Tag: safety

Ergonomic Wheel Design Improves Productivity

In our last post we talked about the importance of wheel design in reducing friction. But why is that important? The answer is that any design element that decreases the force that must be exerted by the operator to manipulate a piece of equipment increases efficiency and decreases the risk of potential injury. The result is greater productivity. This is the goal of ergonomic design both in the design of equipment and the environment in which it will be used.

When a wheeled piece of equipment is used, the operator must first overcome inertia and friction. The initial force necessary to start an object in motion is far greater than the sustained force necessary to keep it moving. Once in motion, optimum sustained, or rolling, force is achieved when a steady, constant velocity is achieved. Any need to decrease or increase velocity requires increased force to combat inertia. This is particularly noticeable during turning and maneuvering when significant force must be applied to change direction. Stopping a piece of wheeled equipment requires the same high level of force as starting it. As when accelerating, the operator must overcome high levels of inertia and friction to decelerate.

The four physical elements required to move a piece of wheeled equipment — starting, rolling, turning and stopping — can place tremendous stress on the operator’s musculoskeletal system. If performing these tasks manually, workers frequently overexert and strain muscles while applying the necessary force to start or stop a piece of equipment. Turning and positioning equipment can cause operators to assume asymmetric body postures during exertion which can cause musculoskeletal injury.

Ergonomically designed carts and tugs seek to achieve the optimal wheel size, type, placement and composition to decrease the force an operator must exert to move a piece of equipment.

Pushing vs Pulling Manual Carts

Pushing and pulling are the two most frequent actions workers execute in the course of doing their jobs. So in maneuvering manual carts, which is easier for the worker and creates less risk of injury — pushing or pulling?

Experts say pushing is preferable to pulling for a number of reasons. Research has demonstrated that people are able to exert higher push forces than pull forces. Given that horizontal push force, not the weight of the load or equipment, is the most significant factor in determining the effort required to move a load, that’s a significant consideration in selecting equipment.

Think of what happens to the body when you push something. Your entire body is used to create push force. In pushing an object, your body is more centered which allows you to concentrate force. Limbs are generally held closer to the body, limiting the possibility of extension injuries.

Pulling on the other hand, creates tremendous stress on individual body parts. When you pull an object and you are facing the direction of travel, one arm is stretched behind your body. This places the shoulder and back in awkward postures, increasing the potential for painful injury through overextension or awkward twisting. If you use two hands to pull an object you must have your back to the direction of travel. Walking backwards without a clear view of your path is an invitation to an accident. On an incline momentum can increase unexpectedly and the cart can careen into the worker or “run over” his feet.

There are times when pulling is the only way to maneuver a manual cart into the proper position, but at all other times pulling should be avoided. Pushing is the safer, more ergonomic way to move a manual cart.

Handhold Design Can Improve Worker Efficiency

Most carts have handholds of one sort or another. Handles are such an ordinary part of everyday equipment that it’s easy to ignore their importance in efficient equipment use. But handholds are the link between the operator and the load. Handholds cue the operator on how much force to exert and where to apply it most effectively to move the load. Handhold placement and design on carts can increase or decrease the ease and efficiency with which a worker moves a load.

In evaluating the usefulness of a cart, consider these important elements of handhold design:

  • Handhold Height. Handhold height defines the operator’s posture, and posture determines the amount of force a person is able to generate when moving a cart. Given the difference in human size, no single handhold height will be optimal for all workers. Handholds that cause operators to bend or stoop can lead to musculoskeletal injuries. When handholds are located at the proper height for an individual’s body, he is able to exert maximum force without straining his body. An adjustable handhold system will accommodate workers of various sizes. Other solutions include a continuous vertical handhold system that can be grasped at any point along its length or a series of handholds at varying heights.
  • Handhold Width. Handholds should allow the operator to grip the cart near its outer edge to provide maximum leverage for turning and positioning. However it’s important that hands, fingers or arms not protrude beyond the side of the cart to prevent crushing injuries should the cart come in contact with a wall or other equipment.
  • Handhold Type. The type of handhold can dramatically affect the amount of force an operator is able to exert when maneuvering a cart. Poor coupling, the contact between hands and equipment, can decrease the force an operator can exert by 65%. Handhold shape should not concentrate pressure on any specific area of the hand. There should be no sharp edges or pronounced ridges. Both the palm of the hand and the fingers should be able to contact the handhold which should be wide enough to accommodate the entire hand.
    Note: Pulling tasks require a handhold that can be gripped with the fingers wrapping around the handle. Pushing tasks need only a good surface that provides stable hand/equipment coupling.

Ergonomics Can Significantly Decrease Worker Injuries

Material handlers and laborers suffer more injuries and illnesses than construction workers, truck drivers or, indeed, any other category of workers, according to the U.S. Department of Labor. Material handlers and laborers miss more work days and therefore cost U.S. businesses more money in lost man-hours and higher insurance and healthcare costs than any other worker class.

Numerous studies have proved that ergonomically-designed equipment and systems can significantly decrease worker injury. Many manual tasks necessary during the handling of materials require repetitive motions — pushing, pulling, bending, lifting and carrying — that place undue strain on the human body. These actions can result in sprains, strains, back pain and other musculoskeletal injuries. Back pain is by far the most commonly reported workplace injury in the material handling industry. Treatment is generally lengthy and expensive, gobbling up the lion’s share of healthcare and workers’ compensation costs.

The implementation of an ergonomics program can significantly reduce injuries and their associated costs while improving productivity and worker morale. The Material Handling Industry of America (MHIA) has published a 68-page booklet of tips for improving ergonomics in the material handling industry. Click this link to download MHIA’s free Ergonomic Guidelines for Manual Material Handling. For more information on ergonomically-designed electric and motorized carts, pushers and tuggers, visit the DJ Products website.

Next time we’ll share some of MHIA’s best tips for improving ergonomics in the material handling industry and reducing worker injury and its associated costs.