Citation

Etherton JR, Stobbe TJ, Wassell JT. Int. J. Ind. Ergonomics 1996; 17(3): 247-258.

Copyright

(Copyright © 1996, Elsevier Publishing)

DOI

unavailable

PMID

unavailable

Abstract

A fault tree analysis indicates that human strength limitations when using hand tools could lead to misuse of adjustable-type rollover protective structures (ROPS) for farm tractors. Manually adjustable designs for ROPS offer one way to provide wider protection against the hazard of farm tractor rollover. A task-strength study of working orchard farmers (n = 23) ranging in age from 21 to 70 was undertaken. Two age groups of working orchardists were studied: younger than 5.5 years of age (n = 12), and 55 and older (n = 11). Pulling tasks similar to those used for adjusting ROPS using wrenches with 12-, 18-, and 24-inch handles were evaluated. The torque (applied force at a given wrench handle length) and consequently the human strength needed to adequately tighten threaded fasteners, becomes easier as threaded-fastener-diameter decreases. For overhead pulling tasks, 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. 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 1/2inch 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.