Noise Barriers and Enclosures

Noise barriers and enclosures are designed to limit noise exposure from various noise sources by blocking or absorbing sound.

Description:

Noise barriers and enclosures are engineering controls that can reduce noise exposure. They are designed to reflect or absorb noise or do both. Dense materials such as steel and concrete are used to reflect or block sound. Soft, porous, low-density materials such as foam and fiberglass are use to absorb sound.

Through the use of specially designed barriers and enclosures, noise levels and exposures can be reduced. However, sound pressure levels within these structures may still be above the OSHA permissible exposure limit and workers may need to wear hearing protection for more than intermittent visits.

The ability of a material or product to block sound at a specific frequency is its transmission loss (TL). Transmission loss ranges from 0 dB, for materials that provide no reduction in sound engery, to greater than 70 decibels (dB) for materials that provide the greatest reduction in sound energy. Tranmission loss is generally measured at frequencies of 125, 250, 500, 1,000, 2,000 and 4,000 Hertz (Hz).  Sound transmission class (STC) is a single-number rating used to describe the ability of a material to act as a sound barrier for sounds from 125 to 4,000 Hz.  In addition to blocking sound energy, most barriers and enclosures will also absorb sound. The fraction of sound energy that is absorbed is called the sound absorption coefficient. A particular material’s noise reduction coefficient (NRC) is the average sound absorption coefficient, measured at 250, 500, 1,000 and 2,000 Hz. An NRC of 0 means the surface is a perfect reflector of sound and an NRC of 1.0 means the surface is a perfect absorber of sound. It is possible to have an NRC above 1.0.

Kinetics Noise Control

Acoustical Louvers

  • Construction Materials: steel, aluminum, baked enamel
  • Applications: building vents, generator room vents, barrier wall systems, acoustical enclosure ventilation, commercial and industrial duct systems
  • Transmission Loss: from 5 dB at 125 Hz to 31 dB at 8,000 Hz

Sound Transmission Loss

Center Frequency (Hz)1252505001,0002,0004,0008,000
VAL/1, 6-inches thick57910101012
VAL/2, 6-inches thick7111516171818
VAL/1, 12-inches thick791316171818
VAL/2, 12-inches thick8142227303031

Sound Barrier Walls

  • Construction Materials: steel, foam, fiberglass
  • Absorption Material: NOISEBLOCKTM, 2 or 4 inches thick
  • Applications: utilities, transportation/highways, rooftop equipment, residential noise compliance, custom designed for each application

Sound Absorption Coefficients

Center Frequency (Hz)1252505001,0002,0004,000NRC
NOISEBLOCK 2-inch Barrier Panels0.150.661.071.060.970.860.95
NOISEBLOCK 4-inch Barrier Panels0.601.131.121.091.030.911.00

Sound Transmission Loss

Center Frequency (Hz)1252505001,0002,0004,000STC
NOISEBLOCK 2-inch Barrier Panels17233447555737
NOISEBLOCK 4-inch Barrier Panels21283948565840

Rigid Enclosures

  • Construction Materials: steel, foam, fiberglass, mineral wool
  • Absorption Material: NOISEBLOCKTM
  • Applications: pumps, compressors, saws, shakers, milling machines, process equipment, custom designed for each application

Sound Absorption Coefficients

Center Frequency (Hz)1252505001,0002,0004,000NRC
NOISEBLOCK HTL 4-inch Panels0.601.131.121.091.030.911.00

Sound Transmission Loss

Center Frequency (Hz)1252505001,0002,0004,000STC
NOISEBLOCK HTL 4-inch Panels27344861667048

Sound Fighter Systems Noise Control

HVAC Equipment Sound Wall

  • Construction Material: steel exterior with a asphalt core or a cement board backing
  • Absorption Material: LSE, mineral fiber
  • Noise Reduction Coefficient: 1.05
  • Transmission Loss: up to 33 dB
  • Applications railroad, aircraft, construction, highways, HVAC, manufacturing and industrial, utilities, oil and gas, custom designed for each application

The LSE Absorptive Noise Barrier System is assembled in panels and locked into place within a steel skeleton.

Eco Sound Barrier Noise Control

Eco Sound Barrier

  • Construction Material: steel
  • Absorption Material: foam
  • Applications: sound barriers custom designed for each application

The Eco Sound Barrier is a reflective barrier that incorporates a specially designed foam core, created by CENTRIA, to absorb sound. The barriers are assembled in panels, then locked into place within a steel skeleton. Optional insulation wrapping is available for greater sound absorption.

Sound Transmission Loss

Center Frequency (Hz)1252505001,0002,0004,000STC
4-inch thick, 36-inch wide25272133515326

Unger Technologies Steel Sound Enclosures

Sound Enclosure

  • Construction Material: steel
  • Absorption Material: absorption foam or mineral wool
  • Applications: custom designed for each application

The Unger Sound Enclosure uses specially designed absorption materials and is assembled in panels and held in place within a steel skeleton.

Sound Absorption Coefficients

Center Frequency (Hz)1252505001,0002,0004,000NRC
Model ETG-4 Enclosure, 2 inches thick0.150.661.071.060.970.860.95
Model ETG-4 Enclosure, 4 inches thick0.601.121.131.091.030.911.00

Sound Transmission Loss

Center Frequency (Hz)1252505001,0002,0004,000STC
Model ETG-4 Enclosure, 2 inches thick17233447555737
Model ETG-4 Enclosure, 4 inches thick212839485658 

Risks Addressed:

Over time, exposure to noise levels at or above 85 decibels will lead to permanent hearing loss. The NIOSH recommended exposure limit (REL) for occupational noise is 85 decibels on an A-weighted scale as an 8-hour time weighted average. OSHA limits noise exposure to 90 decibels, also on an A-weighted scale and as an 8-hour time weighted average (U.S. Department of Health and Human Services, 1998). A-weighting is an adjustment that gives lower frequencies less weight or significance than higher frequencies. An A-weighted sound level more closely resembles the human ear’s response to noise.

The American Conference of Governmental Industrial Hygienists (ACGIH) assigned noise a Threshold Limit Value (TLV) of 85 dBA as an 8-hour time weighted average. Exposure to 88 dBA is limited to 4 hour, exposure to 91 dBA is limited to 2 hours, exposure to 94 dBA is limited to 1 hour and so on. (ACGIH, 2011).

TLVs for Noise

 

Duration per Day

Sound Level, dBA

Hours

24

80

16

82

8

85

4

88

2

91

1

94

Minutes

30

97

15

100

7.50

103

3.75

106

1.88

109

0.94

112


Noise exposure has also been associated with temporary hearing loss, decreased perception of noisiness and masking, increased stress, fatigue, disturbance of sleep and decreased concentration and mental performance (Osada, 1988).  Noise-induced hearing loss starts in the higher frequencies (3,000 to 6,000 Hz) and slowly develops from chronic exposure to excessive sound. Sound must exert a shearing force on the hair cells lining in order to be perceived, and if the force is too strong, cell damage and cell death can occur (Berger et al., 2003).

A study of noise in a residential area near a heavily-travelled road found that impacted residents were annoyed with the noise and outdoor communication was difficult. The occupants of houses nearest the road reported some trouble communicating indoors and difficulty sleeping as well (Nilsson, 2006). Awareness of noise pollution has increased significantly over the past few decades. Highway traffic, industrial parks and backup generators are examples of sources of sound that can greatly disrupt residential or work environments.

The benefit to construction workers from these structures during the erection of barrier walls has not been studied, but is undoubtedly limited for most trades. The noise from the heavy equipment would definitely exceed that of road noise for equipment operators. NIOSH reported that bulldozer operators had a range of exposure from 92-109 dBA (Spencer, CDC) while exposures for residents near busy streets has been reported as 70 dBA (Nilsson et al., 2006).

How Risks are Reduced:

Barriers and enclosures are designed to reflect or absorb noise or both. Through the use of high gauge steel and/or specially designed absorption materials, sound is reduced when it reaches the barrier or enclosure. The enclosures often feature specially designed baffles and louvers to allow for airflow through the structure while keeping noise levels low. This allows for heat and exhaust dissipation from enclosures containing generators or other equipment.

While there are no published sampling data on these specific products, there are studies indicating that exposure to noise can be significantly reduced through the use of sound barriers and enclosures. Using noise control techniques will reduce exposure to hazardous levels of noise and reduce environmental or community noise. The extent that they reduce noise exposure is expected to be significant. The extent of the reduction is dependent on the type of barrier or enclosure used, the method of noise reduction, such as absorption versus reflection, the level of noise in the environment, the absorptive properties, and the proximity to the noise source.

Over a two-year period, a study determined that a sound barrier wall improved living conditions for a residential community located off a busy road where approximately 20,000 cars travelled per day. After construction of the eight-foot wall was completed, the houses closest to the new barrier saw a sound reduction from approximately 70 decibels to 62 decibels. Residents also reported easier communication when outside and better communication inside, along with better sleeping conditions. Occupants in the community also stated that annoyance levels dropped with the sound level (Nilsson, 2006).

Industrial hygienists use sound level meters or noise dosimeters to determine noise levels and recommend the use of quieter techniques to prevent hearing loss and reduce the risk of accidents. Proper maintenance and retrofitting existing equipment can decrease excess sound as well (Suter, 2002).

Sound Fighter Systems states that its LSE Absorptive Noise Barrier Systems can obtain a transmission loss of up to 33 dBA.

Unger Technologies claims that its sound enclosures can obtain a transmission loss of up to 58 dBA, depending on the frequency range.

Effects on Productivity:

Lower noise levels are expected to reduce stress and fatigue, and increase the concentration and mental performance of workers. Improved worker health, comfort and concentration may lead to greater productivity. Reduced sound levels can also lower the risk of accidents as communication among workers is easier and more effective. The number of noise-related complaints received, particularly from the impacted community may be reduced, thereby increasing productivity.

Additional Considerations:

The use of diesel and especially gas-powered equipment poses the risk of carbon monoxide exposure, especially in enclosures and areas where airflow is reduced. Steps to control exposure are important because the gas is invisible, odorless and tasteless. Poisoning by carbon monoxide can occur quickly indoors or in enclosures, but working outdoors does not ensure operators won’t be overcome. Small, inexpensive personal monitors should be worn by the operator to warn of unacceptable exposures. Equipment should not be left idling to cut down on carbon monoxide and to conserve fuel.

As is the case with any construction equipment, users should follow manufacturer safety recommendations and comply with any applicable local, state or federal regulations.

Contributors:

Andrew Kingston, Michael R. Cooper and Bruce Lippy - The Lippy Group, LLC

Availability

Sound Fighters Systems Noise Control
To obtain information, visit http://soundfighter.com/ or contact 1-866-348-0833 info@soundfighter.com

Kinetics Noise Control
To obtain information, visit http://kineticsnoise.com or contact 1-877-457-2695 http://kineticsnoise.com/replocation.asp

EchoBarrier NoiStop Fencing
To obtain information, visit http://www.echobarrier.com or contact 1-800-728-9098

Eco System Sound Control
To obtain information, visit http://www.ecosoundbarrier.com or contact 1-866-348-0833 http://www.ecosoundbarrier.com/ContactUs.html

Return on Investment

To calculate the return on investment (ROI) for your specific application, please visit our Return on Investment Calculator. While a specific ROI example has not been developed for this particular solution, the ROI Calculator provides a useful tool and guidance on how to generate your own on investment analysis.