The hearing mechanism, being very sensitive to sound stimuli, is also very susceptible to injury. Many workplaces are hazardous to hearing health due to exposure to (1) noise, (2) physical trauma, and/or (3) toxic materials. Each of these elements comprises a separate subchapter in this review. The majority of the review is focused on noise damage as it is far and away the most prevalent type of occupational auditory injury. The final section discusses some medicolegal aspects of occupational hearing loss.
Occupational hearing loss is noise-induced hearing loss (NIHL) due to chronic overexposure to hazardous levels of noise in the workplace. NIHL may also occur from nonworkplace (eg, recreational) noise overexposure. Because the pattern of hearing loss is essentially the same, allocating occupational versus recreational noise damage remains a challenge. NIHL represents about 15% of the total societal burden of hearing loss among American adults. People with occupational NIHL represent approximately half that total, or about 2.5 million adults; another 2 million suffer NIHLs from nonoccupational or leisure activities such as hunting and target shooting, listening to loud music, or engaging in noisy hobbies or recreational activities.
In spite of considerable attention aimed at limiting noise overexposure–through wearing of personal hearing protection, engineered reductions in noise levels, and industrial hygiene measures–loss of hearing still occurs. The additive effect of aging upon the auditory system complicates the evaluative process even if serial examinations are available. Traumatic hearing loss in the military–both NIHL and acoustic trauma–is an increasing source of disability and compensation in the Veteran's administration.
The goal of this review is to provide guidance for physicians who evaluate and treat people with suspected NIHL. We will focus primarily on diagnosis and evaluation, with updated information on prevention and remediation.
Noise may be defined as unwanted, undesirable, or excessively loud sounds as experienced by an individual. The effects of chronic noise exposure vary with the characteristics of the sound: damage is related to intensity, exposure duration, and exposure pattern (continuous exposures are more damaging than interrupted exposures for the same overall duration and intensity). Daily exposure to hazardous noise over years produces the characteristic loss of high-frequency sensitivity in the 4–6 kHz range (Noise notch–See Figure 58–1).
Relative consonant and vowels sounds on an audiogram are a function of frequency.
A less common but potentially more devastating form of occupational hearing loss results from acoustic trauma, wherein high-intensity impulse noises (eg, explosions) physically disrupt any or all parts of the ear resulting in immediate and irreversible hearing loss. Blast damage generally follows energy levels of >140 dB on the A scale (dBA), and increases as the intensity increases. The damage from the improvised explosive devices (IED) being used in the current military conflicts is often total owing to the ...