Occupational Noise Exposure - 1910.95
1910.95
(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 determined as follows:
-
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 1.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 Exposure ¹ |
Duration per day,
hours |
Sound level, 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 |
Footnote (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: C(1)/T(1) + 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.
Top
(c)Hearing Conservation
Program
(1) The employer shall administer a continuing, effective
hearing conservation program, as described in paragraphs
(c) through (o) of this section, whenever employee noise
exposures equal or exceed an 8-hour time-weighted average
sound level (TWA) of 85 decibels measured on the A scale
(slow response) or, equivalently, a dose of fifty percent.
For purposes of the hearing conservation program, employee
noise exposures shall be computed in accordance with
appendix A and Table G-16a, and without regard to any
attenuation provided by the use of personal protective
equipment.
(2) For purposes of paragraphs (c) through (n) of this
section, an 8-hour time-weighted average of 85 decibels
or a dose of fifty percent shall also be referred to
as the action level.
Top
(d) Monitoring
(1) When information indicates that any employee's
exposure may equal or exceed an 8-hour time-weighted
average of 85 decibels, the employer shall develop and
implement a monitoring program.
(i) The sampling strategy shall be designed to identify
employees for inclusion in the hearing conservation
program and to enable the proper selection of hearing
protectors.
(ii) Where circumstances such as high worker mobility,
significant variations in sound level, or a significant
component of impulse noise make area monitoring generally
inappropriate, the employer shall use representative
personal sampling to comply with the monitoring requirements
of this paragraph unless the employer can show that
area sampling produces equivalent results.
(2)
(i) All continuous, intermittent and impulsive sound
levels from 80 decibels to 130 decibels shall be integrated
into the noise measurements.
(ii) Instruments used to measure employee noise exposure
shall be calibrated to ensure measurement accuracy.
(3) Monitoring shall be repeated whenever a change
in production, process, equipment or controls increases
noise exposures to the extent that:
(i) Additional employees may be exposed at or above
the action level; or
(ii) The attenuation provided by hearing protectors
being used by employees may be rendered inadequate
to meet the requirements of paragraph (j) of this
section.
Top
(e) Employee Notification
The employer shall notify each employee exposed at or
above an 8-hour time-weighted average of 85 decibels of
the results of the monitoring.
Top
(f) Observation
of Monitoring
The employer shall provide affected employees or their
representatives with an opportunity to observe any noise
measurements conducted pursuant to this section.
Top
(g) Audiometric
Testing Program
(1) The employer shall establish and maintain an audiometric
testing program as provided in this paragraph by making
audiometric testing available to all employees whose
exposures equal or exceed an 8-hour time-weighted average
of 85 decibels.
(2) The program shall be provided at no cost to employees.
(3) Audiometric tests shall be performed by a licensed
or certified audiologist, otolaryngologist, or other
physician, or by a technician who is certified by the
Council of Accreditation in Occupational Hearing Conservation,
or who has satisfactorily demonstrated competence in
administering audiometric examinations, obtaining valid
audiograms, and properly using, maintaining and checking
calibration and proper functioning of the audiometers
being used. A technician who operates microprocessor
audiometers does not need to be certified. A technician
who performs audiometric tests must be responsible to
an audiologist, otolaryngologist or physician.
(4) All audiograms obtained pursuant to this section
shall meet the requirements of Appendix C: "Audiometric
Measuring Instruments."
(5) Baseline audiogram
(i) Within 6 months of an employee's first exposure
at or above the action level, the employer shall establish
a valid baseline audiogram against which subsequent
audiograms can be compared.
(ii) "Mobile test van exception." Where
mobile test vans are used to meet the audiometric
testing obligation, the employer shall obtain a valid
baseline audiogram within 1 year of an employee's
first exposure at or above the action level. Where
baseline audiograms are obtained more than 6 months
after the employee's first exposure at or above the
action level, employees shall wearing hearing protectors
for any period exceeding six months after first exposure
until the baseline audiogram is obtained.
(iii) Testing to establish a baseline audiogram shall
be preceded by at least 14 hours without exposure
to workplace noise. Hearing protectors may be used
as a substitute for the requirement that baseline
audiograms be preceded by 14 hours without exposure
to workplace noise.
(iv) The employer shall notify employees of the need
to avoid high levels of non-occupational noise exposure
during the 14-hour period immediately preceding the
audiometric examination.
(6) Annual audiogram. At least annually
after obtaining the baseline audiogram, the employer
shall obtain a new audiogram for each employee exposed
at or above an 8-hour time-weighted average of 85 decibels.
(7) Evaluation of audiogram
(i) Each employee's annual audiogram shall be compared
to that employee's baseline audiogram to determine
if the audiogram is valid and if a standard threshold
shift as defined in paragraph (g)(10) of this section
has occurred. This comparison may be done by a technician.
(ii) If the annual audiogram shows that an employee
has suffered a standard threshold shift, the employer
may obtain a retest within 30 days and consider the
results of the retest as the annual audiogram.
(iii) The audiologist, otolaryngologist, or physician
shall review problem audiograms and shall determine
whether there is a need for further evaluation. The
employer shall provide to the person performing this
evaluation the following information:
(a) A copy of the requirements for hearing conservation
as set forth in paragraphs (c) through (n) of this
section;
(b) The baseline audiogram and most recent audiogram
of the employee to be evaluated;
(c) Measurements of background sound pressure levels
in the audiometric test room as required in Appendix
D: Audiometric Test Rooms.
(d) Records of audiometer calibrations required
by paragraph (h)(5) of this section.
(8) Follow-up procedures
(i) If a comparison of the annual audiogram to the
baseline audiogram indicates a standard threshold
shift as defined in paragraph (g)(10) of this section
has occurred, the employee shall be informed of this
fact in writing, within 21 days of the determination.
(ii) Unless a physician determines that the standard
threshold shift is not work related or aggravated
by occupational noise exposure, the employer shall
ensure that the following steps are taken when a standard
threshold shift occurs:
(a) Employees not using hearing protectors shall
be fitted with hearing protectors, trained in their
use and care, and required to use them.
(b) Employees already using hearing protectors
shall be refitted and retrained in the use of hearing
protectors and provided with hearing protectors
offering greater attenuation if necessary.
(c) The employee shall be referred for a clinical
audiological evaluation or an otological examination,
as appropriate, if additional testing is necessary
or if the employer suspects that a medical pathology
of the ear is caused or aggravated by the wearing
of hearing protectors.
(d) The employee is informed of the need for an
otological examination if a medical pathology of
the ear that is unrelated to the use of hearing
protectors is suspected.
(iii) If subsequent audiometric testing of an employee
whose exposure to noise is less than an 8-hour TWA
of 90 decibels indicates that a standard threshold
shift is not persistent, the employer:
(a) Shall inform the employee of the new audiometric
interpretation; and
(b) May discontinue the required use of hearing
protectors for that employee.
(9) Revised baseline. An annual audiogram
may be substituted for the baseline audiogram when,
in the judgment of the audiologist, otolaryngologist
or physician who is evaluating the audiogram:
(i) The standard threshold shift revealed by the
audiogram is persistent; or
(ii) The hearing threshold shown in the annual audiogram
indicates significant improvement over the baseline
audiogram.
(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, allowance 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."
Top
(h) Audiometric
Test Requirements
(1) Audiometric tests shall be pure tone, air conduction,
hearing threshold examinations, with test frequencies
including as a minimum 500, 1000, 2000, 3000, 4000,
and 6000 Hz. Tests at each frequency shall be taken
separately for each ear.
(2) Audiometric tests shall be conducted with audiometers
(including microprocessor audiometers) that meet the
specifications of, and are maintained and used in accordance
with, American National Standard Specification for Audiometers,
S3.6-1969, which is incorporated by reference as specified
in Sec. 1910.6.
(3) Pulsed-tone and self-recording audiometers, if
used, shall meet the requirements specified in Appendix
C: "Audiometric Measuring Instruments."
(4) Audiometric examinations shall be administered
in a room meeting the requirements listed in Appendix
D: "Audiometric Test Rooms."
(5) Audiometer calibration
(i) The functional operation of the audiometer shall
be checked before each day's use by testing a person
with known, stable hearing thresholds, and by listening
to the audiometer's output to make sure that the output
is free from distorted or unwanted sounds. Deviations
of 10 decibels or greater require an acoustic calibration.
(ii) Audiometer calibration shall be checked acoustically
at least annually in accordance with Appendix E: "Acoustic
Calibration of Audiometers." Test frequencies
below 500 Hz and above 6000 Hz may be omitted from
this check. Deviations of 15 decibels or greater require
an exhaustive calibration.
(iii) An exhaustive calibration shall be performed
at least every two years in accordance with sections
4.1.2; 4.1.3.; 4.1.4.3; 4.2; 4.4.1; 4.4.2; 4.4.3;
and 4.5 of the American National Standard Specification
for Audiometers, S3.6-1969. Test frequencies below
500 Hz and above 6000 Hz may be omitted from this
calibration.
Top
(i) Hearing Protectors
(1) Employers shall make hearing protectors available
to all employees exposed to an 8-hour time-weighted
average of 85 decibels or greater at no cost to the
employees. Hearing protectors shall be replaced as necessary.
(2) Employers shall ensure that hearing protectors
are worn:
(i) By an employee who is required by paragraph (b)(1)
of this section to wear personal protective equipment;
and
(ii) By any employee who is exposed to an 8-hour
time-weighted average of 85 decibels or greater, and
who:
(a) Has not yet had a baseline audiogram established
pursuant to paragraph (g)(5)(ii); or
(b) Has experienced a standard threshold shift.
(3) Employees shall be given the opportunity to select
their hearing protectors from a variety of suitable
hearing protectors provided by the employer.
(4) The employer shall provide training in the use
and care of all hearing protectors provided to employees.
(5) The employer shall ensure proper initial fitting
and supervise the correct use of all hearing protectors.
Top
(j) Hearing Protector
Attenuation
(1) The employer shall evaluate hearing protector attenuation
for the specific noise environments in which the protector
will be used. The employer shall use one of the evaluation
methods described in Appendix B: "Methods for Estimating
the Adequacy of Hearing Protection Attenuation."
(2) Hearing protectors must attenuate employee exposure
at least to an 8-hour time-weighted average of 90 decibels
as required by paragraph (b) of this section.
(3) For employees who have experienced a standard threshold
shift, hearing protectors must attenuate employee exposure
to an 8-hour time-weighted average of 85 decibels or
below.
(4) The adequacy of hearing protector attenuation shall
be re-evaluated whenever employee noise exposures increase
to the extent that the hearing protectors provided may
no longer provide adequate attenuation. The employer
shall provide more effective hearing protectors where
necessary.
Top
(k) Training Program
(1) The employer shall institute a training program
for all employees who are exposed to noise at or above
an 8-hour time-weighted average of 85 decibels, and
shall ensure employee participation in such program.
(2) The training program shall be repeated annually
for each employee included in the hearing conservation
program. Information provided in the training program
shall be updated to be consistent with changes in protective
equipment and work processes.
(3) The employer shall ensure that each employee is
informed of the following:
(i) The effects of noise on hearing;
(ii) The purpose of hearing protectors, the advantages,
disadvantages, and attenuation of various types, and
instructions on selection, fitting, use, and care;
and
(iii) The purpose of audiometric testing, and an
explanation of the test procedures.
Top
(l) Access to Information
and Training Materials
(1) The employer shall make available to affected employees
or their representatives copies of this standard and
shall also post a copy in the workplace.
(2) The employer shall provide to affected employees
any informational materials pertaining to the standard
that are supplied to the employer by the Assistant Secretary.
(3) The employer shall provide, upon request, all materials
related to the employer's training and education program
pertaining to this standard to the Assistant Secretary
and the Director.
Top
(m) Recordkeeping
(1) Exposure measurements. The employer shall
maintain an accurate record of all employee exposure
measurements required by paragraph (d) of this section.
(2) Audiometric tests
(i) The employer shall retain all employee audiometric
test records obtained pursuant to paragraph (g) of
this section.
(ii) This record shall include:
(a) Name and job classification of the employee;
(b) Date of the audiogram;
(c) The examiner's name;
(d) Date of the last acoustic or exhaustive calibration
of the audiometer; and
(e) Employee's most recent noise exposure assessment.
(f) The employer shall maintain accurate records
of the measurements of the background sound pressure
levels in audiometric test rooms.
(3) Record retention. The employer shall retain
records required in this paragraph (m) for at least
the following periods.
(i) Noise exposure measurement records shall be retained
for two years.
(ii) Audiometric test records shall be retained for
the duration of the affected employee's employment.
(4) Access to records. All records required
by this section shall be provided upon request to employees,
former employees, representatives designated by the
individual employee, and the Assistant Secretary. The
provisions of 29 CFR 1910.20 (a)-(e) and (g)-(i) apply
to access to records under this section.
(5) Transfer of records. If the employer ceases
to do business, the employer shall transfer to the successor
employer all records required to be maintained by this
section, and the successor employer shall retain them
for the remainder of the period prescribed in paragraph
(m)(3) of this section.
Top
(n) Appendices
(1) Appendices A, B, C, D, and E to this section are
incorporated as part of this section and the contents
of these appendices are mandatory.
(2) Appendices F and G to this section are informational
and are not intended to create any additional obligations
not otherwise imposed or to detract from any existing
obligations.
(o) Exemptions.
Paragraphs (c) through (n) of this section shall not
apply to employers engaged in oil and gas well drilling
and servicing operations.
(p) Startup date
Baseline audiograms required by paragraph (g) of this
section shall be completed by March 1, 1984.
Top
Appendix A - Noise Exposure Computation
This Appendix is Mandatory
I. Computation of Employee Noise Exposure
(1) Noise dose is computed using Table G-16a as follows:
(i) When the sound level, L, is constant over the entire
work shift, the noise dose, D, in percent, is given
by: D=100 C/T where C is the total length of the work
day, in hours, and T is the reference duration corresponding
to the measured sound level, L, as given in Table G-16a
or by the formula shown as a footnote to that table.
(ii) When the workshift noise exposure is composed
of two or more periods of noise at different levels,
the total noise dose over the work day is given by:
D = 100 (C(1)/T(1) + C(2)/T(2)
+ ... + C(n)/T(n))
where C(n) indicates the total time of exposure at
a specific noise level, and T(n) indicates the reference
duration for that level as given by Table G-16a.
(2) The eight-hour time-weighted average sound level
(TWA), in decibels, may be computed from the dose, in
percent, by means of the formula:
TWA = 16.61 log(10) (D/100) + 90.
For an eight-hour workshift with the noise level constant
over the entire shift, the TWA is equal to the measured
sound level.
(3) A table relating dose and TWA is given in Section
II.
TABLE G-16A
_________________________________________________
Reference
A-weighted sound level, L (decibel) duration,
T (hour)
_________________________________________________
80................................... 32
81................................... 27.9
82................................... 24.3
83................................... 21.1
84................................... 18.4
85................................... 16
86................................... 13.9
87................................... 12.1
88................................... 10.6
89................................... 9.2
90................................... 8
91................................... 7.0
92................................... 6.1
93................................... 5.3
94................................... 4.6
95................................... 4
96................................... 3.5
97................................... 3.0
98................................... 2.6
99................................... 2.3
100.................................. 2
101.................................. 1.7
102.................................. 1.5
103.................................. 1.3
104.................................. 1.1
105.................................. 1
106.................................. 0.87
107.................................. 0.76
108.................................. 0.66
109.................................. 0.57
110.................................. 0.5
111.................................. 0.44
112.................................. 0.38
113.................................. 0.33
114.................................. 0.29
115.................................. 0.25
116.................................. 0.22
117.................................. 0.19
118.................................. 0.16
119.................................. 0.14
120.................................. 0.125
121.................................. 0.11
122.................................. 0.095
123.................................. 0.082
124.................................. 0.072
125.................................. 0.063
126.................................. 0.054
127.................................. 0.047
128.................................. 0.041
129.................................. 0.036
130.................................. 0.031
______________________________________________
In the above table the reference duration, T, is computed
by:
T = 8 / ( 2 ((L-90)/5) )
where L is the measured A-weighted sound level.
II. Conversion Between "Dose" and "8-Hour
Time-Weighted Average" Sound Level
Compliance with paragraphs (c)-(r) of this regulation is
determined by the amount of exposure to noise in the workplace.
The amount of such exposure is usually measured with an audiodosimeter
which gives a readout in terms of "dose." In order
to better understand the requirements of the amendment, dosimeter
readings can be converted to an "8-hour time-weighted
average sound level." (TWA).
In order to convert the reading of a dosimeter into TWA,
see Table A-1, below. This table applies to dosimeters that
are set by the manufacturer to calculate dose or percent exposure
according to the relationships in Table G-16a. So, for example,
a dose of 91 percent over an eight hour day results in a TWA
of 89.3 dB, and, a dose of 50 percent corresponds to a TWA
of 85 dB.
If the dose as read on the dosimeter is less than or greater
than the values found in Table A-1, the TWA may be calculated
by using the formula: TWA = 16.61 log(10) (D/100) + 90 where
TWA=8-hour time-weighted average sound level and D = accumulated
dose in percent exposure.
TABLE A-1 - CONVERSION FROM "PERCENT NOISE EXPOSURE"
OR "DOSE" TO "8-HOUR TIME-WEIGHTED
AVERAGE SOUND LEVEL" (TWA)
______________________________________________
Dose or percent noise exposure TWA
______________________________________________
10 ............................. 73.4
15 ............................. 76.3
20 ............................. 78.4
25 ............................. 80.0
30 ............................. 81.3
35 ............................. 82.4
40 ............................. 83.4
45 ............................. 84.2
50 ............................. 85.0
55 ............................. 85.7
60 ............................. 86.3
65 ............................. 86.9
70 ............................. 87.4
75 ............................. 87.9
80 ............................. 88.4
81 ............................. 88.5
82 ............................. 88.6
83 ............................. 88.7
84 ............................. 88.7
85 ............................. 88.8
86 ............................. 88.9
87 ............................. 89.0
88 ............................. 89.1
89 ............................. 89.2
90 ............................. 89.2
91 ............................. 89.3
92 ............................. 89.4
93 ............................. 89.5
94 ............................. 89.6
95 ............................. 89.6
96 ............................. 89.7
97 ............................. 89.8
98 ............................. 89.9
99 ............................. 89.9
100 ............................ 90.0
101 ............................ 90.1
102 ............................ 90.1
103 ............................ 90.2
104 ............................ 90.3
105 ............................ 90.4
106 ............................ 90.4
107 ............................ 90.5
108 ............................ 90.6
109 ............................ 90.6
110 ............................ 90.7
111 ............................ 90.8
112 ............................ 90.8
113 ............................ 90.9
114 ............................ 90.9
115 ............................ 91.1
116 ............................ 91.1
117 ............................ 91.1
118 ............................ 91.2
119 ............................ 91.3
120 ............................ 91.3
125 ............................ 91.6
130 ............................ 91.9
135 ............................ 92.2
140 ............................ 92.4
145 ............................ 92.7
150 ............................ 92.9
155 ............................ 93.2
160 ............................ 93.4
165 ............................ 93.6
170 ............................ 93.8
175 ............................ 94.0
180 ............................ 94.2
185 ............................ 94.4
190 ............................ 94.6
195 ............................ 94.8
200 ............................ 95.0
210 ............................ 95.4
220 ............................ 95.7
230 ............................ 96.0
240 ............................ 96.3
250 ............................ 96.6
260 ............................ 96.9
270 ............................ 97.2
280 ............................ 97.4
290 ............................ 97.7
300 ............................ 97.9
310 ............................ 98.2
320 ............................ 98.4
330 ............................ 98.6
340 ............................ 98.8
350 ............................ 99.0
360 ............................ 99.2
370 ............................ 99.4
380 ............................ 99.6
390 ............................ 99.8
400 ............................ 100.0
410 ............................ 100.2
420 ............................ 100.4
430 ............................ 100.5
440 ............................ 100.7
450 ............................ 100.8
460 ............................ 101.0
470 ............................ 101.2
480 ............................ 101.3
490 ............................ 101.5
500 ............................ 101.6
510 ............................ 101.8
520 ............................ 101.9
530 ............................ 102.0
540 ............................ 102.2
550 ............................ 102.3
560 ............................ 102.4
570 ............................ 102.6
580 ............................ 102.7
590 ............................ 102.8
600 ............................ 102.9
610 ............................ 103.0
620 ............................ 103.2
630 ............................ 103.3
640 ............................ 103.4
650 ............................ 103.5
660 ............................ 103.6
670 ............................ 103.7
680 ............................ 103.8
690 ............................ 103.9
700 ............................ 104.0
710 ............................ 104.1
720 ............................ 104.2
730 ............................ 104.3
740 ............................ 104.4
750 ............................ 104.5
760 ............................ 104.6
770 ............................ 104.7
780 ............................ 104.8
790 ............................ 104.9
800 ............................ 105.0
810 ............................ 105.1
820 ............................ 105.2
830 ............................ 105.3
840 ............................ 105.4
850 ............................ 105.4
860 ............................ 105.5
870 ............................ 105.6
880 ............................ 105.7
890 ............................ 105.8
900 ............................ 105.8
910 ............................ 105.9
920 ............................ 106.0
930 ............................ 106.1
940 ............................ 106.2
950 ............................ 106.2
960 ............................ 106.3
970 ............................ 106.4
980 ............................ 106.5
990 ............................ 106.5
999 ............................ 106.6
___________________________________________
Top
Appendix B - Methods for Estimating
Adequacy of Hearing Protectors
This Appendix is Mandatory
For employees who have experienced a significant threshold
shift, hearing protector attenuation must be sufficient to
reduce employee exposure to a TWA of 85 dB. Employers must
select one of the following methods by which to estimate the
adequacy of hearing protector attenuation.
The most convenient method is the Noise Reduction Rating
(NRR) developed by the Environmental Protection Agency (EPA).
According to EPA regulation, the NRR must be shown on the
hearing protector package. The NRR is then related to an individual
worker's noise environment in order to assess the adequacy
of the attenuation of a given hearing protector. This appendix
describes four methods of using the NRR to determine whether
a particular hearing protector provides adequate protection
within a given exposure environment. Selection among the four
procedures is dependent upon the employer's noise measuring
instruments.
Instead of using the NRR, employers may evaluate the adequacy
of hearing protector attenuation by using one of the three
methods developed by the National Institute for Occupational
Safety and Health (NIOSH), which are described in the "List
of Personal Hearing Protectors and Attenuation Data,"
HEW Publication No. 76-120, 1975, pages 21-37. These methods
are known as NIOSH methods No. 1, No. 2 and No. 3. The NRR
described below is a simplification of NIOSH method No. 2.
The most complex method is NIOSH method No. 1, which is probably
the most accurate method since it uses the largest amount
of spectral information from the individual employee's noise
environment. As in the case of the NRR method described below,
if one of the NIOSH methods is used, the selected method must
be applied to an individual's noise environment to assess
the adequacy of the attenuation. Employers should be careful
to take a sufficient number of measurements in order to achieve
a representative sample for each time segment.
NOTE: The employer must remember that calculated attenuation
values reflect realistic values only to the extent that the
protectors are properly fitted and worn.
When using the NRR to assess hearing protector adequacy,
one of the following methods must be used:
(i) When using a dosimeter that is capable of C-weighted
measurements:
(a) Obtain the employee's C-weighted dose for the entire
workshift, and convert to TWA (see appendix A, II).
(b) Subtract the NRR from the C-weighted TWA to obtain
the estimated A-weighted TWA under the ear protector.
(ii) When using a dosimeter that is not capable of C-weighted
measurements, the following method may be used:
(a) Convert the A-weighted dose to TWA (see appendix
A).
(b) Subtract 7 dB from the NRR, and
(c) Subtract the remainder from the A-weighted TWA to
obtain the estimated A-weighted TWA under the ear protector.
(iii) When using a sound level meter set to the A-weighting
network:
(a) Obtain the employee's A-weighted TWA.
(b) Subtract 7 dB from the NRR, and subtract the remainder
from the A-weighted TWA to obtain the estimated A-weighted
TWA under the ear protector.
(iv) When using a sound level meter set on the C-weighting
network:
(a) Obtain a representative sample of the C-weighted
sound levels in the employee's environment.
(b) Subtract the NRR from the C-weighted average sound
level to obtain the estimated A-weighted TWA under the
ear protector.
(v) When using area monitoring procedures and a sound level
meter set to the A-weighing network.
(a) Obtain a representative sound level for the area
in question.
(b) Subtract 7 dB from the NRR and subtract the remainder
from the A-weighted sound level for that area.
(vi) When using area monitoring procedures and a sound
level meter set to the C-weighting network:
(a) Obtain a representative sound level for the area
in question.
(b) Subtract the NRR from the C-weighted sound level
for that area.
Top
Appendix C - Audiometric Measuring
Instruments
This Appendix is Mandatory
1. In the event that pulsed-tone audiometers are used, they
shall have a tone on-time of at least 200 milliseconds.
2. Self-recording audiometers shall comply with the following
requirements:
(a) The chart upon which the audiogram is traced shall
have lines at positions corresponding to all multiples
of 10 dB hearing level within the intensity range spanned
by the audiometer. The lines shall be equally spaced and
shall be separated by at least 1/4 inch. Additional increments
are optional. The audiogram pen tracings shall not exceed
2 dB in width.
(b) It shall be possible to set the stylus manually at
the 10-dB increment lines for calibration purposes.
(c) The slewing rate for the audiometer attenuator shall
not be more than 6 dB/sec except that an initial slewing
rate greater than 6 dB/sec is permitted at the beginning
of each new test frequency, but only until the second
subject response.
(d) The audiometer shall remain at each required test
frequency for 30 seconds (+ or - 3 seconds). The audiogram
shall be clearly marked at each change of frequency and
the actual frequency change of the audiometer shall not
deviate from the frequency boundaries marked on the audiogram
by more than + or - 3 seconds.
(e) It must be possible at each test frequency to place
a horizontal line segment parallel to the time axis on
the audiogram, such that the audiometric tracing crosses
the line segment at least six times at that test frequency.
At each test frequency the threshold shall be the average
of the midpoints of the tracing excursions.
Top
Appendix D - Audiometric Test
Rooms
This Appendix is Mandatory
Rooms used for audiometric testing shall not have background
sound pressure levels exceeding those in Table D-1 when measured
by equipment conforming at least to the Type 2 requirements
of American National Standard Specification for Sound Level
Meters, S1.4-1971 (R1976), and to the Class II requirements
of American National Standard Specification for Octave, Half-Octave,
and Third-Octave Band Filter Sets, S1.11-1971 (R1976).
TABLE D-1 - MAXIMUM ALLOWABLE OCTAVE-BAND SOUND PRESSURE LEVELS
FOR AUDIOMETRIC TEST ROOMS
_______________________________________________________________
Octave-band center
frequency (Hz)............... 500 1000 2000 4000 8000
Sound pressure level (dB) ... 40 40 47 57 62
_______________________________________________________________
Top
Appendix E - Acoustic Calibration
of Audiometers
This Appendix is Mandatory
Audiometer calibration shall be checked acoustically, at
least annually, according to the procedures described in this
appendix. The equipment necessary to perform these measurements
is a sound level meter, octave-band filter set, and a National
Bureau of Standards 9A coupler. In making these measurements,
the accuracy of the calibrating equipment shall be sufficient
to determine that the audiometer is within the tolerances
permitted by American Standard Specification for Audiometers,
S3.6-1969.
(1) Sound Pressure Output Check
(a) Place the earphone coupler over the microphone of
the sound level meter and place the earphone on the coupler.
(b) Set the audiometer's hearing threshold level (HTL)
dial to 70 dB.
(c) Measure the sound pressure level of the tones at
each test frequency from 500 Hz through 6000 Hz for each
earphone.
(d) At each frequency the readout on the sound level
meter should correspond to the levels in Table E-1 or
Table E-2, as appropriate, for the type of earphone, in
the column entitled "sound level meter reading."
(2) Linearity Check
(a) With the earphone in place, set the frequency to
1000 Hz and the HTL dial on the audiometer to 70 dB.
(b) Measure the sound levels in the coupler at each 10-dB
decrement from 70 dB to 10 dB, noting the sound level
meter reading at each setting.
(c) For each 10-dB decrement on the audiometer the sound
level meter should indicate a corresponding 10 dB decrease.
(d) This measurement may be made electrically with a
voltmeter connected to the earphone terminals.
(3) Tolerances
When any of the measured sound levels deviate from the
levels in Table E-1 or Table E-2 by + or - 3 dB at any test
frequency between 500 and 3000 Hz, 4 dB at 4000 Hz, or 5
dB at 6000 Hz, an exhaustive calibration is advised. An
exhaustive calibration is required if the deviations are
greater than 15 dB or greater at any test frequency.
TABLE E-1 - REFERENCE THRESHOLD LEVELS FOR TELEPHONICS -
TDH-39 EARPHONES
_____________________________________________________________
Reference
threshold Sound
level for level
Frequency, Hz TDH-39 meter
earphones, reading,
dB dB
_____________________________________________________________
500 .................................. 11.5 81.5
1000 ................................. 7 77
2000 ................................. 9 79
3000 ................................. 10 80
4000 ................................. 9.5 79.5
6000 ................................. 15.5 85.5
_____________________________________________________________
TABLE E-2 - REFERENCE THRESHOLD LEVELS FOR TELEPHONICS -
TDH-49 EARPHONES
_____________________________________________________________
Reference
threshold Sound
level for level
Frequency, Hz TDH-49 meter
earphones, reading,
dB dB
____________________________________________________________
500 .................................. 13.5 83.5
1000 ................................. 7.5 77.5
2000 ................................. 11 81.0
3000 ................................. 9.5 79.5
4000 ................................. 10.5 80.5
6000 ................................. 13.5 83.5
___________________________________________________________
Top
Appendix F - Calculations and
Application of Age Correction to Audiograms
This Appendix is Non-Mandatory
In determining whether a standard threshold shift has occurred,
allowance may be made for the contribution of aging to the
change in hearing level by adjusting the most recent audiogram.
If the employer chooses to adjust the audiogram, the employer
shall follow the procedure described below. This procedure
and the age correction tables were developed by the National
Institute for Occupational Safety and Health in the criteria
document entitled "Criteria for a Recommended Standard
. . . Occupational Exposure to Noise," ((HSM)-11001).
For each audiometric test frequency;
(i) Determine from Tables F-1 or F-2 the age correction
values for the employee by:
(a) Finding the age at which the most recent audiogram
was taken and recording the corresponding values of age
corrections at 1000 Hz through 6000 Hz;
(b) Finding the age at which the baseline audiogram was
taken and recording the corresponding values of age corrections
at 1000 Hz through 6000 Hz.
(ii) Subtract the values found in step (i)(b) from the
value found in step (i)(a).
(iii) The differences calculated in step (ii) represented
that portion of the change in hearing that may be due to
aging.
EXAMPLE: Employee is a 32-year-old male. The audiometric
history for his right ear is shown in decibels below.
_____________________________________________________________
Audiometric test frequency (Hz)
Employee's age ___________________________________
1000 2000 3000 4000 6000
_____________________________________________________________
26....................... 10 5 5 10 5
*27...................... 0 0 0 5 5
28....................... 0 0 0 10 5
29....................... 5 0 5 15 5
30....................... 0 5 10 20 10
31....................... 5 10 20 15 15
*32...................... 5 10 10 25 20
_____________________________________________________________
The audiogram at age 27 is considered the baseline since
it shows the best hearing threshold levels. Asterisks have
been used to identify the baseline and most recent audiogram.
A threshold shift of 20 dB exists at 4000 Hz between the
audiograms taken at ages 27 and 32.
(The threshold shift is computed by subtracting the hearing
threshold at age 27, which was 5, from the hearing threshold
at age 32, which is 25). A retest audiogram has confirmed
this shift. The contribution of aging to this change in
hearing may be estimated in the following manner:
Go to Table F-1 and find the age correction values (in
dB) for 4000 Hz at age 27 and age 32.
____________________________________________________________
Frequency (Hz)
________________________________
1000 2000 3000 4000 6000
____________________________________________________________
Age 32................... 6 5 7 10 14
Age 27................... 5 4 6 7 11
___________________________________
Difference 1 1 1 3 3
____________________________________________________________
The difference represents the amount of hearing loss that
may be attributed to aging in the time period between the
baseline audiogram and the most recent audiogram. In this
example, the difference at 4000 Hz is 3 dB. This value is
subtracted from the hearing level at 4000 Hz, which in the
most recent audiogram is 25, yielding 22 after adjustment.
Then the hearing threshold in the baseline audiogram at
4000 Hz (5) is subtracted from the adjusted annual audiogram
hearing threshold at 4000 Hz (22). Thus the age-corrected
threshold shift would be 17 dB (as opposed to a threshold
shift of 20 dB without age correction).
TABLE F-1 - AGE CORRECTION VALUES IN DECIBELS FOR MALES
____________________________________________________________
Audiometric Test Frequency (Hz)
Years _________________________________
1000 2000 3000 4000 6000
____________________________________________________________
20 or younger........... 5 3 4 5 8
21 ..................... 5 3 4 5 8
22 ..................... 5 3 4 5 8
23 ..................... 5 3 4 6 9
24 ..................... 5 3 5 6 9
25 ..................... 5 3 5 7 10
26 ..................... 5 4 5 7 10
27 ..................... 5 4 6 7 11
28 ..................... 6 4 6 8 11
29 ..................... 6 4 6 8 12
30 ..................... 6 4 6 9 12
31 ..................... 6 4 7 9 13
32 ..................... 6 5 7 10 14
33 ..................... 6 5 7 10 14
34 ..................... 6 5 8 11 15
35 ..................... 7 5 8 11 15
36 ..................... 7 5 9 12 16
37 ..................... 7 6 9 12 17
38 ..................... 7 6 9 13 17
39 ..................... 7 6 10 14 18
40 ..................... 7 6 10 14 19
41 ..................... 7 6 10 14 20
42 ..................... 8 7 11 16 20
43 ..................... 8 7 12 16 21
44 ..................... 8 7 12 17 22
45 ..................... 8 7 13 18 23
46 ..................... 8 8 13 19 24
47 ..................... 8 8 14 19 24
48 ..................... 9 8 14 20 25
49 ..................... 9 9 15 21 26
50 ..................... 9 9 16 22 27
51 ..................... 9 9 16 23 28
52 ..................... 9 10 17 24 29
53 ..................... 9 10 18 25 30
54 ..................... 10 10 18 26 31
55 ..................... 10 11 19 27 32
56 ..................... 10 11 20 28 34
57 ..................... 10 11 21 29 35
58 ..................... 10 12 22 31 36
59 ..................... 11 12 22 32 37
60 or older ............ 11 13 23 33 38
___________________________________________________________
TABLE F-2 - AGE CORRECTION VALUES IN DECIBELS FOR FEMALES
____________________________________________________________
Audiometric Test Frequency (Hz)
Years _________________________________
1000 2000 3000 4000 6000
____________________________________________________________
20 or younger........... 7 4 3 3 6
21 ..................... 7 4 4 3 6
22 ..................... 7 4 4 4 6
23 ..................... 7 5 4 4 7
24 ..................... 7 5 4 4 7
25 ..................... 8 5 4 4 7
26 ..................... 8 5 5 4 8
27 ..................... 8 5 5 5 8
28 ..................... 8 5 5 5 8
29 ..................... 8 5 5 5 9
30 ..................... 8 6 5 5 9
31 ..................... 8 6 6 5 9
32 ..................... 9 6 6 6 10
33 ..................... 9 6 6 6 10
34 ..................... 9 6 6 6 10
35 ..................... 9 6 7 7 11
36 ..................... 9 7 7 7 11
37 ..................... 9 7 7 7 12
38 ..................... 10 7 7 7 12
39 ..................... 10 7 8 8 12
40 ..................... 10 7 8 8 13
41 ..................... 10 8 8 8 13
42 ..................... 10 8 9 9 13
43 ..................... 11 8 9 9 14
44 ..................... 11 8 9 9 14
45 ..................... 11 8 10 10 15
46 ..................... 11 9 10 10 15
47 ..................... 11 9 10 11 16
48 ..................... 12 9 11 11 16
49 ..................... 12 9 11 11 16
50 ..................... 12 10 11 12 17
51 ..................... 12 10 12 12 17
52 ..................... 12 10 12 13 18
53 ..................... 13 10 13 13 18
54 ..................... 13 11 13 14 19
55 ..................... 13 11 14 14 19
56 ..................... 13 11 14 15 20
57 ..................... 13 11 15 15 20
58 ..................... 14 12 15 16 21
59 ..................... 14 12 16 16 21
60 or older ............ 14 12 16 17 22
____________________________________________________________
Top
Appendix G - Monitoring Noise
Levels
Non-mandatory Informational Appendix
This appendix provides information to help employers comply
with the noise monitoring obligations that are part of the
hearing conservation amendment.
WHAT IS THE PURPOSE OF NOISE MONITORING?
This revised amendment requires that employees be placed in
a hearing conservation program if they are exposed to average
noise levels of 85 dB or greater during an 8 hour workday.
In order to determine if exposures are at or above this level,
it may be necessary to measure or monitor the actual noise
levels in the workplace and to estimate the noise exposure
or "dose" received by employees during the workday.
WHEN IS IT NECESSARY TO IMPLEMENT A NOISE MONITORING PROGRAM?
It is not necessary for every employer to measure workplace
noise. Noise monitoring or measuring must be conducted only
when exposures are at or above 85 dB. Factors which suggest
that noise exposures in the workplace may be at this level
include employee complaints about the loudness of noise, indications
that employees are losing their hearing, or noisy conditions
which make normal conversation difficult. The employer should
also consider any information available regarding noise emitted
from specific machines. In addition, actual workplace noise
measurements can suggest whether or not a monitoring program
should be initiated.
HOW IS NOISE MEASURED?
Sound Level Meter |
|
Audio Dosimeter |
Basically, there are two different instruments
to measure noise exposures: the sound level meter and the
dosimeter. A sound level meter is a device that measures
the intensity of sound at a given moment. Since sound level
meters provide a measure of sound intensity at only one
point in time, it is generally necessary to take a number
of measurements at different times during the day to estimate
noise exposure over a workday. If noise levels fluctuate,
the amount of time noise remains at each of the various
measured levels must be determined.
To estimate employee noise exposures with a sound level meter
it is also generally necessary to take several measurements
at different locations within the workplace. After appropriate
sound level meter readings are obtained, people sometimes
draw "maps" of the sound levels within different
areas of the workplace. By using a sound level "map"
and information on employee locations throughout the day,
estimates of individual exposure levels can be developed.
This measurement method is generally referred to as "area"
noise monitoring.
A dosimeter is like a sound level meter except that it stores
sound level measurements and integrates these measurements
over time, providing an average noise exposure reading for
a given period of time, such as an 8-hour workday. With a
dosimeter, a microphone is attached to the employee's clothing
and the exposure measurement is simply read at the end of
the desired time period. A reader may be used to read-out
the dosimeter's measurements. Since the dosimeter is worn
by the employee, it measures noise levels in those locations
in which the employee travels. A sound level meter can also
be positioned within the immediate vicinity of the exposed
worker to obtain an individual exposure estimate. Such procedures
are generally referred to as "personal" noise monitoring.
Area monitoring can be used to estimate noise exposure when
the noise levels are relatively constant and employees are
not mobile. In workplaces where employees move about in different
areas or where the noise intensity tends to fluctuate over
time, noise exposure is generally more accurately estimated
by the personal monitoring approach.
In situations where personal monitoring is appropriate, proper
positioning of the microphone is necessary to obtain accurate
measurements. With a dosimeter, the microphone is generally
located on the shoulder and remains in that position for the
entire workday. With a sound level meter, the microphone is
stationed near the employee's head, and the instrument is
usually held by an individual who follows the employee as
he or she moves about.
Manufacturer's instructions, contained in dosimeter and sound
level meter operating manuals, should be followed for calibration
and maintenance. To ensure accurate results, it is considered
good professional practice to calibrate instruments before
and after each use.
HOW OFTEN IS IT NECESSARY TO MONITOR NOISE LEVELS?
The amendment requires that when there are significant changes
in machinery or production processes that may result in increased
noise levels, remonitoring must be conducted to determine
whether additional employees need to be included in the hearing
conservation program. Many companies choose to remonitor periodically
(once every year or two) to ensure that all exposed employees
are included in their hearing conservation programs.
WHERE CAN EQUIPMENT AND TECHNICAL ADVICE BE OBTAINED?
Noise monitoring equipment may be either purchased or rented.
Sound level meters cost about $500 to $1,000, while dosimeters
range in price from about $750 to $1,500. Smaller companies
may find it more economical to rent equipment rather than
to purchase it. Names of equipment suppliers may be found
in the telephone book (Yellow Pages) under headings such as:
"Safety Equipment," "Industrial Hygiene,"
or "Engineers-Acoustical." In addition to providing
information on obtaining noise monitoring equipment, many
companies and individuals included under such listings can
provide professional advice on how to conduct a valid noise
monitoring program. Some audiological testing firms and industrial
hygiene firms also provide noise monitoring services. Universities
with audiology, industrial hygiene, or acoustical engineering
departments may also provide information or may be able to
help employers meet their obligations under this amendment.
Free, on-site assistance may be obtained from OSHA-supported
state and private consultation organizations. These safety
and health consultative entities generally give priority to
the needs of small businesses.
Top
Appendix H - Referenced Documents
Paragraphs (c) through (o) of 29 CFR 1910.95 and the accompanying
appendices contain provisions which incorporate publications
by reference. Generally, the publications provide criteria
for instruments to be used in monitoring and audiometric testing.
These criteria are intended to be mandatory when so indicated
in the applicable paragraphs of 1910.95 and appendices.
It should be noted that OSHA does not require that employers
purchase a copy of the referenced publications. Employers,
however, may desire to obtain a copy of the referenced publications
for their own information.
The designation of the paragraph of the standard in which
the referenced publications appear, the titles of the publications,
and the availability of the publications are as follows:
____________________________________________________________________
Paragraph Referenced Available
designation publication from --
____________________________________________________________________
Appendix B ..... "List of Personal Hearing National Technical
Protectors and Information
Attenuation Data," Service,
HEW Pub. No. 76-120, Port Royal Road,
1975. NTIS-PB267461. Springfield, VA
22161.
Appendix D ..... "Specification for Sound American National
Level Meters," Standards
S1.4-1971 (R1976). Institute, Inc.,
1430 Broadway,
New York, NY
10018.
1910.95(k)(2),
Appendix E ... "Specifications for American National
Audiometers," Standards
S3.6-1969. Institute, Inc.,
1430 Broadway,
New York, NY
10018.
Appendix D ..... "Specification for Octave, Back Numbers
Half-Octave and Department,
Third-Octave Band Dept. STD,
Filter Sets," American
S1.11-1971 (R1976). Institute of
Physics,
333 E. 45th St.,
New York, NY
10017;
American National
Standards
Institute, Inc.,
1430 Broadway,
New York, NY
10018.
____________________________________________________________________
The referenced publications (or a microfiche of the publications)
are available for review at many universities and public libraries
throughout the country. These publications may also be examined
at the OSHA Technical Data Center, Room N2439, United States
Department of Labor, 200 Constitution Avenue, NW., Washington,
DC 20210, (202) 219-7500 or at any OSHA Regional Office (see
telephone directories under United States Government - Labor
Department).
Top
Appendix I - Definitions
These definitions apply to the following terms as used in
paragraphs (c) through (n) of 29 CFR 1910.95.
Action level - An 8-hour time-weighted average of
85 decibels measured on the A-scale, slow response, or equivalently,
a dose of fifty percent.
Audiogram - A chart, graph, or table resulting from
an audiometric test showing an individual's hearing threshold
levels as a function of frequency.
Audiologist - A professional, specializing in the
study and rehabilitation of hearing, who is certified by the
American Speech-Language-Hearing Association or licensed by
a state board of examiners.
Baseline audiogram - The audiogram against which future
audiograms are compared.
Criterion sound level A sound level of 90 decibels.
Decibel (dB) - Unit of measurement of sound level.
Hertz (Hz) - Unit of measurement of frequency, numerically
equal to cycles per second.
Medical pathology - A disorder or disease. For purposes
of this regulation, a condition or disease affecting the ear,
which should be treated by a physician specialist.
Noise dose - The ratio, expressed as a percentage,
of (1) the time integral, over a stated time or event, of
the 0.6 power of the measured SLOW exponential time-averaged,
squared A-weighted sound pressure and (2) the product of the
criterion duration (8 hours) and the 0.6 power of the squared
sound pressure corresponding to the criterion sound level
(90 dB).
Noise dosimeter - An instrument that integrates a
function of sound pressure over a period of time in such a
manner that it directly indicates a noise dose.
Otolaryngologist - A physician specializing in diagnosis
and treatment of disorders of the ear, nose and throat.
Representative exposure - Measurements of an employee's
noise dose or 8-hour time-weighted average sound level that
the employers deem to be representative of the exposures of
other employees in the workplace.
Sound level - Ten times the common logarithm of the
ratio of the square of the measured A-weighted sound pressure
to the square of the standard reference pressure of 20 micropascals.
Unit: decibels (dB). For use with this regulation, SLOW time
response, in accordance with ANSI S1.4-1971 (R1976), is required.
Sound level meter - An instrument for the measurement
of sound level.
Time Weighted Average sound level - That sound level,
which if constant over an 8-hour exposure, would result in
the same noise dose as is measured.
Top
|