ASA 127th Meeting M.I.T. 1994 June 6-10

2pNS1. Z24-X-2 forty years later.

W. Dixon Ward

Dept. of Otolaryngol., Univ. of Minnesota, 2001 Sixth St. S.E., Minneapolis, MN 55455

In 1954, Exploratory Subcommittee Z24-X-2 of the American Standards Association issued a report entitled ``The Relations of Hearing Loss to Noise Exposure'' in which the first attempt was made to integrate the existing evidence concerning how exposure to industrial noise produced hearing loss. Although the subcommittee members were fully aware that limits of exposure would ultimately depend as much on political (social, monetary, and legal) considerations as on scientific evidence, it was judged worthwhile to try to provide as firm a scientific basis as possible for setting those limits. Considering the meager amount of reliable audiometric data that existed then, it is amazing how well their conclusions have been substantiated by subsequent evidence, even though those conclusions have sometimes been overridden by political forces. Present knowledge will be compared with some of the Report's main aspects: the biological baseline; age corrections; additivity of noise-induced loss and age effect; individual susceptibility; contamination of data by temporary threshold shift; susceptibility of the already-damaged ear; and the inadequacy of total energy as a measure of exposure. Progress toward solution of a list of ``unsolved problems'' will also be summarized.