ISO estimations of noise-induced hearing impairment.

Abstract

The 1990 (second) edition of ISO 1999, ‘‘Acoustics−Determination of Occupational Noise Exposure and Estimation of Noise-Induced Hearing Impairment’’ purports to provide a more accurate and generalized model of the relationship between hearing threshold level and occupational noise exposure than the 1971 (first) edition. While the 1990 standard states that hearing risk statistics are in agreement with those in the 1971 standard, this is not the case. ISO 1999 (1990) consistently underestimates hearing risk by about 10% at 90 and 95 dBA when compared to ISO 1999 (1971). While ISO 1999 (1990) is based upon Burns and Robinson (1970) and Passchier-Vermeer (1968) noise and hearing study databases, the mathematical expression of these data in ISO 1999 (1990) underestimates hearing threshold levels for these databases on average by more than 2 dB; a similar comparison to the NIOSH (1972) database shows that ISO 1999 (1990) underestimates hearing threshold levels by an average of 4.5 dB. Using the hearing threshold level index recommended by NIOSH to compute hearing risk, ISO 1999 (1990) underestimates risk for retirement age populations by an average of 12% when compared to Burns and Robinson, Passchier-Vermeer, and NIOSH databases. Further comparison of this new standard formulation to the original data upon which it is based, is recommended.