The purpose of this
ergonomics study of workers at the Anniston Army Depot in June 2000 was
to evaluate the effect of replacing currently used impact wrenches
with new ergonomically designed models. It was theorized
that the introduction of these newer impact wrenches would improve
productivity, decrease vibration exposure, decrease physiologic demands
and improve the body posture of the workers on the depot's tank
disassembly line.
Eleven workers
volunteered to test 13 impact wrenches (9 new, 4 current). The impact
wrenches varied in drive size (3/8”, 1/2”, 3/4”, 1”) as well as
manufacturer. Workers were asked to remove bolts from a wheel hub of a
tank. Vibration and electromyography (EMG) readings were taken during the nut
removal task. At the completion of the task, the workers were asked to
complete the Borg Scale of perceived exertion. Also, Rapid Upper Limb
Assessments (RULA) were completed via videotape. To complete the data
collection process, each worker was given the opportunity to use each of the
impact wrenches for a period of one week in which they were asked to rate
the hammers in order of preference for each drive size category.
Analysis of the data
showed that the introduction of the new impact wrenches significantly
decreased the amount of time needed to remove the wheel hub nuts by an
average of 2.5 seconds—in fact, the amount of time the
workers needed to remove the wheel hub nuts was cut by almost 50%.
Also, the introduction of the new impact wrenches significantly decreased
the amount of vibration experienced by the workersfor both the 3/8” and
1/2” drive impact wrenches. (Due to instrumentation constraints, conclusions
for the 3/4" and 1” drive impact wrench could not be made.)
The introduction of
the new impact wrenches did not have an impact on the postures assumed by
the workers (RULA) nor did the new impact wrenches decrease the magnitude of
physiologic demand the workers needed to complete the tasks (as measured by
electromyography).
The workers who
returned the ratings forms for the impact hammers consistently rated the
newer tools higher in order of preference but, due to a small sample size,
statistical significance could not be obtained.
In conclusion, a
combination of proper tools and appropriate workstation setup will have the
greatest impact on worker performance and comfort.
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