Concepts of the Lift-Lower Analysis

This area of the dialog box has two functions:

• Display and choose postures (Initial and Final toggle buttons) Use these two toggle buttons to select which posture you want to record or modify. When the postures are recorded, use these buttons to switch back and forth between the two postures. The manikin in the scene displays the current posture selected.
• Record or modify the selected posture (Record/Modify push button) Use this push button to record a posture. Use the Initial and Final buttons to select the posture to be recorded. If the manikin's current posture does not respect the lifting task definition, an error message is displayed with the list of the missing or bad prerequisites.

From this list, select the guideline to perform the lift-lower analysis. The guidelines available are NIOSH 1981, NIOSH 1991, and Snook & Ciriello.

The Specifications and Scores change depending on which guideline is selected.

Specifications:

• 1 lift every: Use this specification to determine lift frequency. Click on the arrows to increase or decrease the value indicated in the text field or directly enter a new value using the keyboard.
• Duration: Use this field to enter the duration of the work in hours per day. The work is considered:

  
  

  • occasional if the value is one hour or less
  • continuous if the value is 8 hours
  
  
  

Score Immediately after the frequency and duration fields are completed, the results are displayed in the Score zone.

• Action Limit (AL): This value represents the weight below which the task could be considered as reasonably safe.
• Maximum Permissible Limit (MPL): This value represents a limit above which the lifting task is considered as hazardous and requires engineering controls.

Specifications

• 1 lift every: Use this specification to determine lift frequency. Click on the arrows to increase or decrease the value indicated in the text field or directly enter a new value using the keyboard.
• Duration: Use this field to enter the duration of the work in hours per day. The work is considered:

  
  

  • occasional if the value is one hour or less
  • continuous if the value is 8 hours

• Coupling condition: Use this function to quantify the quality of the hand-to-object. The coupling quality is classified as Good, Fair, and Poor.

  
  

  • Good - a comfortable grip in which the hand can easily wrap around the object
  • Fair - a grip in which the hand can be flexed about 90 degrees.
  • Poor - when the object is hard to handle (irregular, bulky, sharp edges, etc.)

• Object weight: Use this field to enter the load weight. This value is used for the lifting index calculation.
  
  

Score Immediately after the frequency and duration fields are completed, the results are displayed in the Score zone.

• Origin This result is based on the initial posture of the manikin.

  
  

  • Recommended Weight Limit: The RWL is the load weight that healthy workers can lift over a certain period of time without risk.
  • Lifting Index: The LI provides a relative estimate of the level of physical stress.

• Destination This result is based on the final posture of the manikin.

  
  

  • Recommended Weight Limit: The RWL is the load weight that healthy workers can lift without risk.
  • Lifting Index: The LI provides a relative estimate of the level of physical stress.

Today in the Human Activity Analysis workbench, the NIOSH 1991 Lift/Lower analysis outputs the Recommended Weight Limit (WRL), and the Lifting Index (LI) in the Score section of the Lift/Lower Analysis . You are able to easily view the various multipliers (intermediate results) that are used in the NIOSH 1991 Lifting Equation, and to copy/paste them in another text editor, for future reference. The goal here is to provide more pertinent information. To attain these results of recommended weight limit and lifting index from the manikin posture, we use the equations prescribed in the literature regarding the NIOSH 1991 study. The text below presents these equations. But because these factors carry substantial information on their own, and because this information is supplemental to the information given by the final output (WRL and LI), there is a need to display these values as well. This way, you can be fully informed of a particular factor change, say the frequency multiplier, and can appreciate precisely how any of the intermediate factors influences the final result.

The following two equations are taken verbatim from the brochure entitled: "Applications Manual for the Revised NIOSH Lifting Equation", U.S. Department of Health and Human Services, Cincinnati, Ohio, January 1994:

RWL = LC * HM * VM * DM * AM * FM * CM

LI = L over RWL

Here, we see that a few intermediate variables ("LC", "HM", and so on) are needed, and calculated internally, in order to produce the two main results of the analysis. These variables are:

• A load constant (LC)
• The horizontal multiplier (HM)
• The vertical multiplier (VM)
• The distance multiplier (DM)
• The asymmetric multiplier (AM)
• The frequency multiplier (FM)
• The coupling multiplier (CM)
• The load weight carried by the subject (L)

This way, you can be fully informed of a particular factor change, say the frequency multiplier, and can appreciate precisely how any of the intermediate factors influences the final result. As this lack of information prevents you from understanding how the analysis operates.

Specifications:

• 1 lift every: Use this specification to determine lift frequency. Click on the arrows to increase or decrease the value indicated in the text field or directly enter a new value using the keyboard.
• Population sample: Three population percentiles are provided: 90th, 75th, and 50th. These percentiles represent the percentage of the population able to perform the task safely. The selected percentile takes the manikin gender into account.

Score

Immediately after the frequency and population sample fields are completed, the results are displayed in the Score zone.

• Maximum Acceptable Weight: The maximum acceptable weight is defined as the weight that the selected population can handle with reasonable safety.