Share article
OSHA 1910.95(d)(2) allows employers to use either a sound level meter (SLM) or a personal noise dosimeter for occupational noise monitoring. Both measure noise exposure, but they answer different questions, serve different purposes, and have different limitations. This guide explains how each instrument works, when OSHA requires which, and how to choose the right tool for each monitoring task.
Soundtrace integrates both area noise monitoring data and individual dosimetry results into a single platform—automatically triggering HCP enrollment when action level exposures are identified.
A sound level meter measures the instantaneous or time-averaged sound pressure level at a fixed point in space. It does not follow the worker—it measures the acoustic environment at a specific location at a specific time. SLMs are ideal for mapping noise zones across a facility, identifying high-noise equipment sources, and conducting preliminary surveys.
Walk the facility with an SLM and record readings at regular grid points. The resulting map identifies which work zones exceed the action level.
Place SLM near individual machines to identify the dominant noise sources contributing to overall exposure—essential for engineering control prioritization.
Periodic SLM spot checks verify that engineering controls continue to achieve target noise reductions after installation.
Before full dosimetry campaigns, SLM walkthrough surveys identify which areas and job classifications need individual dose monitoring.
Sound level meters cannot capture a worker's actual TWA exposure if that worker moves through areas with different noise levels during the shift. A worker who spends 2 hours in a 95 dBA zone and 6 hours in a 78 dBA zone has a significantly different dose than either reading alone suggests. For mobile workers, personal dosimetry is required.
A personal noise dosimeter is worn by the worker throughout the shift. It continuously measures and integrates all noise the worker is exposed to and computes the total noise dose and TWA at shift end. Dosimeters are required when OSHA needs to know whether a specific worker's exposure meets or exceeds the action level, especially for mobile or variable-task workers.
Mount the microphone at the collar or lapel on the side of the worker's dominant noise source—within 1 foot of the ear. Improper placement is the leading source of dosimetry error.
Confirm threshold (80 dBA), criterion level (90 dBA), exchange rate (5 dB), A-weighting, and slow response. Never use NIOSH or ISO settings for OSHA compliance determinations.
Use a calibrator generating a known sound level at the microphone. Record pre- and post-calibration levels. If the difference exceeds 0.5 dB, the measurement is invalid.
Worker should not cover or remove the microphone during the shift. Non-occupational noise during breaks may be excluded from the analysis.
| Factor | Sound Level Meter | Personal Dosimeter |
|---|---|---|
| What it measures | Noise level at a fixed point in space | Individual worker's integrated noise dose over shift |
| OSHA required for | Area surveys, equipment assessments | Individual TWA determination for mobile workers |
| Worn by worker? | No — held or placed by technician | Yes — worn at collar/lapel for full shift |
| Output | dB or dBA at moment or time-average | Dose %, TWA (dBA), LAVG, peak levels |
| Best for | Facility mapping, source identification | Mobile workers, variable-noise jobs, HCP enrollment decisions |
| Calibration | Before and after use with acoustic calibrator | Before and after use; settings must be verified |
| ANSI standard | S1.4 Type 2 minimum | S1.4 Type 2 minimum |
Modern dosimeters can be configured for multiple standards (OSHA, NIOSH, ISO). Using the wrong settings produces results that cannot be used for OSHA compliance determinations. Always verify settings before initiating any monitoring.
| Parameter | OSHA Required Setting | NIOSH (Do Not Use for OSHA) |
|---|---|---|
| Exchange rate | 5 dB | 3 dB |
| Criterion level | 90 dBA | 85 dBA |
| Threshold | 80 dBA | 80 dBA |
| Weighting | A-weighting (dBA) | A-weighting (dBA) |
| Response | Slow | Slow |
• Conducting an initial facility walkthrough to identify high-noise zones
• Mapping noise levels to create a visual hazard map
• Measuring noise output from specific equipment for engineering control planning
• Verifying that installed noise controls have achieved target reductions
• Workers are stationary throughout their shift
• Determining whether a specific worker's TWA meets or exceeds 85 dBA
• Workers move between areas with different noise levels
• Tasks vary throughout the shift
• Determining HCP enrollment for a specific job classification
• Workers operate near intermittent high-noise sources (presses, stamping, pneumatic tools)
Sound level meters answer “how loud is this area?” Dosimeters answer “how much noise did this specific worker receive today?” Both questions are necessary for a defensible noise monitoring program.
Both instruments must be calibrated before and after each monitoring session using an acoustic calibrator traceable to NIST standards. If the post-monitoring calibration shows a deviation exceeding 0.5 dB from the pre-monitoring calibration, the monitoring data is invalid and must be repeated. Both SLMs and dosimeters also require periodic laboratory calibration—maintain a calibration certificate for each instrument.
Soundtrace connects monitoring results to employee audiometric records—automatically enrolling workers who reach the action level and flagging classification changes.
Book a DemoGet a quote for your facility →A sound level meter measures noise level at a fixed point in space at a specific time. A personal noise dosimeter is worn by the worker and integrates all noise exposure over the shift to compute a TWA. SLMs are used for area surveys and source identification; dosimeters are used to determine individual worker TWA for hearing conservation program enrollment decisions.
For OSHA compliance determinations, a dosimeter must be configured with: exchange rate of 5 dB, criterion level of 90 dBA, threshold of 80 dBA, A-weighting, and slow response. Using NIOSH settings (3 dB exchange rate, 85 dBA criterion) produces different results and cannot be used for OSHA compliance determinations.
OSHA does not always require dosimetry, but it is necessary when workers move through areas with varying noise levels, when tasks change throughout the shift, or when the employer needs to determine the TWA for a specific individual for HCP enrollment decisions. Area SLM readings cannot accurately represent a mobile worker's personal exposure.