The risk of noise to hearing is based upon two factors: noise intensity level (loudness) and the duration 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.
Length of Exposure | NIOSH(3 dBExchange Rate) | OSHA(5 dB Exchange Rate) |
---|---|---|
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 |