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When it Hurts to Haul

Summarizing an ergonomic study of solid waste collection.

Municipal solid waste collection is an important task that is required all around the world; yet it is associated with occupational injuries due to ergonomic risk factors including lifting, heavy load handling, awkward postures, long task durations and high levels of repetition. A research project titled “An Ergonomic Study of Solid Waste Collection” is being conducted by researchers in the departments of Industrial Engineering and Management Systems and Civil, Environmental and Construction Engineering at the University of Central Florida. This research, funded by the Environmental Research and Education Foundation (EREF), is a comprehensive ergonomic study of different types of collection, including manual, semi-automated and automated.

The inherent ergonomic risk factors associated with manual waste collection often result in occupational injuries. These injuries not only have a negative effect on workers but also on the companies that employ them. The industry lacks a comprehensive study that assesses and compares the ergonomic and biomechanical issues associated with the different types of waste collection.

The results of the study will provide insights to enhance the workers’ safety and productivity by decreasing the injuries in the industry and reducing the compensation costs and the labor requirements associated with waste collection. Additionally, the study should help justify the investment in automated equipment.

The research team conducted observational analysis, site visits and laboratory analysis in addition to a detailed review of historical data. Furthermore, solid waste collectors and safety personnel were surveyed to better understand the factors affecting the safety of collection workers.

The research showed workers were careless and unconcerned with following the proper safety techniques during waste collection even though 57 percent of the participants stated that they receive safety training on monthly basis and another 23 percent on a quarterly basis. For example, workers were observed riding on the running step of the truck collecting waste from both sides of the street, which creates an impact hazard with other vehicles. Many workers used the wrong techniques in lifting or dumping containers, putting their bodies in awkward postures. Collection workers need reminders to improve their awareness and to ensure that they use safe handling and lifting techniques. Also, safety personnel need to observe workers periodically to address early signs of occupational disorders.

The survey also revealed that the type of waste truck used plays a major role in occupational injuries: 64 percent of the workers were using manual trucks, 29 percent fully automated trucks and 7 percent semi-automated trucks. In the interviews, the majority of the waste collectors stated that they prefer automated trucks since they are not required to manually lift the waste container.

Constant repetition of tasks, long work duration and frequent lifting of heavy loads are significant factors that could result in chronic injuries. Of the workers surveyed, 63 percent reported that the number of collection stops on their average daily route exceeded 800. Also, 54 percent estimated that the average container on their routes weighs between 40 - 62 pounds (18 - 28 kilograms). Of those surveyed, 69 percent said they work more than eight hours per day, while 31 percent work eight hours or less.

The survey also included questions related to musculoskeletal injuries; the lower back was the most affected body part, due to torso twisting and heavy lifting of waste containers, which exposes the spine to compression forces and causes low back pain. Forearms, upper arms and upper back were the next body parts that were most frequently affected by injuries and pain. It was noticed that during lifting or dumping the container, waste collectors were working with hands above the shoulders, which represents a risk factor for musculoskeletal disorders.

The research team used ergonomic software as an aid in the evaluation of the physical demands of the waste collection tasks. The 3D Static Strength Prediction Program (3DSSPP), developed by the University of Michigan, helps in specifying the body parts that are most prone to injury from observed activities. According to the analyses, collecting waste using semi-automated vehicles places less force on the body joints than manual operation since pulling or pushing requires exerting force backward or forward rather than lifting the waste container. Perhaps unsurprisingly, the task of dumping a container was the riskiest due to the way the worker lifts. The low back compression force is calculated as 3491 N, which exceeds the National Institute for Occupational Safety and Health (NIOSH) Back Compression Design Limit of 3400 N. Workers should also minimize twisting of the upper body while dumping the waste container to avoid awkward postures of the body joints and reducing the lifting capability.

Another ergonomic tool used by the research team was the Rapid Entire Body Assessment (REBA). It estimates risks of work performance musculoskeletal disorders by giving a fast, systematic and effective assessment of full-body postural risks. Lifting and dumping tasks got higher REBA scores (meaning higher risk) as compared to pushing and pulling tasks. Overall, the dumping task logged the highest score due to the unstable postures adopted by the workers while performing the task. The lifting and dumping tasks were evaluated at an action level of “very high,” which requires immediate action, while the pushing and pulling scores were “high,” warranting action in the near future.

Going forward, this study will be expanded by using more ergonomic tools to conduct more in-depth biomechanical analysis for greater insight into the ergonomic risks of waste collection tasks. It is hoped that this additional analysis will generate ergonomics-based guidelines for enhancing task performance, safety and productivity in the waste management industry.

Pamela McCauley Bush, Ph.D., is an associate professor in the Department of Industrial Engineering at the University of Central Florida and is director of the department’s ergonomics laboratory. Debra Reinhart, Ph.D., is a Pegasus Professor in the Civil, Environmental and Construction Engineering Department at the University of Central Florida. Fatina Gammoh is a recent alumna of the Industrial Engineering Department at the University of Central Florida. Mousa Maimoun is a full-time Ph.D. student in the Environmental Engineering Department at the University of Central Florida.

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