Risks Associated with Material Handling Water Softening Salt Bags

Contributed by Robertson Insurance & Risk Management

Material Handling

In order to maintain the water quality for its facility, a manufacturer uses salt to condition its water system.  Due to the system’s location and design, it can only be manually loaded with prepackaged plastic bags. Over time, the frequency, weight, and characteristics of how the system is loaded have raised some concerns on its safety and efficiency to their operations.

To quantify the material handling risk, the business turned to the National Institute of Occupational Safety and Health (NIOSH) and their lift index analysis tool. This tool provides a mathematical assessment of the manual material handling risks associated with lifting and lowering an object in the workplace.

Recommended Weight Limit (RWL)

This is the primary calculation of the NIOSH equation. It defines the maximum acceptable weight or load that nearly all healthy employees could lift over the course of an 8-hour shift without increasing the risk of musculoskeletal disorders to the lower back. By calculating the recommended weight limit, you are determining if the weight being lifted is too heavy for the task.

The NIOSH equation starts with a load constant of 51 pounds, which represents the maximum recommended load weight to be lifted under ideal conditions. From that starting point, the
equation uses several task variables expressed as multipliers that will decrease the recommended weight limit to a lower limit.

Factors That Affect the Recommended Weight Limit and Respective Lift Index

  • Horizontal location – How far are your arms extended when carrying the load?
  • Vertical location – How far above the ground is the object at the beginning of the lift?
  • Distance – What is the vertical distance in inches the object is moved?
  • Asymmetry – Does the employee twist his back to perform the task and how far is the twisting in degrees?
  • Frequency – How often and for how long is the lifting activity?
  • Coupling – The level of grasping that is involved with the lift. Items that have handholds or that are rigid have good coupling factors. Salt bags that sag in the middle and require greater
    grasping to control have poor coupling factors.

Lifting Index (LI)

This index is the difference between the actual lift activity and the calculated Recommended Weight Limit. As the lift index increases, so do the probability of a worker being injured. It directly answers how significant is the risk of lifting this item. A Lifting Index value of less than 1.0 indicates a nominal risk to healthy employees. A Lifting Index of 1.0 or more denotes that the task is a high risk for some fraction of the population. As the index increases, the level of low back injury risk increases correspondingly. Therefore, the goal is to design all lifting jobs to accomplish a lifting index of less than 1.0.