A seven-year review of measured hearing levels in male manual steelworkers with high initial thresholds.

Audiometric records of 449 male manual steelworkers were reviewed to see whether the hearing of men with high initial threshold levels deteriorated more rapidly than that of those men with more normal thresholds when exposed to similar noise levels. Subjects were between 15 and 54 years old at the time of initial examination, and had a repeat audiogram 6-8 years later. They were classified into three occupational noise exposure groups: below 90 dB(A), 90-99 dB(A), and 100 dB(A) or over, without knowledge of their audiometric threshold levels, age, or aural history. Measurements at 0'5, 1, 2, 3, 4 and 6 kHz for the right ear were considered, first as the mean for all six frequencies, then for 0 5, 1 and 2 kHz only, and finally for 6 kHz only. After standardisation for age, it was found that those in the high initial threshold groups deteriorated no faster than the remainder of the series. At the 90-99 dB(A) noise exposure level, x2 tests showed that the differences between the groups, in terms of mean measured hearing loss, were not significant at the 0-05 probability level. The age-standardised mean threshold shifts for the 0-5-6 kHz range of frequencies over the seven-year review period were 7-5, 8'7 and 7'1 dB at a noise exposure level of 100 dB(A) or more, for workers with an initial threshold level of < 12 dB, 12-26 dB and >26 dB respectively; for those exposed to noise of 90-99 dB(A) the corresponding mean shifts were 7'8, 6'8 and 7'3 dB respectively; while for those exposed to noise of less than 90 dB(A) the mean shifts were 6'2, 5-0 and 5-2 dB respectively. There may be a marked and natural reluctance on the part of industrial medical officers to advise men with elevated measured hearing levels to continue to work in noisy environments, partly because there may be little or no margin between current threshold levels and social impairment, and partly because of the fear that those with markedly elevated levels may continue to deteriorate at a faster rate, under similar conditions, than those with more normal levels. I have been unable to discover, from published studies based on reasonable numbers, whether or not those with high initial threshold levels do continue to deteriorate more rapidly. This study was designed to analyse the audiometric records of 449 male manual workers who had a second examination 6-8 years (mean 7 years) after an initial audiogram. *Epidemiologist. Present address: Courage (Central) Ltd., Bridge Street, Reading, Berkshire. Received for publication 22 December 1976 Accepted for publication 3 August 1977 Methods The noise exposure at work of 533 men who had had a second audiometric examination 6-8 years after an initial examination, was reviewed without reference to age or initial or subsequent hearing threshold levels. Thus any errors in the classification of noise exposure experience would be unbiased by such knowledge and would be randomly distributed among subgroups formed by such factors. Eightyfour men had either changed their place of work and noise exposure in the period under review, and were thus unsuitable for inclusion, or were rejected because of uncertainty about their exposure histories, particularly where jobs involved intermittent noise. The remaining 449 subjects were each classified into one of three noise exposure groups: less than 90 dbB(A), 90-99 db(A), or 100 dB(A) or over. All audiograms were made by the same operator, thus obviating one major potential source of error (Howell and Hartley, 1972). Men were between 15 and 54 years of age at the initial audiometric 27 group.bmj.com on June 20, 2017 Published by http://oem.bmj.com/ Downloaded from