OSHA's permissible exposure limit for noise is 90 dBA as an 8-hour time-weighted average, using a 5 dB exchange rate. NIOSH recommends 85 dBA over 8 hours with a 3 dB exchange rate. Both numbers are real, only one is enforceable — and the gap between them is far bigger than 5 decibels once you work through the allowed exposure times.
Two limits, two purposes
| OSHA PEL | OSHA action level | NIOSH REL | |
|---|---|---|---|
| 8-hour level | 90 dBA | 85 dBA | 85 dBA |
| Exchange rate | 5 dB | 5 dB | 3 dB |
| Legal status | Enforceable limit | Enforceable trigger | Recommendation |
| What it triggers | Controls required; protection must be worn | Hearing conservation program | Best-practice target for controls |
| Where it is written | 1910.95 Table G-16; 1926.52 Table D-2 | 1910.95(c)(1) | NIOSH 1998 criteria document |
OSHA states it plainly on its own noise page: "OSHA's permissible exposure limit (PEL) is 90 dBA for all workers for an 8 hour day. The OSHA standard uses a 5 dBA exchange rate." And about NIOSH: "NIOSH has recommended that all worker exposures to noise should be controlled below a level equivalent to 85 dBA for eight hours", with "a 3 dBA exchange rate".
Why the exchange rate matters more than the limit
The exchange rate is how many decibels of increase halve the allowed time. Five decibels versus three sounds like a technicality until you put both tables side by side:
| Sound level | OSHA (5 dB) | NIOSH (3 dB) |
|---|---|---|
| 85 dBA | 16 hours | 8 hours |
| 90 dBA | 8 hours | 2 h 30 min |
| 95 dBA | 4 hours | 47 minutes |
| 100 dBA | 2 hours | 15 minutes |
| 105 dBA | 1 hour | 5 minutes |
| 110 dBA | 30 minutes | 1.5 minutes |
| 115 dBA | 15 minutes | 28 seconds |
The OSHA column is Table G-16 of 1910.95 (identical to Table D-2 of 1926.52). The NIOSH column comes from the same arithmetic the 3 dB rule implies: T = 8 ÷ 2(L − 85)/3 hours. A chop saw at 100 dBA is a two-hour job under OSHA and a fifteen-minute job under NIOSH — same saw, same ears.
Neither table is how a real day works, because a real day is a mix of levels. That is what a dose calculation is for: our free noise exposure TWA calculator adds up the time spent at each level and returns the OSHA dose, the 8-hour TWA, and the NIOSH equivalent for comparison.
What crossing 85 dBA obliges you to do
In general industry, an 8-hour TWA at or above 85 dBA — the action level — requires "a continuing, effective hearing conservation program" under 1910.95(c)(1). In practice that means five things:
- Monitoring — 1910.95(d): a program that identifies who is exposed at or above the action level and produces data good enough to select hearing protectors. Employees may observe the measurements.
- Audiometric testing — 1910.95(g): a baseline audiogram and annual tests, at no cost, for every employee at or above the action level.
- Hearing protectors — 1910.95(i): made available at no cost to every employee at or above 85 dBA, with a choice of at least one type of plug and one type of muff, and actually worn above the PEL or after a standard threshold shift.
- Training — 1910.95(k): annual, covering the effects of noise, the protectors and the audiometric program.
- Records — 1910.95(m): exposure measurements for two years, audiometric records for the duration of employment.
Above the 90 dBA PEL, 1910.95(b)(1) requires feasible administrative or engineering controls first — hearing protection is what you use when those controls have not brought the level down, not instead of trying.
Construction plays by a shorter rule
Construction sites fall under 29 CFR 1926.52, not 1910.95. The permissible table is the same — 90 dBA for 8 hours, 5 dB exchange, down to 115 dBA for 15 minutes — and 1926.52(b) requires feasible administrative or engineering controls when it is exceeded, with hearing protection under 1926.52(e) if those controls fall short. 1926.52(d)(1) then requires "a continuing, effective hearing conservation program" wherever the levels in the table are exceeded.
What construction does not have is the detailed 85 dBA machinery of 1910.95 — the baseline audiogram, the annual test, the standard threshold shift follow-up. That is a real gap, and it is one of the places where State Plan states have gone further than federal OSHA. Check your state rule before assuming the federal minimum is the whole story.
The NRR on the package is not what reaches the ear
A hearing protector's Noise Reduction Rating comes from a laboratory fit on trained subjects. Real ears, hard hats, safety glasses and a rushed fit do worse. OSHA accounts for that in two steps:
- Appendix B to 1910.95: when the noise is measured in dBA, subtract 7 from the NRR before subtracting it from the exposure. A 33 NRR plug becomes 26 dB of assumed protection.
- OSHA's 50% derating for judging whether a hearing conservation program is adequate: (NRR − 7) ÷ 2. That same 33 NRR plug is now worth 13 dB.
- Dual protection: plugs plus muffs do not add their NRRs. OSHA allows 5 dB to be added to the NRR of the more protective device.
Run the numbers for your own protector with the NRR derating calculator — it shows the Appendix B result, the 50% derated result and the NIOSH derating by protector type side by side. If the derated result still sits above 85 dBA, the answer is not a bigger plug; it is a quieter process.
Bottom line
- 90 dBA over 8 hours is the enforceable OSHA limit, in both general industry and construction.
- 85 dBA over 8 hours is the action level that turns on a hearing conservation program in general industry — and the level NIOSH recommends nobody exceed.
- The 5 dB versus 3 dB exchange rate is the real difference: at 100 dBA, OSHA allows 2 hours and NIOSH allows 15 minutes.
- Controls come before protection. Hearing protection is the last line, and it delivers roughly half its label once derated.
- Noise-induced hearing loss is permanent and painless while it happens. The dose is what matters — measure it, do not guess it.