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Figure 2. Prevalence of hearing loss by time period and industry sector, 1981–2010 for 1,816,812 workers as reported by Masterson (2015).
Manufacturing sector (Figure 2). Think for a moment what this means. One in four noise-exposed workers in mining and construction and one in five noise-exposed workers in manufacturing jobs are suffering material hearing impair- ment, in large part due to earning a living in these sectors. In 2015, more than forty years after the promulgation of the Occupational Safety and Health Act, the question lingers: “Why are workers still losing their hearing?”
One simplistic answer is that hearing loss rarely causes vis- ible injury. The answer is certainly more complicated. For the most part, occupational hearing loss occurs gradually as a result of prolonged exposure to noise or an ototoxic sub- stance. When a person experiences a sudden or immediate change in hearing statues, such as a loss due to a firecracker or a gunshot, it grabs their attention. The sudden change is memorable, but gradual losses slowly rob the ear of its sen- sitivity.
The National Institute for Occupational Safety and Health (NIOSH) defines material hearing impairment as an average loss of the hearing threshold levels for both ears that exceeds 25 dB at 1,000, 2,000, 3,000, and 4,000 Hz (NIOSH, 1998). NIOSH has been at the forefront of establishing exposure limits for noise since it was formed in 1972 and has estab- lished recommended exposure limits of 85 dB for a time- weighted eight-hour exposure. A rule of thumb that can be derived from the Industrial Noise Manual (American Indus- trial Hygiene Association, 1975) can help determine the po- tential for excess noise:
“If you need to raise your voice to be heard by someone who is at an arm’s length, then the noise level is prob- ably above 85 dB SPL and you should either leave the area or don hearing protection to prevent exposure.”
Even workers exposed to noise at 85 dB are at risk of hearing loss. When the noise levels are not so loud, the risk is not perceived to be great. Thus, a worker is less inclined to wear hearing protection in less hazardous, lower levels of noise. In fact, Rabinowitz (2012) showed that the workers most at risk were those exposed to 80 to 90 dB noise levels because they were less vigilant about wearing protection.
NIOSH’s research in hearing loss prevention has tradition- ally focused on the hearing mechanism and how to identify and prevent hearing loss at the ear. As can be seen in the diagram in Figure 3, personal protective equipment is the least effective means of controlling a hazard in the industrial hygiene hierarchy of control. The most effective method to protect hearing is elimination of the hazard. If the hazard cannot be eliminated, is there a process that can be substi- tuted and still accomplish the job? If the elimination and substitution are not possible, then what engineering noise control solutions can be used to reduce the exposure? Some- times the noise cannot be eliminated, and administrative controls must be used to limit the amount of time a worker is exposed. Personal protective equipment falls at the bottom of the hierarchy of control because it is the most difficult to effectively implement. And yet hearing protection has been one of the first solutions provided for noise-exposed workers.
Figure 3. Hierarchy of controls for reducing workplace hazards. The top three are considered most effective, whereas the bottom two are least effective because the worker is responsible for the control. Adapted from NIOSH (2015).
Engineering Noise Control
In order to control noise, you must identify the source and measure whether it is hazardous. For example, if the goal is to achieve safe noise levels of 82 dB, then control of a 110-
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