(a) Protection against the effects of noise exposure shall be
provided when the sound levels exceed those shown in Table I of this
section 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 determined as follows:
[GRAPHIC] [TIFF OMITTED] TC21OC91.015
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.
(b) When employees are subject to sound exceeding those listed in
Table I of this section, feasible administrative or engineering controls
shall be utilized. If such controls fail to reduce sound levels within
the levels of the table, personal protective equipment shall be provided
and used to reduce sound levels within the levels of the table.
(c) If the variations in noise level involve maxima at intervals of
1 second
or less, it is to be considered continuous.
(d) In all cases where the sound levels exceed the values shown
herein, a continuing, effective hearing conservation program shall be
administered.
Table I
permissible noise exposures \1\
------------------------------------------------------------------------
Sound level
Duration per day, hours dBA slow
response
------------------------------------------------------------------------
8..................................................... 90
6..................................................... 92
4..................................................... 95
3..................................................... 97
2..................................................... 100
1\1/2\................................................ 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.
[34 FR 7946, May 20, 1969, as amended at 35 FR 1015, Jan. 24, 1970]
