# Engineering Controls Database

Minus

## Motor Generator Set – Noise Case Study

| Problem:                         | Overview: The case history presented here is one of sixty-one case histories that were published by the National Institute for Occupational Safety and Health (NIOSH) in 1978 as part of an industrial noise control manual [NIOSH 1979].  The case histories are examples of engineering tasks that have been completed not only by professional noise control engineers but also by non-acoustical specialists who used common sense to solve their noise problems. The case histories were chosen primarily because the amount of noise reduction actually achieved was measured. Such engineering results, even if not directly applicable to a specific situation, illustrate general principles that may point the way to a successful result.  They are intended to be useful to production and safety engineers, health personnel, and other factory personnel who are not specialists in noise control.Case study: Operation of a motor generator set caused a 94-dBA sound level at a position 5 ft from the unit, giving rise to complaints from nearby workers. |
|----------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| What this means to you:          | A 94 dBA sound level only allows for 1 hour of exposure time for a worker (using the 85 dBA criteria with a 3 dB exchange rate).  The level needed to be dropped to a level where workers can safely work around the machine throughout their shift.Hearing loss is one of the most common occupational diseases in America today and the second most self-reported occupational illness or injury.  Approximately 30 million workers are exposed to hazardous noise on the job and there are approximately 16 million Americans with noise-induced hearing loss.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Description of control:          | An enclosure was selected to control the noise.  The enclosure was built of 3/4-in. plywood lined on the inside with 1/2-in.-thick glass fiber, such as is used for lining ducts.  Figure 1 shows a cross section of the enclosure. Note the gap at the base of the enclosure, which allows for air supply.**Figure 1. Cross-sectional sketch of the high-frequency motor generator set**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| 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.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| NAICS Codes:                     | 335312                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| Keywords:                        | motor generatormotor generatornoisenoisenoise controlnoise control                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| How well does this control work? | Figure 2 shows before, after, and predicted data. A 10-dB reduction in sound level was achieved.[img=2]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |

November 16, 2018
National Institute for Occupational Safety and Health