Development of guidelines for the use of powered hand tools using psychophysical data.

Abstract

This study was designed to investigate the relationship between perceived exertion during the use of powered hand tools and workplace variables such as work orientation, location, pace, and tool shape and mass. These findings can be used to design workstations and tools that minimize perceived stress on workers. Four laboratory studies were performed to investigate changes in perceived exertion for various screw driving tasks. Subjects drove number six hex head screws using air powered drivers into 18 gauge perforated sheet metal. Subjects drove screws at vertical work locations ranging from 38-191 cm, at horizontal work locations ranging from 13-88 cm, at 8, 10 and 12 screws per minute, with a pistol, in-line and right-angle driver, and using tools with a mass of 1, 2, and 3 kg. The Borg 10-point ratio rating scale was used to assess each work combination studied. In study 1, thirty-six subjects rated seven vertical and four horizontal locations (positioned at elbow height) after using pistol, right-angle and in-line tools. The tool and work location configurations with the lowest ratings of perceived exertion were at 114 cm on the vertical surface using a pistol shaped tool, and at 13-38 cm on the horizontal surface using the in-line or right-angle tools. Thirty subjects rated four horizontal locations after using pistol, right-angle and in-line tools for study 2. The horizontal beam was positioned vertically at mid-thigh, elbow and mid-chest height. The lowest ratings of perceived exertion occurred when using the pistol tool at mid-thigh height, and the in-line and right-angle tools at elbow and mid-chest height. For study 3, eighteen subjects drove screws with a pistol tool at three vertical locations (knee, elbow and shoulder height) and with an in-line tool at two horizontal locations (lower arm perpendicular to the torso and the arms fully extended) at three different work paces (8, 10 and 12 screws per minute). The lowest ratings of perceived exertion were at 8 screws per minute across all vertical and horizontal work locations. In study 4, eighteen subjects drove screws with a pistol tool at three vertical locations (64, 114, and 165 cm) and with an in-line tool at two horizontal locations (13 and 63 cm). Each tool varied in mass (1, 2 and 3 kg). For all vertical and horizontal work locations, the ratings of perceived exertion were significantly lower when a tool of mass 1 kg was used, and the ratings increased 18% to 100% with each 1 kg increase in tool mass. Physical stress as measured using perceived exertion varies significantly with work location, tool shape, work orientation, work pace and tool mass. These results provide a basis for selection of tool/workstation configurations that reduce perceived physical stress.