Introduction to Industrial Engineering

By Jane M. Fraser

Chapter 9


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9.1 Physical ergonomics

People who perform repetitive hand tasks can experience pain, tingling, and numbness called Carpal Tunnel Syndrome (CTS). According to NIOSH

Research conducted by the National Institute for Occupational Safety and Health (NIOSH) indicates that job tasks involving highly repetitive manual acts, or necessitating wrist bending or other stressful wrist postures, are connected with incidents of CTS or related problems. The use of vibrating tools also may contribute to CTS. Moreover, it is apparent that this hazard is not confined to a single industry or job but occurs in many occupations especially those in the manufacturing sector. Indeed, jobs involving cutting, small parts assembly, finishing, sewing, and cleaning seem predominantly associated with the syndrome. The factor common in these jobs is the repetitive use of small hand tools.

Methods to prevent CTS include designing tools so that the wrist is held correctly, designing the work layout so wrists are not stressed, scheduling work breaks for workers in jobs with potential hazard, and rotating such work among several workers. The Mayo Clinic provides advice to workers such as:

Reduce your force and relax your grip. Most people use more force than needed to perform many tasks involving the hands. If your work involves a cash register, for instance, hit the keys softly. For prolonged handwriting, use a big pen with an oversized, soft grip adapter and free-flowing ink. This way you won't have to grip the pen tightly or press as hard on the paper.

CTS is an example of a Repetitive Stress Injury (RSI), meaning an injury not caused by one incident, but by a repetitive activity. Often the cause of such injuries is difficult to determine since workers may be involved in different types of activities. The even broader class of such injuries is called musculoskeletal disorders (MSDs). Even if conditions do not threaten workers with short-term or long term injury, conditions can reduce efficiency and quality through fatigue.

IEs must be aware of and prevent situations where work methods can cause harm to workers. Besides being the right thing to do, such prevention can save the organization money and can reduce the liability exposure of the organization. This web page has a good discussion of types of MSDs, conditions that can cause them, and ways to mitigate hazards.

Researchers in physical ergonomics often rely on physics to understand the effects of work on human bodies. Specialists in this area often have to know anatomy and physiology. Lab studies of people doing a task may monitor the personís physiological condition (for example, heart rate and oxygen uptake) in order to determine the exact effects of different work on humans.

The IE may redesign jobs to reduce the need to stand, provide better chairs for workers, provide better hand tools for workers, and reduce the need for workers to lift heavy objects. Ergonomics stresses adapting the workplace to the worker. Such adaptions must be individual. Work stations that allow adjustments can help; for example, tables and chairs that can be raised or lowered, or a work station that accomodates left-handed and right-handed workers.

OSHA provides short case studies describing how job redesign has reduced ergonomic issues. Advanced Filtration Systems Inc. redesigned an inspection process to reduce the number of cases of CTS.