Real-Ear Attenuation under Laboratory and Industrial Test Conditions as Provided by Selected Hearing Protectors

Abstract

To determine if controlled laboratory measurement procedures could yield realistic estimates of actual hearing protector performance achieved in the workplace, laboratory and field studies were performed using a like set of test protocols and hearing protection devices (HPDs). The laboratory experiment, using 40 naive subjects, investigated the effects of HPD wearing time, activity movement, and 2 fitting conditions (naive subject-fit vs. trained subject-fit), on spectral attenuation afforded by a slow-recovery foam earplug, premolded plug, foam cushion earmuff, and the muff worn over the foam plug. The field study, using 40 noise-exposed industrial workers, determined the protection obtained over 6 weeks of HPD use in 5 industrial workplaces. Statistical contrasts of mean data across frequency showed that the laboratory post-activity task (i.e., worst case) attenuation results overestimated the field attenuation by 8.3 dB (under the subject-fit) and 5.7 dB (under the trained-fit) for the user-molded foam plug, and by 10 dB and 6 dB, respectively, for the premolded plug. The laboratory results provided a much better prediction of field protection for the earmuff than for the plugs. Because of the discrepancies in prediction accuracy for different types of HPDs, schemes which have been proposed to “derate” the manufacturers' attenuation data by a constant factor across protectors are not justifiable.