noise sources are preferred but are less commonly used. Engineering solutions and expenditures that can actually reduce noise emissions are sometimes “sold to management” by highlighting their other advantages, such as gains in productivity or quality.

The cost of NIHL can be assessed in two ways. First, there are the impacts on quality of life, such as strained relationships, difficulty or inability to communicate, feelings of isolation, lost friendships, ridicule from peers, and a general inability to relate well to others. Accidents and absenteeism also should be included in the cost of NIHL. Second is the amount of money spent on compensation for NIHL. However, studies have shown that these costs are underrepresentative of the total cost of NIHL (Shampan and Ginnold, 1982; Suter, 1990).

Data for calculating the costs are difficult to come by. In a recent study by the Institute of Medicine (IOM, 2005), it was stated that disabilities of the auditory system, including tinnitus and hearing loss, were the third most common type of disability, accounting for nearly 10 percent of the total number of disabilities among veterans. For the roughly 158,000 veterans who began receiving disability compensation in 2003, auditory disabilities were the second most common type of disability. These veterans had approximately 75,300 disabilities of the auditory system, out of a total of some 485,000 disabilities. At the end of 2004, the monthly compensation payments to veterans with hearing loss as their major form of disability represented an annualized cost of some $660 million. The corresponding compensation payments to veterans with tinnitus as their major disability were close to $190 million on an annualized basis. A 1997 study by the World Health Organization estimated that the cost of NIHL in developed countries was in the range of 0.2 to 2.0 percent of a country’s gross domestic product (GDP)—or roughly $28 billion to $280 billion for the United States (WHO, 2007). In a 2006 study in Australia, it was estimated that the real cost of hearing loss amounted to 11.75 billion AUD, or 1.4 percent of GDP (AE, 2006).

The remainder of this chapter focuses on criteria for acceptable risk of damage from hazardous noise in industry and government, hazardous noise from consumer products, research on impulsive noise, engineering controls in industry and the establishment of “buy-quiet” programs, HPDs, and the current status of HPD research.


Exchange Rate

Criteria for estimating the risk of damage from hazardous noise must be based on both the level of noise (almost always A-weighted sound pressure level) and the duration of noise exposure. In setting the level at which there is believed to be no hazard, the level at which action must be taken, and the level believed to be hazardous to hearing, it is common practice to define an exchange rate that takes into account exposure time.

Studies have shown that there is no exact value for the exchange rate (Stephenson, 2008).2 An exchange rate of 3 dB, which corresponds to equal energy,3 was first proposed by Eldred et al. in 1955. The 3-dB exchange rate, recommended by the National Institute for Occupational Safety and Health (1998a) is the most widely adopted and the most widely accepted rate by scientists (Stephenson, 2008; Suter, 1993), as well as by many government agencies in the United States, including the U.S. Department of Defense (DOD), the military services, and the National Aeronautics and Space Administration. It is also accepted by the American Conference of Government Industrial Hygienists. According to Beth A. Cooper, a member of the study committee, a 3-dB exchange rate is considered “best practice” among hearing conservation professionals (Cooper, 2009). This rate has also been standardized nationally (ANSI, 2006a) and internationally (ISO, 1990).

Not all U.S. government agencies, however, accept the 3-dB exchange rate. OSHA and the Mine Safety and Health Administration (MSHA), both part of the U.S. Department of Labor, use a 5-dB exchange rate (29 CFR 1910.95 and 30 CFR 62.0), as does the Federal Railroad Administration (49 CFR 229.121).

Using the 3-dB rate, an 85-dB level exposure for 8 hours would be considered as hazardous as an 88-dB level exposure for 4 hours. Using the 5-dB rate, the 85-dB exposure for 8 hours would be considered as hazardous as 90-dB exposure for 4 hours. As an example, it is estimated in American National Standard S3.44 (ANSI, 2006a) that an 8-hour daily exposure to 90 dB(A) would, after 20 years, result in a noise-induced threshold shift of 10 dB at 3,000 Hz for 50 percent of the population. Data for different levels, frequencies, and exposure times are given in Appendix F of the standard.

Considering the accuracy of sound-level meters and the difficulty of determining exposure over a period of eight hours, or even four hours, the difference is relatively small. However, it becomes significant for short exposure times, as shown in Table 4-2.


For continuous hazardous noise, A-weighted sound pressure levels are used as the metric worldwide. Table 4-3 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


Stephenson, M.R. 2008. The Scientific Basis for the 85 dB Criterion and 3 dB Exchange Rate. Presentation at the NAE workshop on Engineering Responses to Hazardous Noise Exposures, Washington, DC, August 14–15.


Equal energy means that when the level goes up by 3 dB (a doubling of energy), the exposure time must be reduced by a factor of 2.

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