Responding is Chuck Ashelin, engineering manager, Zoneworks, Milwaukee, WI.
Answer: Noise abatement is a common concern for managers of plants, warehouses and other facilities where workers are exposed to noise from power tools, assembly and process machinery, conveyors, fork trucks, or other equipment. Currently, OSHA requires employers to limit employee noise exposure to 90 dB or less (on an 8-hour time-weighted average basis). Workplaces found to be above the 90 dB limit are required to take action to bring noise levels into compliance.
There are many ways to do that. Often, facility managers will start at the source by redesigning or replacing noisy equipment with new, quieter models. Because machine replacement is not always feasible, noisy machines sometimes can be modified to reduce or eliminate noise-producing vibration. Machines also may be muffled by encasing them in sound-absorbing enclosures or materials.
In addition, noise reduction barriers can be placed between offending equipment and the affected employees. These barriers typically are rigid insulated walls or partitions strategically placed to block the path of transmitted sound waves and absorb and scatter them, reducing the total sound power level (dB) that actually reaches workers.
Another approach is to provide personal hearing protection, such as earplugs or earmuffs, for employees. Although effective, both earplugs and earmuffs have the obvious shortcoming of only being useful while actually worn, and only when worn and fitted properly.
A new noise reduction tool: flexible acoustic curtain walls
In recent years, another noise reduction tool has become increasingly popular: flexible acoustic curtain walls. These fabric curtains can be used effectively for both noise source insulation and noise path insulation. Flexible sound curtains can be wrapped around noisy machines or attached to a support frame around the equipment. Larger sound enclosures can be formed by them as well, including complete rooms or separating walls.
In a typical curtain wall application, a metal mounting angle is installed across or along a run of the roof supporting bar joists (welded, clamped or bolted), and the insulated curtain is secured to this angle along its top edge using self-drilling screws. The curtains are made of 5-foot-wide panels and have vertical Velcro attachment hems to join multiple panels, creating a full width curtain.
Sound-insulating industrial fabric curtains normally consist of two layers of a woven, coated fabric surrounding one or more layers of various insulating materials, each of which plays a role in reducing sound levels. The interior core typically consists of a layer of sound-dampening loaded vinyl and a layer of antimicrobial polyester batting as an additional sound buffer. This core is captured between two outer layers of 18-ounce flame-retardant vinyl. Typically, the loaded vinyl side of the core is positioned between the offending noise source and the desired ambient sound area. In a completed installation, the wall acts to trap the sound in a specific area and limit the migration of the sound to employee areas.
Advantages of acoustic curtain walls
In addition to their excellent noise reduction performance (lowering sound by 22-25 dBs), flexible curtain walls offer advantages over rigid wall noise barrier solutions. Curtain walls can be configured to fit virtually any interior space and do not require the amount of time required to build permanent walls.
Unlike a rigid wall, a curtain wall can be easily reconfigured to adapt to changing production demands and floor layouts. It is easy to add to or enlarge an initial curtain wall installation. If source sound levels increase, it is very simple to add a second layer of flexible sound curtain to an existing one, or even to augment an existing rigid wall (which is a fairly common application).
Editor’s Note: This article represents the independent views of the author and should not be construed as National Safety Council endorsements.