An audiogram is the central document of every occupational hearing conservation program — yet most workers who receive one have never had it explained to them, and many safety managers who review them have never been shown how to read one. This guide covers everything: what the audiogram measures, how to read the axes and symbols, what normal hearing looks like, what NIHL looks like vs. age-related loss, how to distinguish patterns that need medical referral, how the STS calculation works, what a PLHCP evaluates during review, and what OSHA requires from every audiometric record.
Soundtrace generates OSHA-compliant audiograms with automated baseline comparison, professional audiologist review, and 30-year digital retention — so workers understand what their audiogram means and employers have the documentation OSHA requires.
An audiogram is not a pass/fail test. It is a surveillance record. Its value is the comparison between this year’s result and the baseline. The change is what matters — not the absolute number.
- What an audiogram measures
- How to read the axes and symbols
- What normal hearing looks like
- Baseline vs. annual audiogram
- The NIHL 4 kHz notch pattern
- NIHL vs. age-related hearing loss
- Standard Threshold Shift: what triggers OSHA action
- What a PLHCP evaluates during review
- The audiogram in OSHA compliance
- Frequently Asked Questions
What an Audiogram Is and What It Measures
An audiogram is the graph produced by pure tone audiometric testing. It plots a worker’s hearing thresholds — the softest level at which they can consistently detect a tone — at multiple frequencies across both ears. OSHA 1910.95 requires testing at 500, 1000, 2000, 3000, 4000, and 6000 Hz. The audiogram is a surveillance record: its primary clinical value comes from comparing results over time, each annual audiogram against the baseline.
How to Read the Axes and Symbols
| Element | What It Represents | Key Detail |
|---|---|---|
| X-axis (horizontal) | Frequency in Hz | Left = low pitch (250 Hz), Right = high pitch (8000 Hz). OSHA-required frequencies: 500, 1000, 2000, 3000, 4000, 6000 Hz |
| Y-axis (vertical) | Hearing level in dB HL | 0 dB HL at top = softest audible sound for average normal hearing. Numbers increase downward — lower on chart = worse hearing |
| O symbol (red) | Right ear air conduction threshold | The threshold at each frequency for the right ear |
| X symbol (blue) | Left ear air conduction threshold | The threshold at each frequency for the left ear |
| [ symbol | Right ear bone conduction threshold | Used when differentiating sensorineural vs. conductive hearing loss |
| ] symbol | Left ear bone conduction threshold | Used when differentiating sensorineural vs. conductive hearing loss |
What Normal Hearing Looks Like
Normal hearing thresholds on an occupational audiogram are generally 25 dB HL or better across all tested frequencies. On the graph, normal results appear near the top, with O (right ear) and X (left ear) symbols clustered in the 0–25 dB HL range. The line connecting thresholds runs roughly flat across frequencies, with minor variation. Any threshold above 25 dB HL is a departure from the normal range, though it does not automatically indicate NIHL — normal thresholds vary by age, and many workers have mild congenital or non-occupational hearing differences.
Baseline vs. Annual Audiogram
Baseline Audiogram
When: Within 6 months of first exposure at or above 85 dBA TWA (or within 1 year if mobile van used with continuous HPD)
Purpose: Establishes the reference point for all future STS calculations
Key rule: Must be preceded by 14 hours of quiet — no exposure above action level before testing
Storage: Retained for duration of employment + 30 years
Annual Audiogram
When: Within 1 year of baseline; annually thereafter for all enrolled workers
Purpose: Compared to baseline to detect STS; drives OSHA compliance actions
Key rule: Must be preceded by 14 hours of quiet before testing
Review: Professional supervisor evaluates for STS, patterns, referral needs
The NIHL 4 kHz Notch Pattern
The classic audiometric signature of noise-induced hearing loss is a notch at 4000 Hz — elevated thresholds specifically at 4000 Hz with better hearing at lower frequencies (500–2000 Hz) and partial recovery at 8000 Hz. This pattern occurs because the outer hair cells in the cochlear region encoding 3–6 kHz sound are preferentially vulnerable to noise damage, and because ear canal resonance amplifies sounds in this frequency range before they reach the inner ear.
Early NIHL may show only a mild notch at 4000 Hz. With continued exposure, the notch deepens and broadens, eventually involving 2000 and 3000 Hz — which is when STS criteria are more likely to be triggered, since those are two of the three frequencies used in the STS calculation.
NIHL vs. Age-Related Hearing Loss on an Audiogram
| Feature | NIHL Pattern | Presbycusis (Age-Related) Pattern |
|---|---|---|
| Shape | Notch at 4000 Hz with partial recovery at 8000 Hz | Gradual downslope from low to high frequencies, no notch |
| Onset | Earlier; can appear after years of occupational exposure | Typically begins appearing after age 50–60 |
| Symmetry | Often bilateral and roughly symmetric | Usually bilateral and symmetric |
| Frequencies affected first | 3000–6000 Hz (notch region) | High frequencies (4000–8000 Hz), spreading toward lower |
| OSHA age correction | N/A (NIHL component) | Appendix F tables used to separate age contribution from STS calculation |
Standard Threshold Shift: What Triggers OSHA Action
An STS is a 10 dB or greater average shift in hearing thresholds at 2000, 3000, and 4000 Hz in either ear, compared to the baseline audiogram. OSHA requires age correction using Appendix F tables before determining whether the shift meets STS criteria, if age correction reduces the apparent shift below 10 dB, the STS is eliminated.
What a PLHCP Evaluates During Audiogram Review
The professional supervisor (a licensed physician or audiologist) who reviews occupational audiograms under 1910.95 evaluates several things beyond the simple STS calculation:
- Validity of the audiogram: Was it conducted in a quiet enough environment? Were testing procedures followed? Are the thresholds internally consistent?
- Pattern of loss: Does the pattern suggest NIHL, age-related loss, conductive hearing loss, asymmetric loss, or another etiology?
- STS determination: Applying age correction from Appendix F and confirming whether the criteria are met.
- Work-relatedness: Whether the hearing loss is likely work-related, which affects 300 Log recordability under 1904.10.
- Medical referral: Whether the pattern warrants referral to an audiologist or ENT physician for further evaluation.
- Baseline revision: Whether the current audiogram should replace the baseline (used when a persistent improvement occurs or when the PLHCP determines prior baseline was invalid).
The Audiogram in OSHA Compliance
The audiogram sits at the center of the OSHA 1910.95 compliance system. Every other element of the HCP — noise monitoring, HPD selection, training — feeds into the audiogram as evidence of protection. The annual audiogram is the instrument that detects whether that protection is working.
| OSHA Requirement | Audiogram Role | Citation Reference |
|---|---|---|
| Baseline audiogram | Establishes reference for STS comparison | 1910.95(g)(5) |
| Annual audiogram | Compared to baseline; triggers STS workflow | 1910.95(g)(6) |
| 14 hrs quiet before testing | Prevents TTS from inflating thresholds | 1910.95(g)(5)(ii) |
| Professional supervisor review | STS determination, work-relatedness, referral | 1910.95(g)(3) |
| Worker notification of STS | Written notice required within 21 days of confirmed STS | 1910.95(g)(8) |
| Record retention | Employment duration + 30 years | 1910.95(m)(2)(ii) |
Frequently asked questions
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