MAXIMUM ACCEPTABLE WEIGHT OF ASYMMETRICAL LIFTING AND LOWERING OF POSTAL SACKS

The asymmetrical lifting of postal sacks without handles was simulated . Type-2 and Type-3 postal sacks (those typically used by the U.S. Pos tal Service) were loaded and unloaded from and to different cart and c onveyor levels. An adjustable table was used to simulate the different conveyor levels. There were six combinations of lift for each of twen ty participants (ten male and ten female). A modified version of the p sychophysical methodology was used to determine the maximum acceptable weight of lift. A significant difference was found between the weight s lifted across cart heights. Specifically, the mean load lifted over the 96.5 cm (38.0 in) cart height was 15.337 kg (33.74 Ib) and was sig nificantly greater than the average load lifted across the 20.40 cm (8 .0 in) and the 104.20 cm (41.0 in) cart heights. However, this differe nce is not practically significantly different (mean difference = 1.44 kg). There was no significant difference (p > 0.05) in the load lifte d across table heights. A significant interaction occurred between car t height and conveyor height (p < 0.05). This interaction indicated th at as the vertical distance between the cart height and the conveyor h eight increased, the acceptable load handling capabilities of the part icipants decreased. The mean MAWL for Type-2 postal sacks (14.5 kg, 31 .91 Ib) was similar to the mean weight lifted at the postal distributi on center (16.4 kg, 36.0 Ib). The mean MAWL for Type-3 sacks (14.5 kg, 31.9 Ibs) was less than half of the mean weight lifted at the postal distribution center (24.6 kg, 54.1 Ib). Relevance to industry The resu lts of this study have direct implication regarding the design of post al operations, the types of lifting and lowering tasks that should and should not be performed, as well as more practical weight limitations than are previously employed in these types of operations.