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Safety managers new to noise monitoring often encounter two instrument options -- noise dosimeters and sound level meters -- and aren't sure which OSHA requires, when each is appropriate, and whether they're interchangeable. They are not. Each instrument serves a distinct purpose in an occupational noise monitoring program, and selecting the wrong one for personal exposure measurement can produce data that doesn't satisfy OSHA's requirements. This guide explains the difference clearly.
Soundtrace integrates personal dosimetry and facility noise monitoring data into a single platform -- giving employers both the individual TWA measurements needed for HCP enrollment decisions and the area-level data needed for engineering control assessments.
Use a noise dosimeter for measuring individual employee TWA exposure -- it's the right instrument for determining who needs to be enrolled in the hearing conservation program. Use a sound level meter for area surveys, identifying noise sources, and informing engineering control decisions. Both require calibration and proper OSHA settings.
A noise dosimeter is a personal exposure measurement device worn by the worker during a shift. It clips to the worker's collar or shoulder, with the microphone positioned in the hearing zone -- within 30 cm of the ear. The dosimeter samples noise levels continuously throughout the shift and integrates them into a cumulative noise dose and calculated 8-hour TWA.
Because the dosimeter travels with the worker through all areas of the facility and captures all noise sources encountered during the actual work shift, it provides the most accurate measurement of individual personal exposure. It's the instrument of choice for determining whether a specific employee's TWA meets or exceeds the 85 dBA action level.
▶ Bottom line: A dosimeter measures the worker's actual cumulative noise dose across the full shift -- including all tasks, locations, and equipment encountered. This is the correct instrument for making HCP enrollment decisions under OSHA 1910.95.
A sound level meter (SLM) is a handheld instrument that measures instantaneous sound pressure levels at a specific location. The safety manager holds or positions the meter at a point of interest -- near a machine, in a work zone, at ear height -- and reads the current noise level on the display. SLMs provide a real-time snapshot of noise at a place, not a time-integrated measure of a person's exposure.
SLMs are indispensable for noise surveys: identifying the loudest machines, mapping noise levels across a facility, comparing before-and-after noise levels when engineering controls are installed, and screening areas to decide where dosimetry is warranted.
▶ Bottom line: A sound level meter measures noise at a location at a point in time. It tells you how loud an area is -- not how much noise a specific worker accumulated over their shift. Use it for area surveys and engineering decisions, not for individual HCP enrollment determinations.
| Feature | Noise Dosimeter | Sound Level Meter |
|---|---|---|
| What it measures | Cumulative personal noise dose + TWA over shift | Instantaneous sound level at a location |
| Worn by worker? | Yes -- clips to worker's clothing | No -- handheld by technician |
| Primary OSHA use | Individual TWA for HCP enrollment | Area surveys, source identification |
| Output | % dose, TWA (dBA), Lavg, Lmax | dB or dBA level, Leq, Lmax, octave bands |
| ANSI standard | S1.25 | S1.4 |
| Best for | Workers with mobile, variable exposure | Fixed positions, area mapping, control verification |
| Can estimate TWA? | Directly -- it's the primary output | Only with area sampling methodology (less accurate) |
For measurements intended for OSHA 1910.95 compliance, both dosimeters and SLMs must be configured correctly:
A dosimeter set to NIOSH's 3 dB exchange rate will produce a higher TWA than the same exposure measured with OSHA's 5 dB rate. Using the wrong settings generates data that cannot be directly compared to OSHA thresholds -- and may overstate or understate compliance risk.
Use a dosimeter when: determining whether a specific employee's TWA meets or exceeds 85 dBA for HCP enrollment; verifying that an employee's exposure is below the PEL; documenting individual exposures for compliance records; monitoring workers with highly variable tasks or routes through the facility.
Use a sound level meter when: conducting an initial noise survey to screen areas and decide where dosimetry is needed; identifying the loudest noise sources for engineering control prioritization; measuring background noise levels in audiometric test rooms; verifying noise reduction after installing controls; conducting octave band analysis to select appropriate HPDs.
Both instruments must be calibrated with a laboratory-grade acoustic calibrator before and after each use. The calibration result -- the measured level compared to the calibrator's reference level -- must be recorded. If the pre- and post-measurement calibration checks differ by more than 1 dB, the monitoring data may be invalid and re-monitoring should be considered. Full electroacoustic calibrations to ANSI standards are typically performed annually or per manufacturer specifications.
For determining an individual employee's TWA exposure for HCP enrollment purposes, a dosimeter is strongly preferred. A sound level meter can be used with area sampling methods to estimate exposure, but personal dosimetry is more accurate and defensible. OSHA accepts area monitoring with SLMs for representative sampling but requires that the method accurately characterize each employee's actual exposure.
OSHA 1910.95 references ANSI S1.25 for dosimeters. The instrument must be set to use slow response, A-weighting, the 90 dBA criterion level, and the 5 dB exchange rate to produce TWA values that correspond to OSHA's permissible exposure limits. Settings that differ from these -- including the 3 dB exchange rate used by NIOSH -- will produce different TWA values not directly comparable to OSHA thresholds.
Both instruments must be calibrated with an acoustic calibrator before and after each use (field calibration). Additionally, full laboratory calibrations are typically required annually or per the manufacturer's schedule. OSHA requires that calibration checks be documented. An instrument showing more than 1 dB drift between pre- and post-use checks may invalidate the monitoring data.
Response setting determines how quickly the meter averages sound levels. Slow response averages over 1 second -- appropriate for continuous and fluctuating noise. Fast response averages over 125 milliseconds -- more appropriate for detecting peak levels in impulsive noise. OSHA requires slow response for TWA and hearing conservation monitoring.
You can rent dosimeters, borrow from a workers comp carrier, hire an industrial hygienist to conduct monitoring, or use a vendor service. OSHA does not require employer-owned equipment -- it requires that monitoring be conducted with appropriate, calibrated instruments by a qualified person. Many employers conduct their initial noise survey using a vendor and purchase equipment only if ongoing monitoring is needed.
Soundtrace integrates personal dosimetry and real-time facility monitoring to keep exposure data current and automatically trigger HCP enrollment when workers reach the 85 dBA action level.
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