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The baseline audiogram and the annual audiogram serve completely different purposes in an OSHA hearing conservation program -- and confusing them leads to compliance gaps, missed Standard Threshold Shifts, and recordkeeping violations. This guide explains the difference, when each is required, what they're compared against, and the rules around revising a baseline after a confirmed shift.
Soundtrace stores every baseline and annual audiogram in a permanent digital record, automatically compares annual results to the correct baseline, and flags any Standard Threshold Shifts for audiology review -- eliminating the manual comparison work that causes missed STS findings.
The baseline audiogram establishes the hearing reference point for each worker. Every annual audiogram is compared against that baseline -- not the prior year -- to detect Standard Threshold Shifts. Losing or confusing these records makes STS calculation impossible and creates OSHA recordkeeping violations.
The baseline audiogram is the initial hearing test that establishes the reference point for each covered employee. It captures the worker's hearing thresholds before significant occupational noise exposure has accumulated -- or at the earliest documented point of enrollment in the hearing conservation program.
Every Standard Threshold Shift calculation performed throughout the employee's career will be compared against this baseline. It is the most important single audiogram in the employee's record.
OSHA 1910.95(g)(5) requires the baseline to be preceded by at least 14 hours away from workplace noise, to prevent temporary threshold shifts from affecting the reference measurement. If a 14-hour quiet period is not feasible, hearing protection must be worn for that period before testing.
▶ Bottom line: The baseline audiogram is the permanent reference audiogram for each employee. All future STS calculations compare against this document -- which is why it must be accurate, well-documented, and never lost.
The annual audiogram is a repeat hearing test conducted at least every 12 months for each employee enrolled in the hearing conservation program. Its purpose is to detect changes in hearing thresholds compared to the baseline -- specifically, to identify Standard Threshold Shifts.
The annual audiogram uses the same pure-tone air conduction protocol as the baseline. The same frequencies are tested (500, 1000, 2000, 3000, 4000, 6000 Hz at minimum), the same equipment standards apply, and the same background noise requirements govern the test environment.
▶ Bottom line: The annual audiogram is the surveillance tool. It does not stand alone -- its value comes entirely from comparison to the baseline. Without a valid baseline on file, the annual audiogram cannot generate an STS calculation.
| Feature | Baseline Audiogram | Annual Audiogram |
|---|---|---|
| Purpose | Establish reference hearing thresholds | Detect changes vs. baseline |
| When required | Within 6 months of first noise exposure ≥85 dBA TWA | At least every 12 months after baseline |
| Quiet period required? | Yes -- 14 hours away from hazardous noise | Recommended but not strictly required |
| Compared against | Not compared -- it is the reference | Always compared to the baseline |
| Can be revised? | Yes, after confirmed persistent STS with clinical review | No -- it feeds the comparison, not the reference |
| Retention requirement | Duration of employment | Duration of employment |
| Must be free to employee? | Yes | Yes |
The baseline must be completed within 6 months of the employee's first occupational noise exposure at or above 85 dBA TWA. Exception: if mobile testing is the employer's primary method, the window extends to 12 months -- but hearing protection must be worn during the extended period.
Annual audiograms must then be conducted at least once every 12 months. The 12-month clock runs from the baseline date for the first annual, and from the prior annual for each subsequent test. A lapsed annual audiogram cycle is one of the most commonly cited 1910.95 violations.
An employee enrolled in January who receives their first annual in December is in compliance. An employee enrolled in January whose first annual occurs the following February is out of compliance -- even if only six weeks late. OSHA counts calendar months, not approximate intervals.
▶ Bottom line: The 6-month baseline window and 12-month annual cycle are hard deadlines. Track them individually per employee -- a single missed annual audiogram is a citable violation.
OSHA's STS calculation requires comparison of each annual audiogram to the original baseline -- not to the most recent prior year's test. This design is intentional: it prevents gradual, cumulative hearing loss from being masked by year-over-year comparisons where each small shift looks insignificant.
Example: An employee whose thresholds increase by 3-4 dB every year for three years would show no STS in year-to-year comparisons. Compared to the original baseline, the total shift after three years may well exceed 10 dB -- triggering the STS finding that protects the worker.
▶ Bottom line: Always compare to the original baseline -- never to last year's audiogram. This is the rule that protects against slow-accumulating hearing loss being missed year after year.
OSHA permits baseline revision in two situations:
Baseline revision requires professional clinical oversight. The original baseline must always be retained in the employee's record even after revision.
Under OSHA 1910.95(m)(2), audiometric test records -- both baseline and all annual audiograms -- must be retained for the duration of the affected employee's employment. This means every audiogram taken across a 20 or 30-year career must be on file for the duration of that employment. Digital records management is effectively required at any meaningful scale.
Each audiometric record must include: the employee's name and job classification, date of the audiogram, the examiner's name and title, the date of the last audiometer calibration, the employee's most recent noise exposure measurement, and the audiometric thresholds per ear per frequency.
OSHA does not require re-baselining when a new employee joins, but does require a new baseline if the employee has not had one within six months of starting noise-exposed work. If a prior audiogram exists and was conducted within the required timeframe, it may serve as the baseline at the new employer's discretion. Most occupational health professionals recommend establishing a fresh baseline.
The baseline captures the hearing status at the time of first documented exposure. If pre-existing loss is present, the baseline reflects that loss. Future STS calculations still measure change from this baseline, which means pre-existing loss does not create an automatic STS -- only further deterioration beyond the baseline does.
Annual audiograms must be conducted at least every 12 months after the baseline. If the baseline is conducted at month one and the first annual at month seven, the second annual is due by month nineteen.
Without a baseline, STS cannot be calculated. The employee effectively needs a new baseline audiogram. OSHA requires baseline records for the duration of employment -- lost records are a recordkeeping violation. This is one of the strongest arguments for digital records management.
The baseline belongs to the employee's occupational health record, not to a specific facility. If the employer's records transfer with the employee, no new baseline is needed. If records are not transferred or are unavailable, a new baseline should be conducted.
Soundtrace stores all audiometric records digitally, compares every annual to the correct baseline, and flags STS findings automatically. No spreadsheets, no lost records, no missed shifts.
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