Chapter 5 Noise pollution

1 sources of noise pollution Noise can be either natural such as wind, thunder and movement of water or man made. If all symbols of civilization---from jet planes, vehicles, railway engines to factories generators, construction, machinery, television and radio sets and public address systems have something in common--- it is the noise.

1 sources of noise pollution 1.1 Industrial noise Stamping metal into auto fenders, punching holes into metal plates, riveting plates together, and crushing different materials all produce impact noise; Grinding and drilling metal produce continuous noise. Rapid air motion caused by jets of air, blower, and fans and vibration of equipment also cause noise.

1 sources of noise pollution 1.2 Domestic noise A residential community abounds with its own sources of noise. Loud radio and television, amplified rock music, loud conversation, children’s screams, barking dogs, roosters, air-conditioners, washing machines, kitchen appliances . People are more annoyed by noise in the evening and at night than at any other time.

1 sources of noise pollution 1.3 Traffic noise Traffic noises are generated by a vehicle’s power unit, such as a jet’s engine or a truck’s motor, and from the contact between the tires or wheels and the road or rails. The greatest amount of aircraft noise is produced upon landing and takeoff because more power is used at these times.

1 sources of noise pollution 1.3 Traffic noise Near the airport, noise levels between 85 and 95 dB were recorded with an increase of 20-25 dB during landing and takeoff. Near railway tracks, ambient noise level increases up to 10-20 dB during train movement.

2 Effects of noise pollution 2.1 Hearing loss Hearing threshold ----The intensity of a sound required to just barely hear it is called the hearing threshold . When there is a shift in the hearing threshold such that sounds have to be louder and louder to be heard, we say that there has been a hearing loss.

2 Effects of noise pollution 2.1 Hearing loss (two types ) Acoustic trauma 听觉创伤, is the result of severe damage to the interior structure of the ear caused by a blast or explosion or some other sudden, intense noise. A shift in the hearing threshold that is less severe than an acoustic trauma, but severe enough to produce a stress that impairs hearing.

2 Effects of noise pollution 2.1 Hearing loss Noise causes discomfort at levels of 100 to 120 dB or higher, and levels of 130 to 140 dB cause pain. Hearing loss may occur from sustained exposure at levels lower than those that cause discomfort and pain, usually about 75 to 90 dB. Auditory perception听力 decreases as person ages ---- a phenomenon called presbycusis老年性耳聋 .

2 Effects of noise pollution 2.2 Psychological and physiological effects Noise causes human psychological stress which can lead to such physiological responses as muscle tension, constriction of blood vessels, and an increase in heartbeat rate. These stresses lead to changes in cardiovascular心血管, endocrine内分泌, neurologic神经, and other functions.

2 Effects of noise pollution 2.2 Psychological and physiological effects On the job or in everyday life, noise interferes with the recognition of sound signals, especially speech. There are times when the masking effects of sound can be beneficial. A low-level noise, such as soothing music, in an office provides a background that is not unpleasant and will mask the noise from rustling papers, typewriters, and conversations of others.

2 Effects of noise pollution 2.2 Psychological and physiological effects Rhythmic music is used to stimulate activity. Noise can also interfere with sleep. The type, intensity, or loudness level of the sound, its suddenness, and the fear associated with the sound cause different kinds of psychological stress. Susceptibility to noise that triggers emotional and physiological reaction varies among individuals.

2 Effects of noise pollution 2.2 Psychological and physiological effects Animals show a variety of ill effects from noise: hearing loss, masking of sounds, and behavioral and physiological reactions. The vibration and stress induced in materials by noise lead to fatigue and failure. A sonic boom produced by an airplane traveling faster than the speed of sound is an extreme example.

3 Noise control methods Substitution of a quieter machine design, process, or material may be an easy and effective means of eliminating or reducing a noise problem.

3 Noise control methods If noise cannot be reduced to acceptable levels in industry, personal protection or special design considerations may be necessary: Fitted earplugs; Enclosing or partly enclosing the noisy operations; Using rugs地毯, curtains, and acoustical ceiling materials隔音材料.

3 Noise control methods Community noise such as those produced by transportation, lawn mowers, and construction equipment can be reduced by modifying the noise generator. Other approaches to noise abatement involve land use controls. By providing open space or locating noisy operations remote from residences, the noise source can be separated from the receptor.

Summary Noise is another waste product of civilization----waste energy. Noise can be a health hazard or a serious annoyance. Unlike some environmental problems, the cause of noise is well understood.

Summary General principles of environmental control are easily applied to noise problems: eliminating the source; substituting less noisy equipment and processes; isolating the sources; shielding processes of people; treating sources and transmission paths to suppress noise.