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D OSHA Regulations OSHA REGULATIONS (STANDARDS - 29 CFR)2 OCCUPATIONAL NOISE EXPOSURE. - 1910.95 (SELECTED PORTIONS) (a) Protection against the effects of noise exposure shall be provided when the sound levels exceed those shown in Table G-16 when measured on the A scale of a standard sound level meter at slow response. When noise levels are determined by octave band analysis, the equivalent A-weighted sound level may be deter- mined as follows (Figure G-9~: 140 - 130 - m - ~ 120- , _ IL 11O- m ~ DO - 90 - 80 - _ i\// ll ~ 00 200 125 120 m 115 11O ~ o 105 ~ .= ~ 00 A, 95 uu on ll 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 11 500 1,000 2,O00 4,000 8,OOO Band Center Frequency (Hz) FIGURE G-9 - Equivalent A-Weighted Sound Level 2 www.osha-slc.gov/OshStd_data/1910_0095.html, accessed 916199. 141
142 APPENDIX D Equivalent sound level contours. Octave band sound pressure levels may be converted to the equivalent A-weighted sound level by plotting them on this graph and noting the A-weighted sound level corresponding to the point of high- est penetration into the sound level contours. This equivalent A-weighted sound level, which may differ from the actual A-weighted sound level of the noise, is used to determine exposure limits from Table G-16. (b) (1) When employees are subjected to sound exceeding those listed in Table G-16, feasible administrative or engineering controls shall be utilized. If such controls fail to reduce sound levels within the levels of Table G-16, personal protective equipment shall be provided and used to reduce sound levels within the levels of the table. (2) If the variations in noise level involve maxima at intervals of 1 second or less, it is to be considered continuous. TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1) Duration per day, hours Sound level dBA slow response 8 6 2 1 1 11/2 -12 1/4 or less 90 92 95 97 100 102 105 110 115 Footnote(l) When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each. If the sum of the following fractions: C(l)/T(l) + C(2)/T(2) C(n)/T(n) exceeds unity, then, the mixed exposure should be considered to exceed the limit value. Cn indicates the total time of exposure at a specified noise level, and Tn indicates the total time of exposure permitted at that level. Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level. (10) "Standard threshold shift." (i) As used in this section, a standard threshold shift is a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear. (ii) In determining whether a standard threshold shift has occurred, al- lowance may be made for the contribution of aging (presbycusis) to the change in hearing level by correcting the annual audiogram according to the procedure described in Appendix F: "Calculation and Application of Age Correction to Audiograms."
