ISO 1999:1990

Acoustics — Determination of occupational noise exposure and estimation of noise-induced hearing impairment

Prescribes a practical relation for these quanitities expressed as A-weighted noise level in dB and duration of exposure within a normal working week (40 hours) and the percentage of personnel that is to be expected to obtain a raised hearing threshold of 25 dB or more as a result of this exposure, averaged from 500, 1000 and 2000 Hz.