Noise Exposure (TWA) Calculator
A free calculator for OSHA noise dose and the 8-hour time-weighted average (TWA) under 29 CFR 1910.95. You enter each noise level a worker is exposed to and for how long, and it flags the 85 dBA action level and the 90 dBA permissible exposure limit (PEL).
It uses OSHA's 5 dB exchange rate. The allowed time at a level L is T = 8 ÷ 2^((L − 90) ÷ 5) hours, so 90 dBA is allowed for 8 hours. Dose (%) = 100 × the sum of (hours at each level ÷ allowed hours at that level). TWA = 16.61 × log10(dose ÷ 100) + 90. Only levels from 80 to 130 dBA are counted. At or above a TWA of 85 dBA, OSHA requires a hearing conservation program: exposure monitoring, audiometric testing, hearing protectors and training. Above the 90 dBA PEL, feasible engineering or administrative controls are required. It does not replace a dosimetry survey or a qualified industrial hygienist.
How to use it
- Enter a noise level in dBA and how many hours the worker is exposed to it.
- Add a row for each different noise level in the shift.
- Read the noise dose and the 8-hour TWA.
- Check the status against the 85 dBA action level and the 90 dBA PEL.