Can the NIOSH lifting equation be applied to patient handling?

When it comes to questions about lifting, many safety professionals rely on the Revised NIOSH Lifting Equation (RNLE). NIOSH researchers developed the RNLE to determine weight limits for preventing back injuries caused by manually lifting objects on the job. Research studies have validated the equation’s usefulness for computing safe weight limits when lifting inanimate objects such as boxes and other packages. As a matter of policy, NIOSH recommends its use for that purpose. The RNLE is not intended to be used for determining safe weight limits when lifting people. (see Waters, T., Putz-Anderson, V., Fine, L. [1993]. Revised NIOSH equation for the design and evaluation of manual lifting tasks. Ergonomics, 36, 749-776.)

The shape and size of the human body differ from person to person, and patient handling situations are often complicated by many other factors such as the potential for unpredictable movements, the patient’s medical condition, and so on. Since the equation was designed to be used for more stable and predictable lifting tasks, it is generally considered to be impractical for patient handling tasks. As the field of safe patient handling grew over the years, practitioners increasingly expressed interest in trying to determine how much weight can be lifted safely using manual methods, and how much weight requires using lifting equipment. Dr. Thomas Waters examined the issue further and published an article entitled, “When is it Safe to Manually Lift a Patient?”. The article describes how the RNLE “can be used to calculate a recommended weight limit for a limited range of patient-handling tasks in which the patient is cooperative and unlikely to move suddenly during the task.” When lifting a box or other inanimate object, the lifter can usually get quite close to the object, which helps minimize strain caused by reaching while lifting. It is usually not possible to get as close when lifting a patient. In order to accommodate the added space needed when lifting a person, Dr. Waters increased the equation’s minimum horizontal distance of 10 inches (between the lifter’s spine and the object) to 14.5 inches (between the lifter’s spine and the patient). After including this change in the equation, he applied the RNLE and determined that under the assumption of an otherwise “ideal” patient handling situation, the maximum recommended weight limit is 35 lbs.

Based on Dr. Waters’ calculation, lifting algorithms developed by the Veterans’ Health Administration and the Association of periOperative Nurses state that assistive equipment should be used if the weight to be lifted by any single person exceeds 35 lbs. However, the guidance provided along with the algorithms advises that the 35 lb. limit is not, by itself, sufficiently protective under all circumstances. NIOSH says that assistive devices are still needed in most situations, even when the weight to be lifted is less than 35 lb, as there are many variables that cannot be accounted for in the workplace. NIOSH shares in the consensus among patient handling professionals that the goal of safe patient handling programs should be to eliminate all manual lifting whenever possible.