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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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Describing Manual Work

• Why would methods for describing manual work be useful?

Review traditional job analysis methods

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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

Review traditional job analysis methods

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Benefits of traditional analysis methods...

• Description of manual work

Review traditional job analysis methods

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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:– 1) Does performing the job expose a worker

to any generic ergonomic risk factors?– 2) What aspects of the job cause or

contribute to worker exposure?

Ergonomic job analysis

*Keyserling et al. (1991)

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Generic Ergonomic Risk Factors

• Characterized by excesses in Intensity, Duration, and/or Frequency:– Force exertion– Posture – Contact stress– Dynamics– Vibration– Temperature

Ergonomic job analysis

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Aspects of a job that may result in exposure to generic

ergonomic risk factors

Ergonomic job analysis

Methods

Tasks

Work

OrganizationEnvironment

Workers

Tools and Equipment

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Elements of Ergonomic Job Analysis

• Preparation– team– equipment

• Method– Adverse health outcomes assessment– Basic job documentation– Identification of risk factor exposures– Evaluation of risk factor exposures– Exposure control

Ergonomic job analysis

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Method - Adverse health outcomes assessment

• Data sources:

Ergonomic job analysis

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Method - Basic Job Documentation

• 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

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Method - Identification of risk factor exposures

• Determine risk factors associated with each work element

– risk factor checklist can be useful, but familiarity with job is essential

• Determine risk factor exposure for total job

Ergonomic job analysis

>>>>>>>>> Generic risk factors <<<<<<<<

Work element Description Force Posture Contact stress……

A Thread wire through Y (based Y (pinch grip) Y (wire into fingertip)

hole in insulator on gage)

B…………..

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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

Ergonomic job analysis

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Method - Exposure control

• Develop alternative solutions• Perform follow-up ergonomic job

analysis to evaluate controls

Ergonomic job analysis

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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

Use of specialized tools in analysis of MMH tasks

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Injury Prevention Strategies

• Task design• Worker selection• Worker training

Use of specialized tools in analysis of MMH tasks

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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

* NIOSH, 1997

Use of specialized tools in analysis of MMH tasks

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MMH System

• In analyzing a MMH task, consider the system characteristics….– worker– material - container– task - workplace– work practices

…and which characteristics might give rise to the risk factors mentioned previously

Use of specialized tools in analysis of MMH tasks

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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.

Use of specialized tools in analysis of MMH tasks

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Form of the NIOSH EquationRecommended 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

Use of specialized tools in analysis of MMH tasks

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Revised NIOSH EquationAssumptions and Limitations

• Assumptions:– 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)

Use of specialized tools in analysis of MMH tasks

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Pushing and Pulling in MMH

• Dangers:– overexertion– slipping

• Important factors:– friction

• shoe/floor• wheels

– handle height– foot location

Use of specialized tools in analysis of MMH tasks

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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

Use of specialized tools in analysis of MMH tasks

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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

Use of specialized tools in analysis of MMH tasks

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MMH job design recommendations

Eliminate MMH if possible• If not possible, then implement

administrative or engineering controls– Administrative controls:

•

– Engineering controls:•

General recommendations for MMH work