NIOSH LIFTING EQUATION

JABA PRABU ABRAHAM

LI is a term that provides a relative estimate of the level of physical stress associated with a particular manual lifting task.

The estimate of the level of physical stress is defined by the relationship of the weight of the load lifted and the recommended weight limit.

Lifting Index (LI)

The LI is defined by

LI= Load weight (L)/RWL

Lifting Index (LI)

The RWL is the principal product of the revised NIOSH lifting equation.

The RWL is defined for a specific set of task conditions as the weight of the load that nearly all healthy workers could perform over a substantial period of time (eg. Up to 8hrs) without an increased risk of developing lifting related LBP.

Recommended Weight Limit (RWL)

By healthy workers, we mean workers who are free of adverse health conditions that would increase their risk of musculoskeletal injury.

The RWL is defined by

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

LC- Load Constant HM- Horizontal Multiplier VM- Vertical multiplier DM- Distant Multiplier AM- Asymmetry Multiplier FM- Frequency Multiplier CM- Coupling Multiplier

Defined as the act of manually grasping an object of definable size and mass with two hands, and vertically moving the object without mechanical assistance.

Lifting Task

Weight of the object to be lifted, in pounds or Kg including the container.

Load Weight

Distance of the hands away from the mid-point between the ankles, in inches or cm.

Horizontal Location (H)

Distance of the hands above the floor

Vertical Location (V)

Absolute value of the difference between the vertical heights at the destination and origin of the lift.

Vertical Travel Distance (D)

Angular measure of how far the object is displaced from the front (Mid sagittal plane)of the workers body at the beginning or ending of the lift, in degrees (measures at the origin and destination of lift)

The asymmetry angle is defined by the location of the load relative to the workers mid saggittal plane, as defined by the neutral body posture, rather than the position of the feet or the extent of body twist

Asymmetry Angle (A)

Lifting Frequency

Average number of lifts per minute over a 15 minute period.

Example Analysis

Work Sheet (Example)

Job Description The job in picture consists of a worker inspecting

compact containers for damage on a low shelf and then lifting them with both hands directly in front of the body from shelf 1 to shelf 2 at a rate of 3/min. for a duration of 45 minutes.

For this Analysis assume that 1. The worker cannot take a step forward when

placing the object at the destination due to the bottom shelf

2. Significant control of the object is required at the destination.

3. The containers are of optimal design but without handles.

Job Analysis Horizontal Distance (origin)- 10” Horizontal Distance (Destination)- 20” Height of the Shelf 1 – 22” Height of the Shelf 2 – 59” Since the container is optimal design

but does not have handles, the coupling is defined as fair

No asymmetric lifting is involved. ( A=0)

Job Analysis

With all the measurements The RWL for this activity is 34.9lbs

at the origin and 15.2lbs at the destination.

Hazard Assessment The weight to be lifted is less than

Recommended Weight Limit (RWL) at the origin (34.9lbs) but greater than the RWL at Destination (15.2lbs)

The Lifting Index (LI) isAt origin- 0.76At Destination- 1.7 These values indicate that the destination of

the lift is more stressful than the origin and that some healthy workers would find this task physically stress full.

Redesign Suggestions

Bring the destination point closer to the worker

Lower the height of the Shelf 2 Decrease the vertical distance

between origin and destination Reduce the lifting frequency rate.

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