A study was conducted to determine the friction characteristics for various materials against human palmar skin. Seven materials were tested using two pinchforce levels under both moist and dry conditions. Using a two-fingered pinch grip, subjects held a specially designed dynamometer covered with one of the test materials. They maintained a constant pinch force as load force was increased at a constant rate until the dynamometer slipped from their fingers. The load force at the slip point was then used to determine the coefficient of friction from Amonton's Law. The: effects of subject, material, moisture, pinch force and the materialmoisture and pinch iorce-moisture interactions were all significant. The coefficient of friction decreased with increased levels of pinch force for every material-moisture combination. The coefficient of friction for porous materials showed a significant increase when moisture was present. This information may be applicable in tool handle and work station surface design.
The effect of friction and load on pinch force was studied in a simple hand transfer task using a repeated measures design and ten men. Subjects moved a container between two targets, 450 mm apart, at a slow, self-paced speed. The levels of mass in the container were set at 0.8, 2.5 and 4.2 kg (7.5, 24.5 and 41.5 N respectively). The handle materials were sandpaper and smooth aluminum. Applied pinch force was measured via a strain gauge mounted in a specially-designed handle attached to the container. Dependent variables were peak and 'steady-state' pinch force. The main and interaction effects of load and friction were significant. The friction effect was significant only for the highest load which, on average, elicited peak pinch forces of 16-70% of maximum voluntary force. This suggests that these men were not sensitive to friction effects at the lower loads. Results suggest that the use of tool handle friction enhancements may reduce required pinch forces for objects requiring upwards of 50% or more of maximum pinch strength.
A Health Hazard Evaluation was conducted by the National Institute for Occupational Safety and Health (NIOSH) to determine if vapors from duplicating fluid (99% methyl alcohol) used in direct-process spirit duplicating machines were causing adverse health effects among teacher aides, or had been responsible for the deaths of three former teacher aides. Death certificates and autopsy data were obtained and evaluated. A self-administered symptom questionnaire was distributed to current teacher aides (exposed group) and to a comparison group of teachers. Fifteen-minute breathing zone air samples for methyl alcohol vapor were collected at operator stations using an infrared gas analyzer. No information supported the claim that the three deaths were related to methyl alcohol exposure. Teacher aides reported significantly more blurred vision, headache, dizziness, and nausea than the comparison group. Concentrations of airborne methyl alcohol ranged from 365-3080 ppm; 15 of 21 measurements exceeded the NIOSH-recommended 15-minute exposure limit of 800 ppm. A mean 96% reduction in vapor concentration was accomplished using inexpensive enclosures and existing room exhaust systems.
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