In-depth survey report: a case for using a-weighted equivalent energy as a damage risk criterion.
Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 350-11a, 2012 Jan; :1-27
Exposure to impulsive noise presents a greater risk of noise induced hearing loss than exposure to an equivalent amount of continuous noise. Noise must be measured, recorded, and analyzed to assess the risk of hearing loss to the persons who are exposed. Traditionally, noise has been analyzed using an equal energy approach where the measured noise exposure is equated to an allowable noise exposure for an eight-hour work day. The National Institute for Occupational Safety and Health (NIOSH), the US Environmental Protection Agency (EPA) and the Department of Labor (DOL) have conducted separate risk analyses that estimate allowable exposure levels for an eight-hour day between 80 and 90 dB sound pressure level time-weighted average. The most recent of these analyses (Prince et al. 1997) established the NIOSH Recommended Exposure Level (REL) of 85 dB. Impulsive noise produced by the collision of objects or the rapid expansion of gases or chemicals presents additional risk for which NIOSH, EPA and DOL suggest that no exposures should occur beyond a critical level of 140 dB SPL. The Department of Defense (DOD) uses the MIL-STD 1474D as its current method to assess impulsive noise exposure (MIL-STD 1474D, 1997). MIL-STD 1474D is based on the peak sound pressure level, the B-duration (reverberant decay) of the impulse, and the number of impulses one is exposed to. Other researchers have proposed damage risk criteria focused on different features of the impulsive waveform. NIOSH has several databases of impulses for gunshots, explosive discharges, manufacturing noises and acoustic shock tube discharges where the free-field impulse and the occluded impulse in an acoustic test fixture were recorded simultaneously. NIOSH has analyzed audiometric databases of impulsive noise exposures for humans and another for chinchilla. These exposure databases were evaluated by estimating the permanent and temporary threshold shifts and comparing the goodness of fit and discrimination for the various damage risk criteria. This report will summarize the background information for the different damage risk criteria. Generally, the impulsive noise reduction performance of a hearing protection device can be described by the reduction of the peak sound pressure level from free-field to occluded ear for the range of exposures 130 to 170 dB. NIOSH evaluated three damage risk criteria (MIL-STD 1474D, A-weighted equivalent 8-hour level LAeq8, and the Auditory Hazard Assessment Algorithm for Human (AHAAH)) with the Albuquerque Blast Overpressure exposures and the LAeq8 was found to provide the best fit and greatest discrimination for exposures. Similarly, LAeq8 was found to give the best-fit and greatest discrimination for the chinchilla impulse noise exposures (Hamernik et al., 1998). The LAeq8 affords the best sensitivity and specificity for discrimination of potential hazards and has the greatest level of integration with present occupational exposure standards and prospective hearing protection labeling regulations.
Control-technology; Engineering-controls; Noise; Noise-exposure; Impulse-noise; Hearing-loss; Noise-induced-hearing-loss; Risk-analysis; Exposure-assessment; Time-weighted-average-exposure; Sound-analyzers; Risk-factors; Hearing-threshold; Noise-analysis; Noise-measurement; Noise-waves; Noise-frequencies; Hearing-protection; Ear-protection; Ear-protectors; Auditory-discrimination; Audiological-testing; Audiometry
Field Studies; Control Technology
NTIS Accession No.
National Institute for Occupational Safety and Health