How long can you run a loud machine before you damage your hearing? US workplace rules answer that with a table: 8 hours at 90 dBA, halving for every 5 dB louder, down to 15 minutes at 115 dBA. The government’s own research agency, NIOSH, recommends a stricter limit: 8 hours at 85 dBA, halving every 3 dB. This chart gives the allowed time at each sound level under both, and the calculator works out your daily noise dose when you spend part of the day at different levels, which is how a shop day usually goes.
Noise exposure chart: permissible time per day
| Sound level | OSHA limit (90 dBA, 5 dB rule) | NIOSH recommended limit (85 dBA, 3 dB rule) | Note |
|---|---|---|---|
| 80 dBA | 32 h | 25 h | |
| 82 dBA | 24 h | 16 h | |
| 85 dBA | 16 h | 8.0 h | |
| 88 dBA | 11 h | 4.0 h | |
| 90 dBA | 8.0 h | 2.5 h | in Table G-16 |
| 92 dBA | 6.1 h | 1.6 h | in Table G-16 |
| 95 dBA | 4.0 h | 48 min | in Table G-16 |
| 97 dBA | 3.0 h | 30 min | in Table G-16 |
| 100 dBA | 2.0 h | 15 min | in Table G-16 |
| 102 dBA | 1.5 h | 9 min | in Table G-16 |
| 105 dBA | 1.0 h | 5 min | in Table G-16 |
| 110 dBA | 30 min | 1 min | in Table G-16 |
| 115 dBA | 15 min | 28 s | in Table G-16 |
Daily noise dose calculator
The dose adds up the fraction of the allowed time you spend at each level: D = 100 × (C1/T1 + C2/T2 + …), where C is the hours at a level and T the allowed hours at that level. 100% is the limit. OSHA converts a dose to an 8-hour time-weighted average with TWA = 16.61 log10(D/100) + 90.
What the OSHA rules require
- Permissible exposure: no more than the Table G-16 levels (8 h at 90 dBA … 15 min at 115 dBA). Above them, employers must use engineering or administrative controls first and hearing protection if those are not enough (1910.95(a)-(b)).
- Action level, 85 dBA (a 50% dose): employers must run a hearing conservation program: noise monitoring, free hearing protectors, annual hearing tests (audiograms) and training (1910.95(c)-(k)).
- Impact noise: should not exceed 140 dB peak (1910.95(b)(1)).
- Construction: the same permissible levels apply on construction sites (1926.52, Table D-2), with hearing protection under 1926.101.
In a home workshop
Nobody enforces these limits in a garage, but the ear does not know the difference. Many routers, planers, table saws, chop saws and shop vacuums are loud enough that the NIOSH limit is reached in well under an hour. Measure your own machines with a sound level meter (NIOSH publishes a free sound level meter app for phones), wear earplugs or earmuffs rated for the job, and remember that the dose adds up across a day. Ringing in the ears after a session is a sign the dose was too high.
Why the two limits differ
The OSHA limit dates from 1971 and uses a 5 dB exchange rate: each 5 dB doubles the sound energy’s effect on the allowed time. NIOSH’s 1998 criteria document found that a 3 dB exchange rate, which follows the physics of sound energy (every 3 dB is twice the energy), and an 85 dBA limit better protect against hearing loss over a working life; it put the excess risk of hearing impairment after 40 years at 85 dBA at about 8%, which is why it calls 85 dBA a limit rather than a safe level. The difference becomes large at high levels: at 100 dBA OSHA allows 2 hours, NIOSH 15 minutes.
Frequently asked questions
What is the OSHA noise limit?
90 dBA averaged over 8 hours (a 100% dose), with the allowed time halving for every 5 dB above that. At 85 dBA averaged over 8 hours employers must start a hearing conservation program.
How long can you be exposed to 100 dB?
2 hours a day under OSHA rules; 15 minutes under the NIOSH recommended limit.
Is 85 dB safe for 8 hours?
It is the NIOSH recommended limit for 8 hours, and the OSHA action level. NIOSH estimates that even at that level some workers will lose hearing over a career, so hearing protection is a sensible precaution.
What is the 3 dB exchange rate?
The rule that every 3 dB increase halves the allowed time, because 3 dB is twice the sound energy. NIOSH uses it; OSHA uses 5 dB.
Sources
- 29 CFR 1910.95, Occupational noise exposure (Table G-16; Appendix A dose and TWA formulas), and 29 CFR 1926.52 (Table D-2). US federal regulations, read at law.cornell.edu (text cached 24 October 2026).
- National Institute for Occupational Safety and Health. Criteria for a Recommended Standard: Occupational Noise Exposure, Revised Criteria 1998. DHHS (NIOSH) Publication No. 98-126. A US Government work.
Last reviewed: 24 October 2026. Numbers in the tables are our arithmetic from the sources listed; code sections are summarised, not quoted. How we check our work: methodology and corrections. Spotted an error? Please let us know.