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PubMed · 1857619

Occupational hearing conservation.

J D Osguthorpe·A J Klein
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Abstract

Chronic exposure to high-intensity noise can produce permanent hearing loss, the amount of which depends on noise intensity, temporal and spectral characteristics, and the length of exposure. OSHA regulates workplace noise exposure in accordance with the Hearing Conservation Amendment of 1983. When noise levels equal or exceed an 85 dBA time-weighted average (TWA), the employer is required to provide annual audiometric screening. When noise levels exceed 90 dBA TWA, the worker's exposure must be reduced by engineering methods, administrative changes, or personal hearing protectors. If a worker demonstrates a standard (significant) threshold shift (10 dB or greater increased average hearing threshold at 2, 3, and 4 kHz in either ear) that is attributed to noise, the worker's exposure must be further reduced by one of the aforementioned methods.

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Ear Protective DevicesHearing Loss, Noise-InducedHumansMaximum Allowable ConcentrationOccupational ExposureUnited StatesUnited States Occupational Safety and Health AdministrationJournal ArticleReview

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BibTeXRIS

J D Osguthorpe, A J Klein. 1991. Occupational hearing conservation.. https://pubmed.ncbi.nlm.nih.gov/1857619/

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PubMed1992

Active noise control: a review of the field.

Active noise control (ANC) is the application of the principle of the superposition of waves to noise attenuation problems. Much progress has been made toward applying ANC to narrow-band, low-frequency noise in confined spaces. During this same period, the application of ANC to broad-band noise or noise in three-dimensional spaces has seen little progress because of the recent quantification of serious physical limitations, most importantly, noncausality, stability, spatial mismatch, and the infinite gain controller requirement. ANC employs superposition to induce destructive interference to affect the attenuation of noise. ANC was believed to utilize the mechanism of phase cancellation to achieve the desired attenuation. However, current literature points to other mechanisms that may be operating in ANC. Categories of ANC are one-dimensional field and duct noise, enclosed spaces and interior noise, noise in three-dimensional spaces, and personal hearing protection. Development of active noise control stems from potential advantages in cost, size, and effectiveness. There are two approaches to ANC. In the first, the original sound is processed and injected back into the sound field in antiphase. The second approach is to synthesize a cancelling waveform. ANC of turbulent flow in pipes and ducts is the largest area in the field. Much work into the actual mechanism involved and the causal versus noncausal aspects of system controllers has been done. Fan and propeller noise can be divided into two categories: noise generated directly as the blade passing tones and noise generated as a result of blade tip turbulence inducing vibration in structures. Three-dimensional spaces present a noise environment where physical limitations are magnified and the infinite gain controller requirement is confronted. Personal hearing protection has been shown to be best suited to the control of periodic, low-frequency noise.

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