The baseline audiogram is the reference standard against which all future annual audiograms are compared. Its timing, technical validity, and documentation determine the quality of STS calculations for the entire duration of the worker’s enrollment in the hearing conservation program. OSHA 29 CFR 1910.95 establishes specific timing requirements for baseline audiograms, and compliance with those requirements has direct implications for both OSHA citations and workers’ compensation proceedings. According to CDC/NIOSH, approximately 22 million U.S. workers face hazardous occupational noise annually.
OSHA Baseline Audiogram Timing Requirements
Under 29 CFR 1910.95(g)(5), employers must establish a baseline audiogram for each employee enrolled in the hearing conservation program within 6 months of their first placement in a noise-exposed role at or above the 85 dBA TWA action level. If a mobile testing van is used, this window extends to 12 months — but hearing protection must be worn throughout the extended window.
The 6-month window is a compliance minimum. For workers compensation defense purposes, the ideal is a pre-placement audiogram — conducted before the worker’s first day of noise-exposed work, establishing hearing status at hire before any noise exposure at the current facility.
Every day between a worker’s first noise-exposed work and the baseline audiogram is a day during which any noise-induced threshold change that occurred cannot be cleanly attributed to prior employment or pre-existing conditions. A worker exposed at 90 dBA for 6 months before the baseline audiogram may already have Stage 1–2 NIHL at baseline. The baseline does not establish what their hearing was at hire — it establishes what it was after 6 months of noise exposure. Pre-placement audiometry eliminates this gap.
The 14-Hour Quiet Period
OSHA Appendix C recommends workers avoid significant noise exposure for 14 hours before a baseline audiogram to prevent temporary threshold shift (TTS) from contaminating the baseline measurement. If a worker has been exposed to hazardous noise and cannot achieve the 14-hour quiet period, they should wear hearing protection during that period. TTS can produce elevated thresholds on the audiogram that resolve with rest — if the baseline is taken during TTS, the recorded thresholds may be worse than the worker’s stable resting thresholds, artificially inflating the baseline and masking future noise-induced shifts.
OSHA 1910.95 allows employers to establish a revised baseline when the professional supervisor determines that an STS is persistent. A revised baseline resets the STS comparison reference. The decision must be made by the professional supervisor — not the employer unilaterally. Revised baselines are appropriate when a genuine, permanent threshold shift has occurred and the new thresholds accurately reflect the worker’s stable hearing status going forward.
Frequently Asked Questions
Baseline Before Day One — The WC Defense Standard
Soundtrace delivers pre-placement baseline audiograms that capture hearing status before any employment-period noise exposure — the cleanest possible foundation for WC defense and STS tracking.
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