1984.03.14 PC Minutes - Laserfiche WebLink

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.. /- 4f/z-: � Hearing loss will occur in 20 to 25 percent of worker:., exposed to the allowable limit of 90 decibels for eight hour:, (the loudness of street traffic or a heavy-duty.truck). Under the newest federal regulations, employers must est,c�t�i i:shi hearing; conservation programs for all workers regularly ex pbsed to noise levels of 85 decibels or more. Repeated exposure to loud noise destroys the delicate hair cells in the Organ of Corti, a part of the cochlea in the inner ear. These cells are responsible for picking up sound -induced pressure waves and transmitting; them to nerve cells, which in turn carry them to the brain. Sounds follow two paths into the brain. One path carries sound to the auditory center where it is perceived and interpreLe,i. The other goes to an activating -regulating center in the brain, called the reticular formation and then on to the brain centers that turn on the autonomic nervous system. The latter path is responsible for the wide range of non-au::•al. effects of noise because it calls into play the classic fiGht- or-flight response to stress: arousal, increased hear rate ;uld blood pressure, constriction of small blood vessels .in the extremities. redirection of blood flow away from the skin ;IUM _ _di estive organs and to the brain and muscles, muscular cont.raot_io�l,-.- release of stress-related hormones from the adrenal gland.,,____,_. dry mouth, dilated pupils and subjective feelings of tensi,on,�-.__ excitement and anxiety. This stress reaction to sound is believed to be an cvoluLLo,itrI holdover from preindustrial times when loud sounds usually meant trouble-$ roaring lion, falling rock or injured ki.nsifan. The stress response enabled people to survive the danker i,y helping them either to run away or fight. Noise researchers have found that most people get used Lo ,ti sound that they hear often and know is not a cause for alarm, but their internal stress reaction continues unabated. if ,you live near train tracks, after a week or so you mzy no longer be awakened by passing trains. But internal reactions to the noise still occur and iwry eventually accumulate to cause bodily damage. Miller sugg;este6 that people who never become habituated to noise "may be bettt�- off because they tend to avoid noisy environments."