The following NIOSH Lifting Equation Example is from the NIOSH Lifting Equation Applications Manual has been adapted to show the proper use of the NIOSH Lifting Equation inside the ErgoPlus Platform.
In addition, this example shows how this tool can be used to evaluate body mechanics recommendations and ergonomic redesign suggestions.
To help you follow along, here are links to download our free guides to recommended ergonomic assessment tools and to create a free ErgoPlus Platform account to use the NIOSH Lifting Equation software tool inside.
Now let’s get to work on the example:
Job Description
A worker manually lifts trays of clean dishes from a conveyor at the end of a dish washing machine and loads them on a cart as shown below. The trays are filled with assorted dishes (e.g., glasses, plates, bowls) and silverware. The job takes between 45 minutes and 1 hour to complete, and the lifting frequency rate averages 5 lifts/min. Workers usually twist to one side of their body to lift the trays (i.e., asymmetric lift) and then rotate to the other side of their body to lower the trays to the cart in one smooth continuous motion. The maximum amount of asymmetric twist varies between workers and within workers, however, there is usually equal twist to either side. During the lift the worker may take a step toward the cart. The trays have well designed handhold cutouts and are made of lightweight materials.
Data Collection
At the origin of the lift, the horizontal distance (H) is 20 inches, the vertical distance (V) is 44 inches, and the angle of asymmetry (A) is 30 degrees. At the destination of the lift, H is 20 inches, V is 7 inches, and A is 30 degrees. The trays normally weigh from 5 lb. to 20 lb., but for this example, assume that all of the trays weigh 20 lb. The coupling is classified as “good”. Significant control of the load is required at the destination of the lift. Therefore, the RWL is computed at both the origin and the destination of the lift.
The task variable data are measured and recorded using the ErgoPlus Platform:
Hazard Assessment
The weight to be lifted (20 lb.) is greater than the RWL at both the origin and destination of the lift (14.3 lb. and 13.3 lb., respectively). The LI at the origin is 1.39 and the LI at the destination is 1.51. These results indicate that this lifting task would be stressful for some workers and controls should be implemented.
Redesign Suggestions
The worksheet shows that the smallest multipliers (i.e., the greatest penalties) are .50 for the HM, .80 for the FM, .83 for the VM, and .90 for the AM. The following job modifications are suggested:
- Bring the load closer to the worker to increase HM.
- Reduce the lifting frequency rate to increase FM.
- Raise the destination of the lift to increase VM.
- Reduce the angle of twist to increase AM by either moving the origin and destination closer together or moving them further apart. Since the horizontal distance (H) is dependent on the width of the tray in the sagittal plane, this variable can only be reduced by using smaller trays. Both the DM and VM, however, can be increased by lowering the height of the origin and increasing the height of the destination. For example, if the height at both the origin and destination is 30 inches, then VM and DM will be increased to 1.0. Moreover, if the cart is moved so that the twist is eliminated, the AM can be increased from .90 to 1.00.
As shown in the modified calculator results below, with these redesign suggestions the RWL can be increased from 13.3 lb. to 20.4 lb., and the LI values are reduced to .98 indicating nominal risk.
Comments
This analysis was based on a one-hour work session. If a subsequent work session begins before the appropriate recovery period has elapsed (i.e., 1.2 hours), then the eight-hour category would be used to compute the FM value.
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