Reducing Noise and Building Accord Between Worksites and Communities
Sponsored by Kinetics Noise Control.
Industrial, commercial, and residential zoned areas are converging, sometimes occupying adjoining locations. This means that noise from machinery and equipment is becoming a common environmental concern for residential communities. City officials, building owners, and community residents—many of whom have never before dealt with environmental noise issues—must be educated to develop fair and obtainable noise ordinances.
Common property line ordinances are 60 dBA during daytime (7 a.m.–10 p.m.) and 55 dBA during nighttime (10 p.m.–7 a.m.). Where clear noise ordinances exist, owners who do not reduce noise levels may be issued a citation. Citations can consist of monetary fines or a business’s forced closing until the sound level dictated by the noise ordinance is met. But regardless of whether clear noise ordinances are set forth, property owners may be “good neighbors” by taking it upon themselves to reduce the noise emanating from their own site or building.
Solving environmental noise issues can involve support from many professions, such as certified industrial hygienists, acoustical consultants, architects, mechanical engineers, contractors, owners, and representatives of equipment manufacturers. Often the owner will begin by hiring an industrial hygienist or acoustical consultant to conduct a site sound survey by recording the time-weighted average of sound levels over a 48- or 72-hour timeframe. These measurements are then used to determine if a local sound ordinance has been exceeded.
Implementing a cost-effective noise control solution involves obtaining as much technical data on the noise source as possible, analyzing all sound propagation paths, and clearly defining the location of the receiver, or the person being affected. Relevant technical data for noise-producing equipment comprises sound power levels, cooling airflow rate, airstream operating temperature, allowable external static pressure, horsepower, heat generation rate per hour, and manufacturers’ configuration and installation guidelines.
Meanwhile, the factors affecting sound propagation paths that IHs or other professionals should consider are the distance between source and receiver, atmospheric conditions, wind direction, terrain, and the presence of wooded areas, nearby buildings, and other noise sources. Concerning the receiver, the IH should note community zoning requirements, the presence or absence of an official noise ordinance, the question of which party—owner or receiver—first took up residence in the area, and the topography between noise source and receiver.
To develop the proper, cost-effective noise control solution, it must be clear how the equipment (the source of the noise) operates. It is not good enough to address only acoustics. Most mechanical equipment is not designed to operate under the adverse effects of enclosure by a structure or barrier. Design of the noise control solution must incorporate routine maintenance access and allow for removal of portions or entire equipment in case of catastrophic failure. Doors and hatches left open will short-circuit any noise control solution; therefore, properly silenced ventilation must be included.
Common environmental noise control products are ventilation silencers, fixed-blade acoustic louvers, sound barrier walls, and sound enclosures. Realistically obtainable noise reductions for common equipment types at 10 feet away and ultra-low pressure losses are 25 dBA for exhaust fans, 25 dBA for air-cooled chillers (but only 10 dBA for locations above the unit), and 10–20 dBA for induced draft cooling towers. Because A-weighted sound levels mimic the human perception of sound, a piece of equipment that has undergone a 10 dBA noise reduction will sound half as loud as it did before to the average human.
Environmental “outdoor” noise control is of great importance today. Educating owners and communities on the available noise control options, using the most up-to-date acoustic algorithms and design standards, and applying independently tested products will yield a solution that contributes to harmony between the worksite owner and local residents.