Hearing Standard Threshold Shift

You Will Learn What is a Standard Threshold Shift? How is a Standard Threshold Shift calculated? What is an employer required to do in Washington State?

Abbreviation This presentation will use the abbreviation “STS” to mean “Standard Threshold Shift”

What Is A Standard Threshold Shift? A Standard Threshold Shift (STS) is a significant change in hearing ability (a hearing loss). Over time, with enough threshold shift, a person will have great deal of trouble understanding speech.

Definition The Standard Threshold Shift definition in the Hearing Loss Prevention Rule, WAC 296-817 is: “A hearing level change, relative to the baseline audiogram, of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear.”

More Definitions dB means “decibel”, a unit of sound measurement. Often called “loudness”. Hz means “Hertz”, a measurement of frequency. Often called “pitch”.

What Is An Audiogram? Before being first exposed to excessive noise, an employer is required to provide hearing tests or audiograms to employees, which is called a “baseline”. Subsequent hearing tests are compared to the original baseline audiogram. Note: Employers who use mobile testing units are allowed up to one year to obtain a valid baseline audiogram for each exposed employee. The employee must still be given training and hearing protection.

What Is An Audiogram? An audiogram is a picture or graph of a hearing test. It measures the quietest sounds you can hear at different frequencies.

The graph, or audiogram, is laid out like a piano keyboard, with low to high frequencies (low to high pitches) going from left to right.

The soft sounds are on the top and the loud sounds are on the bottom.

When your graph is filled in, it shows your hearing sensitivity for different frequencies at different intensities (at different pitches and different volumes).

This audiogram shows a person with relatively normal hearing This audiogram shows a person with relatively normal hearing. Normal hearing is defined as a hearing threshold between 10 and 25 decibels. In other words, the person can hear the softest sounds. This graph only shows one ear.

The hearing loss shown in this audiogram is in the higher frequencies which is commonly caused by exposure to workplace noise. This person can only hear loud sounds at the higher frequencies. An “X” is for the left ear, and an “O” is for the right ear.

Audiograms and STS Although the audiogram usually measures frequencies between 125 and 8000 Hz, only the 2000, 3000 and 4000 frequencies are used to calculate a Standard Threshold Shift.

Calculation of STS When you have an annual re-test, or subsequent audiogram, the health care professional will compare the results of the baseline test with the new hearing test. The annual hearing test can be conducted during the work shift while you are experiencing typical workplace noise exposure.

Calculation of STS The health care professional will look at your test results for the 2000, 3000 and 4000 Hz frequencies. A change in these three frequencies that averages 10 db or more, in either ear, is called a Standard Threshold Shift.

Calculation-Example One 2000 Hz 3000 Hz 4000 Hz 2004 Baseline Audiogram dB 5 10 2005 Annual Audiogram dB 15 30 Shift in hearing dB 20 The table shows an excerpt from a baseline audiogram and an annual audiogram. It includes results from just one ear and only the frequencies used to calculate the STS. The STS is calculated by adding the “Shift in Hearing” results and averaging. Thus: (10+10+25)/3 = 45/3 = 15 The average shift is greater than 10 so the follow-up procedures to prevent further hearing loss must be followed.

Calculation-Example Two 2000 Hz 3000 Hz 4000 Hz 2004 Baseline Audiogram dB 20 25 30 2005 Annual Audiogram dB 40 Shift in hearing dB 5 10 The baseline audiogram shows a person with an existing mild hearing loss. The annual audiogram shows a change in hearing ability, but not enough to be a Standard Threshold Shift. (5+0+10)/3 = 15/3 = 5 Although the hearing change is not enough to have a Standard Threshold Shift, there has been a 10 dB change at 4000 Hz, the most likely frequency to be damaged by workplace noise. It would be a good idea for the employer to re-evaluate the noise protection program for this employee to prevent further hearing loss.

Follow-up Requirements If a STS has occurred: The employee must be informed of the decrease or improvement in your hearing, in writing, within 21 days. AND The audiogram must be reviewed by an audiologist, otolaryngologist, or other qualified physician.

Follow-up Requirements The health care professional supervising the audiograms must give an opinion as to whether any STS’s indicate a possible occupational hearing loss and if there are any recommendations for changes in the hearing protection program.

Follow-up Requirements A re-test can be ordered, within 30 days of the test that showed a STS. The re-test can then be considered an annual audiogram.

Follow-up Requirements The employer must pay for any clinical audiological evaluation or otological exam required by the reviewer if: Additional review is necessary to evaluate the cause of hearing loss OR There is indication of a medical condition caused or aggravated by the use of hearing protectors.

Follow-up Requirements The audiogram reviewer must communicate to the employee any suspected medical conditions that are found that are unrelated to the workplace. This information is confidential between the reviewer and the employee.

Follow-up Requirements The employer must keep the baseline audiogram without revision, unless a qualified reviewer determines: The STS is persistent OR The hearing shown in the annual audiogram indicates significant improvement over the baseline audiogram.

Follow-up Requirements The employer must keep records: Name and job title of the employee Date of audiogram Examiner’s name Date of last calibration of audiometer Employee’s most recent noise exposure assessment Background sound levels in the audiometric test room.

Resources Hearing Loss Prevention Rule Chapter 296-817 WAC Noise Audits Training Kit Hearing Protection Training Kit On-Line Course for Noise Library of safety videos Noise Reduction Ideas Bank

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