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HARk IOM IWFECTS OF NOISE <br />Exposure to noise can cause temporary physical and psychological <br />responses in humans. The chronic recurrence of these physical <br />reactions has been shown to aggravate headaches, fatigue, diges- <br />tive disorders, heart disease, circulatory and equilibrium dis- <br />orders. Moreover, as a source of stress, noise is a contributory <br />factor in stress - related ailments such as ulcers, high blood <br />pressure and anxiety. <br />Two other harmful effects of noise which are commonly of concern <br />involve speech interference and the prevention or interruption of <br />sleep. Figure 6 illustrates how excessive background noises can <br />reduce the amount and quality of verbal exchange and thereby <br />impact education, family lifestyles, occupational efficiency and <br />the quality of recreation and leisure time. Speech interference <br />begins to occur at about 40 to 45 decibels and becomes severe at <br />about 60 decibels. Background noise levels affect performance <br />and learning processes through distraction, reduced accuracy, <br />increased fatigue, annoyance and irritability, and the inability <br />to concentrate (particularly when complex tasks are involved or <br />in schools where younger children exhibit imprecise speech pat- <br />terns and short concentration spans). <br />Several factors determine whether or not a particular noise event <br />will interfere with or prevent sleep. These factors include the <br />noise level and characteristics, the stage of sleep, the individ- <br />ual's age, motivation to waken, and so forth. Ill or elderly <br />people are particularly susceptible to noise- induced sleep inter- <br />ference, which can occur when intruding noise levels exceed the <br />typical 35 -45 decibel background noise level in bedrooms. Sleep <br />prevention can occur when intruding noise levels exceed 50 dBA. <br />13 <br />