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Nelson & Associates :: Manual Lifting & Materials Handling :: Liberty Mutual Tables

Liberty Mutual Materials Handling Guidelines


Since the late 1970's, Liberty Mutual has been analyzing and evaluating lifting, lowering, pushing, and carrying tasks using "Psychophysical Tables" based on the research of Drs. Stover Snook and Vincent Ciriello at the Liberty Mutual Research Institute for Safety. Their research used psychophysical methodology to derive information about the capabilities and limitations of workers and the design of manual handling tasks to reduce low back disability.

Psychophysical methodology includes measurements of oxygen consumption, heart rate, and anthropometric characteristics. Subjects were given control of either the weight or force variable, while other task variables such as frequency of lift, object of lift size, height of the lift, and distance of carry were controlled by the experimenter. Subjects then monitored their own feelings of exertion of fatigue, and adjusted the weight or force of the object accordingly.

While the previously published (1978, 1980, 1991) "Snook Tables" provided an indication of the maximum acceptable weights and forces for 10, 25, 50, 75, and 90 percent of the male and female populations, the Liberty Mutual Tables present the male and female populations percentages that are able to performs certain listed tasks.

At the same time, Liberty Mutual offers the following caution on using their tables: Tasks should not be evaluated based solely on population percentages. Other important considerations include:

  • Injuries -

    Any job that is producing injuries is a good candidate for redesign.

  • Bending –

    Any task that begins or ends with the hands below knuckle height presents some degree of risk. The deeper the bending motion, the greater is the physical stress on the low back. Frequent bending regardless of weight is not recommended.

  • Twisting –

    This motion puts uneven forces on the back thereby presenting additional physical stress. The greater the twist, the more physically stressful the task.

  • Reaching –

    The distance away from the body that a load is held greatly affects the forces on the back, shoulder, and arms. The farther the reach, the more physically stressful the task.

  • One-Handed Lifts –

    The tables cannot be used to evaluate one-handed tasks. By nature, these tasks place uneven loads on the back and present a greater physical stress than two-handed lifts.

  • Hand-holds –

    Inability to get a good grip on the load presents a greater physical stress.

  • Catching or Throwing Items –

    The tables cannot be used to evaluate these types of tasks. Any tasks involving catching or throwing items are physically stressful and , therefore, are good candidates for redesign.

The population percentages presented in the Liberty Mutual Tables are based on weights selected by subjects in the laboratory working as hard as they could without straining themselves, or without becoming unusually tired, weakened, overheated, or out of breath. The Liberty Mutual Tables may be used for designing manual handling tasks with physical requirements such that as many workers as possible can perform such tasks without risk of injury. Liberty Mutual recommends that tasks having population percentages of less than 10% should be prioritized for task redesign.

For more information regarding the Liberty Mutual Tables, use the following links to go directly to the Liberty Mutual website:

Liberty Mutual's web page for the lifting tables
PDF of Liberty Mutual's lifting tables

© Nelson & Associates, 2010