Introduction
This topic covers occupational hearing impairment, which in practice means sensorineural hearing loss caused by work exposure, most often to noise. It includes the other physical and chemical causes, the pathogenesis, clinical picture, diagnosis, treatment, medical expertise and prophylaxis. It ends with the health effects of ultrasound (above 20 kHz) and infrasound (roughly 1 to 20 Hz).
Definition and etiology
Occupational hearing impairment is a sensorineural hearing disorder (damage to the cochlea, its nerve or central pathways) that develops after prolonged exposure to hazards above safe levels. It is usually bilateral, slowly progressive and irreversible once the sensory cells are lost.
- Physical factors:
- Noise, the most important cause; risk depends on intensity, frequency content, daily duration and total years of exposure
- Head and ear trauma, including temporal bone fracture, perilymph fistula and barotrauma
- Whole-body and hand-arm vibration, which add to noise injury and may coexist with vibration disease
- Ultrasound above 20 kHz and infrasound, discussed at the end of this note
- Rapid pressure changes (diving, caisson work, unpressurised flight)
- Toxic metals and salts, which are ototoxic and often act together with noise:
- Mercury, lead, arsenic, phosphorus and their compounds
- Organic solvents such as benzene, toluene, styrene, carbon disulfide and trichloroethylene