Liberty Mutual — Manual Handling Tables (Snook)
A psychophysical design reference for the safety of manual handling tasks — including pushing, pulling, and carrying alongside lifting and lowering.
What is Liberty Mutual?
The Snook (Liberty Mutual) tables are based on extensive psychophysical testing to determine what forces and weights are acceptable to defined percentages of the working population. The standard design target is a task acceptable to at least 75% of the female population, which automatically protects over 90% of male workers.
When to use Liberty Mutual
Deploy when assessing manual handling that includes significant horizontal pushing and pulling forces (such as moving carts), or when designing jobs specifically to accommodate a diverse-gender workforce.
Primary citation: Snook, S.H. & Ciriello, V.M. (1991). The design of manual handling tasks: revised tables of maximum acceptable weights and forces. Ergonomics, 34(9), 1197–1213.
What Liberty Mutual assesses
The body segments and task variables evaluated in a Liberty Mutual assessment.
What it assesses
- Initial force to start movement vs sustained force to keep moving
- Hand distance from the body
- Lift / lower vertical zones
- Task frequency and travel distance
Scoring and action levels
Final score range: Population acceptability (% of workers)
Developed by: Snook & Ciriello, Liberty Mutual
How Ergocure.ai applies Liberty Mutual
Ergocure AI reads the lift geometry from a phone capture and combines it with the self-reported load weight, frequency and grip to look up the Snook & Ciriello maximum-acceptable-weight tables, returning the share of the working population who could safely perform the task. A certified ergonomist reviews and signs off before the worker sees the result.
Captured on any phone, scored for Liberty Mutual, and validated by a certified ergonomist — face-blurred on-device.
Liberty Mutual and your ISO 45001 audit
ISO 45001 Clause 6.1.2 requires you to assess ergonomic risk — and triggers the technical ISO standard this method runs. Your auditor names the standard; Ergocure runs the assessment and a qualified ergonomist signs it off.
How we assess it
The Liberty Mutual (Snook) tables implement ISO 11228-2 for manual pushing, pulling and carrying — weighing the force a task demands against population-based acceptable limits. Ergocure derives the task parameters from an on-device capture plus load details (or a camera-free survey), computes the percentage of the working population the task is acceptable for, and a qualified ergonomist signs off the result as documented ISO 11228-2 evidence for your ISO 45001 audit.
See all ISO standards & how we assess themLiberty Mutual — frequently asked questions
What is Liberty Mutual (Manual Handling Tables (Snook))?
A psychophysical design reference for the safety of manual handling tasks — including pushing, pulling, and carrying alongside lifting and lowering.
What is a good Liberty Mutual score?
Population acceptability (% of workers). A score of ≥ 75% acceptability is safe — task matches general human capability — while < 75% acceptability is hazardous and means workstation or tool redesign required.
When should you use Liberty Mutual?
Deploy when assessing manual handling that includes significant horizontal pushing and pulling forces (such as moving carts), or when designing jobs specifically to accommodate a diverse-gender workforce.
How does Ergocure score Liberty Mutual?
Ergocure AI reads the lift geometry from a phone capture and combines it with the self-reported load weight, frequency and grip to look up the Snook & Ciriello maximum-acceptable-weight tables, returning the share of the working population who could safely perform the task. A certified ergonomist reviews and signs off before the worker sees the result.
Who developed Liberty Mutual?
Liberty Mutual was developed by Snook & Ciriello, Liberty Mutual. Snook, S.H. & Ciriello, V.M. (1991). The design of manual handling tasks: revised tables of maximum acceptable weights and forces. Ergonomics, 34(9), 1197–1213.
Related assessment methods
Methods commonly used alongside Liberty Mutual in a complete ergonomic assessment.
See Liberty Mutual in a live assessment
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