HANDTOOL-TASK STRENGTH COMPARISON BETWEEN YOUNGER AND OLDER TRACTOR OPERATORS USING ADJUSTABLE ROLLOVER PROTECTIVE STRUCTURES

A fault tree analysis indicates that human strength limitations when u sing hand tools could lead to misuse of adjustable-type rollover prote ctive 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 fa rmers (n = 23) ranging in age from 21 to 70 was undertaken. Two age gr oups of working orchardists were studied: younger than 55 years of age (n = 12), and 55 and older (n = 11). Pulling tasks similar to those u sed for adjusting ROPS using wrenches with 12-, 18-, and 24-inch handl es were evaluated. The torque (applied force at a given wrench handle length) and consequently the human strength needed to adequately tight en threaded fasteners, becomes easier as threaded-fastener-diameter de creases. For overhead pulling tasks, the older group's mean strength ( 133.8 lb) was 97% of the younger group's strength (137.4 Ib). However, when the pull was shoulder-height, there was a statistically signific ant difference in capabilities. The older group's mean strength was 78 % of the younger group's mean. Results of the study suggest that for w orking men between the ages of 55 and 70, (1) easy to use coarse-threa ded fasteners no larger than 1/2-inch diameter/l3 threads per inch wil l 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 diame ter/20 threads per inch for the same expected wrench. Larger diameter fasteners would be appropriate if it is expected that longer wrench ha ndle extensions will be used.