NIOSH Lifting Equation

Q: What is the NIOSH Lifting Equation?
A: The NIOSH Lifting Equation is a tool used to identify, evaluate, or classify some risks associated with a lifting task.

Q: When is this tool applicable?
A: The Lifting Equation is an appropriate tool to use when: estimating the risk of a two-handed, manual lifting task; evaluating a job characterized by multiple lifting tasks; evaluating a lifting task that may include trunk rotation, different types of hand coupling (how it is gripped), repetitiveness, and duration of task; determining a relatively safe load weight for a given task; determining a relatively unsafe load weight for a given task; deciding the appropriate style of abatement for a job that has been identified as having a lifting hazard; comparing the relative risk of two lifting tasks; prioritizing jobs for further ergonomic evaluation.

Q: What data do I need to collect to be able to use this tool?
A: The Lifting Equation requires the weight of the object being lifted, the horizontal and vertical hand locations at key points in the lifting task, the frequency of the lift, the duration of the lift, the type of hand-hold on the object being lifted, and any angle of twisting.

Q: What is the output of this tool?
A: The Lifting Equation will calculate the Recommended Weight Limit (RWL) and the Lifting Index (LI). The RWL is the recommended weight of the load that nearly all healthy workers could lift over a period of time (up to eight hours) without an increased risk of developing lifting related low back pain or injury, given all other task parameters remain unchanged. The LI is a relative estimate of the physical stress associated with a manual lifting job. As the magnitude of the LI increases, the level of the risk for a given worker increases, and a greater percentage of the workforce is likely to be at risk for developing lifting-related low back pain.

From the NIOSH perspective, it is likely that lifting tasks with a LI > 1.0 pose an increased risk for lifting-related low back pain and injury for some fraction of the workforce. NIOSH considers that the goal should be to design all lifting jobs to achieve a LI of 1.0 or less, although many practitioners find it difficult to achieve 1.0 or less.

The Revised NIOSH Lifting Equation is not a perfect tool, but it is an excellent method through which to evaluate a lifting job and can be an extremely useful guide to developing and prioritizing strategies to improve the lifting job.

–Rachel Michael, M.Sc., A.E.P.

This article originally appeared in The Ergonomics Report™ on 2002-11-01.