The effectiveness of various types of ear plugs was evaluated. Attenuation tests were performed of 28 subjects in 15 industrial facilities. Ear plugs tested were a twin flanged type, the V-51R ear plug, ear plugs made of acoustic wool or acoustic foam, and a custom molded ear plug. In each facility, the workers used the same ear plug type and were tested 5 times over a 5 day period. The attenuation test procedure was given with ear plugs inserted and with ear plugs removed. Testing was performed after the start of the work shift when workers had been performing their regular duties with ear plugs inserted. Noise reduction values were calculated for each test. Fifty percent of the workers tested were receiving less than 50 percent of the potential attenuation of the hearing protectors. Median noise reduction value from laboratory data was 13 versus 28 decibels (dB) over all ear plug types for all subjects. Greatest attenuation was provided by the expandable foam ear plugs. Attenuation values for custom molded ear plugs were smaller than those for preformed and acoustic wool ear plug types, but field attenuation values were larger. The authors conclude that for any ear plug design there will be large differences between laboratory established attenuation values and those actually received in the industrial setting.
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