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audiometric testing

Introduction Establish a Regular Schedule for Audiometric Monitoring
Identifying Job Descriptions and Employees Determine How Feedback and Follow-up will be Provided to Employees
Determine How Audiograms will be Performed and Evaluated Commonly Asked Questions

Introduction
Engineering controls, administrative controls, and hearing protective devices, if properly selected and used, reduce employee exposures to noise to acceptable levels.  One way to better ensure that your program and controls are effective is to periodically measure the hearing sensitivity of employees.  Audiometric testing is used to establish each employee's base line hearing level, and through annual testing, detect any significant threshold shift, or hearing loss, due to failure of controls.

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Identifying Job Descriptions and Employees
From your noise survey results, you have identified the jobs and employees with exposure at or above 85 dBA as an 8-hour average.  All employees in these jobs need to be included in the audiometric testing program.  This includes baseline audiograms, annual audiometric evaluation, and exit audiograms.  When employees are hired into jobs where the potential for noise-induced hearing loss exists, baseline audiograms should be obtained as soon as possible, preferably before work in the noisy area begins.

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Determine How Audiograms will be Performed and Evaluated

Your company has two options:

  1. Set up an in-house testing program and purchase the necessary testing equipment, have an individual trained in audiometric testing and use the plant or outside physician to evaluate the audiograms; or,

  2. Contract with a testing firm, audiologist or otolaryngologist to perform the tests, evaluate the audiogram and advise of any action needed as a result of the evaluation.  Some firms provide mobile, onsite services to your facility.  Others required employees to be sent to the testing location.

Many companies without an in-house medical staff choose the second option.  Either way, the audiometric test must be performed by a licensed or certified audiologist, otolaryngologist, physician or by a technician accredited by the Council of Accreditation in Occupational Hearing Conservation (CAOHC).  The CAOHC sponsors countrywide seminars that certify these technicians.  Most contract firms have a CAOHC technician perform the test and an audiologist with a Certificate of Clinical Competence (CCC) review and evaluate the results.

Contracted audiometric testing firms generally provide all the testing equipment and documentation required by the OSHA standards, and can implement the required follow-up procedures.

In general, testing is best performed by audiologists or technicians supervised by audiologists.  Otolaryngologists and other physicians are most needed when the testing indicates some medical examination is called for.  A CCC audiologist can make that determination.  If a technician performs the test, he or she must be responsible to an audiologist, otolaryngologist or other physician.

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Establish a Regular Schedule for Audiometric Monitoring
Audiograms should be performed annually as long as the employee remains in the hearing conservation program.  It is also to a company's advantage to perform exit audiograms when an employee is reassigned out of a noisy job and at the termination of employment to protect against unjustified Worker's Compensation claims.  Most mobile testing services will assist in making arrangements for baseline audiograms and setting up a schedule for annual audiograms.

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Determine How Feedback and Follow-up will be Provided to Employees
If noise-related hearing changes are detected, individual counseling, refitting, and retraining for hearing protective devices are needed.  Immediate feedback during audiometric testing sessions or written feedback from the professional reviewer will provide information to the employee about his/her hearing status and motivate employees about hearing conservation.  When hearing shifts appear unrelated to noise exposure, the employee should be urged to seek otological or audiological evaluation and treatment.

If audiograms are filed and forgotten rather than being used to guide follow-up actions, then the audiometric testing program may simply document progressive hearing loss rather than help to prevent it.  Feedback to employees about their audiometric results motivates employees to protect their own hearing.  Audiometric test results provide important feedback to management on the effectiveness of the Hearing Conservation Program and Hearing Protection Devices.

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Commonly Asked Questions

What is an audiogram?
An audiogram is basically a graph of the results of an audiometric test.  Frequency (expressed in Hertz) is indicated along the horizontal axis and intensity (expressed in decibels) along the vertical axis.  Two examples of audiograms are shown below:

Audiograms (click for larger view)
Audiograms (click for larger view)

For hearing conservation programs, the test frequencies must include as a minimum, 500, 1000, 2000, 3000, 4000 and 6000 Hertz (Hz).  The intensity scale represents the sound pressure level presented to the subject through the audiometer.  The smaller the number, the fainter the sound.  When a subject's hearing is measured, the threshold of hearing at each test frequency is established as the intensity level at which the sound can just barely be heard.  The farther a subject's threshold is below the zero line of the audiogram, the greater the loss of hearing.

What is a threshold shift?
A threshold shift is a change in hearing sensitivity.  Temporary threshold shifts can occur after exposure to sound.  It is temporary when there is a return to the pre-exposure hearing level after a period of hours away from sound.  Permanent hearing loss (a permanent threshold shift) occurs when the recovery of hearing is less than total after a lengthy period away from loud noise.

Typically, a noise induced threshold shift occurs at high frequencies (around 4000 Hz) before a significant hearing loss occurs in the speech frequencies (500 - 3000 Hz).  It is the loss of hearing in the speech frequencies that is considered disabling.  If a sound must be made louder than 25 dB to be heard in the speech important frequencies, the thresholds begin to fall in the range of hearing impairment.  These are referred  to as "elevated" thresholds.

How is an audiometric test performed?
Audiometric tests conducted in hearing conservation programs are pure tone, air conduction tests.  Pure tone refers to the test frequencies being discreet, single values.  Air conduction means that the test signal is presented through earphones and thus measures the threshold of sound conducted to the eardrum through the air.  Since the ear canal, eardrum and middle ear are conducting the sound, any medical problems in the middle and outer ear (wax build-up, ear infection) will indicate some loss of hearing on an audiogram.  In contrast, bone conduction threshold testing bypasses the outer and middle ear to measure the amount of sound conducted to the inner ear.  This testing is performed to distinguish sensori-neural hearing loss from conductive hearing loss.  Since noise-induced hearing loss is sensori-neural, bone conduction testing is often used to determine if hearing loss may be a result of excessive exposure to noise.  However, bone conduction testing is not part of routine audiometric testing.

What type of equipment and facilities are needed?
Audiometers must meet the specifications of, and be maintained in accordance with, American National Standard Specification for Audiometers, S3.6-1969.  Audiometer calibration is to be checked acoustically at least annually and an exhaustive calibration is required at least every two years in accordance with S3.6-1969.

Testing rooms must be free of excessive background noise that would interfere with the subject hearing the test signal, even though earphones are used.  The following Table lists the permitted maximum levels.

Table of Permitted Background Noise
Octave-band center frequency (Hz) 500 1000 2000 4000 8000
Sound pressure level (dB) 40 40 47 54 62


Most pre-fabricated testing booths set up in a reasonably quiet area easily conform with this requirement.  Contract firms should be documenting the last audiometer calibration and the background sound pressure levels of the test room when they conduct the employee's audiometric testing.

What is the purpose of the baseline audiogram?
The baseline audiogram is performed at the time of or as soon after employment as possible, and will be used as a reference against which all future audiograms will be compared.  If the hearing protectors are effective and being worn properly, an employee's hearing should not deviate from the baseline, except for the gradual loss from presbycusis (aging) or further medical problems not related to noise-induced hearing loss.

When should baseline audiograms be obtained?
Although OSHA allows up to six months after an employee's initial exposure before baselines must be established, it is possible that a new employee may have a pre-existing hearing loss from a previous job or nonoccupational activities.  In the case of Mobile Van Testing Services, OSHA allows you up to a year before establishing a baseline for a new employee.  Most state compensation statutes require only 60 to 120 days of employment before an employee can file a loss of hearing claim.  Thus, a new employee with pre-existing hearing loss could file a claim before the pre-existing loss is documented.  It is best to have your employee's baselines measured as soon as possible after employment, to help you avoid potential liability for pre-existing hearing losses.

Baseline audiograms must be obtained on "rested" ears.  The employee must not be suffering from any Temporary Threshold Shift (TTS) that would occur if he or she worked in a noisy area all or part of the day and the test was given immediately after the exposure.  There are two permitted solutions to this problem:

  • Test after a 14-hour quiet period, thus first thing in the morning; or,
  • Test during the day, but ensure that hearing protectors are properly fitted and supervise continual wearing before the test.

Studies show that elevated hearing thresholds are more likely to occur when relying on the use of HPDs than after allowing a 14 hour quiet period prior to administering baseline audiograms.  Although it is often difficult to confine workers to areas below 80 dBA until it is their turn for the test, a 14-hour quiet period results in more accurate audiograms.  Either way, employees must be notified of the need to avoid high levels of nonoccupational noise during that period.

What is the purpose of annual audiograms?
The purpose of this audiogram is to monitor the effectiveness of the hearing protective devices.  At least annually after the baseline audiogram, a new audiogram must be obtained.  If no significant elevation of hearing thresholds have occurred since the baseline audiograms were administered, then the hearing conservation measures are considered to be effective.  A shift or hearing loss that results in significant impairment should not be occurring.

How are annual audiograms evaluated?
Each employee's annual audiogram is compared to that employee's baseline audiogram to determine (1) if the test is valid, and (2) if a Standard Threshold Shift (STS) has occurred.

The validity of a test depends on the subject's response, the qualifications of the technician, and the equipment and facilities.  Validity checks are usually performed by the technician administering the test.  Microprocessor audiometers may perform a validity check mathematically.

A Standard Threshold Shift (STS) is defined as a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more in either ear at 2000, 3000, and 4000 Hz.  For example, a 30 dB threshold shift at 4000 Hz and no shift at the other two frequencies would be defined as an STS.  Action is required when shifts reach or exceed this specified point.  Technicians, microprocessors and audiologists may make the STS determination.  Deduction for the effects of presbycusis (aging) may be made to the annual audiogram before comparing it to the baseline audiogram.

In early stages, noise-induced hearing loss is represented by a "notch", or elevated threshold at 4000 Hz.  The thresholds may be quite good through the speech frequencies, then elevate at 4000 Hz.  As exposure to noise (and hearing loss) continues, the elevated thresholds will move into the speech frequencies.

What is a "problem" audiogram?
Audiograms showing an STS are considered "problem" audiograms.  Problem audiograms must be reviewed by the audiologist, otolaryngologist or physician supervising the testing program.  That individual determines if there is a need for further evaluation (i.e., medical exam, additional audiometric tests, etc).  Persons performing the audiograms are to be provided with:

  • A copy of 1910.95 (c) through (n);
  • Baseline and most recent audiogram of individual being evaluated;
  • Background sound levels in the test booth; and,
  • Audiometer calibration records.

What type of follow-up is necessary for "problem" audiograms?
Generally, the supervising professional will have a retest done within 30 days of the notice of a problem audiogram to see if the STS is persistent.  If the professional determines that the STS may be work related, the employee must be referred for a clinical audiological evaluation if additional hearing testing is called for, or for an ear exam if a medical pathology, such as an ear infection, is suspected of being caused or aggravated by the use of HPDs.  Often the pattern of the STS on the audiogram will indicate to the professional which exam is more appropriate.  The clinical exam may include bone conduction threshold testing, speech reception thresholds and tests for functional hearing loss (psychosomatic or feigned).  If a problem is not related to the use of HPDs, the employee is advised to see a physician.  When an STS occurs, the following additional steps are required:

  • Employees not wearing HPDS must be fitted with HPDs, trained in their use and care, and required to wear them;

  • Employees already wearing HPDs shall be refitted and retrained in the use of HPDs and provided with HPDs offering greater attenuation if needed; and,

  • The employee shall be informed of the existence of an STS, in writing, within 21 days of the determination.

Are audiometric test results provided to employees who do not have a standard threshold shift?
If the employee's hearing thresholds have remained stable, this is a good opportunity to commend the employee for his/her active participation in the company's Hearing Conservation Program.  Understanding the audiogram results, and the reasons to adhere to the company's HCP encourages the employees to take the lead in protecting their hearing.  Even if a slight shift has occurred that is not a standard threshold shift, this is an opportunity to determine the cause(s) of the hearing change, such as medical problems or improper use of hearing protective devices on the job.  These problems can be addressed and corrected before a standard threshold shift, or compensable hearing loss occurs.

Many companies have had a long-standing policy of communicating the results of hearing tests (whether a STS exists or not).  Very few claims or other disagreeable consequences have resulted.  In fact, many hearing conservation program managers credit the communication process for all employees in the audiometric testing program as a major aid in securing day-to-day cooperation of employees, without which the entire program cannot succeed.

What is an exit audiogram?
Although not required by OSHA, it is recommended that an audiogram be performed just prior to termination of employment.  Many states allow two to three years after employment to file a claim.  Since the employer has no control over what a former employee does to their hearing in that time, the exit audiogram is needed to document thresholds at the time of termination.

Audiometric Testing Record Summary (PDF)

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