Agenda - 10-06-1981 - Laserfiche WebLink

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~ ' Page 2 The range of response of the human ear is extremely large. The smallest :tote overpressure that can be distinguished by the ear is 3X lU-, or .000000003 9� � : `ounds per square inch43 The largest steady-state sound pressure that is perceived _ � ithout pain is 3 X lO or ,003 psi. This represents a range o f response of the human ear (without pain) of l s impractical. 000,000 to 1 . Using an arithmetic scale to cover � j ructical ^An a result, a decibel scale is commonly used to �«ch a range level's.^ Thfs js n,logarithmic scale with the range from 0 to 120 decibels representing�easure sound pressure �n the same range of response discussed above. The simplest measure of a noise is a determination of the overall sound pressure level. However, such a measurement gives no information on the human perception of the noise,noise and it is more or less meaningless. It is possible to give to a »nsemeasur'nginytroment characteristics which make the results more useful, n 'de'^iUningintu the meter a set of frequency weighting networks. A detailed 4scusion of the design principles will not be presented here. It is sufficient �` discussion out that evaluation of noise problems in terms of human reaction can be to po� t made with an instrument containing an achieved relatively well by measurements n sma«e "A" weighting network. The use of this t of network corrects for the frequency such an approach is supported by response of the human ear. The propriety � standards fn� noise measurement the fact that present national and internatiuna and analysis recommend the use of a sound meter with an ,A° network. for the evaluation I summary, A-scale measurement of noise levels is appropriate r �/ su ` - The unit of measurement is the dBA (for decibels as ��ured on the "�" scale). The table on of potential nuisance effe�ts` ebu» othe following page gives the dBA levels l af some familiar steady-state noise sources an d related human reactions. With the foregoing discussion in mind, our recommended limit on noise levels from the operation of quarrying machinery and equipment is as follows. The sound pressure level from the operation of producing equipment or machinery at a quarry shall not exceed 68 dBA between the hours of 7;00 A. M. and 6 P. M. as measured outside and,adjacent to the nearest residential , commercial, or industrial building not on quarry property. At other times, this limitation shall be reduced by 10 dBA. Th e airborne borne waves produced by blasting can be broken down into two categories, the noise that is heard (that portion of the airborne waves being transmitted at frequencies in the audible range), and the concussion which may be trans- d doors ftte dbelow the audible range of frequencies but which can rattle windows an :n and even produce perceptible movement inside buildings. It should be noted that airblast measurements are customarily made with equipment that has a � �han instruments:having only the:-"A" weighting much hroaJer' frenc�_ e network. Extensive investigations into the effects of' these airborne waves have been con- ' by the Ballistics Research Laboratory and other military gencies, by the' n U ited States Bureau of Mines, and by numerous consultants. For many years, a peak overpressure (variation of atmospheric pressure from the ambient or normal level) of 0.5 pound per square inch was generally considered an acceptable limit for "'irblast". Somewhat more definitive standards follow. . ' '. � ^ ��?�` �� `' |� ' - ` � ' ^ �.^/ ' .� . ``, . ' `