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Noise and Hearing Conservation
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Audiometric testing monitors the sharpness and acuity of an employee's hearing over time, and also provides an opportunity for employers to educate employees about their hearing and the need to protect it.

Employers must establish and maintain an audiometric testing program for all employees exposed at or above the action level of 85 dBA-TWA (time-weighted average). [29 CFR 1910.95(g)(1)]

The program must be provided at no cost to employees. [29 CFR 1910.95(g)(2)]

Important elements of the audiometric testing program include:

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Baseline and Annual Audiograms
  • Within six months of an employee's first exposure at or above the action level, the employer must establish a valid baseline audiogram against which subsequent audiograms can be compared. [29 CFR 1910.05(g)(5)(i)]
  • Mobile Test Van Exception:
    • If mobile test vans are used, the employer must obtain a valid baseline audiogram within one year of an employee's first exposure at or above the action level. [29 CFR 1910.95(g)(5)(ii)]
    • Where baseline audiograms are obtained more than six months after the employee's first exposure at or above the action level, employees must wear hearing protection devices for any period over six months after the first exposure until the baseline audiogram is obtained. [29 CFR 1910.95(g)(5)(ii)]
  • At least 14 hours without exposure to workplace noise must precede baseline audiogram testing. (Hearing protection devices may be worn during this time as a substitute for this requirement.) [29 CFR 1910.95(g)(5)(iii)]
    • Employers must also notify employees of the need to avoid high levels of non-occupational noise exposure during the 14 hour period immediately preceding the audiometric exam. [29 CFR 1910.95(g)(5)(iv)]
  • After obtaining the baseline audiogram, employers must obtain a new audiogram annually for each employee whose exposure is at or above the action level. [29 CFR 1910.95(g)(6)]


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Standard Threshold Shift (STS)
As used in this section, a standard threshold shift (STS) 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. [29 CFR 1910.95(g)(10)(i)]

In determining whether an STS has occurred, allowances 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 29 CFR 1910.95 Appendix F: Calculations and Application of Age Corrections to Audiograms. [29 CFR 1910.95(g)(10)(ii)]


Computing the Standard Threshold Shift
Example 1
Frequency (Hz) Baseline audiogram threshold (db) Annual audiogram threshold (dB) Change
500 5 5 0
1,000 5 5 0
2,000 0 10 +10
3,000 5 20 +15
4,000 10 35 +25
6,000 10 15 +5

Considering the Hearing Threshold Level (HTL) values at 2,000, 3,000, and 4,000 Hz, there are changes in hearing threshold of 20, 15, and 25 dB, respectively. Thus:

STS = (10 + 15 + 25)/3 = 50/3 = 16.7 dB
 

Conclusion: The STS is +16.7 dB; hearing has deteriorated, the employee must be notified in writing within 21 days, and, depending on professional discretion, the employer may elect to retest the employee and/or revise the baseline audiogram.

Example 2
Frequency (Hz) Baseline audiogram threshold (db) Annual audiogram threshold (dB) Change
500 5 5 0
1,000 5 0 -5
2,000 0 -10 -10
3,000 5 -5 -10
4,000 10 -5 -15
6,000 10 5 -5

Again, considering the HTL values at 2,000, 3,000, and 4,000 Hz, the hearing threshold has changed by -10, -10, and -15 dB, respectively. Thus:

STS = (-10 -10 -15)/3 = -35/3 = -11.6 dB
 

Conclusion: The STS is -11.6 dB; hearing has improved, the employee should be notified, and, depending on professional discretion, the baseline audiogram may be revised.


With regard to recordkeeping requirements, OSHA has developed a  "decision tree" [7 KB PDF*, 1 page] to determine whether the results of an audiometric exam given on or after January 1, 2003 reveal a recordable STS. See 29 CFR 1904 for additional information on recording and reporting occupational injuries and illness.


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Evaluation of Audiogram


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Revised Baseline
An annual audiogram may be substituted for the baseline audiogram when the audiologist, otolaryngologist, or physician evaluating the audiogram determines that:
  • The standard threshold shift (STS) revealed by the audiogram is persistent [29 CFR 1910.95(g)(9)(i)] or
  • The hearing threshold shown in the annual audiogram indicates significant improvement over the baseline audiogram. [29 CFR 1910.95(g)(9)(ii)]


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Follow-up Procedures
  • If comparison of the annual audiogram to the baseline audiogram indicates a standard threshold shift (STS) has occurred, the employee must be informed in writing within 21 days of the determination. [29 CFR 1910.95(g)(8)(i)]
  • 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 STS occurs [29 CFR 1910.95(g)(8)(ii)]:
    • Employees not using hearing protectors must be fitted with hearing protectors, trained in their use and care, and required to use them. [29 CFR 1910.95(g)(8)(ii)(A)]
    • Employees already using hearing protectors must be refitted and retrained in their use, and provided with hearing protectors offering greater attenuation if necessary. [29 CFR 1910.95(g)(8)(ii)(B)]
    • The employee must 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. [29 CFR 1910.95(g)(8)(ii)(C)]
    • 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. [29 CFR 1910.95(g)(8)(ii)(D)]
    Note: The above items are not required if a physician determines that the STS is not work-related or aggravated by occupational noise exposure.
  • If subsequent audiometric tests show that the STS identified on a previous audiogram is not persistent, the employer must inform the employee of the new audiometric interpretation. [29 CFR 1910.95(g)(8)(iii)(A)]
  • Employees whose exposure to noise is less than a time-weighted average (TWA) of 90 dB may discontinue wearing hearing protectors. [29 CFR 1910.95(g)(8)(iii)(B)]


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Testing and Equipment
General
  • Audiometric tests must be performed by [29 CFR 1910.95(g)(3)]:
    • A licensed or certified audiologist, otolaryngologist, or other physician, or
    • 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 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.
  • All audiograms obtained pursuant to this section must meet the requirements of 29 CFR 1910.95 Appendix C: Audiometric Measuring Instruments. [29 CFR 1910.95(g)(4)]
  • Audiometric tests must be pure tone, air conduction, hearing threshold examinations, with test frequencies including as a minimum 500, 1000, 2000, 3000, 4000, and 6000 Hertz (Hz). [29 CFR 1910.95(h)(1)]
  • Audiometric tests must 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. [29 CFR 1910.95(h)(2)]
  • Audiometric examinations must be administered in a room meeting the requirements listed in 29 CFR 1910.95 Appendix D: Audiometric Test Rooms. [29 CFR 1910.95(h)(4)]
Calibration
  • The functional operation of the audiometer must 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 ten decibels (dB) or greater require an acoustic calibration. [29 CFR 1910.95(h)(5)(i)]
  • Audiometer calibration must be checked acoustically at least annually in accordance with 29 CFR 1910.95 Appendix E: Acoustic Calibration of Audiometers. Test frequencies below 500 Hz and above 6000 Hz may be omitted from this check. Deviations of 15 dB or greater require an exhaustive calibration. [29 CFR 1910.95(h)(5)(ii)]
  • An exhaustive calibration must be performed at least every two years in accordance 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. [29 CFR 1910.95(h)(5)(iii)]

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