Get Standard Threshold Shift Notification Letter

The opposite of a temporary threshold shift is a permanent threshold shift. A permanent threshold shift is when the ability to hear is reduced permanently, which causes a permanent hearing loss. A professional hearing test can measure the level of the threshold shift and the results can be seen on an audiogram.

A Standard Threshold Shift, or STS, is defined in the occupational noise exposure standard at 29 CFR 1910.95(g)(10)(i) as a change in hearing threshold, relative to the baseline audiogram for that employee, of an average of 10 decibels (dB) or more at 2000, 3000, and 4000 hertz (Hz) in one or both ears. 1904.10(b)(2)

The opposite of a temporary threshold shift is a permanent threshold shift. A permanent threshold shift is when the ability to hear is reduced permanently, which causes a permanent hearing loss. A professional hearing test can measure the level of the threshold shift and the results can be seen on an audiogram.

A Standard Threshold Shift, or STS, is defined in the occupational noise exposure standard at 29 CFR 1910.95(g)(10)(i) as a change in hearing threshold, relative to the baseline audiogram for that employee, of an average of 10 decibels (dB) or more at 2000, 3000, and 4000 hertz (Hz) in one or both ears.

A permanent threshold shift can be caused by exposure to noise. Another common cause is age. We all lose our hearing as we age and hearing loss is a natural consequence of getting older. A permanent threshold shift may also occur as a result of disease, infection or drugs.

Threshold shifts of up to ~50 dB immediately after a single noise exposure may recover completely, while more extensive immediate hearing losses are likely to result in permanent losses of hearing sensitivity (e.g. 3, 4).

The employee will also be informed of what will be done as a consequence (e.g. provide repeat testing within 30 days). A Standard Threshold Shift letter (see Form #2) is an appropriate method of documenting this information to the employee. A copy of the STS letter will also be forwarded to the employee's supervisor.

When an STS is identified, the employee must be notified in writing within 21 days. If an STS is present and the average hearing level at 2000, 3000, and 4000 Hz is equal to or greater than 25 dB(HL), then it should be recorded on the OSHA 300 Log.