Standard Threshold Shift (STS): The Complete Employer Action Guide

A Standard Threshold Shift notification arrives. An employee’s annual audiogram shows a 10 dB average shift at 2000, 3000, and 4000 Hz in one ear. What happens now — and in what order, with what deadlines? Most EHS managers know an STS is significant. Fewer know the exact sequential obligations OSHA requires once one is flagged.

Soundtrace’s audiology team handles STS determinations, 21-day notifications, retest scheduling, and OSHA 300 recordability reviews as part of every hearing conservation program — ensuring no step in the employer action chain is missed.

What Is a Standard Threshold Shift Under OSHA?

Under 29 CFR 1910.95(g)(10), a Standard Threshold Shift is a change in hearing threshold, relative to the baseline audiogram, of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear. The calculation is ear-specific: left and right are evaluated independently. An STS in one ear is still an STS regardless of the other ear’s status.

To calculate whether an STS has occurred:

1. Compare the current annual audiogram to the baseline audiogram at 2000, 3000, and 4000 Hz in each ear separately
2. Calculate the average threshold difference across those three frequencies per ear
3. Apply age correction values from OSHA Appendix F (optional but permitted and recommended)
4. If the age-corrected average shift in either ear is 10 dB or more, an STS has occurred

▶ Bottom line: The STS calculation is straightforward arithmetic — but the age correction step is frequently omitted, producing false positive determinations that trigger unnecessary compliance actions.

Age Correction: The Step Most Programs Skip

OSHA’s Appendix F provides age correction values that account for natural, age-related hearing decline (presbycusis) independent of noise exposure. Applying these corrections is permitted and can reduce or eliminate an STS when the threshold shift is primarily attributable to aging rather than occupational noise.

The procedure: find the employee’s age at baseline in OSHA Appendix F Table F-1 (males) or F-2 (females), find their current age in the same table, subtract the baseline-age value from the current-age value at each STS frequency, subtract the resulting age correction from the observed shift at each frequency, then average across three frequencies. If the age-corrected average is under 10 dB, no STS has occurred.

Many programs that generate STS flags without age correction are inadvertently triggering notifications and recordability reviews for employees whose hearing changes are consistent with normal aging.

▶ Bottom line: Always apply age correction before concluding an STS occurred. It is the single most common reason a flagged STS resolves without requiring further employer action.

The Employer Action Timeline After an STS

▶ Bottom line: Missing the 21-day written notification is one of the most frequently cited violations in OSHA hearing conservation audits. Set a calendar trigger the moment an STS is flagged — before retest decisions are made.

The 30-Day Retest Window

OSHA permits employers to conduct a retest audiogram within 30 days of the annual audiogram that triggered the STS. If the retest does not confirm the shift, the retest audiogram substitutes for the annual — effectively reversing the STS determination.

This is particularly valuable in two scenarios. First, temporary threshold shift (TTS): if an employee was exposed to noise before testing, a temporary elevation in thresholds can mimic a permanent STS. A retest after 14 hours without occupational noise exposure typically resolves a TTS-driven false positive. Second, measurement variability: even under ideal conditions, audiometric thresholds have test-retest variability of 5–10 dB. A shift driven by variability rather than real hearing change typically resolves on retest.

▶ Bottom line: Schedule the retest as early as possible within the 30-day window — ideally after a 14-hour noise-free period — to give maximum time to confirm or resolve the STS before OSHA 300 recordability decisions are required.

Written Notification Requirements

Within 21 days of determining that an STS occurred, the employer must inform the employee in writing. OSHA does not specify exact content, but best practice includes: a clear statement that an STS was identified; the specific threshold values from both baseline and annual audiograms; an explanation that this may or may not represent permanent change; information about the retest option and timing; confirmation that hearing protection will be fitted or upgraded; and contact information for questions or additional evaluation.

The written notification satisfies the OSHA requirement, creates a documented record of employer action, and gives employees agency in their own hearing health. Employees who understand what an STS means are more likely to improve hearing protection compliance independently.

▶ Bottom line: A clear, non-alarming notification treats employees as partners in their own hearing health — and builds the program participation that actually reduces STS rates over time.

Mandatory Hearing Protection Actions After STS

Upon STS confirmation, OSHA requires specific hearing protection actions depending on the employee’s current protection status.

If not currently using hearing protection: The employer must fit the employee with appropriate hearing protectors, provide training in use and care, and require their use going forward.

If already using hearing protection: The employer must refit the employee, retrain, and provide hearing protectors offering greater attenuation if current devices are inadequate. Simply reissuing the same protectors does not satisfy this requirement if the STS suggests current protection is insufficient.

When to Revise the Baseline Audiogram

The baseline is the reference against which all future annual audiograms are compared. Revising it is consequential — a revised baseline resets the clock on detecting further hearing loss.

OSHA permits baseline revision in two circumstances. For persistent STS: if the shift is confirmed on retest (or not retested within 30 days) and determined to be permanent, the annual audiogram showing the STS may be substituted as the new baseline. For improved hearing: if the annual audiogram shows significant improvement over the baseline, it should be substituted to avoid comparing future tests against an artificially worse starting point.

The audiologist or physician overseeing the program must make the baseline revision determination. An inappropriately revised baseline can mask ongoing noise-induced hearing loss and should never be made unilaterally by program administrators.

▶ Bottom line: Revising a baseline should be a documented clinical decision — not an administrative shortcut to reset a program generating too many STS flags.

OSHA 300 Log Recordability After STS

Not every STS is OSHA-recordable. Under 29 CFR 1904.10, a work-related hearing loss case must be recorded when: an STS has occurred, AND the employee’s total hearing level in the affected ear averages 25 dB HL or more at 2000, 3000, and 4000 Hz, AND the loss is determined to be work-related.

If a physician or licensed health care professional determines the STS is not work-related or not aggravated by occupational noise exposure, the case is not recordable.

▶ Bottom line: Complete, accurate audiometric records from a well-run program are the employer’s most important asset in both OSHA compliance and workers’ compensation proceedings involving hearing loss claims.