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The Liberty Mutual manual materials handling (LM-MMH) equations.
Jim R Potvin1,2, Vincent M Ciriello1, Stover H Snook1
1Liberty Mutual Insurance, Boston, MA, USA.
Ergonomics
|March 17, 2021
Summary
New predictive equations for manual materials handling tasks can replace the 1991 Liberty Mutual Tables. These equations are based on extensive psychophysical research and provide more accurate and flexible estimations of maximum acceptable loads (MALs).
Area of Science:
- Ergonomics
- Occupational Health
- Human Factors Engineering
Background:
- The 1991 Liberty Mutual Tables are a standard for assessing manual materials handling.
- Over 40 years of psychophysical research has been conducted by Liberty Mutual on lifting, lowering, pushing, pulling, and carrying tasks.
- This research includes the data used for the original tables and 12 subsequent studies.
Purpose of the Study:
- To develop and propose new predictive equations for manual materials handling.
- To replace the existing 1991 Liberty Mutual Tables with more current and comprehensive models.
- To provide practitioners with easier-to-use tools for assessing safe load limits.
Main Methods:
- Developed predictive equations based on 612 mean maximum acceptable loads (MALs) from 388 unique conditions.
- Included data from 123 female and 149 male participants.
- Scaled a maximum reference load based on task-specific factors like frequency, height, distance, and reach.
Main Results:
- The new equations explained 90% of the variance in MAL values.
- Root Mean Square (RMS) differences were 6.7% for females and 4.8% for males.
- Coefficients of variation are provided for calculating MALs at any percentile.
Conclusions:
- The proposed predictive equations offer a superior replacement for the 1991 Liberty Mutual Tables.
- These equations are more accurate, easier to use, and allow for more specific input parameters.
- They are based on a larger and more recent dataset, improving their applicability.
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