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.
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.
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.