Ergoweb receives questions every day on ergonomics topics from lifting, to website design, to office set up. We are often asked about the NIOSH Lifting Equation. Following are answers to some of the most frequently asked questions about this tool.
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. NIOSH stands for the National Institute for Occupational Safety and Health. The original reference for this tool is: Badger, Donald W. "Work Practices Guide For Manual Lifting." U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Publication No. 81-122, Cincinnati, Ohio, 1981.
NIOSH updated this tool by issuing the Revised 1991 NIOSH Lifting Equation. The new equation increased the types of task variables the tool could assess. A reference for the revised document is: Waters, Thomas R.; Putz-Anderson, Vern; Garg, Arun. Applications Manual For The Revised NIOSH Lifting Equation. U.S. Department of Health and Human Services. DHHS (NIOSH) Publication No. 94-110, 1994.
Q: When is this tool applicable?
A: The Revised NIOSH Lifting Equation is an appropriate tool to use when, for instance:
- 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, repetitiveness, and duration.
- 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 Revised NIOSH 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 rate 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 NIOSH 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.
The Revised NIOSH Lifting Equation is not a perfect tool. Understood and used properly, however, it is an excellent method through which to evaluate a lifting job. If that evaluation indicates some level of risk, the tool then becomes an extremely useful guide to developing and prioritizing strategies to improve the lifting job.
For more information and assistance with the original NIOSH Lifting Equation and the Revised NIOSH Lifting Equation, consider these Ergoweb resources, from which portions of this article were taken: