Evaluation and management of workers’ musculoskeletal injury risks during handling/installation of the driver car seat in Iran-Khodro industrial group

Low back and musculoskeletal injuries are prevalent and costly especially among workers performing manual material handling (MMH) activities. To manage risk of injury, first, one needs to quantify spine loads during the MMH activity under consideration and then, design effective prevention programs. Installing driver car seat in Iran-Khodro industrial group is a physically heavy and cyclic MMH activity that generates large loads on the worker’s spine and therefore needs to be assessed and redesigned. This study uses various quantitative and qualitative lifting analysis tools to assess this activity and subsequently provide affordable engineering interventions to reduce risk of injury. Spinal loads including L4-L5 disc compressive loads and L5-S1 shear loads were evaluated using various quantitative (musculoskeletal biomechanical) tools/models (3DSSPP, Anybody, and predictive equations). As the job had a cyclic nature (22 seats per hour and 8 hours per day), various qualitative tools were also employed to assess the risk of injury (RULA, REBA, NIOSH, WISHA, MAC, V3, and MatTra). Motion analysis was performed on the worker in the workstation to determine body posture during this MMH task. Worker’s posture, weight of the seat (~16 kg), and position of the seat with respect to body were the most important inputs in the foregoing assessment tools. Results of the biomechanical analyses indicated that the task caused L4-L5 compressive and shear loads beyond the recommended safe limits (3400 N for disc compression and 1000 N for shear loads). Further qualitative analysis using the foregoing qualitative tools confirmed the high risk of injury during this MMH activity. The main reason for such high risk injuries to the spine was found to be the large trunk flexion of the worker when installing the seat inside the car. To manage the risk of injury, it is recommended that this MMH activity be eliminated using manipulators. As the workspace did not allow for the installation of such manipulators, the worker’s working height was lowered so to reduce trunk flexion angle. Reassessment of the job after this intervention indicated that spinal loads remained below recommended safe limits and risk of injury considerably reduced.