Date of Graduation

1995

Document Type

Dissertation/Thesis

Abstract

If older working people (age 55 and over) do not have the strength needed to adjust the safety equipment they use, the consequences can be fatal. Also, there may be deadly results if safety equipment is not used correctly because the tasks involved in adjusting it are perceived as inconvenient and unacceptable. This study was part of a safety assessment designed to determine how to proceed in encouraging the design of manually adjustable rollover protective structure (ROPS) retrofits for older farm tractors. In particular, how acceptable are different locations and torquing requirements for threaded fasteners that must be loosened to adjust a ROPS into its up or down position? What amount of torque, if any, should users be expected to provide on threaded fasteners that need to be retightened after an adjustment? To answer these questions, an empirical field study was conducted to assess the level of strength and psychophysical demand that fastener tightening and untightening tasks might place on intended users of adjustable retrofit ROPS. Two age groups of working orchardists were studied: younger than 55 years of age, and 55 or older. For overhead pulls, the older group's mean strength (133.8 lb) was 97% of the younger group's strength (137.4 lb). However, when the pull was shoulder-height, there was a statistically significant difference in capabilities. The older group's mean strength was 78% of the younger group's mean. Psychophysical measures of pulling task difficulty did not vary significantly between age groups. Results of the study suggest that for working men between the ages of 55 and 70, (1) easy to use coarse-threaded fasteners no larger than 1/2-inch diameter/13 threads per inch will not compromise safety when the expected handtool is a 12-inch wrench and (2) fine-thread fasteners should be no larger than 1/2-inch diameter/20 threads per inch for the same expected wrench. Larger diameter fasteners would be appropriate if it is expected that longer wrench handle extensions will be used. Two particular strength-related areas of user preference for ROPS retrofit designs were: (1) an adjustability feature, whether manual or power-assisted, was strongly preferred and (2) applying strong exertions through hand tools to accomplish an adjustment was generally perceived to be acceptable, but was of some concern among the older group studied.

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