How noise damages hearing
Loud sound overstimulates the hair cells of the inner ear. With enough energy, they are damaged or die, and they do not grow back. Noise-induced hearing loss builds up slowly and without pain, often first as ringing in the ears (tinnitus) or difficulty following conversations in noisy rooms.
The risk depends on both the sound level and the duration. Decibels are logarithmic: every 3 dB increase doubles the sound energy, so the safe exposure time is cut in half.
The NIOSH and OSHA limits
- NIOSH recommendation: 85 dBA for 8 hours, with a 3 dB exchange rate. Safe time = 8 h ÷ 2^((level − 85) ÷ 3).
- OSHA legal limit for workplaces: 90 dBA for 8 hours, with a 5 dB exchange rate. Employers must also run a hearing conservation program from 85 dBA.
The NIOSH limit is more protective and is the one hearing specialists recommend for everyone, at work or at play.
Worked example
You spend 4 hours at 91 dBA, about the level of a gas lawn mower or a loud workshop.
- Safe time under NIOSH: 8 ÷ 2^((91 − 85) ÷ 3) = 8 ÷ 4 = 2 hours.
- Daily dose: 4 ÷ 2 = 200% of the recommended limit.
- 8-hour equivalent level: 91 + 10 × log₁₀(4 ÷ 8) = 88 dBA.
- OSHA permissible time: about 7 hours, so this exposure is legal at work but still harmful.
Typical sound levels
| Sound | Level (dBA) | Safe daily time (NIOSH) |
|---|---|---|
| Normal conversation | 60 | No limit |
| Busy city traffic | 85 | 8 hours |
| Lawn mower, power tools | 90 to 95 | 2.5 hours to 48 minutes |
| Motorcycle, subway | 95 to 100 | 48 to 15 minutes |
| Rock concert, nightclub | 105 to 110 | 5 minutes to under 2 minutes |
| Siren at close range | 120 | Under 10 seconds |
Protecting your hearing
- Turn it down: keep headphones at 60% of maximum volume or less, and use the listening exposure tools built into many phones.
- Move away: doubling your distance from a source lowers the level by about 6 dB outdoors.
- Wear earplugs or earmuffs: foam earplugs, properly inserted, cut exposure by about 15 to 30 dB. High-fidelity musician earplugs keep music clear.
- Give your ears a break: after a loud event, allow quiet time to recover.
Use a sound level meter app for a rough reading. Have your hearing tested if you notice ringing, muffled sound or trouble understanding speech.
This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.