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The baseline audiogram is the reference audiogram taken near the start of employment against which all future annual audiograms are compared to detect standard threshold shifts. It is the most important single document in a hearing conservation program — not because OSHA requires it (though it does), but because it is the employer’s primary defense in a workers’ compensation hearing loss claim. An employer without a valid baseline audiogram for a claimant has no way to demonstrate what hearing loss predated employment. An employer with one can.
Soundtrace schedules and conducts baseline audiograms at or before enrollment in the HCP, establishing the reference record that protects employers and workers alike.
In a workers’ compensation hearing loss claim, liability is proportional to what hearing loss the employer can prove predated the claimant’s employment. An early, accurate baseline audiogram showing pre-existing high-frequency loss at hire substantially limits the employer’s exposure. An employer without a baseline audiogram bears full liability for any hearing loss the worker presents at claim time, regardless of prior employment history.
The baseline audiogram is the first audiogram an employee receives as part of the hearing conservation program. It establishes the hearing thresholds that serve as the reference for all future comparisons. A standard threshold shift is always calculated relative to the baseline, not the most recent prior audiogram. Every annual audiogram for the duration of the worker’s employment is compared back to this single reference point.
Because the baseline is the permanent reference, its accuracy directly determines the accuracy of every subsequent STS determination. A baseline taken during temporary threshold shift — after a noisy workday, without the required quiet period — may show elevated thresholds that make the worker’s true hearing appear worse than it is. Subsequent audiograms may then show apparent “improvement” relative to an artificially high baseline, masking real progressive loss.
OSHA requires the baseline audiogram to be obtained within 6 months of an employee’s first exposure at or above the 85 dBA action level. For employers using mobile testing services (test vans), an extended window of 1 year applies, provided that hearing protection is worn by the employee from 6 months after first exposure until the baseline is obtained.
The clocks start at first exposure at the action level, not at the hire date. An employee hired into an administrative role who is later reassigned to a production area with noise at or above 85 dBA starts the 6-month clock on the first day of that assignment.
The single most common baseline audiogram compliance failure is assigning a new employee to a noise-exposed role before a baseline audiogram is scheduled. Safety onboarding focuses on training, HPD fitting, and noise monitoring — but the baseline audiogram scheduling step gets missed. By the time the annual testing cycle rolls around, the worker has been exposed for months without a valid baseline. Any STS detected in that first annual audiogram has no accurate baseline to compare against.
Under 1910.95(g)(5)(iii), testing to establish a baseline audiogram must be preceded by at least 14 hours without exposure to workplace noise. This requirement exists because noise exposure causes temporary threshold shift (TTS) — a temporary elevation in hearing thresholds that resolves after adequate quiet time. A baseline audiogram taken without the quiet period may capture TTS rather than the worker’s true permanent hearing thresholds.
Hearing protectors may be used as a substitute for the 14-hour quiet period when the employer determines that a true quiet period is not practical. The worker wears hearing protection continuously during the 14 hours preceding the test instead of avoiding noise exposure. This is documented in most mobile testing programs.
The cleanest way to satisfy the 14-hour quiet requirement is to schedule baseline audiograms before the employee’s first day in a noise-exposed role — before any occupational noise exposure has occurred at all. This eliminates TTS concerns entirely, produces the most accurate baseline, and starts the WC defense clock on day one.
A revised baseline replaces the original baseline audiogram as the reference for future STS comparisons. Under 1910.95(g)(9), an annual audiogram may be substituted for the baseline when: (a) the STS revealed by the annual audiogram is persistent (confirmed by the Professional Supervisor), or (b) the hearing threshold shown in the annual audiogram indicates significant improvement over the baseline — for example, following medical treatment of an ear condition.
The decision to revise the baseline must be made by the audiologist, otolaryngologist, or physician supervising the program. It cannot be made unilaterally by the employer or the audiometric technician. When a revised baseline is established, it becomes the new reference for all subsequent STS comparisons.
An audiogram obtained before OSHA’s current hearing conservation requirements took effect, or an audiogram obtained by a prior employer, may be used as the baseline audiogram for a current employee if it was obtained under conditions that would satisfy current OSHA requirements. In practice, this means the prior audiogram must have been conducted using a calibrated audiometer, in an appropriate acoustic environment, after an adequate quiet period, and must show frequencies required by the standard.
In workers’ compensation hearing loss claims, the baseline audiogram is the employer’s primary evidentiary tool. It documents what hearing thresholds existed at or near the start of employment — establishing the baseline from which any occupational contribution must be measured. An employer with a clean, accurate baseline audiogram obtained on day one of employment can credibly demonstrate what hearing loss, if any, developed during current employment.
An employer without a valid baseline for the claimant faces a much harder position. Without that reference, any hearing loss the worker presents at claim time may be attributed to current employment, regardless of what prior occupational or non-occupational exposures may have contributed. States vary in how WC adjudicators treat missing baselines, but the absence is almost never advantageous to the employer.
Soundtrace schedules baseline audiograms as part of new employee onboarding for noise-exposed roles — creating the accurate, early reference record that protects both employer and worker.
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