Every EHS professional overseeing a hearing conservation program should be able to read a workplace audiogram. Understanding what the audiogram shows — and what it doesn’t — is essential for communicating results to workers, identifying concerning patterns before they become Standard Threshold Shifts, and evaluating the effectiveness of the hearing conservation program. OSHA 29 CFR 1910.95 requires audiometric records to be reviewed by a professional supervisor, but EHS professionals who understand audiograms can flag potential issues and ask the right questions. According to CDC/NIOSH, approximately 22 million U.S. workers undergo occupational audiometric testing annually.
The Audiogram Format
An audiogram plots hearing thresholds on a grid. The x-axis shows test frequencies from low to high (250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz, 8000 Hz). The y-axis shows hearing level in decibels (dB HL), with 0 dB HL at the top (best hearing) and higher numbers (worse hearing) progressing downward. OSHA’s required test frequencies are 500, 1000, 2000, 3000, 4000, and 6000 Hz.
Symbols distinguish between ears: Os or circles typically represent the right ear; Xs represent the left ear. Air conduction thresholds are plotted with these symbols, and bone conduction thresholds (where tested) use brackets or angles. In occupational audiometry, air conduction is the standard measurement.
| Hearing Level Range | Classification | Occupational Significance |
|---|---|---|
| 0–25 dB HL | Normal hearing | No occupational hearing loss detected at these frequencies |
| 26–40 dB HL | Mild hearing loss | Stage 3 NIHL may be present; speech-in-noise difficulty begins |
| 41–55 dB HL | Moderate hearing loss | Stage 4 NIHL; significant communication impairment |
| 56–70 dB HL | Moderately severe | Significant occupational hearing impairment; WC implications |
| 71+ dB HL | Severe to profound | Severe impairment; major occupational and daily life impact |
Identifying the 4 kHz Notch
The 4 kHz notch is the characteristic audiometric signature of noise-induced hearing loss. Look for:
- Elevated threshold (worse hearing) at 4000 Hz compared to lower frequencies
- Relative recovery at 8000 Hz (the notch shape)
- Better thresholds at 500–2000 Hz than at 4000 Hz
A Stage 1 NIHL worker may show only a mild notch at 4000 Hz. Stage 2 shows a deepening notch extending toward 3000 Hz. Stage 3 shows the notch spreading into speech frequencies (2–3 kHz), when communication impairment in noise begins. Stage 4 shows loss spreading across speech frequencies.
A 4 kHz notch on a single audiogram identifies a pattern consistent with NIHL but does not by itself establish occupational causation, document an STS, or support a WC claim. The notch’s significance depends on comparison to prior audiograms (to establish progression), noise monitoring data (to establish occupational exposure), and professional supervisor interpretation. The single-audiogram notch is a flag that requires expert review, not a standalone diagnosis.
Calculating STS from Audiogram Data
Standard Threshold Shift is calculated as the average threshold change at 2000, 3000, and 4000 Hz (the speech-high frequency range most sensitive to NIHL) in one ear compared to the baseline audiogram. To calculate:
- Average the baseline thresholds at 2000, 3000, and 4000 Hz for one ear
- Average the current audiogram thresholds at 2000, 3000, and 4000 Hz for the same ear
- Subtract the baseline average from the current average
- If the result is 10 dB or more, an STS has occurred in that ear
OSHA Appendix F provides age correction tables that can be applied to reduce the apparent STS by subtracting the expected age-related threshold change from the measured change. Age correction is optional, not required. If applied, it can reduce the frequency of apparent STSs that reflect age-related degeneration rather than noise-induced progression. The professional supervisor makes all STS determinations with or without age correction.
Frequently Asked Questions
Professional Supervisor Review of Every Audiogram
Soundtrace licensed audiologist Professional Supervisors review every audiometric result, calculate STS comparisons against baseline, and make all required STS determinations — so employers don’t have to interpret audiograms themselves.
Get a Free Quote