Audiometric Evaluation

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Audiometric evaluation is crucial to the success of the hearing loss prevention program in that it is the only way to determine whether occupational hearing loss is being prevented. When the comparison of audiograms shows temporary threshold shift (a temporary hearing loss after noise exposure), early permanent threshold shift, or progressive occupational hearing loss, it is time to take swift action to halt the loss before additional deterioration occurs. Because occupational hearing loss occurs gradually and is not accompanied by pain, the affected employee will not notice the change until a large threshold shift has accumulated. However, the results of audiometric tests can trigger changes in the hearing loss prevention program more promptly, initiating protective measures and motivating employees to prevent further hearing loss.

OSHA and NIOSH presently have differing definitions of the amount of change in hearing indicated by repeated audiometry that should trigger additional audiometric testing and related follow up. OSHA uses the term Standard Threshold Shift to describe an average change in hearing from the baseline levels of 10 dB or more for the frequencies of 2,000, 3,000, and 4,000 Hz. Upon finding the OSHA STS, certain actions are required including retest, evaluation of the adequacy of hearing protectors or requiring their use if not used until the STS event, and revision of baseline. NIOSH uses the term Significant Threshold Shift to describe a change of 15 dB or more at any frequency 500 through 6,000 Hz from baseline levels that is present on an immediate retest in the same ear and at the same frequency. NIOSH recommends a confirmation audiogram within 30 days with the confirmation audiogram preceded by a quiet period of at least 14 hours. The NIOSH STS, called 15 dB twice, same ear, same frequency, can only be tested if the baseline audiogram is available at the time of the annual audiometric test.

The reader is encouraged to consult Appendix A, items no. 12-30 and 52-54, for a summary of OSHA's requirements for audiometric evaluations. The sections entitled "Monitoring Audiometry" and "Referrals" in Appendix B's checklists also should be helpful.

For maximum protection of the employees (and for that matter, the company), audiograms should be performed on the following five occasions:

1. Pre-employment.

2. Prior to initial assignment in a hearing hazardous work area.

3. Annually as long as the employee is assigned to a noisy job (a time-weighted average exposure level equal to or greater than 85 dBA).(1)

4. At the time of reassignment out of a hearing hazardous job.

5. At the termination of employment.

In addition, it is suggested that employees who are not exposed be given periodic audiograms as part of the company's health care program. The audiograms of these employees can be compared to those of the exposed employees whenever the overall effectiveness of the hearing loss prevention program is evaluated. In an optimally effective program, the two employee groups will show essentially the same amount of audiometric change.

Management Responsibilities

Managers should support the audiometric evaluation phase by allocating sufficient resources. Because the audiometric phase is sometimes the most expensive element of a hearing loss prevention program, it is prudent to set aside enough funds to provide for the performance of reliable hearing tests and the collection of accurate information. Noise is a HAZARDOUS agent. Management must ensure all employees (even mobile/itinerant workers) are included in the audiometric phase.

Management may opt to contract for audiometric services with an external source such as a mobile testing contractor or a local hearing clinic. Alternatively, management may choose to purchase audiometric equipment and train a company employee to perform audiometric testing on-site under the supervision of an audiologist or a qualified physician. The third option is to combine internal and external resources. The choice depends upon economic considerations as well as the size, policies, and geographical location of the company. If contract services are used, it is critically important that management still assign responsibility for overseeing the hearing loss prevention program to a key on-site individual. Whether the audiometric testing is performed internally or externally, the company will not receive the benefit of quality audiometric evaluations unless the following practices are adhered to:

1. The audiograms must be administered using properly calibrated audiometers in a sound-treated room with acceptable background sound levels during testing. Circumaural earphone enclosures (earphones inside earmuffs), which are designed to reduce external noise, should not be substituted for a sound treated room, and generally should not be used because of inherent problems with calibration and earphone placement.

2. The same type of audiometer (and preferably the same instrument) should be used from year to year. This may help prevent measurement variations caused by subtle differences among machine models/types or by the type of responses required from the person being tested.

3. The training of audiometric technicians should meet as a minimum the current requirements of the Council for Accreditation in Occupational Hearing Conservation. Use of microprocessor-controlled or computer-based audiometric equipment should NOT exempt a technician from receiving training.

4. All audiometric technicians should use the same testing methods for all of the company's employees.

5. All testing should be done under the supervision of an audiologist or a physician knowledgeable about hearing loss prevention.

Management should provide the audiometric technician with sufficient time to perform the tests thoroughly and to give noise-exposed employees proper attention. Because the audiometric session provides an ideal opportunity to motivate employees' concern for hearing loss prevention, technicians should have time to inform employees about their hearing status immediately after completing the audiogram and to check their hearing protection devices. When the technician is too hurried to do more than a rapid screening audiogram because of other duties, the employee correctly perceives that the exercise is performed only in response to regulatory requirements, without a sincere interest in protecting anyone's hearing. In such a situation employees often lose their motivation to participate in the hearing loss prevention program.

One of the best ways to assure the quality of the audiograms collected is to make prior audiograms for each employee available to the tester at the time of the test. If the tester's comparison of audiograms reveals a threshold shift (equal to 15 dB or more at any frequency), the tester can refit the earphones, reinstruct the employee, and conduct a retest. If the shift persists on the retest, the change can be considered as reliable. If not, the retest can be taken as the reliable test and it will be included in the record system and the first test will be discarded. It is estimated that as many as 70% of all audiograms showing shift will be resolved if the earphones are refitted, the employee is reinstructed, and a retest is administered at the time of the initial test. Management can facilitate quality assurance by providing the audiometric technician with time to conduct the retest and with authority to hold the employee back for a retest.

Management should also make sure that the individual who reviews the audiograms is a qualified professional with specific training and experience in the area of occupational hearing conservation. All employees, not just those with threshold shifts, should receive prompt written summaries of their current hearing status from the professional reviewer. Employees also should receive summaries of their hearing trends over time, along with recommendations for further evaluation or any extra precautions needed, such as more careful use of hearing protectors.

Program Implementor Responsibilities

The program implementor has important responsibilities in the audiometric testing phase of the hearing loss prevention program. This individual and the person conducting audiometric testing may be the same person, but if not, the program implementor must ensure that the person performing the audiometric testing is well-trained and carries out the necessary functions. The

individual who performs the testing needs to demonstrate enthusiasm for the program and show sincere interest in each employee while carrying out his or her duties. The results of the hearing testing are most valuable to the employee if they are provided immediately following the test. The audiogram should be compared to the baseline or reference audiogram while the employee is watching. The employee should be advised that the audiogram either shows no change in hearing, implying that hearing loss prevention efforts are working for him or her, or that a change has occurred. If the hearing test shows a change, the employee should be returned to the test booth, be instructed in how to take the test, be refitted with earphones, and retested. If the second test confirms the change, the employee should be advised to have a confirmation audiogram within 30 days. The confirmation audiogram should be preceded by a quiet period of at least 14 hours and earmuffs or earplugs should not be used to achieve the quiet period. Regardless of whether or not there is a shift, the immediate feedback should also provide information to the employee as to how his or her hearing compares to others of the same age, gender, and race.

The program implementor should make sure that the records include the employee's auditory history, which is the history of diseases and disorders of hearing and balance, and related factors (such as diabetes and high blood pressure), and history of exposure to noise and other ototraumatic agents, both on and away from the job. This information provides the professional audiogram reviewer with insight concerning probable causes for threshold shifts and enhances specific recommendations for follow-up.

Annual audiometric examinations (but not baselines) should be scheduled well into the work shift so that comparisons with baseline audiograms will reveal any early indications of hearing loss or temporary threshold shifts due to hearing protector inadequacies. In the early stages of noise-induced hearing loss, noise exposure causes temporary shifts in hearing threshold level, which, if repeated on a regular basis, become permanent. By testing toward the end of the workday, rather than before or early into the workday, these temporary threshold shifts can be identified, and steps can be taken to counteract them. Interventions at this stage thus prevent subsequent, permanent hearing loss.

Direct contact between the person performing the audiometric testing and the employee during the hearing test provides the chance to intervene by checking the condition of the employee's hearing protector. The tester can observe whether the employee is using the device correctly, and reevaluate the adequacy of hearing protector selection, fit, and condition. The employee should be asked whether the hearing protector is performing in a satisfactory manner. If necessary, a new protector of a different size or type can be issued and the employee can be instructed in the proper care, fitting, and use of the device.

Daily functional and listening checks of audiometer function are critical if audiogram are to be accurate, and the program implementor must ensure that these checks are properly documented. To measure thresholds accurately, the test room must be quiet enough to meet appropriate American National Standards Institute requirements (ANSI S3.1-1991 or its successor), which is especially important for employees with normal hearing. Complete audiometer calibrations should be scheduled annually, but the audiometer should not actually be adjusted unless it fails to meet standard tolerances. Too frequent adjustments add "seesaw" variability to the audiometric data, interfering with the interpretation of both individual and group hearing trends. To prevent another source of measurement variability, the same audiometer types should be used consistently rather than switching between models, and especially between types of audiometers (manual, self-recording, and microprocessor). Failure to follow these practices jeopardizes the validity of the audiometric data and may reduce employee protection as a consequence. If the audiometer is changed from one year to the next, the change should be noted in the audiometric records.

Program implementors should see that the audiometric record indicates:

1. The specific purpose of the audiometric examination: for example, baseline, annual, retest, threshold shift confirmation, or other.

2. The specific equipment used and most recent calibration date.

3. The name of the tester.

4. The date and time of day of the test (if there are work shifts, shift should be noted).

5. The auditory history information.

6. The hearing threshold values obtained.

7. The tester's judgment of the subject's response reliability.

8. The results of the hearing protector inspection and a record of any refitting, reissuing, or retraining.

9. The tester's comments, if any.

The program implementor must make sure that every baseline, annual, retest, and follow-up audiogram is reviewed. The supervising professional may set up criteria for the person conducting the audiometric tests or for a computer program to assess all records and identify only the remaining noteworthy records for review. Routine records are those depicting normal hearing or no significant hearing decrements or improvements for a given employee. Only the professional is qualified to revise the reference "baseline" audiogram, either because of improvements in hearing or because of a persistent decline in hearing level. The reviewer should look for threshold shifts at any test frequency, not just "standard threshold shifts" as defined by OSHA(2), and for audiometric patterns indicative of medical problems. If the audiometric data indicate a degeneration of hearing, the reviewer must alert both the employee and management about these findings.

OSHA requires follow-up referrals under certain conditions (see item number 23 in Appendix A, and section (g)(8)(ii) in the OSHA noise standard). The program implementor must be familiar with these provisions, and must see that they are carried out. Sometimes medical referrals are necessary to determine the cause of a hearing loss, and medical treatment can be an important next step. Not all hearing losses are caused by occupational factors and sometimes medical intervention can be crucial to the worker's health.

Although OSHA regulations specify required follow-up actions when a standard threshold shift is identified, follow-up for smaller shifts in hearing is recommended for optimal protection. Studies of effective hearing loss prevention programs show procedures that go beyond the OSHA regulations. For example: 1) employees with "beginning" shifts (smaller than OSHA's standard shift) get a written notification or "alert" from the professional reviewer; 2) employees receive face-to-face counseling from on-site program implementors and, based on the reviewer's suggestions, retesting, reevaluation of hearing protector efficiency, and extra instruction in hearing protector use; and 3) individuals with possible medical conditions of the ear are counseled to seek evaluation and treatment from their own physicians, or they may be referred to a company physician or a health provider covered under the company's health-care program.

Employee Responsibilities

To help the professional reviewer interpret the audiogram, employees need to disclose relevant details of their ototraumatic exposure histories (on past jobs, in the military, and in hobbies and non-occupational activities). Employees should consider themselves partners with management. Employees must ensure accurate audiometry by cooperating with the audiometric test process, by keeping their appointment for hearing testing, and by carefully following the instructions of the hearing tester.

Employees should also provide histories of ear diseases, treatment, and current ear conditions, including signs of over-exposure to noise such as tinnitus (ringing in the ear). Employees who understand that audiometric findings will be used to help conserve their hearing, not to penalize or blame them, will respond more effectively to the audiometric listening task. Employees should let the audiometric tester know if the instructions are unclear, if tinnitus is interfering with audiometric responses, or if the audiometer produces sounds other than those described in the instructions.

Once the audiometric results have been reviewed, employees should actively cooperate with the program to protect their own hearing by following the recommendations of the professional supervisor. They should follow the employer's policies concerning the use of hearing protectors on and off the job, and should obtain any recommended medical evaluation or care.

Sample Audiometric and Identification Information
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OSHA Requirements

Code of Federal Regulations, Title 29, Chapter XVII, Part 1910, Subpart G, 1910.95: sections (g), (h), Appendix C, Appendix D, Appendix E, and Appendix F.

See checklist in Appendix A of this guidebook,
items no. 12-30, and 52-54
See checklist in Appendix B of this guidebook,
sections entitiled "Monitoring Audiometry and
Record Keeping" and "Referals."

Further Reading

Gasaway DC [1985]. Hearing Conservation: A Practical Manual and Guide. Englewood Cliffs, NJ: Prentice-Hall, Chapters 10, 12, and 13.

Lipscomb DM [1988] Hearing testing and interpretation. In: Lipscomb DM ed. Hearing Conservation in Industry, Schools, and the Military. Boston, MA: Little, Brown and Co., Chapter 8.

Miller MH, Wilber LA [1991]. Hearing evaluation. In Harris CM ed. Handbook of Acoustical Measurements and Noise Control. 3rd ed. New York: McGraw-Hill, Inc., Chapter 19.

Morrill JC [1986]. Hearing measurement. In: Berger EH, Ward, WC, Morrill JC, Royster LH, eds. Noise and Hearing Conservation Manual 4th ed. Akron, OH: American Industrial Hygiene Assoc., Chapter 8.

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