Minimal acceptable handling time intervals for lifting and lowering tasks.

Area of Science:

• Occupational Health
• Ergonomics
• Human Factors Engineering

Background:

• Manual materials handling (MMH) tasks are prevalent in many industries.
• Prolonged MMH can lead to physical strain, discomfort, and fatigue.
• Determining optimal rest periods is crucial for preventing injuries and maintaining worker well-being.

Purpose of the Study:

• To establish the minimal acceptable handling time interval (MAHTI) for 4-hour endurance manual materials handling tasks.
• To investigate the influence of load weight and handling range on MAHTI.
• To validate the psychophysical approach for determining MAHTI.

Main Methods:

• A psychophysical approach was employed with nine experienced male subjects.
• Subjects performed MMH tasks with loads of 10, 15, and 20 kg across six different handling ranges.
• Participants adjusted the handling time interval to the minimum sustainable level for a 4-hour period.

Main Results:

• Increased load weight resulted in a significantly larger MAHTI.
• The descending order of MAHTI for handling ranges was Floor to Shoulder (FS), Knuckle to Shoulder (KS), Shoulder to Floor (SF), Floor to Knuckle (FK), Knuckle to Floor (KF), and Shoulder to Knuckle (SK).
• Lifting tasks consistently required a higher MAHTI than their corresponding lowering tasks (p<0.05).

Conclusions:

• The MAHTI is influenced by both load weight and the vertical range of the handling task.
• Lifting actions necessitate longer recovery intervals compared to lowering actions.
• The psychophysical method provides a reliable approach for determining acceptable handling time intervals in occupational settings.