a glove with the least interference for gripping. Provide a range of glove sizes to permit people to get the best fit for both large and small hands.
The guidelines in the above section address wrist and hand controls because the use of the wrists and hands are usually required in repetitive motion tasks.
Hand Tool Design for Repetitive Tasks:
Many repetitive tasks require the use of hand tools. Ergonomic design of these tools can help reduce the potential for repetitive trauma disorders.
- Design handles that make use of the power grip involving the palm. Avoid pinch grips. The preferable diameter for handles is 1.5 inches.
- Make handles long enough (4 inches) to avoid applying repeated pressure to the base of the thumb as when using a putty knife or a paint scraper.
- Orient the tool handle so it does not cause the wrist to be bent or twisted.
- Design tools to reduce the need to exert a sustained force on a cold and hard surface. Properly-textured handles increase the feeling of control on a power tool.
- Reduce the vibration from a powered hand tool as far as practical.
Management of Repetitive Trauma Disorders in the Workplace:
Even if many of the preceding guidelines are followed, some workers may still experience RTDs. Careful management of workload and work practices will be required.
- Rotate workers between jobs having different force requirements so no one person has to spend a full shift on the heaviest tasks. If rotation between jobs or tasks is not feasible, intersperse the primary task with several lighter tasks that provide a break for the heavy involved muscles and joints.
- Train workers to recognize early signs of RTDs and report them immediately. This will allow that worker to be reassigned to a less stressful position until symptoms subside. Further investigation by supervisors and staff can be initiated to identify and control RTD risk factors with a specific task.
- Safe work practices that focus on the best way to safely do a highly-repetitive task should be developed. All employees should be trained in these safe techniques. These techniques should be constantly reinforced by supervision and lead workers. Operators should always be involved when developing safe work practices.
- When people are starting a highly-repetitive job with forceful exertions or are returning to work after more than two weeks’ absence, rotate them between several activities until their muscles, tendons, and joints are accustomed to the work. A maximum of two hours of continuous work for a total of four hours per shift is recommended for the first few days if musculoskeletal symptoms have been seen.
Ergonomic Design for People at Work, Volume 2; The Ergonomics Group, Von Nostrand Reinhold, New York, NY.
WCF Insurance Safety Department
NOTICE: This guide may make reference to the Occupational Safety and Health Administration (OSHA) regulations; however the guide is not legal advice as to compliance with OSHA or other safety laws, codes, or regulations. Compliance with OSHA and other safety laws codes or regulations, and maintaining a safe work environment for your employees remains your responsibility. WCF Insurance does not undertake to perform the duty of any person to provide for the health or safety of your employees. WCF Insurance does not warrant that your workplace is safe or healthful, or that it complies with any laws, regulations, codes, or standards.