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Ergonomics of task performance on slippery surfaces.

Bhattacharya-A; Succop-P; Bagchee-A; Mitchell-T; Cox-C; Chiou-SY; Wang-B; Lai-CF
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, R01-OH-003079, 1997 Dec; :1-133
This study provided an experimental design which investigated the interaction between age, sex and other fall/postural instability risk factors such as surface slipperiness, shoe wear/tear, and lighting. In this study, postural instability, fall potential, slip incidents were quantitated during static and dynamic task performance by 40 industrial workers (21 to 60 years of age) on dry, slightly, medium and very slippery surfaces. The dynamic coefficient of friction (COF) values for dry, slightly, medium and very slippery surfaces were 0.67, 0.35, 0.18 and 0.11, respectively. The static and dynamic tasks performed simulated conditions which occur in nonoccupational and occupational environments while standing or walking on a slippery surface. From these results, the effects of various risk factors on static and dynamic postural sway and instability were rank ordered. Based on objective measures of postural sway and instability, the type of task performed and environmental lighting had the, largest and the second largest, respectively, detrimental impact on postural stability, while performing tasks in a stationary position (i.e. static task). The gender, surface and shoe type had the third, fourth and fifth, respectively, largest effect on postural sway. For the dynamic task performance, the largest and the second largest detrimental impacts on workers' postural stability/sway were associated with surface slipperiness and the type of walking path negotiated (Straight vs. Turning path), respectively. The turning path caused a significantly higher postural instability than those observed for the gait task in a straight path. The shoe worn (new vs. used) followed by the subjects' gender displayed the next largest effects. Finally, light intensity was the remaining experimental condition which displayed a significant multivariate difference in terms of dynamic gait outcomes. For both static and dynamic tasks, the effects of age and height were not significant. The results from both static and dynamic tasks, implied that the slipping events are not dictated solely by the frictional properties of the shoe/floor interface. Body movements which modify the postural stability also contribute to the occurrence of a slip event. This implication is supported by the fact that the total number of slips were significantly correlated with measures of postural sway/instability but the shoe COF did not show any significant correlations. Workers who were cautious in assessing surface slipperiness had less postural instability during static task performance, as indicated by indices of postural instability. However, the current study did not address the issue of whether there is a learning trend in assessing surface slipperiness with repeated assessment. If the ability to assess surface slipperiness can be improved by training, then a training program can be developed to help minimize slip incidence while performing tasks on slippery surfaces. In addition, workers can also be instructed to avoid working on potentially hazardous surfaces without first carefully assessing the slip potential of working surface using the new and validated subjective scale developed in this study. The variables defined and tested in this study can be used to assess the degree of difficulty of a task and the fall/slip/instability risks associated with it. This study also provides a biomechanical basis for differentiating the utilized COF based on the dynamics of the task. Based on the prominent slide direction (due to slipping incident) during task performance in a turning path, it is important to redesign working shoes' sole tread to provide adequate COF in this direction.
Surface-properties; Sex-factors; Age-factors; Age-groups; Posture; Industrial-factory-workers; Industrial-hazards
University of Cincinnati, College of Medicine, Department of Environmental Health, Epidemiology-Biostatistics Division, Biomechanics-Ergonomics Research Laboratories, 231 Albert Sabin Way, Cincinnati, OH 45267-0056
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National Institute for Occupational Safety and Health
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University of Cincinnati, College of Medicine, Cincinnati, Ohio