FOOTNOTES

1. Noise-induced hearing loss can develop rapidly in workers exposed to relatively high noise levels on a daily basis. For example, the most susceptible ten percent of a population exposed to daily average unprotected noise levels of 100 dBA could be expected to develop hearing threshold shifts in excess of OSHA's criterion for standard threshold shift before the end of one year. This prediction can be made using the international standard, "Determination of Noise Exposure and Estimation of Noise-Induced Hearing Impairment" (see ISO, in Appendix D). Thus, it may be good practice to provide audiometry twice a year to workers exposed to more than 100 dBA.

2. OSHA defines a standard threshold shift as a change, relative to baseline, of 10 dB or more in the average hearing level at 2000, 3000, and 4000 Hz in either ear. NIOSH defines significant threshold shift as a 15 dB change, relative to baseline, at any of the frequencies 500, 1000, 2000, 3000, 4000, or 6000 Hz, demonstrated on a retest audiogram administered immediately after the audiogram that showed the shift for the same ear and same frequency.

3. OSHA's definition of a standard threshold shift is a change, relative to baseline, of 10 dB or more in the average hearing level at 2000, 3000, and 4000 Hz in either ear. NIOSH's definition of significant threshold shift is a 15 dB change at any of the frequencies 500, 1000, 2000, 3000, 4000, or 6000 Hz, demonstrated on a repeat audiogram for the same ear and same frequency, with the retest being administered immediately after the audiogram that showed the shift as compared to the baseline audiogram.