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Ask the Expert: Ergonomics

If the shoe fits

A: The importance of footwear flexibility is an interesting but subjective topic. It's also qualitative when it comes to defining a suitable degree of flexibility. The amount of flexibility in footwear is a function of the rigidity and thickness of the materials used for the footwear uppers and soles. Certain safety considerations (for example, steel toes) would also influence flexibility.

While the degree of acceptable flexibility is a personal preference, generally more is better. Increased flexibility allows for increased bone and joint movement that likely translate directly into increased comfort. Conversely, reduced flexibility could increase the potential for ankle joint soreness and muscle discomfort around the upper rim of the footwear.

In reviewing several standard ergonomics textbooks, I'm afraid I haven't been able to locate any quantitative reference material on suitable levels of flexibility. (You may wish to consider a Web search.)

While not truly a flexibility issue, it is well accepted that cushioned insoles can directly increase comfort, especially for people who stand for long periods of time.

W. Tim McGlothlin, C.P.E. 


Shifting shift work

A:  From an ergonomics and physiologic standpoint, I am not supportive of 12-hour shifts. This is especially true if the work is highly repetitive or physically demanding.

Highly repetitive work is a key stressor and contributor to musculoskeletal disorders. The body needs adequate recovery time within a shift (to minimize muscle fatigue) and between shifts (to allow the body to repair musculoskeletal microtrauma). Working 12-hour shifts robs the body of timely recovery time. Evenly spaced recovery throughout the week appears to be better for the body than longer, grouped recovery periods.

Performing physically demanding work for longer durations may increase wholebody fatigue. The National Institute of Occupational Safety and Health guide on work practices (Document DHHS No. 81-122) indicates that on average, workers should work at 33 percent of their maximal capacity when performing eighthour shifts. This number decreases to 28 percent of their maximal capacity when working 12-hour shifts. The 5 percent difference (between eight- and 12-hour shift workers) will likely translate into reduced productivity, especially in physically demanding environments.

Also consider the work force age. As people near 60, strength and endurance decrease while the rate of fatigue increases. The average age of many work forces is approaching 50. Generally , 12-hour shifts for the aging work force is not good. Older workers tend to have increased sleep and digestive concerns when coping with shift work. This could translate into productivity and quality problems as well as quality-of-life issues.

The 12-hour shift option should be considered carefully. There are many potential downsides to evaluate. Another good NIOSH reference to review concerning shift work is "Plain Language about  Shiftwork" (Document DHHS No. 97-145). A free version can be obtained at  www.cdc.gov/niosh/topics/workschedules. 

W. Tim McGlothlin, C.P.E. 


Sit or stand?

A: The decision to have workers sit or stand should take into account process design and impact on fatigue. For highly repetitive light assembly, it depends on whether assemblers move to the work pieces or if the work pieces move to assemblers. From a lean perspective, look for ways to sequence activities in a work cell. In this case, more flexibility is possible with a standing operation: Assemblers can cover multiple assembly stations as work pieces move.If the assembly is more finely divided into smaller tasks and work pieces come to assemblers, seated work may make more sense.

In all cases, it is good to build periodic large muscle movement, such as walking, into the job. Standing or sitting in one place can cause cramping and sore muscles. Provide opportunities for assemblers to get up and restock parts periodically. It may also be good to rotate positions on the line periodically to avoid repetitive motion injuries. Rotating up to four times per day allows workers to get up to speed on the job quickly and remain productive while still providing relief. If workers are rotated more frequently than that, expect a drop in productivity.

There are some good antifatigue mats on the market and some bad ones.Don’t skimp on quality:Choose one that is about an inch thick with beveled edges.

Also consider workers’ posture, putting them in situations where stooping and twisting are avoided.Bench height should allow for assembly using arms and small muscle movements in a comfortable,neutral position. If the job is monotonous, provide opportunities for mental breaks to avoid fatigue. Avoid eye strain if the job requires fine detail or computer work by offering opportunities to look away or otherwise rest.

The bottom line is that either sitting or standing can be fatiguing ...or not. It is far more important to consider the overall job design and ergonomics. If the job design fits sitting, I would contend that it is less fatiguing.

Marc Resnick may be able to provide some additional information from an ergonomics perspective.

Greg Hart 


Ergo processes

A: Anyone serious about developing an ergonomics process in a company should model it around OSHA's recommendations. While there's currently no federal standard governing ergonomics, that may not always be the case. By following OSHA's suggestions, your company will be better positioned against potential general-duty citation. It will also be better able to grandfather its ergo process if a standard is ever mandated.

The OSHA ergonomics Web site at www.osha.gov/SLTC/ergonomics/index.htmlis loaded with good information. OSHA's Ergonomics Program Management Guidelines for Meatpacking Plants (www.osha.gov/Publications/osha3123.pdf) is the guide many non-meatpacking companies use to develop successful proactive ergonomic processes.

W. Tim McGlothlin, C.P.E. 


Sizing up text

A: Human Factors in Engineering and Design by Mark Sanders and Ernest McCormick addresses this subject (specifically, in Chapter 4).

For appropriate text height, you must consider the stroke width of the character, visual acuity of the subject population, and illumination of the room. The book supplies an equation.

W. Tim McGlothlin, C.P.E. 

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