STS — Standard Threshold Shift in Hearing | Glossary

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STS (Standard Threshold Shift)

A change of 10 dB or more in average hearing thresholds at 2000, 3000, and 4000 Hz in either ear, triggering employer action under OSHA.

Key Facts

Defined as ≥10 dB average shift at 2000, 3000, and 4000 Hz
Compared against baseline audiogram in either ear
Employer must notify employee in writing within 21 days
May need to be recorded on OSHA 300 Log if work-related

OSHA defines STS as an average shift of 10 dB or more at 2000, 3000, and 4000 Hz relative to the baseline audiogram in either ear. Age correction may be applied per Table F-1 in 29 CFR 1910.95 Appendix F. When an STS is detected, the employer must: notify the employee in writing within 21 days, refit/retrain on hearing protection, require HPD use if not already required, and refer for clinical evaluation if indicated. The STS may also need to be recorded on the OSHA 300 Log if work-related.

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