A Comparison Study of Impact Hammers Steven G. Chervak, MS, CPE

FHP, 2003 Steven Chervak Presentation Outline u Background Information u Methodology u Results u Conclusion FHP, 2003Steven Chervak

FHP, 2003 Steven Chervak Background u Purpose of Project: Evaluate effectiveness of replacing current tools with newer, better designed tools as related to: Evaluate effectiveness of replacing current tools with newer, better designed tools as related to: - Productivity - Vibration levels - Worker’s physiologic demand

FHP, 2003 Steven Chervak Background u Worker Focus Group  Anniston Army Depot  Injury records  Determine study focus  Problematic tool identification u Initial Study  Anniston Army Depot  Tank Disassembly Line

FHP, 2003 Steven Chervak Methodology

FHP, 2003 Steven Chervak Methodology -Subjects u 11 Volunteer Subjects  Male  Avg. Age: 49.9 years  Time at Job: 12.1 years

FHP, 2003 Steven Chervak Methodology - Tools u Three – 3/8 Inch impact wrenches  Tool # 1 – New, Manuf. A  Tool # 2 – New, Manuf. B  Tool # 3 – Old, Manuf. C u Similar Weight, Shape & Size

FHP, 2003 Steven Chervak Methodology – Task u Remove 4 bolts from wheel guard with each impact hammer/wrench.  Randomized order  Bolt tightened to 175 ft-lbs. prior to removal

FHP, 2003 Steven Chervak Methodology - Measurements u Productivity u Electromyography u Vibration

FHP, 2003 Steven Chervak Measurements u Productivity  Average Bolt Removal Time  Via accel. measurements

FHP, 2003 Steven Chervak Measurements u Electromyography (EMG)  Surface Electrodes  Band pass filter ( 13 hz – 150 hz)  Sampled at 200 hz  Full wave rectified

FHP, 2003 Steven Chervak EMG - Continued u Two muscles measured  Flexor digitorum profundus  Flexes phalanges and hand  % Maximum Voluntary Contraction (%MVC) via hand dynamometer Copyright Spencer, 1987

FHP, 2003 Steven Chervak EMG - Continued u Two muscles measured  Brachioradialis  Flexes forearm  % Maximum Voluntary Contraction (%MVC) via isometric contraction Copyright Spencer, 1987

FHP, 2003 Steven Chervak Measurements u Vibration  100 mv/g Triaxial Accelerometer  Sampled at 2000 hz  1000 hz low pass filter  Root Mean Square (RMS) values

FHP, 2003 Steven ChervakResults

FHP, 2003 Steven Chervak Productivity - Bolt Removal Times Tool Performance ANOVA

FHP, 2003 Steven Chervak Post Hoc Test for Bolt Removal Student-Neuman-Keuls

FHP, 2003 Steven Chervak Surface EMG Results % MVC Flexor Digitalis Profundus ANOVA

FHP, 2003 Steven Chervak Surface EMG Results % MVC Brachioradialis ANOVA

FHP, 2003 Steven Chervak Vibration Results Mean Accelerometer Values

FHP, 2003 Steven Chervak Conclusions u New impact wrenches performed significantly better than older tool. u New impact wrenches had less vibration than older tool. u Performance of new impact hammers were similar. u Physiologic differences were negligible.

FHP, 2003 Steven Chervak Future work u Can we optimize tool replacement?  ½” impact wrench  Date in service  Cost  Service history  Vibration level/Production level

FHP, 2003 Steven Chervak Lessons Learned u Pilot Study, Pilot Study, Pilot Study.  Labs great – no substitute for reality u Heavy tools – look at non- dominant hand u 375 ft/lbs of torque is a lot of torque!