Basics of Audiometric Testing
Setting up a Hearing Check (Audiometry) Program
Audiometric testing programs can be accomplished in several different ways. Making the best choice usually depends on knowing what your company needs and understanding the advantages and disadvantages of the model options and selecting the option that makes the most sense for the employer and employees.
In general, the broadly used models can be categorized as:
- In-house: the employer has dedicated space, equipment, and personnel to conduct the hearing tests on-site.
- Mobile service provider: a third-party service provider comes to the job site with equipment and personnel to conduct the tests, typically in a mobile van or trailer.
- Off-site medical/audiology clinic or hospital: workers travel to an off-site facility that offers hearing testing services.
- Combination: using two or more of the models to complete the baseline, annual, and follow-up tests.
The number of workers who are tested annually is usually a factor in which delivery model works best.
Audiometric test programs need qualified people to conduct the hearing checks and also a professional, either an audiologist or physician, to provide program oversight and review “problem audiograms.” The term audiometric technician or occupational hearing conservationist (OHC) describes the person giving the tests. There is education and certification available for audiometric technicians through the Council for Accreditation in Occupational Hearing Conservation (CAOHC). Successfully completing the course work and standardized examination earns the credential Certified Occupational Hearing Conservationist. See www.caohc.org for details about how to become certified.
Professional oversight of the audiometric testing program is required by regulation and can be provided by either an audiologist or physician. There is also a voluntary certification for the professional through CAOHC. This credential is called Professional Supervisor of the Audiometric Monitoring Program® (CPS/A). Visit www.caohc.org for details as to the role of the professional supervisor and how to become certified.
Audiologists or physicians are also permitted by regulation to conduct the hearing checks. So in some programs, both the administration of the testing and the program review may be done by the same person.
If you are setting up an in-house audiometric testing program, you will need several pieces of equipment. The typical equipment list includes:
- Audiometer: A device used to measure the sensitivity of hearing with pure-tones of various frequencies. The audiometer has earphones that must be calibrated to the audiometer. There are different types of audiometers, including manual, microprocessor, and coumputer controlled.
- Otoscope: A bright light with a magnifying lens that is used to view the outer ear and eardrum. It is helpful to know the condition of the ear canal before doing a hearing test and when inserting hearing protection devices.
- Bioacoustic simulator: A specialized device that is used to verify the performance of the audiometer. Each day that hearing testing is to be done, the technician places the earphones onto the simulator and a quick check of its hearing thresholds is performed. Changes in thresholds of the bioacoustic simulator can indicate a malfunctioning audiometer. Technicians often refer to this device as a “Bio Betty” or “Oscar” – names used by certain manufacturers for these simulators.
- Audiometric database management system: A commercial software program specifically designed to collect, analyze, and store audiometric data and related hearing conservation information. Using an audiometric database management system can help with recordkeeping, generating reports, and trend analysis.
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What is a “Problem Audiogram”?
OSHA specifies that “problem audiograms” must be reviewed by a licensed or certified audiologist, otolaryngologist, or other physician. A letter of interpretation from OSHA (5-9-94) provides some explanation.
According to OSHA “Examples of problems audiograms are: Audiograms that show large differences in hearing thresholds between the two ears, audiograms that show unusual hearing loss configurations that are atypical of noise induced hearing loss, and audiograms with thresholds that are not repeatable.”
Often times, the professional supervisor will guide the employer and/or audiometric technician in identifying problem audiograms.
Example Calculation of Standard Threshold Shift
Standard Threshold Shift
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The term standard threshold shift (STS) is defined by OSHA as the amount of hearing shift that triggers mandatory follow-up actions.
The steps OSHA defines for calculating STS are:
- Compare the worker’s baseline test to the current test.
- Find the difference in hearing thresholds at 2000, 3000, and 4000 Hz.
- Compute the average change in these thresholds for each ear separately.
- STS is present if the average difference is 10 dB or more, in either ear.
OSHA permits factoring in an allowance for age-related hearing loss when calculating the STS, reasoning that if a change in hearing occurs between the baseline and the annual test, part of the change is due to aging. The age correction amounts are specified in the regulation and depend on the age and sex of the worker. Although age corrections are allowed, using them will likely delay the identification of hearing shift and may inhibit the ability to intervene effectively. The OSHA method of applying age correction values is described in regulation 1910.95 appendix F.
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Abnormal Thresholds
Normal hearing thresholds are in the range of 0 – 25 dB hearing level (HL). Thresholds that are greater than 25 dB HL are said to be outside the normal range and indicate that a hearing loss is present. There are typical patterns of hearing loss, sometimes associated with the cause of the hearing loss.
Thresholds that are either outside the normal range of hearing or atypical for a type of hearing loss are considered to be abnormal.
When thresholds are abnormal, more attention is needed in order to determine the best approach to managing the hearing loss and worker.
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Invalid Tests
There are times when test results are either incomplete, were not done according to the regulatory requirements, or do not represent the actual hearing ability of a worker. Invalid tests cannot be used to meet regulatory requirements and do not serve the purpose of identifying early stages of noise-induced hearing loss. Sometimes the test can be repeated to correct errors, either due to improper testing protocols or equipment malfunction. Other times a worker may need to be referred to an audiologist for more comprehensive testing.
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Standard Threshold Shift Follow-Up
Results of the audiometric testing program must be evaluated to determine if the tests are valid and if there is a change in hearing that requires follow-up action. The OSHA definition of Standard Threshold Shift (STS) in regulation 1910.95 is a change in hearing of an average of 10 dB or more when comparing the current test to the annual test at the frequencies of 2000, 3000, and 4000 Hz in either ear. Age corrections are allowed when calculating STS. A retest may be done within 30 days of the annual test to verify the results. The retest may be substituted for the annual test if the STS is no longer present.
If STS is identified, OSHA requires the employer to notify the worker of the results in writing within 21 days of the determination. Unless a physician determines that the STS is not related to workplace noise, then the employer must provide follow-up:
- Hearing protection is required for all workers with noise exposure at 85 dBA TWA and higher. Workers who had not been using HPDs before the STS must be fitted with an HPD, trained on the use and care of the HPD, and required to use them.
- Worker who had been using an HPD may need greater attenuation to reduce the exposure to 85 dB TWA. If so, alternative hearing protectors with more attenuation must be provided. Workers must be refitted and retrained on HPDs.
- If additional testing is needed, or if there is a reason to suspect that the HPDs are causing a medical problem, the worker must be referred for an audiological or a medical evaluation.
- The worker must be informed of the need for a medical examination if it appears there is a medical condition that is not related to the use of HPDs.
Resources to Learn About Audiometric Testing
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IMPORTANT NOTE: This information is based on selected current national requirements. Other country or local requirements may be different. Always consult User Instructions and follow local laws and regulations. This website contains an overview of general information and should not be relied upon to make specific decisions. Reading this information does not certify proficiency in safety and health. Information is current as of the date of publication, and requirements can change in the future. This information should not be relied upon in isolation, as the content is often accompanied by additional and/or clarifying information. All applicable laws and regulations must be followed.
