The 1968 CHABA recommendations to limit impulsive noise exposure to levels below 140 dB sound pressure level form the basis of current United States occupational and military standards. The U.S. military standard, MIL-STD 1474D, estimates the number of allowable shots to which a person may be exposed using peak level, B-duration, for varying levels of hearing protection usage. The French Weapons Noise Committee uses the 85 dBA A-weighted equivalent level, LAeq8 hr, as the limit for allowable exposures. The U.S. Army sponsored a series of noise exposures with chinchillas to investigate the effects of level, number of impulses, and interstimulus interval. Several types of impulses were created ranging from acoustic shock tubes to narrow band impacts reproduced by a loudspeaker. The goodness-of-fit and the discrimination of five noise exposure metrics were evaluated in this study: MIL-STD 1474D, AHAAH model, LAeq8 hr, Pfander's C-duration metric, and Smoorenburg's D-duration metric. Goodness-of-fit was evaluated with a logistic regression and discrimination was evaluated using the area under the receiver operator characteristic curve. The LAeq8 hr was found to best predict the temporary threshold shifts and the AHAAH model was found to best predict the permanent threshold shifts. [Partial funding provided by US Army Aeromedical Research Laboratories MIPR8J07586218].
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