Many counties and municipalities enforce some form of nuisance regulation, which may or may not include noise.  If noise is included, a typical regulation might state, “It is unlawful for any person to make, or cause to be made any noise disturbance.” This sort of statement is often accompanied by definitions of what constitutes a noise disturbance. 

A violation, however, is typically a judgment call on the part of the enforcer.  Thus, if someone calls the police because a noise is keeping them up at night, the police or local code enforcement official must then make a subjective assessment on whether the offending sound constitutes an actionable nuisance or disturbance.  

The degree of nuisance may ultimately depend on the perceptions of the complainant or the enforcer.  A good acoustical consultant will have tools at his disposal that can probabilistically assess the potential for noise complaints resulting from a new noise source, such as a power plant.

Actual quantitative sound level limits are imposed in some states, as well as in many counties and municipalities across the U.S.  These sound level limits, typically expressed as A-weighted decibels (dBA), vary widely.  The limits often depend on the time of day, the type of sound emitter and the type of property where the noise is heard – residential, commercial or industrial. 

Residential sound level limits are typically the most stringent. For example, an ordinance might state, “The sound level at the boundary of a residential receiving property resulting from the operation of a source on the emitter’s property shall not exceed 45 dBA during the nighttime.”  Sometimes, more detail regarding the method of measurement to determine compliance is provided, such as, “The statistical median sound level for a one-hour period between the hours of 10 p.m. and 7 a.m. shall not exceed 50 dBA.”  

Some jurisdictions even impose sound level limits in individual octave bands, that is, different sound level limits for different frequency ranges.  These are typically the most challenging since  low-frequency sound level limits could put significant design constraints on something like a simple-cycle gas turbine generator or a cooling tower.

When it comes to facility acoustical design, having a firm sound level limit can provide a good design target.  However, due diligence is still required to ensure that the sound level limit is not too permissive, particularly if there is also a nuisance regulation in place.  In other words, meeting a 55-dBA sound level limit could be straightforward in terms of facility design, but if the existing ambient background is fairly quiet – say 40 dBA during the nighttime – the possibility for noise complaints remains. This means a facility’s compliance with the rules could become more complex.

Limits to the allowable increase of an existing ambient sound level have the advantage of not allowing a noise source to dominate a community’s acoustical environment.  For example, “A noise source shall not cause an increase to the existing, pre-construction ambient sound level of more than 5 dBA.”  The disadvantage to this type of regulation is that it inadvertently permits “acoustic creep.”  In other words, the ambient sound level in an area could creep several decibels higher each time a new noise source is added.

Disadvantage aside, ensuring a facility is compliant with this type of noise pollution regulation depends heavily upon the results of a thorough pre-construction ambient sound level survey.  In order to establish the design requirements, the existing ambient level must be measured and evaluated, preferably in a continuous manner over a period of several days.  Once the lowest existing ambient sound level is known, a design target can be developed and noise control measures can be planned.

Since regulations controlling noise pollution are not uniform in the U.S., the acoustical design of any new facility or facility expansion will depend on the noise regulations in place, as well as on the potential acoustical impact on the neighbors.  

Project developers can benefit from qualified acoustical professionals who can provide noise assessment services for a wide range of facilities, from small residential substations and pumping stations, up to large combined-cycle power plants and liquefied natural gas processing facilities.  These noise assessments may include a thorough regulatory review, a survey of the ambient acoustical environment, an acoustical model of the facility with consideration of all future noise sources, and acoustical design recommendations and specifications for the equipment. 

Whether the goals are to minimize noise complaints, comply with regulatory sound level limits, or comply with a limit to the allowable increase in sound level, the development of any new facility or facility expansion will often benefit from a thorough noise assessment.

 

Subject Matter Expert
Jeff Szymanski: SzymanskiJD@bv.com