Short answer: NIOSH recommends no more than 85 dB(A) averaged over 8 hours, halving the allowed time for every 3 dB more (100 dB = 15 minutes). OSHA’s legal US limit is 90 dB(A) for 8 hours with a 5 dB exchange rate (100 dB = 2 hours), and employers must run a hearing conservation programme once workers reach an 85 dB(A) average.
This guide compares the two US standards side by side, with the full exposure-time chart, the exchange rate explained, OSHA’s action level and hearing conservation rules, and how the EU, UK and WHO limits compare. To calculate your own daily dose from several activities, use the noise exposure calculator.
NIOSH vs OSHA: Key Differences
| NIOSH REL | OSHA PEL | |
|---|---|---|
| What it is | Recommended exposure limit (research-based guidance) | Permissible exposure limit (US federal law, 29 CFR 1910.95) |
| 8-hour limit | 85 dB(A) | 90 dB(A) |
| Exchange rate | 3 dB | 5 dB |
| Levels included in the dose | 80 dB(A) and above | 90 dB(A) and above for the PEL; 80 dB(A) and above for the action level |
| Time allowed at 100 dB(A) | 15 minutes | 2 hours |
| Ceiling | No exposure above 140 dB peak | No continuous exposure above 115 dB(A); impulse noise below 140 dB peak |
| Year set | 1998 criteria document | 1971 (general industry), amended 1983 |
| Estimated excess risk of hearing loss over a working life | 8% at 85 dB(A) | About 25% at 90 dB(A) (NIOSH estimate) |
Noise Exposure Time Limits Chart
| Level dB(A) | NIOSH (3 dB) | OSHA (5 dB) | Note |
|---|---|---|---|
| 85 | 8 h | 16 h | OSHA action level (8-h average) |
| 88 | 4 h | 10 h 33 min | |
| 90 | 2 h 31 min | 8 h | OSHA PEL |
| 91 | 2 h | 6 h 58 min | |
| 94 | 1 h | 4 h 36 min | |
| 95 | 48 min | 4 h | |
| 97 | 30 min | 3 h 2 min | |
| 100 | 15 min | 2 h | |
| 103 | 7.5 min | 1 h 19 min | |
| 105 | 4.7 min | 1 h | |
| 110 | 1.5 min | 30 min | |
| 115 | 28 s | 15 min | OSHA maximum for continuous noise |
Times are the total allowed per day at that level. For typical sources at each level see the decibel chart, and for levels below 85 dB the safe noise levels chart. Real days mix several levels, so the fractions are added up as a dose; see “How Noise Dose Works” below.
The Exchange Rate Explained
The exchange rate is how many decibels halve the allowed time. NIOSH uses 3 dB because every 3 dB doubles the sound energy: 88 dB for 4 hours delivers the same energy as 85 dB for 8 hours (the equal-energy principle, also used in the EU and by the WHO). OSHA’s 5 dB rule assumes that noise with breaks is less harmful, and allows much more time at high levels: at 100 dB(A), 2 hours instead of 15 minutes. Most hearing scientists consider the 3 dB rule more protective. The maths behind it is in the logarithmic decibel scale guide.
How Noise Dose Works
- Dose = 100 × (C₁/T₁ + C₂/T₂ + …), where C is the time at a level and T the allowed time at that level. 100% is the limit.
- NIOSH TWA = 10 × log10(D/100) + 85; OSHA TWA = 16.61 × log10(D/100) + 90.
- Example: 2 hours at 90 dB(A) + 4 hours at 85 dB(A) = 129% of the NIOSH limit, but only 25% of the OSHA PEL, and exactly the 50% OSHA action-level dose that requires a hearing conservation programme.
OSHA Action Level and Hearing Conservation Programmes
When a worker’s 8-hour time-weighted average reaches 85 dB(A) (a 50% dose), OSHA requires a hearing conservation programme, including:
- noise monitoring to identify exposed workers;
- a baseline audiogram and annual hearing tests (a home screening such as our online hearing test is no substitute), with follow-up of any standard threshold shift (an average change of 10 dB or more at 2, 3 and 4 kHz);
- hearing protectors made available free of charge, and required for workers above the PEL or with a threshold shift;
- annual training, and records of exposure measurements and audiograms.
Above the PEL, employers must first try engineering or administrative controls (quieter machines, enclosures, rotating staff) before relying on hearing protection. How much protectors really reduce noise is explained in the calculator’s NRR section.
EU, UK and WHO Limits Compared
| Standard | Daily limit | Exchange rate | Other values |
|---|---|---|---|
| EU Directive 2003/10/EC and UK Control of Noise at Work Regulations 2005 | Action values 80 and 85 dB(A); limit 87 dB(A) including hearing protection | 3 dB | Peak action values 135 and 137 dB(C); limit 140 dB(C) (why dB(C)) |
| NIOSH (US, recommended) | 85 dB(A) | 3 dB | 140 dB peak |
| OSHA (US, law) | 90 dB(A); action level 85 dB(A) | 5 dB | 115 dB(A) maximum; 140 dB peak |
| WHO / ITU safe listening (leisure) | 80 dB for 40 hours a week (adults); 75 dB for 40 hours a week (children) | 3 dB | Venues: 100 dB LAeq over 15 minutes |
Which Standard Should You Follow?
Employers in the US must meet OSHA as the legal minimum, but following NIOSH protects far more workers and is recommended by hearing professionals. Individuals checking their own work, hobbies or music should use the NIOSH (or WHO weekly) figures. In Europe and the UK, the national regulations based on the EU directive apply. Whatever the rule, measuring is the first step; see how to measure decibels, and use dB(A) (why dBA).
Measuring for Compliance
Formal assessments use personal dosimeters or Class 1/Class 2 sound level meters (see the difference). A phone calibrated against a known source and running the free sound decibel meter, or a day-long log with the noise monitor, is a good way to screen whether a workplace or hobby is likely to be above the limits and needs a proper survey.
Frequently Asked Questions
Is 85 dB dangerous?
Not in short bursts. 85 dB(A) for 8 hours a day is the NIOSH limit, and years at that level cause measurable hearing loss in a minority of workers.
Why is OSHA’s limit higher than NIOSH’s?
OSHA’s rule dates from 1971 and balances protection with feasibility; NIOSH’s 1998 recommendation is based on newer risk data and the equal-energy principle.
Does OSHA require hearing protection at 85 dB?
At an 85 dB(A) 8-hour average, protectors must be made available; they are mandatory above 90 dB(A) or after a standard threshold shift.
How long can you be exposed to 100 dB?
About 15 minutes a day by NIOSH, 2 hours by OSHA, and about 24 minutes a week under the WHO safe listening allowance.