Analysis of Manual Work
• Objectives
– Review traditional job analysis methods
– Introduce ergonomic job analysis methods for
identifying potential for worker exposure to physical
ergonomic stressors
– Examine specialized tools for assessing risk associated
with manual materials handling work
• special focus on revised NIOSH Lifting Equation
– Review general recommendations for manual
materials handling work
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Review traditional job analysis methods
Describing Manual Work
• Why would methods for describing
manual work be useful?
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Review traditional job analysis methods
Job Analysis
Traditional IE methods
• Tools and procedures for describing certain
aspects of a job
• Taylor and the Gilbreths were pioneers
• Methods:
– Descriptive methods
• ex: operation process charts, flow process charts
– Predictive methods
• ex: MTM, MOST - repetitive tasks
– Assessment methods
• ex: work sampling, time study
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Review traditional job analysis methods
Benefits of traditional analysis
methods...
• Description of manual work
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Ergonomic job analysis
Ergonomic Job Analysis*
• A method for identifying and
evaluating generic risk factors
associated with work-related
musculoskeletal disorders
• Based on collection of data about a job,
designed to address these questions:
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– 1) Does performing the job expose a
worker to any generic ergonomic risk
factors?
– 2) What aspects of the job cause or *Keyserling et al. (1991)
Ergonomic job analysis
Generic Ergonomic Risk Factors
• Characterized by excesses in Intensity,
Duration, and/or Frequency:
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Force exertion
Posture
Contact stress
Dynamics
Vibration
Temperature
Ergonomic job analysis
Aspects of a job that may result in
exposure to generic ergonomic risk
factors
Methods
Tasks
Tools and Equipment
Workers
Work
Environment
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Organization
Ergonomic job analysis
Elements of Ergonomic Job Analysis
• Preparation
– team
– equipment
• Method
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Adverse health outcomes assessment
Basic job documentation
Identification of risk factor exposures
Evaluation of risk factor exposures
Exposure control
Ergonomic job analysis
Method - Adverse health outcomes
assessment
• Data sources:
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Ergonomic job analysis
Method - Basic Job Documentation
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Job analysis team members and date
Uniquely identify job
Describe worker(s)
Describe work objectives
Work schedule
Production &/or work pace info
Describe job rotation
Sketch work station layout
List tools and equipment
List all handled parts and materials
Describe work methods
Ergonomic job analysis
Method - Identification of risk factor
exposures
• Determine risk factors associated with each
work element
>>>>>>>>> Generic risk factors <<<<<<<<
Work element
A
Description
Contact stress……
Force
Posture
Thread wire through
Y (based
Y (pinch grip) Y (wire into fingertip)
hole in insulator
on gage)
B…………..
– risk factor checklist can be useful, but familiarity
with job is essential
• Determine risk factor exposure for total job
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Ergonomic job analysis
Method - Evaluation of risk factor
exposures
• Bases for evaluation of risk:
– epidemiological data
– company data
– specialized tools
• examples:
– Lifting: NIOSH lifting equation, Michigan model, LMM, ...
– Posture: RULA, OWAS, …
– distal upper extremity: Strain Index (combines posture, force,
etc)
• After identification and evaluation, summarize
findings
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Ergonomic job analysis
Method - Exposure control
• Develop alternative solutions
• Perform follow-up ergonomic job
analysis to evaluate controls
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Use of specialized tools in analysis of MMH tasks
Analysis of Manual Materials
Handling Tasks
• Importance of MMH tasks relative to
workplace MSDs
– 1994 workplace stats: 529,741 injuries due
to overexertion in lifting, pushing or
pulling, holding, carrying or turning
objects
– low back region is the primary area of
injury
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Use of specialized tools in analysis of MMH tasks
Injury Prevention Strategies
• Task design
• Worker selection
• Worker training
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Use of specialized tools in analysis of MMH tasks
MMH Risk Factors Associated with Low
Back Disorder/Low Back Pain*
Lifting and force movements
Heavy physical work
Awkward postures
Whole body vibration (in conjunction with
lifting and awkward postures)
 Static work postures
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* NIOSH, 1997
Use of specialized tools in analysis of MMH tasks
MMH System
• In analyzing a MMH task, consider the
system characteristics….
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worker
material - container
task - workplace
work practices
…and which characteristics might give
rise to the risk factors mentioned
previously
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Use of specialized tools in analysis of MMH tasks
Establishing Lifting Limits Revised NIOSH Equation
• Bases:
– Epidemiology:
• injury rates for workers on jobs with LI>3 are quite
high
– Biomechanics:
• 3400 N of disc compression
– Physiology:
• 2.2-4.7 kcal/min (task dependent)
– Psychophysics:
• acceptable to 75% of females, and 99% of males.
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Use of specialized tools in analysis of MMH tasks
Form of the NIOSH Equation
Recommended weight limit (RWL) = LC * (HM * VM * DM * AM * FM * CM)
where:
LC: recommended maximum load, under optimal conditions
and, all other factors are discounts to that maximum, to account for less-than-optimal conditions
HM: accounts for horizontal distance from spine - as distance increases, RWL decreases
VM: accounts for vertical height of start or end of lift - penalized if start or end varies from 75 cm,
(about table/knuckle height)
DM: accounts for vertical travel distance of load - penalized if distance exceeds 25 cm
AM: accounts for lifting outside of the sagittal plane - penalized as move further away from sagittal
CM: accounts for hand-handle coupling - poorer coupling results in reduction of RWL
FM: accounts for rate of lifting - as rate increases, RWL decreases
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Use of specialized tools in analysis of MMH tasks
Revised NIOSH Equation
Assumptions and Limitations
• Assumptions:
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smooth lifting (no acceleration)
moderate sized object
unrestricted lifting postures
two-handed, various hand-load coupling
steady lifting while standing
favorable temperature
main job is MMH, others require little energy
good traction for feet, no foot movement
same risk for lifting and lowering
• Limitations:
– Individual risk is not assessed (protective at the group level)
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Use of specialized tools in analysis of MMH tasks
Pushing and Pulling in MMH
• Dangers:
– overexertion
– slipping
• Important factors:
– friction
• shoe/floor
• wheels
– handle height
– foot location
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Use of specialized tools in analysis of MMH tasks
Asymmetric Loading in MMH
• Recommendation:
– two-handed symmetric lifts
• But asymmetry is more common:
– one-handed handling
– twisting or lateral bending of trunk
• Problems with asymmetry:
– capability decreases as:
• stability decreases
• greater reliance on one muscle instead of right-left pair
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Use of specialized tools in analysis of MMH tasks
Additional analysis tools for more
complex MMH tasks
• Shoaf et al equation - determines maximum predicted load
for condition
– accounts for push, pull, carry, lift
– accounts for personal factors
• Michigan model - determines % capable at every joint
(determines weak link)
– considers individual anthropometry
– accounts for various postures throughout kinematic chain
• Lumbar Motion Monitor model - determines LBD risk
associated with task
– considers trunk dynamics and moment of hand load
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General recommendations for MMH work
MMH job design recommendations
Eliminate MMH if possible
• If not possible, then implement
administrative or engineering controls
– Administrative controls:
•
– Engineering controls:
•
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