Magazine article Occupational Hazards

NIOSH's Lifting Equation: Can Industry Bear the Load

Magazine article Occupational Hazards

NIOSH's Lifting Equation: Can Industry Bear the Load

Article excerpt

Is it the 51-pound solution, or ivory tower overkill?

Whatever the answer, NIOSH's revised lifting equation is proving a potent formula for controversy.

Ergonomics researcher Jerome Congleton has a vision of what American workplaces would look like if they follow the new NIOSH lifting guide and equation. He says it is not a pretty picture.

"If you buy into this, you buy into the idea of design for extreme," said Congleton, Ph.D., associate professor of safety engineering at Texas A&M University, College Station, Texas. "Eventually, nobody will be able to lift anything with any frequency. Employees will be doing nothing but sedentary jobs, and they will lose what little conditioning they do have."

According to Congleton, the revised equation is more stringent than the 1981 version and may force employers to design jobs for the "weakest link of the working population," like a small-stature, 40-year-old female, even if they employ no such people. He is especially concerned that NIOSH published it before validating it, and now, OSHA is using it.

Tom Waters, Ph.D., NIOSH's lead scientist on the project, defends the equation - which sets a weight limit of 51 pounds that can be substantially reduced due to the presence of less-than-ideal lifting conditions - as a "fantastic job design and evaluation tool."

He said it meets NIOSH's goal to protect at least 90 percent of the working population to the extent feasible from back injuries due to manual material handling. He acknowledged, however, that NIOSH still has to guide employers on how and when to use it and when other analysis tools might be called for.

Original Guide

Since NIOSH published its original liftiNg guide in 1981, it has been used by tens of thousands of employers, consultants and regulators to evaluate lifting tasks. Although OSHA has no definitive numbers, the agency probably used the guide in as many as 300 general duty clause citation cases over the last decade.

The 1981 equation contains four variables to compute weight limits for lifting: horizontal location for the distance of the load from the body; vertical location for height of hands from the floor; vertical travel distance for the difference between the height at which an object is picked up and put down; and frequency of lift.

Starting with a load constant of 90 pounds, weight limits decline dramatically if the variables result in adverse lifting conditions. The resulting numbers are the maximum permissible limit (MPL) and action limit (AL), which are compared to the weight of the load to determine if the job poses an excess risk that should be addressed with engineering and/or administrative controls.

"People liked it because it was easy to use," Waters said of the original guide. "it was better than waiting for injuries to tell them where the problems were. There was nothing, and still is nothing, to tell you what an individual's risk is."

New Version

By the mid-1980s, NIOSH was exploring ideas for updating and expanding the 1981 equation.

The work culminated in NIOSH presenting revisions at a 1991 University of Michigan ergonomics conference. The equation was published in the July 1993 issue of Ergonomics and in January 1994 in the 120-page "Applications Manual for the Revised NIOSH Lifting Equation." The government has sold more than 8,000 copies of the new guide, and numerous software versions are available from private vendors.

Waters said the new guide refines the equation and allows it to be applied to a wider range of lifting tasks. According to the Ergonomics article, "the revised 1991 equation is more likely than the 1981 equation to protect most workers" because it considers additional factors and carries a lower load constant.

The revised equation contains a lower load constant of 51 pounds, compared to the previous 90 pounds. It includes the 1981 version's four variables, but some were adjusted. …

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