Comparison of NIOSH noise criteria and OSHA hearing conservation criteria

BACKGROUND: This study was conducted to compare noise exposure measurements based on the recently revised noise exposure criteria recommended by the U.S. National Institute for Occupational Safety and Health (NIOSH) and the current U.S. Occupational Safety and Health Administration (OSHA) Hearing Conservation Amendment to the occupational noise standard. METHODS: Daily 8-hour time-weighted average (TWA) personal noise exposures were obtained for 61 workers using dosimeters set simultaneously to the NIOSH and OSHA Hearing Conservation Amendment (OSHA-HCA) criteria. A variety of work groups with the potential for noise exposure were evaluated as a part of this investigation. RESULTS: Noise dose based on the NIOSH criteria was higher than the corresponding OSHA-HCA noise dose with differences in noise exposures measured under the two criteria equal to 6.6 dBA. Should the new NIOSH recommendation on noise measurement be adopted as standard, the number of workers to be enrolled in a hearing loss prevention program was estimated to increase by 2. 7-fold from 23% to 75% of the study population. CONCLUSIONS: The results of this study indicate that if the NIOSH criteria are to be adopted as an OSHA standard, there is likely to be a substantial increase in the number of workers in hearing conservation programs.     

Surveillance of hearing loss among older construction and trade workers at Department of Energy nuclear sites

BACKGROUND: Medical screening programs at three Departments of Energy (DOE) nuclear weapons facilities (Hanford Nuclear Reservation, Oak Ridge, and the Savannah River Site) have included audiometric testing since approximately 1996. This report summarizes hearing evaluations through March 31, 2003. METHODS: Occupational examinations included a medical history, limited physical examination, and tests for medical effects from specific hazards, including audiometric testing. Hearing thresholds by frequency for DOE workers were compared to age-standardized thresholds among an external comparison population of industrial workers with noise exposures <80 dBA. Multivariate analyses were used to explore the risk of hearing impairment by duration of construction trade work and self-reported noise exposure, while controlling for potential confounders such as age, race, sex, smoking, elevated serum cholesterol, hypertension, solvent exposures, and recreational noise exposures. RESULTS: Hearing thresholds among DOE workers were much higher than observed in a comparison population of industrial workers with low noise exposures. Overall, 59.7% of workers examined were found to have material hearing impairment by NIOSH criteria. Age, duration of construction work, smoking, and self-reported noise exposure increased the risk of hearing loss. The risk of material hearing impairment was significantly elevated for construction trade workers compared to the external comparison population (odds-ratio = 1.6, 95% CI = 1.3-2.1) and increased with the duration of trade work. CONCLUSIONS: These medical screening programs confirm worker concerns about risks for hearing loss and the need for hearing conservation programs for construction workers, with emphasis on the prevention of noise exposures.     

Noise exposure and hearing conservation in U.S. coal mines--a surveillance report

This study examines the patterns and trends in noise exposure documented in data collected by Mine Safety and Health Administration inspectors at U.S. coal mines from 1987 through 2004. During this period, MSHA issued a new regulation on occupational noise exposure that changed the regulatory requirements and enforcement policies. The data were examined to identify potential impacts from these changes. The overall annual median noise dose declined 67% for surface coal mining and 24% for underground coal mining, and the reduction in each group accelerated after promulgation of the new noise rule. However, not all mining occupations experienced a decrease. The exposure reduction was accompanied by an increase of shift length as represented by dosimeter sample duration. For coal miners exposed above the permissible exposure level, use of hearing protection devices increased from 61% to 89% during this period. Participation of miners exposed at or above the action level in hearing conservation programs rapidly reached 86% following the effective date of the noise rule. Based on inspection data, the occupational noise regulation appears to be having a strong positive impact on hearing conservation by reducing exposures and increasing the use of hearing protection devices and medical surveillance. However, the increase in shift duration and resulting reduction in recovery time may mitigate the gains somewhat.     

An assessment of occupational noise exposures in four construction trades

Three hundred thirty-eight noise exposure samples were collected from 133 construction workers employed in 4 construction trades: carpenters, laborers, ironworkers, and operating engineers. Four sites using a variety of construction techniques were sampled at least 12 times on a randomly chosen date over a 22-week period. Up to 10 volunteer workers were sampled for an entire work shift on each sampling day using datalogging noise dosimeters, which recorded both daily time-weighted averages (TWAs) and 1-min averages. Workers also completed a questionnaire throughout the workday detailing the tasks performed and tools used throughout the day. Regression models identified work characteristics associated with elevated exposure levels. Comparisons were made between exposures measured using the Occupational Safety and Health Administration (OSHA) exposure metric and the 1996 draft National Institute for Occupational Safety and Health/International Organization for Standardization (NIOSH/ISO) metric to examine the effects of differing exchange rates and instrument response times on construction noise exposures. The mean OSHA TWA for 338 samples was 82.8 dBA +/- 6.8 dBA, whereas the mean NIOSH/ISO TWA for 174 samples was 89.7 dBA +/- 6.0 dBA. Forty percent of OSHA TWAs exceeded 85 dBA, and 13% exceeded 90 dBA, the OSHA permissible exposure limit. The tasks and tools associated with the highest exposure levels were those involving pneumatically operated tools and heavy equipment. Trade was a poor predictor of noise exposure; construction method, stage of construction, and work tasks and tools used were found to be better exposure predictors. An internal validation substudy indicated excellent agreement between worker self-reporting and researcher observation. These data provide substantial documentation that construction workers in several key trades are frequently exposed to noise levels that have been associated with hearing loss, and demonstrate the need for targeted noise reduction efforts and comprehensive hearing conservation programs in the industry.     

Does health promotion work in relation to noise?

Noise is a health risk. The only scientifically established adverse health effect of noise is noise-induced hearing loss (NIHL). Besides noise may affect quality of life and cause annoyance and sleep disturbance. The present scientific evidence of potential non-auditory effects of noise on health is quite weak. Whether health promotion works in relation to noise may be reflected by permanent hearing threshold shift development in population studies. Hearing impairment continues to be the most prevalent disability in Western societies. The National Institute of Occupational Safety and Health (NIOSH) still rates noise induced hearing loss among the top ten work-related problems. Recent studies report that employees continue to develop noise induced hearing loss although to a lesser extent than before, in spite of occupational hearing conservation programmes. Besides socio-acusis and leisure noise seem to be an increasing hazard to hearing, also in young children and adolescents. This seems partly related to acute leisure noise exposure (e.g. toy pistols, amplified music). However, population studies increasingly find non-normal high-frequency hearing including the characteristic NIHL-"notch" around 6 kHz also in subjects who do not report noise exposure incidents or activities. Today 12.5% of US children 6-19 years show a noise-"notch" in one or both ears (n= 5249, Niskar et al 2001). A Norwegian county audiometry survey on adults >/= 20 years n=51.975) showed mean unscreened thresholds +10 dB at 6 kHz for both genders even or the youngest age group 20-24 years (Borchgrevink et al 2001). Accordingly, the present health promotion initiatives seem insufficient in relation to noise and noise-induced hearing loss.     

Occupational noise exposure and hearing loss of workers in two plants in eastern Saudi Arabia.

OBJECTIVE: To determine the prevalence of hearing loss associated with occupational noise exposure and other risk factors. DESIGN: A cross-sectional study involving 269 exposed and 99 non-exposed subjects (non-industrial noise exposed subjects) randomly selected. Current noise exposure was estimated using both sound level meter and noise-dosimeter. Past noise exposure was estimated by interview questionnaire. Otoscopic examination and conventional frequency (0.25-8 kHz) audiometry were used to assess the hearing loss in each subject. RESULTS: 75% (202 subjects) from the exposed group were exposed to a daily Leq above the permissible level of 85 dB(A) and most (61%) of these did not and had never used any form of hearing protection. Hearing loss was found to be bilateral and symmetrical in both groups. Bivariate analysis showed a significant hearing loss in the exposed vs non-exposed subjects with a characteristic dip at 4 kHz. Thirty eight percent of exposed subjects had hearing impairment, which was an 8-fold higher rate than that found for non-exposed subjects. Multivariate analysis indicated exposure to noise was the primary, and age the secondary predictor of hearing loss. Odds of hearing impairment were lower for a small sub-group of exposed workers using hearing protection (N=19) in which logistic regression analysis showed the probability of workers adopting hearing protective devices increased with noise exposure, education, and awareness of noise control. Hearing loss was also greater amongst those who used headphones to listen to recorded cassettes. CONCLUSION: Gross occupational exposure to noise has been demonstrated to cause hearing loss and the authors believe that occupational hearing loss in Saudi Arabia is a widespread problem. Strategies of noise assessment and control are introduced which may help improve the work environment.     

Occupational hearing loss

Hearing loss is a significant and unfortunately common occupational malady. Over the past several decades both the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have initiated efforts to better understand and to limit the occurrence of occupational hearing loss, particularly as it relates to excessive noise exposure. This paper briefly addresses the pathophysiology of noise-induced hearing loss and then describes the occupational and non-occupational factors which influence a worker's risk of hearing loss. The primary foci of this discussion are the clinical evaluation, diagnosis, and management of occupational hearing loss. Issues of prevention, OSHA-mandated hearing conservation efforts and compensation are reviewed.     

Noise exposure assessment among groundskeepers in a university setting: A pilot study

Approximately 870,000 U.S. workers are employed as landscaping and groundskeeping workers who perform various tasks and use a variety of tools that expose them to high noise levels, increasing their risk to noise-induced hearing loss (NIHL). Several studies on noise exposure and NIHL in other job sectors have been published, but those on groundskeepers are very limited. This study aims to characterize the noise exposure of groundskeepers. Participants were monitored over their entire work shift for personal noise exposure by wearing noise dosimeters at shoulder level, 4 in from the ear. Using two different dosimeter settings (OSHA and NIOSH), the time-weighted averages (TWAs) and 1-min averages of noise exposure levels in decibels (dBA) were obtained. The participants were also asked to fill out an activity card daily to document their tasks, tools used, location and noise perception. Sound pressure levels (SPLs) produced by various groundskeeping equipment and tools were measured at full throttle near the ear of the operator using a sound level meter. These measurements were used to assess worker noise exposure profiles, particularly the contributing source of noise. The overall mean OSHA and NIOSH TWA noise exposures were 82.2±9.2 (range of 50.9–100 dBA) and 87.8±6.6 dBA (range of 67.2–102.9 dBA), respectively. Approximately 46% of the OSHA TWAs exceeded the OSHA action limit of 85 dBA. About 76% of the NIOSH TWAs exceeded 85 dBA, and 42% exceeded 90 dBA. The SPLs of equipment and tools measured ranged from 75– 106 dBA, most of which were at above 85 dBA and within the 90–100 dBA range. Hand-held power tools and ride-on equipment without enclosed cab may have contributed significantly to worker noise exposure. This study demonstrates that groundskeepers may be routinely exposed to noise levels above the OSHA and NIOSH exposure limits, and that the implementation of effective hearing conservation programs is necessary to reduce their risk to NIHL.     

Occupational Noise Exposures Among Three Farm Families in Northwest Ohio

ABSTRACT

A pilot project was conducted to evaluate occupational noise exposures of three families living and working on farms in Northwest Ohio. Noise exposures were measured continuously for 7 consecutive days for each participant for 1 week each during planting, growing, and harvesting seasons. The dosimeters were programmed to evaluate noise exposures using both the Occupational Safety and Health Administration (OSHA) action level and the National Institute for Occupational Safety and Health (NIOSH)/American Conference of Governmental Industrial Hygienists (ACGIH) guidelines. One family was evaluated per year and a total of nine family members (six adults and three children) participated. Adult noise exposures for on-farm activities (occupational exposures) ranged from 46.1 to 89.6 decibels on the A-weighted scale (dBA) as an 8-hour time-weighted average (8HR TWA) using the OSHA action level and from 62.6 to 92.1 dBA 8HR TWA using the NIOSH/ACGIH guidelines. Occupational noise exposures for the children ranged from 15.4 to 81.2 dBA 8HR TWA using the OSHA action level and from 42.4 to 85.5 dBA 8HR TWA using the NIOSH/ACGIH guidelines. Six of 45 exposures among the adults and none of the 11 exposures among the children exceeded the OSHA action level. In addition, 10 of 45 exposures among the adults and 1 of 11 exposures among the children exceeded the NIOSH/ACGIH guidelines. The results of this pilot project indicate noise exposures among farm families can exceed recommended levels.     

Occupational exposures during routine activities in coal-fueled power plants

Limited information is available on occupational exposures during routine, nonoutage work activities in coal-fueled power plants. This study evaluated occupational exposures to the principal contaminants in the facilities, including respirable dust (coal dust), arsenic, noise, asbestos, and heat stress. The data were collected over a 3-month period, during the summer of 2001, in 5 facilities that were chosen to be representative of the coal-fueled power plants of a large southeastern power-generating company. Each of the facilities was divided into 5 similar exposure groups based on previous exposure assessments and job tasks performed. From 4 of the 5 facilities, 392 air samples and 302 noise samples were collected with approximately 50 respirable coal dust, 32 arsenic, 15 asbestos, and 70 noise samples from each of the 4 plants. One of the previously surveyed facilities was also evaluated for heat stress, and 1 additional coal-fueled power plant was surveyed for a total of 20 personal heat stress samples. Personal monitors and area WBGT monitors were used. Of the nearly 400 air samples collected, only 1 exceeded the allowable occupational exposure value. For the noise samples, 55 (approximately 18%) were equal to or greater than the Occupational Safety and Health Administration (OSHA) 8-hour hearing conservation program level of 85 dBA, and 12 (approximately 4%) were equal to or greater than the OSHA 8-hour permissible exposure level of 90 dBA. Heat stress monitoring at the facilities indicates that 26% of the 1-hour TWAs were exceeded for one or all of the recommended heat stress limits. The data also concluded that some work sites were above the heat stress ceiling values recommended by the National Institute for Occupational Safety and Health (NIOSH). Four of the 20 employees personally monitored exceeded the recommended limits for heart rate or body core temperature. This suggests there is a potential for heat strain if signs and symptoms are ignored. Recommendations are made to better control the heat stress exposure.     

Respirable silica and noise exposures among stone processing workers in northern Thailand

Silica and noise are highly prevalent occupational exposures in the stone processing industry. Monitoring for silica and noise are expensive tasks that may be especially difficult to perform in low-resource settings, but exposure awareness is vital for protecting worker health. This study evaluated personal noise and silica measurements at a stone processing facility in northern Thailand to investigate the differing exposure potentials and risk for overexposure among the varying job categories. Our research team performed repeated personal noise and respirable silica measurements on 46 workers, over three separate workshifts for each of 46 workers. While 36.2% of noise measurements exceeded the recommended exposure limit of 85 dBA, only three silica measurements (2.4%) were above the threshold limit value (TLV) of 25 µg/m³. Self-reported personal protective equipment use was low, with only 27.5% of participants wearing hearing protection in noisy environments during their monitored shift and 29.7% of workers wearing respiratory protection during dusty portions of their shift. We identified a significant positive correlation between measured noise and silica levels (r = 0.54, p < 0.01), with stone loaders having the highest average noise (mean = 89 dBA, standard deviation = 4.9 dBA) and silica (geometric mean = 6.4 µg/m³, geometric standard deviation = 1.8) exposure levels. In a multivariate model, the stone loader job category was a significant predictor of exposure to detectable levels of respirable silica (p < 0.01). These results provide useful guidance regarding the need for noise and silica exposure interventions in order to reduce incidences of workplace disease in the stone processing industry.     

Hearing loss among workers exposed to moderate concentrations of solvents.

OBJECTIVES: It is known that some industrial organic solvents are ototoxic. This study was aimed at evaluating the hearing effects of a mixture of organic solvents alone or in combination with noise on employees in paint and lacquer enterprises. The concentration of solvents was below the occupational exposure limits (OEL) for most of the subjects. METHODS: Altogether 517 subjects were divided into the following three groups: persons with no risk due to noise or organic solvent exposure at the workplace, workers exposed to organic solvents only, and workers exposed to both organic solvents and noise. RESULTS: The relative risk (RR) of hearing loss in the solvent-only exposure group was significantly increased (RR 4.4 and RR 2.8 for noise exposure of < 80 dB-A and < 85 dB-A, respectively) in a wide range of frequencies (2-8 kHz). No additional risk in the solvent + noise exposure group was found (RR 2.8). Hearing thresholds were significantly poorer in a wide range of frequencies (1-8 kHz) for both groups exposed to solvents, when compared with the reference group. The mean hearing thresholds at frequencies of 2-4 kHz were poorer for workers exposed to solvents + noise than for the solvent-only group; this finding suggests an additional effect for noise. However, there was no correlation between hearing loss and the extent of solvent exposure. CONCLUSIONS: The results indicate that occupational organic solvent exposure at moderate concentrations increases the risk of hearing loss, and the ototoxic effects should be considered when the health effects of exposed workers are monitored.     

Assessment of respiratory exposures during gilsonite mining and milling operations

An industrial hygiene study of the entire United States gilsonite industry was done by the National Institute for Occupational Safety and Health (NIOSH) to evaluate the potential for occupational health problems resulting from exposures to gilsonite and its constituents. Gilsonite is a solidified hydrocarbon substance mined only in northeastern Utah to Colorado. Industrial hygiene samples were collected at four gilsonite mining companies including nine mines and three mills. Gilsonite workers had no measurable exposures to polynuclear aromatic hydrocarbon (PNA) compounds, asbestos fibers, or hydrogen sulfide gas. Several organic gases/vapors and metals were detected in the airborne samples; but, none exceeded the current exposure standards/health criteria of the Mine Safety and Health Administration (MSHA), the American Conference of Governmental Industrial Hygienists (ACGIH), or NIOSH. Gilsonite workers in some job categories were exposed to high levels of dust, exceeding ACGIH nuisance dust recommendations. These dusts, comprised largely of aliphatic hydrocarbons, had a large aerodynamic size distribution with average mass median aerodynamic diameters (MMAD) above 30 microns.     

Evaluation of individual susceptibility to noise-induced hearing loss in textile workers in China

The authors applied noise exposure and audiometry information collected on 156 Chinese textile workers to develop a method of identifying individuals susceptible to noise-induced hearing loss. They estimated noise-induced hearing threshold shift (NIHTS) by averaging the adjusted hearing thresholds at 3, 4, and 6 kHz of both ears, and they fitted a quadratic model to describe the dose-response relationship between cumulative noise exposure and NIHTS. The residual between the actual NIHTS and the model-predicted NIHTS indicated susceptibility. A comparison of the 20% of the subjects with the greatest residuals (those who were susceptible to hearing loss) with the 20% of the subjects with the smallest residuals (those who were resistant to hearing loss) revealed that the former had poorer hearing, although the noise exposures were similar. The identified susceptible individuals also had the poorest hearing thresholds within each subgroup of homogenous noise exposures. With their model-based procedure, the authors were able to identify individuals susceptible to noise-induced hearing loss from subjects with heterogeneous noise exposures.     

Hearing health of workers exposed to noise and insecticides

OBJECTIVE: To examine the peripheral auditory disorders in a group of workers exposed to organophosphate and pyrethroid insecticides, used in vector control campaigns. METHODS: The prevalence study examined a population of 98 individuals who sprayed insecticides in campaigns for the prevention of Dengue, Chagas disease and Yellow fever. The sampling approach was finalistic, and included the workers in a health district of Pernambuco, during the year 2000. A questionnaire was used to collect data on occupational and non-occupational risks, safety measures utilized, family history of auditory problems and health symptoms. Previous noise exposure history was also investigated, since noise can be a confounding factor for hearing loss. Hearing sensitivity and middle ear function were assessed by pure tone audiometry. RESULTS: Among those exposed to insecticides, 63.8% demonstrated a hearing loss. For the group of workers exposed to both noise and insecticides, hearing loss was observed in 66.7% of the cases. The median exposure time necessary to detect high-frequency losses was 3.4 years for workers exposed to both agents and 7.3 years for workers exposed to insecticides only. Hearing thresholds were poorest among workers exposed to both agents. Auditory damage for those with combined exposures to the two factors was more severe than the hearing losses observed among those exposed only to insecticides. CONCLUSIONS: There is evidence that exposure to insecticides was associated with peripheral sensorioneural hearing loss and that noise exposure can potentiate the ototoxic effects of insecticides. It is necessary to evaluate this possible association through epidemiological studies.     

Assessment of noise exposure for indoor and outdoor firing ranges

The National Institute for Occupational Safety and Health (NIOSH) received an employee request for a health hazard evaluation of a Special Weapons Assault Team (SWAT) in January 2002. The department was concerned about noise exposures and potential hearing damage from weapons training on their indoor and outdoor firing ranges. NIOSH investigators conducted noise sampling with an acoustic mannequin head and 1/4 -inch microphone to characterize the noise exposures that officers might experience during small arms qualification and training when wearing a variety of hearing protection devices provided by the department. The peak sound pressure levels for the various weapons ranged from 156 to 170 decibels (dB SPL), which are greater than the recommended allowable 140 dB SPL exposure guideline from NIOSH. The earplugs, ear muffs, and customized SWAT team hearing protectors provided between 25 and 35 dB of peak reduction. Double hearing protection (plugs plus muffs) added 15-20 dB of peak reduction.     

The effectiveness of hearing protection among construction workers

Effective hearing conservation programs in the construction industry are rare. Where programs are present, they often rely on workers' use of hearing protection devices (HPDs) rather than on exposure controls to reduce noise exposure levels. Dependence on HPDs for protection from high noise is problematic, as the protection provided by the HPD depends on both the HPD's attenuation level and the time the HPD is used. This article presents an analysis of data on noise exposure and hearing protection among construction workers drawn from several large datasets covering nine construction trades. A unique combination of 1-min dosimetry noise exposure levels and simultaneous self-reported use of HPDs was evaluated, as were occupational and nonoccupational HPD use data collected by questionnaire as part of a longitudinal study of noise exposure and hearing loss among apprentices. Direct measurements of HPD attenuation were also made on workers at their work site. The workers assessed in this study were found to use hearing protection less than one-quarter of the time that they were exposed above 85 dBA. Workers who reported always using HPDs in high noise on questionnaires were found to wear them only one-third of the time their exposures exceeded 85 dBA. Workers' self-reported use of HPDs during most noisy nonoccupational activities was also found to be low. Direct attenuation measurements found that workers were able to achieve more than 50% of the rated attenuation of their HPD on average, but that the variability in achieved attenuation was large. When the measured HPD attenuation levels and use time data were combined, the effective protection afforded by HPDs was less than 3 dB, a negligible amount given the high exposure levels associated with construction work. However, there was substantial variation in effective protection among the different trades assessed. These results demonstrate the need for better hearing conservation programs and expanded noise control efforts in the construction industry.     

Noise exposures aboard catcher/processor fishing vessels

BACKGROUND: Commercial fishing workers have extended work shifts and potential for 24 hr exposures to high noise. However, exposures in this industry have not been adequately characterized. METHODS: Noise exposures aboard two catcher/processors (C/P) were assessed using dosimetry, sound-level mapping, and self-reported activities and hearing protection device (HPD) use. These data were combined to estimate work shift, non-work, and 24 hr overall exposure levels using several metrics. The length of time during which HPDs were worn was also used to calculate the effective protection received by crew members. RESULTS: Nearly all workers had work shift and 24 hr noise levels that exceeded the relevant limits. After HPD use was accounted for, half of the 24 hr exposures remained above relevant limits. Non-work-shift noise contributed nothing to 24 hr exposure levels. HPDs reduced the average exposure by about 10 dBA, but not all workers wore them consistently. CONCLUSIONS: The primary risk of hearing loss aboard the monitored vessels comes from work shift noise. Smaller vessels or vessels with different layouts may present more risk of hearing damage from non-work periods. Additional efforts are needed to increase use of HPDs or implement noise controls.     

Do ambient noise exposure levels predict hearing loss in a modern industrial cohort?

Background

Much of what is known about the exposure–response relationship between occupational noise exposures and hearing loss comes from cross‐sectional studies conducted before the widespread implementation of workplace hearing conservation programmes. Little is known about the current relationship of ambient noise exposure measurements to hearing loss risk.

Aim

To examine the relationship between rates of high frequency hearing loss and measured levels of noise exposure in a modern industrial workforce.

Methods

Ten‐year hearing loss rates were determined for 6217 employees of an aluminium manufacturing company. Industrial hygiene and human resources records allowed for reconstruction of individual noise exposures. Hearing loss rates were compared to ANSI 3.44 predictions based on age and noise exposure. Associations between hearing loss, noise exposure, and covariate risk factors were assessed using multivariate regression.

Results

Workers in higher ambient noise jobs tended to experience less high frequency hearing loss than co‐workers exposed at lower noise levels. This trend was also seen in stratified analyses of white males and non‐hunters. At higher noise exposure levels, the magnitude of hearing loss was less than predicted by ANSI 3.44 formulae. There was no indication that a healthy worker effect could explain these findings. The majority of 10 dB standard threshold shifts (STS) occurred in workers whose calculated ambient noise exposures were less than or equal to 85 dBA.

Conclusions

In this modern industrial cohort, hearing conservation efforts appear to be reducing hearing loss rates, especially at higher ambient noise levels. This could be related to differential use of hearing protection. The greatest burden of preventable occupational hearing loss was found in workers whose noise exposure averaged 85 dBA or less. To further reduce rates of occupational hearing loss, hearing conservation programmes may require innovative approaches targeting workers with noise exposures close to 85 dBA.