A study was done to determine if workshift noise exposure of letter sorting machine operators could generate post shift temporary threshold shift (TTS) under conditions of no hearing protection, use of an inactive radio headset, and use of an active radio headset. Subjects comprised 12 letter sorting machine operators aged 27 to 37 years without active ear disease and with pure tone air conduction thresholds of less than 25 decibels hearing level at all tested frequencies. Pre and post work thresholds were determined audiometrically for octave frequencies 500 to 4000 hertz (Hz) and for 3000 and 6000Hz. Sound levels were 84 to 87 decibels-A (dBA) at the machine and 80 to 82dBA at other locations where operators worked. The typical 8 hour time weighted average was 85dBA. TTS was significantly greater for unprotected ears (3 to 4.5 decibels) than for either headset condition at 3000 to 6000Hz except for inactive headset at 4000Hz and active headset at 4000Hz. There was no significant difference between the two headset conditions. The real ear attenuation of headsets was tested in ten graduate students aged 20 to 32 years. The postal service radio headset was compared to a commercial ear muff. Binaural thresholds were tested from 125 to 8000Hz. Consistently greater attenuation was obtained with the commercial ear muff, especially at frequencies below 6000Hz. The authors conclude that the radio headset appears to be a highly accepted and marginally adequate hearing protection device in an automated mail sorting environment under these noise conditions.
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