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Further studies of psychophysically determined maximum acceptable weights and forces
V M Ciriello1, S H Snook, G J Hughes
1Liberty Mutual Insurance Company, Hopkinton, Massachusetts 01748.
Human Factors
|March 1, 1993
Summary
Lifting boxes without handles and with extended reach significantly reduced maximum acceptable weights for industrial workers. Task combinations were limited by their most strenuous component.
Area of Science:
- Ergonomics and Occupational Health
- Human Factors Engineering
- Industrial Physiology
Background:
- Manual material handling tasks are a common source of workplace injuries.
- Understanding the biomechanical and psychophysical effects of specific handling variations is crucial for injury prevention.
- Previous research has focused on individual tasks, but combined and modified tasks require further investigation.
Purpose of the Study:
- To quantify the effects of specific manual material handling variations on psychophysical responses.
- To determine maximum acceptable weights and forces for different lifting, lowering, pushing, pulling, and carrying tasks.
- To evaluate the impact of box design (handles), reach distance, and task combinations on worker capacity.
Main Methods:
- A psychophysical methodology was employed, assessing subjective worker exertion.
- Six male industrial workers participated in the study.
- Forty-two task variations were performed, including lifting without handles, long-distance pulling, varied box sizes, combined tasks, and extended reach lifting.
Main Results:
- Lifting boxes without handles decreased maximum acceptable weights by a median of 16% compared to boxes with handles.
- Lifting with extended horizontal reach (48 cm) reduced maximum acceptable weights by a median of 48% compared to lifting close to the body (17 cm).
- Longer pulling distances (15.2 m) resulted in lower maximum acceptable pulling forces. Box size did not significantly affect carrying capacity, and combined tasks' limits were set by the most demanding single task.
Conclusions:
- The absence of handles and extended horizontal reach are significant risk factors in manual material handling, reducing acceptable work loads.
- Task design, including handle availability and reach, directly impacts worker capacity and should be optimized for safety.
- These findings provide valuable data for establishing safe work practices and designing ergonomic interventions in industrial settings.