Handtool-task strength comparison between younger and older tractor operators using adjustable rollover protective structures

J. R. Etherton, T. J. Stobbe, J. T. Wassell

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


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 55 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 1/2 -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.

Original languageEnglish (US)
Pages (from-to)247-258
Number of pages12
JournalInternational Journal of Industrial Ergonomics
Issue number3
StatePublished - Mar 1996
Externally publishedYes


  • Design
  • Safety equipment
  • Strength
  • Threaded fasteners

ASJC Scopus subject areas

  • Human Factors and Ergonomics
  • Public Health, Environmental and Occupational Health


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