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A standard threshold shift — an average hearing threshold change of 10 dB or more at 2000, 3000, and 4000 Hz in either ear compared to the baseline audiogram — is the defining event in OSHA’s hearing conservation program. When one is detected, a specific sequence of employer obligations begins immediately. Most employers know the STS exists. Far fewer have a written protocol for what to do when one is flagged, which is exactly when costly mistakes happen.
Soundtrace automatically flags STSs when audiograms are reviewed, notifies the Professional Supervisor, and tracks the 21-day notification and 30-day retest windows — so nothing falls through the cracks.
An STS is not just an audiometric finding. It triggers written notification, mandatory follow-up steps, potential HPD upgrade requirements, a possible OSHA 300 Log entry, and a potential revised baseline. An employer who files the audiogram and moves on has failed to comply with at least four separate provisions of 1910.95 — each citable independently.
Under 29 CFR 1910.95(g)(10), a standard threshold shift is defined as 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 uses the average of those three frequencies, not a shift at any single frequency. A worker with a 5 dB shift at 2000 Hz, 10 dB at 3000 Hz, and 15 dB at 4000 Hz has an average of 10 dB — exactly at the STS threshold.
The comparison is always made against the baseline audiogram, not the most recent annual audiogram. If a revised baseline has been established, that revised baseline is the reference point. Age correction (presbycusis adjustment per Appendix F) may optionally be applied to the most recent audiogram before comparison, which can reduce or eliminate an apparent STS in older workers.
OSHA permits age correction using the tables in Appendix F when determining whether an STS occurred. Age correction cannot be used for the OSHA 300 Log 25 dB hearing threshold level test. Employers should decide at the program level whether to apply age correction and document that decision consistently — inconsistent application is a compliance gap.
Under 1910.95(g)(7)(ii), if an annual audiogram shows a possible STS, the employer may obtain a retest within 30 days. If the retest does not confirm the STS, the retest results can be substituted for the annual audiogram — and the follow-up obligations that would otherwise apply do not trigger.
The retest must be preceded by at least 14 hours without workplace noise exposure. Hearing protection may be used as a substitute for the quiet period when a true quiet period is operationally impractical. The retest must be conducted in both ears simultaneously, at the same location, within 30 days of the original test.
An employer who intends to retest must do so within 30 calendar days of the original audiogram. A retest conducted on day 31 cannot substitute for the annual audiogram for purposes of avoiding the 300 Log entry. Document the original test date and set a firm deadline. If the employee is on leave, the clock still runs.
Under 1910.95(g)(8)(i), when an STS is determined — whether through the initial audiogram or a confirming retest — the employee must be informed in writing within 21 days of that determination. The 21-day clock starts from the date of determination, not the date the test was performed. If the Professional Supervisor reviews the audiogram three weeks after it was taken and determines an STS occurred, the 21-day clock starts at that review date.
The notification does not need to be elaborate, but it must be in writing and must convey that an STS has occurred. Best practice is to include what the STS means, that it does not necessarily indicate occupational hearing loss, what steps the employer is taking in response, and that the worker should see a healthcare provider if they have hearing-related concerns.
Unless a physician determines that the STS is not work-related or aggravated by occupational noise exposure, the employer must ensure all of the following steps are taken:
1. Fit or refit with hearing protection. A worker who was not previously using HPD must be fitted, trained, and required to use it. A worker already using HPD must be refitted and retrained, and provided with a device offering greater attenuation if necessary.
2. Retrain on HPD use and care. Retraining is not optional — it is a separate requirement from fitting. The worker must receive instruction on proper insertion, care, maintenance, and the importance of consistent use.
3. Audiological or otological referral if indicated. If additional testing is necessary, or if the employer suspects a medical pathology of the ear is caused or aggravated by hearing protector use, a clinical referral is required. If an ear pathology unrelated to HPD use is suspected, the employee must be told where such an examination is available.
4. Written employee notification. As described above — within 21 days of determination.
5. OSHA 300 Log entry if the two-part test is met. STS alone does not require a 300 Log entry. The two-part test under 1904.10 must also be satisfied: the STS must be work-related, and the employee’s overall hearing level must be 25 dB or more above audiometric zero at the same frequencies. If both criteria are met, the case must be recorded within 7 days of the retest (or 30 days of the original test if no retest was conducted).
An STS under 1910.95 does not automatically require a 300 Log entry. The separate recordability test under 29 CFR 1904.10 requires two criteria to both be met: (1) the worker has experienced a work-related STS of 10 dB or more averaged at 2000, 3000, and 4000 Hz, and (2) the worker’s total hearing level is 25 dB or more above audiometric zero at those same frequencies in the same ear.
The 25 dB hearing threshold level test cannot be age-corrected. A worker with a 10 dB average STS but excellent baseline hearing (e.g., 5 dB at all tested frequencies) would have a total level of only ~15 dB after the shift — below the 25 dB threshold — so no 300 Log entry is required even though an STS occurred under 1910.95.
| Step | Criterion | Result |
|---|---|---|
| Step 1 | Is the STS work-related? (Did occupational noise cause or contribute?) | If NO: no 300 Log entry required |
| Step 2 | Is the total hearing level ≥25 dB above audiometric zero at 2000/3000/4000 Hz? | If NO: no 300 Log entry required |
| Both YES | Both criteria met | Record on OSHA 300 Log within 7 days of confirming retest (or 30 days if no retest) |
Under 1910.95(g)(9), an annual audiogram may be substituted for the baseline audiogram (creating a revised baseline) when, in the judgment of the audiologist, otolaryngologist, or physician evaluating the program: (a) the STS is persistent, or (b) the hearing threshold shown in the annual audiogram indicates significant improvement over the baseline.
A revised baseline is important for two reasons. First, it prevents the same STS from generating a new notification and follow-up requirement on every subsequent annual audiogram. Second, if the revision is for improvement, it captures a better true hearing threshold as the new reference. The decision to revise the baseline must be made by the Professional Supervisor, not by the employer unilaterally.
Soundtrace flags STSs automatically at audiogram review, tracks the 21-day notification deadline and 30-day retest window, and provides the Professional Supervisor with the data needed to determine work-relatedness and baseline revision.
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