To determine the levels at which noise becomes harmful, sound pressure is measured in
decibels(dB). Sounds also have pitch (frequency), with high-pitched sounds seeming to
be louder and more annoying than low-pitched sounds. Normally sound pressure measurement
is weighted for high-pitched sounds, to which people are more sensitive, and measured in
decibel-A (dbA) units. Sound pressure becomes damaging at about 75 dbA and painful at
around 120 dbA; it can kill at 180 dbA. Sounds above 120 dbA can leave one with a
high-pitched whine or ringing in ears. Persistent ringing in the ears is called tinnitus,
a distressing disorder for which there is no treatment (Miller, 1992).
The absence fo formal control are often
blamed for rising noise levels, and yet are so difficult to ascertain due to the fact that
each individual is affected differently by noise. There are, however, certain health
hazards linked to excessive exposure to nuisance noise that heighten the importance of
providing noise control. In South Africa, noise pollution is controlled by regulation
under the Environmental Conservation Act 73 of 1989. The noise control regulations
stipulate what kinds of noise are permissible in what areas and when it is acceptable to
create such noise. The contents of the regulations are also linked to a number of SABS
guidelines. In general any noise that is 7 dB above ambient noise levels, may be
considered a nuisance. The following table shows the acceptable levels of vehicle noise
emissions (Walmsley, 1997).
SABS noise standards for motor
vehicles (SABS 0181-1981)
Type of vehicle |
Sound level dBA |
| Two and three wheeled vehicles |
95 |
| Vehicles with spark ignition and with four or more wheels
used for conveyance of passengers or goods |
96 |
| Vehicles with diesel engines and not equipped with an
engine brake |
105 |
Vehicles with diesel engines and equipped
with an engine brake:
i) engine brake switched off
ii) engine brake switched on |
105
109 |
Noise levels of some sources in Greater
Johannesburg
Noise level: source Miller |
dbA |
Noise levels : source GJMC |
Air raid siren |
135 |
Pain Threshold |
Earphones at
loud level |
130 |
|
Aeroplanes at
loud level |
125 |
Jet at 166
metres |
Car stereo
system |
115 |
Machine shop |
Rock music |
105 |
Jackhammer (1
metre) |
Chain saw |
95 |
In a
discotheque |
Lawn
mower |
90 |
Inside
a bus |
|
85 |
Vehicle
noise limit (7 metres) |
Permanent damage begins after 8-hour exposure at 85 dbA |
Average
factory |
75 |
Street corner |
Normal
conversation |
65 |
Conversation
(1 metre) |
| |
55 |
Business
office |
Rainfall |
50 |
Living room |
Quiet room |
40 |
Public library |
| |
30 |
Rustle of
leaves |
Quiet rural
area |
25 |
Broadcast
studio |
| |
10 |
Tick of watch |
Normal
Breathing |
0 |
Threshold of
hearing |
|
