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 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 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 Shielded house Unshielded house Noise barrier Shadow zone

Sources and Control of Noise Mechanism to reduce traffic noisePrinciple Engine enclosuresEnclosure absorbs noise Seal exhaust joints effectivelyReduces vibration Fans turn off when not neededReduces number of moving parts Buffer zones or barriers- e.g. treesAbsorbs noise Traffic calmingSlows traffic, reducing tyre noise Traffic flow managementBan 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 surfacesIts texture helps it to absorb noise 20% of volume is pore space, thus water infiltration is rapid, reducing noisy spray Improve house insulationDouble 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 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 ,000Hz, most sensitive between Hz Frequency = No. of waves per second Units: Hertz (Hz) Human ear able to detect frequencies between ,000Hz, most sensitive between Hz Wavelength = distance (m) between waves Inverse relationship with frequency i.e. long wavelength sounds have low frequency, short wavelengths have high frequency 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 ,000Hz, but most sensitive between Hz

DBA scale Used for human hearing The range of frequencies audible to humans extends from 20 Hertz (Hz) to 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 NNI (0600–1800 h GMT) Average reaction 0Not noticeable 20Noticeable 35Intrusive 45Annoying 60Very annoying 70Unbearable