THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

13.3 The Occupational Safety and Health Act of 1970 321governments are enjoined from adopting different standards except when renderednecessary by special local conditions and then only with the permission ofEPA and the Secretary of Transportation. The provisions of Section 18 are nearlyidentical to those of Section 17 except they apply to motor carriers engaged ininterstate commerce.13.3 The Occupational Safety and Health Act of 1970Under the directive of the Walsh–Healey Public Contract Act which was passed byCongress in 1969, the U.S. Department of Labor developed the first occupationalnoise exposure standard. In 1970, the Occupational Safety and Health Act waspassed to apply the requirements of the standard to cover all workers engaged ininterstate commerce. The Occupational Safety and Health Administration (OSHA)exists as an arm of the Department of Labor. The assigned task of this agency is toestablish safety regulations (including those pertaining to noise levels) and enforcethem.According to OSHA regulations, the daily noise dose D in percent is given interms of slow-response time-average A-weighted sound levels byD = 100n∑i=1C iT i(13.1)where C i is the duration of exposure to a specific sound pressure level (SPL) and T iis the allowable daily duration for exposure to noise at that value of SPL. Table 13.1lists the A-weighted slow-response noise levels and their corresponding maximumdaily exposure times T i . Under OSHA regulations noise dosage exceeding 100%is not permitted. It will be noted in Table 13.1 that each 5 dB(A) increase in soundlevel cuts in half the allowable exposure time. For a time-average A-weightedaverage of 90 dB(A), the permitted exposure time is 8 h. Elevation of this noiseTable 13.1. OSHA Noise ExposureLimits (OSHA, 1978).SPL, dB(A)(slow response)Permissible Exposure,h/day90 892 695 497 3100 2102 1.5105 1110 0.5115 0.25 or less