Designing Safe Lifting Tasks for Occupational Workers

Abstract

Ergonomic risks involved in a variety of real-life lifting tasks in manufacturing units near Agra are studied. Firstly, two case studies involving repetitive asymmetric lifting of (1) hand-pump body (HPB), and (2) centrifugal-pump casings (CPC) are taken up. Both of these lifting tasks appear highly unsafe as per the initial results based on revised NIOSH equation. To verify these results mean heart rate (MHR) of the subjects is recorded during entire lifting in a simulated laboratory setup. MHR data averaged on number of subjects is referred to as average MHR . On comparing average MHR with standard available in the literature, lifting of both, HPB and CPC, turns out to be safe lifting tasks. So, an important inference in this case is the non-applicability of revised NIOSH lifting equation in estimating the safe load limit. In the next investigation, maximum acceptable weight of lift (MAWL) of male subjects comprising construction workers and university students is endeavored using psychophysical method. Results indicate that job-habit does not improve MAWL significantly which may be attributed to the fact that students selected as subjects are physically active in their daily routine. Thereafter, the effects of stature of subjects on MAWL and maximum weight limit (MWL) in symmetric lifting (SL) as well as in asymmetric lifting (AL) with 90o trunk rotation are examined. The subjects were grouped into three statures viz., short stature, medium stature and tall stature. Results show that the consideration of stature of subjects is important to determine MAWL/MWL correctly. Further, MAWL of SL is significantly higher than that of AL for each of 3 statures. However, no significant change was observed in MHR across three statures. Lastly the risks involved in the repetitive asymmetric lifting task of raw crank-shafts (RCS) in an automotive factory are analyzed. RCS are lifted from trolley with varying task variables (H, D and A) which adds to the complexity in determining the risks involved in this task. Results b