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.
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.
What is a baseline audiogram?
The baseline audiogram is the initial hearing test that establishes the reference point for each covered employee. Every STS calculation performed throughout the employee’s career will be compared against this baseline. OSHA 1910.95(g)(5) requires the baseline to be preceded by at least 14 hours away from workplace noise (or hearing protection worn for that period) to prevent TTS from affecting the reference measurement.
▶ Bottom line: The baseline audiogram is the permanent reference audiogram. All future STS calculations compare against this document — which is why it must be accurate, well-documented, and never lost.
What is an annual audiogram?
The annual audiogram is a repeat hearing test conducted at least every 12 months for each enrolled employee. Its purpose is to detect changes in hearing thresholds compared to the baseline — specifically to identify Standard Threshold Shifts. Without a valid baseline on file, the annual audiogram cannot generate an STS calculation.
Side-by-Side Comparison
| 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 |
Timing Requirements
Baseline: within 6 months of first noise exposure at or above 85 dBA TWA (12 months if mobile testing is the primary method; hearing protection required during the extended period). Annual: at least every 12 months, with the 12-month clock running 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.
OSHA counts calendar months, not approximate intervals. An employee enrolled in January whose first annual occurs in the following February is out of compliance — even if only six weeks late. Track deadlines individually per employee.
The Baseline Comparison Rule
OSHA’s STS calculation requires comparison of each annual audiogram to the original baseline — not to the most recent prior year’s test. This prevents gradual, cumulative hearing loss from being masked by year-over-year comparisons where each small shift looks insignificant. 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.
▶ Bottom line: Always compare to the original baseline — never to last year’s audiogram.
When Can the Baseline Be Revised?
OSHA permits baseline revision in two situations: (1) after a confirmed persistent STS, the employer may revise the baseline to the current annual audiogram thresholds once the STS has been confirmed as persistent through professional audiological review; (2) when the annual audiogram shows improvement (suggesting the baseline captured a TTS), the employer may revise the baseline downward to reflect the improved thresholds. Baseline revision requires professional clinical oversight and the original baseline must always be retained in the employee’s record.
Recordkeeping Obligations
Under OSHA 1910.95(m)(2), both baseline and all annual audiograms must be retained for the duration of the affected employee’s employment. Each record must include: employee name and job classification; date of audiogram; examiner’s name and title; date of last audiometer calibration; employee’s most recent noise exposure measurement; and audiometric thresholds per ear per frequency.
Frequently Asked Questions
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 a fresh baseline.
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.
The baseline belongs to the employee’s occupational health record, not a specific facility. If records transfer with the employee, no new baseline is needed. If records are unavailable, a new baseline should be conducted.
Every baseline and annual audiogram — tracked, compared, and audit-ready
Soundtrace stores all audiometric records digitally, compares every annual to the correct baseline, and flags STS findings automatically.
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