NIOSH Lifting Equation
Low back pain and injuries attributed to manual lifting activities
continue to be one of the leading occupational health and safety issues in
workplaces across the nation. According to the National Safety Council,
overexertion injuries represent more than 30 percent of all workplace injuries. In
addition, overexertion injuries of the back, shoulders and knees are some
of the most costly to workers' compensation systems.
In order to assist employers in reducing the risk of lifting-related
injuries, the National Institute for Occupational Safety and Health (NIOSH)
developed a lifting equation designed to determine the safety of lifting
tasks. The NIOSH lifting equation is one of several important tools used in
a comprehensive effort to prevent overexertion injuries.
The following calculator is based on the NIOSH lifting
equation. Upon entering the necessary information, you can
determine if the lifting task is safe or if changes are needed. Please be
aware that the NIOSH lifting equation is designed only for two-handed manual
lifting tasks. For a list of the situations where the NIOSH lifting equation
does not apply, click here.
For additional information on the NIOSH lifting equation:
Note: The following tool uses JavaScript to make calculations.
If you have scripting disabled or the device you are using does not support
JavaScript, visit the
NIOSH website
for more information on this equation.
Model Inputs
Vertical Location DestinationVertical Location Destination is
the distance of the hands (in inches) from the plane of the floor at the
destination, or ending point, of the lift. The diagram below illustrates
how to measure the vertical location at the destination. Select the
vertical location from the drop-down list that is closest to the actual
vertical destination (i.e., 52 inches = 50; 53 inches = 55).
Vertical Location OriginVertical Location Origin is the
distance of the hands (in inches) from the plane of the floor at the
origin, or starting point, of the lift. The diagram below illustrates
how to measure the vertical location at the origin. Select the vertical
location from the drop-down list that is closest to the actual vertical
origin (i.e., 32 inches = 30; 33 inches = 35).
CouplingCoupling is the classification that affects how much
force is required to grip the object to complete the lifting task.
Coupling quality is classified as good, fair, or poor. The table below
describes how to determine the coupling quality of the object being
lifted.
| GOOD |
FAIR |
POOR |
| 1. For containers of optimal design, such as
boxes, crates, etc., a "Good" hand-to-object coupling would be
defined as handles or hand-hold cut-outs of optimal design |
1. For containers of optimal design, a "Fair"
hand-to-object coupling would be defined as handles or hand-hold
cut-outs of less than optimal design. |
1. Containers of less than optimal design or
loose parts or irregular objects that are bulky, hard to handle,
or have sharp edges. |
| 2. For loose parts or irregular objects, which
are not usually containerized, such as castings, stock, and supply
materials, a "Good" hand-to-object coupling would be defined as a
comfortable grip in which the hand can easily be wrapped around
the object. |
2. For containers of optimal design with no
handles or hand-hold cut-outs or for loose parts or irregular
objects, a "Fair" hand-to-object coupling is defined as a grip in
which the hand can be flexed about 90 degrees. |
2. Lifting non-rigid bags (i.e., bags that sag in
the middle). |
DurationDuration is the length of time the worker performs the
lifting task. Duration is either classified as short (1 hour or less),
moderate (1-2 hours), or long (2-8 hours).
Frequency RateFrequency Rate is measured in the number of
lifts performed each minute. In situations where less than one lift is
performed each minute, the frequency rate will be less than 1 (e.g., one
lift every five minutes = 0.2 lifts/minute).
Angle of Asymmetry DestinationAngle of Asymmetry Destination
is the displacement angle of the load from the sagittal or median plane
of the body at the destination, or ending point, of the lift. In other
words, it is the number of degrees the back and body trunk are twisted
at the end of the lift. The diagram below illustrates how to measure the
angle of asymmetry. Select the angle of asymmetry from the drop-down
list that is closest to the actual angle of asymmetry (i.e., 20 degrees
= 15; 25 degrees = 30).
Angle of Asymmetry Origin
Angle of Asymmetry Origin is the displacement angle of the load from
the sagittal or median plane of the body at the origin, or starting
point, of the lift. In other words, it is the number of degrees the back
and body trunk are twisted at the beginning of the lift. The diagram
below illustrates how to measure the angle of asymmetry. Select the
angle of asymmetry from the drop-down list that is closest to the actual
angle of asymmetry (i.e., 20 degrees = 15; 25 degrees = 30).
Vertical Travel DistanceTravel distance is the distance the hands
travel between the origin and destination of the lift. Select the
vertical travel
distance that is closest to the actual distance traveled.
Horizontal Location DestinationHorizontal Location Destination
is the distance of the hands (in inches) from the vertical plane of the
midpoint of the ankles at the destination, or ending point, of the lift.
The diagram below illustrates how to measure the horizontal location at
the destination.
Horizontal Location OriginHorizontal Location Origin is the
distance of the hands (in inches) from the vertical plane of the
midpoint of the ankles at the origin, or starting point, of the lift.
The diagram below illustrates how to measure the horizontal location at
the origin.
Calculated Recommended Weight Limits:
| |
RWL = |
LC |
X |
HM |
X |
VM |
X |
DM |
X |
AM |
X |
FM |
X |
CM |
| Origin |
|
51 |
X |
|
X |
|
X |
|
X |
|
X |
|
X |
|
| Destination |
|
51 |
X |
|
X |
|
X |
|
X |
|
X |
|
X |
|
Lifting Index (LI) = Object Weight / RWL
| Origin |
LI = |
|
/ |
|
= |
|
| Destination |
LI = |
|
/ |
|
= |
|
Recommendation Based on Lifting Index:
Click here
to learn how to improve the multiplier information categories shown above.
- RWL: Recommended Weight Limit
The RWL is the principal product of
the 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 (e.g., up to 8 hours) without an
increased risk of developing lifting-related injuries. NIOSH defines
healthy workers as those who are free of adverse health conditions that
would increase their risk of musculoskeletal injury.
- LI: Lifting Index
The Lifting Index is the 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 object being
lifted and the recommended weight limit (RWL). The LI is defined by the
following equation:
LI = Weight of Object divided by Recommended Weight Limit
- If Horizontal Multiplier is less than 1.0
- Bring the load closer to the worker by removing any horizontal
barriers.
- Reduce the size of the object being lifted.
- Avoid lifts on or near the floor.
- If the lifts are near the floor, the object should easily fit between
the legs.
- If Vertical Multiplier is less than 1.0
- Raise or lower the vertical location of the hands at the beginning of
the lift. The goal is to have the hands located 30 inches from floor
level.
- Avoid lifting near the floor or above the shoulders.
- If Distance Multiplier is less than 1.0
- Reduce the vertical distance between the origin and the destination of
the lift.
- If Asymmetric Multiplier is less than 1.0
- Move the origin and destination of the lift closer together to reduce
the angle of twist.
- Move the origin and destination of the lift further apart to force the
worker to turn the feet, rather than twist the body.
- If the Frequency Multiplier is less than 1.0
- Reduce the lifting frequency rate.
- Reduce the lifting duration.
- Provide longer recovery periods (i.e., light work period).
- If the Coupling Multiplier is less than 1.0
- Improve the hand-to-hand object coupling by providing optimal
containers with handles or handheld cutouts.
- Improve the handholds for irregular objects.
The NIOSH Lifting Equation does not apply if
any of the following occur:
- Lifting/lowering with one hand
- Lifting/lowering for over 8 hours
- Lifting/lowering while seated or kneeling
- Lifting/lowering in a restricted workspace
- Lifting/lowering unstable objects
- Lifting/lowering while carrying, pushing or pulling
- Lifting/lowering with wheelbarrows or shovels
- Lifting/lowering with high-speed motion (faster than 30 inches/second)
- Lifting/lowering with unreasonable foot floor coupling (<0.4
coefficient of friction between the sole and the floor)
- Lifting/lowering in an unfavorable environment (i.e., temperature
significantly outside of 66-79 degree F range; relative humidity outside
35-50% range
For more information on the applicability of the NIOSH lifting equation,
visit the NIOSH website.
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| Job Analysis Worksheet |
| Department: |
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Job Description: |
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| Job Title: |
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| Analyst's Name: |
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| Date: |
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Step 1. Measure and record task Variables
Object
Weight (lbs) |
Hand Location (in) |
Vertical
Distance (in) |
Asymmetric Angle (Degrees) |
Frequency Rate |
Duration |
Object
Coupling |
| Origin |
Dest. |
Orign |
Destination |
lifts/min. |
(HRS) |
| H |
V |
H |
V |
D |
A |
A |
F |
|
C |
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|
|
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Step 2. Determine the multipliers and compute the RWL's
| |
RWL = |
LC |
X |
HM |
X |
VM |
X |
DM |
X |
AM |
X |
FM |
X |
CM |
| Origin |
|
51 |
X |
|
X |
|
X |
|
X |
|
X |
|
X |
|
| Destination |
|
51 |
X |
|
X |
|
X |
|
X |
|
X |
|
X |
|
|
Step 3. Compute the LIFTING INDEX = Object Weight / RWL
| Origin |
LI = |
|
/ |
|
= |
|
| Destination |
LI = |
|
/ |
|
= |
|
|
Recommendation Based on Lifting Index:
