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NOISE AND MILITARY SERVICE

Description

This source contains excerpts from a report titled "NOISE AND MILITARY SERVICE" [8]. It details the committee's work regarding noise-induced hearing loss and tinnitus in military personnel [8, 9]. The report's methodology involved reviewing existing research literature and receiving information from presentations [8]. It notes that the majority of available data was not epidemiological but came from clinical, descriptive, cross-sectional studies [9].

Abstract

This document is from a report on noise and military service, specifically addressing noise-induced hearing loss and tinnitus [8, 9]. It discusses the committee's methodology, including literature review and the use of data from various clinical and descriptive studies [8, 9].

Implications for Hearing Loss and Tinnitus

Committee on Noise-Induced Hearing Loss and Tinnitus Associated with Military Service from World War II to the Present Medical Follow-up Agency Larry E. Humes, Lois M. Joellenbeck, and Jane S. Durch, Editors THE NATIONAL ACADEMIES PRESS Washington, DC www.nap.edu THE NATIONAL ACADEMIES PRESS • 500 Fifth Street, N.W. • Washington, DC 20001

This study was supported by Contract No. V101(93)P-1637 #29 between the National Academy of Sciences and the Department of Veterans Affairs. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for this project.

Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, http://www.nap.edu. For more information about the Institute of Medicine, visit the IOM home page at: www.iom.edu.

“Knowing is not enough; we must apply. Willing is not enough; we must do.” —Goethe

Advising the Nation. Improving Health. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences.

This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process.

Although the reviewers listed have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by Hyla Napadensky, Napadensky Energetics Inc. (retired), and Linda D. Cowan, Health Sciences Center, University of Oklahoma. Appointed by the National Research Council and Institute of Medicine, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

Preface

This study included the collection and analysis of data from the service medical records of some 3,500 veterans by members of the staff of the Medical Follow-up Agency of the IOM. The large data collection and data management task was overseen by Harriet Crawford, with the work of data collection and entry performed by Noreen Stevenson, John Larson, and Al Mattei. The data analysis was performed by William Page, a biostatistician with the Medical Follow-up Agency. Identifying and obtaining these records required the assistance of personnel from the Department of Veterans Affairs, the Department of Defense, and the National Archives and Records Administration. On behalf of the committee and staff, I want to thank the many individuals from those agencies for their assistance, and to offer special thanks to Lynda Russell, Yvonne Hamilton, and James White from the Department of Veterans Affairs.

The work of the committee was also supported by other staff members from the Medical Follow-up Agency, particularly the director, Rick Erdtmann, and the administrative assistant, Pamela Ramey-McCray. In addition, on behalf of the committee and staff, I wish to thank Liesl Peters, Clyde Behney, Janice Mehler, Jennifer Bitticks, Jennifer Otten, and Andrea Cohen from the IOM and NRC staffs, who participated in the report review, preproduction, dissemination, and financial management. I would like to acknowledge the assistance of Lauren Strauser in the preparation and analyses of the data from the many cross-sectional studies of noise-induced hearing loss in military personnel that are the basis for Figures 3-3 through 3-6. In addition, the time needed for these analyses, as well as for my writing and editorial duties, would not have been available were it not for a generous release from teaching responsibilities granted to me by Indiana University for the spring 2005 semester.

The committee reviewed material from peer-reviewed journals, books, reports prepared by or for the military services, and documents and data provided by the military services at the committee’s request. The committee’s information gathering also included testimony and presentations from veterans and representatives of the military services. Published peer-reviewed reports generally carried the most weight. Ideally, the committee would like to have drawn on data from reports of longitudinal, population-based studies of noise-induced hearing loss and tinnitus in humans in military settings. There are few such studies, and therefore, the committee was compelled to turn to other sources of evidence to address its charge.

The committee’s findings and conclusions concerning each element of its charge are summarized here. Also summarized are needs the committee identified for operational changes and further research. These proposals for operational changes and research are aimed at improving hearing protection, preventing hearing loss and noise-induced tinnitus during military service, and gaining a better understanding of noise hazards, noise-induced hearing loss, and tinnitus, especially among military personnel.

A standardized value representing the average thresholds measured in a large group of young normal-hearing adults at a given frequency is said to be 0 dB “hearing level” or 0 dB HL. Hearing thresholds are commonly measured at the following frequencies: 250, 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz.

SOURCES OF NOISE DURING MILITARY SERVICE

Many sources of potentially damaging noise have long existed in military settings. For the period addressed by this report—World War II to the present—some of these sources include weapons systems (e.g., handguns, rifles, artillery pieces, rockets), wheeled and tracked vehicles, fixed- and rotary-wing aircraft, ships, and communications devices (Chapter 3). Service members may encounter these noise sources through training, standard military operations, and combat. Exposure to combat-related noise may be unpredictable in onset and duration. Service members may also be exposed to hazardous noise through activities that are not unique to the military environment, including various engineering, industrial, construction, or maintenance tasks.

Throughout the period since World War II, the military services have collected data on noise levels associated with various kinds of equipment and activities, but a complete catalog of noise sources and the noise levels they produce is not feasible. The committee compiled an illustrative listing of documents reporting on sound levels in military settings (see Chapter 3 and Appendix F).

HAZARDOUS NOISE LEVELS

The specific noise levels that cause noise-induced hearing loss vary with the duration of the exposure, the type of noise, and the frequency content of the noise, as well as the susceptibility of the exposed individual (Chapters 1 and 2). Time-weighted average noise exposures of approximately 85 dBA for 8 hours per day for a 40-hour work week, or the equivalent, are considered to be hazardous, but a person must be so exposed for a number of years before developing noise-induced hearing loss. On the other hand, impulse noise with peak levels exceeding approximately 140 dB SPL may be hazardous even for a single exposure. With regard to noise-induced tinnitus, specific parameters of hazardous noise exposure have not been defined, but noise levels associated with hearing loss are also likely to be associated with tinnitus (Chapter 4).

OPERATIONAL CHANGES SUGGESTED BY THE REPORT

... 6. Enforce hearing conservation requirements for annual monitoring audiograms, as well as for follow-up audiograms if a significant threshold shift is detected in annual monitoring audiograms. 7. Continue to develop the Defense Occupational and Environmental Health Readiness System (DOEHRS) to improve its reporting capabilities to match and exceed those available with the services’ previous systems. Further development of this system should include modification of the hearing conservation component (DOEHRS-HC) to track reports of tinnitus. It should also include implementation of the industrial hygiene component (DOEHRS-IH) to provide information on exposures to hazardous noise and other chemical, physical, biological, and ergonomic hazards. 8. Develop mechanisms to provide VA personnel access to records from DOEHRS-HC for review of disability claims for hearing loss or tinnitus that are not otherwise supported by audiometric records in the service medical record.

RESEARCH NEEDS SUGGESTED BY THE REPORT

The committee also saw areas where further research would be valuable for improving understanding of broad scientific questions concerning the relationship between noise exposure and hearing loss and tinnitus. Research could also address more targeted questions concerning noise exposure, hearing loss, tinnitus, and hearing conservation measures related to military service.

1. Obtain valid estimates of the incidence, prevalence, and severity of noise-induced hearing loss and tinnitus among military personnel, including gender-specific estimates. If the reporting ability and completeness of existing databases, such as DOEHRS-HC, improve, greater use might be made of their data for analyses for personnel enrolled in hearing conservation programs. 2. Establish cohorts of military veterans with various documented noise exposures, immediately on discharge, and survey them periodically for ototoxic exposures, subsequent nonmilitary noise exposures, and hearing function, as well as presence and severity of tinnitus, in order to determine whether there is a delay in the effects of military noise exposure. These cohorts will need to be followed through the remainder of members’ lifetimes, but this longitudinal study will reveal elements of the natural history of noise-induced hearing loss and tinnitus that otherwise will not be determined. The Millennium Cohort Study, which is designed to evaluate the long-term health of people who have served in the military, might provide a mechanism for conducting a longitudinal investigation of hearing health.

CHARGE TO THE COMMITTEE

The charge to this committee arose from Public Law 107-330, which required VA to contract with the National Academies to review and evaluate the evidence regarding the association between military service and noise-induced hearing loss and tinnitus. Veterans may have hearing loss and other disabilities that have been determined to have been incurred during or aggravated by military service but that do not qualify for disability compensation payments (a “zero percent” service-connected disability). Veterans with service-connected hearing loss who do not qualify for any disability compensation payments are not included in the VA data on numbers of disabilities or numbers of veterans with disabilities. All veterans determined to have service-connected tinnitus qualify for compensation payments.

Staff of the Medical Follow-up Agency will identify veterans from each of the armed services (Army, Navy, Air Force, Marine Corps, and Coast Guard) and from each of the time periods from World War II to the present. A sample of the service medical records of these individuals will be obtained, examined for regulatory compliance regarding audiometric surveillance (including reference, periodic, and termination audiograms), abstracted, recorded, and tabulated. The charge does not include consideration of effects of noise other than upon the auditory system, including hearing loss and tinnitus, nor of the issues surrounding assisted hearing through hearing aids or prosthetic devices. The study committee was selected to include members with expertise in audiology, bioacoustics, military preventive medicine, occupational medicine, industrial hygiene and hearing conservation programs, epidemiology, and otology.

It was also determined that the committee’s charge did not include assessment of the disability or handicap resulting from noise-induced hearing loss or the means of assigning compensation to specific amounts or degrees of disability.

The committee met five times from May 2004 through March 2005 and held numerous telephone conference calls through August 2005. During these meetings and conference calls, the committee reviewed and discussed the existing research literature on the topics central to its charge and received information during oral presentations made by representatives from various organizations, including several veterans and representatives of veterans’ organizations, branches of the military, and consultants. In addition to these face-to-face meetings and telephone conference calls, the committee communicated frequently among themselves and with IOM staff via e-mail. This report represents the product of that information gathering and discussion.

Research is also being done to explore pharmacological approaches to reducing susceptibility to noise-induced hearing loss. For example, studies with laboratory animals have found beneficial effects from the administration of antioxidants (e.g., Henderson et al., 1999; Kopke et al., 2005; McFadden et al., 2005). A clinical trial is testing an antioxidant compound in Marine Corps recruits (Boswell, 2004), but results had not been reported at the time the committee completed its work. Studies in animals and humans have also investigated protective effects of supplemental oral magnesium (e.g., Attias et al., 1994; Scheibe et al., 2000; Attias et al., 2004).

EVALUATING THE STRENGTH OF EVIDENCE

To address the questions posed to the committee by the statement of task, efforts were made to identify a relevant body of evidence through searches of the indexed medical literature and catalogues of reports prepared by or for the military services. Studies and reports were also identified from the reference lists of other documents, and some documents were provided by the military services at the committee’s request. Published peer-reviewed reports generally carried the most weight in drawing conclusions because the methods and findings of those reports could be assessed. Reports that had not undergone peer review and some unpublished data were also considered by the committee and evaluated in the context of the available body of published literature.

Ideally, in addressing the charge to the committee, the committee would have preferred to draw on data from reports of longitudinal, population-based studies of noise-induced hearing loss or tinnitus in humans in military settings. Clearly, such studies would offer the greatest strength of evidence to support the committee’s findings and recommendations. Unfortunately, there are few such studies. Therefore, the committee was compelled to turn to other sources of evidence to address its charge. The sources of evidence considered by the committee included epidemiological, laboratory, and clinical studies directly addressing the question at hand. Epidemiological studies generally carry the most weight in evaluating evidence for or against an association between an exposure (noise) and the resulting health outcome (hearing loss or tinnitus) in humans. These studies measure health-related exposures and outcomes in a defined set of human subjects and use that information to make inferences about the nature and strength of associations between such exposures and outcomes in the population from which the study sample was drawn. Epidemiological studies can be categorized as experimental (clinical trial) or observational and as controlled (analytic) or uncontrolled (descriptive).

The primary outcome of interest in epidemiological studies is usually the incidence or prevalence of the health condition under investigation. The incidence of a particular condition refers to the number of newly occurring cases of that condition that develop over a specific period of time in a particular population and is expressed as either a risk (a probability) or a rate. A condition’s prevalence is the proportion of individuals in a sample who have that condition at a single point in time or during an interval of time. Risk, in the epidemiological sense, is defined as the probability of developing a particular health condition. The term “relative risk” refers to the ratio of the incidence of the condition in a population exposed to some potential hazard of interest, such as occupational noise, to the corresponding incidence in a similar but nonexposed group. Cross-sectional studies do not directly measure the risk associated with an exposure for two important reasons: (1) these studies do not automatically define whether the exposure or the condition came first; and (2) cross-sectional samples usually contain old as well as new cases (i.e., incident and prevalent cases), further obscuring the temporal sequence of exposure and condition.

Among epidemiological research designs, case reports and case series are generally weakest. They are inadequate by themselves to establish an association, but they can be valuable in drawing the attention of the scientific community to the problem and in generating testable hypotheses. The committee did not rely on case reports in reaching its conclusions. The vast majority of data available on noise-induced hearing loss and tinnitus in military personnel is not epidemiological. The data came from a variety of clinical, descriptive, cross-sectional studies of variously defined groups of military personnel. The data were reported in ways that gave little or no indication of the prevalence or incidence of either hearing loss or tinnitus. Instead, the dependent measures were generally hearing thresholds at various pure-tone frequencies, which were reported as average thresholds for groups defined by age or length of service in the military. In the absence of control groups in most of these studies, the committee turned to standardized compilations of “control data” on hearing thresholds for groups of screened or unscreened individuals of various ages for comparison purposes.

Some aspects of the committee’s charge were best addressed with data from well-designed and carefully executed human epidemiological studies. When such data were not available, the committee turned to alternate data with the resulting caveats to its findings noted. Other aspects of the committee’s charge were best addressed with data from well-designed and carefully executed laboratory studies with humans and animals. Both forms of evidence are considered valid, depending on the issue or questions being addressed, and have been weighed by the committee in evaluating the strength of evidence supporting its findings.

With the foregoing in mind, the committee adopted the following scale for the strength of evidence. As will be seen, the strength of evidence in this scale is tied to the presence and number of “strong studies” supporting a particular committee finding. In general, observational epidemiological studies cannot by themselves establish causal associations. Strong epidemiological studies in support of a statistical association between an exposure and a condition, whether causal or not, could include well-designed cross-sectional studies where the likelihood of chance findings has been minimized, known confounding factors have been considered in the analysis, and known or potential biases have been eliminated. However, in support of a causal association, “strong studies” are generally well-designed, prospective observational human population studies or randomized controlled trials in which chance, bias, and confounding are similarly treated. With respect to laboratory studies, “strong studies” are well-designed and carefully executed and interpreted human or animal studies in which chance, bias, and confounding have also been treated in a similar way.

However, when applying the foregoing scale for strength of evidence, the context of the specific question being addressed must be kept in mind. For example, if the specific question posed or the issue addressed pertains to the effect of noise on humans and the only evidence available is from studies of laboratory animals, this evidence is considered not to be sufficient regardless of the number of “strong” studies available from laboratory animals.

THE COMMITTEE’S REPORT

The remainder of the report summarizes the evidence regarding the questions put to the committee concerning military service and noise-induced hearing loss and tinnitus and presents the committee’s findings. Chapter 2 reviews the mechanisms of noise-induced hearing loss and evidence regarding the impact of various risk factors. Chapter 3 reviews noise and noise hazards associated with military service. Chapter 4 focuses on tinnitus, especially its association with noise exposure and hearing loss. Chapter 5 turns to the nature and effectiveness of hearing conservation programs in the armed services. Chapter 6 presents the results of an audit of the service medical records of military personnel sampled from various periods of service from World War II to 2002. Finally, Chapter 7 provides a summary that draws on the information presented in preceding chapters to address the specific questions and issues posed in the Statement of Task and in Public Law 107-330.

References

• ANSI (American National Standards Institute). 1996. ANSI S3.44 Determination of Occupational Noise Exposure and Estimation of Noise-Induced Hearing Impairment. New York: Acoustical Society of America.
• Attias J, Weisz G, Almog S, Shahar A, Wiener M, Joachims Z, Netzer A, Ising H, Rebentisch E, Guenther T. 1994. Oral magnesium intake reduces permanent hearing loss induced by noise exposure. American Journal of Otolaryngology 15(1):26–32.
• Attias J, Sapir S, Bresloff I, Reshef-Haran I, Ising H. 2004. Reduction in noise-induced temporary threshold shift in humans following oral magnesium intake. Clinical Otolaryngology and Allied Sciences 29(6):635–641.
• Rench ME, Johnson S, Sanders T. 2001. Cost Benefit Analysis for Human Effectiveness Research: Bioacoustic Protection. Wright-Patterson Air Force Base, OH: Air Force Research Laboratory.
• Scheibe F, Haupt H, Ising H. 2000. Preventive effect of magnesium supplement on noise-induced hearing loss in the guinea pig. European Archives of Oto-Rhino-Laryngology 257(1):10–16.
• Veterans Benefits Administration. 2004. Veterans Benefits Administration Annual Benefits Report for FY 2003. Washington, DC: Department of Veterans Affairs.

A typical noise-notch audiogram is illustrated. There have been attempts to define the presence or absence of a noise notch more objectively than by simply relying on visual inspection of the pattern of hearing loss in the high frequencies, the latter approach not being particularly reliable (e.g., McBride and Williams, 2001a,b). One such approach to objectively define the presence or absence of a noise notch was advocated initially by Coles et al. (2000) and further refined by Dobie and Rabinowitz (2002). A graphic demonstration is provided by drawing a line to connect the hearing thresholds at 1000 and 8000 Hz, as illustrated by the dashed line in Figure 2-3. Having thresholds between 1000 and 8000 Hz (especially those at 2000, 3000, and 4000 Hz) that fall at or below the dashed line is thought to indicate the presence of a high-frequency notch in the hearing loss. Dobie and Rabinowitz (2002) describe a corresponding metric, referred to as the notch index (NI), that is simply the mean of the hearing thresholds at 1000 and 8000 Hz subtracted from the mean of the hearing thresholds at 2000, 3000, and 4000 Hz. Values of NI greater than 0 dB are thought to indicate the presence of a notch, whereas those less than 0 dB do not. Other approaches to objective determination of the presence or absence of a noise notch have been described previously (e.g., Gates et al., 2000). The simplicity of the notch index and similar metrics is appealing, although additional research is needed to establish its reliability, as well as sensitivity and specificity in the identification of noise-induced hearing loss in the general population.

With severe noise damage, where an entire portion of the organ of Corti is absent, it is replaced on the basilar membrane (BM) by an undifferentiated, squamous epithelium. Nerve fibers to the area are also missing.

Certain exogenous and endogenous factors may interact with noise exposure to increase the hearing loss beyond that resulting from exposure to either agent alone. Although an effort was made to focus on recent human studies, for some factors, the only studies have been in laboratory animals. In many of the animal studies, the exposures were exploratory and often not relevant to the occupational setting. In addition, in the human studies, details of the exposures to noise and other agents were not always available, especially for an individual subject. Dose-response information was rarely available. Finally, the studies reviewed included a wide range of methods to assess hearing loss.

Finally, whole-body vibration increases temporary hearing loss when noise is present (see review by Humes, 1984), but only when body temperature is elevated (Manninen, 1988). An increase in body temperature is known to increase the effects of noise on hearing (e.g., Drescher, 1976). Exercise during noise exposure and cardiovascular fitness have been shown to decrease (Manson et al., 1994), increase, or have no effect on temporary hearing loss (Wilson and Herbstein, 2003). The effect of exercise on noise-induced hearing loss may also relate to increases in body temperature (Pekkarinen, 1995). Many of these studies included relatively small (n < 20) convenience samples, with no randomized designs or control groups.

These national and international standards represent the synthesis of the best available data on industrial noise-induced hearing loss. The available data, however, are not without limitations. For example, sample sizes were often small, the studies were cross-sectional rather than longitudinal and subject to cohort effects, and specification of the noise exposure was by group or area of the industry, rather than for each individual. An illustration of the age-corrected “noise-induced permanent threshold shift,” NIPTS, estimated with ISO-1999 (1990) is provided in Figure 2-5. The top panel demonstrates the development of NIPTS at one frequency, 4000 Hz, with increasing years of exposure to 8-hour equivalent continuous noise levels of 85, 90, 95, or 100 dBA. These estimates reveal two key features of NIPTS: (1) that NIPTS increases with noise level and, for an 8-hour equivalent continuous noise level of 85 dBA (or less), is negligible at 4000 Hz, the frequency showing the greatest amount of NIPTS; and (2) that NIPTS grows most rapidly during the first 10–15 years, with only slight increases beyond that. It is important to emphasize here, however, that this is the hearing loss associated with noise exposure only (NIPTS). Also, the values displayed are the predicted median values from ISO-1999. The same standard provides for the generation of other percentiles or quartiles.

With regard to the estimation of noise-induced hearing loss, the following represents a summary of the main points of this section of the chapter:

• Without measurement of pure-tone thresholds prior to and following a given exposure to noise, it is impossible to document the effects of that exposure on hearing or to know what portion of the hearing loss in an older individual is due to earlier noise exposure.

References

• Bohne BA, Harding GW. 2000. Degeneration in the cochlea after noise damage: Primary versus secondary events. American Journal of Otology 21(4):505–509.
• Botte MC, Variot MH. 1979. [Auditory fatigue in individuals having sustained an acoustic trauma (author’s transl)]. Annales d’Oto-Laryngologie et de Chirurgie Cervico-Faciale 96(12):827–833.
• Bredberg G. 1968. Cellular pattern and nerve supply of the human organ of Corti. Acta Oto-Laryngologica Supplement 236:1–135.
• Humes LE, Koval CB. 1981. Temporary threshold shifts for masked pure tones. II. Broad-band masker. Audiology 20(4):325–335.
• Humes LE, Dirks DD, Bell TS, Kincaid GE. 1987. Recognition of nonsense syllables by hearing-impaired listeners and by noise-masked normal hearers. Journal of the Acoustical Society of America 81(3):765–773.
• Ishii EK, Talbott E. 1998. Race/ethnicity differences in the prevalence of noise-induced hearing loss in a group of metal fabricating workers. Journal of Occupational and Environmental Medicine 40(8):661–666.
• McGill TJI, Schuknecht HF. 1976. Human cochlear changes in noise induced hearing loss. Laryngoscope 86(9):1293–1302.
• Melinek M, Naggan L, Altman M. 1976. Acute acoustic trauma—a clinical investigation and prognosis in 433 symptomatic soldiers. Israel Journal of Medical Sciences 12(6):560–569.
• Melnick W. 1976. Human asymptotic threshold shift. In: Henderson D, Hamernik RP, Dosanjh DS, Mills JH, eds. Effects of Noise on Hearing. New York: Raven Press. Pp. 277–289.
• Miller JD, Watson CS, Covell WP. 1963. Deafening effects of noise on the cat. Acta Oto-Laryngologica Supplement 176:1–91.
• Morata TC. 2003. Chemical exposure as a risk factor for hearing loss. Journal of Occupational Environmental Medicine 45(7):676–682.
• Morata TC, Campo P. 2001. Auditory function after single of combined exposure to styrene: A review. In: Henderson D, Prasher D, Kopke R, Salvi R, Hamernik R, eds. Noise Induced Hearing Loss: Basic Mechanisms, Prevention and Control. London: Noise Research Network Publications. Pp. 293–304.
• Morata TC, Lemasters GK. 1995. Epidemiologic considerations in the evaluation of occupational hearing loss. Occupational Medicine 10(3):641–656.
• NRC (National Research Council). 1992. Hazardous Exposure to Impulse Noise. Committee on Hearing, Bioacoustics, and Biomechanics. Washington, DC: National Academy Press.
• Ohlemiller KK, Wright JS, Heidbreder AF. 2000. Vulnerability to noise-induced hearing loss in ‘middle-aged’ and young adult mice: A dose-response approach in CBA, C57BL, and BALB inbred strains. Hearing Research 149(1-2):239–247.
• Wang Y, Hirose K, Liberman MC. 2002. Dynamics of noise-induced cellular injury and repair in the mouse cochlea. Journal of the Association for Research in Otolaryngology 3:248–268.
• Ward WD. 1965. The concept of susceptibility to hearing loss. Journal of Occupational Medicine 7(12):595–607.
• Ward WD. 1968. Susceptibility to auditory fatigue. In: Neff WD, ed. Contributions to Sensory Physiology. Vol. 3. New York: Academic Press. Pp. 191–226.
• Ward WD. 1973. Noise-induced hearing damage. Otolaryngology 2:377–390.
• Ward WD. 1995. Endogenous factors related to susceptibility to damage from noise. Occupa-

The first part of the chapter briefly reviews the services’ policies and programs to collect data on noise levels generated by equipment used by military personnel and the noise doses received by military personnel working in certain settings. Examples of the kinds of data collected through these efforts are provided. The remainder of the chapter focuses on the committee’s assessment of data on hearing thresholds and hearing loss among military service members since World War II.

NOISE IN THE MILITARY ENVIRONMENT

Hazardous noise exposures may occur in various military settings, including industrial-type workplaces (aircraft refurbishing, shipbuilding), as well as military-unique environments, such as combat. Although complete control of hazardous noise in combat is clearly impossible, there are many circumstances in which limiting or reducing hazardous noise at its source is possible. Indeed, the Department of Defense Design Criteria Standard (MIL-STD-1474D), first issued in 1973, emphasizes the importance of incorporating noise control considerations into the design and purchase requirements for military materiel (DoD, 1997). However, as noted in Chapter 3, DoD regulations give priority to maintaining combat readiness and permit tradeoffs between noise reduction and weight, speed, cost, or other factors crucial to the effectiveness of the equipment (DoD, 2004b).

Appendix F provides an illustrative list of documents, most of which are available in the published literature or in electronic form from government sources, that report sound levels generated by a variety of military aircraft, vehicles, equipment, and weapons systems.

Estimating Cumulative Noise Exposures Despite the existence of data on sound pressure levels generated by weapons and equipment, and dosimetry estimates of noise exposure for certain personnel, arriving at an estimate of the cumulative noise exposure of any service member or group of service members is nearly impossible. To an even greater extent than civilian workers, military personnel are not likely to experience homogeneous noise exposures over the course of their military service.

In sum, despite the availability of data on sound pressure levels and some dosimetry data, the complexity of military noise exposures precludes ready estimates of service members’ cumulative noise doses.

FINDING: The evidence is sufficient to conclude that hazardous noise levels are and have been present in many military settings. FINDING: Extensive collections of data on sound pressure levels produced by equipment and activities in military settings are available from World War II to the present. Many estimates of noise exposures (doses) are also available for certain personnel.

EVIDENCE REGARDING THE EFFECTS OF NOISE ON HEARING AMONG U.S. MILITARY PERSONNEL

The committee was asked to review the evidence that hearing loss has been incurred by members of the armed services as a result of noise exposures during military service since World War II. To investigate this subject, the committee examined information from various sources, including studies reported in the published literature, reports prepared for the military services, and data from the military services’ hearing conservation databases, which were provided at the request of the committee. The committee also undertook additional analyses of some of the data.

One way to place the hearing thresholds observed in military personnel in context is to compare them with those of other groups of people who are representative of the general population and for whom there are data on the average amount of age-related hearing loss. Two such reference populations were used. One is based on an unscreened sample that may include people who have a history of certain types of otologic disease or noise exposure. The other type is a screened sample that is designed to exclude such individuals. For an unscreened reference point, the committee used data drawn from the results of a U.S. Public Health Service (USPHS) survey completed in 1962, whose participants were a nationally representative sample (n = 6,672) of the civilian adult population in the United States at that time (Glorig and Roberts, 1965). The better-ear thresholds from the 1962 USPHS study comprise database B from the ISO-1999 standard, but most of the studies of military personnel did not report better-ear thresholds. As a result, the reference set of data from the 1962 USPHS study was used to derive an average amount of hearing loss for both ears for each age group. The screened sample used was database A from the ISO-1999 standard (ISO, 1990). For both the screened and unscreened reference data, the specific measure used for comparison was an average high-frequency threshold, calculated as the arithmetic average of the mean or median (depending on the source) thresholds at 3000, 4000, and 6000 Hz, for both ears combined. This average was selected to focus on the frequencies most closely associated with noise-induced hearing loss.

Average high-frequency thresholds for both ears for selected Navy enlisted personnel in the 1970s and for Navy enlisted men enrolled in the hearing conservation program in 1995–1999 are shown in Figure 3-4. The 1970s data are for eight occupational specialties considered to have high noise exposure and eight considered to have low noise exposure, plus recruits. Average high-frequency thresholds for men for screened (A; ISO-1999, 1990) and unscreened (U; Glorig and Roberts, 1965) reference groups are also shown.

Average high-frequency thresholds for the better ear for selected Marine Corps personnel (officers and enlisted men) in the 1970s and for both ears for enlisted Marine Corps men in the hearing conservation program in 1995–1999 are shown in Figure 3-5. Average high-frequency thresholds (both ears) for men for screened (A; ISO-1999, 1990) and unscreened (U; Glorig and Roberts, 1965) reference groups are also shown.

Although other reports of additional data on the distributions of pure-tone thresholds in military personnel were not available, some reports did provide percentages for individuals in each of several age groups who had hearing thresholds greater than some criterion amount of hearing loss. Goldenberg (1977), for example, reported on the percentage of better-ear hearing thresholds that were greater than 25 dB HL among 11,580 Marine Corps personnel whose hearing was tested at one base during a 13-month period. These percentages for Marine Corps personnel are displayed by the dashed lines in Figure 3-9 for pure-tone frequencies of 3000, 4000, and 6000 Hz and each of five age groups. The solid lines in Figure 3-9 provide comparison percentages from the 1962 USPHS unscreened sample for better-ear pure-tone thresholds greater than 25 dB HL (adjusted to ANSI (1969) standards) at the same three frequencies and for the same five age groups.

FINDING: The evidence is sufficient to conclude that certain military personnel from World War II to the present have exhibited hearing thresholds while in the military that are typical of noise-induced hearing loss. FINDING: The evidence is not sufficient to reach conclusions regarding the number or proportion of service members, overall or in specific occupational groups or eras since World War II, who have experienced noise-induced hearing loss while in the military. FINDING: The evidence is not sufficient to determine the probability of acquiring noise-induced hearing loss associated with service in the military, or in specific branches of the military, for a given individual. The probability of acquiring noise-induced hearing loss can only be determined precisely with well-controlled, longitudinal epidemiological studies.

References

• Air Force Hearing Conservation Registry. 2004b. DOEHRS Data Repository: Positive Significant Threshold Shift, 1999–2004. Data provided to the Institute of Medicine Committee on Noise-Induced Hearing Loss and Tinnitus Associated with Military Service from World War II to the Present, Washington, DC.
• Air Force Hearing Conservation Registry. 2004c. DOEHRS Data Repository: Positive Significant Threshold Shift, 1999–2004. Data provided to the Institute of Medicine Committee on Noise-Induced Hearing Loss and Tinnitus Associated with Military Service from World War II to the Present, Washington, DC.
• CHABA (National Academy of Sciences–National Research Council Committee on Hearing, Bioacoustics, and Biomechanics). 1968. Proposed Damage-Risk Criterion for Impulse Noise (Gunfire). Report of Working Group 57 (Ward WD, ed.). Washington, DC: National Academy of Sciences.
• Chandler DW, Fletcher JL. 1983. Hearing levels in U.S. Army engineers. Journal of Audiology Research 23(1):23–32.
• Department of the Air Force. 1980. Hearing Conservation Program Status Report: January–June 1980. Washington, DC: Department of the Air Force.
• Gasaway DC. 1988. Occupational hearing conservation in the military. In: Lipscomb DM, ed. [Jacobson JT, advisory ed.]. Hearing Conservation in Industry, Schools, and the Military. Boston: Little, Brown. Pp. 243–262.
• Glorig A. 1952. Field investigations on military personnel as regards sound. In: University of Michigan School of Public Health, Institute of Industrial Health. The Acoustical Spectrum. Sound—Wanted and Unwanted. Ann Arbor: University of Michigan Press. Pp. 99–106.
• Navy Environmental Health Center. 2004b. Navy Medical Department Hearing Conservation Program Procedures. NECH-TM 6260.51.99-2. Portsmouth, VA: U.S. Navy, Bureau of Medicine and Surgery.
• Nixon CW. 1998. A Glimpse of History: The Origin of Hearing Conservation Was in the Military? Wright-Patterson Air Force Base, OH: Air Force Research Laboratory.
• Noe CM, Cruickshanks KJ, Nondahl D, Wiley TL, Wilson RH. 2002. Prevalence of Hearing Loss Among the Veteran Population in the Beaver Dam (WI) Cohort (abstract). Third Rehabilitation Research and Development Conference, Arlington, VA. February 10–12.
• Ohlin D. 1992. 15 Years Revisited: The Prevalence of Hearing Loss Among Selected U.S. Army Branches. Hearing Conservation Special Study No. 51-01-PM82-93. Aberdeen Proving Ground, MD: U.S. Army Environmental Hygiene Agency.
• U.S. Army Center for Health Promotion and Preventive Medicine. 2004d. Noise Levels of Common Army Equipment. [Online]. Available: http://chppm-www.apgea.army.mil/hcp/NoiseLevelsPrint.htm [accessed April 21, 2004].
• Walden BE, Worthington DW, McCurdy HW. 1971. The Extent of Hearing Loss in the Army: A Survey Report. Washington, DC: Walter Reed Army Medical Center.
• Walden BE, Prosek RA, Worthington DW. 1975. The Prevalence of Hearing Loss Within Selected U.S. Army Branches. Washington, DC: Walter Reed Army Medical Center.
• Wolgemuth KS, Luttrell WE, Kamhi AG, Wark DJ. 1995. The effectiveness of the Navy’s hearing conservation program. Military Medicine 160(5):219–222.
• Adams PF, Hendershot GE, Marano MA. 1999. Current estimates from the National Health Interview Survey, 1996. Vital and Health Statistics, Series 10, No. 200. Hyattsville, MD: National Center for Health Statistics.
• Aggleton JP, Mishkin M. 1986. The amygdala: Sensory gateway to the emotions. In: Pultchik R, Kellerman H, eds. Emotion, Theory, Research, and Experience. Vol. 3. New York: Academic Press. Pp. 281–289.
• Alberti PW. 1987. Tinnitus in occupational hearing loss: Nosological aspects. Journal of Otolaryngology 16(1):34–35.
• Cruickshanks K. 2005. Comments. E-mail to J. Durch, Institute of Medicine, June 13.
• Kim J, Morest DK, Bohne BA. 1997. Degeneration of axons in the brainstem of the chinchilla after auditory stimulation. Hearing Research 103:169–191.
• Kleinjung T, Eichhammer P, Langguth B, Jacob P, Marienhagen J, Hajak G, Wolf SR, Strutz J. 2005. Long-term effects of repetitive transcranial magnetic stimulation (rTMS) in patients with chronic tinnitus. Otolaryngology–Head and Neck Surgery 132:566–569.
• Kuk FK, Tyler RS, Russell D, Jordan H. 1990. The psychometric properties of a tinnitus handicap questionnaire. Ear and Hearing 11(6):434–445.
• Metternich FU, Brusis T. 1999. [Acute hearing loss and tinnitus caused by amplified recreational music.] Laryngorhinootologie 78(11):614–619.
• Moody DB. 2004. Animal models of tinnitus. In: Snow JB, Jr., ed. Tinnitus: Theory and Management. Hamilton, Ontario, Canada: B.C. Decker. Pp. 80–95.
• Morest DK, Kim J, Potashner SJ, Bohne BA. 1998. Long-term degeneration in the cochlear nerve and cochlear nucleus of the adult chinchilla following acoustic overstimulation. Microscopy Research and Technique 41:205–216.
• Tambs K, Hoffman HJ, Borchgrevink HM, Holmen J, Samuelsen SO. 2003. Hearing loss induced by noise, ear infections, and head injuries: Results from the Nord-Trøndelag Hearing Loss Study. International Journal of Audiology 42(2):89–105.
• Temmel AF, Kierner AC, Steurer M, Riedl S, Innitzer J. 1999. Hearing loss and tinnitus in acute acoustic trauma. Wiener Klinische Wochenschrift 111(21):891–891.
• Tyler RS, Noble WS, Preece JP, Dunn C, Witt S. 2004. Psychological treatments for tinnitus. In: Snow JB, Jr., ed. Tinnitus: Theory and Management. Hamilton, Ontario, Canada: B.C. Decker. Pp. 314–325.
• Van Campen LE, Dennis JM, Hanlin RC, King SB, Velderman AM. 1999. One-year audiologic monitoring of individuals exposed to the 1995 Oklahoma City bombing. Journal of American Academy of Audiology 10(5):231–247.
• Young DW. 2000. Biofeedback training in the treatment of tinnitus. In: Tyler RS, ed. Tinnitus Handbook. San Diego, CA: Singular Publishing Group. Pp. 281–296.

5 Responding to Noise Risks: Hearing Conservation Programs in the Military

The committee’s charge to identify when hearing conservation measures were adequate to protect the hearing of service members derives from legislative language. The legislation requested that the committee identify when audiometric measures used by the military became adequate to evaluate individual hearing loss (threshold shift) and when hearing conservation measures to prevent hearing loss were available to service members. The evaluation of hearing conservation programs is not a simple task of either assessing a checklist of necessary components or performing a straightforward analysis of an audiometric database. This chapter describes key aspects of hearing conservation programs and reviews the development and adequacy of programs in the military. Current hearing conservation programs do not include monitoring or prevention of tinnitus. As described in Chapter 4, the relationship between noise exposure and tinnitus is not yet well understood. However, the committee makes the presumption that measures taken to protect against noise-induced hearing loss are likely to help in the prevention of tinnitus. Thus, many of the elements of a hearing conservation program could be applied to prevention of tinnitus as well as hearing loss.

A timeline of major conflicts and milestones in hearing conservation programs is shown in Figure 5-1.

The Coast Guard does not yet formally participate in DOEHRS-HC. DoD forms 2215 and 2216 or similar forms for recording baseline and monitoring audiogram data are filed in an individual’s medical folder.

ASSESSING THE ADEQUACY OF HEARING CONSERVATION PROGRAMS

Criteria for Evaluating Hearing Conservation Program Effectiveness

Although there is general consensus concerning the necessary components of a hearing conservation program (several authors, cited by Royster and Royster, 1990), there is less agreement regarding how to assess the effectiveness of a program. Several approaches have been proposed, among them the use of checklists to assess the presence of important program components and the use of audiometric databases for population and criteria comparisons.

Chapter 3 presented some of the data available to the committee to examine changes in hearing thresholds in a few samples of different military service populations over decades from the 1970s to the 1990s, albeit with limitations in the availability of appropriate reference populations. It is difficult to determine the extent to which service members have experienced hearing loss, even for the period since audiometric testing has been required. In this section the committee reviews additional evidence pertaining to aspects of the process, rather than the outcomes, of military hearing conservation programs since World War II. The committee was unable to carry out an audit of the countless sites at which military hearing conservation programs are implemented; instead it relied on information regarding hearing protection and audiometric monitoring from the published literature and from information, such as that from DOEHRS-HC, provided to the committee by the services. The information available to the committee regarding these features is incomplete but, taken together, may provide some indication of the adequacy of the services’ hearing conservation programs over time.

Noise Control

Hazardous noise exposures may occur in various military settings, including industrial-type workplaces (aircraft refurbishing, shipbuilding), as well as military-unique environments, such as combat. Although complete control of hazardous noise in combat is clearly impossible, there are many circumstances in which limiting or reducing hazardous noise at its source is possible. Indeed, the Department of Defense Design Criteria Standard (MIL-STD-1474D), first issued in 1973, emphasizes the importance of incorporating noise control considerations into the design and purchase requirements for military materiel (DoD, 1997). However, as noted in Chapter 3, DoD regulations give priority to maintaining combat readiness and permit tradeoffs between noise reduction and weight, speed, cost, or other factors crucial to the effectiveness of the equipment (DoD, 2004b).

Hearing protection devices available from World War II to the present are listed in Table 5-2. For WWII, typical devices included cotton, fingers (used by artillery crews), and nothing. From 1945-late 1950s, devices included Vaseline-impregnated cotton, the V-51R earplug, hard custom earmolds, and early circumaural earmuff designs. Navy “cranial earmuffs” were introduced in the mid-1950s. The 1960s saw extra-small and large sizes added to the V-51R plug, the introduction of a triple-flange earplug, canal caps, malleable putty earplugs (not widely used), and improved earmuffs. By the 1970s, conventional plugs and muffs technology was essentially mature, with some material improvements and color-coded sizing. The roll-down slow-recovery foam earplug was a new concept providing better protection, though limited in military use initially. Tanker helmets and aircraft flight helmets began to provide impact protection with internal ear cups for acoustical protection, though low-frequency attenuation was not as good as conventional earmuffs. The 1980s saw no major technology advances in conventional plugs and muffs. Tanker helmets with Active Noise Reduction (ANR) began to appear, improving communication and providing protection. The 1990s saw minor technology advancements, mostly cosmetic, with performance essentially unchanged. Widespread use of roll-down slow-recovery foam earplugs became common. Communication earplugs using an earphone in foam earplugs were used in tanker and helicopter applications for enhanced communication and increased protection. Widespread use of ANR for tanker helmets and limited applications in aircraft flight helmets began to appear. From 2000-present, devices are similar to prior decades, except the V-51R plug was dropped. Level-dependent “combat arms” earplugs provide protection against weapons and blast noise while allowing communication of lower-level sounds when impacts are not present.

Representative minimum and maximum mean attenuation values of well-fitted hearing protectors under laboratory conditions are listed in Table 5-3. For example, fingertip insertion in the ear canal shows a mean attenuation range of 25-30 dB across octave band center frequencies from 125 Hz to 3000 Hz, and 30-35 dB at 4000 and 8000 Hz.

A separate study reported that while all flight deck personnel wear headgear (“cranials”) with earmuffs rated at 23 dB, only 1 of the 22 individuals in the study wore dual hearing protection (Rovig et al., 2004).

References

• Acoustical Society of America. 2002. Evaluating the Effectiveness of Hearing Conservation Programs Through Audiometric Data Base Analysis. ANSI Technical Report: ANSI S12.13 TR-2002. New York: Acoustical Society of America.
• Acton WI. 1987. History and development of hearing protection devices. Journal of the Acoustical Society of America 81(Suppl 1):S4.
• Adera T, Donahue AM, Malit BD, Gaydos JC. 1993. Assessment of the proposed Draft American National Standard method for evaluating the effectiveness of hearing conservation programs. Journal of Occupational Medicine 35(6):568–573.
• Air Force Hearing Conservation Registry. 2004a. DOEHRS Data Repository: Hearing Conservation Compliance Report, 2000–2003. Data provided to the Institute of Medicine Committee on Noise-Induced Hearing Loss and Tinnitus Associated with Military Service from World War II to the Present, Washington, DC.
• Berger EH, Franks JR, Lindgren F. 1996. International review of field studies of hearing protector attenuation. In: Axelsson A, Borchgrevink HM, Hamernik RP, Hellstrom PA, Henderson D, Salvi RJ, eds. Scientific Basis of Noise-Induced Hearing Loss. New York: Thieme Medical Publishers. Pp. 361–377.
• Bergman M. 2002. On the Origins of Audiology: American Wartime Military Audiology. Audiology Today. Monograph No. 1. McLean, VA: American Academy of Audiology.
• Department of the Navy. 2000. Marine Corps Order 6260.1E: Marine Corps Hearing Conservation Program Procedures. Washington, DC: Department of the Navy.
• Department of the Navy. 2001. OPNAVINST 5100.19D: Navy Occupational Safety and Health: Program Manual for Forces Afloat. Washington, DC: Department of the Navy.
• Department of the Navy. 2002. OPNAVINST 5100.23F: Navy Occupational Safety and Health Program Manual. Washington, DC: Department of the Navy.
• Department of Veterans Affairs. 2004. Handbook of Standard Procedures and Best Practices for Audiology Compensation and Pension Examinations. Dennis KC, Beck LB, Chandler DW, Schafer J, eds. Washington, DC: Department of Veterans Affairs.
• DoD. 1996. Department of Defense Instruction 6055.12: DoD Hearing Conservation Program. Washington, DC: U.S. Department of Defense.
• DoD. 1997. MIL-STD-1474D: Department of Defense Design Criteria Standard—Noise Limits. Washington, DC: Department of Defense.
• DoD. 2004b. Department of Defense Instruction 6055.12: DoD Hearing Conservation Program. Washington, DC: Department of Defense.
• DoD. 2005. Active Duty Military Strength Report for March 31, 2005. Military Personnel Statistics. [Online]. Available: http://www.dior.whs.mil/mmid/military/miltop.htm [accessed May 9, 2005].
• Donahue AM, Ohlin DW. 1993. Noise and the impairment of hearing. In: Deeter DP, Gaydos JC, eds. Occupational Health: The Soldier and the Industrial Base. Falls Church, VA: Office of the Surgeon General.
• Gwin LP, Lacroix PG. 1985. A prevalence study of hearing conservation in the United States Naval Submarine Force. Military Medicine 150(12):652–656.
• Mozo BT, Murphy BA. 1998. Novel Communications and Hearing Protection for Helmet Systems: Communications Earplug. USAARL Rept. No. 98-23. Fort Rucker, AL: U.S. Army Aeromedical Research Lab.
• NIOSH. 1998. NIOSH Criteria for a Recommended Standard: Occupational Noise Exposure. DHHS (NIOSH) Pub. No. 98-126. Cincinnati, OH: NIOSH.
• NIOSH. 2005. Noise and Hearing Loss Prevention: Hearing Conservation Program Evaluation Checklist. [Online]. Available: http://www.cdc.gov/niosh/topics/noise/workplacesolutions/ hearingchecklist.html [accessed May 17, 2005].
• Ohlin D. 1999. Web-based self-audit protocol and effectiveness measures in the military. In: Proceedings: Best Practices in Hearing Loss Prevention. DHHS (NIOSH) Pub. No. 2001-157. Cincinnati, OH: NIOSH. Pp. 13–15.
• Page JC, Bohnker BK, Rovig G, Betts LS, Sack DM. 2002. Navy hearing conservation program: Threshold shifts in enlisted personnel, 1995–1999. Military Medicine 167(1):48–52.
• Pluta R. 2003. HCDR Annual Report 2003. Brooks City–Base, TX: U.S. Air Force.
• Pluta R. 2004. The USAF Hearing Conservation Program—Sustaining Readiness Through Healthy Communities. Presentation to the Institute of Medicine Committee on Noise-Induced Hearing Loss and Tinnitus Associated with Military Service from World War II to the Present, Meeting IV, Washington, DC. December 7.
• Price IR, Whitaker G. 1986. Noise exposure during shotblasting and the acoustic properties of air-fed helmets. In: Lotz R, ed. Proceedings of Inter-Noise 86. Poughkeepsie, NY: Noise Control Foundation. Pp. 559–564.
• Ridgley CD, Wilkins JR. 1991. A comparison of median hearing thresholds from U.S. Navy and U.S. Army audiometric data bases. Military Medicine 156(7):343–345.
• Robertson RM, Williams CE. 1984. Development of a Navy Hearing Conservation Management Information System (HECMIS). Pensacola, FL: Naval Aerospace Medical Research Laboratory.
• U.S. Army Center for Health Promotion and Preventive Medicine. 2005. Hearing Conservation Program Evaluation Profile (HCPEP). [Online]. Available: http://chppm-www.apgea.army.mil/hcp//HCPEP/ [accessed January 28, 2005].
• U.S. Coast Guard. 1982. Recommendations on Control of Excessive Noise (Navigation and Vessel Inspection Circular No. 12-82). Washington, DC: U.S. Coast Guard.

6 REPORTS OF AUDIOMETRIC TESTING IN SERVICE MEDICAL RECORDS OF MILITARY VETERANS

The specific language of the Statement of Task called for records to be “examined for regulatory compliance regarding audiometric surveillance (including reference, periodic, and termination audiograms)”. Service members enrolled in a hearing conservation program are to receive “reference, periodic, and termination” audiograms at the beginning, annually, and at the end of their enrollment in the program. As noted in Chapter 5, only service members who meet certain noise-exposure criteria are placed in a hearing conservation program (see Table 5-1).

As conducted, this study assessed the extent to which audiometric test results were present in the medical records of 3,570 randomly selected service members who had separated from military service during one of five eras spanning the period from World War II to 2002. These records were reviewed, and the dates of all reports of audiometric tests were abstracted. The information on these tests was used to assess the proportion of service members who received audiometric tests at the beginning and the end of their military service. The study was to have included a review of records for Coast Guard personnel, but the Coast Guard did not grant the Institute of Medicine permission to have access to Coast Guard service medical records. Therefore, Coast Guard records were not included in this study.

The study protocol was approved by the Institutional Review Board of the National Academies.

STUDY METHODS

Selection of Study Sample

Individual service medical records were selected for use in the study in the following manner. Random samples of service member identifiers were selected from listings of service members (referred to as rosters) available to the Medical Follow-up Agency (MFUA) of the Institute of Medicine. These rosters span the period from World War II to 2002. Five service eras were defined: 1940 to 1949, 1950 to 1969, 1970 to the year hearing conservation program regulations were implemented, the year hearing conservation program regulations were implemented to 1993, and 1994 to 2002. Lists of service members were generated from the available rosters for each branch of service (Army, Navy, Air Force, Marine Corps) and for each of the five service eras used. Records were assigned to one of the five service eras based on the service member’s date of separation from service (release from active duty).

Box 6-1 describes the sampling frames for service eras. No single comprehensive list exists of persons who served in the Armed Forces during the period from World War II to 2002, or of service members for whom a service medical record is available. Several different representative listings of service members were used to span this time period. The MFUA’s World War II database (Roster #500) is derived from 1 percent or 2 percent samples of National Service Life Insurance policyholders. This insurance program for service members and veterans issued roughly 22 million policies from October 1940 through April 1951, and most of the participants served during World War II. Because Roster #500 differs from the other listings in that it is not based on year of separation from military service, the potential existed for persons selected from this roster to also be selected from one of the other listings. The records selected from Roster #500 were reviewed to identify any duplication, and none was found. Where available, entrance and separation dates for service members identified through this roster were ascertained using dates provided through the Beneficiary Identification and Records Locator Subsystem (BIRLS).

Sample-size targets were set at 100 records for each service and era prior to 1970, and 200 records for each service and era after 1970. These targets were established based on a priori estimates of the percentages of files with audiograms and the degree of confidence sought in those numbers. On the basis of MFUA experience in obtaining service medical records, rosters were oversampled for each service branch–service era category to take into account files that were missing or otherwise unavailable. To reach the overall target of 3,200 records, 6,218 records were requested. When the desired sample size for a branch of service and service era had been met or exceeded, record review for that time period was discontinued and any remaining files were returned without review.

Record Access and Data Abstraction

It was possible for the service medical records that were sought for the study to be located at the National Personnel Records Center (NPRC) in St. Louis, Missouri, the VA Regional Management Center in St. Louis, or VA regional offices across the country. Lists of service members selected for the study were matched against VA’s Beneficiary Identification and Records Locator Subsystem (BIRLS) to ascertain the location of the records. Records were requested from the appropriate source. Records held by VA regional offices were mailed to the National Research Council office at the VA Regional Office in Washington, D.C., where they were abstracted under the supervision of MFUA staff. Records stored in St. Louis, at either the VA Regional Management Center or NPRC, were abstracted on-site under the supervision of MFUA staff.

Table 6-1 shows the number of service medical records reviewed and abstracted. Table 6-2 shows the percentages of service medical records with reports containing any numeric data from an audiogram.

This analysis used a time window of ±60 days around entry and separation dates to determine the percentage of service medical records in which these audiometric records were present. Appendix E provides tables identical to Tables 6-3 through 6-5, but using the larger (±120-day) time window.

It should be noted that this analysis did not evaluate the extent to which the services obtained reference or termination audiograms for personnel entering and leaving hearing conservation programs. The reasons for not focusing exclusively on those personnel in hearing conservation programs were noted previously. The following findings are based on the data in Tables 6-2 through 6-5, each of which makes use of a ±60-day time window. Although the specific percentages cited in some of the findings are dependent upon the time window used in the analysis, the general features of the data are the same for time windows of ±60 days (Tables 6-3 through 6-5) or ±120 days (Appendix E).

7 CONCLUSIONS AND COMMENTS

In this chapter the committee draws on the evidence it has reviewed to respond more directly to the specific points in its charge. The chapter also discusses potential opportunities identified by the committee to improve the effectiveness of the military services’ hearing conservation programs designed to prevent noise-induced hearing loss and tinnitus. Finally, research needs and opportunities suggested by the committee’s review are described. They cover the science of noise and hearing loss and tinnitus, as well as the protection of hearing and the course of hearing loss and tinnitus among military personnel.

RESPONDING TO THE ELEMENTS OF THE CHARGE

1. What sources of potentially damaging noise have been present in military settings since the beginning of World War II? Many sources of potentially damaging noise have long existed in military settings. For the period addressed by this report—World War II to the present—some of these sources include weapons systems (e.g., hand guns, rifles, artillery pieces, rockets), wheeled and tracked vehicles, fixed- and rotary-wing aircraft, ships, and communications devices (Chapter 3). Service members may encounter these noise sources through training, standard military operations, and combat. Exposure to combat-related noise may be unpredictable in onset and duration. In addition, service members may be exposed to hazardous noise through activities that are not unique to the military environment, including various engineering, industrial, construction, or maintenance tasks.

4. Enforce, and establish where they do not presently exist, requirements for audiograms at the completion of military service to ensure that any hearing loss or tinnitus arising during military service is adequately documented. The Department of Defense and the Department of Veterans Affairs should explore whether resources are available within the VA system to aid the military services in conducting audiometric tests and tinnitus assessments for personnel completing their military service.

8. Develop mechanisms to provide VA personnel access to records from DOEHRS-HC for review of disability claims for hearing loss or tinnitus that are not otherwise supported by audiometric records in the service medical record.

RESEARCH NEEDS SUGGESTED BY THE REPORT

The committee also saw areas where further research would be valuable for improving understanding of broad scientific questions concerning the relationship between noise exposure and hearing loss and tinnitus. Research could also address more targeted questions concerning noise exposure, hearing loss, tinnitus, and hearing conservation measures related to military service.

APPENDIXES

A Legislative Language from P.L. 107-330

(b) FLAG TO DRAPE CASKET.—Section 2301 is amended— (1) by redesignating subsection (g) as subsection (h); and (2) by inserting after subsection (f) the following new subsection (g): ‘‘(g) A flag may not be furnished under this section in the case of a person described in section 2411(b) of this title.’’ (c) HEADSTONE OR MARKER FOR GRAVE.—Section 2306 is amended by adding at the end the following new subsection: ‘‘(g)(1) A headstone or marker may not be furnished under subsection (a) for the unmarked grave of a person described in section 2411(b) of this title.

References

• Berger EH, Royster LH, Royster JD, Driscoll DP, Layne M, eds. 2000. The Noise Manual. 5th ed. Fairfax, VA: American Industrial Hygiene Association.
• Last JM. 1995. A Dictionary of Epidemiology. New York: Oxford University Press.

Appendix D Summary Tables on Epidemiological Studies

Appendix E Results from Alternative Analyses of Data on Reports of Audiometric Testing in Service Medical Records

Chapter 6 reports the results of a review of service medical records to assess the availability of audiometric test records dating from a service member’s entry into and separation from military service. The analysis reported in Chapter 6 used a ±60-day window around entry and separation dates to determine the percentage of service medical records in which these audiometric records were present. To assess the effect of the ±60-day window, an alternative analysis was conducted using a ±120-day window. The results of that alternative analysis are shown below.

Appendix F Selected Sources of Information on Sound Pressure Levels Measured in and Around Military Systems and Equipment

• 8. Garinther GR, Kalb JT. 1983. An Acoustical Assessment of the Impulse Noise of Grenade Simulators Exploding in Enclosures. Aberdeen Proving Ground, MD: Human Engineering Laboratory.
• 9. Gasaway DC. 1964. Characteristics of noise associated with the operation of military aircraft. Aerospace Medicine 35:327–336.
• 10. Gasaway DC. 1975. A-Weighted Sound Levels in Cockpits of Fixed- and Rotary-Wing Aircraft. Brooks Air Force Base, TX: School of Aerospace Medicine.
• 11. Gasaway DC. 1976. Noise Levels Measured within Aircraft during Takeoff, Climb, and Cruise (Low, Normal, and High). Brooks Air Force Base, TX: School of Aerospace Medicine.
• 12. Gasaway DC. 1986. Noise levels in cockpits of aircraft during normal cruise and considerations of auditory risk. Aviation, Space, and Environmental Medicine 57(2):103–112.
• 13. Gasaway DC. 2002. Donald C. Gasaway’s Aircraft Noise Compendia. Brooks City-Base, TX: U.S. Air Force.
• 14. Gasaway DC, Hatfield JL. 1963. A Survey of Internal and External Noise Environments in US Army Aircraft. USAARU Report No. 64-1. Fort Rucker, AL: U.S. Army Aeromedical Research Unit.
• 21. Hille HK. 1979. USAF Bioenvironmental Noise Data Handbook—Volume 127 F-15A In-Flight Crew Noise. Wright-Patterson Air Force Base, OH: Aerospace Medical Research Laboratory.
• 22. Jones CM. 1983. C-9A Interior Noise Evaluation. Brooks Air Force Base, TX: Air Force Occupational and Environmental Health Laboratory.
• 23. Karta Technologies, Inc. 1999. Lead-Free Small Arms Ammunition Study. IERA-RS-BR-SR-2000-0001. San Antonio, TX: Air Force Institute for Environment, Safety and Occupational Health Risk Analysis.
• 24. Kugler AB, Hale ME, Rentz PE. 1977. Occupational Noise Exposure on FF 1052 (KNOX) and DD 963 (SPRUANCE) Class Ships. Canoga Park, CA: Bolt Beranek and Newman, Inc.
• 25. Lambert DR. 1980. Airborne Noise Levels on U.S. Navy Ships. NOSC TD 317. San Diego, CA: Naval Ocean Systems Center.
• 26. Lambert DR. 1981. Setting Airborne Noise Limits for Navy Shipboard Compartments: Considerations Based on Data from Existing Ships. NOSC TR 712. San Diego, CA: Naval Ocean Systems Center.
• 27. Luz GA. 1983. Data Base for Assessing the Annoyance of the Noise of Small Arms. Technical Guide TG-135. Aberdeen Proving Ground, MD: U.S. Army Environmental Hygiene Agency.
• 28. Magliozzi B, Metzger FB, Bausch W, King RJ. 1975. A Comprehensive Review of Helicopter Noise Literature. Washington, DC: Federal Aviation Administration.
• 29. McBryan JC, Schomer PD. 1976. Noise in Dishwashing Rooms. Champaign, IL: Construction Engineering Research Laboratory.
• 30. Mozo BT, Gordon E. 1994. The Assessment of the AH-64D, Longbow, Mast-Mounted Assembly Noise Hazard for Maintenance Personnel. USAARL Report No. 94-37. Fort Rucker, AL: U.S. Army Aeromedical Research Laboratory.
• 31. Newman JS, Rickley EJ. 1979. Noise Levels and Flight Profiles of Eight Helicopters Using Proposed International Certification Procedures. Report No. FAA-EE-79-03. Washington, DC: U.S. Department of Transportation.
• 34. Powell RG, Rose JF. 1977. USAF Bioenvironmental Noise Data Handbook: C130E Aircraft, Near and Far-field Noise. Wright-Patterson Air Force Base, OH: Aerospace Medical Research Laboratory.
• 35. Ribera JE, Mozo BT, Mason KT, Murphy BA. 1995. Communication and Noise Hazard Survey of CH-47D Crewmembers. Fort Rucker, AL: U.S. Army Aeromedical Research Laboratory. [Related publication: Ribera JE, Mozo BT, Mason KT, Murphy BA. 1996. Communication survey of CH-47D crewmembers. Military Medicine 161(7):387–391.].
• 36. Rickley EJ, Jones KE, Keller AS, Fleming GG. 1993. Noise Measurement Flight Test of Five Light Helicopters. Cambridge, MA: John A. Volpe National Transportation Systems Center.
• 37. Rose JF. 1969. Measurement and Analysis of Bioacoustic Environments Aboard AC-119G and AC-130A Gunships. AMRL-TR-68-176. Wright-Patterson Air Force Base, OH: Aerospace Medical Research Laboratory.
• 38. Schomer PD, Averbuch A, Raspet R. 1982. Operational Noise Data for UH-60A and CH-47C Army Helicopters. Champaign, IL: U.S. Army Construction Engineering Research Laboratory.
• 45. True HC, Letty RM. 1977. Helicopter Noise Measurements Data Report. Washington, DC: U.S. Department of Transportation.
• 47. Webster JC. 1981. Noise Levels on Aircraft Carrier Flight Decks, and Their Effects. NELC 1762. San Diego, CA: Naval Electronics Laboratory Center.

Appendix H Biographical Sketches of Committee Members

Karen J. Cruickshanks, Ph.D., is a professor in the Department of Ophthalmology and Visual Sciences as well as in the Department of Population Health Sciences at the University of Wisconsin School of Medicine. Her research interests are in the epidemiology of age-related sensory disorders, diabetes and its complications, and aging. She has written more than 100 articles on these topics and is the principal investigator for two major studies of the epidemiology of age-related hearing loss. Dr. Cruickshanks serves as frequent advisor or reviewer for the National Institute on Deafness and Other Communication Disorders and as a reviewer for a variety of journals, including the American Journal of Epidemiology, the American Journal of Public Health, Ear and Hearing, and the New England Journal of Medicine. She is a member of the Society for Epidemiological Research and the American Epidemiological Society. Dr. Cruickshanks received her Ph.D. in epidemiology from the University of Pittsburgh.

Josef M. Miller, Ph.D., is a professor of otolaryngology, adjunct professor of bioengineering, and director of the Kresge Hearing Research Institute at the University of Michigan Health System, Ann Arbor. His research focuses on inner ear physiology and pathophysiology and the development of treatments for sensorineural hearing loss and tinnitus. He is principal investigator of the Michigan Center for Human Therapeutics for Age-Related Hearing Loss (Presbycusis) at MUSC, which is funded by the National Institute on Deafness and Other Communication Disorders. He is a former chair of the National Research Council Committee on Hearing, Bioacoustics, and Biomechanics (CHABA) and also served on its Working Group on Hazardous Exposure to Impulse Noise. He is a fellow of the American Speech-Language-Hearing Association and the Acoustical Society of America and a scientific fellow of the American Academy of Otolaryngology–Head and Neck Surgery. Dr. Miller holds a Ph.D. in audiology from the University of Iowa.