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Terminology |
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Audiometric Terms & Definitions. |
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Noise Measurement Terms & Definitions. |
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Audiometric Report Terms & Definitions. |
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Noise Code Chart.
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Audiometric Terms & Definitions:
THRESHOLD: The minimum sound pressure level at which a person can hear a sound at a given frequency.
DECIBEL (dB): Unit of measurement of sound level.
TEST FREQUENCY: A specific range of sound in the sound wave spectrum, measured in cycles per seconds called Hertz (Hz).
BASELINE AUDIOGRAM: An audiogram against which all future audiograms are compared.
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Medical Baseline: The first reliable hearing test on record. |
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OSHA Revised Baseline: Once a persistent shift has occurred, a new Baseline is established for future comparison to determine STS's. |
AUDIOGRAM: A chart, graph, or table resulting from an audiometric test showing an individual's hearing threshold levels as a function of frequency.
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Noise Measurement Terms & Definitions:
AVERAGE (Lavg or Leq): The average sound level measurement over the run time.
TIME WEIGHTED AVERAGE (TWA): The TWA always averages the sampled sound over an 8 hour period.
(TWA is less than Lavg or Leq for a sample duration of less than 8 hours.
THRESHOLD (Cut Off): All sound below the threshold is considered non-existing noise for the averaging and integrating functions.
CRITERION LEVEL: If exposed to SPL, on average for eight hours, it would result in a maximum allowable exposure.
DOSE: The allowable daily exposure value. A maximum allowable exposure is equal to 100% dose.
EXCHANGE RATE: Results in a doubling or having of the maximum allowable exposure.
"A" & "C" WEIGHTING: These are two of the standard weighting networks available and are frequency filters that cover the frequency range
of human hearing (20 Hz to 20kHz).
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"A" weighting is the most commonly used filter in industrial noise applications (OSHA) and is often reported as dBA.
The "A" weighted filter attempts to make the dosimeter respond closer to the way the human ear hears.
It attenuates the frequencies below several hundred hertz as well as the high frequencies above six thousand hertz. |
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"C" weighting provides a fairly flat frequency response with only slight attenuation of the very high and very low frequencies.
"C" weighting is intended to represent how the ear perceives sound at high decibel levels and is often used as a "flat" response when
LINEAR is not available. "C" weighted measurements are often reported as dBC and the Noise Reduction Ratings (NRR) for hearing
protection are calculated on the "C" weighted scale. |
"A" & "C" Weighting Scales
NOISE REDUCTION RATING (NRR): The NRR is a single number rating which is required by law to be shown on the label of each hearing protector sold in the United States. The NRR is specified by the 40 CFR code of Federal Regulations, Part 211, Product Noise Labeling,
Subpart B - Hearing Protection Devises. The NRR is the measure, in decibels, of how well a hearing protector reduces noise, as specified by the EPA. The higher the NRR number specified on the hearing protector package, the greater the noise reduction. When dual protectors are used,
the combined NRR provides approximately 5 decibels more than the higher rated of the two hearing protectors.
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Audiometric Report Terms & Definitions:
ORIGINAL MEDICAL BASELINE: The first reliable hearing test on record, against which all future tests are compared to measure and evaluate
hearing loss. The baseline has both medical and legal significance and must be administered within the first 6 months of employment if testing
is performed in-house, or within 1 year if performed by mobile van. The medical baseline is shown in the Audiometric Report section.
IMPROVED MEDICAL BASELINE: An annual audiogram may be substituted for the baseline audiogram when, in the judgment of the audiologist who is
evaluating the audiogram, the hearing threshold shown in the annual audiogram indicates significant improvement over the baseline audiogram.
A new baseline is selected and substituted for future comparisons. This is noted in the Audiometric Report, below the name for each applicable individual.
OSHA STANDARD THRESHOLD SHIFT (STS): A 10 dB adverse, age-adjusted shift in hearing of 10 decibels or greater on average in the 2K, 3K
and 4K frequencies in either ear, from the referent OSHA Baseline to the current test.
OSHA RECORDABLE SHIFT: An STS as defined above, AND the average at 2K, 3K, and 4K frequencies on the current test is greater than or
equal to 25dB from audiometric zero – without age correction.
AUDIOMETRIC ZERO: An established mathematical value that represents in simple terms the lower end of the sound spectrum for a population
with healthy ears, and therefore reflects 0 dB as the best threshold that can be obtained for any frequency on a hearing test.
OSHA BASELINE/REVISED OSHA BASELINE: The hearing test being used for comparison to the current test to calculate STS.
Once an STS has occurred and is determined to be persistent (not just temporary) the OSHA Baseline is revised.
If a shift occurs in only one ear, then only the baseline for that ear is revised. The Revised OSHA Baseline is shown in the OSHA Report section.
CHANGE GROUPS: Change groups represent special comparisons between the annual hearing tests of each employee to determine the type
and degree of change that may be occurring in the speech and the high frequency ranges. This is done in an effort to quantify and measure small
to large amounts of change over time, and also to establish stable, adverse, or improved trends in hearing. Specific recommendations for each group
are outlined to assist in managing your hearing conservation program effectively.
Gradual, incremental changes over time are indicative of noise induced hearing loss, while small changes in a short period of time may indicate that
hearing protection is not being worn, or is worn improperly. Large changes in a short time are indicative of both temporary conditions such as colds
or allergies, and of more serious medical involvements unrelated to noise. When employees continue to exhibit the typical noise induced hearing
loss pattern, any further hazardous noise exposure, without hearing protection, places them at higher risk for hearing impairment, and for potential liability.
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First Test Group: |
Employees in this group fall into one of two categories: the current test is the first test on record;
or the current test represents the first test on record since the employee was rehired. |
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?- 1st - Questionable 1st
Test (baseline) result: |
Hearing ability in the speech range reflects moderate to severe loss. Review employee's record for possible cause,
and/or retest to confirm validity of this result. |
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Stable Group: |
Employees in this group show a change from the baseline but no change between the last three tests,
indicating a stable trend in hearing has been established. |
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No Change Group: |
Employees in this group who have only two tests show no change from the current test to the baseline.
For employees with three or more tests there is no change from the two most recent tests nor from the baseline. |
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Noise Trend Group: |
Employees in this group show a significant change in high frequencies from the two most recent tests and from
the baseline. This may be indicative of noise induced loss and needs special action and monitoring. |
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Monitor Group: |
Employees in this group show no change from the two most recent tests only but do show a change from the baseline.
The change needs to be monitored as it may or may not stabilize. |
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Medical Group: |
Employees in this group show a significant adverse change in the speech frequencies (low pitches) from the two
most recent tests. This type of change may be caused by something other than noise and therefore specific follow-up
to include are test/referral is recommended. |
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Unreliable Group: |
Employees in this group have given invalid test results or demographic information, therefore an accurate
assessment cannot be made. Contact the HCI office to determine if a retest is recommended or to supply accurate
demographic information. |
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Unable to Calculate
Group: |
Employees in this group have necessary demographic information missing from their records, such as date-of-birth,
that is required to evaluate their test results. Submit the missing information in order to have these tests evaluated.
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STATUS GROUPS:
Are based on current hearing test results and the degree of hearing loss that currently exists from Audiometric Zero. Each group has a range,
or classification of hearing loss, which gives a prediction of how the hearing loss may affect the employee's ability to understand speech.
Employees are categorized into the one of the following four groups based on the average of their current test results in the lower three speech
frequencies (.5K, 1K, 2K) for their less capable ear. The Normal range, between 0dB and 25dB, is recognized professionally as being both medically
and legally normal. The goal of a Hearing Conservation Program is to preserve hearing, and to prevent the progression of hearing loss. Status Groups
identify each employee's current hearing ability, and provide a means of focusing your prevention efforts effectively.
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NORMAL-(0-25dBAverage): The Employee is within normal ability to understand speech. |
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MILD-(26-44dB Average Loss): The Employee may experience some difficulty in understanding speech. |
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MODERATE-(45-59dBAverage Loss): The Employee will experience difficulty in understanding speech especially in noisy environments. |
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SEVERE-(Greater than 60dB Average Loss): The Employee will have great difficulty understanding any speech and/or warning signals.
Employees experiencing this degree of hearing loss will have communication difficulties, both in occupational and non-occupational environments. |
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Noise Code Chart:
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