# Engineering Controls Database

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## Spiral Vibratory Elevator – 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: Spiral vibratory elevators are used as part of the handling equipment to cool hot processed ingredients while lifting them from one level to another 6 m higher at a pet foods factory. The sound level in the immediate vicinity of the elevators is 104 dBA. Plant management aimed at reducing elevator noise to below that of the existing workshop ambient level of 84 dBA.                                                                                                                                                                                                                                                                                                                                                                         |
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| What this means to you:          | 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:          | A reduction of the elevator noise of at least 30 dB was required in this situation. Because the operation is automated, consideration was given to enclosing the two units involved. Such a treatment would normally be considered routine. In this case, however, because a food processing facility is involved, there are rigid require¬ments to prevent contamination of the food products from acoustic infill particles used in the construction of the enclosure panels. In addition, the enclosure had to accommodate product heat lossAn acoustic enclosure was designed to surround both elevators using their 100-mm-thick modular NoiseshieldTM panels (see Figures1 and 2). Acoustic tunnels were incorporated in the design at the feed conveyor inlets to the elevators. A forced ventilation system was also incorporated in the design to supply a flow of air sufficient for process and machinery cooling. Two IAC Power-FLOWTM silencer units were included at the intake and discharge points of the system to ensure that there would be no leakage of elevator noise through the ventilation system.Access to the interior of the acoustic enclosure, mainly for machinery maintenance, was afforded by a double-leaf acoustic door having a clear opening of 2000 mm x 1530 mm. An acoustic observation window of double safety glass was provided on each side of the access door.The sanitation problem was met by the inclusion of a polyethylene membrane between the acoustic infill and the perforated skin of the interior side of the panels.**Figure 1. Detail of acoustic enclosure: doors.****Figure 2. Acoustic enclosure around elevators.**      |
| 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:                     | 311111                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Keywords:                        | elevator noiseelevator noisenoise controlnoise controlpet foodpet food                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| How well does this control work? | After the erection of the enclosure was completed, a noise survey determined that the planned minimum noise reduction had been comfortably achieved and that, at a distance of 10 ft from the acoustic structure, the elevator noise could not be distinguished above the general shop sound level, 84 dBA.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |

November 16, 2018
National Institute for Occupational Safety and Health