Introduction
Occupational hearing loss is an increasingly prevalent occupational condition and occurs
across many countries. It can be induced by several factors in workplace, such as noise, organic
solvents, and other ototoxic substances. [1]. Noise is a common occupational hazard worldwide,
and continues to be one of the largest causes of hearing loss [2,3]. In the United States,
approximately 30 million people are occupationally exposed to hazardous noise every year. In
2009 alone, the US Bureau of Labor Statistics reported more than 21,000 hearing loss cases [4].
According to an analysis of adult hearing loss, China, Mongolia and South Korea have the
highest proportion of sensorineural hearing loss attributable to occupational noise exposure all
over the world [2].