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Preventing Occupational Hearing Loss
dB process will be significantly more complicated than an 85-dB process. For instance, a hammer forge can produce peak impulse levels in excess of 140 dB. Time-weighted aver- ages (TWA, see Table 1) for the hammer operator and helper range between 88 and 110 A-weighted noise exposure lev- els (dBA) (Brueck et al., 2015). Sixty-five percent (65%) of the workers in the drop forge facility reported that they had hearing loss. Even workers with only a few years of exposure reported hearing loss. Control of the noise exposures in a hammer forge operation is difficult. Enclosing the worker is not a feasible option because the workpieces have to be manipulated during forging. Elimination and substitution are particularly difficult because the workpiece is being hardened through the forging process. Although acoustic treatments can best be used to reduce the reflected sound pathways, the most effective solution would be blocking the sound from reaching the ears.
Table 1: Explanation of Time-Weighted Average (TWA)
the ears to reduce the sound reaching the middle and inner ear. Frost and Sullivan (2005) reported that 2.1 billion hear- ing protectors were sold in the United States, with estimated total sales of $249 million. The concept is simple: “Stick it in your ear.” Although some industrial sectors have expe- rienced a reduction in the prevalence of hearing loss com- pared to 1981, the reductions are not across all sectors (Mas- terson et al., 2015). What these trends call for is a change in the paradigm by which hearing loss prevention and noise control are achieved.
NIOSH “Buy Quiet” Initiative
Starting in 2004, NIOSH initiated an effort to develop a da- tabase of sound power, sound pressure, and vibration levels for hand held power tools. The NIOSH Power Tools Data- base (http://www.cdc.gov/niosh/topics/buyquiet/) for elec- tric-powered hand tools contains about 200 different tools that were tested for sound power emissions at the University of Cincinnati Acoustics Testing Laboratory. Typical tools that can be found in the database are circular saws, drills, electric screwdrivers, chop-saws, sanders, and other carpen- try tools. Tools were tested in configurations described by the ANSI S12.15 standard for the measurement of sound emission of hand-held power tools (ANSI, 2012). Unlike sound pressure, sound power is a constant for an acousti- cal source operating under specific conditions and permits comparisons of the emissions of devices. As well, economic decisions can be made regarding the cost of reducing noise exposures and improving health and safety of workers.
The development of the Power Tools database led to the de- velopment of the NIOSH Buy Quiet Initiative. Two parts are necessary to successfully implement Buy Quiet:
1) A stated process that allows an organization to pur- chase quieter equipment and
2) Sound emission data that are readily accessible and comprehensible to the purchasing agent.
These elements permit informed decisions that will reduce noise levels in the workplace and reduce hearing loss.
Process
The process of procurement will vary significantly between large and small companies. Large companies, such as au- tomobile manufacturers, have the ability to include noise specifications in procurement documents, which must be met after installation. In 2004/5, the Hearing Loss Preven- tion Team at NIOSH conducted a research study with a major US auto manufacturer. During the yearlong study, the company replaced several of the large stamping presses
This leads to an interesting dilemma for the health and safety professional. The noise control engineer is concerned about reducing the emission level of noise for a particular piece of equipment. The hearing conservationist is concerned with reducing the immission received by the worker’s ears. For the noise control engineer, each machine is unique. One might have gears while another may have belts and pulleys. Tools that have identical functionality differ in shape and power depending upon the manufacturer. As tools become more powerful, the noise levels may tend to increase. The dilemma is how to protect a worker’s hearing without every health and safety professional becoming a trained noise con- trol engineer.
Historically, health and safety has resorted to controlling the immission that a worker receives by covering or plugging
30 | Acoustics Today | Spring 2016