September 5, 2008
When my company gets called into a workplace to conduct an ergonomic-related evaluation, there is generally one of two possible thoughts running through the facility manager’s mind. He may see ergonomics as a great way to reduce the costs associated with injury, or he may only see the upfront costs.
But the truth is, both of these points of view miss the boat on modern practices of ergonomics. It is true that a good ergonomics program, or even a thorough walkthrough once in a while, will reap rewards in lower injury-related costs, often with triple-digit ROI and six-month payback periods. But there are bigger benefits under the surface when ergonomics is integrated into the job design process.
Ergonomics is a great partner for lean process design and Six Sigma®* programs. Popular ergonomics tools, long used to reduce injury risk, can also be used to make jobs more efficient and more effective. How is this magic achieved? The first step is to examine the basic relationship between physical exertion and performance.
Price of physical exertions
Physical exertion can range from moving the body (walking, bending, standing, repeated arm movements, etc.) to moving objects (lifting, carrying, pushing, manipulating). In order to complete the physical exertion, the body recruits muscles in a quantity proportional to the perceived effort. The more physically demanding the task appears, the more muscle fibers will be recruited. If the exertion is done repeatedly, the body will adjust based on learning more details about the task requirements or compensating for fatigue.
When the body is fatigued, it has trouble recruiting muscles in a coordinated way. This can increase the chance that not enough muscles will be recruited to complete the exertion and result in an overexertion injury. It can also result in lack of motor coordination, leading to many types of errors. The physical discomfort of fatigue may also encourage the worker to use suboptimal methods to complete the task, either reducing productivity or leading to even higher overexertion injury risk. Some kinds of repeated exertions can increase the risk of cumulative trauma injuries such as carpal tunnel syndrome or chronic low back pain. Even when these conditions are minor, the discomfort may lead to even more suboptimal work methods.
Physical exertion can lead to OSHA recordable injuries with the associated workers’ comp and human resource costs. But it can also lead to an increased error rate, reduced productivity, and lower worker morale. These factors increase labor costs, raise product and service defect rates and rework requirements, and decrease customer service.
Lean job designs
Typically, ergonomics is perceived as a discipline that reduces injury risk. But the same tools can be integrated in the job design process along with lean process design and Six Sigma programs. The results are lean job designs that optimize productivity, quality, and safety.
For example, the Standard Posture Classification System is an ergonomic tool that is designed to tabulate extreme postures at each joint over multiple work cycles. It is generally used to evaluate jobs that allow variability in the postures workers can use to accomplish the various task components. It can be customized to focus only on the joints that have significant movement, such as the back for lifting or the shoulders for reaching. It can also be customized for any definition of an “extreme” posture. The traditional ergonomic objective of the tool is to identify task components where workers are using extreme postures and either redesign the layout so that these postures are not needed or train the worker to use a safer method.
Shoulder posture “all over the map”
A biomedical products manufacturer had a workstation that required a worker to do some coordinated assembly procedures on delicate medical devices that were delivered on a rack with four shelf heights. The task cycle required ten elements to be repeated once every two to three minutes. The SPCS results showed that when doing element five, the worker bent her back to an extreme degree in order to access the lowest shelf height. It also showed that the worker’s shoulder postures for element eight were all over the map: sometimes elevated, sometimes abducted and sometimes neutral.
What do we do with this information?
For element five, we used the bad posture as the driver to initiate a lean-process improvement project. By reducing the work in process inventory required at that workstation, we eliminated the need for the low shelf position. This led to a significant reduction in inventory cost and an increase in throughput for the entire line, in addition to reducing the risk of a back injury. For element eight, we applied the Six Sigma approach to identify the cause of the variation, which turned out to be due to an inconsistent method being used by the upstream workstation to orient the workpiece in the rack. The upstream workers were instructed to place the workpiece in the orientation that allowed the worker at this station to use a neutral shoulder posture every time. Not only did this make the job easier at this workstation, but it also reduced variability at several downstream workstations. This increased throughput for the line still further.
Many safety professionals are constantly challenged to provide evidence of the ROI of their activities. In some cases, reducing injury costs is sufficient. In others it is not, either because injury rates are low or because of idiosyncrasies in the organization’s accounting. But when safety practices are integrated into other process improvement programs, such as lean and Six Sigma, the leverage allows productivity, quality, and safety to be improved together. The SPCS is just one tool that can be used in this way. Every safety professional should look inside his or her toolkit to identify others.
Keyserling W.M. (1986). Postural Analysis of the Trunk and Shoulders in Simulated Real Time. Ergonomics, 29, 4, 569-583.
* ®Six Sigma is a registered trademark and service mark of Motorola, Inc.