Transcript Noise pollution ppt

Noise
Pollution
Noise pollution
Noise = sound which is unwanted by the recipient
Sound is produced by vibrations passing through air, liquids or solids sound cannot pass through a vacuum
Effect of noise on objects
• If noise causes an object to
vibrate at its natural resonant
frequency, this may result in
stress cracks, an indication of
acoustic fatigue
• Repetitive vibration can
structurally damage roads,
bridges, buildings and aircraft
Effect of noise on organisms
Physiological effects:
• muscle constriction
• increased heart rate & blood pressure
• constriction of blood vessels
• stress
• irritability
• headaches
• temporary/permanent damage to hearing
Loud noises cause overstimulation and eventual death of the microscopic hair
cells which line the organ of Corti in the cochlea of the inner ear. Once killed,
these hair cells cannot be replaced and hearing loss is permanent.
Loud noises may disturb wildlife, result in nest abandonment and breeding
failure
Sources and Control of Noise
Industrial noise
Noise from machinery can be reduced by:
• reducing the weight/ height of fall of any
impacting masses
• reducing the speed of moving and rotating
parts
• reducing the pressure and flow velocities in
air, gas and liquid circulation systems
• encasing it in acoustic insulation
• using damping materials e.g. viscous
materials to dissipate and attenuate
vibrational energy
• partitioning areas of the factors to reduce
noise spread
Workers can be protected by:
• using ear protectors
• limiting their period of exposure to the
noise
Sources and Control of Noise
Transport noise
Traffic noise accounts for 66% of outside noise
Road vehicle noise is a combination of:
• engine noise
• exhaust noise
• the vibration of tyres on the road surface
Barriers made of earth, wood, metal or concrete or composites may
reduce noise levels by 10-15dB. However, such barriers will not protect
houses above the height of the barrier
Unshielded
house
Shadow zone
Noise
barrier
Shielded house
Sources and Control of Noise
Mechanism to reduce traffic noise
Principle
Engine enclosures
Enclosure absorbs noise
Seal exhaust joints effectively
Reduces vibration
Fans turn off when not needed
Reduces number of moving parts
Buffer zones or barriers- e.g. trees
Absorbs noise
Traffic calming
Slows traffic, reducing tyre noise
Traffic flow management
Ban lorries at times or places
Control flow by sequencing traffic
lights
Build new roads below the level of
the land surface
Embankments absorb and reflect
noise
Use porous asphalt for road surfaces
Its texture helps it to absorb noise
20% of volume is pore space, thus
water infiltration is rapid, reducing
noisy spray
Improve house insulation
Double or triple glazing + composite
wall materials to absorb sound
Sources and Control of Noise
Aircraft noise
Noise is generated from:
• moving parts within the engines
• the combustion process
• jet flow from the nozzle
• air flow over the wing flaps and around
the landing gear
Control
• Airport location away from dense residential areas
• Restrictions on night flying
• Preferential routes for aircraft taking off and landing to minimise no. of
people who experience fly-over
• Adoption of continuous descent approaches with late deployment of flaps
and landing gear
• Runway alternation
• Embankments to deflect noise upwards
• Development of larger diameter jets and turbofans
Sources and Control of Noise
Railway noise
Train noise is a combination of:
• engine noise
• the vibration of wheels on the tracks
Control
• Timing of freight and passenger movement
• Ballast e.g. aggregates under and between the tracks to absorb noise
Domestic noise
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Domestic noise is a combination of:
Appliances e.g. televisions, dishwashers
Garden equipment
Music
Control
• Insulation e.g. double glazing to absorb or reflect noise inwards
• Considerate use
Measuring noise pollution
Frequency = No. of waves per second
Units: Hertz (Hz)
Human ear able to detect frequencies
between 20 - 20,000Hz, most sensitive
between 1000-4000Hz
Wavelength = distance (m) between waves
Inverse relationship with frequency
i.e. long wavelength sounds have low
frequency, short wavelengths have high
frequency
Decibel (dB) scale
• A measure of the size of the fluctuations in air pressure caused by sound
waves - doesn’t measure sound volume
• Decibel scale is logarithmic, not arithmetic - an increase of 10dB doubles the
sound intensity
• A logarithmic scale is needed because of the wide range of the human
hearing response
• Human ear able to detect frequencies between 20 - 20,000Hz, but most
sensitive between 1000-4000Hz
DBA scale
Used for human hearing
The range of frequencies audible to humans extends from 20 Hertz (Hz)
to 20000 Hz.
Most environmental noise
includes a wide band of
frequencies so sound-level
meters use an “A” filter,
which shuts out very low or
very high frequencies,
weighting the sound
spectrum to the
frequencies most audible
to the human ear (1000 –
4000Hz)
The dBA scale starts at 0 – the
faintest sound detectable by a
human with good hearing
Noise and Number Index (NNI scale)
• Measures no. of flights and noise level of aircraft > 80dB
• Provides long-term measure so can be used in land-use
planning
• NNI scale runs from 0 – 70. Aircraft noise reaches an
unreasonable level in the range 50 - 60
NNI
(0600–1800
h GMT)
Average
reaction
0
Not noticeable
20
Noticeable
35
Intrusive
45
Annoying
60
Very annoying
70
Unbearable