Revolutionizing Roll: Re-Evaluating Push/Pull Testing in Caster Ergonomics

In the realm of ergonomics and workplace safety, the methods by which we analyze risk are instrumental in lowering injury rates. It is typical to assess the worst-case scenario the worker will have to undertake and improve from there; this is typically when peak force is produced. Sometimes this can be obvious, like an awkward posture or lifting heavy equipment. But in terms of push/pull testing, that “worst case” or peak force can be less clear. Most practitioners would say it’s the initial force; the force required to overcome inertia. Which might not be wrong. But did you check to see which way your casters were facing? Assuming they will always be facing forward is a big stretch and not one we choose to do at Darcor. We advocate for testing that includes when the casters are perpendicular to the direction of travel, defined as swivel force. Swivel force is where practitioners will find this peak force or worst-case scenario. Let’s dive into why you should test your casters for swivel force, beginning with the subjectivity in testing.

The Subjectivity in Push/Pull Testing

Imagine two ergonomists, equally skilled and experienced, using the same force gauge for a push/pull assessment. You’d expect identical results, right? Surprisingly, that’s not always the case. This discrepancy has been observed in tools like the modified RULA (Rimando et al., 2019). The subjectivity is further highlighted when assessing initial and sustained forces, and other well-defined terms in the field.

The Misconception of Initial Force

Initial force refers to the amount of force needed to overcome inertia, while sustained is the force required to maintain motion (ISO, 2007). It is well known that significant force is required to overcome inertia, thus many practitioners will base their recommendations on lowering this initial force, assuming it’s the worst scenario. However, this doesn’t consider the orientation of the casters before motion begins. Speaking from experience, several practitioners fail to consider caster orientation, or simply test the cart when the casters are in the direction of travel. In reality, consistently aligned casters don’t accurately represent task demands.

The Importance of Swivel Force – The True Peak Force

Peak force is a more valuable metric as it shows the maximum force exerted throughout the task. Concerning push force testing, peak force would be experienced during the initial force when the casters are perpendicular to the direction of travel, i.e. swivel force. Traditional testing protocols and push/pull analysis tools overlook this, leading to incomplete assessments and potentially unsafe recommendations. An example of this scenario would be if an ergonomist negated caster orientation or conducted tests exclusively with the casters aligned in the direction of travel. In such cases, the practitioners would emphasize the importance of ensuring that the task complies with relevant guidelines, being push forces pf 50lbs or less (Canadian Centre for Occupational Health and Safety, 2023). Moreover, recommendations will address this initial reading, but that is not the limiting factor. So, an improvement could be made but the peak forces were never identified or addressed, leaving room for risk.

The Need for Re-evaluation

It’s time to redefine push/pull testing to include caster orientation, finally capturing the peak force. By incorporating swivel forces into our standard testing procedures, we can provide higher-quality assessments that prioritize worker safety and well-being.

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