Complementing the Washington
Ergonomics assessment method with
the Strain Index
Abraham Robledo Gallegos, IE
Keith White, Ph.D., CPE
AGENDA
• Problem definition.
• Information provided by the Washington
Ergonomics assessments and the Strain
Index.
• Methodology and examples.
• Conclusion.
• References.
• Questions.
Problem Definition
Only reacting to injury claims does
not allow a company work toward
preventing injuries.
Problem Definition
To date , a considerable number of risk
identification and injury prevention tools
have been developed to help companies
prevent accidents and injuries before
they happen.
Problem Definition
• Assessment methods vary in
information content.
• Washington Ergonomics method is well
suited for general approaches.
• The Strain Index adds exposure time
factors and more specific information.
Problem Definition
• Using WE assessments, high risk activities
were identified at an Allied Air
manufacturing facility.
• The agreed upon one solution was to
implement a job rotation program.
• The Strain Index added information to
generate the rotation pattern.
Washington Ergonomics
• The Washington Ergonomics
assessment method:
– Identifies jobs with elevated
ergonomic risk factors across the
manufacturing facility.
– It is more of a general approach that
provides enough information to
initiate actions to resolve concerns.
Washington Ergonomics
• The WE method considers the important
factors outlined below.
– Movement required to perform the
task.
– Hands, wrist and arms position
– Force and grip requirements
– Contact stress
– Vibration
– Environment
– Opinion
Strain Index
• The Strain Index considers six variables
and multipliers:
– Intensity of exertion
– Speed of work
– Duration of exertion
– Efforts per minute
– Duration of Task per Day
– Hand/wrist posture
Together
1. Movement factors / Exertions per
minute factors
2. Position factors / Hand-Wrist
Posture factors
3. Force-Grip factors / Intensity of
exertion factors
4. Contact stress factors
Together
5. Vibration factors
6. Environment factors
7. Workers opinions
8. Duration of exertion factors
9. Speed of work factors
10.Duration per day factors
Methodology
• The first step to build a job rotation
pattern is to assess the jobs with the
Washington Ergonomics method.
• The second step is to identify the
high risk tasks that require a
possible job rotation program.
Methodology
• Tasks that expose different parts of the
body to the musculoskeletal stress
should match. If the task of interest
gets an 8 for wrist position, it should be
matched with a task that avoids bad
wrist position with a low score for this
factor (4 or less).
Washington Ergonomics - Methodology
Methodology
• The next step is to find the Strain Index
scores for all the selected jobs in order
to confirm the Washington Ergonomics
findings and to add exposure time
factors to the analysis.
Methodology
• The time factors will let us now how
much time it is recommended to spend
performing certain task.
Strain Index - Methodology
Strain Index - Methodology
Combined - Methodology
Combined - Methodology
Combined - Methodology
• Using the last two tables, we can
suggest a rotation to minimize the risk,
where the task of interest is performed
less than 1 hour; time after which, the
worker could perform the candidate
tasks 1, 2, 4, 5 or 6 for the rest of the
shift or the candidate task 7 for a
period of time between 1 and 4 hours.
Methodology
• Sometimes it is needed to deal with
administrative restrictions. For
instance, it might be impossible to
rotate workers every two hours, but
it might be allowed to rotate every
half a shift.
Methodology
• The last step is to look for medical
validation for the rotation designed.
Conclusion
Different ergonomics assessment
methods vary in information
content and can complement each
other under certain conditions.
Conclusion
Washington Ergonomics and Strain
Index methods can work together
to generate good job rotation
programs.
References
• Brough, William R. Hands and Arms evaluation
booklet. Washington Ergonomics Inc., 1991.
• Brough, William R. Washington Ergonomics.
< http://www.washingtonergonomics.com
/philosophy.html>
• Moore, J. Steven, and Garg Arun. The Strain
Index: A Proposed Method To Analyze Jobs For
Risk Of Distal Upper Extremity Disorders. AM.
IND. HYG. ASSOC. J. (56)/ May 1995, pages 443456.
QUESTIONS???
Special Thanks to
• Keith White, Ph.D., CPE,CEM
• Allied Air Enterprises. Blackville, SC plant.
• Lennox International