Controlling Facility Noise with Curtain Walls

If source sound levels increase for any reason, 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.

Why is facility noise control important? The effects of machine or process noise in a commercial/industrial facility can range from an annoyance to a serious, long-term safety issue for employees. It is an issue common to most industrial environments. OSHA estimates more than 30 million workers annually are exposed to hazardous noise levels in the United States.

This exposure takes many forms. Assembly and machine tool operation, process equipment such as pumps, compressors and blowers, material handling equipment such as conveyors and fork trucks, and power hand tools such as saws, grinders, and drills are just a few examples.

Reduction of excessive noise levels is important as an employee safety issue. The effects of human exposure to noise levels above 90 dB are cumulative — permanent hearing loss is related to accumulated time exposed to these high dB levels over a lifetime.

What does OSHA say about facility noise? OSHA requires employers to limit employee noise exposure to 90 dB or less on an eight-hour time weighted average basis. In typical industrial environments, employers are required to monitor workplace sound levels to determine where they stand in relation to this threshold. If found to be above the 90 dB limit, they are required to take action to reduce employee exposure to levels below the limit. The more common methods of noise mitigation are discussed below.

Addressing Facility Noise

Understanding the noise level in question is key to being able to affect noise transmission. The lower the sound frequency (think of bass speakers from the car next to you at a stoplight), the harder it is to mitigate. Mid-range and slightly higher frequencies are easier to manipulate. Also, it is important to know how the noise is being transmitted: Is the noise being carried by vibration through a concrete floor (e.g., a stamping operation) or through the air from the inner working of machinery (gears grinding, compressors running, etc.)?

There are multiple ways to address noise control issues in an industrial environment. These include redesign or replacement of the contributing equipment with new, quieter models. This approach, however, may not always be feasible due to the cost or availability of quieter equipment. Noisy machines can sometimes be modified to reduce or eliminate noise-producing vibration — adding isolation pads or vibration dampeners are common approaches. Machines also may be encased in sound-absorbing enclosures or materials.

If these approaches do not offer the desired result or prove to be impractical to implement, noise reduction barriers can be placed between offending equipment and the affected employees. This classically consists of 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 reaches the affected employees.

The final line of defense against excessive noise involves personal hearing protection worn by individual employees, such as ear plugs or ear muffs (either passive or noise canceling). While effective protection, these have the obvious shortcoming of being useful only while actually worn and only when worn and fitted properly. Additionally, in a facility where hearing protection is required, regular hearing testing of affected employees is mandated by OSHA.

Flexible acoustic curtain walls are a new approach to controlling facility noise. Sound-insulating industrial fabric curtains normally will consist of two layers of a woven, coated fabric surrounding one or more layers of various insulating materials. These materials might include fiber batting (polymer or glass), open cell foam, or densified “loaded” vinyl or other flexible polymer sheet material. Each of these components plays its own important role in reducing sound levels impinging on the curtain surface. For instance, the mass-loaded vinyl sheet in a sound curtain is more effective in reducing lower-frequency noise than the other components (low-frequency sound is best absorbed or deflected with high-density solid materials). Fiber batting is effective in reducing sound at mid to higher range frequencies. Open cell foam (such as a viscoelastic) also offers noise reduction over a range of frequencies, but care must be taken to ensure the foam used is effectively treated for flame retardance.

The interior core of a typical sound curtain will consist of a layer of sound dampening, loaded vinyl and a layer of antimicrobial polyester batting as an additional sound buffer, which also serves to fill out and maintain the body of the panel. This core is captured between two outer layers of 18-ounce flame retardant vinyl, which is available in a number of colors for aesthetics. 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 the ambient employee areas.

Flexible acoustic curtain walls offer a relatively new approach to providing employee safety and comfort when it comes to noise levels in a commercial or industrial facility. These fabric curtains can be very effectively used for noise source insulation, as well as for noise path insulation. Noisy machines can be wrapped in flexible sound curtains like a “blanket.” They also can be attached to a close quarters support frame around the equipment.

Larger sound enclosures can be formed using these curtains, including complete rooms or separating walls. In a typical application of this sort, 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 simply screwed to this angle along its top edge using self-drilling screws. The curtains are normally made of 5-foot-wide panels and have vertical Velcro attachment hems to join multiple panels to create a full-width curtain.

In addition to their excellent noise reduction performance (Sound Transmission Coefficients ranging from 15 to 30+), flexible curtain walls as noise barriers offer additional advantages over rigid wall solutions. Curtains can be configured to fit virtually any interior space and don’t require nearly the time required to build permanent walls. Curtains are constructed of durable, fire-retardant industrial fabric surrounding multiple layers of recyclable, antimicrobial polyester batting. Individual fabric panels of virtually any length are interconnected to form each continuous wall.

Unlike a rigid wall, a curtain wall can be easily reconfigured to adapt to changing production demands and floor layouts. It’s easy to add to or enlarge an initial curtain wall installation. If source sound levels increase for any reason, 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 (a fairly common application). Also, these fabric-covered walls can be easily cleaned with simple detergent and water.

Summary

High noise levels in the workplace are a significant health hazard to employees. Dealing with high noise levels can be a difficult and expensive undertaking, but it is also necessary. Insulated curtain walls represent a cost-effective and flexible alternative to classic methods used for noise abatement and bring their own value in other ways to an industrial environment. From employee safety to employee comfort resulting in higher productivity, the benefits of keeping noise levels under control are real and obvious.

This article originally appeared in the October 2012 issue of Occupational Health & Safety.

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