Industrial audiometry and the otologist.

Abstract

The Hearing Conservation Amendment published by the Occupational Safety and Health Administration (OSHA) in 1983 requires hearing conservation programs to be provided for over 5 million workers whose daily noise exposures exceed 85 dBA time-weighted average. The permissible exposure level is 90 dBA, above which the use of hearing protectors is mandatory. Current policies rely heavily on periodic audiometry to detect early threshold shifts due to inadequate use of hearing protection or to individual variation in susceptibility to noise induced hearing loss (NIHL). Studies including over 1,000 noise exposed workers have shown that audiometry in the industrial setting is less reliable than clinical audiometry. Pure tone averaging markedly reduces test-retest variability and should be incorporated into rules for decision-making based on industrial audiometry. However, at least half of observed shifts are spurious. In addition, aging is an important confounding variable; in our data, about half of the population mean threshold shift seen was attributable to aging. Thus, only a minority of threshold shifts seen in industrial audiometry are due to NIHL. The large number of "false positive" shifts will inevitably eventually have the effect of a de facto lowering of the permissible exposure level to 85 dBA. Otologic referral and major administrative action should be reserved for large or repeated threshold shifts. OSHA does not specify rules for otologic referral, but the criteria recommended by the American Academy of Otolaryngology-Head and Neck Surgery are reasonable and should be supported. The necessity for otologic evaluation in the differential diagnosis of NIHL from other entities (particularly baseline audiometric abnormalities) is not universally appreciated; otolaryngologists need to educate their medical and nonmedical colleagues about this.