i found this on the bbc website. hope it might help
The damage to hearing depends not only on the level of noise but how long it lasts. So hearing can be damaged by very sudden short bursts of extremely loud noise, such as an explosion, or by prolonged exposure to lower levels of noise, such as if you work in a factory surrounded by machinery without ear protection.
As well as this direct damage to hearing, constant unwanted noise is very stressful, even at lower levels, causing rises in blood pressure and heart rate, or disturbing sleep (even noise as low as 30dB can affect sleep if it's continuous).
Research has shown that:
at 55dB to 60dB noise creates annoyance
at 60dB to 65dB annoyance increases considerably
above 65dB serious damage caused by noise occurs
Numerous legislation laws
The problem with legal noise control is that no single agency has overall responsibility for all aspects of environmental noise policy and legislation. So there's no one single piece of legislation which makes clear what noise levels are allowed. Instead there are more than 100 different noise-related laws controlling different types of noise in different places, all of which may contribute to background noise.
The World Health Organization has suggested a standard guideline value for average outdoor noise levels of 55dB, applied during normal daytime to prevent significant interference with the normal activities of local communities (also 50dB for indoors, 30dB for bedrooms, and more specific limits such as a 100dB for a four-hour period for concert halls).
If you're bothered by background noise you should seek advice. The experts should assess the noise to find the sources and see whether individual restrictions apply or where controls may be brought in to resolve one-off noise problems.