Tens of millions of Americans, including 12 percent to 15 percent of schoolchildren, have permanent hearing damage caused by everyday noise--
What Causes Hearing Loss - NYTimes.com: ". . . We are born with a fixed number of hair cells; once they are dead, they cannot be replaced, and auditory sensitivity is permanently lost. Usually, sensitivity to high-frequency sounds is first to go, followed by an inability to hear the frequencies of speech. Furthermore, the effects of noise exposure are cumulative, as Robert V. Harrison, an auditory specialist at the University of Toronto, noted recently in The International Journal of Pediatrics. Although we start out with a redundancy of hair cells, with repeated noisy insults, enough are destroyed to impair hearing. Thus, damage to hair cells incurred early in life, as has happened to many rock musicians and rock concert aficionados, can show up in midlife as difficulty understanding speech. Sound volume is measured in decibels (dB), and the level at which noise can cause permanent hearing loss begins at about 85 dB, typical of a hair dryer, food processor or kitchen blender. . . ." (read more at link above)
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