Control of Hazardous Noise

Hearing loss can result from exposures to high levels of occupational and nonoccupational noise. Occupational exposures are a by-product of working in close proximity to machinery and systems that are commonly used in industrialized societies. In most cases the equipment and the job of operating the equipment have been inadequately designed, so that the only way operators can perform their job is to be exposed to these noises. Nonoccupational exposures include listening to loud music, street conditions in urban areas, and other short-term and/or voluntary exposures. The main focus of this chapter is on exposures in occupational settings.

“Hearing loss due to occupational noise exposure is our most prevalent industrial malady,” according to Robert Sataloff, a prominent physician, and it affects nearly every American household (Sataloff, 1993). The hearing loss related to exposure to excessive noise, which has been known since before the Industrial Revolution, was first documented by Bernardo Ramazzini in 1713 among millers and copper-smiths (Ramazzini, 1964). The dangers have been studied for well over a century, and many laws and regulations have been passed recognizing the hazards of noise. Today, concerns include how noise exposure can also impact non-auditory health, but these effects are beyond the scope of this report.1

Very few studies have been done recently on the number of people exposed to hazardous occupational noise. In 1981 the Occupational Safety and Health Administration (OSHA) estimated that 7.9 million workers were exposed to noise levels of, or exceeding, 80 dB(A). Also in 1981, the U.S. Environmental Protection Agency estimated that more than 9 million people were exposed to daily noise levels above 85 dB(A) (EPA, 1981). Table 4-1 shows the economic sectors included in the EPA study. These numbers have probably remained stable or even increased since these studies were conducted.

TABLE 4-1 Number of Workers Exposed to Noise of >85 dB(A)

Industrial Sector

Number of Workers







Manufacturing and utilities








SOURCE: EPA, 1981.

The prevalence and long history of noise exposure on the job have often led to the realization by the working population that exposure to hazardous noise is an inevitable condition of employment. Since the onset of noise-induced hearing loss (NIHL) is typically slow and not painful, workers may be more accepting of hazardous noise than of other dangers in industrial settings.

Employers today are responsible for preventing NIHL by controlling hazardous noise exposures through the use of engineering controls, by monitoring the effects of exposure on employees through the administration of audiometric exams, and by providing hearing loss prevention programs that include hearing protection devices (HPDs). However, the effectiveness of HPDs and how well they comply with workplace rules are inconsistent, at best. As illustrated in the discussion below, the difference between reductions in noise levels in the laboratory and in the “real world” can be significant.

It is generally acknowledged that most large employers administer hearing loss prevention programs, although this is not the case with most small and many medium-sized companies. The effectiveness of these programs, when provided, is often inadequate. Engineering controls to suppress


New information concerning the general relationship between noise and health is becoming available (Babisch, 2008; DEFRA, 2009). However, it will require a multidisciplinary study committee to evaluate these results and determine their relevance to the health of the American people.

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4 Control of Hazardous Noise Hearing loss can result from exposures to high levels TABLE 4-1 Number of Workers Exposed to Noise of of occupational and nonoccupational noise. Occupational >85 dB(A) exposures are a by-product of working in close proximity to Industrial Sector Number of Workers machinery and systems that are commonly used in industri- Agriculture 323,000 alized societies. In most cases the equipment and the job of Mining 255,000 operating the equipment have been inadequately designed, Construction 513,000 so that the only way operators can perform their job is to be Manufacturing and utilities 5,124,000 exposed to these noises. Nonoccupational exposures include Transportation 1,934,000 listening to loud music, street conditions in urban areas, and Military 976,000 Total 9,125,000 other short-term and/or voluntary exposures. The main focus of this chapter is on exposures in occupational settings. SOURCE: EPA, 1981. “Hearing loss due to occupational noise exposure is our most prevalent industrial malady,” according to Robert Sataloff, a prominent physician, and it affects nearly every remained stable or even increased since these studies were American household (Sataloff, 1993). The hearing loss re- conducted. lated to exposure to excessive noise, which has been known The prevalence and long history of noise exposure on the since before the Industrial Revolution, was first documented job have often led to the realization by the working popula- by Bernardo Ramazzini in 1713 among millers and copper- tion that exposure to hazardous noise is an inevitable condi- smiths (Ramazzini, 1964). The dangers have been studied tion of employment. Since the onset of noise-induced hearing for well over a century, and many laws and regulations loss (NIHL) is typically slow and not painful, workers may have been passed recognizing the hazards of noise. Today, be more accepting of hazardous noise than of other dangers concerns include how noise exposure can also impact non- in industrial settings. auditory health, but these effects are beyond the scope of Employers today are responsible for preventing NIHL this report.1 by controlling hazardous noise exposures through the use of Very few studies have been done recently on the number engineering controls, by monitoring the effects of exposure of people exposed to hazardous occupational noise. In 1981 on employees through the administration of audiometric the Occupational Safety and Health Administration (OSHA) exams, and by providing hearing loss prevention programs estimated that 7.9 million workers were exposed to noise that include hearing protection devices (HPDs). However, levels of, or exceeding, 80 dB(A). Also in 1981, the U.S. the effectiveness of HPDs and how well they comply with Environmental Protection Agency estimated that more than workplace rules are inconsistent, at best. As illustrated in the 9 million people were exposed to daily noise levels above 85 discussion below, the difference between reductions in dB(A) (EPA, 1981). Table 4-1 shows the economic sectors noise levels in the laboratory and in the “real world” can be included in the EPA study. These numbers have probably significant. It is generally acknowledged that most large employers administer hearing loss prevention programs, although this 1 New information concerning the general relationship between noise and is not the case with most small and many medium-sized health is becoming available (Babisch, 2008; DEFRA, 2009). However, it companies. The effectiveness of these programs, when pro- will require a multidisciplinary study committee to evaluate these results and vided, is often inadequate. Engineering controls to suppress determine their relevance to the health of the American people. 

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 TECHNOLOGY FOR A QUIETER AMERICA noise sources are preferred but are less commonly used. the level believed to be hazardous to hearing, it is common Engineering solutions and expenditures that can actually practice to define an exchange rate that takes into account reduce noise emissions are sometimes “sold to manage - exposure time. ment” by highlighting their other advantages, such as gains Studies have shown that there is no exact value for the exchange rate (Stephenson, 2008).2 An exchange rate of in productivity or quality. 3 dB, which corresponds to equal energy,3 was first proposed The cost of NIHL can be assessed in two ways. First, there are the impacts on quality of life, such as strained by Eldred et al. in 1955. The 3-dB exchange rate, recom- relationships, difficulty or inability to communicate, feel- mended by the National Institute for Occupational Safety ings of isolation, lost friendships, ridicule from peers, and and Health (1998a) is the most widely adopted and the most a general inability to relate well to others. Accidents and widely accepted rate by scientists (Stephenson, 2008; Suter, absenteeism also should be included in the cost of NIHL. 1993), as well as by many government agencies in the United Second is the amount of money spent on compensation for States, including the U.S. Department of Defense (DOD), the NIHL. However, studies have shown that these costs are military services, and the National Aeronautics and Space underrepresentative of the total cost of NIHL (Shampan and Administration. It is also accepted by the American Confer- Ginnold, 1982; Suter, 1990). ence of Government Industrial Hygienists. According to Data for calculating the costs are difficult to come by. In Beth A. Cooper, a member of the study committee, a 3-dB a recent study by the Institute of Medicine (IOM, 2005), it exchange rate is considered “best practice” among hearing was stated that disabilities of the auditory system, includ- conservation professionals (Cooper, 2009). This rate has also ing tinnitus and hearing loss, were the third most common been standardized nationally (ANSI, 2006a) and internation- type of disability, accounting for nearly 10 percent of the ally (ISO, 1990). total number of disabilities among veterans. For the roughly Not all U.S. government agencies, however, accept the 158,000 veterans who began receiving disability compensa- 3-dB exchange rate. OSHA and the Mine Safety and Health tion in 2003, auditory disabilities were the second most com- Administration (MSHA), both part of the U.S. Department mon type of disability. These veterans had approximately of Labor, use a 5-dB exchange rate (29 CFR 1910.95 and 75,300 disabilities of the auditory system, out of a total of 30 CFR 62.0), as does the Federal Railroad Administration some 485,000 disabilities. At the end of 2004, the monthly (49 CFR 229.121). compensation payments to veterans with hearing loss as their Using the 3-dB rate, an 85-dB level exposure for 8 hours major form of disability represented an annualized cost of would be considered as hazardous as an 88-dB level expo- some $660 million. The corresponding compensation pay- sure for 4 hours. Using the 5-dB rate, the 85-dB exposure for ments to veterans with tinnitus as their major disability were 8 hours would be considered as hazardous as 90-dB expo- close to $190 million on an annualized basis. A 1997 study sure for 4 hours. As an example, it is estimated in American by the World Health Organization estimated that the cost of National Standard S3.44 (ANSI, 2006a) that an 8-hour daily NIHL in developed countries was in the range of 0.2 to 2.0 exposure to 90 dB(A) would, after 20 years, result in a noise- percent of a country’s gross domestic product (GDP)—or induced threshold shift of 10 dB at 3,000 Hz for 50 percent roughly $28 billion to $280 billion for the United States of the population. Data for different levels, frequencies, and (WHO, 2007). In a 2006 study in Australia, it was estimated exposure times are given in Appendix F of the standard. that the real cost of hearing loss amounted to 11.75 billion Considering the accuracy of sound-level meters and the AUD, or 1.4 percent of GDP (AE, 2006). difficulty of determining exposure over a period of eight The remainder of this chapter focuses on criteria for ac- hours, or even four hours, the difference is relatively small. ceptable risk of damage from hazardous noise in industry However, it becomes significant for short exposure times, as and government, hazardous noise from consumer products, shown in Table 4-2. research on impulsive noise, engineering controls in industry and the establishment of “buy-quiet” programs, HPDs, and HAZARDOuS NOISE LEVELS IN gOVERNMENT AND the current status of HPD research. INDuSTRy For continuous hazardous noise, A-weighted sound CRITERIA FOR DETERMININg ACCEPTABLE RISK OF pressure levels are used as the metric worldwide. Table 4-3 DAMAgE shows levels of 70 and 75 dB and higher that are known to pose some level of risk. The level in the first row (24-hour Exchange Rate Criteria for estimating the risk of damage from hazardous 2 Stephenson, M.R. 2008. The Scientific Basis for the 85 dB Criterion and noise must be based on both the level of noise (almost always 3 dB Exchange Rate. Presentation at the NAE workshop on Engineering Re- A-weighted sound pressure level) and the duration of noise sponses to Hazardous Noise Exposures, Washington, DC, August 14–15. exposure. In setting the level at which there is believed to 3 Equal energy means that when the level goes up by 3 dB (a doubling of be no hazard, the level at which action must be taken, and energy), the exposure time must be reduced by a factor of 2.

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 CONTROL OF HAZARDOUS NOISE TABLE 4-2 Hazardous Noise Exposures as a Function of exposure) is 5 dB below the level in the second row (8-hour Exposure Time for 3-dB and 5-dB Exchange Rates (based exposure; 10 log10{8/24} = –5 dB). This corresponds to a on exposure to 85 dB for 8 hours) 3-dB exchange rate. Because sound pressure levels vary with time, the levels in the table are generally time-weighted Hazardous Levels Hazardous Levels averages (TWAs). OSHA and MSHA, however, have their Exposure Time (3-dB Exchange Rate) (5-dB Exchange Rate) own methods of calculating noise dose (29 CFR 1910.95, 8 hr 85 dB 85 dB 30 CFR 62.0). 4 hr 88 dB 90 dB The International Institute of Noise Control Engineering 2 hr 91 dB 95 dB (I-INCE) has studied regulations on exposure to noise world- 1 hr 94 dB 100 dB wide (I-INCE, 1997). An updated version of the I-INCE data 30 min 97 dB 105 dB 15 min 100 dB 110 dB is shown in Table 4-4 (Suter, 2006). As the table shows, an 8- 7.5 min 103 dB 115 dB hour average A-weighted sound pressure level of 85 dB and a 3-dB exchange rate is used in many countries. The original references for the table are given in Suter (2006). HAZARDOuS NOISE FROM CONSuMER PRODuCTS AND LEISuRE ACTIVITIES TABLE 4-3 Action Points, References, and Type of Sound Level Noise from consumer products can sometimes be as haz- ardous as occupational noise in the workplace. In both cases A-Weighted Sound Exposure Pressure Level Time Explanation the degree of hazard depends on noise level and exposure time. One major difference is that noise in the workplace 70 dB 24 hr Adequate to protect the most sensitive tends to come from a number of sources, whereas noise from person at the most sensitive frequency (EPA, 1974). Equivalent sound level. the products discussed in this section tends to come from a single source. When exposure to occupational noise is added 75 dB 8 hr Adequate to protect the most sensitive person at the most sensitive frequency to exposure to noise during a leisure activity, the degree of (EPA, 1974), assuming that the hazard increases. remaining 16 hrs are quiet. Equivalent sound level. Consumer Products 80 dB 8 hr Required lower limit for beginning the integration to determine TWA Noise from consumer products and other hazardous (29CFR1910.95(d)(2)(i)). Instantaneous sounds can be generated by a variety of sources, including sound pressure level. kitchen appliances, audio systems, power tools (both hand- 85 dB 8 hr A widely used upper limit for exposure held and stationary), and all types of yard equipment. High to hazardous noise (see Table 4-4; levels of noise from these products and long exposure times NASA, 2007; NIOSH, 1998b). Required “action level” in OSHA can contribute to the risk of NIHL from occupational noise. hearing conservation amendment It is reasonable to assume that the 3-dB exchange rate applies (OSHA, 1981). Equivalent sound level. to exposures longer than 8 hours, from either or both. Noise 87 dB 8 hr European Union exposure limit levels from a variety of consumer products, including toys, value from 2003/10/EC (EC, 2003). have been published by Schwela (2006). Equivalent sound level. 90 dB 8 hr OSHA (29 CFR 1910.95) and MSHA Recreational Noise limits for exposure to hazardous noise (30 CFR 62.0). Time-weighted average Sources of hazardous recreational noise include on-road level. and off-road vehicles, loud music at concerts, and small 100 dB 8 hr OSHA-specified level at which aircraft engines. Like exposure to noise from consumer engineering controls should be used products, the degree of risk depends on the sound pressure (OSHA, 2009). This is often known as level and exposure time, as well as the amount of noise the “100-dB Directive.” It is the time- weighted average exposure level below exposure in the workplace. which OSHA inspectors are encouraged not to issue citations for the absence of engineering or administrative controls, Noise from Personal Listening Devices unless there is evidence that workers Personal listening devices are known to emit sound pres- are losing their hearing. sure levels that can be hazardous, if they are abused. It has NOTE: Except for the 80-dB level, the sound pressure levels in this table been estimated that at least 5 percent of users of these devices are related to how much risk is acceptable.

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4 TECHNOLOGY FOR A QUIETER AMERICA TABLE 4-4 Worldwide Regulations for Exposures to Hazardous Noise in the Workplace dBA Level for dBA Level for Audiology Tests Nation, Date (if available) PEL (8-hr average) dBA Exchange Rate dBA Engineering Controls and Other HC Practices Comments Argentina, 2003 85 3 85 85 Notea Australia, 2000 85 3 85 85 Brazil, 1992 85 5 85 b Canada, 1991 87 3 87 84 Chile, 2000 85 3 China, 1985 85 3 85 Colombia, 1990 85 5 c European Union, 2003 87 3 85 85 d 80 Finland, 1982 85 3 85 France, 1990 85 3 85 e Germany, 1990 85 3 90 85 Hungary 85 3 90 f India, 1989 90 Israel, 1984 85 5 Italy, 1990 85 3 90 85 Mexico, 2001 85 3 90 80 g Netherlands, 1987 80 3 85 New Zealand, 1995 85 3 85 85 Norway, 1982 85 3 80 Spain, 1989 85 3 90 80 Sweden, 1992 85 3 85 85 United Kingdom, 1989 85 3 90 85 d United States, 1983 90 5 90 85 Uruguay, 1988 85 3 85 85 Venezuela 85 3 NOTE: PEL is the permitted exposure level in each country. dBA rather than dB(A) is used because it was used in the referenced table. aEach Australian state and territory has its own legislation for noise, but all have now adopted the 8-hour PEL of 85 dBA and the 3-dBA exchange rate (ER). bDespite the existence of a Canadian national standard, there is some variation among the standards in individual provinces: Ontario, Quebec, and New Brunswick use 90 dBA with a 5-dBA ER; Alberta, Nova Scotia, and Newfoundland use 85 dBA with a 5-dBA ER; and British Columbia uses 85 dBA with a 3-dB ER. Most require engineering controls to the level of the PEL. Manitoba requires certain hearing conservation practices above 80 dBA, hearing protec - tors and training on request above 85 dBA, and engineering controls above 90 dBA. cThe European Union (EU; Directive 2003/10/EC) puts forward three exposure values: an exposure limit value of 87 dBA; an “upper action” level of 85 dBA; and a “lower action” level of 80 dBA, all using the 3-dBA ER. The attenuation of hearing protectors may be taken into account when assessing the exposure limit value but not for requirements driven by the upper and lower action values. At no time shall an employee’s noise exposure exceed the exposure limit value. When exposures exceed the upper action level, the employer must implement a program of noise reduction, taking into account technology and the availability of control measures. dEU continued: Hearing protectors must be made available when exposures exceed the lower action value of 80 dBA. Hearing protectors must be used by workers whose exposures equal or exceed the upper action value of 85 dBA. Audiometric testing must be available to workers whose exposures exceed the upper action value, and when noise measurements indicate a risk to health, these measures must be available at the lower action value. eThe German standard (UVV Larm-1990) states that it is not possible to give a precise limit for the elimination of hearing hazard and the risk of other health impairments from noise. Therefore, the employer is obliged to reduce the noise level as far as possible, taking technical progress and the availability of control measures into account. fIndia: This is a recommendation, not a regulation. gThe Netherlands’ noise legislation requires engineering noise control at 85 dBA ”unless this cannot be reasonably demanded.” Hearing protection must be provided above 80 dBA, and workers are required to wear protection devices at levels above 90 dBA. hThese levels apply to the OSHA noise standard, which cover workers in maritime and general industries. The U.S. military has more stringent standards; DOD as a whole uses the 85-dBA PEL and the 3-dBA exchange rate. The Air Force and Army have similar requirements, and the Navy is about to adopt the 3-dB ER. are exposed to A-weighted TWA levels of greater than 85 such devices sold, and the frequent long exposure times, it dB (Fligor, 2008).4 Considering the very large number of has been estimated that 50,000 people develop NIHL from listening to such devices for more than 4 hours per day over a period of years (Fligor, 2009; SCENIHR, 2008). Recom- 4 F ligor, B. 2008. Non-occupational hazardous noise. Recreational equipment, personal music devices, toys, buses, etc. Focus on children. At - mendations for avoiding NIHL are listed below (Fligor and tribution of hearing loss/damage to variety of sources. Presentation at the Cox, 2004): NAE workshop on Engineering Responses to Hazardous Noise Exposures, Washington, DC, August 14–15.

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 CONTROL OF HAZARDOUS NOISE • Limit listening level to 60 percent of the maximum sponsored by the National Academy of Engineering (NAE) in August 2008 (Dancer, 2008; Murphy, 2008).5,6 volume. • Limit listening time to 1 hour. Physical measures of an impulsive noise depend on its • Use a lower gain setting and shorter listening times character, and relating the degree of auditory hazard to a when over-the-ear rather than in-ear earphones are physical measure is a complex undertaking. For a single used. burst of noise, the instantaneous sound pressure is usually of most interest. However, measuring it requires a system Exact limits are difficult to specify because the sensitiv- with a wide frequency response, a wide dynamic range, and ity of earphones varies with the manufacturer and because a small phase shift. different earphones can be used with the same amplifier. A conventional sound-level meter with a peak-reading Assessments of NIHL caused by personal listening devices circuit and C-weighting can provide a reasonably good mea- have also been made in Switzerland (Hohmann et al., 1999) sure of the peak value of the instantaneous sound pressure, and the Netherlands (Passchier-Vermeer, 1999). and this peak value, expressed in decibels, has been widely used as a damage risk criterion. However, peak values cannot be measured using the fast or slow dynamic characteristics Noise from Toys of a sound-level meter because of their long time constants. A survey of toy safety standards for noise levels (ASTM, Also, A-frequency weighting does not satisfy the criterion 2008) and recommendations have been published by the U.S. of a wide bandwidth. Public Information Research Group (PIRG, 2005). Another At one time, an impulse sound-level meter was standard- survey that includes epidemiological studies as well as vari- ized. The instrument had a time constant believed to ap- ous national and international activities is available (Altkorn proximate the loudness of a transient sound and a decay time et al., 2005). The League for the Hard of Hearing provides constant long enough to obtain a peak reading. However, examples of noise levels from toys (LHH, 2009). A report standards committees discouraged use of this meter, and it by the Institute of Sound and Vibration Research provides is no longer standardized. measurement data and recommendations about noise from Another quantity that can be measured with a sound-level toys (ISVR, 1997); for example, the recommendation for the meter is sound exposure, which is the integral of the squared C-frequency weighted instantaneous sound pressure level instantaneous pressure over the duration of the burst. Ex- from cap-firing toys is that it not exceed 120 dB when mea- pressed in decibels, this becomes the sound exposure level, sured 25 centimers from the ear and 125 dB when measured which has been used to characterize, for example, aircraft 2.5 centimers from the ear. Contrast this with an undated alert flyovers. The relationship to auditory hazard is discussed in from the U.S. Product Safety Commission (CPSC, 2001a) the next section. that states, “CPSC reminds parents that caps may also pose One parameter that cannot be measured with a conven- a noise hazard. A current CPSC regulation limits the decibel tional sound-level meter is the A-duration (unrelated to level of caps to no more than 158 decibels. A warning label is A-frequency weighting). A-duration is the time from the mandatory on caps in the 138 to 158 decibel level as follows: beginning of the burst to the time that the instantaneous WARNING—Do not fire closer than 1 foot to the ear. Do not sound pressure is 20 dB below the peak value. A-duration use indoors.” See CPSC (2001b) for the full requirement. and other characteristics of impulsive noise are described in The measurement method is specified in 16 CFR 1500.47. an American National Standard (ANSI, 2006b). For a series of bursts or for continuous noise with an im- pulsive component, two other parameters are of interest. The IMPuLSIVE NOISE peak and root mean square sound pressure can be measured, and the ratio, expressed in decibels, is the crest factor. Impul- Physical Characteristics sive noise is characterized by a crest factor higher than that of In contrast to continuous noise, impulsive noise comes in random noise, which is why a system with a wide dynamic many different forms and is much more difficult to describe. range is necessary for making accurate measurements. High Impulsive noise may consist of a single burst, such as impact crest factors are related, in a statistical sense, to the ratio noise generated by a hammer hitting a nail, a sonic boom, or of the fourth moment and second moment about the mean a single rifle shot. It may also consist of a series of bursts, either closely spaced or more or less isolated—such as a 5 Dancer, A.L. 2008. DRCs for High-Level Impulsive Noise and Valida - tion Data. Presentation at the NAE workshop on Engineering Responses to series of hammer blows. Thus, characterizing a particular Hazardous Noise Exposures, Washington, DC, August 14–15. impulsive noise has been a subject of interest to engineers 6 Murphy, W.J. 2008. Impulsive Noise in Industry and in the Commu - for many years (IEEE, 1969). Characterizing impulsive noise nity: Considerations for Measuring Impulsive Noise. Presentation at the and associated auditory hazards was the subject of a NIOSH NAE workshop on Engineering Responses to Hazardous Noise Exposures, workshop in 2005 and two presentations at a workshop Washington, DC, August 14–15.

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6 TECHNOLOGY FOR A QUIETER AMERICA show that the equal energy rule adequately predicts hearing of the signal (kurtosis). Although not widely used, kurtosis damage. Therefore, at these levels impulsive noise, even is a measure of the impulsiveness of noise. when superimposed on a background of continuous noise, can probably be treated similarly to continuous noise for the Auditory Hazard purposes of assessing auditory hazard. Dancer (2008) presented results from a number of studies The peak value of the instantaneous pressure, expressed of hearing damage (i.e., Price 2007) and concluded that an in decibels and with C-frequency weighting, has been widely 8-hour, A-weighted equivalent level of 85 dB (LAeq8) should used as a measure of auditory hazard for impulsive noise. be used as the damage risk criterion for both continuous and For example, OSHA has set a limit on the peak sound pres- impulsive noise, whether military or occupational. If this sure level: “Exposure to impulse or impact noise should not conclusion is accepted, it would extend the equal energy con- exceed 140 dB peak sound pressure level” (OSHA, 1971c). cept for hazardous noise to even very short bursts of noise, The European Union sets an upper limit of 200 Pa (1 Pa = 1 N/m2) for instantaneous sound pressure using C-frequency which would greatly simplify the determination of auditory hazard. The sound exposure of an impulse would be deter- weighting (EC, 2003). This limit is not expressed in decibels, mined, averaged over an 8-hour time interval, and compared presumably to avoid confusion with the lower limits for with current damage risk criteria for continuous noise. continuous noise. The 200-Pa peak sound pressure can be converted to a sound pressure level: 10 log (p2/pref2) = 140 Another approach to assessing auditory hazard from im- pulsive noise is the Auditory Hazard Assessment Algorithm dB, where the reference pressure, pref, is 20 micropascals. for Humans (AHAAH), developed by G.R. Price for the World Health Organization guidelines state that peak U.S. Army (U.S. Army Research Laboratory, 2010). This sound pressure levels should not exceed 140 dB(A) for adults mathematical model of the human auditory system requires and 120 dB(A) for children (WHO, 1999). Note the use of as input the incident sound pressure as a function of time. A-frequency weighting in this case. An assessment of this model is well beyond the scope of this The use of peak sound pressure level as a measure of audi- report. We simply note that Dancer (2008) suggested it be tory hazard was questioned by Dancer at an NAE-sponsored used as a laboratory tool to clarify some specifics of weap- workshop (Dancer, 2008). He showed data from French mili- ons noise. Dancer also concluded that the AHAAH model tary studies comparing auditory hazard from howitzer and provides better estimates of auditory hazard than LAeq8 for rifle rounds. Soldiers were exposed to 20 rounds at the same the sound of air bags and high-level noise. peak sound pressure level (159 dB) but with an A-duration of In the preceding discussion of physical characteristics of 9 and 0.25 milliseconds, respectively. Almost no temporary impulsive noise, kurtosis was identified as another measure threshold shift (TTS) was observed for the howitzer rounds, of the impulsiveness of noise. Recent data from a series of but significant TTS was found for the rifle rounds. Since it animal experiments and at least one epidemiological study is generally accepted that repeated exposure to noise that indicate that the kurtosis metric, with possible adjustments causes TTS leads to permanent threshold shift, these results for frequency spectrum and bandwidth, in combination lead one to question the peak level and emphasize the impor- with equal energy would be an effective predictor of the tance of the A-duration in determining auditory hazard. They traumatic effects of complex noise (Davis et al., 2009; Zhao also show that very high sampling rates are necessary when et al., 2010). recording digital samples of a short burst of noise. The study committee concluded that damage risk criteria Because impulsive noise can be a series of bursts or con- for impulsive noise need further study and that such studies tinuous noise with an impulsive component, the question is and an agreement in the international standards community whether such noise, generally recognized by its high crest on optimal damage risk criteria for impulsive noise should factor, has the same auditory hazard as continuous noise serve as a basis for changing national, European Union, when the two have the same A-weighted sound pressure and international criteria for assessing auditory hazard from level. This question has been raised for more than 30 years. impulsive noise. Such studies will require the participation Brüel (1977) asked if damaging noise was being mea- of both engineers and experts in the physiology of the ear. sured correctly. He noted that studies at the time showed that Military experience will be a very valuable input to the industrial noise, presumably with an impulsive component, process. appeared to be more damaging than music at a higher noise level. Similarly, he noted that pilots with no ear protection in certain airplanes do not suffer as much hearing loss as pilots ENgINEERINg CONTROLS who listen to radio communications with their attendant HPDs and hearing protection programs are not the best clicks and bursts. This suggests that the peaks in the time way to protect the hearing of workers. The preferred way, waveform are significant contributors to auditory hazard. often called “engineering controls,” is to reduce workers’ NIOSH (1998b) cites a number of studies that indicate exposure by reducing the noise of the machinery or equip- that impulsive noise is more dangerous than continuous noise ment that generates the noise. If it is not possible to reduce of the same level. However, NIOSH also cites studies that

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7 CONTROL OF HAZARDOUS NOISE the noise from the source, then noise control along the path driven by an electric motor. These two items would probably by which the noise propagates to workers, such as inserting be mounted on a metal frame called a skid. The noise sources a noise control element between the machinery and workers, would be those of the motor (including a cooling fan, motor can be used. casing that radiates magnetic and mechanical noise, and a However, the most effective way, indeed, perhaps the only skid that radiates structure-borne noise), and the compressor way, to eliminate NIHL from occupational noise exposure (including intake and discharge air, intake and/or discharge is well-designed engineering controls, which are permanent, piping, engine casing of the compressor, and a supporting are effective with or without worker/supervisor compliance, structure). reduce absenteeism, make communication easier, reduce This brief description of noise sources illustrates that worker compensation costs, and reduce legal costs. For all of industrial equipment often has numerous sources of noise. these reasons, engineering controls are the protection method Thus, noise control requires controlling the most powerful of choice according to OSHA and MSHA. noise component first and then treating all of the other com- ponents in turn. For example, on a large fan with an open intake, the intake noise is dominant. Once the intake has Noise Mechanisms been appropriately silenced, it is necessary to review other The main differences between noise generated by indus- sources, such as the cooling fan for the motor, the casing- trial machinery and noise generated by other sources are radiated noise of the fan and motor, and possible structure- size, complexity, and diversity. Compressors, for example, borne noise from the skid. can be as small as a compact refrigerator or enormous, with a footprint of 20 × 30 feet. The main sources of noise are fluid Engineering Controls flow, friction, magnetic forces, mechanical forced vibration, impact, and combustion. Some engineering controls (Bruce, 2007) modify the Noise from fluid flow is generated by the movement of noise source to reduce the amount of radiated noise. This air (e.g., intake or exhaust air for engines, compressed air can be accomplished in several ways: used to clean off a workbench), gas (e.g., process gas flow- ing through valves and piping), and liquids (e.g., fluid flow • modifying the source so that it produces less noise through pipes and valves). Mechanical vibration includes • changing the operating parameters so that less noise is noise radiated from machinery casing compressing air or gas generated or pumping liquid. It includes noise radiated from surfaces • adding mufflers or silencers to intakes and exhausts mechanically attached to a noise source. • providing damping to reduce vibration Friction sounds can be characterized as stick-slip sounds, • isolating vibration to reduce excitation of other struc- like the screech of Styrofoam cups on a table top, chalk on tures a blackboard, or the squeal of tires when brakes are applied • providing acoustical shielding from the source sharply; rubbing sounds, like sanding on a surface or pistons • enclosing the source with lagging or a partial or total moving inside cylinders in an engine; and rolling friction, enclosure like ball bearings or tire noise. Sounds generated by magnetic forces can be emitted from electrically powered equipment, A number of “obvious” engineering controls can usually such as transformers, motors, and circuit breakers. Typically, be implemented in existing facilities to address 25 to 33 per- cent of noise problems in most workplaces (Driscoll, 2008).7 these noises have strong tonal components. Impact tools, like pneumatic chippers, generate impact Some are so obvious that they can easily be overlooked. noise when the equipment impacts the surface, but the re- Nevertheless, although these controls can be easily stated, sponse of the surface to the impact often dominates what their application requires careful selection. Some “obvious” is heard. Chipping on a rubber surface is obviously much controls are listed below: quieter than chipping on a metal plate. Combustion noise, such as noise from a furnace or the sound from the ignition • Maintain equipment properly (e.g., fix steam or air of fuel inside a gasoline or diesel engine, has strong low- leaks). In operations that require high-pressure steam, frequency components. steam leaks are often the dominant noise source. Industrial machines have drivers (i.e., power sources), • Change operating procedures (e.g., relocate the opera- such as electrical, compressed air, or hydraulic motors; tor and controls to a quieter position). gasoline or diesel engines; or gas or steam turbines. The • Replace equipment (e.g., buy a quieter version of the power sources drive blowers, fans, compressors, pumps, and product). countless other mechanisms. Depending on the application, a gearbox might be placed 7 Driscoll, D.P. 2008. Noise Control Engineering: The Reader’s Digest between the power source and the driven equipment. An Version. Presented at the NAE workshop on Engineering Responses to example of a complex noise source might be a compressor Hazardous Noise Exposures, Washington, DC, August 14–15.

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8 TECHNOLOGY FOR A QUIETER AMERICA Radiated Noise from Machine Housings • Modify the room (e.g., install sound absorptive materi- als). If the noise source and worker are some distance Airborne noise can be radiated by any surface. For ex- apart, sound absorption in the intervening space can ample, consider a piano. The keys strike hammers that strike reduce noise in the reverberant field. the strings. The strings do not produce much sound by them - • Relocate equipment (e.g., put noisy equipment in areas selves, but they are attached to the much larger sound board that are often unoccupied). that radiates the sound. In general, the larger the vibrating • Use equipment at proper operating speed (e.g., the panel, the greater the sound radiated from the surface. higher the speed, the louder the noise; run equipment Another example is a parts bin into which metal parts are at the lowest practical speed). dropped. If the bin is made of perforated metal, the radiat- ing area is smaller than if it is made of solid metal; thus, the Noise from Fluid Flow level of radiated sound will be lower. Of course, materials with high internal damping radiate even less noise. If the Noise sources with fluid flow include fans, compressors, bin were made of rubber (which has high internal damping), engines, pumps, and valves. Controls for reducing intake rather than metal (which has low internal damping), it would and discharge noise include lining ducts, installing dissipa- radiate even less sound. tive and reactive silencers, and installing special-purpose Sometimes machinery is housed inside an enclosure silencers. provided by the original equipment manufacturer. In such The inlet or exhaust duct can be lined with a sound- situations it is desirable for the panels of the housing to be absorbent material, such as fiberglass or mineral wool. appropriately treated. Damping compound should be applied Typical thicknesses range from 1 to 4 inches, depending on to the panels if there is any possibility that the resonance fre- the strength of the low-frequency component. Dissipative quencies of the panels will be excited. If the machine inside silencers also use sound-absorbing materials to attenuate the enclosure produces significant vibration into the enclo- noise. A simple dissipative silencer might be a set of parallel sure housing and structure, the panels should be vibration baffles running lengthwise to direct airflow and reduce noise. isolated from the structure. In addition, it may be useful for The absorptive material might be mineral wool or fiberglass the machinery enclosure to be mounted on vibration isolators covered with glass fiber cloth to reduce erosion from airflow. to keep it from transmitting vibration to the floor. In addition, a perforated or expanded metal facing could be added to the material to protect against contact damage. The Machinery Shields, Outdoor Barriers, and Enclosures longer the baffles and the closer they are together, the more effective they are as silencers. Reactive silencers operate on Shields. An acoustical shield may be inserted between the principle of mismatching acoustic impedance. A change the worker and a noisy section of a machine. Shields are in acoustic impedance causes a portion of the sound energy often mounted directly on the machine and reduce noise by to be reflected back to the source or back and forth within 8 to 10 dB under the following conditions: the silencer. Special-purpose silencers are available to fit exhaust ports • The worker is near the noisy operation. on pneumatic equipment, air wipes, and parts blowoffs. Re- • The smallest dimension of the shield is at least three cently, an innovative silencer called a duct resonator array times the wavelength of the dominant noise. (DRA) was developed based on the principles of a Helmholtz • The ceiling above the machine is covered with sound- resonator (Liu, 2003). DRAs positioned at the diffusers in absorptive material. larger centrifugal compressors effectively reduce noise levels from these machines; DRAs can also be placed in discharge Shields can be manufactured from safety glass, one- piping in a pipe spool. Basically, they reduce the A-weighted quarter-inch clear plastic, metal, or wood. Durability, sound pressure level by at least 10 dB—which is similar to expense, need for visual observation of the operation, and “halving” the loudness of the sound. need for access to the operation should all be considered Lagging is a noise control treatment that consists of lay- in selecting a material. If possible, oil-resistant, cleanable, ers of treatment around piping to reduce radiated noise in sound-absorptive materials should be incorporated into the refineries and noise from forced-draft and induced-draft fan machine side of the shield. ducts. The first layer wrapped around the pipe consists of glass fiber or mineral wool, typically 2 to 4 inches thick and Outdoor Barriers. A ny solid impervious wall that 6 to 8 pounds per cubic foot. Next a mass-loaded vinyl layer blocks the line of sight between a noise source and an ob- weighing 1 to 2 pounds per square foot is wrapped around server will reduce the noise level at the observer. The reduc- the glass fiber or mineral wool. The outer layer is a weather- tion depends on the frequency of the noise, the distance of the proof covering. Depending on the details of the installation, source from the barrier wall, the distance of the receptor from lagging can reduce the A-weighted sound pressure level by the barrier wall, and the height of the wall. Low-frequency 10 to 20 dB.

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 CONTROL OF HAZARDOUS NOISE Advantages of Designing for Noise Control sound diffracts around the ends of the wall and over the top more readily than high-frequency sound. Thus, the wall has Good industrial hygiene (as well as common sense) lower values of attenuation for low-frequency sound than involves removing hazards. In addition, workers may need for high-frequency sound. Typically, low-frequency sound is personal protective equipment. For example, steel-toed shoes attenuated by less than 5 dB, whereas high-frequency sound may protect workers from unexpected events, such as a large can be attenuated by as much as 20 dB. casting falling on a worker’s foot. The same precautions should be taken to protect workers’ hearing. Protecting hear- Partial Enclosures. A partial enclosure is a series of ing should not require constant intervention on the part of the walls around a machine with the top left open. A partial worker, such as wearing earplugs or other HPDs. Workers’ enclosure can be effective inside a plant if located near a hearing can be protected by engineering controls designed wall. However, some noise will still radiate out the top and into equipment or even added after the fact. With engineering contribute to the reverberant sound in the room. Reflections controls, the noise level remains constant, whereas with HPDs, from the ceiling will increase the sound pressure level at protection is dependent on the availability and proper selec- distances farther from the enclosure. A sound-absorptive tion of the HPD, proper training of the worker, proper action ceiling can reduce reflected sounds and thereby increase the by the worker, and appropriate supervision. effectiveness of the enclosure. For maximum effectiveness, Controlling noise in the workplace has many advantages, the sound-absorptive ceiling should extend out to the loca- such as reducing absenteeism, improving communication tion of the receivers. Sound-absorptive materials should also among workers, reducing the number of accidents, improv- be applied to the inside of the enclosure walls. ing efficiency, and increasing productivity. The two examples For equipment handling flammable liquids/gases, appro- below show how designing engineering controls into a priate fire-retardant systems and alarms will be required. system can lead to process improvements. Both of these companies worked with their suppliers to develop engineer- Total Enclosures. A total enclosure with a closed top ing controls, which they then purchased. provides better noise reduction than a partial enclosure. An automobile company used a procedure published by However, openings are usually necessary to provide (1) ac- the Association for Manufacturing Technology (formerly cess by personnel, either for inspection, maintenance proce - the National Machine Tool Builders Association) to mea- dures, or operator usage, or (2) access to (or for) materials, sure noise levels in its facilities (AMT, 2006) and then such as raw materials, products, or scrap. proceeded to use engineering controls to control the noise. Sound leakage around doors, windows, and hatches make In one instance the company replaced some equipment in its enclosures much less effective. Leaks can be handled with metal assembly weld cells. According to Robert Anderson, properly sealed doors, windows, and hatches. Closed-cell, an acoustical consultant, “Replacing pneumatic drives with elastomeric weather stripping with a pressure-sensitive ad- servo drives has reduced noise from spot weld impacts, hesive can be effective seals. Special acoustical gaskets are while extending weld tip life and saving energy” (Anderson, available, as well as magnetic-strip gaskets similar to those 2008).8 used on refrigerator doors. Michael Bobeczko, director of marketing, Sukut Con- If workers must have visual access to machines, lighting struction, documented improvements in production that may be required. If workers use the sound of the machinery resulted from noise control measures in the manufacturing to evaluate its performance, it may be necessary to retrain equipment industry (see Table 4-5). He described a typical them or to place a rugged microphone inside the enclosure manufacturing facility (Bobeczko, 1978).9 and send the signal to a small adjustable loudspeaker at the A process line in a typical aluminum can plant produces ap - worker’s position. Occasionally, it is possible to develop proximately 800 cans per minute. This high-speed process processors that incorporate the worker’s knowledge to au- starts at a cup press where sheet aluminum is blanked and tomatically adjust the machinery for optimal performance. drawn into cups. The cups are distributed to bodymakers Openings for raw materials, product, and scrap flow can where each machine redraws and irons the cup into a long be tunnels lined with sound-absorptive material. The noise seamless can. The can is then usually trimmed to a specific reduction will depend on the length and cross section of height and conveyed to a washer where it is cleaned, chemi- the tunnel, as well as the thickness of the sound-absorptive cally treated and dried. The can exterior is decorated by dry material. offset methods and the can interior is sprayed with a protec- Ventilation is required for all total enclosures and some partial enclosures. Ventilation openings can be acoustically 8Anderson, R.R. 2008. Application of Sound Level Specifications for In- lined ducts, elbows, or mufflers, depending on the severity dustrial Equipment. Presentation at the NAE workshop on Engineering Re - of the problem. sponses to Hazardous Noise Exposures, Washington, DC, August 14–15. Enclosure panels and structures should not contact any 9 Bobeczko, M. 2008. Industrial Noise Control Solutions Have Improved part of the machinery. If the enclosure is mounted on the Productivity. Presentation at the NAE workshop on Engineering Responses machinery, it should be vibration isolated. to Hazardous Noise Exposures, Washington, DC, August 14–15.

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40 TECHNOLOGY FOR A QUIETER AMERICA TABLE 4-5 Noise Reduction and Productivity in a In 1983, OSHA put forward an enforcement directive (see Beverage Can Manufacturing Plant OSHA, 2009, for the current version) setting a 100-dB action point for requiring engineering control of noise as long as Operating workers’ hearing was adequately protected by HPDs. This A-Weighted Sound Pressure Speed in Cans/ weak enforcement policy signaled the death knell for the Level at 1 meter (dB) Minute Manufacturing engineering control of noise in all but the most progressive Equipment Before After Noise Reduction Before After and innovative companies. As a result, original equipment Conveyors 110 77 33 600 2,400 manufacturers no longer had an incentive to manufacture Body maker 104 82 22 120 240 quiet products because there was no more market for them Trimmer 102 80 22 120 250 in the United States. Necker/flanger 105 85 20 600 1,100 Scrap 105 80 25 600 2,400 conveyor “Buy QuIET” PROgRAMS SOURCE: Bobeczko, 1978. In general, retrofitting existing machinery for noise sup- pression, especially if it has already been installed in the tive coating. The last forming operation necks and flanges workplace, can be very expensive. Even though many large the open end of the can. manufacturers are acutely aware of the noise problem created by their equipment, many companies adopt hearing conser- These same results might be possible through regulation vation programs in lieu of engineering controls. (Porter and van der Linde, 2005): There is some pressure, however, for companies to purchase quieter equipment. For example, EU regulations [R]egulation creates pressure that motivates innovation and specify noise emission limits for many kinds of outdoor progress. Our broader research on competitiveness highlights equipment. In addition, the Physical Agents Directive (EC, the important role of outside pressure in the innovation 2003) sets limits for workplace noise levels lower than process, to overcome organization inertia, foster creative thinking and mitigate agency problems. Economists are used the limits in the United States. In addition, one industry, to the argument that pressure for innovation can come from the information technology industry, has requirements for strong competitors, demanding customers or rising prices of noise emissions from their products defined by the Swedish raw materials; we are arguing that properly crafted legisla- government and spelled out in a Swedish standard (Statskon- tion can also provide such pressure. toret, 2004). Many purchasers of equipment—for example, in the automotive and oil refining industries—also have noise In the early days of OSHA’s regulation of noise exposure, specifications for new equipment. Thus, U.S. companies that many companies made considerable efforts to find ways to want to sell their products or equipment in the European reduce noise levels, and trade associations conducted noise market must meet these standards. studies on behalf of their members. However, when OHSA The federal government has the authority to purchase compliance officers began citing companies for not having low-noise products (42 USC 65, Section 4914, Development engineering controls in place, company attorneys turned of Low-Noise-Emission Products), and NIOSH and NASA the noise exposure questions into legal ones. Companies both promote “buy quiet” programs and specifications for contended that economic feasibility was important and that low-noise products. engineering controls had to be both technically and economi- NIOSH is involved in a number of efforts to promote cally feasible. The Occupational Safety and Health Review noise declarations that can facilitate the implementation of Commission (OSHRC), the federal agency that decides dis- buy-quiet programs.11 One works within existing hand-arm puted citations and penalties issued by OSHA, decided that vibration efforts by the U.S. Army, U.S. Navy, NASA, and economic feasibility had to be considered. This decision the General Services Administration. The groups are collabo- caused OSHA to slow down on its citations and many com- rating to develop and disseminate a database of equipment panies to sue before OSHRC rather than pay penalties. For sound and vibration exposure levels. This work includes sample cases, see OSHRC, 2009.10 vetting equipment through GSA acquisition channels for implementation throughout the Department of Defense. Addi- tionally, the effort may persuade machinery and equipment 10 Occupational Safety and Health Review Commission (OSHRC). 2009. manufacturers to make reduced noise a marketing feature and For sample cases, see: invest in developing, testing, and selling quieter products. http://www.oshrc.go/decisions/html_78/78_06_06_76- NIOSH is also working to translate research on sound levels 00.html http://www.oshrc.go/decisions/html_8/647.html and engineering noise controls into practical information http://www.oshrc.go/decisions/html_78/77.html by making a revised NIOSH Noise Control Compendium http://www.oshrc.go/decisions/html_84/4.html http://cases.justia.com/us-court-of-appeals/F/6/64/74/ 11 Charles Hayden, personal communication, March 17, 2009. http://cases.justia.com/us-court-of-appeals/F/4/66/480/

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4 CONTROL OF HAZARDOUS NOISE (NIOSH, 1978) and a revised Compendium of Materials noise emitted by a machine may depend on the work being for Noise Control (NIOSH, 1975) available on the Internet. done, for example, when forming metal. The manufacturer In addition, they are updating and expanding their existing may control the noise of motors, cooling equipment, etc., powered hand tool database. but the buyer must take some responsibility for the noise or Stringent federal noise regulations in the mining industry the operating conditions of the machine must be very care- have led to successful noise control collaborations between fully specified when the noise emission levels are specified. NIOSH and mining machinery manufacturers. Mining com- Thus, manufacturer and buyer must work together closely to panies are committed to “buy quiet,” and machinery manu- produce a satisfactory design. facturers are amenable to any collaborative effort to assist Nevertheless, there are several good reasons for a buyer them in reducing noise levels from their products. Similarly, and seller to come to agreement on a noise specification: noise regulation outside of mining would greatly assist in creating an environment of collaboration and openness to • In areas with hazardous noise levels, the noise hazard reduce levels, for example, in the construction industry can be reduced, saving the costs of a hearing conserva- (Hayden and Zechmann, 2009). tion program. In 1996, NASA implemented a “buy quiet” program • Speech communication in low-noise workplaces is (Cooper and Nelson, 1996). The program was updated and much better than in high-noise workplaces. In addition, reviewed in 1999 (Cooper et al.) and described in detail at the because no hearing protection is necessary, desired INTER-NOISE conference in 2009 (Cooper, 2009). sounds, such as announcements via public address “Buy quiet” programs and a new “buy-quiet” criterion for systems, are not attenuated. industrial equipment have also been reviewed by a member • Low-noise workplaces promote safety (e.g., alarms are of the NAE study committee, Robert D. Bruce (2009). He clearly audible). described how one global company had set a criterion of 80 • Low-noise workplaces make it easier for workers to dB(A) at 1 meter as the purchase requirement for new equip- concentrate and reduce fatigue. ment. However, he said, this specification cannot stand alone; • Low-noise workplaces are more productive and more it must be accompanied by information about the acoustical comfortable. environment, measurement locations, and machine operating conditions. Bruce also described how new equipment should Generally, low-noise equipment is easier to maintain than be installed in existing facilities. retrofitted equipment, and controls are easier to use. Although the energy radiated as noise is a very small fraction of the electrical or mechanical energy in any process, a low-noise Buying and Selling Low-Noise Equipment machine is usually thought of as being more energy efficient When considering the cost of purchasing quieter equip- and of good design. Guidelines for low-noise design can be ment, the potential buyer must take into consideration found in international documents (ISO, 1995b, 1998). the costs of a long-term hearing conservation program for workers in environments with hazardous noise levels. Responsibilities of Buyers and Sellers Hearing conservation programs incur costs for annual au- diometric monitoring, medical follow-up of hearing loss Both supplier and purchaser have responsibilities in cases, monitoring of noise exposure, posting of warning implementing a “buy quiet” program. For individual pieces signs and controlling access to high-noise areas, annual of machinery, such as compressors, motor generators, and training for employees and supervisors, recurring purchases similar equipment, the supplier must make available the of personal hearing protectors, ongoing administration and noise specification for the equipment, usually in terms of record keeping, and inevitable workers’ compensation claims the sound power level it emits. Several sets of standards have for hearing loss. been established for determining sound power. For example, Even if the buyer has made the decision to proceed, the International Organization for Standardization (ISO) has specifying a limit for the noise emissions of a product can generic standards for noise emissions. In addition, many be difficult. First, neither the seller nor the purchaser may be other international standards have been developed for noise emissions from specific kinds of equipment.12 Other industry familiar with noise emission specifications. Second, the type of specification varies with the type of equipment, and the standards and other national standards may also be used. For specification must be meaningful to the seller. For example, example, ANSI Standard S12.15-1992 (R 2007) defines mi- a specification such as “must meet OSHA requirements” is crophone positions and other information to determine noise not adequate. If a manufacturer relies on vendors to supply emissions for a wide variety of equipment (ANSI, 2007a). In subassemblies, the manufacturer/vendor relationship may addition, ANSI S12.16-1992 (R 2007) provides information be complicated. In addition, small vendors usually do not have the facilities to determine the noise emissions of com- 12 See Chapter 6 and Appendix C for more on ISO standards and other ponents and subassemblies. Another complication is that the international standards.

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44 TECHNOLOGY FOR A QUIETER AMERICA protect hearing. Permanent NIHL is typically a progressive neural injury that damages or destroys the hair cells and neu- Noise Reduction (dB) ral pathways of the inner ear. However, NIHL can also be an immediate response to an acoustic trauma if the elastic limits of the tympanum, ossicular chain of the middle ear, or co- chlear structures are overwhelmed by a powerful acoustical insult, such as an explosion. For the great majority of noises to which people are exposed, HPDs can mitigate NIHL, provided they are properly selected, fitted, and worn. In industry, where 90 percent of noise exposures are at TWA levels less than or equal to 95 dB(A), compliance with the OSHA 1983 Hearing Conservation Amendment Various Earplugs requires only a 10-dB reduction, which most HPDs can supply (Berger, 2003b). However, HPDs are not a panacea. They may be ineffective if the acoustical pathways, such Lab fitted Real world as air leaks around the seal, HPD material transmission, HPD vibration, and flanking via bone conduction interfere FIGURE 4-2 Comparative noise reduction ratings for various with their noise reduction features. In addition, though rare, earplugs. Source: NIOSH, 1996. extremely high noise levels may overwhelm the attenuation Figure_4-2.eps capabilities of even the best HPDs. For example, for 8-hour bitmap with some vector labels daily TWA exposures that exceed about 105 dB(A), espe- healthy workplace, not the employee’s duty to provide cially with dominant low-frequency content below about that protection. 500 Hz, double passive hearing protection (i.e., an earmuff • Hearing protectors often provide insufficient attenuation. worn over a well-fitted earplug) is advisable (Berger, 2003b). • Hearing protectors are often uncomfortable and there- However, because of such factors as discomfort and concerns fore not accepted by workers. about safety, workers often complain about wearing even • Hearing protectors are often counterproductive in that one earmuff or earplug, and convincing them of the neces- they reduce the worker’s ability to hear speech com- sity of wearing both during the course of a workday can be munication and warning signals. a challenge. • Hearing protectors can have an adverse effect on the In even more severe noise environments, such as on air- ability to localize sounds and therefore pose a safety craft carrier decks during flight operations, prevailing noise hazard. exposures can be extremely high, and short-term levels may range from 146 to 153 dB(A) at 50 feet from military jet The focus of noise reduction efforts should certainly be on aircraft on afterburner power (McKinley, 2001). These levels the development and purchase of quieter consumer products will overtax even the double passive HPDs. In those cases and industrial machinery and on reducing noise via engineer- very specialized HPDs are required and are mainly of inter- ing controls at the noise source or in the noise path. However, est only in military applications. These devices are described when engineering controls are not economically or techni- briefly in the section on multicomponent systems for extreme cally feasible, or when an employer or manufacturer (un- noise later in the chapter. fortunately) does not consider them a high priority, hearing protection may supplant engineering and/or administrative Hearing Protection Devices in Nonoccupational Settings controls (e.g., setting time limits to a worker’s exposure). For these reasons the use of HPDs has proliferated, espe- Home and Recreational Use cially in industrial and military settings. In situations where it is difficult, or even infeasible, to “engineer out” noise, In contrast to the use of HPDs in most occupational set- such as that from weapons or aircraft, HPDs may be the only tings in the United States, the use of HPDs in recreational practical countermeasure. In addition, there are some cases in and home settings is generally up to the individual—and in which engineering and/or administrative controls have been most cases depends on awareness of what constitutes unsafe implemented but do not reduce the noise to an acceptable (or noise and a person’s willingness to take risks. Despite pro- even legal) level. In these situations, HPDs may be used to grams to educate people about noise-related dangers and the “make up the difference” and protect against NIHL. importance of HPDs, public awareness about the hazardous effects of noise is low (ASHA, 2009; WHO, 1997). In addition to conventional passive hearing protectors, Limitations of Hearing Protection Devices which have been available for decades, HPDs styled and If exposures to noise at hazardous levels persist even after sized specifically for children, designed for spectator events noise controls have been tried, HPDs may be the only way to (e.g., earmuffs that incorporate radios for sporting events),

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4 CONTROL OF HAZARDOUS NOISE HPDs with signal pass-through circuitry (e.g., electronic an ear canal cap can also be used to store the device around earmuffs for hunters), lightweight active noise cancellation the neck when not in use. HPDs for reducing low-frequency noise in aircraft cabins, Earmuffs are ear cups, usually made of a rigid plastic ma- uniform attenuation earplugs for musicians and concert at- terial with a noise-absorptive liner, that completely enclose tendees, and other innovative and attractive devices are now the outer ear and seal around it with foam- or fluid-filled on the market. cushions. On some models the headband that connects the ear cups is adjustable so that it can be worn over the head, behind the neck, or under the chin, depending on the presence Local Ordinances on Hearing Protection of other headgear, such as a welder’s mask. Helmets, which In contrast to long-standing federal laws for occupational enclose a large portion of the head, are usually designed to exposures, noise in community and recreational settings, if provide impact protection, but they can have integrated ear governed at all, is usually addressed in local ordinances, cups or a liner material that seals around the ears (Berger and most of which relate to noise annoyance rather than to hear- Casali, 1997). Furthermore, for extreme noises that substan- ing risks. However, in venues having recreational exposures tially transmit sound through bone conduction to the neural from amplified music, or gaming arcades, there may be warn- ear, helmets that cover the temporal and mandibular areas, as ing signs stipulating that hearing protection is required upon well as the cranium, can provide additional protection against entry. However, ordinances to protect hearing are in the mi- bone-conducted noise (Gerges and Casali, 2007). nority, often passed in response to public complaints and/or In general, earplugs provide better attenuation than civil litigation for premises’ liability. Again, the committee earmuffs for noise below about 500 Hz and equivalent and questions why noise is not controlled to within safe limits better protection for sounds above 2,000 Hz. At intermediate by engineering means or by “turning down the volume,” frequencies, earmuffs generally provide better attenuation. rather than by warning people to wear hearing protection and Earmuffs are generally easier than earplugs or ear canal depending on them to have such protection at hand. caps for the user to fit properly. However, in high tempera- tures and humidity, earmuffs can be uncomfortable; in cold temperatures they can be welcome insulators. Semi-inserts HEARINg PROTECTION DEVICES: TECHNOLOgIES generally provide less attenuation and are more uncomfort- AND EFFECTS ON AuDIBILITy able than earplugs or earmuffs. However, because they can be stored around the neck, they are convenient for workers Conventional (Passive) Hearing Protection Devices who frequently move in and out of noisy areas. For a compre- The vast majority of HPDs are so-called conventional hensive review of conventional HPDs and their applications, hearing protectors that attenuate noise by static passive see Gerges and Casali (2007) and Berger (2003b). means. Conventional, or passive, HPDs do not have dynamic Although conventional HPDs provide adequate protection mechanical elements, such as valves or reactive ports, or elec- for most noise exposures, a potential disadvantage, due to tronic circuitry, such as active noise cancellation or signal the static, passive nature of the attenuation, is a deleterious pass-through circuitry. The effectiveness of passive HPDs effect on hearing quality and auditory performance. This depends on a combination of acoustical factors, including the effect varies with the user’s hearing ability and the noise airborne sound transmission loss imposed by the construc- and signal conditions. For more specific information on the tion materials, the reflection characteristics of the HPD for effects of HPDs on speech communication and signal audi- incident sound waves, the quality and integrity of the seal bility, the reader is referred to Casali (2006), Robinson and against the ear canal or outer ear or its surrounding tissue, Casali (2003), and Suter (1992). the ability of the HPD to dampen vibrations of the ear canal wall, and the resonance frequency characteristics and acous- HEARINg PROTECTION DEVICES: EFFECTS ON tical impedances of the HPD. There are four general types of SIgNAL AND SPEECH AuDIBILITy conventional HPDs—earplugs, semi-insert or ear canal caps, earmuffs, and helmets—each defined by the way the device Overprotection Versus underprotection interfaces with the ear or head. Earplugs are vinyl, silicone, spun fiberglass, cotton/wax Safety professionals must select HPDs for the workplace combinations, or closed-cell foam products inserted into that provide adequate attenuation for the noise threat but not the ear canal to form a noise-blocking seal. Proper fit to the so much attenuation that the worker cannot hear important user’s ears and training in insertion procedures are critical signals and/or speech communications. Users may reject to their effectiveness. A related, but different, category of an HPD if it compromises hearing to the point that sounds HPD is the semi-insert or ear canal cap, which consists of an seem unnatural, signals are undetectable, and/or speech is not earplug-like pod positioned at the rim of the ear canal and/or understandable. Too much attenuation for a particular noise in the concha bowl of the external ear (pinna). The device situation is commonly referred to as oerprotection. is held in place by a lightweight headband positioned under The selection of an overprotective or underprotective the chin, behind the head, or over the head. The headband of HPD can have serious legal ramifications. Here is a hypo-

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46 TECHNOLOGY FOR A QUIETER AMERICA thetical statement by a workers’ compensation plaintiff: “The (e.g., Suter, 1992) have concluded that people with sufficient hearing protector provided inadequate noise attenuation for hearing impairments usually experience additional reduc- defending my ears against the damaging effects of noise, so tions in communication abilities with conventional HPDs in I lost my hearing over time.” Also: “The hearing protector noisy environments. provided more attenuation than needed for the noise I was Moreover, because of the phenomenon known as the oc- exposed to at work, and therefore was a causal factor in the clusion effect, people who wear HPDs lower their voices by accident when I could not hear the forklift backup alarm and about 2 to 4 dB, so that when both talker and listener wear was run over.” protectors, the resulting decrease in speech recognition will These are extreme examples, but in civil court such tend to offset any benefits, even with normal-hearing listen- arguments can potentially lead to theories on which a legal ers (Howell and Martin, 1975; Hoermann et al., 1984). foundation for recovery of damages may be based. Consider HPDs with electronic hearing-assistive circuits, some- product liability, for example. The “failures” claimed in the times called electronic sound transmission or sound restora- statements above would typically fall under the category of tion HPDs, can be offered to hearing-impaired individuals defective design and/or availability of superior alternative to determine if their hearing, especially in quiet-to-moderate design features, and/or breach of warranty. The threat of noise levels below about 85 dB(A), can be improved and litigation is of great concern to both HPD manufacturers and their hearing still somewhat protected. However, the benefits employers. Thus, HPDs must be matched to workers and job of electronic sound transmission HPDs for hearing-impaired requirements. The above paragraphs lend even more support users have not been empirically demonstrated in scientific to the principle that engineering noise controls should have studies. priority over HPDs. Nonlinear Passive Attenuation Effects on Audibility Leading to Technological Conventional passive HPDs cannot selectively relay Augmentations speech or nonverbal signals (or speech) energy rather than Research on people with normal hearing suggests that noise energy at a given frequency. Therefore, conventional conventional passive HPDs have little or no degrading ef- HPDs do not improve the speech/noise ratio in a given fect on their understanding of external speech or signals in frequency band, which is the most important factor for ambient noise levels above about 80 dB(A); they may even achieving reliable signal detection and speech intelligibil- provide some improvements, with a crossover from disad- ity. As shown in Figure 4-3, conventional earplugs (labeled vantage to advantage between 80 and 90 dB(A) (Berger and fiberglass, premolded, or foam) attenuate high-frequency Casali, 1997; Casali and Gerges, 2006). However, in lower sound substantially more than low-frequency sound; there- sound pressure levels, they often do increase misunderstand- fore, they attenuate high-frequency consonant sounds, which ing and poorer detection. In these situations, HPDs are usu- are important for word discrimination. They also attenuate ally used not to protect hearing but to reduce annoyance. In frequencies that are dominant in many warning signals. the presence of intermittent noise, HPDs may be worn during This nonlinear attenuation profile, which generally increases quiet periods so that when a loud noise occurs, the wearer with frequency for most conventional earplugs and nearly will be protected. However, during the quiet periods, hearing acuity may be reduced. Technological enhancements are sometimes incorporated to create leel-dependent augmented HPDs that provide m inimal or moderate attenuation (or sometimes more amplification of external sounds) during quiet times and increased attenuation (or less amplification) as the noise level increases. However, commercially available versions of these devices have not been associated with a demonstrated improvement in signal detection over conventional HPDs in most situations (e.g., Casali and Lancaster, 2008; Casali and Robinson, 2003). Noise- and age-induced hearing losses generally occur in the high-frequency range first, making it difficult to deter- mine the effects of HPDs on speech perception for people with early impairment. Because their elevated thresholds for FIGURE 4-3 Comparative noise reduction ratings based on manu- mid- to high-frequency speech sounds are elevated further by facturers’ laboratory tests and real-world “field” performance of dif- Figure_4-3-G-1.eps the protector, hearing-impaired individuals are usually dis- ferent types of hearing protection devices. Adapted with permission from Berger, 2003b, bitmapsp. 421. Fig. 10.18, (4 wedges) advantaged by conventional HPDs. Comprehensive reviews

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47 CONTROL OF HAZARDOUS NOISE all conventional earmuffs, allows more low-frequency than perceptions of the loudness of various pitches (Casali and high-frequency noise through the protector, which causes an Robinson, 2003). “upward spread of masking” if the penetrating noise levels Some high-frequency binaural cues (especially above are high enough (Robinson and Casali, 2003). about 4,000 Hz) that depend on the external ears (pinnae) Certain augmented HPD technologies help overcome are altered by HPDs, compromising judgments of sound these weaknesses, particularly low-frequency attenuation. direction and distance. Earmuffs, which completely obscure These include a variety of actie noise reduction (ANR) the pinnae, may interfere with localization in the vertical devices that capture the offending noise and its electronic plane and may also cause horizontal-plane errors in both phase cancellation at the ear via superposition through contralateral (left-right) and ipsilateral (front-back) judg- feedback and/or feed-forward control loops. ANR devices ments (Suter, 1992). Earplugs may cause some ipsilateral boost low-frequency attenuation below about 1,000 Hz. judgment errors but generally cause fewer localization errors ANR is especially effective in earmuffs, which are gener- than earmuffs because they do not completely destroy cues ally weakest in low-frequency attenuation and which also from the pinnae. have enough space for the electronics of ANR circuitry to Dichotic sound transmission H PDs compensate for be packaged in/on the muff. ANR has also been used in lost pinnae-derived cues. These devices have an external earplug designs in the past decade (e.g., McKinley, 2001). microphone on each earmuff cup that transmits a specified The benefits of ANR-based HPDs can include reduction of passband of the noise incident on each microphone to a upward spread of masking of low-frequency noise into the small loudspeaker under the earmuff cup. Binaural cues are speech and warning signal bandwidths and reduction of noise thus maintained, as least partly, as long as the between-ear annoyance in environments dominated by low-frequency gain controls are properly balanced, the microphones are noise, such as jet cockpits and passenger cabins (Casali and sufficiently directional, and the passband includes frequen- Robinson, 2003). cies outside the range that cannot be typically localized (i.e., The tendency of conventional HPDs to exhibit a sloping outside the range of about 1,000 to 3,000 Hz). However, a nonlinear attenuation profile with changes in frequency cre- recent experiment with a dichotic sound transmission ear- ates an imbalance from the listener’s perspective because the muff in an azimuthal localization task of determining the relative amplitudes of different frequencies are heard differ- approach vector of a vehicular backup alarm demonstrated ently than they would be without the HPD. Thus, broadband no advantage in localization over a conventional earmuff or acoustic signals are heard as spectrally different (more earplug (Casali and Alali, 2009). “bassy”) from normal acoustic signals (Berger, 2003b). All of the augmentations described above—uniform People whose jobs depend on accurate sound interpreta- attenuation, ANR, electronic sound transmission, and level- tion (aural inspections by machinists, miners, engine trouble- dependent or amplitude-sensitive attenuation—are effective shooters), as well as people who perform or listen to music, in certain applications. For more information on these and may be adversely affected. Figure 4-4 shows attenuation other technologies that are commercially available, the curves for two uniform (or flat) attenuation deices (ER-15 reader is referred to a review by Casali and Robinson (2003). and ER-20). These devices are more popular with musi- The major goals of these augmentations are (1) to encour- cians than conventional HPDs because they do not distort age the use of hearing protection by producing HPDs that are more acceptable to the user population, amenable to the working environment, and adjustable to the noise exposure and (2) to improve hearing in a protected state, which may also make workers safer. Unfortunately, these noble goals are not always realized in practice. One reason is that these devices can be considerably more expensive than conven- tional passive HPDs, and most employers are reluctant to incur the cost. EMERgINg TECHNOLOgIES To overcome some of the limitations of HPDs, several recent innovations have been developed or prototyped or in some cases made commercially available. Indeed, emerging technologies continue to be developed. The brief overview FIGURE 4-4 Spectral attenuation obtained with real-ear attenua- that follows includes examples of new technologies known tion at threshold (REAT)Figure_4-4.eps procedures for three conventional passive to the committee. However, the list is not exhaustive, and earplugs (premolded, user-molded foam, and spun fiberglass) and bitmap (inverted colors) the study committee does not advocate or promote these two uniform-attenuation, custom-molded earplugs (ER-15, ER-20). particular devices or technologies. Provided courtesy of E.H. Berger, AEARO—3M.

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48 TECHNOLOGY FOR A QUIETER AMERICA Adjustable Attenuation Devices ent sounds via a microphone on the outside of the HPD; those sounds are then bandpass filtered to an amplified earphone To “tailor” the attenuation of an HPD to a particular inside the HPD. noise problem (i.e., in lieu of selecting different HPDs for Using elements of rapid-response automatic gain control different exposures), earplug designs have recently been with high pass-through gain capability, these devices can be developed that give the user some control over the amount used as assistive listening devices for military and other ap- of attenuation. These devices incorporate a leakage path that plications, as aids in threat detection, and as sound localizers. can be adjusted via a valve that obstructs a tunnel, or “vent,” They can also improve hearing of low-level speech. When cut through the body of the plug (e.g., a Dutch earplug, the gunfire occurs, the amplification rapidly decays, causing the Ergotec Varifone) or by selecting a filter or dampers that device to quickly revert to a passive hearing protector. These can be inserted into the vent (e.g., Canadian devices, such devices typically have more sophisticated and powerful as the Sonomax SonoCustom and the Custom Protect Ear pass-through filtering/gain circuits than industrial versions dB Blocker). of sound transmission earmuffs. Some of these systems incorporate elements that provide Verifiable Attenuation Devices two-way communication capabilities, including versions with covert microphones located under the HPD in the ear To establish a quality fit of an HPD to a user, and in canal, to pick up the wearer’s voice by bone/tissue conduc- keeping with the OSHA (1983) Hearing Conservation tion. At least one device can transduce the noise level under Amendment requirement, per 29 CFR 1910.95 (i)(5), that the HPD, use it to determine cumulative noise exposure, “the employer shall insure proper initial fitting and supervise and modulate the system pass-through gain based on these the correct use of all hearing protectors,” several systems data. Examples of HPDs that provide enhanced situational have been developed to verify the attenuation of a device awareness include the Communications and Enhancement worn by a given user. For example, the original SonoPass Protection System from Communications & Ear Protection, system, now called the AEARO/3M E•A•RFit, is sold as Inc.; the QuietProby NACRE AS (Norwegian); and the Si- a system with a probe tube microphone test apparatus that lynx QuietOPS. Because of their very recent development, verifies the attenuation level achieved via microphone-in- some of these devices have not yet undergone experimenta- real-ear, noise reduction measurements on each user as he tion to test their operational performance. Some, however, or she is fitted with the product. A similar system is the have already been deployed for use in combat settings. Sperian VeriPRO. Further discussion of HPDs with situational enhancement, All of these verifiable-attenuation HPDs measure attenu- and experimentation on a subset of them, can be found in ation by placing a microphone or probe tube through a duct Casali et al. (2009). that runs lengthwise through an earplug and then measuring noise reduction in a sound field. “Verified attenuation” is Multicomponent Systems for Extreme Noise thus established for that ducted earplug for that particular fitting on the user. Thereafter, for use in the field the ducted Multicomponent HPD systems have recently been de- earplug is replaced with a solid (i.e., nonducted) earplug of veloped and tested for use in noise environments that the same type/model; alternatively, a noise-blocking insert is greatly exceed the attenuation capabilities of even double used to occlude the duct. The attenuation achieved by these passive protectors (i.e., earmuffs worn over earplugs). The systems is not recognized by OSHA as a means for determin- most prominent of these environments is an aircraft carrier ing the adequacy of the hearing protector for a given noise deck during flight operations, where flight deck personnel exposure, and it does not replace the EPA-required label of are subject to sound pressure levels as high as the mid- HPD attenuation data. However, with policy amendments, 150-dB(A) range (McKinley, 2001). Some large-caliber it may someday be recognized for either or both of these weapons and explosive blasts can also produce exceedingly applications. high exposures. Specialized HPDs have been developed for use in these Devices with Enhanced Situational Awareness and extreme conditions, including devices with multiple com- Communication Capabilities ponents for staged hearing protection for use on aircraft carriers. These HPDs provide both high passive attenua- In the past few years several HPD-based devices have tion through very deep insertion, custom-molded earplugs been developed that have multiple objectives, which include coupled with active noise cancellation in the in-canal sound hearing protection from continuous noise, hearing protection field under the earplug, all covered with a tightly fitted ear- from impulsive noise (particularly gunfire), measurement muff with custom-fitted cushions (McKinley, 2001). Other of protected noise exposure (i.e., at the ear under the HPD), devices are full-head-coverage helmets with circumaural improved hearing of ambient sounds and uttered speech, and active noise cancellation earcups inside, all worn over deeply improved communication capabilities. All of these products fitted passive earplugs. incorporate sound transmission circuitry to transduce ambi-

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4 CONTROL OF HAZARDOUS NOISE Composite Material Devices effect since 1971 and calls for employers to use “feasible administrative or engineering controls” for all employees A few HPDs have been produced from a combination exposed above a daily time-weighted average level (TWA) of of materials, typically in sandwich- or concentric-type con- 90 dB(A). In 1981 and 1983 OSHA amended the regulation struction, to take advantage of impedance mismatching (and for hearing conservation requiring employers to supply hear- the resultant attenuation benefit) that occurs with materials ing protection devices and other components of the hearing that differ in density, elasticity, and other physical param- conservation program at and above a TWA of 85 dB(A). Since eters. This design practice has long been used in earmuffs, 1983, workers who have exhibited a “standard” threshold but composite structures in earplugs will require further shift in hearing must be required to wear hearing protection investigation. devices above a TWA of 85 dB(A); in addition certain follow- up measures must be taken by the employer. The primacy of SuMMARy engineering and administrative controls over the use of hear- ing protection devices remains in effect, although OSHA has Hearing protection is a very important component of not enforced it in recent years. In practice, employers have a hearing conservation program and is currently essential often used technical and/or economic infeasibility as a justi- to combating the problem of noise-induced hearing loss. fication for not implementing engineering controls. However, there are disadvantages that accompany the use In 1983 OSHA issued a policy directive advising its of HPDs, including but not limited to the high cost of compliance officers not to issue citations to companies with certain augmented HPDs that are needed for specialized “effective” hearing conservation programs until workers’ applications, situation- and user-specific interference with TWAs exceed 100 dB(A). This policy still exists in the signal detection and speech communications, discrepancies agency’s Field Operations Manual (OSHA, 2009); however, between laboratory ratings and actual field performance of it has never had the authority of regulation and could be both conventional passive and electronic protectors, and a revoked at any time. perception reported by some workers that HPDs may be The original OSHA noise regulation used an exchange rate “unsafe” (Morata et al., 2005). Furthermore, it must be of 5 dB per doubling or halving of exposure time, and this rule noted that OSHA (1971a, 1971c, 1983) specifically assigns has not yet been changed, despite recommendations by EPA the responsibility for hearing protection to employers, not and NIOSH to change both the exchange rate to 3 dB and workers, and thus the performance of the hearing conserva- the permissible exposure limit from 90 to 85 dB(A). MSHA tion program is largely dependent on employer commitment promulgated a revised noise regulation in 1999 that is similar to exposure measurement, HPD selection, and training of but not identical to the OSHA regulation, although here the workers to fit and use the devices properly. primacy of engineering noise control is clear. The agency Returning to the systems approach to noise abatement discussed the issues of changing from the 5 dB to the more shown in Figure 4-1, it is important to reiterate that hearing protective 3-dB exchange rate and from the 90-dB(A) permis- protection is a noise countermeasure that is only imple- sible exposure limit to 85 dB(A) but failed to do so at the time, mentable at the ery end of the noise propagation chain, although the preamble to the rule stated that “[i]n both cases, that is, at the receiver’s ear. In the great majority of noise the scientific evidence was strong.” Ultimately, the change was exposure situations the priority should be to reduce or elimi- not adopted because of significantly increased costs for small nate the noise at its source or in its path through engineering mine operators. The 85/3 limits are used by several other U.S. controls and not to rely on hearing protection to curb the government agencies and are also written into most national noise just before it enters the ears. Hearing protection, though and international standards. effective when selected and applied properly, is not a panacea The OSHA Field Operation Manual (OSHA, 2009) con- for combating the risks posed by noise, and its effectiveness tains a statement widely known as the “100-dB Directive.” will always be dependent on human behavior. It should thus With reference to issuing citations for noise violations, it not be viewed as a replacement for noise control engineering. states that “[h]earing protectors which offer the greatest However, in those cases where noise control engineering’s attenuation may reliably be used to protect employees when afforded reduction is simply insufficient, or it is truly eco- their exposure levels border on 100 dB(A).” The effect of this nomically and/or technically infeasible (as perhaps with a statement has been to negate the well-recognized goal of us- personally shouldered, high-caliber weapon), hearing protec- ing engineering controls as the primary means of controlling tion devices become the primary countermeasure. industrial noise. FINDINgS AND RECOMMENDATIONS Recommendation 4-1: To comply with the recommen- dation of the National Institute for Occupational Safety Regulatory Changes in Damage Risk Criteria for Hearing and Health, the policy of several other government agen - cies, and widespread national and international scientific OSHA has promulgated a noise regulation for gen- opinion, the U.S. Department of Labor should adopt the eral industry, 29 CFR 1910.95. This regulation has been in

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0 TECHNOLOGY FOR A QUIETER AMERICA 85-dB(A)/3-dB limit for exposure to hazardous noise. This and the human factor is always a weak link in the “safety would replace the current 90-dB(A)/5-dB requirement. chain.” HPDs must be comfortable, easily sized and fitted to the user, and straightforward to meet the hearing-critical needs of a particular job or situation. They must still provide Measurement and Evaluation of the Hazard of situational awareness (e.g., communication enhancements Impulsive Noise where needed and attenuation performance labels that reflect The peak sound pressure level is currently widely used to the level of protection they provide in actual use). HPD determine noise hazard, but recent studies have indicated that technology has advanced greatly in the past 30 years, but the duration of the impulse plays an important role. There HPD regulations have not kept pace. This discrepancy was is also evidence that impulsive noise and continuous noise recognized in the publication of EPA’s proposed new rules can be included in a single measurement of equivalent sound (EPA, 2009), which should be adopted. However, despite the level. The committee concluded that current damage risk cri- improvements of recent devices, they cannot be considered a teria in the United States and internationally are inadequate substitute for engineering noise control because of the many and should be the subject of future research. factors cited above, and their efficacy simply has not been proven. Moreover, this represents an unacceptable shifting Recommendation 4-2: The National Institute for Occu- of the burden from employer to employee, which is contrary pational Safety and Health should be the lead agency and to both the letter and the intent of the Occupational Safety should be tasked by its parent agencies (U.S. Department and Health Act of 1970. of Health and Human Services/Centers for Disease Control Although an HPD is useful when the listener has no and Prevention) to develop new damage risk criteria with control over the noise level and when engineering controls assistance from the military services that have experience cannot be applied, the committee concluded that engineer- with high-amplitude impulsive noise. ing controls of noise in the workplace should be the primary method of protecting workers from hazardous noise expo- sure. Accordingly, the committee recommends the following Promoting Engineering Control to Reduce actions by U.S. government agencies, engineering and trade Hazardous Noise societies, and other stakeholders to promote the development Engineering noise controls provide significant long-term and use of engineering controls. advantages over personal hearing protection. If workplace Recommendation 4-3: The U.S. Department of Labor noise levels are limited by engineering controls, “buy quiet” programs, or other means to a level below the OSHA action should revoke the Occupational Safety and Health Ad - level of 85 dB(A) TWA, the need for individual hearing ministration (OSHA) “100-dB Directive” of 1983, which protection devices (HPDs) is obviated from an OSHA stand- effectively raised the action point for engineering control point. HPDs may still be desirable for reducing noise annoy- of noise from 90 to 100 dB by allowing the substitution of ance or ensuring that a noise hazard is fully mitigated. hearing protectors for noise control up to 100 dB and thereby In 42 USC 65, Section 4914, the federal government is devastated the market for quiet machinery and equipment. required to encourage the procurement of low noise emis- At the same time, OSHA should reconfirm that engineering sion products: controls should be the primary means of controlling noise in the workplace. (1) Certified low-noise-emission products shall be acquired by purchase or lease by the Federal Government for use by Recommendation 4-4: The National Institute for Occupa- the Federal Government in lieu of other products, if the ad- tional Safety and Health and the U.S. Department of Labor ministrator of General Services determines that such certified should develop and distribute widely an electronic database products have procurements costs which are no more than of noise control problems, solutions, and materials—taking 1.25 percentum of the retail price of the least expensive type of product for which there are certified substitutes. (2) Data into account the many handbooks and articles devoted to relied on by the administrator in determining that a product is industrial noise control. a certified low-noise-emission product shall be incorporated in any contract for the procurement of such product. Recommendation 4-5: Engineering societies and trade organizations should develop guidelines for defining the re- The same principle applies in the consumer setting. Thus, lationship between noise emission specifications in terms of the engineering of quieter products, such as power tools, toys, sound power level and/or emission sound pressure level and yard equipment, and recreational vehicles, would reduce the noise immission levels in industrial situations. They should need for and reliance on HPDs. Even though an HPD may provide a primer for buyers and sellers of machinery and protect the wearer’s hearing, it may create hazards if the user equipment that includes descriptions of how noise propa- is unable to hear approaching vehicles or alarms. gates in rooms; how to determine noise from a large number The effectiveness of HPDs depends on human behavior, of machines; standards available to manufacturers and others

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 CONTROL OF HAZARDOUS NOISE for measuring noise emissions; and case histories of noise Pp. 2–17 in The Noise Manual, Revised 5th Ed., edited by E.H. Berger, L.H. Royster, J.D. Royster, D.P. Driscoll, and M. Layne. Fairfax, VA: levels measured in in situ environments. American Industrial Hygiene Association. Berger, E.H. 2003b. Hearing protection devices. Pp. 379–454 in The Noise Recommendation 4-6: Government agencies should be Manual, revised 5th ed., edited by E.H. Berger, L.H. Royster, J.D. instructed by a presidential directive or in congressional Royster, D.P. Driscoll, and M. Layne. Fairfax, VA: American Industrial report language to show leadership in promoting “buy quiet” Hygiene Association. Berger, E.H., and J.G. Casali. 1997. Hearing protection devices. Pp. activities by developing and implementing programs for 967–981 in Encyclopedia of Acoustics, edited by M. Crocker. New the purchase of low-noise products, as required by 42 USC York: John Wiley. 65, Section 4914. American industry should adopt “buy Berger, E.H., J.R. Franks, A. Behar, J.G. Casali, C. Dixon-Ernst, R.W. quiet” programs that require noise emission specifications Kieper, C.J. Merry, B.T. Mozo, C.W. Nixon, D. Ohlin, J.D. Royster, and on all new equipment and “declared values” in purchase L.H. Royster. 1998. Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices, Part specifications. III: The validity of using subject-fit data. Journal of the Acoustical Society of America 103(2):665–672. Bobeczko, M.S. 1978. Noise Control Solutions for Can Manufacturing REFERENCES Plants. Pp. 413–418 in Proceedings of INTER-NOISE 78, The 1978 AE (Access Economics Pty Ltd). 2006. Listen Hear! The Economic Impact International Congress on Noise Control Engineering, San Francisco, and Cost of Hearing Loss in Australia. Available online at http://www. CA, May. 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