EFFECTS OF NOISE

Any undesirable and unwanted sound may be considered noise. However, its perception is subjective. One person’s noise may be music to the ears of others.

Regardless, the exposure to high levels of noise or music may have harmful physical or emotional effects. It may be manifested in minor psychological irritation, or severe, sometimes extreme pain to the ear.

The physical damage to the ear could be temporary hearing loss (temporary threshold shift or TTS) manifested in reduced perception of low level sound. If the patient is removed from the noisy environment, recovery could be expected within a couple of months. Permanent loss of hearing is possible (noise-induced permanent threshold shift or NIPTS). It means that the patient will not perceive low level sounds, and the condition may be corrected only with the use of electronic hearing aids.

Although some individuals may be more sensitive to noise than others, the exposure to loud (100 decibel) music — so fashionable today — may eventually lead to NIPTS, 10-15 decibel hearing loss at the lower end of the perception range.

The extent of the loss in ones hearing depends on the level and duration of the exposure. It is likely that one hour of exposure to 100 decibel noise may cause short term TTS, with a recovery period of one to five days. Continuous exposure to high levels of sound, in the vicinity of 90 decibel, for a period of more than 5 years, may eventually lead to 15-20 decibels of NIPTS.

Apart from the direct physical effects to one’s hearing, the indirect physiological effects of continuous exposure to noise pollution could be significant. Heart diseases, raised blood pressure, change in the pulse rate could be related to extended exposure to noise. However, at the time of writing there is not enough data available to establish the physical impact beyond reasonable doubt.

The emotional impact could be far more severe, but again the research data is woefully inadequate to draw “iron clad” conclusions. It is however undeniable that continuous exposure to elevated noise levels will cause irritability, anxiety, stress and in extreme cases depression.

In noisy factories, unless the workers are protected with earplugs or specially designed muffs, mental fatigue and loss of concentration is common, leading to lower levels of productivity, and in extreme cases accidents. Construction sites where hydraulic equipment (jackhammers) is used, the accident rate have been significantly reduced by the introduction of ear muffs to the operators of such machinery.

In a community the impact of high noise level is significant, since it interferes with sleep as well as conversation. The psychological effects could be far reaching. For example, if the rumors can be counted on, in an American University a research application is pending to examine the divorce rates in communities under the approaches to major airports. It may take many years of concentrated research and impact studies to connect these sociological problems to noise pollution, in such manner that it would stand up in the court of law.

One may therefore conclude that noise pollution is not just a minor annoyance, but serious and sometimes fatal environmental hazard. Public health officials should look into the physical and emotional impact of noise pollution especially in communities exposed to frequent low level overflight.

PROTECTION

In essence there are two ways to protect the public against noise pollution. One may elect to intercept the noise, using acoustic barriers or increasing the distance from the source of the sound.

Personal protection, earplugs or muffs may reduce the sound level by up to 40 decibels. Conventional highway barriers built of concrete or bricks may reduce the sound level by 15 decibels. However, one must be very careful selecting the materials for sound barriers. High density poorly placed barriers may reflect the sound and could superimpose the waves in such manner that the noise level will actually increase.

The primary source of highway traffic noise is the movement of the tires on the pavement. The secondary source is the engine noise (exhaust) and the wind resistance. It is therefore evident that with higher speed the noise increases. Tests have suggested that increasing the speed from 40 to 70 km/hr adds about 8-10 decibels to the sound levels. Higher traffic volume obviously elevates the noise levels, but the actual increase cannot be generalized. In case of stop-and-go traffic, the engine noise would increase significantly and lead to an additional 3-5 decibel higher output. Perhaps the most efficient barriers are berms, dams or building the highway below street level.

To soundproof a building is a difficult task, requiring the in depth knowledge of acoustic materials and their applications.

The increase in distance between the source of sound and the target, is governed by the following formula:

(a) Noise penetration in air (see the sound-2.wb2 program, developed by the writer)

SLb = Sla – 10 x log (Db/Da)

Where

SLa = sound level at Da from the source,

SLb = sound level at Db from the source

In essence this means that the sound levels decrease in a logarithmic rate of the ratio of the distances from the source.

(b) Combining noises (Based on J. Nathanson “Basic Environmental Technology”)

As the decibel scale is logarithmic, the decibel value of simultaneously applied noises cannot be added arithmetically. Therefore, based on a logarithmic chart, four simultaneously operating modern aircraft engines are estimated to put out approx. 104 dB. (Each engine generating 100 dB at 10 meters distance) Although the above noise output was extrapolated from random measurements, it is considered conservative.

CONCLUSION

In the case of Pearson international airport the writer developed an area where the aircraft taking off (including climb-out) and landing distribute objectionable levels of noise. For the determination of the impact area boundaries, the noise penetration from a single 747 was modeled, and the boundaries were drawn at the line where the noise level of 80 dB is possible.

The above theory was applied to the four-runway configuration, at LBPIA. The noise patterns were plotted, and the boundaries were developed as illustrated on Fig. 1.

Incidentally the same boundaries were applied for an air quality study.

RECOMMENDATIONS

It is recommended that the area illustrated on Fig. 1 should be considered an area where noise pollution represent a hazard, and action to mitigate the impact should be taken by GTAA as soon as possible.

SOUND LEVEL
decibels / Environmental condition
140-130 / Pain threshold
130-120 / Pneumatic chipper (jackhammer)
120-110 / Automobile horn (at one meter)
110-100 / Jet aircraft overhead (low level flight)
110-90 / Interior of subway train
90-80 / Inside of bus, cab of a transport truck
80-70 / Busy street traffic
70-60 / Normal conversation
60-50 / Office background
50-40 / Living room background (suburban residence)
30-40 / Library
30-20 / Bedroom at night (suburban home)
20-10 / Sound studio background noise
10-0 / Threshold of hearing

SOUND LEVELS