Hand Tools Study, Anniston Army Depot

Vibration and EMG readings taken during the nut removal task.

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.)

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 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.

Issue 11 (PDF)

Reports on the positive results of the use of ergonomically designed impact wrenches.
 

Fact Sheet 4 (PDF)

Proper use of hand tools can make your work safer and easier.
 

Fact Sheet 5 (PDF)

Proper use of powered hand tools can make your work safer and easier.
 

Last Modified: 31 August 2011 at 11:19