How this calculator works
NIOSH recommends an occupational exposure limit of 85 dBA averaged over eight hours, with exposure duration halved for every 3 dB increase. This calculation applies that equal-energy relation to a steady level. It is not an environmental community-noise limit or a personal hearing-safety guarantee. Daily exposure from multiple activities adds together; impulse noise is not adequately represented by one average level. The tool limits the model to 70-140 dBA, rather than extrapolating indefinitely. The result is an estimate for information only and is not medical advice.
Formula
Time(seconds) = 28,800 × 2^((85 - level_dBA)/3). Level_dBA = 85 - 3 log₂(time/28,800).
Worked example
At 88 dBA the criterion time is 4 hours. At 94 dBA it is 1 hour. A 15-minute duration corresponds to 100 dBA under the same relation.
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Frequently asked questions
Is the criterion time safe for everyone?
No. Susceptibility varies. NIOSH recommends hearing protection when levels exceed 85 dBA regardless of duration.
What if I visit several noisy places?
The daily dose combines the exposure fractions from all periods. A separate fresh allowance does not begin at each location.
Are phone readings sufficient?
Measurement accuracy, calibration, weighting and placement affect the result. Occupational assessment may require suitable instrumentation.