Introduction: How to Use the NIOSH Lifting Equation
NIOSH lifting equation helps determine if an object or weight is unsafe to lift over a standard eight hour work day. There are 10 steps you can take to determine if your lift is safe.
Materials you will need:
Estimated time to complete : 15 minutes
RWL = Recommended Weight Limit
LI = Lifting Index
HM = Horizontal Multiplier
VM = Vertical Multiplier
DM = Distance Multiplier
AM = Asymmetry Multiplier
CM = Coupling Multiplier
FM = Frequency Multiplier
Step 1: NIOSH Requirements
Watch the video to determine if the NIOSH lifting equation is applicable in your situation.
Step 2: Horizontal Multiplier
Measure, in inches, the horizontal distance between the center knuckle of your hands and the center of your body while holding the object at the beginning of your lift. The center of your body can be found by measuring the midpoint between your ankles, as seen in figure above. Label and record this measurement as your horizontal multiplier, HM.
Step 3: Vertical Multiplier
Measure, in inches, the vertical distance from your hands to the floor at the beginning of your lift. Label and record this measurement as your vertical multiplier, VM.
Step 4: Distance Multiplier
Measure, in inches, the vertical distance between your hand position at the beginning and end of your lift. This can be easily measured taking the absolute value difference between your vertical multiplier and the distance between your hands and the floor at the end of the lift. Label and record this as your distance multiplier, DM.
In the example provided above, the absolute values difference is 58 in. - 15 in. = 43 in. = DM.
Step 5: Asymmetry Multiplier
Measure, in degrees, how far you turn your torso from the direction your feet are facing at the beginning of the lift. Label and record this your value as your asymmetric multiplier, AM.
Note: Many times lifts do not require turning your torso without moving your feet, if this is the case your measurement is 0°.
Step 6: Coupling Multiplier
Determine which of the following categories your objects handles fall into:
• Good: The object has handles designed for easy grip with little wrist tension.
• Fair: The object has handles but are placed in naturally awkward positions to be easily held or the object has an irregular shape that requires less than optimal grip with the handle.
• Poor: The object has poorly designed handles or no handles at all. Requires extra effort to handle the object as a result of no handles or cut-outs.
Label and record your coupling multiplier, CM, as follows; 1 = Good, .95 = Fair, .9 = Poor.
In the example above the box on the top would be identified as "Good." The box on the bottom would be identified as "Fair" because the string handle creates extra stresses on the wrist. A box without any sort of cut out or handle would be identified as "Poor."
Step 7: Frequency Multiplier
Determine the frequency in which you will be lifting your object, in terms of average lifts per minute. Now using your lifts per minute, your expected work duration and your vertical multiplier (VM) located the appropriate value on the table in table above. Label and record this value as you frequency multiplier, FM.
For example if you were to on average lift 12 objects in an hour, over an 5 hour work day and my VM was found to be 25 inches I would find the table value that matches .2 lifts/min 5 hour work duration and a VM < 30. This value would be .85, as seen with the highlighting in the table above.
Step 8: Repeat
Repeat steps 2-7 again but for the values at the end of your lift. The multipliers that will not change are: DM, CM, FM.
Step 9: Calculation
Step 10: Lifting Index
Step 11: Acknowledgments
Images were supplied by Google images.