What is a Standard Threshold Shift (STS)?

A Standard Threshold Shift (STS) is defined under OSHA’s occupational noise exposure standard as a change in an employee’s hearing threshold of an average of 10 decibels (dB) or more at 2000, 3000, and 4000 Hertz (Hz) in either ear, when compared to their baseline audiogram. https://www.osha.gov/laws-regs/regulations/standardnumber/1904/1904.10

In simpler terms: an STS is OSHA’s way of saying that a worker’s hearing has measurably worsened. Their latest hearing test shows at least a 10 dB loss at key speech frequencies compared to their baseline. When this happens, the employer is required to evaluate hearing protection, retrain the employee, and complete any required follow-up actions.