# Engineering Controls Database

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## Transformer (2) – Noise Case Study

| Problem:                         | Overview: The National Institute for Occupational Safety and Health (NIOSH) published an industrial noise control manual in 1978 [NIOSH 1979].  As part of this manual, a number of general noise control methods were provided.  These methods are meant to reduce the amount of sound energy released by the noise source, or divert the flow of (sound) energy away from the receivers, or protect the receivers from (sound) energy reaching them. The key to noise control is finding the control that is both and economical.  One of the general noise control methods provided in the NIOSH noise control manual is summarized in this write-up.Case study: A transformer at the Puerto Rico Water Resources Authority (PRWRA), Santa Maria Substation, Ponce, Puerto Rico, is located just 22 ft from a neighboring home. The people living next to the substation complained about the noise radiated by the transformer. |
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| What this means to you:          | A sound survey conducted by PRWRA confirmed that the sound levels resulting from the transformer operation exceeded the ambient noise levels in the area. From the data obtained, the degree of noise control required was ascertained.  A minimum of 9 dB of noise reduction is required in sound level.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Description of control:          | An 18-ft-high barrier was chosen as the control here. The barrier design incorporated IAC Noishield® prefabricated panels. Such units are easy to install and provide flexibility in erection or relocation. The overall configuration of the barrier design is shown in Figure 1.**Figure 1. Plan view of sound barrier arrangement.**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| References:                      | NIOSH [1979]. Industrial noise control manual – revised edition. Cincinnati, OH:  U.S. Department of Health Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 79-117.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Keywords:                        | community noise controlcommunity noise controlelectrical transformerelectrical transformernoise controlnoise control                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| How well does this control work? | Overall ambient sound pressure levels, together with levels mea¬sured in the complaint area before and after installation of the barrier, are shown in Table 1.[img=1]The noise reductions noted in Table 1 indicate that, after the barrier was installed, the sound levels at the neighboring home were no longer controlled by the transformer, but by the existing ambient levels. Consequently, complaints concerning the substation transformer ceased.                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |

November 16, 2018
National Institute for Occupational Safety and Health