\nIn a 1930s pulp magazine entitled The Avenger, a character walking down a street saw a building explode. He did not hear it <\/p>\n
explode because, according to the narrative, the sound was so loud that his hearing was temporarily stunned. He watched as <\/p>\n
the building silently collapsed, and his hearing returned to normal a few pages later. <\/p>\n
\nNaturally, a pulp magazine—especially one with a central character who can transform to look like anyone else in the <\/p>\n
world—does not have to adhere strictly to the facts. However, in the real world, excess noise and subsequent hearing damage <\/p>\n
and loss pose a significant risk in the workplace.<\/p>\n
\nIn 1991, the Occupational Safety and Health Administration’s (OSHA’s) Directorate of Compliance Programs issued a memo <\/p>\n
instructing regional offices to cite employers for failure to record instances of occupational hearing loss. This is defined <\/p>\n
as “an average shift in hearing of 25 dB or more at 2,000, 3,000 and 4,000 Hz in either ear, if an exposure in the work <\/p>\n
environment either caused, aggravated or contributed to the case.” The shift must be calculated by comparing the current <\/p>\n
hearing test with the original baseline audiogram for the employee, adjusting for age if appropriate. OSHA formally codified <\/p>\n
hearing loss recordability as part of its record-keeping rule in 2001, and it was implemented on January 1, 2003. Hearing <\/p>\n
loss is now officially recognized as a workplace hazard.<\/p>\n
\nLoud Noise Can Affect More Than Hearing<\/b><\/p>\n
\nCatherine Palmer, Ph.D., is director of the Center for Audiology and Hearing Aids at the University of Pittsburgh Eye and Ear <\/p>\n
Institute and is an associate professor of otolaryngology and of communications science and disorders at the university. Dr. <\/p>\n
Palmer notes there are many reasons why noise can be a problem. Audiologists worry about noise when it interferes with <\/p>\n
communication or is loud enough to cause permanent hearing loss. Noise also contributes to the perception of tinnitus <\/p>\n
(ringing in the ears), which can be an annoying or disabling condition. In addition, loud noise is known to elevate blood <\/p>\n
pressure in some individuals.<\/p>\n
\nDavid C. Byrne, a research audiologist for the National Institute for Occupational Safety and Health (NIOSH), agrees. “Noise <\/p>\n
is often defined as ‘unwanted sound,'” he says. Sometimes the noise level is not loud enough to produce a health hazard, but <\/p>\n
it may present a nuisance to nearby individuals. Everyday noise (i.e., loud music, recreational activities, barking dogs, <\/p>\n
road\/air traffic, etc.) can be annoying and is exacerbated by factors such as time of day, particular location (e.g., <\/p>\n
urban\/rural) and the duration, volume and character of the noise. Too much noise can also be an issue in indoor office areas, <\/p>\n
particularly where the noise is comprised of conversations that can be overheard between cubicles.<\/p>\n
\nIs this as big a problem as OSHA believes? Byrne thinks it is. “Exposure to high sound levels results in the development of <\/p>\n
noise-induced hearing loss, which can be a serious physical, psychological and social problem. Occupational hearing loss is <\/p>\n
the most common occupational disease in the United States and is listed among the 21 priority research areas, as described in <\/p>\n
the NIOSH National Occupational Research Agenda. Efforts to prevent occupational hearing loss appear to be hindered because <\/p>\n
the problem is insidious and occurs without causing pain in affected workers. One consequence of noise-induced hearing loss <\/p>\n
is a reduced quality of life due to the inability to communicate with family, friends and the general public. However, this <\/p>\n
normally occurs after the hearing loss has progressed too far and the damage is irreversible.”<\/p>\n
\nAbsorption, Isolation and the Combination of Both<\/b><\/p>\n
\nDr. Palmer believes that there are several solutions to the problem of excess noise: “Remove oneself from the situation; wear <\/p>\n
hearing protection; reduce the actual noise source; or treat the environment to reduce the noise that impacts the <\/p>\n
individual.” Many sources of noise in the workplace cannot easily be reduced; therefore, environmental treatment must be <\/p>\n
implemented.<\/p>\n
\nByrne discussed the use of insulation in combating sound, saying, “The important concept to remember here is that there is a <\/p>\n
distinction between absorption and attenuation (isolation) of sound.” <\/p>\n
\nAbsorption, as measured by the absorption coefficient (a), is desirable for reducing noise within a space, he went on to <\/p>\n
explain. Sound absorption is realized by materials—usually porous and often lightweight—that dissipate the acoustical energy <\/p>\n
as heat (in negligible amounts) when the sound waves propagate through. Tables containing frequency-by-frequency absorption <\/p>\n
coefficients for various materials are printed in acoustical textbooks and manufacturer’s product data. The absorption <\/p>\n
coefficient is always a number between 0 and 1 and represents the percentage of sound absorbed by the material (e.g., 0 = no <\/p>\n
acoustical energy absorbed; 0.5 = 50 percent absorbed and 0.99 = 99 percent absorbed).<\/p>\n
\nA high sound isolation factor, measured by the number of decibels lost in transmission, is desirable for preventing sound <\/p>\n
transmission. This is achieved using materials that sound waves cannot easily penetrate. A good attenuating material is <\/p>\n
typically nonporous, dense and relatively heavy. Unlike sound-absorption materials (e.g., soft foam), sound-isolation <\/p>\n
materials usually have structural functions (e.g., concrete or bricks). Tables\/charts are available that list the sound <\/p>\n
transmission class (STC) of common construction materials.
\nAcoustical absorbers are usually poor attenuators or sound barriers. A good attenuator reflects sound waves and thus has a <\/p>\n
low absorption coefficient. Manufacturers often combine materials with different properties to achieve both absorption and <\/p>\n
isolation (e.g., urethane foam bonded to a dense substrate). <\/p>\n
\nThe Best Type of Insulation for the Job<\/b><\/p>\n
\nWhen asked whether mineral wool or fiberglass is better for sound control, Byrne had mixed feelings. “The answer depends on <\/p>\n
exactly what you want the material for,” he said. In general, both materials work on the same acoustical principle of <\/p>\n
absorption.<\/p>\n
\nOpen-cell or open-structure products are better than closed-cell or closed-structure for acoustical purposes. Some examples <\/p>\n
of open-cell products are commonly known. “Mineral wool” refers to three types of insulation that are basically the same: <\/p>\n
glass wool or fiberglass, which is made from recycled glass; rock wool, which is made from basalt (an igneous rock); and slag <\/p>\n
wool, which is made from steel-mill slag. For many years, mineral wool was the most widely used insulation in the United <\/p>\n
States, Canada and Europe. Although mineral wool is much heavier and costs more than fiberglass and cellulose, it offers some <\/p>\n
substantial benefits such as being more heat resistant than fiberglass. <\/p>\n
\nRegarding acoustics, the combined effect of the surface openings, internal structure, flow resistance and thickness <\/p>\n
determines the absorption coefficient of the material. Proper installation is necessary for optimal performance of acoustical <\/p>\n
materials. For example, unless approved by the manufacturer, a material should not be compressed to less than the original <\/p>\n
thickness when being installed. Likewise, paint or other surface treatments\/coverings may severely degrade a material’s <\/p>\n
absorptive properties. To determine the best material for the job, it is helpful to consult the manufacturer or a table of <\/p>\n
the representative physical characteristics and absorption coefficients for different forms\/thicknesses of fiberglass and <\/p>\n
mineral wool. The best-suited material for a particular application may depend on environmental conditions rather than <\/p>\n
acoustical considerations.<\/p>\n
\nImportant Elements of Sound Control<\/b><\/p>\n
\nSTC and noise reduction coefficient (NRC) are important elements of sound control. Everything in acoustics, particularly <\/p>\n
regarding noise-control issues, is frequency dependent. Significantly different treatments\/solutions may be required, <\/p>\n
depending on whether the offending noise is at a very high or very low frequency. It can be helpful to condense a set of <\/p>\n
acoustical properties into a single number.<\/p>\n
\nSTC is a single-number rating used primarily to measure the speech privacy of a barrier or other structure (e.g., walls, <\/p>\n
doors, windows, office partitions, etc.). It is determined from a plot of frequency-specific transmission loss data measured <\/p>\n
in 1\/3-octave bands from 125 to 4,000 Hz. STC is often specified as a performance criterion by architects and engineers for <\/p>\n
places where speech privacy is of primary interest. It is important to note that STC is measured in an acoustical laboratory <\/p>\n
(where the test specimen is mounted between two reverberation chambers); therefore, the labeled STC value of a product will <\/p>\n
be fully realized only if it is installed correctly.<\/p>\n
\nNRC is also a single-number rating. It is typically used when specifying the desired and\/or required absorptive <\/p>\n
characteristics of a material. The NRC for a material can be obtained easily by taking the mathematical average of the <\/p>\n
absorption coefficients at 250, 500, 1,000 and 2,000 Hz. Careful consideration is necessary when using NRC values to compare <\/p>\n
or select materials because absorption coefficients can vary widely in frequency even if NRC values are similar.<\/p>\n
\nSound insulation comes in many forms, including panels with perforated steel coverings that help trap sound and fiberglass <\/p>\n
cloth, which can be draped over an object and sealed with vinyl, for a less permanent control attempt. <\/p>\n
When asked about a new advance in mastic, or insulating paint, Byrne said, “If you are referring to spray-on <\/p>\n
thermal\/acoustical (typically cellulose) insulation, then everything [we have] discussed regarding acoustical absorption <\/p>\n
applies here as well. Again, the exact characteristics of the material and the final thickness will govern its acoustical <\/p>\n
qualities.”<\/p>\n
\nHe continued, saying, “It looks like this particular sound-reduction paint coating also works on the principle of acoustical <\/p>\n
absorption. In other words, this paint apparently adds an absorptive layer to the wall surface, where the incident sound <\/p>\n
waves are dissipated (absorbed) by the coating instead of just bouncing back off the wall. In theory, this should work fine. <\/p>\n
However, I would question its usefulness for a couple of reasons. First, the resulting ‘thickness’ is actually so thin that <\/p>\n
only the very highest audio frequencies would likely be absorbed (typically, the lower the frequency, the greater the <\/p>\n
thickness required). Also, they advertise a 30-percent reduction of sound. I’m not sure exactly what they are referring to or <\/p>\n
how they calculated it, but a 30-percent reduction may only be measured as a 1- to 2-decibel difference, which is barely <\/p>\n
noticeable to most people.”<\/p>\n
\nInsulation Is Working<\/b><\/p>\n
\nExcess sound remains a danger in commercial work areas. Even in an office, free from the sounds of spinning turbines and <\/p>\n
pounding jackhammers, excess noise can be a problem. If not for insulation around us, the constant whine of a Xerox machine <\/p>\n
or dot-matrix printer would be significantly more grating. At home, a teenager’s loud stereo can contribute to discomfort or <\/p>\n
partial hearing loss. To combat such noises, we have the acoustical engineers of the insulation industry. They may not be <\/p>\n
able to stop exploding buildings from causing temporary deafness, but they can help keep noise in the workplace under <\/p>\n
control. <\/p>\n","protected":false},"excerpt":{"rendered":"
Excess noise can have long-term effects on building workers, but insulation can help.<\/p>\n","protected":false},"author":[137],"featured_media":0,"template":"","categories":[298,301,20],"class_list":["post-7283","articles","type-articles","status-publish","hentry","category-installation","category-design","category-acoustics","author-bruce-and-amy-kent"],"acf":[],"yoast_head":"\n