Perennially chaotic Dhaka streets
Sound is one of many forms of expression and a very important aspect of human life. It can, however, be pleasant or unpleasant. Whether sound is as pleasant as music or as unpleasant as noise depends on its intensity, duration, rhythm and mood of the person. But when intensity goes beyond what is pleasant, it becomes a problem, and hence, a pollutant.
Noise pollution is a plague of modern society from which there is virtually no escape, no matter where we are – in our homes or gardens, on our streets, inside our cars, at theatres or concerts, social events, restaurants, parks or in other public places. Like second-hand smoke, noise has become an unwanted airborne pollutant produced by others and imposed on us without our consent, often against our will.
The unit used to gauge the loudness or sound intensity is decibel (dB). Decibel is one-tenth of a bel (B). The bel (B) measures the ratio of one intensity or power of sound to the intensity or power of the reference sound in a logarithmic scale (log to the base of 10). After that, bel is converted to dB scale by multiplying by 10. The reference level of sound intensity is 1 and hence its dB value is 0, which is taken as the threshold of hearing. A sound 10 times as loud as the reference level has a dB value of 10. A 20 dB is 100 times as loud as the threshold of hearing, 30 dB is 1000 times, and so on. The maximum loudness humans can be subjected to, after which sound can be felt rather than heard, is approximately 120 dB. This is known as the threshold of pain.
Among the many sources of outdoor noise pollution, automobiles are the worst offenders in the western world, followed closely by trucks, buses, motorcycles and low-flying airplanes. Construction equipment, such as jackhammers, compressors and bulldozers, also contribute substantially to noise pollution. Noise levels of these sources range from 50 dB to 120 dB. But in Bangladesh, high dB speakers at the top of mosques are the worst offenders. In some residential places close to the mosques, noise levels exceed 120 dB or 130 dB quite regularly.
Those living within 600 metres of an airport are exposed to 100-120 dB of noise from jet planes taking off. At 1,500 metres away, the level drops to 80 dB. A car cruising at 100 kmph, 80 metres from the pavement’s edge would produce 75 dB. Because of the logarithmic nature of decibel, adding sound intensity from two cars would increase the level by 3 dB; three cars would augment the level by 4.8, and so on.
Some household appliances, such as dishwasher, food blender, air conditioner and vacuum cleaner, are annoyingly loud – 70 to 100 dB. Depending on the distance from the source, sound from living room audio and video systems could be near 80 dB.
In Dhaka, irrespective of where you live, the noise intensity level is very close to the threshold of pain. Most of it is due to the religious cacophony and noise produced by the horns of vehicles plying on the roads, highways, byways and lanes of the city. Although noise is a controllable pollution, government of Bangladesh has done very little to alleviate the suffering of its citizens from this pestilence.
Hearing damage from loud noise depends on the decibel level, length of exposure and distance from the source. According to the US Occupational Safety and Health Administration, if you are exposed to 95 dB and above for four hours a day over a long period, you will slowly start to lose your hearing ability. As the damage from noise exposure is usually gradual, you might not notice hearing loss until it becomes acute.
Damage from loud noise can be temporary or permanent, depending on whether the organs of Corti, the receptor organs in the inner ear, are impaired or destroyed. In the extreme case, exposure to 150 dB would rupture the eardrum. Less intense, but severe noise can interfere with cellular processes in the organs that cause their eventual breakdown. Unfortunately, the cells of these organs do not regenerate.
Generally, younger persons are more tolerant of loud noise than older persons because their protective mechanisms are more effective. This tolerance does not necessarily make them immune to adverse effects from loud noise. For example, blood tests done on children living near airports in Munich, Germany reveal significantly higher levels of adrenaline and cortisol – the body’s stress hormones, than children living in quieter neighbourhoods. The increase in cortisol adds to the risk of having a heart attack or stroke later in life. Similar impacts have been documented among adults near Amsterdam’s Schiphol and Stockholm’s Arlanda airports, where chronic noise as low as 55 dB correlated with more doctor visits, high blood pressure and treatments for heart troubles.
And what about the sound of music? The line that separates music and noise is thin and subjective. While to some people noise may not be an issue, others consider contemporary music and music from other cultures to be noise pollution. Take heavy-metal and rap, for example. They are considered to be music by many people, though most of the songs cannot be transcribed into notes and some of them don’t even have melody.
Is hearing permanently impaired when attending concerts that feature very loud music? Yes, they are because typical sound intensity level of a loud rock concert is near the threshold of pain. Of course, the extent of impairment will depend on how long you are exposed to the noise and how often you attend such concerts. That’s why many musicians and DJs wear earmuffs to protect their hearing organ from the harmful effects of noise. A drop of 30 dB corresponds to a decrease in intensity (not intensity level) by a factor of 1000.
A growing body of evidence confirms that noise pollution is taking a toll on our health and happiness, too. Studies have linked excessive noise levels to the occurrence of aggressive behaviour, constant stress, fatigue and hypertension. These in turn can cause more severe and chronic health issues later in life. Repeated exposure to noise also reduces sleeping hours, thereby, decreasing the productivity of a person.
According to a World Health Organisation (WHO) report to the UN Conference on Environment, “Of all environmental problems, noise is the easiest to control.” However, the question of control will arise only after we become aware of the seriousness of the problem, and the government finds some solution for it.
The writer is a Professor of Physics at Fordham University, New York.