Field and laboratory analyses of manual tasks in the South African automotive industry

by James, J.P.

Abstract (Summary)
The present study adopted a “field-laboratory-field” approach in the assessment of the efficacy of ergonomics interventions specific to two selected tasks evaluated in a South African automotive industry.

Initial field testing was conducted in an Eastern Cape (South Africa) automotive plant where high risk areas were identified during walkthrough ergonomics surveys in conjunction with interaction with operators. Temporal factors and working postures of 12 industrial workers were recorded and observed, while physiological and perceptual responses were assessed. Two priority areas were focused upon for analysis, namely the Paintshop and Bodyshop with the former identified as being the more taxing of the two tasks. Responses of 30 students participating in rigourously controlled laboratory simulations were subsequently collected while completing the two tasks, namely the Paintshop Trolley Transfer (PTT) and Car Door Carriage (CDC) for participants. Working postures, kinematic, physiological and perceptual responses were assessed pre- and post-intervention. Following the laboratory experimentation a basic re-evaluation was conducted at the plant to assess whether the proposed changes had a positive effect on working postures, physiological and perceptual responses.

The results of the preliminary field investigation revealed a prevalence of awkward working postures and excessive manual work in both areas. Laboratory experimentation revealed a notable reduction in task demands pre- versus post-intervention. The PTT mean lean angle for two-handed pre-intervention pulling observations of 23.7° (±3.51) was reduced to 13.9° (±2.21) post-intervention. Low back disorder (LBD) risk was reduced during the two-handed pull intervention (from 36.8% ±8.03 to 21.7% ±5.31). A significant decrement in heart rate responses from 103 bt.min-1 (±11.62) to 93 bt.min[superscript -1] (±11.77) was recorded during the two-handed symmetrical pushing intervention. The electromyography (EMG) responses for one-handed pushing and pulling pre-intervention showed the highest levels of muscular activity in the right medial deltoid due to an awkward and asymmetrical posture.

CDC responses demonstrated that minor changes in the storage height of the door resulted in a significant reduction in sagittal flexion from 28.0° (±4.78) to 20.7° (±5.65).

Predictions of average probability of LBD risk were significantly reduced from 50.3% (±5.91) to 39.8% (±5.10) for post-intervention car door lifting. In addition, the greatest reduction in EMG activity as a %MVC was achieved during sub-task ii (reduced from 35.1 to 13.7% and 30.5 to 13.9% for left and right erector spinae respectively) which was associated with the introduction of the transfer trolley for the door transfer phase of the CDC.

Re-evaluation in the automotive plant revealed that the most notable change has been the implementation of automated ride on trolleys in the Paintshop. The Bodyshop area has also been modified to allow more effective job rotation and the step into the storage bin has been reduced via a “low-cost” stepping platform. Mean heart rate recordings were reduced from 94 (±9.77) bt.min[superscript -1] to 81 (±3.72) bt.min[superscript -1] in the Paintshop. Overall the results demonstrate the effect of “low-cost” interventions in reducing the physical stresses placed on workers in the automotive industry where much of the work is still done manually.

Bibliographical Information:


School:Rhodes University

School Location:South Africa

Source Type:Master's Thesis

Keywords:human kinetics ergonomics


Date of Publication:01/01/2007

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