Nonauditory injury threshold for repeated intense freefield impulse noise.

Exposure to impulse noise is an important occupational health concern. The risk of injury to auditory structures is well recognized and provides the cornerstone for present safety standards. For freefield impulse noise, nonauditory injury is dependent on peak pressure, positive phase duration (or impulse), and number of exposures. Trivial laryngeal petechiae are shown to precede nonauditory injury to more critical organs (ie, pulmonary and gastrointestinal systems). This study identifies the critical impulse noise thresholds causing trivial laryngeal petechial changes resulting from exposure to 5, 25, and 100 repetitions of specific levels of impulse noise. Because of anatomical differences, sheep should be slightly more susceptible to impulse noise laryngeal petechial changes than man; therefore, it seems reasonable to set the absolute limits for human occupational exposure levels below those causing laryngeal petechiae in sheep for persons wearing adequate hearing protection. This study does not address human auditory injury that may occur above or below these exposure limits even with proper hearing protection.