By Rowland Benjamin

Noise can have a negative effect on humans, domestic and wild animals, ecological systems, buildings and other structures.

Effects of noise on humans

Different individuals have different susceptibility to noise. Men and blue-eyed people have the greatest sensitivity to noise and are the most susceptible to noise fatigue and hearing loss. Hearing loss and deafness can occur from a single very loud noise or as a result of long-term exposure.

a) Auditory effects interfering with hearing; auditory fatigue and deafness

b) Non-auditory effects interfering with social behaviour; problems with communications, sleep, recreation, mental equilibrium (peace), and the ability to concentrate at work

c) Physiological effects affecting biological functions; anxiety, neurosis, insomnia, dizziness, nausea, fatigue, visual symptoms, hypertension, cardiovascular symptoms, liver changes, nervous symptoms, changes in skin, fast irregular heart beats (tachycardia).

d) Endocrine and hormonal changes relating to stress and noise levels. i.e. raised adrenaline and cholesterol. Noise causes blood vessels to close cutting down blood supply to the fingers and toes. Respiratory changes occur due to noise.

e) Psychological effects; physical and mental fatigue, loss of concentration, lower efficiency, reduced output, absenteeism, higher rates of accidents, behavioural changes, errors at work, loss of sleep, psychosomatic disorders, diseases related to stress, mental illness, aggravation of existing stress problems and mental illness, neurotic effects, rage anger, crime.

Generally noise raises our blood pressure, heart rate and blood cholesterol level, causes constriction of blood vessels, tension, irritability, fatigue and nervous exhaustion, and affects our relaxation and sleep.

Brief noise exposure may result in temporary fatigue and ringing in the ears. This is called a Temporary Threshold Shift (TTS).

Longer noise exposure may result in permanent hearing loss. This is called Permanent Threshold Shift (PTS).

The longer the noise exposure the longer the recovery period of a TTS will be. A change from a TTS to a PTS depends on the noise level and the individual's susceptibility to noise.

Initial exposure to loud noise usually results in an elevation in the threshold of hearing of the higher frequencies. Depending on the loudness and the duration of the noise hearing will return to normal if the person has a period away from the noise. For example it will take 36 hours to recover from a noise level between 1000 and 2000 Hz at 100 dB for 90 minutes.

PTS starts at around 4 kHz and spreads into neighbouring frequencies. People become aware of hearing loss when it enters the lower frequencies i.e. 2-3 kHz. For example people become unable to hear whispered conversation. As it progresses some words become indistinct.

Acoustic trauma is the result of very short bursts of loud noise (more than 150 dB) such as from an explosion at a mine site or war zone.

Characteristics

Intensity (louder is more annoying)

Frequency (higher is more annoying)

Duration (longer is more annoying)

Tone

Localisation

Distance

Information content (meaningful information is generally less irritating than pure noise)

Rhythm.

Environmental factors - neighbourhood noise is less tolerated in quieter rural areas than in city areas.

Time of day or night - noise is less tolerated at night.

Seasons of the year - noise is more annoying during summer when windows are open.

Individual differences - some people are more tolerant of noise than others.

Effects of noise on wildlife

• Reduced migration of birds and other animals.

• Loss of food habitats if animals are driven away.

• Animals in city zoos tend to become lethargic and their health deteriorates.

• Animals tend not to reproduce, which threatens their survival.

• Other effects include duodenal ulcers, atrophy of the thymus gland, and changes to adrenal glands.

Effects of noise on structures

Physical effects from noise include: vibration to buildings, damage to glass windows, plaster cracking, damage to building foundations. Jet aircraft have damaged roads and buildings.

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