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Baseline and annual audiograms serve different regulatory functions under OSHA 1910.95 — confusing them is one of the most common hearing conservation compliance errors. This guide explains what each requires, when each is required, and how they interact with Standard Threshold Shift determinations.
Soundtrace automates baseline and annual audiogram scheduling, STS calculations, and required follow-up notifications so nothing falls through the cracks.
The baseline audiogram is the reference point. The annual audiogram is the measurement. An STS exists only in relation to a valid baseline — which means a defective baseline invalidates years of subsequent comparisons.
The baseline audiogram under OSHA 1910.95(g)(5) establishes the starting hearing threshold for an enrolled employee. A valid baseline requires: administration within 6 months of first exposure at or above 85 dB(A) TWA; 14 hours of noise-free time before the test; administration by qualified personnel under 1910.95(g)(3); and audiometer calibration within ANSI S3.6 specifications.
Allowing employees to wear hearing protection during the 14-hour quiet period does not satisfy the requirement. The purpose is to eliminate temporary threshold shift — HPDs cannot accomplish that if the worker is still in a noisy environment.
▶ Bottom line: An invalid baseline means no valid reference exists for STS determination. Every subsequent annual audiogram is essentially orphaned.
Annual audiograms under 1910.95(g)(6) must be provided to every enrolled employee within 12 months of the last audiogram. Unlike the baseline, annual audiograms do not require a preceding quiet period. They must be compared to the baseline by a qualified audiologist or physician; reviewed within 30 days (21 days if an STS is found); and use a calibrated ANSI S3.6-compliant audiometer.
▶ Bottom line: The annual audiogram has no validity unless compared to a valid baseline. Annual audiograms without that comparison satisfy the scheduling requirement but not the monitoring purpose of 1910.95.
| Requirement | Baseline Audiogram | Annual Audiogram |
|---|---|---|
| Timing | Within 6 months of first exposure; 1 year if mobile van used | Every 12 months after baseline |
| Quiet period required | Yes — 14 hours, no workplace noise | No requirement, but recommended |
| Professional review | By audiologist or physician | By audiologist or physician within 30 days |
| Purpose | Establishes reference threshold | Detects threshold shifts vs. baseline |
| Can be revised | Yes, per 1910.95(g)(9) | Becomes revised baseline if STS is permanent |
| OSHA 300 Log trigger | No | Yes, if STS ≥25 dB HL work-related |
Under 1910.95(g)(5)(ii), the employer shall not permit a baseline audiogram to be used as a valid reference unless the employee was not exposed to workplace noise at or above 85 dB(A) TWA for at least 14 hours preceding the test. If TTS is present during baseline testing, the resulting reference threshold is artificially elevated — making future STS detection harder and masking genuine deterioration.
An STS is determined by comparing the annual audiogram to the baseline at 2000, 3000, and 4000 Hz. If the average change equals or exceeds 10 dB in either ear, an STS has occurred. OSHA requires: written employee notification within 21 days of the STS determination; HPD refitting and retraining; referral to an audiologist or otolaryngologist if the STS is not reduced on retest; evaluation of whether the STS is work-related for OSHA 300 Log purposes. An employer may retest within 30 days of an apparent STS — if the retest does not confirm the shift, the STS need not be recorded.
▶ Bottom line: The 21-day clock for employee notification starts at the STS determination date, not the audiogram date. Delays in professional review directly create late-notification citation risk.
Under 1910.95(g)(9), a revised baseline must be substituted when: an STS is confirmed as a permanent threshold shift; an audiologist or physician determines the original baseline is not an accurate representation of the worker’s non-occupational baseline hearing; or an improved threshold occurs in subsequent testing. The original baseline must be retained in the employee’s record even after revision.
OSHA permits employers to age-correct threshold data before determining whether an STS has occurred, using the correction tables in Appendix F. When applied, some apparent STSs are reduced or eliminated because the threshold change is consistent with expected age-related decline rather than noise-induced hearing loss. Age correction is optional, not required, and must use the OSHA Appendix F tables with documented calculations.
Under OSHA 1910.95(m)(3): all audiograms must be retained for the duration of employment; calibration records for each test day must be retained for two years; STS determinations, age-correction calculations, and revised baseline justifications must be in writing and retained; and employee notification letters for STS must be retained.
Soundtrace tracks scheduling deadlines, calculates STS automatically, and flags required follow-up actions.
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