Transcript 12__mmh-ho - ~ Continuous Improvement

12. Manual Material
Handling
NIOSH Work Practices Guide
for Manual Lifting
TI 2111 Work System Design and Ergonomics
NIOSH WPG for Manual Lifting
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The NIOSH Work Practices Guide (WPG) for Manual
Lifting was compiled by a panel of experts in 1981 for
the following purposes:
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Review and summarize current knowledge with regard to
manual material handling.
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Provide concrete guidelines to assist industry in the
prevention of overexertion injuries during lifting.
A second panel of experts (many the same as the first
panel) was convened in the late 1980’s to review
recent developments and research in this area and to
revise the work practices guide.
TI 2111 Work System Design and Ergonomics
Criteria for 1991 NIOSH WPG
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Assumptions:
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“Overexertion injury is the result of job demands
that exceed a workers capacity”
“These injuries result by direct trauma, a single
exertion (‘overexertion’), or potentially as the
result of multiple exertions (‘repetitive trauma’).
TI 2111 Work System Design and Ergonomics
Example
Start
End
TI 2111 Work System Design and Ergonomics
Lifting Equation
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A ‘load constant’ is the maximum recommended weight for
lifting at the standard lift location under ideal conditions.
LOAD CONSTANT = 23 kg
Decrease the load constant to account for the influence of
known risk factors using 6 multipliers:
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horizontal location (HM)
vertical location (VM)
vertical travel distance (DM)
asymmetry (AM)
frequency (FM)
coupling (CM)
All Multipliers are ≤ 1
Recommended Weight Limit (RWL) =
23kg  HM  VM  DM  AM  FM  CM
TI 2111 Work System Design and Ergonomics
Position Measurement
HD
VD
HO
VO
TI 2111 Work System Design and Ergonomics
Horizontal Multiplier
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HM = (25/H)
H = horizontal
distance (in cm)
of the hands
from the
midpoint
between the
ankles.
HD
HO
TI 2111 Work System Design and Ergonomics
Horizontal Multiplier
Multiplier
1.2
1
0.8
0.6
0.4
0.2
0
20
30
25
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
40
50
60
70
80
Horizontal Distance (cm)
If H ≤ 25, HM = 1
Relatively big, non-linear effect
TI 2111 Work System Design and Ergonomics
Vertical Multiplier
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VM = (1-(0.003|V-75|))
V = vertical distance (in
cm) of the hands from the
floor. Measure at the origin
and destination of lift.
VD
VO
TI 2111 Work System Design and Ergonomics
Vertical Multiplier
overhead reach
torso flexion
Multiplier
1.2
1
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
120
140
160
180
Vertical Distance (cm)
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Moderate, non-linear effect
TI 2111 Work System Design and Ergonomics
Distance Multiplier
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DM = (0.82 +(4.5/D))
D = vertical travel distance (in
cm) between the origin and
destination of the lift.
D = |VD-VO|
DM accounts for metabolic
demand, task dynamics, but
not lift vs. lower
D
TI 2111 Work System Design and Ergonomics
Distance Multiplier
Multiplier
1.2
1
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
120
140
160
180
Distance Moved (cm)
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Relatively small, non-linear effect
TI 2111 Work System Design and Ergonomics
Asymmetric Multiplier
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AM = (1(0.0032|A|))
A = angle (deg)
of asymmetry —
angular
displacement of
the load from the
sagittal plane.
Measure at the
origin and
destination of
lift.
A
sagittal
plane
TI 2111 Work System Design and Ergonomics
Asymmetric Multiplier
Multiplier
1.2
1
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
120
140
160
180
Asymmetry Angle (deg)
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Moderate, linear effect
TI 2111 Work System Design and Ergonomics
Coupling Multiplier
Table lookup
 Accounts for differences in capability and
acceptability with changes in coupling
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Coupling
Initial load height
V•
75 cm
V<75 cm
Good
1.0
1.0
Fair
.95
1.0
Poor
.90
.90
Good:
Fair:
handles or objects that can be comfortably grasped
less than optimum handles or load contacted by
fingers up to the palm
Poor:
bulky, shifting, sagging loads
orWork
loads
with sharp
TI 2111
System
Designedges
and Ergonomics
Frequency Multiplier
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Accounts for fatigue and differences in load height (arms vs.
legs/back)
Frequency
lifts/min
0.2
≤ 0.5
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
>15
Š 1 hour
V<75 V•
75
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
Š 2 hour
V<75
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
Š 8 hour
V•
75
V<75
0.95
0.92
0.88
0.84
0.79
0.72
0.60
0.50
0.42
0.35
0.30
0.26
0.23
0.21
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
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
V•
75
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
initial load
height
(cm)
Model may
not be
appropriate
TI 2111 Work System Design and Ergonomics
Recommended Weight Limits and Lift
Index
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RWL = 23 kg  HM  VM  DM  AM  CM  FM
Lift Index = (Actual Load)/RWL
Interpretation: increased risk of low-back injury if the LI
exceeds 1.
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< 1 OK
= 1 boarderline
> 1 may have increased risk
> 3 likely have increased risk
Some believe that if workers are properly screened (based on
the task requirements) and trained, that they can safely work at
lift indexes greater than 1 but less than 3.
What are ideal lifting conditions??
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Maximize RWL (keep load close to the body, …)
TI 2111 Work System Design and Ergonomics
Assumptions and Limitations
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Manual work activities other than lifting are assumed to be
minimal
The equation does not account for unpredictable situations
such as shifting loads
A favorable ambient environment is assumed (19°- 26° C or
66° - 79° F)
Risk of slips not accounted for (good floor surface assumed)
Lifting and lowering tasks are assumed to pose the same risk
of injury
Tasks involving one-handed lifts, lifting while seated or
kneeling, or lifting in a constrained work area are not
appropriate for this model
Does not account for individual anthropometric differences
TI 2111 Work System Design and Ergonomics
Example
Start
H = 13.0 cm
V = 13.5 cm
A = 0 deg
End
H = 41.5 cm
V = 89.0 cm
A = 0 deg
D = 75.5 cm; F = 1/min; Couplings = Fair
TI 2111 Work System Design and Ergonomics
Criteria for 1991 NIOSH WPG
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Methodologies used:
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Epidemiology: Injury rates vs. task characteristics
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Biomechanics: Infrequent lifting tasks and low
back injury risk.
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Physiology: Energy requirements during
repetitive lifting
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Psychophysical: Maximum acceptable weights in
different tasks
TI 2111 Work System Design and Ergonomics
Biomechanical Criterion
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Assumptions of the
1991 NIOSH WPG:
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The L5/S1 vertebral joint
is the site of the greatest
stress during lifting.
Compressive force at
that joint is the critical
stress vector.
The criterion (at risk)
level for compressive
force at this joint is 3400
N (760#).
cervical
vertebrae
thoracic
vertebrae
lumbar
vertebrae
sacral
vertebrae
coccygeal
vertebrae
TI 2111 Work System Design and Ergonomics
Physiological Criterion
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Lifting activities can place large metabolic demands
on workers, leading to fatigue. Fatigue is
associated with a decrease in strength and an
increased likelihood of injury
Assumptions of the 1991 NIOSH WPG:
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WHO: The baseline maximum aerobic capacity of U.S.
workers is 9.5 kcal/min (aerobic lifting capacity of an
average 40-year old female worker)
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WHERE: Aerobic capacity for lifts above waist level is 70%
of that for those below waist level
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HOW LONG: The criterion (at risk) level for energy
expenditure is: 50% of max. for 1 h or less; 40% of max. for
1 to 2 h; 33% of max. for 2 to 8 h
TI 2111 Work System Design and Ergonomics
Psychophysical Criterion
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Psychophysical Evaluations:
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Maximum Acceptable Weights of Lift (MAWLs)
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Studies of Isometric Lift Strength
Assumptions of the 1991 NIOSH WPG:
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The criterion (at risk) level for maximum acceptable weight
of lift is the load acceptable to 75% of female workers.
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A criterion acceptable to 75% of female workers will be
acceptable to approximately 99% of male workers and 90%
of the working population (assuming 50% male and 50%
female).
TI 2111 Work System Design and Ergonomics