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).