Page 46 - Occupational Health & Safety, November/December 2019

HEARING PROTECTION
Three Basic Methods: Workplace Noise Control
Managing noise exposure is complex in terms of accurately assessing sound levels, identifying and ranking the dominant noise sources, and finding effective control solutions.
BY ROB STEVENS
Noise-induced hearing loss is a prevalent workplace injury in the modern industrial plant. Employers must manage workplace noise exposure. Doing so is complex in
terms of accurately assessing sound levels and noise exposure in the workplace, identifying and ranking the dominant noise sources to be targeted for mitiga- tion, and finding practicable, effective, and affordable noise control solutions.
Many aspects of acoustics and noise control are counterintuitive, and there is a great deal of myth and misinformation cluttering the common knowledge about noise. But there is a “convenient truth” we can use to cut through the confusion. Quite simply, there are really only a few ways to reduce noise indoors. All workplace noise control measures are really just varia- tions of the three basic methods, which are:
1. Reduce the amount of sound that is produced by a given process, operation or activity.
2. Block, or contain-and-dissipate the sound.
3. Reduce excessive room reverberation.
That’s it. Three options. A bit of explanation will
make this clear.
Some Important Basics of Acoustics
The reason that all indoor noise control measures fall into just three broad categories arises from the core fact of acoustics that there are fundamentally just four factors that determine the sound level at a given loca- tion indoors: the sound emission levels of the sound sources in the room; any physical measures that may impede or dissipate the sound as it propagates from the sources to the locations of interest; the distances from the sources to the locations of interest; and the amount of reverberation. (Reverberation is the ten- dency of sound to linger, and it occurs as a result of the sound bouncing around inside an enclosed space, reflecting and re-reflecting off of the many room sur- faces. Excessive reverberation in a room increases the amount of noise by allowing the sound to build up in a cumulative fashion.)
Assuming that the distances generally cannot be changed between the sound sources and worker loca- tions, the other three factors correspond to the three categories of noise control measures.
For reasons we will cover in the following sections, reducing the amount of sound that is produced by a given process or operation is the most effective noise control method, but is often also the most difficult to implement. Blocking or containing-and-dissipating the sound is the next most effective noise control method, and covers all of the most commonly used methods. Reducing room reverberation is only effec- tive in a very limited number of cases.
Reducing the Amount of Sound Produced
When a way can be found to reduce or eliminate the sound that is generated by a particular manufactur- ing processes, doing so is typically the most effective solution.
Some manufacturing methods are inherently noisy when, in fact, there may be a quieter method of achieving the same production task. For example, it is common to use compressed air to guide components around turns in moving conveyors to prevent jams. It is also common to use rotating/vibrating hoppers to orient lightweight parts before they are fed into a processing unit. The intense “hiss” of compressed air, and the tumbling of parts in a hopper, can create levels greatly exceeding workplace noise exposure limits.
While this sound can be challenging to mitigate, there can be simple solutions by finding alternative
42 Occupational Health & Safety | NOVEMBER/DECEMBER 2019
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