NIOSH noise exposure limits and OSHA compared
Quick answer
NIOSH recommends a limit of 85 dBA averaged over an 8 hour day, with a 3 decibel exchange rate, so every 3 dB increase cuts the permitted exposure time in half: about 2.5 hours at 90 dBA, 15 minutes at 100 dBA, and roughly 1 second at 130 dBA. OSHA's enforceable limit is different and more permissive, 90 dBA over 8 hours with a 5 decibel exchange rate, which allows about 2 hours at 100 dBA where NIOSH allows only 15 minutes.
NIOSH, the National Institute for Occupational Safety and Health, and OSHA, the Occupational Safety and Health Administration, publish two different noise exposure standards, and quoting one as though it were the other is a genuine, consequential error. NIOSH's recommended exposure limit is 85 dBA over an 8 hour time weighted average, with a 3 decibel exchange rate. OSHA's enforceable permissible exposure limit is 90 dBA over the same 8 hours, but with a 5 decibel exchange rate, which is considerably more permissive at every level above the reference point.
The exchange rate is what does the real work in both standards. It sets how much the permitted exposure time falls for each decibel of increase, and because the decibel scale itself is logarithmic, a smaller exchange rate number means the permitted time falls faster as the level climbs. That is the entire reason the two ladders below diverge so sharply once the level passes about 95 dBA.
NIOSH and OSHA, side by side
NIOSH's reference level is 85 dBA with a 3 dB exchange rate; OSHA's reference level is 90 dBA with a 5 dB exchange rate, and only OSHA's limit is legally enforceable.
| NIOSH (recommended) | OSHA (enforceable) | |
|---|---|---|
| Reference level | 85 dBA | 90 dBA |
| Reference time | 8 hours (480 minutes) | 8 hours (480 minutes) |
| Exchange rate | 3 dB (every 3 dB increase halves the allowed time) | 5 dB (every 5 dB increase halves the allowed time) |
| Status | A recommendation, not enforceable | An enforceable federal limit |
The full exposure ladder, 85 to 130 dBA
At 100 dBA, NIOSH's recommended permissible time is 15 minutes, while OSHA's enforceable limit permits about 2 hours at the same level.
| Level (dBA) | NIOSH permissible time | OSHA permissible time |
|---|---|---|
| 85 | 8 hours | 16 hours |
| 88 | 4 hours | 10.6 hours |
| 91 | 2 hours | 7 hours |
| 94 | 1 hour | 4.6 hours |
| 97 | 30 minutes | 3 hours |
| 100 | 15 minutes | 2 hours |
| 103 | 7.5 minutes | 1.3 hours |
| 106 | 3.8 minutes | 52.2 minutes |
| 109 | 1.9 minutes | 34.5 minutes |
| 112 | 56 seconds | 22.7 minutes |
| 115 | 28 seconds | 15 minutes |
| 118 | 14 seconds | 9.9 minutes |
| 121 | 7 seconds | 6.5 minutes |
| 124 | 4 seconds | 4.3 minutes |
| 127 | 2 seconds | 2.8 minutes |
| 130 | 1 second | 1.9 minutes |
Common questions
- What is the difference between the NIOSH and OSHA noise limits?
- NIOSH recommends 85 dBA over an 8 hour day with a 3 decibel exchange rate; it is a recommendation, not a legal requirement. OSHA's enforceable permissible exposure limit is 90 dBA over the same 8 hours with a 5 decibel exchange rate, which permits substantially longer exposure at the same level. The two are frequently confused, and quoting one as the other misstates what is actually a safe or a legal exposure.
- How long can I safely be around 100 dBA noise?
- Under NIOSH's recommended limit, about 15 minutes over an 8 hour day. Under OSHA's separate, more permissive enforceable limit, about 2 hours over the same day. The two numbers differ by a factor of eight at exactly the same sound level, which is the clearest illustration of how differently their exchange rates behave as the level climbs.
- Why does OSHA allow longer exposure than NIOSH at the same level?
- OSHA uses a 5 decibel exchange rate, meaning the permitted time only halves for every 5 dB increase, while NIOSH uses a 3 decibel exchange rate, halving the permitted time for every 3 dB increase. The smaller the exchange rate number, the faster permitted time falls as the level rises, which is why NIOSH's recommended limit is consistently stricter than OSHA's enforceable one above the reference point.
- What does "8 hour time weighted average" mean?
- It means the reference level, 85 dBA for NIOSH or 90 dBA for OSHA, describes an average sound energy dose spread across a full 8 hour period, not a ceiling that can never be touched for even a moment. A louder level for a shorter time, or a quieter level for longer, can add up to a similar total dose, which is exactly what the exchange rate and the permissible time ladder calculate.
- Is the NIOSH exposure limit legally enforceable?
- No. NIOSH's 85 dBA limit is a recommended exposure limit, published as guidance rather than as a regulation with legal force. OSHA's separate 90 dBA permissible exposure limit is the one that is actually enforceable under federal law. Many workplaces and hearing conservation programs choose to follow the stricter NIOSH recommendation voluntarily, but only OSHA's limit carries a legal requirement.
- What happens if I am exposed to more than one noisy activity in the same day?
- Both standards are built around cumulative exposure over the full day, so time spent at multiple loud activities adds toward the same daily dose rather than each one being evaluated on its own in isolation. The practical response is to use hearing protection during each loud activity individually, rather than trying to track a running total across the day by hand.
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Last updated 2026-09-17.