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Noise Intensity Level and Duration of Exposure

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.

Noise Intensity Time Exchange
Length of
Exposure
NIOSH
(3 dB
Exchange 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

Examples:

  • 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).