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”.
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This presentation will use the abbreviation
“Standard Threshold Shift”
measurement of frequency.
Often called “pitch”.
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.
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.
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. 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.
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.
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.
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.
Thank you for taking the time to learn about safety and health and how to prevent future injuries and illnesses.