Actual Effectiveness of Hearing Protection in High Level Impulse Noise ( Reprint

Current exposure limits for high intensity impulse noise contain factors for hearing protection which are based on very limited data. Recent studies in the U.S. and in France have provided new insights into the protection afforded by hearing protective devices. For impulses with an Aduration of approximately 3.0 ms, protection was found to be adequate for peak pressures up to 190 dB SPL for 6 impulses and 187 dB for 100 impulses. Protection was found to be adequate for 6 impulses with an A-duration of approximately 0.8 ms up to 196 dB SPL. For this Aduration, protection was adequate for 12 impulses up to 190 dB SPL and for 50 and 100 -impulses at 187 dB SPL. The hearing protectors used in these studies were earmuffs with perforations in the cushions which provided essentially no attenuation below 500 Hz. In a series of French studies, hearing protection was found to be adequate for impulses produced by a variety of weapons with peak pressures ranging from 165 dT3 SPL to 180 dB SPL. These included small arms with A-durations less than 1 .O ms, artillery with A-durations of approximately 3 .O ms, and other weapons with durations between these extremes. A variety of insert hearing protectors (earplugs) was used in these studies. All had perforations which resulted in poor low frequency attenuation. In both sets of studies, conventional attenuation rating schemes greatly underestimated the actual protection afforded by the hearing protective devices. Direct measurements of the pressures under the earmuff showed these peak levels can be as high as 182 dB SPL without significant effects on hearing. EffkacotC RCelle des Protecteurs Auditifs Pour des Expositions k des Bruits Impulsionnels de Niveau de C&e Clevd Les criteres d’exposition usuels aux bruits impulsionnels de fort niveau permettent de tenir compte de la protection auditive utilisee mais seulement a partir de resultats tres limit&. Des