There has been an alarming rise in noise pollution in most Indian cities. This can be attributed to the increase in number of vehicles, urbanisation and industrialisation. The Central Pollution Control Board (CPCB), New Delhi, has set standards for ambient noise levels in residential, commercial and industrial areas and in silence zones. A 1994-95 study by the CPCB in select cities found that the noise levels exceed the standards set. While Calcutta is the worst case, Chennai generally fares better. Noise pollution can cause irreversible hearing impairment, mental stress and sleep disorders.