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 highest 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 I.
Table I
permissible noise exposures1
Duration per day, hours | Sound level dBA slow response |
8 | 90 |
6 | 92 |
4 | 95 |
3 | 97 |
2 | 100 |
11/2 | 102 |
1 | 105 |
1/2 | 110 |
1/4 or less | 115 |
1 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: C1/T1 + C2/T2 * * * Cn/Tn 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.
41 C.F.R. §50-204.10