The baseline audiogram is the foundation of every OSHA 1910.95 hearing conservation program. It is the reference audiogram against which all future annual audiograms are compared to detect threshold shifts — and it must be obtained within 6 months of a worker’s first exposure at or above the 85 dBA action level. According to the CDC, approximately 22 million U.S. workers face hazardous noise exposure annually — and for every one of them, a missing, delayed, or invalid baseline does not just create a compliance gap; it eliminates the employer’s ability to defend against occupational hearing loss workers’ compensation claims.
Soundtrace audiometric testing automatically tracks baseline deadlines for every enrolled worker, flags approaching expirations, and maintains frequency-specific ambient noise documentation for every test — producing baselines that hold up to OSHA audit and legal scrutiny as part of a complete 1910.95 hearing conservation program.
What a Baseline Audiogram Is and Why It Matters
A baseline audiogram is a set of hearing threshold measurements taken at the start of a worker’s enrollment in a hearing conservation program. OSHA 1910.95(g)(5) requires it to be obtained within 6 months of first exposure at or above the 85 dBA action level — before significant occupational hearing damage has accumulated. It must test hearing at 500, 1000, 2000, 3000, 4000, and 6000 Hz in each ear.
Every subsequent annual audiogram is compared to this baseline. If the average threshold at 2,000, 3,000, and 4,000 Hz worsens by 10 dB or more in either ear, that is a Standard Threshold Shift (STS) — triggering notification, HPD refitting, retraining, and possible OSHA 300 Log entry under 29 CFR 1904.10. Without a valid baseline, there is no reference point for this comparison.
In an occupational hearing loss workers’ compensation claim, the baseline audiogram is the employer’s primary evidence that the worker’s hearing was normal at the start of employment and that any subsequent loss can be tracked to a specific period. An employer without a baseline for an enrolled worker is defending a hearing loss claim without any starting reference — a position courts and administrative law judges consistently treat as favorable to the claimant. See: Workers’ Compensation for Occupational Hearing Loss.
The 6-Month and 12-Month Deadline Rules
OSHA 1910.95(g)(5) establishes the baseline timing rule. The standard provides two paths:
- 6-month rule (default): The baseline audiogram must be obtained within 6 months of the worker’s first exposure at or above the 85 dBA action level. This applies to all employers except those using mobile test vans.
- 12-month rule (mobile van exception): Employers that use mobile audiometric testing vans may obtain the baseline within 12 months of first exposure. During the interim period, the employee must wear hearing protection. This extension acknowledges the scheduling limitations of mobile van programs.
The 12-month exception is frequently misused. It applies only when a mobile van is the testing method — not as a general extension. Employers with in-house audiometry who simply fail to schedule the baseline within 6 months are out of compliance, not covered by the 12-month rule. Additionally, the worker must actually be wearing HPDs during the interim period — this is a condition of the extension, not just a recommendation.
Baseline Audiogram Deadline Calculator
Enter a worker’s first enrollment date to calculate their baseline audiogram deadline under OSHA 1910.95(g)(5). Workers in mobile van programs qualify for the 12-month extension only if they are actively wearing hearing protection during the interim period.
If using a mobile van, the worker must wear HPDs during the interim period as a condition of the 12-month extension — this is not optional. Failure to document HPD use during the interim period undermines the validity of the extension.
What Makes a Baseline Valid
A baseline audiogram is only as defensible as its documentation. OSHA 1910.95(g)(5) and Appendix C-II specify the requirements. A valid baseline requires:
- A 14-hour noise-free period before testing (documented or verified)
- An ANSI S3.6-compliant audiometer with current calibration
- Test room ambient noise levels within OSHA Appendix D to 1910.95 Table D-1 limits (documented)
- Testing conducted by or under the supervision of a licensed audiologist or physician Professional Supervisor
- A complete record containing: worker name, job classification, test date, examiner name and credentials, audiometer calibration date, noise exposure assessment, and test room ambient noise levels
Test room ambient noise levels must be documented and retained with each audiogram record. Many employers using mobile vans or informal test setups never document ambient noise — making every audiogram taken in that environment potentially invalid. This is one of the most commonly cited deficiencies in OSHA audiometric testing inspections. Soundtrace stores frequency-specific ambient noise data linked to each confirmed threshold response event.
The 14-Hour Quiet Period Requirement
OSHA 1910.95(g)(5)(i) requires that baseline audiograms be preceded by at least 14 hours without exposure to workplace noise. The purpose is to eliminate any temporary threshold shift (TTS) — a transient, reversible shift in hearing thresholds caused by recent noise exposure — from the baseline measurement. A baseline taken after a noisy shift will show artificially elevated thresholds, making future annual audiograms appear to show improvement when thresholds return to their true resting state.
The 14-hour period applies to workplace noise. Workers may still be exposed to recreational noise during this period, but documenting workplace noise abstention is the employer’s obligation. The simplest approach is to schedule baseline audiograms at the start of a shift, following a rest day or weekend. When this is not possible, the employer should document that the worker was instructed to avoid noise exposure for 14 hours and that HPDs were available if exposure was unavoidable.
Temporary threshold shifts (TTS) from acute noise exposure typically resolve within 16–48 hours. Permanent threshold shifts (PTS) represent actual cochlear hair cell damage and do not resolve with rest. A baseline taken without a 14-hour quiet period may capture TTS as if it were the worker’s true baseline — artificially elevating thresholds and making the worker appear to have worse baseline hearing than they actually do. This benefits neither the employer nor the worker.
When a Baseline Can Be Revised
OSHA 1910.95(g)(7)(ii) permits baseline revision under two circumstances:
- Improved thresholds: If an annual audiogram shows that thresholds have improved relative to the baseline (i.e., the worker’s hearing appears better), the Professional Supervisor may establish the improved audiogram as the new baseline. This prevents the original baseline from artificially suppressing future STS detection.
- Invalid original baseline: If the Professional Supervisor determines the original baseline did not represent the worker’s true hearing (e.g., due to TTS contamination, equipment malfunction, or procedural error), a new valid baseline may be established.
A revised baseline replaces the original for all future STS calculations. The original baseline should be retained in the record with documentation of why it was revised. Baseline revision is a Professional Supervisor decision — it cannot be made unilaterally by a testing technician.
The Baseline and Workers’ Compensation Defense
In occupational hearing loss litigation, the baseline audiogram is the single most important document in the employer’s file. Here is why:
- A valid baseline demonstrates the worker’s hearing at the time of hiring — establishing what pre-existing loss existed before current employment exposure.
- The STS history built on top of the baseline documents when and how quickly threshold shifts accumulated — supporting or undermining causation arguments.
- A missing baseline allows a claimant to attribute the entire hearing loss to current employment, with no documentary evidence to counter the claim.
- An invalid baseline (taken without a quiet period, on faulty equipment, in a noisy room) may be challenged and disqualified, producing the same outcome as a missing baseline.
Most occupational health attorneys recommend retaining all audiometric records, including baselines and annual audiograms, for 30 years beyond employment termination. OSHA requires retention for the duration of employment — but given the decades-long latency between exposure and hearing loss claim, the 30-year standard is the defensible approach. See: Digital vs. Paper Audiometric Testing: Why Cloud Retention Matters.
Frequently Asked Questions
The baseline audiogram is the reference point for all future Standard Threshold Shift calculations. Without a valid baseline, an employer cannot demonstrate that any hearing change occurred during current employment versus pre-existing loss. In workers’ compensation claims, a missing or invalid baseline systematically inflates the apparent shift attributable to current exposure — a position courts consistently treat as favorable to the claimant.
A baseline audiogram must be established within 6 months of the employee’s first exposure at or above the 85 dBA action level. Employers using mobile audiometric testing vans may extend this to 12 months, provided the employee wears hearing protection during the interim period. The 12-month extension applies only to mobile van programs — not as a general scheduling grace period.
A baseline is invalid if: it was taken without the required 14-hour noise-free period; the audiometer was not properly calibrated; the test room ambient noise exceeded OSHA Appendix D limits; required fields are missing from the record; or the audiogram was conducted without the oversight of a licensed audiologist or physician Professional Supervisor. Any of these deficiencies can disqualify the baseline in a WC proceeding.
Yes. OSHA 1910.95(g)(7)(ii) permits baseline revision when a persistent threshold shift represents improved hearing, or when the Professional Supervisor determines the original baseline was not a valid representation of the worker’s hearing. A revised baseline replaces the original for all future STS calculations. Revision is a Professional Supervisor decision and must be documented.
Never miss a baseline deadline
Soundtrace tracks every enrolled worker’s baseline deadline automatically, flags overdue and approaching tests, and stores audiograms with frequency-specific ambient noise documentation — producing records that withstand OSHA audit and legal review.
Schedule a Demo Get a quote for your facility →- OSHA Hearing Conservation Program: The Complete Guide
- Baseline vs. Annual Audiograms: OSHA Compliance Guide
- Standard Threshold Shift: Definition, Calculation & Action Steps
- Audiometric Testing for Employers: Complete OSHA Guide
- Workers’ Compensation for Occupational Hearing Loss: 50-State Guide
- Digital vs. Paper Audiometric Testing: Why Cloud Retention Matters