A CASE-STUDY OF FACTORS INFLUENCING THE EFFECTIVENESS OF SCISSOR LIFTS FOR BOX PALLETIZING

This case study investigated why scissor lifts installed by a meat processing plant for a conveyor-to-pallet manual materials handling (MMH) task were not used by employees, despite apparent workplace improvement. A lumbar motion monitor (LMM) was used to assess tri-axial trunk motions and the Velocities and accelerations associated with the job. Three palletizing conditions were evaluated. at the floor, a? a scissor lift, and at a modified scissor lift. Front and back box positions at three levels of the floor palletizing task and three box positions at the scissor lift were assessed. Analysis combined observations, probability of ''high risk'' for low back disorder (LBD),and the National Institute for Occupational Safety and Health 1991 Work Practices Guide lifting index. Results showed the original scissor lift workplace had a higher probability of LED risk than floor palletizing due to subtle barriers. These included a raised edge on the conveyor and a railing around the scissor lift where boxes were placed, which increased maximum sagittal flexion and maximum lateral velocity during lifting. However, the NIOSH lifting index suggested an improvement of the scissor lift over the floor palletizing task, but the guideline is not sensitive to dynamic factors. After modifications to the barriers, MMH at the scissor lift workstation had a risk comparable to the medium level of floor palletizing. The changes reduced the higher risk associated with the identified installation problems and the low level of MMH at the floor. Results showed that measurement of dynamic factors provided greater sensitivity to the subtleties of workstation barriers and illustrated the effect of sma II barriers on task performance a nd associated risk. Further studies of trunk motions with alternative mechanical aids and different starting heights in MMH are indicated.