Elements of Ergonomics Programs A Primer Based on Workplace Evaluations of Musculoskeletal Disorders

The site was a plant that produced window balance systems. The product was made from either stamped, roll-formed aluminum or extruded vinyl. Both metal fabrication and extrusion operations were performed at the plant. All 12 jobs in the assembly department were targeted for analyses on the basis of earlier State inspection reports describing conditions associated with the development of carpal tunnel syndrome. These jobs were observed in a plant walk-through and videotaped for later analyses. Information was collected concerning the number of employees engaged, the task elements, the number of pieces assembled per work shift, the tools used, the difficulties workers perceived in the job, and worker suggestions for improvements. Measurements were also taken of work surface heights (both worktable and conveyor). A review of the videotape in real time and slow motion yielded data on repetitiveness of movements, awkward hand/wrist and shoulder postures, and indicators of muscular force requirements. The task cycle times were derived from these observations, along with the number of hand/wrist motions (flexion, extension, ulnar and radial deviation, pinching) and the number of unnatural shoulder positions. Particularly extreme postures were noted in the videotape analyses as one means for rating muscular force exerted. Other bases for rating force were the number of forceful manipulations in a given job cycle, the size and type of tool used, and the weight of the product handled.

Jobs were rated for ergonomic stress to prioritize interventions needed to eliminate the stress. The job ratings were determined by combining the observed level of repetitiveness or movements per day with the level of force. Three levels of repetitiveness were defined and assigned values. A value of "1" was given for jobs with low (fewer than 10,000) movements per day, "2" for jobs with medium (10,000–20,000) movements per day, or "3" for high (more than 20,000) movements per day. Average and peak levels of force were also judged by the investigators and given ratings of "1" or "2" (low force), "3" (medium force), or "4" or "5" (high force).

The total stress score for each job was determined by adding the assigned values for the repetition and force. Two jobs (pulling springs to attach them to window liners and hooking springs into window liners) were found to represent the greatest musculoskeletal stress when rated in this way. However, all of the assembly jobs were found to pose problems requiring ergonomic hazard control actions [HETA 88–361–2091].