These three common mistakes, when not accounted for, will increase manufacturing costs, develop operational inefficiencies, destroy on-time deliveries and lead to poor process performance capabilities. Specifically, with ergonomic design, even the best intentions of creating a safer work task or environment can lead to an unwanted outcome to our “Y.” (Otherwise known as an output, effect, symptom or dependant variable).
Along with developing and implementing ergonomic recommendations, safety professionals should have to perform an oath. Please raise your right hand and repeat after me: “When correcting any hazard associated with my ‘Y,’ I shall not create or negatively impact another ‘Y.’” For example, you determine that there is a significant biomechanical hazard after conducting an ergonomic assessment. To eliminate that risk factor, you implement a new strategy or tool.
This process change must not create additional negative outcomes to occur within your process. This is most true if you want to maintain credibility in your injury prevention methodology. Unfortunately, it is very common for safety managers to look at a job task with blinders on and only focus on what they want to correct and not the entire picture of the process.
The most common undesirable outcome (Y) from an ergonomic change is in the form of diminished throughput or time. It is understandable that there are some instances that an ergonomic recommendation may slow a process down and decrease throughput for the sake of safety, but if that is not the desired intent, it most definitely must not be negatively affected.
In this article, I will discuss the three most common mistakes in ergonomic job designing that lead to diminished throughput or time. For consistency in explaining these mistakes, I will refer to a linear three step work cell process where each step requires on average 10 minutes to complete with a total average cycle time of 30 minutes.
MISTAKE #1 — INCREASING AVERAGE CYCLE TIME WITHIN A STEP
Cycle time is referred to as the amount of time it takes to make one unit from the beginning to the end of a physical process. Implementing any ergonomic recommendation where time or throughput is essential should not increase the average cycle time of a particular process. Quite simply, if an ergonomic recommendation increases the average cycle time of our three-step process example from 30 minutes to 35 minutes, your throughput will decline. This is assuming that slowing the process down does not positively impact your percent defective metric.
Many years ago, I consulted for a company that had a similar linear work cell process as in the example mentioned above, where their workers were lifting and carrying a 50-pound part a total 5 feet between each manufacturing step.
Prior to my guidance, they attempted to resolve the ergonomic risk factor by installing hoists between each manufacturing step. Their concept was to eliminate the need for their workers to lift and carry the heavy product. Although this did eliminate any lifting and carrying risk, a throughput “Y” was negatively affected. Their hoist recommendation added approximately 5 minutes to the average cycle time and decreased the throughput. A roller table would have been one of many appropriate choices to eliminate the lifting and carrying risk while not negatively affecting the throughput.
A great concept in increasing throughput is to avoid performing tasks in a linear or sequential fashion all together. Careful process design allows some tasks from a sequential system to be performed in parallel. In other words, while the first step is being completed, the third step also can be completed.
MISTAKE #2 — INCREASING WITHIN STEP VARIATION
Any normal process will have some degree of variability within it. Understanding a process's throughput or cycle time means that you understand the average time it takes to complete a step (mean), the standard amount of deviation from that mean (standard deviation) and the distribution of your data.
For example, if the first step in our three-step linear work cell process takes 10 minutes to complete and has a standard deviation of 2 minutes, 99.7 percent of the time the worker will complete the step between 4 minutes and 16 minutes. In a normal process, 99.7 percent of all your data will fall between +/- 3 standard deviations from the mean.
Time variability is a critical process parameter and must be kept to a minimum and controlled. Increasing the variability of time within a step will make a process less stable and less controlled, and could result in an increase in inventory, work in process (WIP) or longer lead times to the customer.
In the three-step linear work cell example, all three steps take an average of 10 minutes to complete. Imagine that originally all three steps had a standard deviation of 1 minute, so that for 99.7 percent of the time, each step will be completed between 7 minutes and 13 minutes.
Now, an ergonomic recommendation at the second step has increased the standard deviation at that step to 2 minutes and the first and third step remain at 1 minute. Now the second step will be completed between 4 minutes and 16 minutes. This will create significant inefficiency because the workers at the second step either are waiting for product or will have a surplus of product waiting for them to complete.
Equally, step three will feel the same effect as the second step. When making ergonomic recommendations, consideration of time or process throughput is essential. Attention must be focused to the step variation of the entire process.
Any ergonomic recommendations should focus on minimizing the variability in all the steps to achieve greater throughputs while minimizing biomechanical risks. Understanding all the different causes of variation in a process and designing standardized approaches in each step will increase throughput as well as make it easier to audit and provide signals when a process is starting to lose control. Failure to do so may result in a chaotic process.
MISTAKE #3 — INCREASING STEP-TO-STEP VARIATION
As there is time variability within each individual step of a process, the third common mistake related to ergonomic recommendations is increasing time variation between steps. For example, I was consulting in a manufacturing facility several years ago and they decided to add several additional tasks to their second-step linear multi-step process.
They decided at the second step to add 10 additional rivets and apply several stickers of the company logo on the product. The rationale was to share and reduce biomechanical wrist stresses placed on one work task all day. This new process of adding stickers and rivets assisted in reducing the biomechanical risks of an injury, but making that change dramatically lengthened the average time to complete their second task.
Originally, it took each step of their six-step linear process an average of 5 minutes to complete the tasks for a total average cycle time of 30 minutes. Now, due to the additional tasks added to the second step, it took an average of 17 minutes to complete the second step for a total average cycle time of 42 minutes.
It was very clear they created a bottleneck in their process as their throughput decreased quicker than the stock market's volume. A manufacturing bottleneck, sometimes called a capacity constraint resource, is where the available capacity of a process cannot meet the product volume demand. In this manufacturing example, the first step was sending the second step a product on average every 5 minutes. The product piled up and the second step was not able to keep up. The result was that work in process (WIP) increased in front of the second step and the third step was consistently waiting for product from the second step. The biomechanical risks were lessened, but they created a system of perfect inefficiency, much like the Detroit Lions of 2008.
It is critical to understand that any overall process only will perform as fast as the bottleneck. Bottlenecks, however, are inherent in every multi-step process performed. A drive home in rush hour is a good example. The demand to get home while driving the speed limit is greater than the capacity of the roads. If time or throughput is essential, bottlenecks must be identified and resolved quickly, and should not be created as a result of ergonomic recommendations.
Effective ergonomic job recommendations and design must take into account these common errors if throughput or time are critical components in the process. There are many different ways to design away from an ergonomic risk factor, but the most effective recommendations are the ones that increase throughput while eliminating the biomechanical risk.
In order to do that, you must understand, identify and eliminate these common mistakes. Creating a passion and strong safety culture within an organization can be tough enough without negative process impacts. So when you lead your organization down the road to safety, avoid these mistakes and don't be road kill!
Ken Vandenberghe, CIPS, OTR/L, CEES, MBA, is the corporate health and safety manager at Rea Magnet Wire, named one of America's Safest Companies by EHS Today in 2008. He is responsible for facilities throughout the United States, Mexico and China. Vandenberghe is a certified infrastructure preparedness specialist (Department of Homeland Security), certified ergonomic specialist and occupational therapist. He graduated from Wayne State University, completed residency at Princeton University Medical School and completed his Masters in Executive Business and Administration from Indiana Wesleyan University. In the last 5 years, under Vandenberghe's guidance, Rea Magnet Wire has reduced its injury rates by 94 percent and worker's compensation exposure by over 3.3 million.