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Liberty Mutual Tables (aka Snook Tables) - Comprehensive Overview

September 19, 2024
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Learn how to evaluate ergonomic risk using the Liberty Mutual Snook Tables

Download the Liberty Mutual Snook Tables Guidelines - here

What are the Liberty Mutual Tables?

Liberty Mutual Material Handling Tables, also known as Snook Tables, are ergonomic tools designed to assess the safety of manual handling tasks, such as lifting, lowering, pushing, pulling, and carrying. Named after Dr. Stover Snook, a key researcher in ergonomics and workplace safety, these tables were developed as part of Liberty Mutual’s research on work-related musculoskeletal disorders (MSDs).

These tables help determine whether at least 75% of females in the workforce can perform a task without injury risk, which also ensures that about 90% of males would be able to perform the same task safely. This approach helps organizations design tasks that minimize injury risk across a diverse workforce, making it a key tool for ergonomic assessments.

This article covers the Liberty Mutual Tables, first released in 1991. While they remain a valuable tool, Liberty Mutual has since introduced updates that streamline and enhance the assessment process. Stay tuned for an upcoming page where we’ll explore the updated Liberty Mutual Equations and how they represent the evolution of ergonomic risk evaluation.

Why Are Liberty Mutual Tables Important?

1. Guideline for Safe Lifting: Snook Tables provide recommendations on weight limits for material handling tasks based on various factors like the distance, height, frequency of lifts, and posture. This helps to prevent injuries such as lower back strain.

2. Reducing MSD Risk: By using Snook Tables, ergonomists and safety professionals can design work tasks in a way that reduces the risk of musculoskeletal disorders, which are common in industries with high levels of manual labor.

3. Standard in Workplace Safety: Snook Tables have become a widely accepted and referenced tool in occupational safety and ergonomics to establish safe working conditions and minimize injury risk.

4. Customization for Different Jobs: The tables allow for the customization of lifting recommendations based on the specific conditions of a job, such as gender, frequency of the task, and the weight being handled.

How to Conduct a Liberty Mutual Tables Assessment:

Step 1: Find the Correct Table

Start by locating the appropriate table for your task. In this example, we’re using Table 2F: Female Population Percentages for Lifting Tasks Ending Between Knuckle and Shoulder Height (28” and 53”).

Step 2: Determine the Weight

Next, find the row that corresponds to the object’s weight. Measure the weight using a scale or force gauge. In our example, the field measurement is 18 lbs. Since the table doesn’t have an exact match, we use the next higher increment, which is 20 lbs. This conservative approach ensures we remain within safe limits.

Step 3: Measure the Hand Distance

Identify the column that matches the hand distance (the horizontal reach). Measure this in the field using a tape measure. For our example, the horizontal reach is 10 inches.

Step 4: Determine the Frequency of the Task

Find the column that corresponds to how often the task is performed. You can track this using a timer and a tally counter. In our case, the task occurs once every 5 minutes during a full shift.

Step 5: Measure the Hand Height

Locate the row for the vertical hand height—the distance between where the lift starts and ends. In our example, the vertical distance is 5 inches, but to stay on the safe side, we round up to 10 inches as per the table’s increments.

Step 6: Locate Your Score

Cross-reference the columns and rows. In this example, the 10-inch hand distance column and 5-minute frequency column intersect with the 20 lbs. weight row and 10-inch hand height row at a population percentage of 89%, meaning 89% of the female workforce can perform this task safely.

Step 7: Consider the Coupling Factor

Check the coupling, which refers to the grip between the handler and the load. If there are no handles or cut-outs, NIOSH rates the coupling as ‘Fair’. According to Snook Tables, we subtract 15% from the initial population score for a ‘Fair’ rating.

Step 8: Final Score

Subtract the 15% due to the ‘Fair’ coupling from our initial score of 89%, giving us a final 74% female population for safely performing the task. Although this is slightly below the ideal threshold of 75%, it may still be considered acceptable depending on the work environment and the specific demands of the task. In many cases, a score near 75% indicates that the majority of the workforce can perform the task safely, but some additional interventions may be needed to fully optimize safety.

How to Apply the Results

Once you’ve calculated the population percentage from the Snook Tables, there are a few key things to consider:

1. Task Adjustments: If the percentage is below 75% for females, it’s a signal that adjustments should be made. You could reduce the load weight, adjust task frequency, or implement ergonomic controls to improve safety.

2. Risk Management: If your score is close to 75%, like in our example, you may be on the borderline of acceptability. Even in this case, it’s important to consider ergonomic interventions that can further reduce the risk and increase the number of workers who can safely perform the task.

TuMeke Ergonomics: Automating Liberty Mutual Tables with AI and Computer Vision

Manually completing Liberty Mutual Snook Tables can be time-consuming and complex, but TuMeke’s ergonomic safety platform simplifies the entire process. By leveraging computer vision and AI, TuMeke automates Snook Tables, reducing the time, effort, and costs associated with collecting, evaluating, and addressing ergonomic risk. Simply record or upload a video of a task, and our software will run a Snook Tables assessment, providing a score in seconds.

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