By Dave Lippert, Contributor
The emphasis on ergonomics in the workplace has never been greater. Motivating this are at least two factors: demographics and cost. The U.S. workforce is getting older and heavier, two significant challenges to physically demanding jobs in the industrial workplace. Since older and heavier workers are generally less fit, they are more prone to injury and likely to be out longer to recover if they are injured. From a cost standpoint, besides the obvious health care costs (workers’ compensation) there are many additional costs associated with finding and training replacement workers.
How can we protect our workers? One way is to provide tools and conditions that reduce the likelihood of injury. When it comes to manually moving things in the workplace, wheels are the predominant. Most people mistakenly think that any round wheel will do. Without delving too deeply into the physics of wheels, let’s consider how prudent wheel selection is for workers.
Selection The Right Wheel
Larger (diameter) wheels roll more easily than smaller ones (there’s the physics!) Within a certain wheel type, larger wheels normally have higher load capacity, too. That can create a dilemma for the one responsible for purchasing the wheels. If a 5in diameter wheel (set of four) will more than carry the required load, why buy larger wheels? It is a fair question, and one that has a good ergonomic answer.
Let’s say the 5in diameter wheels cited above have more than ample capacity for the maximum load. But consider that the force required to move a full load on those wheels may be excessive. It is entirely possible that workers’ health could be in danger with wheels that were purchased to fit the load being carried (but not the push required to move it.)
What is an acceptable pushing (or pulling) force? It is another great question, and one that doesn’t have a “right” answer. Ergonomists have worked on this for decades and have not come up with a simple number. Instead, there are guidelines such as the Liberty Mutual Manual Material Handling tables. Developed in the late 1970s, these tables consider factors including men or women doing the pushing, handle height of the cart being pushed, distance being pushed and frequency. The chart guidelines suggest using the criteria of 75% of women can push the load with minimal likelihood of injury. Fortunately for those looking for specific numbers, that will provide them. There are numbers for an initial push or pull (moving the loaded cart from a dead stop) and maintaining the push or pull once it is moving.
Another resource based on newer technology was developed by researchers at The Ohio State University Spine Research Institute. Extensive research looking at lumbar spine forces led to a very simple and useful tool published on the Ohio Bureau of Workers’ Compensation website. Using the tool provides a relatively simple green/yellow/red answer for a given push or pull. A challenge is that one must know the actual push/pull force, or at least guess some “trial” forces to find one that is acceptable (green result).
Armed with an acceptable force or two (initial and sustained pushes), gained either through use of the Liberty Mutual tables or the Ohio Bureau of Workers’ Compensation website, one can use these numbers to select acceptable wheels. Industry data is available that, based on extensive testing, describes the performance of wheels under various loads. Check with leading industrial caster and wheel manufacturers to find this data.
An ergonomically acceptable wheel may have far more load capacity than the job requires! It may have a larger diameter, or it may be comprised of more expensive materials (such as polyurethane.) It is likely that there will be multiple options, varying in size, type and cost, to safely move the load. The best news is that, from the workers’ perspective, any of the available “ergonomically correct” choices will be safe to use.
As one seeks to narrow the choices, other criteria may be helpful. Noise, for example. Extremely hard wheels, those made of steel, cast iron, plastic or nylon roll very easily but are also very noisy. Excessive noise is actually another type of ergonomic problem! Use the manufacturers’ data to gauge the anticipated noise level of certain wheel materials.
Frequently the question of wheel bearings comes up. Testing indicates that most antifriction bearings, regardless of type, have very similar push/pull outcomes. The wheel material and diameter are the dominant factors. That said, a wheel without an antifriction bearing will be considerably more difficult to push.
Wheels do matter, and the industrial market offers a slew of choices. Armed with new information about wheel performance under load and acceptable push/pull forces from an ergonomic viewpoint, we can reduce the likelihood of injuries in the workplace. That is good news for both the workers and the finance department! WMHS
Dave Lippert has worked in the industry since 1982 and has served as President of Hamilton Caster since 1995. Hamilton Caster is a family-owned and managed manufacturing company located in Hamilton, OH. In business since 1907, the company designs and makes industrial wheels and casters for industry, and produces industrial carts and trailers (www.hamiltoncaster.com).