An STS is a hearing change of 10 dB or more, averaged at 2000, 3000, and 4000 Hz in either ear, compared to the employee's baseline audiogram. Once confirmed, it starts a sequence of employer obligations with fixed deadlines.
You may retest within 30 days to confirm; the employee must be notified in writing within 21 days of determination; and if the shift is work-related and total hearing level is 25 dB or more above audiometric zero — averaged at 2000, 3000, and 4000 Hz in the same ear as the shift — it’s recordable on the OSHA 300 Log and must be entered there within seven calendar days of receiving that information. You may apply age correction (Appendix F) when determining the shift.
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