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Fall potential of work on elevated and inclined surfaces.

Bhattacharya-A; Succop-P; Bagchee-A
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-003107, 1998 Dec; :1-58
This study provides an experimental design for investigating the interaction between age, sex and other fall risk factors such as standing surface elevation/inclination, job-task and lighting. In this study, postural instability and propensity of loss of balance risk factors were evaluated for 74 industrial workers' performance (22 to 60 years of age) on test conditions which represent combinations of these risk factors. There are environmental (lighting), job-task (stationary versus dynamic) and personal (age) risk factors which can individually and/or collectively jeopardize one's ability to perform tasks on elevated/inclined surfaces without experiencing postural imbalance and, eventually, a fall. All test conditions (encompassing all fall risk factors) evaluated in the present study are rank-ordered for postural balance/instability. This study addressed the following questions: (a) How do work surface inclination and elevation and distraction affect postural balance under conditions of good and poor lighting? and (b) What type and positioning of visual cues are beneficial in reducing postural instability while performing simulated industrial tasks on inclined and elevated surfaces? The results from the current study with 74 industrial workers suggest the following ordering for the effects of risk factors and covariates on postural balance: (1) task; (2) lighting; (3) visual cue; (4 and 5) inclination/elevation; (6) gender; (7) arm/leg reaction time; with weight, height, race and age all seldom significantly affecting postural sway. The task performed was found to significantly affect all ten outcome sway variables. For each postural sway outcome, the reach task evoked the greatest sway, followed by the bending task, with the stationary task evoking the least postural sway. Lighting was found to affect 8 of the 10 postural sway outcomes. In general, sway increased in poor lighting; however, the maximum excursion in the anterior-posterior (AP) direction and the minimum Horizontal force/Vertical forces (RN) were actually diminished in poor lighting as compared to good lighting. Low HN values imply lesser demand on coefficient of friction (COF) requirement. This could be due to "cautious" slow body motions (which in turn will decrease shear forces) used in poor light to prevent a potential fall. Presence of a visual cue significantly affected four of the ten postural sway outcomes: sway area, sway length, average excursion in the AP direction and minimum HN. The presence of either visual cue tended to decrease sway relative to having no visual cue implying better balance. The effects of the inclination and elevation factors are difficult to separate, given the many models in which they significantly interacted with each other and with other factors and also the nonmonotonic nature of many of their relationships with the outcomes. The subjective Perceived Sense of Slip or Fall (PSOF) response to inclination showed that subject's were showing increasing sense of loss of balance (as PSOF values increased monotonically with increasing inclination levels) even though the objective measures of sway (sway length) were not giving consistent and significant association with increasing values of inclination. This discrepancy between subjective and objective measures of postural balance imply that subjects were overcautious as they stood on inclined surfaces of increasing angles. This increased "awareness" of their own body sway might have elicited counteracting postural muscle activities to overcompensate which can only be validated with measures of electromyographic outcomes of the postural muscles. In the workplace, it is probably advantageous to have a somewhat overcautious response [i.e. a higher PSOF values even though the objective measures (i.e. sway length) show a smaller value] while performing tasks on inclined and elevated surfaces. In the present study, the WRTI values show monotonically decreasing with increasing inclination implying that the body is overcautious and is trying to keep the whole body CG closer to the center of its stability boundary as the inclination is increasing. The objective measure of sway length showed significant interaction between inclination and elevation but the subjective measure PSOF did not show a significant association. It is interesting to note that sway length was generally increased at higher elevations when the inclination angle increased, implying overcompensation by the postural muscles due to psychophysical fear of fall or height. However, the subjective response of PSOF did not show significant inclination by elevation interaction implying that while working on elevated inclined surfaces there exists the potential mismatch between actual danger of loss of stability (as measured by sway variables) and the workers' ability to subjectively judge the need to deploy the necessary compensatory postural muscle contractions. Results obtained from this study with industrial worker subjects now provide the basis for future prospective studies using a larger sample from the worker population. The results obtained from this study will now help enhance our existing statistical model showing the relationship between propensity of loss of balance and the independent variables characterizing the environmental, job-task, and personal risk factors. A determination of which of the risk factors need to be corrected to reduce the fall potential at the workplace will then be possible.
Work-areas; Work-environment; Demographic-characteristics; Risk-factors; Injuries; Industrial-factory-workers; Environmental-factors; Posture; Lighting; Age-factors; Age-groups; Sex-factors
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Final Grant Report
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National Institute for Occupational Safety and Health
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University of Cincinnati, Cincinnati, OH