A field study on occupational deafness.

Abstract

Fosbroke (1830-31) described deafness in black smiths since when there have been many investi gations of deafness caused by noise in industry. But there are still many questions of practical importance to the industrial medical officer as yet unanswered. He needs to know how loud a noise must be to cause deafnesss, how to measure noise, and the methods of protecting the workman's hearing where the noise is very loud. These questions cannot be answered simply as there are many factors to be considered, the more important of which are the duration of exposure to noise, its loudness when it reaches the ear, and the suscepti bility of the ear to damage (Perlman, 1945). If a group of men have worked in a loud but steady noise for the same number of years the effects on the hearing of the men will vary widely. Thus it is not possible to give a precise level of noise above which hearing will be impaired. Bunch (1942) and MacLaren and Chaney (1947) agree that noise of an average overall value of 70 dbf above a standard reference intensity of 0-0002 dyne/sq. cm. is innocuous and that a noise of 100 db or more greatly increases the incidence of impaired hearing. The assessment of the hearing loss produced by acoustic trauma requires a method which will exclude deafness due to other causes. Larsen (1939), Fowler (1928), Bunch (1937), Perlman (1945), Nussdorfer (1942), Maclaren and Chaney (1947), and Weiss (1947) agree that a circumscribed loss of hearing in the high tones, 3,000-6,000 c.p.s., the so-called C5 dip, is to a certain extent typical of traumatic deafness. It is known, however, that this circumscribed hearing loss may be due to other