Noise dosimetry is how OSHA 1910.95 compliance actually gets measured. A compliance program built on estimates rather than measurements is a program with an undocumented exposure baseline — and no defense when a worker files a WC claim or OSHA conducts an inspection. According to the CDC, approximately 22 million U.S. workers are exposed to hazardous occupational noise annually — and for each of them, personal dosimetry is the most defensible method to establish individual exposure for HCP enrollment, engineering control decisions, and records that hold up under legal scrutiny. This guide covers how noise dosimetry works, what OSHA requires, how to set up a dosimeter correctly, and how to interpret and document results.
What Noise Dosimetry Actually Measures
A noise dosimeter is a small device worn on the worker’s shoulder, near the ear, throughout the work shift. It continuously samples the acoustic environment and accumulates a noise dose — expressed as a percentage of the permissible daily dose and as a time-weighted average (TWA). Unlike a sound level meter, a dosimeter captures exposure across the entire shift including periods of variable noise, task transitions, and intermittent high-level events.
The key output metrics from dosimetry are:
- Dose (%): The percentage of the maximum permissible noise exposure. 100% dose = exposure at exactly the PEL (90 dBA TWA under OSHA). 50% dose = exposure at the action level (85 dBA TWA).
- TWA: The 8-hour time-weighted average noise level. This is the value used to determine HCP enrollment (at 85 dBA) and PEL compliance (at 90 dBA).
- LAVG: The average noise level during the sample period, without exchange rate weighting. Used for reference and comparison.
- Peak: The highest instantaneous noise level captured during the sampling period. Used to evaluate compliance with the 140 dB impulse noise limit.
Required Dosimeter Settings Under OSHA 1910.95
OSHA specifies dosimeter settings in 1910.95(b) and Appendix A. To produce results valid for OSHA compliance determinations, dosimeters must be configured with these exact settings:
| Setting | OSHA-Required Value | Purpose |
|---|---|---|
| Criterion level | 90 dBA | The reference level defining 100% dose |
| Exchange rate | 5 dB | Halving time relationship for dose accumulation |
| Threshold | 80 dBA | Lower cutoff — sound below 80 dBA not counted in dose |
| Response time | Slow | Matches OSHA’s measurement protocol |
A dosimeter set to NIOSH settings (85 dBA criterion, 3 dB exchange rate) will produce higher TWA and dose values than the same exposure measured with OSHA settings. Results from incorrectly configured dosimeters cannot be used for OSHA compliance determinations — and using NIOSH-configured results to defend against an OSHA citation can create confusion. Always document the instrument settings used for each monitoring session.
How to Conduct a Dosimetry Survey
- Calibrate the dosimeter before and after each monitoring session using a calibrator at a known sound level. Record the pre- and post-calibration check values in the monitoring record.
- Attach the dosimeter to the worker’s shoulder or collar, with the microphone positioned near the ear in the noise field. The microphone should not be covered by clothing or positioned where it would be shielded from the noise source.
- Inform the worker that monitoring is occurring (as required by OSHA 1910.95(e)) and that they should perform their normal work tasks. They should not cover or disturb the microphone, and should not intentionally expose or shield the device from noise sources.
- Monitor for the full shift or for a minimum representative period. Full-shift monitoring is strongly preferred. If a partial-shift sample is used, document the start and end times and the extrapolation method used to produce the full-shift TWA.
- Download results and document: worker name and job classification, date, dosimeter make/model/serial number, calibration values, sample start/end times, and the TWA, dose, and LAVG results.
- Notify the worker of their results as required by 1910.95(e) — the notification must occur regardless of whether the result is above or below the action level.
Interpreting Results: TWA, Dose, and HCP Enrollment
| TWA Result | Dose Equivalent | OSHA Implication |
|---|---|---|
| Below 80 dBA | <25% | No HCP obligation; monitoring record retained |
| 80–84 dBA | 25–49% | Below action level; monitor may be required but HCP enrollment not triggered |
| 85 dBA (action level) | 50% | HCP enrollment required — all six elements apply |
| 90 dBA (PEL) | 100% | Engineering/administrative controls required; HPDs mandatory |
| Above 90 dBA | >100% | Over PEL — immediate engineering control evaluation required |
Workers with TWA results at or above 85 dBA must be enrolled in the hearing conservation program and receive audiometric testing, HPD provision, training, and all other HCP elements. The dosimetry result is the enrollment trigger and becomes part of the worker’s audiometric record per 1910.95(m)(2)(i)(E).
Recordkeeping Requirements for Dosimetry Results
OSHA 1910.95(m)(3) requires noise exposure records to be retained for at least 2 years. Each record must include: date of measurement, instrument make/model/serial/calibration, worker name and job classification, and the measurement results. See: Noise Monitoring Recordkeeping: OSHA Requirements.
Critically, 1910.95(m)(2)(i)(E) requires that each audiometric test record include the employee’s most recent noise exposure assessment. This creates a required linkage between dosimetry records and audiometric files that paper-based systems routinely fail to maintain.
NIOSH vs. OSHA Dosimetry Settings
Many industrial hygienists run dosimeters configured to both OSHA and NIOSH settings simultaneously — some instruments support dual measurement. NIOSH uses an 85 dBA criterion level and 3 dB exchange rate, producing a more conservative (higher) dose calculation for the same exposure. Running both settings provides the complete picture: OSHA compliance status and best-practice protection assessment. See: NIOSH vs. OSHA Exposure Limits: PEL, REL, and Exchange Rate Explained.
Frequently Asked Questions
OSHA 1910.95 requires dosimeters to be set to a 90 dBA criterion level, 5 dB exchange rate, 80 dBA threshold, and slow response time. These settings produce the dose percentage and TWA used for HCP enrollment and compliance determinations under the standard. Results from dosimeters set to other configurations (e.g., NIOSH settings) cannot be used for OSHA compliance determinations without recalculation.
OSHA guidelines recommend sampling for at least a full representative work shift or a minimum of 2 hours. A full-shift sample is always preferable because it captures actual task variation, equipment cycles, and noise level changes throughout the workday. Short samples require extrapolation and introduce error — especially for workers with variable tasks.
OSHA uses a 90 dBA criterion level, 5 dB exchange rate, and 80 dBA threshold. NIOSH uses an 85 dBA criterion level, 3 dB exchange rate, and 80 dBA threshold. The same dosimeter worn by the same worker will produce different dose percentages and TWA values depending on which settings are used. NIOSH settings consistently produce higher calculated doses.
Noise dosimetry linked directly to audiometric records
Soundtrace noise monitoring produces per-worker dosimetry results automatically linked to each enrolled worker’s audiometric file — satisfying the 1910.95(m)(2)(i)(E) cross-reference requirement without manual documentation.
Get a Free Quote