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The OSHA noise action level is 85 dBA -- measured as an 8-hour time-weighted average, or TWA. Cross that line with any employee and you are legally required to implement a full hearing conservation program. But what does 85 dBA actually feel like in a real workplace? How is it measured? And what does "TWA" mean when noise levels change throughout the shift? This guide answers all of it.
The OSHA noise action level is 85 dBA as an 8-hour TWA. It does not mean a worker needs to be at 85 dBA for a full 8 hours -- it means their cumulative daily noise dose, accounting for varying levels throughout the shift, averages out to 85 dBA. Exceeding this threshold triggers your full legal hearing conservation obligations under 29 CFR 1910.95.
The OSHA noise action level is 85 dBA as an 8-hour time-weighted average, as defined in 29 CFR 1910.95(c). When any employee's noise exposure meets or exceeds this threshold, the employer must establish and maintain a continuing, effective hearing conservation program covering noise monitoring, audiometric testing, hearing protection, training, and recordkeeping.
Research consistently shows that cumulative exposure at 85 dBA TWA over a working lifetime carries a meaningful risk of permanent noise-induced hearing loss. OSHA set the action level here as the threshold below which risk drops to an acceptable level for most workers -- though NIOSH sets its recommended limit even lower.
A time-weighted average (TWA) is the average noise level a worker experiences across an 8-hour workday, accounting for the fact that noise levels typically vary throughout the shift. It is a logarithmic calculation -- not a simple average -- that weights higher noise levels more heavily because decibels operate on a logarithmic scale.
OSHA uses a 5 dBA exchange rate: every 5 dBA increase in noise level cuts the allowable exposure time in half.
| Noise Level (dBA) | Max Duration at That Level | Equivalent Dose |
|---|---|---|
| 85 dBA | 16 hours | Action level threshold |
| 90 dBA | 8 hours | 100% of PEL dose |
| 95 dBA | 4 hours | 100% of PEL dose |
| 100 dBA | 2 hours | 100% of PEL dose |
| 105 dBA | 1 hour | 100% of PEL dose |
| 110 dBA | 30 minutes | 100% of PEL dose |
| 115 dBA | 15 minutes | Maximum -- no exceptions |
Imagine a worker who spends their shift like this: 2 hours at 100 dBA on a press, 4 hours at 88 dBA on an assembly line, and 2 hours at 78 dBA in a quieter area. Even though two-thirds of the shift is below 90 dBA, those 2 hours at 100 dBA contribute so heavily to the cumulative dose that the 8-hour TWA likely exceeds 85 dBA -- triggering full hearing conservation program requirements.
Many employers assess their loudest machine and -- if it is under 90 dBA -- assume they are compliant. OSHA requires a cumulative dose assessment across the full shift. A worker bouncing between an 88 dBA press room and an 85 dBA packaging line can easily accumulate a TWA above the action level even if no single area exceeds the PEL.
| Threshold | Level | What It Requires | Hearing Protection |
|---|---|---|---|
| Action Level (AL) | 85 dBA TWA | Full hearing conservation program: monitoring, audiograms, training, records | Must be made available |
| Permissible Exposure Limit (PEL) | 90 dBA TWA | All of the above PLUS feasible engineering and administrative controls | Use becomes mandatory |
Even if engineering controls bring employee exposures below the PEL, if those workers still reach 85 dBA TWA, the full hearing conservation program is still required. Only dropping below the action level eliminates your program obligations.
| Sound Source | Approximate dBA | OSHA Status at 8-hr Exposure |
|---|---|---|
| Normal conversation | 60-65 dBA | No concern |
| Busy restaurant | 70-75 dBA | No concern |
| Heavy city traffic | 80-85 dBA | At or near action level |
| Factory floor (moderate) | 85-90 dBA | Action level -- program required |
| Power saw or lawn mower | 90-95 dBA | Above PEL -- HPD mandatory |
| Stamping press, pneumatic tools | 95-105 dBA | Well above PEL -- serious risk |
| Chainsaw or jet engine at distance | 105-115 dBA | Severe risk -- minutes matter |
A useful field rule: if you have to raise your voice to speak to someone at arm's length, background noise is likely at or above 85 dBA. This is not a substitute for calibrated measurement, but it is a reliable indicator that monitoring is warranted.
A dosimeter is worn by the worker throughout a representative shift, continuously logging noise levels and calculating the cumulative TWA. Dosimeters are the preferred method for workers with variable or mobile work patterns and are required when workers move between areas with different noise levels.
Measures instantaneous noise levels at specific locations. Useful for area mapping and identifying noise hotspots, but less accurate for assessing personal exposure when workers move throughout the shift. Must use the A-weighted slow response setting (dBA) for compliance purposes.
OSHA requires all continuous, intermittent, and impulsive sounds between 80 dB and 130 dB to be integrated into the TWA calculation. Some older sound level meters do not capture impulsive noise properly. When in doubt, use a dosimeter that meets ANSI S1.25 specifications.
If monitoring confirms all employee TWAs remain below 85 dBA, you are not required to implement a formal hearing conservation program. However, you should document your monitoring results, re-monitor when conditions change, and consider voluntary hearing protection for workers consistently in the 80-85 dBA range -- cumulative lifetime exposure matters even below the OSHA action level.
OSHA's action level is the legal minimum. NIOSH's Recommended Exposure Limit (REL) is 85 dBA TWA using a 3 dBA exchange rate -- stricter than OSHA's 5 dBA rate. NIOSH estimates that following OSHA's PEL alone results in significant occupational hearing loss for a portion of workers over a 40-year career.
| Agency | Limit | Exchange Rate | Legal Force |
|---|---|---|---|
| OSHA | 90 dBA TWA (PEL) / 85 dBA TWA (Action Level) | 5 dBA | Legally enforceable |
| NIOSH | 85 dBA TWA (REL) | 3 dBA | Recommended only |
| ACGIH | 85 dBA TWA (TLV) | 3 dBA | Recommended only |
It depends on their total TWA for the shift. Two hours at 85 dBA combined with quieter work for the remaining 6 hours will likely result in a TWA below 85 dBA. But 2 hours at 95 dBA, even with quiet time afterward, could push the TWA above the action level. Always calculate the cumulative dose.
Not necessarily. OSHA allows representative monitoring -- measuring a sample of workers in similar roles and applying those results to the broader group. For jobs with highly variable noise exposure, individual dosimetry is recommended.
dB measures sound pressure level across all frequencies. dBA is A-weighted -- it approximates how the human ear perceives sound by filtering out frequencies the ear is less sensitive to. OSHA requires A-weighted measurements for occupational noise compliance.
Yes. Reducing time any individual spends in a high-noise area is a recognized administrative control. If rotating workers keeps every individual's shift TWA below 85 dBA, the action level is not triggered. OSHA expects this to be genuinely implemented and documented, not just on paper.
Yes. OSHA requires re-monitoring whenever there are significant changes in machinery or production processes that may increase noise levels. If new equipment generates more noise than before, new monitoring is required to determine whether additional employees now meet or exceed the action level.
Soundtrace includes integrated noise monitoring alongside audiometric testing and recordkeeping -- everything you need to assess, manage, and document your entire hearing conservation program.
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