Moving raw materials and finished products through a facility is a common process in industry. Throughout the process, operators routinely lift/lower, push/pull and carry an object, which presents a significant challenge to health and safety professionals. When investigating manual material handling (MMH), health and safety professionals must determine the most practical ways to move objects while decreasing ergonomic risk and positively affecting production and cost.
Why Improve Manual Material Handling?
Recognizing the importance of proper manual material handling is a critical step in the job improvement process. There are many types of manual material handling tasks in industry, such as lifting raw materials and finished products, pushing carts and carrying boxes. These tasks represent a continuum of ergonomic exposure from low risk to high risk.
The most common body part affected by manual material handling is the back, which often suffers strains, sprains, herniated discs, joint inflammation and dislocation. The average cost of each low back injury is $24,000, as reported by the National Council on Compensation Insurance. Low back injuries cost American corporations billions of dollars each year in medical costs, re-training and lost production.
Determining Which Jobs to Improve
In order to make planned and practical MMH improvements in a facility, we must first quantify the exposure to ergonomic risk in a job by gathering three pieces of data:
- Previous musculoskeletal disorders
- Operator discomfort
- Ergonomic risk based on force, frequency, posture and duration
From this data, we can develop a prioritized task list (Table 1), which allows management to plan and budget for job improvements based on the amount of associated ergonomic risk. Other factors that help determine priority for improvement are the number of operators exposed to the MMH tasks, the number of shifts during which the tasks are performed and how often the tasks are completed (daily, weekly, semi-annually or annually).
Developing Practical Solutions: Some Considerations
Once we've determined which jobs involve the highest ergonomic risk, we can develop practical solutions to address those risks. Organizations typically look for inexpensive and easy solutions that mitigate the operator exposure to ergonomic risk. Important considerations when implementing practical material handling solutions are:
- Ergonomic risk reduction
- Number of operators affected
- Time line
- Ease of implementation
The most critical of these considerations is reducing the amount of ergonomic risk experienced by the operator. The prioritized task list helps determine the magnitude of the material handling challenge in the facility by quantifying the ergonomic risk by task. If there are numerous high-risk tasks, appropriate capital must be budgeted to make improvements. The health and safety professional must determine if all tasks will receive equal funding, or if funding will be targeted to certain high-risk tasks. Fund allocation should be based on tasks that are critical to production and the number of operators assigned. Evaluate all potential solutions based on the time and resources required to implement them. Experience shows organizations typically expect changes to be in place within 30 to 60 days, with limited staff involvement.
A Hierarchy of Controls
When developing solutions to ergonomic issues, there is an accepted hierarchy of controls: (1) engineering improvements, (2) administrative controls and (3) work practices modifications.
Engineering controls, such as changes to equipment or workstations, are the method of ergonomic risk reduction certified professional ergonomists prefer. Engineering controls provide an excellent opportunity to remove the source of ergonomic risk from a job.
Administrative controls are changes to task responsibilities that reduce exposure to ergonomic risk factors. These types of controls are dependent on good planning and require management or supervisor oversight. They do not eliminate ergonomic risk factors but may reduce risk exposures to an acceptable level.
Work practices modifications are changes to procedures and work methods that reduce exposure to ergonomic risk factors. These controls depend on individual work behaviors and require ongoing supervision, monitoring and correction by leaders. They do not eliminate ergonomic risk factors but may reduce some contributing factors.
Although engineering controls are the preferred method for risk reduction, there are pros and cons for each.
Although engineering controls may require higher initial expense and can be slower to implement, they remain the preferred method because they have the most significant impact on ergonomic risk.
There are a number of options to consider when implementing engineering controls including changes to workstation design, equipment and work flow.
Workstation Design Changes Changing the workstation design provides the best opportunity for improving material handling. For example, reduce the width of a conveyor with adjustable diverter bars to decrease operator reach when accessing materials. Design U-shaped workstations to minimize material handling and operator walking by reducing the overall work area and transfer distances.
Mechanical lifting systems such as vacuum lifts, hoists and articulating arms, are typically perceived as impractical solutions because of high cost, lengthy installation timelines and the potential to slow the operator. However, when these systems are developed with operator input and consideration for work flow, they can significantly reduce ergonomic risk, which helps justify the cost and installation time. If designed well, mechanical lift systems can move more than one part at a time, thereby improving operator efficiency.
Equipment Changes Making small changes to current equipment can reduce risk and may be less costly than purchasing new capital:
- Redesign carts with low-force casters and proper handle design and positioning (5.5-inches long and 1.5-inches diameter) to reduce push forces and ensure a neutral hand/wrist posture.
- Purchase boxes with cutouts from suppliers to improve hand postures when lifting/lowering from conveyors and onto pallets. Change the shape and orientation of boxes to bring the center of the load closer to the operator and reduce the amount of strain on the back.
- Minimize the weight of a load by marking limits on the totes to reduce overfilling, purchase smaller capacity totes, and incorporate a scale into the workstation to weigh totes and display load weights prior to lifting.
- Provide adjustable equipment and ensure that it is used. Adjustability can be incorporated into the design of the equipment. For example, install a height-adjustable cart rather than a fixed-height cart, or use load levelers to ensure the load is at approximately waist height when lifted. In addition, simply stacking product onto a pallet that is raised by two empty pallets can reduce repetitive bending.
Workflow Changes The flow of material throughout a work area can present its own set of material handling challenges. In many jobs, operators must move equipment, raw material or finished products within and between workstations. Retractable ball transfer tables, gravity chutes and conveyors can significantly reduce lifting. Flooring that is in good condition and properly maintained can decrease push/pull forces when operators move materials using carts. In addition, be sure that carts are equipped with low-force casters.
In combination with engineering controls, administrative controls can help control exposure to ergonomic risk. Administrative controls may include these simple methods:
Job rotation Rotate operators through less strenuous tasks to reduce the amount of risk exposure. Understanding the ergonomic risk associated with each operation can help management develop effective job rotation schedules, and rotate operators from high-risk operations to low-risk operations.
Rest breaks Provide operators with rest breaks throughout a shift that requires high-risk manual material handling tasks to decrease the exposure to the risk and to provide the body time to heal between the more demanding tasks.
Work Practices Modifications
When engineering controls are implemented, concurrent improvements to work practices ensure that employees understand the ergonomic benefit of the changes and promote proper use of the equipment. Work practices modifications may include the following:
Proper use of material handling aids and work procedures Train operators in the principles of ergonomics to allow them to understand the proper techniques to use when performing manual material handling tasks. For example, teach operators: to push carts rather than pull them; the proper function of manipulators, hoists and adjustable carts; the OHIO principle (Only Handle It Once); keeping the load close; proper lifting techniques; and when and how to use team lifts. Familiarity with these principles can reduce operator exposure to ergonomic risk.
Proper equipment positioning Teach employees to limit horizontal reaches, carrying distances, and box weights, dimensions and stacking heights.
After training employees in any work practice, it is important to develop a method to positively reinforce the practice. When operators learn a new work practice, it takes approximately 21 days to develop the new habit. Therefore, management and supervisors must actively work with operators to ensure the material handling aids are used, and used properly.
Manual material handling is a critical function in industry. Implementing practical improvements requires health and safety professionals to first develop a prioritized task list to focus their efforts on the tasks with the highest quantified ergonomic risk. Prioritization will ensure that the appropriate resources and sufficient time are available to improve the tasks. When developing practical ways to improve MMH tasks, first consider engineering controls that reduce ergonomic risk. Next, consider administrative and work practices controls to support the engineering solutions. Remember that the primary focus for implementing any solution for the improvement of MMH tasks is ergonomic risk reduction.
Woody Dwyer, CPE, is a managing consultant and ergonomics engineer for Humantech, Inc. and Christy Lotz is a recent graduate joining Humantech. Since 1979, Humantech has assisted companies throughout North America in successful ergonomics initiatives in a variety of workplace settings including production and assembly, offices and laboratories. Through a clear focus on low-cost workplace improvements that produce quantifiable savings, Humantech clients benefit from health and safety improvements and business results. For additional information related to successful ergonomics programs, visit Humantech's Web site, www.humantech.com.