The effect of the shape of the handle on special hand tools for opening and closing steel pipes in the dairy industry on the amount of discomfort, wrist torque and usability

Abstract

Purpose: The aim of this study was evaluating of effect of the handle shape of hand tools used for opening and closing steel pipes in dairy industries (three modified designs of wrenches with 30–50 mm diameter cylindrical handles and traditional design with rectangular cross-sectional (5 mm × 25 mm) handle), workpiece orientation (vertical/horizontal) and workpiece size (small/large) on wrist ulnar/radial (U/R) torque strength, usability and discomfort. Method: This semi experimental study by means of 18 workers from eastpegah dairy company, without history of upper limb injury or musculoskeletal disorders, was conducted. Wrenches were evaluated from wrist ulnar/radial (U/R) torque strength, usability and discomfort. Results: The highest and lowest levels of maximal wrist U/R torque strength were recorded for the 30 mm diameter handle and traditional wrench design, respectively. The prototype handle with 30 mm diameter, together with 40 mm diameter handle, was also better than other designs as they received higher usability ratings and caused less discomfort. The mean wrist torque strength exerted on a vertically oriented workpiece (in the sagittal plane) was 23.8% higher than that exerted on a horizontally oriented one (in the transverse plane). Conclusion: The results showed that wrenches with 30 mm diameter and with 40 mm diameter handle, were beter than othere wrenches especially from usability ratings and less discomfort. Generally the mean wrist torque strength exerted on a vertically oriented workpiece higher that exerted on a horizontally oriented one.