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

322 13. Criteria and Regulations for Noise Controllevel by 5 dB(A) cuts the allowable exposure time to 4 h. Exposure to noise levelsabove 115 dB(A) is not permitted. Moreover, for exposure to noise having a slowresponsetime-average A-weighted sound level of any value, the instantaneouspeak sound pressure level may not exceed 140 dB. It should also be noted thatthe dosage levels are considered to be attributable to noise that actually reach aworker’s station at the ear level. If a worker moves from place to place in thecourse of his or her occupational assignment, the dosage must be based on thenoise exposure and the time spent at each station during the work period.Example Problem 1Monitoring of a factory noise environment at a worker’s station yielded the followingtime samplings over the course of a normal 8 h: Compute the dosage andcomment on the result.Exposure Level, dB(A)Exposure Period, h85 1.590 3.092 2.595 0.597 0.3100 0.2SolutionApplying Equation (13.1) and using Table 13.1, we obtain( 3D = 100 ×8 + 2.56 + 0.54 + 0.33 + 0.2 )= 112%2This dosage of 112% violates OSHA regulations. However, if this 8-h workdayis cut down by 100/117 to 6.8 h or less (assuming the noise level distribution isfairly consistent throughout the day), the daily dosage will not exceed 100%. It canalso be arranged to move the worker to a region, where the noise level averages86 dB(A) or less (i.e., below the OSHA noise level range), for 1.16 h in order toround out 8 h daily on the job.Annual audiology tests of all workers exposed to this environment are mandatedif the noise level equals or exceeds 85 dB(A) over the course of a work day.Corrective measures must be taken when the dosage D exceeds unity. Aside fromshortening time exposures to the offending noise, noise control measures describedin the next chapter must be taken to decrease the sound level pressure of noisesources. Hearing protection devices such as earplugs, earmuffs, and special helmetsare considered to be temporary stopgaps, and these do not necessarily remove theobligation of the work facility management to cut down on noise levels. OSHA