Noise Pollution

Noise pollutionNoise = 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 organisms Physiological effects:• muscle constriction• increased heart rate & blood pressure• constriction of blood vessels• stress• irritability• headaches• temporary/permanent damage to

hearing

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

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 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

Sources and Control of Noise Industrial noiseNoise 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 NoiseTransport noiseTraffic 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 surfaceBarriers 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

Shielded house

Unshielded house Noise

barrier

Shadow zone

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 placesControl 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 NoiseAircraft noiseNoise 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 NoiseRailway noiseTrain 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• 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 secondUnits: Hertz (Hz)Human ear able to detect frequencies between 20 - 20,000Hz, most sensitive between 1000-4000Hz

Frequency = No. of waves per secondUnits: Hertz (Hz)Human ear able to detect frequencies between 20 - 20,000Hz, most sensitive between 1000-4000Hz

Wavelength = distance (m) between wavesInverse relationship with frequencyi.e. long wavelength sounds have low frequency, short wavelengths have high frequency

Wavelength = distance (m) between wavesInverse relationship with frequencyi.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 scaleUsed for human hearingThe range of frequencies audible to humans extends from 20 Hertz (Hz) to 20000 Hz.

The dBA scale starts at 0 – the faintest sound detectable by a human with good hearing

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)

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