What to Do When Ergonomics Design Criteria Fall into a Gray Area
Posted on April 6, 2022 | in Ergonomics
As more and more corporations establish continuous improvement processes in their production facilities to improve ergonomics and reduce musculoskeletal disorders, one thing has become clear: fixing poorly designed equipment and processes is expensive and not always practical. It’s significantly more cost effective to adjust workstations and equipment as they’re being designed on a computer screen, rather than after they’re built and installed.
While looking at a computer drawing, engineers can use ergonomic design guidelines to make sure a design won’t introduce new risk factors to the production floor, and if it does, change the design to eliminate or minimize the impact. This is an easy fix when dimensions or force estimates fall into the extremes of human capabilities, but what do you do when a measurement falls somewhere in the middle? A single data point isn’t enough information to determine the true risk to the future operator. This workstation now must be considered as a whole, to determine how many risk factors are connected with this task and see what can be changed in the design. To empower design engineers to make more of these decisions without waiting for consultation from an ergonomics specialist, here are a few decision points that can often help to provide a simple answer.
Step 1: Determine the Frequency
The frequency of an action can be calculated by using the cycle time of the related job (total part-to-part time at the station) and the number of occurrences of that specific action per cycle.
Understanding the prevalence of this action can, at the extremes, be enough to determine the level of risk factor exposure. But, when you have a short cycle time job (i.e., less than 1 minute) you want to pay attention to any risk factor exposure, because it will inherently be performed at a higher frequency than a job that has a much longer cycle time. For example, a moderate weight lifted every 30 seconds is automatically a high-frequency task, but if that same job had a 10-minute job cycle, then the number of occurrences is needed to determine acceptability. In the latter scenario, a frequency of once per 10-minute cycle is most likely acceptable, even if not ideal, whereas a frequency of 6 times per cycle is less clear and would push you on to step 2 in the evaluation.
Step 2: Connect to Related Movement
While step 1 can be applied to either a force or a physical dimension (horizontal or vertical position), this second step is when you need to evaluate the opposite dimension.
Continuing with the previous example, the focus of the evaluation was on lifting a questionable amount of weight. In this step, you need to investigate the physical dimensions of the object being lifted to understand body positioning during this task. Similarly, if the design element being evaluated is the action of a far reach, then you need to understand any forces being applied while in this extended position. The combination of posture, force, and frequency determines the risk (acceptability) of the design.
Step 3: Determine Combined Risk Level
Assessing musculoskeletal disorder (MSD) risk is all about combining the severity of a risk factor (i.e., weight of an object or length of a reach) with the associated body movement for a holistic analysis of the total risk exposure within a given task. Therefore, the final step of this evaluation is to combine the risk levels of every force with the risk levels of the associated body position to determine their combined risk. For instance, a force that is on the border of being high risk and performed infrequently with good body positioning introduces relatively low risk to the employee and does not necessitate an engineering design change. However, an extended-reach posture related to a high-force operation exposes that employee to an elevated level of overall risk, which requires a design change to either reduce that force or bring the task closer to the employee.
In some instances, the equipment or workstation force associated with an extended reach might also fall into a more moderate category (i.e., 10-15 lbs). In this case, the combination of these risk levels requires a more advanced and technical analysis by a professional ergonomist. Armed with this information, engineers can apply the logic of these 3 steps to decide when a design is acceptable, when a change is required to make the design safer, or when to request the support of an ergonomist for a more detailed evaluation.
As the market for the latest and greatest product pushes industries to invest in research and development while racing to sell each innovation, it’s critical that design engineers are provided with the right tools to make safe and effective designs. Most design processes that include a safety and/or ergonomics review are bulky and time consuming, calling for potentially multiple reviews of every design by a subject matter expert. This process—to submit all applicable information, wait for the results of the review, and complete any recommended changes before re-submitting the design for another review—can take up a lot of valuable time. In contrast, the steps presented above will empower engineers to logically determine the acceptability of their design and train them to understand which changes have the greatest impact on MSD risk levels, ultimately resulting in a more efficient continuous improvement process.