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Alternative ergonomic job analysis methods for manufacturing.
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R03-OH-004105, 2005 Mar; :1-38
This study focused on the development and evaluation of new exposure assessment strategies for non-cyclic as and cyclic manufacturing jobs. New methods for the evaluation of ergonomic problems in special trades work and self-paced assembly work within a forging plant were developed. A work-sampling based approach was used to evaluate the postural and manual material handling requirements of millwrights work. Over 8,000 observations were made on 8 workers taken over 8 days to allow an assessment of the between worker and between day variability of exposures for this occupation. For the self-paced manufacturing jobs, a video-based ergonomic job analysis method was used to estimate the frequency of awkward postures, manual materials handling, average cycle times, and estimated rest allowance for different muscle groups. One-hundred eight video recordings of approximately 10-15 cycles were made on three workers of two different occupations for up to 3 times per day on approximately 10 days to allow an assessment of inter-worker and inter-day variability of each of the ergonomic exposures. Analysis of variance was used to estimate the inter-worker and inter-day components of variability for both the skilled trades and self-paced manufacturing jobs. Bootstrapping, a statistical re-sampling method, was used to examine the reliability of different exposure assessment strategies so that recommendations could be made about the appropriate use of the alternative exposure assessment methods. The recommended strategies were then pilot tested on a third self-paced manufacturing job for which 45 videos were recorded to provide a preliminary assessment of the generalizability of the results. Key findings of the study included: 1. Exposure variability across workers of the same occupation was large among those included in this study. Therefore, epidemiologic studies that use occupation as a proxy for exposure estimation may result in significant random misclassification of exposure, at least for the types of occupations studied here. 2. Results of the analysis of variance for millwrights work demonstrated that the manual material handling requirements were fairly low, but the frequencies of awkward trunk, arm and leg postures were high and variable across workers and days. Bootstrapping analysis suggested that groups of workers should be sampled for multiple days (e.g., >6) for a reliable estimate of average exposure to awkward postures. 3. Results of the analysis of variance on the self-paced manufacturing jobs demonstrated that there was large variability among workers and over time for many of the ergonomics exposures. Assessment strategies used in research or practice that involve observing one individual for limited time periods are likely not to provide reliable estimates ergonomic exposures over the long term. 4. For both types of work studied, strategies required for the reliable estimate of exposure will differ across exposure variables since of the sources of exposure variability are not the same across exposure variables. For example, for the self-paced manufacturing work, the contribution of inter-worker variability tended to be higher for the estimation of required rest allowance for different muscle groups than for exposure to trunk flexion or repetition for the self-paced manufacturing jobs. As a result, more workers may be needed for a reliable estimate of required rest allowance than for the other exposure variables considered in this study. 5. For self-paced manufacturing work, the collection and analysis of at least 3 different videos recordings of at least 10 cycles taken on different days and on different workers was recommended as the most efficient (I.e., fewest videos for a reliable assessment of exposure) among those strategies tested in this study. This finding was supported in the analysis of the third self-paced manufacturing jobs. Attempts to find associations between the exposure data collected in this study and health outcome data (i.e., injury rates and muscular discomfort) were unsuccessful due limitations in statistical power (exposure measurements were only available for only a few occupations) and due to poor quality of the forging plant's health surveillance data.
Statistical-analysis; Human-factors-engineering; Musculoskeletal-system; Musculoskeletal-system-disorders; Muscular-disorders; Ergonomics; Materials-handling; Injury-prevention; Injuries; Repetitive-work; Cumulative-trauma; Cumulative-trauma-disorders; Exposure-assessment
Department of Industrial Engineering, School of Engineering and Applied Sciences, Bell Hall, Room 411, University at Buffalo, State University of New York, Buffalo, New York 14260-2050
Final Grant Report
NTIS Accession No.
Research Tools and Approaches: Exposure Assessment Methods
National Institute for Occupational Safety and Health
State University of New York, Buffalo