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Variability in background risk and distribution of various risk factors for hearing loss may explain some of the diversity in excess risk of noise-induced hearing loss (NIHL). This paper examines the impact of various risk factors on excess risk estimates of NIHL using data from the 1968-1972 NIOSH Occupational Noise and Hearing Survey (ONHS). Previous analyses of a subset of these data focused on 1172 highly "screened" workers. In the current analysis, an additional 894 white males (609 noise-exposed and 285 controls), who were excluded for various reasons (i.e., nonoccupational noise exposure, otologic or medical conditions affecting hearing, prior occupational noise exposure) have been added 2066) to assess excess risk of noise-induced material impairment in an unscreened population. Data are analyzed by age, duration of exposure, and sound level (8-h TWA) for four different definitions of noise-induced hearing impairment, defined as the binaural pure-tone average (PTA) hearing threshold level greater than 25 dB for the following frequencies: (a) 1-4 kHz (PTA1234), (b) 1-3 kHz (PTA123), (c) 0.5, 1, and 2 kHz (PTA512), and (d) 3, 4, and 6 kHz (PTA346). Results indicate that populations with higher background risks of hearing loss may show lower excess risks attributable to noise relative to highly screened populations. Estimates of lifetime excess risk of hearing impairment were found to be significantly different between screened and unscreened population for noise levels greater than 90 dBA. Predicted age-related risk of material hearing impairment in the ONHS unscreened population was similar to that predicted from Annex B and C of ANSI S3.44 for ages less than 60 years. Results underscore the importance of understanding differential risk patterns for hearing loss and the use of appropriate reference (control) populations when evaluating risk of noise-induced hearing impairment among contemporary industrial populations.

Concern is raised by Dobie [J. Acoust. Soc. Am. 103, 2734 (1998)] regarding a recent analysis [, J. Acoust. Soc. Am. 101, 950–963 (1997)] of the NIOSH Occupational Noise and Hearing Survey data. Specifically, issues are raised concerning (1) definition of hearing handicap, (2) the use of frequency-specific articulation index (AI) weights applied to the binaural pure-tone average of 1, 2, 3, and 4 kHz, and (3) conclusions regarding significant excess risk based on this definition. We have reviewed the development of the definitions of hearing handicap and provide additional support for the use of a hearing handicap definition based on the binaural pure-tone average of 1, 2, 3, and 4 kHz and the weighting of specific frequencies. Furthermore, our definition of noise-induced hearing handicap is similar to one of several proposed by the International Standards Organization (Reference 1999Reference 1990) and the American National Standards Institute (Reference 3Reference 44Reference 1996). Additional analyses show that there is significant evidence of excess risk at daily exposure levels below 85 dB using any of the pure-tone average and/or weighting strategies we have examined. Hence we have provided additional support for our conclusions regarding exposure-response curves and we have reaffirmed that our methods are appropriate for the scope of our analysis.

This paper presents an analysis of hearing threshold levels among 2066 white male workers employed in various U.S. industries studied in the 1968–72 NIOSH Occupational Noise and Hearing Survey (ONHS). The distribution of hearing threshold levels (HTL) is examined in relation to various risk factors (age, prior occupational noise, medical conditions) for hearing loss among a population of noise exposed and control (low noise-exposed) industrial workers. Previous analyses of a subset of these data from the ONHS focused on 1172 highly “screened” workers. An additional 894 male workers (609 noise-exposed and 285 controls), who were excluded for various reasons (i.e., nonoccupational noise exposure, otologic or medical conditions affecting hearing, prior occupational noise exposure) have been added to examine hearing loss in an unscreened population. Data are analyzed by age, duration of exposure, and sound level (8-h TWA) by individual test frequency. Results indicate that hearing threshold levels are higher among unscreened noise-exposed and control workers relative to screened workers. Analysis of risk factors such as nonoccupational noise exposure, medical conditions, and type of industry among unscreened controls indicated that these factors were not significantly associated with increased mean HTLs or risk of material impairment over and above what is expected due to age. Age-specific mean hearing threshold levels (and percentiles of the distribution) among the unscreened ONHS control population may be used as a comparison population of low-noise exposed white male industrial workers for evaluating the effectiveness of hearing conservation programs for workers less than 55 years of age. To make valid inferences regarding occupational noise-induced hearing loss, it is important to use hearing data from reference (control) populations that are similar with respect to the degree of subject screening, type of work force (blue vs white collar), and the distribution of other risk factors for hearing loss.

Studies indicate that the statistical properties and temporal structure of the sound signal are important in determining the extent of hearing hazard. As part of a pilot study to examine hearing conservation program effectiveness, NIOSH collected noise samples of impact noise sources in an automobile stamping plant, focusing on jobs with peak sound levels (Lpk) of greater than 120 dB. Digital tape recordings of sounds were collected using a Type I Precision Sound Level Meter and microphone connected to a DAT tape recorder. The events were archived and processed as .wav files to extract single events of interest on CD‐R media and CD audio media. A preliminary analysis of sample wavelet files was conducted to characterize each event using metrics such as the number of impulses per unit time, the repetition rate or temporal pattern of these impulses, index of peakedness, crest factor, kurtosis, coefficient of kurtosis, rise time, fall time, and peak time. The spectrum, duration, and inverse of duration for e...

This paper reviews the ISO‐1999 and ANSI S3.44 standards and the literature related to prediction of noise‐induced hearing loss (NIHL) in humans. The dearth of contemporary population‐based studies of hearing loss among industrial, low noise‐exposed individuals have made the ISO‐1999 and ANSI S3.44 standards a key source of comparative data for assessing the risk of NIHL. This paper will highlight how these standards have been used in several published papers to examine the magnitude of NIHL risk, predictions of noise‐induced thresholds in hearing conservation data, and to generate hypotheses regarding the biologic plausibility of hearing loss due to chemicals or other ototoxic agents.

Noise‐induced hearing loss (NIHL) has been recognized as a serious health concern for decades. ISO Standard 1999:1990 provides a means to predict noise‐induced hearing loss (NIHL) based on LAeq measurements in the working environments of workers. This standard seems to work well for predicting hearing loss in continuous noise fields. However, it is possible that ISO 1999 does not apply well to impact, impulsive, or other transient noise fields. NIOSH and University of Pittsburgh are currently developing noise‐sampling strategies to measure impact and impulse noise in a manufacturing environment with the aim of developing new impulsive noise metrics. As part of the study, broadband impact/impulse pressure measurements will be made. Issues such as instrumentation, data quality, repeatability, spatial sampling, equipment portability, and calibration are addressed. Also, the annotation, digitization, and editing of the waveforms will be discussed. As part of the project, an archival database of manufacturing ...

As part of a NIOSH study examining factors affecting hearing conservation program (HCP) effectiveness, a job‐noise exposure matrix was constructed using these data sources: (1) task‐based sound level survey data; (2) noise exposure data (dosimetry and sound level surveys) provided from plant historical reports; (3) information on process changes and engineering controls; (4) interviews with plant personnel (in engineering and safety departments); and (5) detailed work history data from personnel records for each employee in the plant HCP. For plants in which changes in exposures have occurred due to engineering control and process changes, exposure estimation becomes a challenge when there are data gaps in exposure and process changes. This paper discusses how data from structured employee interviews can be used in conjunction with available quantitative, records‐based data to reconstruct processes and machinery/layout history. The goal was to characterize how noise exposure determinants (manufacturing environment, equipment, processes, shift lengths) have changed and to estimate exposure by department, job, and era. The first step was to identify employees for interview whose jobs were located in departments where exposure data were sparse or nonexistent. Data collection efforts were then geared towards reconstructing noise exposure for specific departments and jobs over time.

NIOSH recommends that hearing loss prevention programs (HLPPs) be implemented for all workers whose unprotected 8‐h TWA exposures equal or exceed 85 dB and that the programs include at least the following components: (1) initial and annual audits of procedures, (2) noise exposure assessment, (3) engineering and administrative control of noise exposures, (4) audiometric surveillance and evaluation, (5) use of hearing protectors (for exposures >85 dB, regardless of duration), (6) education and motivation, (7) recordkeeping, and (8) program evaluation. All components except program evaluation and routine in‐hour audits are generally discussed in the Occupational Safety and Health Administration (OSHA) Hearing Conservation Amendment (HCA). This paper presents research approaches for systematically evaluating OSHA‐mandated hearing conservation programs. The intent of such research is to (a) develop methods for evaluating hearing conservation programs that can be used across several industrial sectors and (b) identify ways in which ‘‘hearing conservation’’ can effectively become ‘‘hearing prevention’’ programs. General approaches are presented for each program element and data collection issues are discussed with specific examples of how various methods can been used for program evaluation. The goal of such research strategies is to identify the best predictors of program effectiveness.

Analyses of data from the NIOSH Occupational Noise and Hearing Survey (OHNS) have previously focused on 1172 highly ‘‘screened’’ workers. This paper examines excess risk estimates for an additional 894 male workers (609 noise exposed and 285 controls) who were excluded for various reasons (i.e., nonoccupational noise exposure, otologic or medical conditions affecting hearing, prior occupational noise exposure). Data are analyzed by age, duration of exposure, and sound level (8‐h TWA) for different definitions of noise‐induced hearing impairment. Hearing impairment was defined as a binaural average hearing threshold level greater than 25 dB at selected frequencies (1–4 kHz, 1–3 kHz, and 0.5, 1, and 2 kHz). The analysis suggests that excess risk estimates are sensitive to population characteristics as well as definition of impairment. Lifetime excess risk estimates for noise‐induced hearing impairment are similar for the unscreened and screened populations for 8‐h TWAs below 85 dB. However, compared to the unscreened population, higher excess risk estimates are observed for the screened population at A‐weighted levels greater than 85 dB. This difference in excess risk was most marked for hearing‐impairment definitions that include 3 and 4 kHz.

Several hearing conservation programs (n=15) from a cross‐section of U.S. industries were examined to test whether there are greater rates of change in hearing levels in relation to increasing cumulative noise exposure during the period of audiometric follow‐up. The analysis also examined whether rates of hearing loss were lower among workers who wear hearing protection relative to workers who do not. These 15 audiometric databases had a total of 15 794 workers with 62 095 audiograms. Differences in a linear combination of 1–4 kHz biaural hearing levels of consecutive audiometric tests were examined using mixed effects models to account for correlated, repeated observations on individuals. These differences were modeled as a function of cumulative noise, gender, race, hearing protection use, age, learning effects, and baseline hearing level (measured after 14 h of quiet time). Analyses were conducted for the combined and individual databases. The analysis indicates there is significant heterogeneity among...

Occupational hearing conservation programs (HCPs) have been implemented in many industries in accordance with the 1983 OSHA hearing conservation amendment. The availability of these longitudinal databases permits an examination of associations between changes in hearing levels with other variables, including noise exposure. This paper examined (1) whether there is an increased risk of NIHL from exposures below 85 dBA; (2) whether workers with noise exposures above 85 dBA who are required to use hearing protection still have an increased risk of NIHL compared to low‐noise‐exposed (less than 70 dBA) workers; and (3) how risk may depend on the type of hearing protection used and reported degree of compliance. The data used in this analysis include most of the data analyzed by the ANSI working group to examine hearing conservation program effectiveness. Variables included age, sex, race, type of hearing protection, industry code, and hearing threshold levels (for both ears, tested at 0.5, 1, 2, 3, and 6 kHz). Databases for comparison included both internal and external ‘‘control’’ groups with low‐noise exposure, as well as noise‐exposed populations in which either the hearing conservation program was highly effective and/or the population was well protected via good hearing protection compliance.