NIOSH.pdf

MANUAL LIFTING TASK EVALUATION
NIOSH ORIGINAL LIFTING MODEL
• In 1981, NIOSH published the Work Practices Guide
(WPG) for Manual Lifting.
• WPG defines a manual lifting task as the act of
manually grasping and raising an object of a definable
size without mechanical aids.
• The WPG was based on the fact that ‘an over exertion
injury is the result of job demands that exceed a
worker’s capacity’.

Strain Index (SI) = Job demands / worker capacity
Therefore, if strain index exceeds 1.0 possibility of
overexertion injury.

The 1981 WPG presented a mathematical equation
for determination of an Action Limit (AL) for manual lifting
task.
Action limit (AL): Magnitude of weight in a given lifting
situation, which would result in Low Back Disorder risk
along a risk continuum.
AL indicates whether a manual materials handling task is
safe or risky.

1981 NIOSH Lifting Guide
If the weight of the object is below the AL, the job is
considered safe.
If the weight lifted by the worker is larger than the AL –
Risk at work.
Assessment tools or guides

NIOSH divided the lifting tasks into three classes:
• Acceptable (below AL)
• Unacceptable for most individuals (above the MPL) -
engineering controls
• Unacceptable for some individuals (between AL and Maximum
Permissible Limit, or MPL) - administrative controls

The general form of AL is defined according to Equation:
AL = k (HF) (VF) (DF) (FF)
AL = Action limit.
K = load constant (40 kg or 90 lb), greatest weight (kg or lb) a subject could
lift if all lifting conditions are optimal.
HF = Horizontal factor. Horizontal location (H) of the hands at the origin of
lift, measured from midpoint between ankles ( in cm or inches). H must be
between 15 to 80 cm (6 – 32 inch). The minimum 15 cm (6 inch) is due to
body interference.
The original NIOSH lifting equation

VF = Vertical factor. Vertical location (V) of the hands at origin of lift,
measured from floor level (in cm or inches). V must be between 0 to 175
cm (0 – 70 inch), which is the range of vertical location of most of
individuals.
DF = Distance factor. Vertical travel distance (D) from origin to destination
of lift (in cm or inches). D must be between 25 cm (10 inch) and (200 – V)
cm [(80 – V) inch]. If travel distance is less than 25 cm (10 inch), then D =
25 cm (10 inch) must be used.

FF = Frequency factor. Average number of lifts per minute. F must be
between 0.2 (one lift every 5 min) and Fmax. If the frequency of lift is less
than once per 5 min, F = 0.
Maximum frequency of lifting (Fmax ), which is determined based on the
duration of period of the task during the work-shift.
Lifting is assumed to be occasional (less than 1 hr) or continuous (more
than 1 hr, upto 8 hrs).

Table: Maximum lifts per minute (Fmax)
Average Vertical Location (V) in cm or inch
Period Standing V>75 (30) Stooped V ≤ 75 (30)
1 hr 18 15
8 hr (>1Hr) 15 12
Source: NIOSH, Work practices Guide for manual lifting, 1981.

AL (kg): = 40 * (15 / H) * [(1-0.004 * (V – 75)] * (0.7+ 7.5/D) * (1 – F/Fmax)

In calculating the four modifying factors (HF, VF, DF and FF), it should be
noted that each factor has to be less than or equal to 1.
If a factor exceeds 1 or falls below lower range, an error has been made.
If the lifting conditions are ideal a worker could safely hold and lift
the load constant, k (40 kg or 90 lb).
Assessment tools or guides

• Did not consider asymmetry
• Needed consideration of quality of coupling
Limitations of the NIOSH Lifting Model

PRINCIPAL COMPONENTS
The revised equation has three principal components:
• Recommended weight limit (RWL).
• Load constant (LC)
• Multipliers
NIOSH REVISED LIFTING MODEL

Recommended weight limit
The revised equation multiplies the load constant by the
six multipliers to determine a RWL:
RWL = LC * HM * VM * DM * FM * AM * CM

• LC is the maximum load that can be lifted safely, given
that the conditions of lift, as defined by the multipliers,
are all optimal.
• The load constant has been reduced from 40 kg to 23
kg in the revised equation.

Multipliers
• The revised NIOSH lifting equation consists of six
multipliers (Waters et al, 1994).
• Depending on the lifting conditions, these multipliers
decrease the LC to determine the amount of weight that
can be lifted safely, or RWL.

• H: Horizontal location of the hands (Load center) from the midpoint
between the ankles, measured at the origin and destination of the
lift.
• In those cases where H can not be measured, H can be estimated
as:
H = 20 + L/2 for V ≥ 25 cm
H = 25 + L/2 for V < 25 cm
• L is the length of the container being handled and V is the location
of the hands (relative to standing surface) at the origin of the lift.

EXAMPLE
For V ≥ 25 cm, H = 20 + L/2
If L = 30 cm, H = 20 + 30/2 or H = 35 cm.
For V < 25 cm, H = 25 + L/2 (bottom layer cartons).
In this case H = 25 + 30/2 or H = 40 cm
If H is measured to be less than 25 cm, then use a minimum value
of H = 25 cm.
The maximum value of H should assume is 63 cm.
Horizontal multiplier (HM) can be calculated from the formula 25/H

• V: Vertical location of hands from the standing surface measured
at the origin of the lift. .
• V can range from 0 to 175 cm (upper safe limit of lifting).

Vertical multiplier (VM) is based on the location of the gripping
surface on each carton.
In case of the card board cartons, with no handles, cartons are
gripped from the bottom.
Vertical multiplier (HM) can be calculated from the formula:
VM = [1 – (0.003*(V – 75)]

• D: Vertical travel distance between the location of the hands at the
origin and the destination of the lift.
• D must be in the range of 25 ≤ D ≤ 175 cm.
• If the measured value of D is less than 25 cm, then the minimum
value of D = 25 cm must be used in the RWL calculation.

Distance multiplier (DM) determined as the distance from
the origin of the lift to the destination of the lift.
Distance multiplier (DM) can be calculated from the formula:
DM = (0.82 + 4.5/D)

Angle of asymmetry: the angular displacement of the
load from the sagittal plane, measured from the origin
and/or the destination of the lift (degrees).
Asymmetry line = Line joining the midpoint between the
ankle with the midpoint of the hands projected on the
floor.

00 ≤ A ≤ 1350
AM = (1 – 0.0032A)
Use of larger angles (A) at origin and destination
If A > 1350, AM = 0

Coupling V< 75 cm (30 inches) V ≥ 75 cm (30 inches)
Good 1.0 1.0
Fair 0.95 1.0
Poor 0.90 0.90

Good
Handle
• L ≥ 11.5 cm, Dia 1.9 – 3.8 cm, clearance ≥ 5 cm
• Cylindrical shape and a smooth non-slip
surface.
Hand-hold cut-out
• L ≥ 11.5 cm, clearance ≥ 5 cm semi- oval
shape.
Container
• Frontal length ≤ 40 cm, H ≤ 30 cm, smooth non-
slip surface.
COUPLING (C)

Fair
• Less than optimal design (as in case of good)
• Container: No handle or cut out. A worker should be
capable of clamping fingers at nearly 900 under the
container (lifting cardboard box from floor).
COUPLING (C)

Poor
• No handles or hand hold cut outs
• Irregular bulky objects.
• Frontal length > 40 cm, height > 30 cm, rough or slipping
surface, sharp edges, asymmetric center of mass,
unstable containers.
COUPLING (C)

Frequency multiplier: Lifts per minute
1. Short duration (work upto 1 hr, recovery at least 120%
of work time)
2. Moderate duration (work upto 2 hrs, recovery at least
30% of work time)
3. Long duration (work upto 8 hr without additional
fatigue allowances other than normally given during
the workshift)

Maximum Allowable Frequency
Lifting Duration Vertical Location of lift
V< 75 cm V > 75cm
(30 inches ) (30 inches)
< 1 Hour 12 15
< 2 Hours 10 12
< 8 Hours 8 10

Frequency
Lifts/min
(F)
Work Duration
< 1 hr > 1 but < 2 hr > 2 but < 8 hr
V < 75 cm
(30 in)
V > 75 cm
(30 in)
V < 75 cm
(30 in)
V > 75 cm
(30 in)
V < 75 cm
(30 in)
V > 75 cm
(30 in)
<0.2
0.5
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
>15
1.00
0.97
0.94
0.91
0.88
0.84
0.80
0.75
0.70
0.60
0.52
0.45
0.41
0.37
0.00
0.00
0.00
0.00
1.00
0.97
0.94
0.91
0.88
0.84
0.80
0.75
0.70
0.60
0.52
0.45
0.41
0.37
0.34
0.31
0.28
0.00
0.95
0.92
0.88
0.84
0.79
0.72
0.60
0.50
0.42
0.35
0.30
0.26
0.00
0.00
0.00
0.00
0.00
0.00
0.95
0.92
088
0.84
0.79
0.72
0.60
0.50
0.42
0.35
0.30
0.26
0.23
0.21
0.00
0.00
0.00
0.00
0.85
0.81
0.75
0.65
0.65
0.45
0.35
0.27
0.22
0.18
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.85
0.81
0.75
0.65
0.55
0.45
0.35
0.27
0.22
0.18
0.15
0.13
0.00
0.00
0.00
0.00
0.00
0.00
(Source: Reprinted from NIOSH, Applications Manual for the Revised NIOSH Lifting Equation)

COMPARISON
Load constant and
and multipliers 1981 Equation 1991 Equation
LC 40 kg 23kg
HM 15/H 25/H
VM 1-0.004(V-75) 1-0.003(V-75)
DM 0.7 + 7.5/D 0.82 + 4.5/D
FM 1 – F/Fmax From Table
AM NA 1 – 0.0032A
CM NA From Table

Lifting index
Lifting index (LI) = Load weight / RWL
LI greater than one presents a risk of
overexertion injury.
Waters et al, 1994

This recommendation applies to most workers for:
• two-handed lifting,
• comfortable environments and non-slip floorings
Applicability

The Revised NIOSH Lifting equation does not apply in
situations where a person is lifting (or lowering):
• for over 8 hours
• while seated or kneeling
• while pushing or pulling
Restriction

The Composite Lifting Index (CLI)
STLI + ∑ delta LI

To prevent occupational back injuries, it is essential to
identify and control the factors of MMH.
1. Organization of workflow
2. Job design/redesign (including environment)
3. Pre-placement screening, wherever necessary
4. Training
How can we prevent back injury
resulting from MMH?

• Poor planning of the workflow results in repeated
handling of the same object.
• Avoid Double handling.
MMH Factors
1. Organization of work flow

2. Job design/redesign
a. Eliminate heavy MMH
b. Decrease MMH demands
c. Reduce stressful body movements
d. Improve environmental conditions
MMH Factors

• Powered or mechanical arm for heavy MMH tasks.
• Mechanical arms lower the risk for back injury
• Mechanical aids like lift tables, conveyors, Pulleys or
fork lifts.
a. Eliminate heavy MMH
MMH Factors

• Decrease the weight of handled objects to acceptable
limits.
• Assign two people, split the load into two or more
containers.
MMH Factors

• Change the type of MMH movement. Pulling objects is
easier than carrying. Pushing is less demanding than
pulling.
• Alternate heavy tasks with lighter ones to reduce the
build-up of fatigue.
MMH Factors

• Keep all materials at waist height.
• Eliminate deep shelves to avoid bending.
• Locate objects within easy reach.
• Change the shape of the load so that the load can be
handled close to the body.
c. Reduce stressful body movements
MMH Factors

• Illuminate the work area for MMH tasks at the level of
200 lux.
• Use task lights or other additional light sources to
improve visibility
• Use angular lighting and colour contrast to improve
depth perception especially during climbing stairs or
moving in through passage ways.
d. Improve environmental conditions
MMH Factors

• Pre-placement screening may be useful as a preventive
measure for the jobs involving heavy MMH.
3. Pre-placement screening
MMH Factors

- make the worker aware of the hazards of MMH
- demonstrate ways of avoiding unnecessary stress
-Ensure a good grip on the load.
4. Training
MMH Factors

✓ Walking surfaces that are uneven, sloping, wet,
icy, slippery, unsteady, etc.
✓ Poor housekeeping that causes slip, trip and fall
hazards
✓ Inadequate lighting
✓Cold or very hot and humid working conditions
✓ Space is small or posture is constrained or both.
Hazardous working condition

Table: Maximum lifts per minute (Fmax)
Average Vertical Location (V) in cm or inch
Period Standing V>75 (3) Stooped V ≤ 75 (3)
1 hr 18 15
8 hr (>1Hr) 15 12

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