Psy 552 Ergonomics

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Psy 552 Ergonomics Biomechanics

• Lecture 17

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Work classification methods

• The need to address productivity, comfort and
  safety dictate the need evaluate work methods.
• In the quest to find the optimal method, early
  methods focused on productivity.
• These work analysis methods have significant
  drawbacks that limit their use in ergonomics and
  biomechanics.

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Historic names

• Frederick Taylor father of timemotion studies.
• Used time analysis of work to enhance
  productivity.
• Devised the four principles of
• scientific management

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4 Principles

• Study work methods specifically.
• Select the best workers for the task and train
  them.
• Develop cooperation between employees and
  managers.
• Divide work according to ability, between workers
  and managers depending upon who was best suited
  to perform it.

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Frank and Lillian Gilbreth

• Studied work methods
• Capitalized on motion studies using illuminated
  markers.
• Categorized motions in to elemental motions
  that now serve as the basis for contemporary time
  and motion studies.

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Method-Time Measurement (MTM)

• MTM is a time estimation based upon elemental
  movements

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MTM (cont)

• Focuses on how
• ...
• Uses TMUs

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Time motion ergonomics

• These early studies created a foundation for
  ergonomic evaluations.
• TM studies do not generalize to ergonomics
  biomechanics because they

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Contemporary classification methods

• Modern systems fall into two categories
• Passive
• Active

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Passive surveillance

• Involves reviewing and analyzing pre-existing
  records such as

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The passive process

• Must be contrasted with results of other
  assessment techniques including

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The passive process (cont)

• Works best when records are computerized.
• Should be conducted monthly if not quarterly.
• Should contain requisite information

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Indices

• Incident rate
• IR ( of illnesses x 200,000)/hours worked
• Point prevalence
• PR ( new old case at a given time)/number
  of workers at the same time
• Severity index
• SI (Total lost work days due to the
  disorder(s))/(Total number of workers or hours
  worked in a period)

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Passive advantages

• Low cost
• Makes use of available data
• Historical perspective
• Can be used to compare departments
• Can be used to evaluate ergonomic interventions

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Passive disadvantages

• There are few accepted signs for WMSD.
• The true causes of WMSD are not well known.
• Putative factors are present in every job.
• These factors dont discriminate or differentiate
  jobs with and without histories of WMSD.
• Underreporting

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Passive disadvantages (cont)

• Inconsistent record collection
• WMSD occur over time and might not be reflected
  in records.
• Unknown reporting thresholds
• Records often fail to record the specific task
  being performed.

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Active surveillance

• There are two types
• Self-report
• Audits
• Advantages

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Active surveillance (cont)

• Success depends on
• Short response times
• Adequate response rates
• Trained personnel
• Employee memory
• Tolerance of false positives

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Active self-report tool features

• 1.
• 2.
• 3.
• 4.
• 5.
• 6.
• 7.
• 8.
• 9.

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Demographic medical work history
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Analyzing WMSD data
WMSD WMSD WMSD
Yes No Total
Risk Factor Present Yes 10 30 40
Risk Factor Present No 4 76 80
Total 14 106 120
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Analyzing WMSD data (cont)

• WMSD incident rates gt 1 per 200,000 should be
  investigated further.
• In Washington State between 1988 and 1991 the
  WMSD incident rate was .82 per 200,000 work
  hours.
• Prioritize
• Jobs with the highest incident rates.
• Jobs with the most effected people.
• Jobs where large changes have taken place.

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Active surveillance Risk factors

• Used by trained ergonomist
• Provide data based on educated observations
• Do not require preexisting symptoms
• Can be used to evaluate work or equipment
  changes.
• Highly correlated with discomfort surveys.

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Risk factors (cont)

• Posture targeting
• Ovac Working Posture Analysis System
• EMG

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Risk factor surveillance Disadvantages

• They are more descriptive than evaluative.
• A risk factor absent an injury requires evaluator
  judgment.
• There are often few comparisons.

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When conducting evaluations

• Cleary state your objectives.
• Understand sponsors desires.
• Understand that you will not be universally
  accepted.
• Select methods using an iterative process to
  promote validity.
• Seek most recent scientific literature.
• Seek advice of experienced colleagues.