OSHA 1910.95 requires noise exposure monitoring whenever employees may be exposed at or above 85 dBA TWA — but it does not prescribe a single instrument type for all situations. Sound level meters measure instantaneous noise levels at fixed locations. Noise dosimeters measure cumulative personal exposure over a full shift. Understanding when each is required, and how OSHA expects them to be used, is essential for building a defensible monitoring program.
Soundtrace combines personal noise dosimetry data and area monitoring into a single platform, automatically calculating TWA exposures and triggering enrollment decisions without manual calculation.
For personal exposure assessment (determining HCP enrollment), use a noise dosimeter. For area surveys and source identification, use a sound level meter. OSHA requires dosimetry for workers with variable or mobile noise exposures. Both instruments must meet ANSI S1.25 or S1.4 Type 2 minimum standards and require calibration before and after each use.
How Each Instrument Works
A sound level meter (SLM) measures instantaneous sound pressure level at the location of the microphone, displaying results in dBA in real time. It can be set to measure slow, fast, or impulse response and can log data over time. An integrating SLM averages sound levels over a measurement period. SLMs are point-in-space instruments — they measure what is happening at a fixed location, not what a moving worker actually experiences.
A noise dosimeter is a wearable device that accumulates noise dose over a measurement period, typically a full work shift. The worker clips the dosimeter to their collar or shirt, near the ear, and goes about normal work activities. The dosimeter integrates varying noise levels over time and calculates the 8-hour TWA and noise dose percentage automatically. This reflects what the worker actually experienced, including variation between quiet and loud zones.
Side-by-Side Comparison
| Feature | Noise Dosimeter | Sound Level Meter |
|---|---|---|
| Measures | Cumulative personal exposure; 8-hr TWA; dose % | Instantaneous dBA at a fixed point |
| Worn by worker | Yes — clips to collar near ear | No — handheld or tripod-mounted |
| Required for personal TWA | Yes — especially for mobile workers | No — area measurement only |
| Best use | HCP enrollment decisions; OSHA compliance documentation | Area surveys; noise mapping; engineering control evaluation |
| ANSI standard | ANSI S1.25 | ANSI S1.4 Type 2 minimum |
| Calibration required | Before and after each use | Before and after each use |
| Data output | TWA, dose %, Lavg, peak dB, time histogram | Leq, Lmax, time history, spectrum (with analyzer) |
| Limitations | Worker must wear correctly for full shift; microphone placement matters | Cannot account for worker movement; may under- or over-estimate personal exposure |
OSHA Instrument Requirements
Under 29 CFR 1910.95 Appendix E, dosimeters must comply with ANSI S1.25-1991. Sound level meters must comply with ANSI S1.4 at Type 2 accuracy or better. The instrument must be set to the OSHA-specified measurement settings: A-weighting, slow response (for continuous or intermittent noise), 5 dB exchange rate, 80 dBA threshold, and 90 dBA criterion level. Using incorrect instrument settings produces results that are not valid for OSHA compliance purposes.
When to Use Each Instrument
Use a noise dosimeter when: the worker moves between areas with different noise levels; the worker’s exposure is episodic or task-dependent; you are making the initial HCP enrollment decision for a specific worker; the worker performs tasks in areas where point measurements may not be representative.
Use a sound level meter when: identifying the location and intensity of noise sources in a facility; evaluating the effectiveness of engineering controls; conducting a preliminary noise survey before personal dosimetry; characterizing noise in a specific fixed-location work area; determining if an area requires mandatory HPD signage.
A common approach: use an SLM for the initial facility walk-through to identify high-noise areas and jobs, then deploy dosimeters on representative workers in those areas for full-shift personal exposure measurement. The SLM survey identifies who to monitor; the dosimeter data determines who to enroll.
Calibration Requirements
Both instruments require an acoustic calibration check immediately before and after each use with a calibrator device. Any drift of more than ±1 dB between pre- and post-measurement calibration checks invalidates the measurement data. Annual calibration by an accredited laboratory is also required. All calibration records must be retained as part of the monitoring documentation file.
Frequently asked questions
Personal exposure data for every worker, without scheduling a monitoring campaign
Soundtrace integrates dosimetry and area monitoring into a single continuous platform — so exposure data stays current automatically rather than requiring periodic manual measurement campaigns.
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