Controlling factory noise is essential for many reasons. The Occupational Safety and Health Administration (OSHA) was established in 1971 by the U.S. Congress to help eliminate job safety and health hazards such as noise, and has established regulations that define acceptable noise level exposure in the workplace, requiring employers to maintain an adequate hearing conservation program. In addition, Federal and local municipalities have regulations in place that put limits on the amount of noise leaving a factory.
Controlling noise in an industrial factory can be challenging due to the wide variance of noise levels being produced by many different types of equipment. Factory spaces are typically large shells with hard surfaces which essentially turns them into echo chambers amplifying noise levels even higher. One of the most cost effective ways of lowering overall sound levels is the addition of absorption materials to the walls and ceilings. By preventing the sound waves from reflecting off of the hard surfaces in the building, an overall reduction of 3 to 5 dBA can be achieved.
Noise mitigation studies in factories can be complicated, involving measuring worker exposure over time with dosimeters, and logging sound levels and the time spent performing each task. In addition, sound level readings taken at each piece of machinery throughout the building must be analyzed to determine the amount of reduction in worker exposure that would be achieved by mitigating the noise generated by that equipment, as well as determining its overall contribution to the direct as well as reverberant field. For this reason it is often more practical to treat factory wide noise reduction with a gradual approach.
The first step in factory noise reduction is to insure that existing equipment is operating properly. Things like worn bearings and belts can significantly increase the amount of noise generated by a piece of machinery. Equipment location is another factor that needs to be looked at. A piece of machinery located in a corner next to two adjacent concrete walls will be much noisier then if it is located in an open area due to the amount of sound being reflected off of those walls. It may also be possible to relocate equipment to a more isolated area where fewer workers are exposed. When it is impractical to relocate a piece of equipment or reduce worker exposure, the addition of acoustical enclosures is needed. Fully enclosed soft portable enclosures constructed with composite barrier/absorber sound curtains can reduce sound levels by 10 to 15 dBA. Enclosed modular steel enclosures can lower sound levels in excess of 40 dBA.
Factories are also plagued by structure borne noise. Vibrating machinery, HVAC equipment, pipes, and conduit attached directly to the walls, floors, and ceilings, will all transfer noise into the building structure treating it like a giant soundboard. Machinery conducive to vibration needs to be mounted on properly sized vibration isolators. Pipe, conduit, and HVAC ductwork can be decoupled from the building with the installation of acoustic isolation hangers. Material handling procedures can also be modified to reduce sound levels. Damping materials can be added to chutes, conveyors, or hoppers that are subject to continual multiple impacts from parts in the manufacturing process. This reduces vibration and resonance.
Sometimes it may be impractical or impossible to shield workers from excessive noise by treating the source. In this instance hearing protection is required. Hearing protection can be as simple as standard ear plugs and ear muffs, to electronic versions that offer noise cancellation and impulse noise suppression which protect the wearer yet still allow them to communicate with co-workers and be audibly aware of their surroundings.
Many times a factory will share office space that is adjacent to or above the work floor. These areas need to be acoustically isolated by insuring that all wall, floor, and ceiling partitions are of sufficient mass to block existing sound levels, and that there are no air leaks or open spaces where sound can penetrate. Building materials such as concrete block or multiple layers of sheetrock are excellent sound blockers. Additional mass can be easily added to a wall or ceiling with the installation of a mass loaded vinyl noise barrier. Wall and ceiling partitions can also be decoupled through the use of resilient isolation clips and standard furring channel, which is particularly important when dealing with low frequency noise. Doors and windows are typical weak spots in factory office areas, and should be acoustically rated at an STC 45 or above. For existing doors that have sufficient mass but leak around the perimeter, it may be possible to get acceptable results by adding an acoustical door seal kit.
Noise leaking into the outside environment also needs to be addressed to be in compliance with Federal and local regulations as well as being a good neighbor. Properly reducing sound levels inside a plant also reduces the amount of noise leaving the plant, and may be sufficient in meeting these regulations. Quite often though, it is necessary to add HVAC silencers and louvers to quiet noisy exhaust systems venting to the outside. As with adjacent interior office space, exterior doors and windows need to be acoustically rated to prevent noise from leaving the building. In metal buildings, barrier septum composite panels can be attached to the walls and ceilings. These panels are comprised of a barrier and an absorber which adds mass to help block noise, as well as adding absorption thereby reducing interior reverberation.