The risk of noise to hearing is based upon two factors: noise intensity level (loudness) and theduration of exposure. Noise induced hearing loss has been found to occur with repeated 8 hour exposures of 85 dBA, but shorter exposures to greater levels can be equally as dangerous.
The chart below identifies equivalent noise exposures. Based upon the equal energy law, a doubling of sound energy will result in a 3 dB increase in measured sound level. This 3 dB exchange rate is the recommended method for evaluating the risk of noise exposure. OSHA action levels (which trigger required inclusion in a hearing conservation program) are based upon a 5 dB exchange rate.
Noise Intensity Time Exchange Length of
16 hours 82 80 8 hours 85 85 4 hours 88 90 2 hours 91 95 1 hour 94 100 30 min 97 105 15 min 100 110 7.5 min 103 115 3.75 min 106 120
- For determining risk, a 4 hour exposure to 88 dBA is equal to an 8 hour exposure to 85 dBA (3 dB exchange).
- For purposes of OSHA compliance, a 4 hour 90 dBA exposure is equivalent to the required action level of 85 dBA Time Weighted Average (TWA).