Noise Regulations

Governments at all levels have responded to complaints about industrial noise with the legislation of noise limits. These regulations vary - from simple nuisance statements ("noise is any sound that causes a disturbance") to very precise guidelines (defined noise limits in each frequency octave band).

Most localities set a dBA (A-weighted decibel) limit at the nearest sensitive receiver (NSR). Receivers are residences, office buildings, and even other industrial sites. Cities or towns that distinguish between land uses (residential, commercial, and industrial) apply different noise limits to them.

The dBA noise limit is sometimes qualified with the symbol Leq. Leq is defined as the equivalent continuous sound pressure level, which represents the average of a 24-hour noise history at a location. The Leq is used when it is important to consider variations in noise over time, such as between day and night. Individuals are more sensitive to noise at night, because background noise levels drop and irritant sounds stand out.

To limit the impact of nighttime noise, some municipalities use the Ldn. The Ldn applies the 24-hour Leq as the baseline noise limit, but then requires the limit to be lowered by 10 dBA at night. Still other communities base their noise limit on the ambient (or existing background) noise level. The ambient noise level is symbolized by L90 or L95 ( the noise level present 90% or 95% of the time). These communities request industry to restrict noise to not more than 5 or 10 dBA above the ambient level.

Here are some noise regulation examples..

• Alberta, Canada - The legislated noise level for rural Alberta varies by residential density and how far away the dwellings are from heavily traveled roads or rail lines. If industry in Alberta locates near an isolated farmhouse, it's required to keep noise down to 40 dBA Leq at the property line, but it need only achieve 56 dBA in a townsite.

• Illinois, USA - Illinois regulates 9 octave bands covering most of the audible spectrum, from 31.5 Hertz (a deep bass rumbling noise that can often be felt as well as heard) to 8000 Hertz (a very high treble hissing type noise). Industry located near residences must not exceed 69 dB (not A-weighted) in the 31.5 Hz band and 40 dB in the 8000 Hertz (Hz) band.

• Poland - Poland distinguishes between different land uses, housing densities and time of day. In Polish cities, residential noise levels can't exceed 55 dBA during the day and 45 dBA at night.

For an excellent resource on community noise definitions and the assessment and mitigation of noise impacts, click here

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