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

Association of Occupational Noise Exposure and Extended High-Frequency Hearing Loss in Young Workers With Normal Hearing

OBJECTIVES

Studies on the relationship between occupational noise exposure and extended high-frequency (EHF) hearing loss are limited. This study investigated the relationship between occupational noise exposure and EHF hearing loss in workers exposed to noise as measured by sound pressure level, exposure duration, and kurtosis to help provide a basis for early detection and prevention of hearing loss in noise-exposed workers.

DESIGN

A cross-sectional survey was conducted among 602 participants with 472 noise-exposed workers and 130 non-noise-exposed controls. General demographic characteristics, noise exposure data, and hearing thresholds at conventional frequencies (0.25 to 8 kHz) and EHF (9 to 16 kHz) were collected and analyzed. Linear mixed-effects model analyses between hearing thresholds of EHF and noise exposure indicators including the 8-h equivalent continuous A-weighted sound pressure level ( LAeq,8h ), cumulative noise exposure (CNE), and kurtosis-adjusted CNE (CNE-K) were conducted.

RESULTS

Among the 602 participants included in the analysis, 472 individuals (78.4%) were occupationally exposed to noise exposures ≥75 dBA. Significant differences ( p < 0.05) were observed in sex, exposure duration, LAeq,8h , CNE, and CNE-K between the noise-exposed group and the nonexposed group. The mean hearing thresholds for all tested extended high frequencies ranging from 9 to 16 kHz were significantly higher in the noise-exposed group than in the nonexposed group ( p < 0.05). The mean hearing thresholds of subjects in different groups of LAeq,8h exposures were generally stable with little variance in the conventional frequencies (0.25 to 8 kHz) but differed in the EHF range. Moreover, EHF hearing loss appeared to be most prominent in the subjects exposed to noise with 80 dBA < LAeq,8h ≤ 85 dBA. After the combination of the sound pressure level, exposure duration, and kurtosis by using the noise exposure indicators CNE and CNE-K, the subjects at the different noise exposures showed significant differences in hearing thresholds at EHF ( p < 0.05). Linear mixed-effected model analyses showed that the CNE-K was the best to indicate noise-induced hearing loss among the three noise exposure indicators at EHF.

CONCLUSIONS

The results indicate that the EHF hearing threshold testing is more sensitive to identifying early occupational noise-induced hearing loss than conventional audiometry. The CNE-K, an indicator combining noise energy, exposure duration, and kurtosis, is a more comprehensive and effective method for assessing the risk of EHF hearing loss due to occupational noise exposure.

Evaluating the Accuracy of Android Applications in Monitoring Environmental Noise Levels

Objective This study aimed to evaluate the accuracy of Android applications (apps) in measuring environmental noise levels, focusing on their potential use for occupational health assessments. Methods The top 10, highly rated, free Android apps were tested on a Samsung Galaxy A54 Smartphone (Samsung Group, Samsung Town, Seoul, South Korea) using pure tones at 100 Hz, 2000 Hz, and 4000 Hz, across four noise levels (25 dB, 40 dB, and 85 dB). Measurements were compared with a calibrated Precision Gold N09AQ environment meter (Maplin Electronics Ltd, Wath-Upon-Dearne, United Kingdom) in a controlled room. Data were analyzed using linear regression to determine R2 values for each app. Results The control meter showed the highest accuracy (R2 = 0.99). SPL Meter dB and sound Meter (KTW apps, Petaling Jaya, Selangor, Malaysia) and Sound Meter (Pony AI Inc.,Guangzhou, Guangdong, China) had the best performance (R2 = 0.98). Accuracy declined at higher noise levels, with Sound Meter (ABC Apps) showing the least accuracy (R2 = 0.85). User ratings did not correlate consistently with app performance. Conclusion Android apps offer potential as affordable noise measurement tools, with some apps demonstrating high accuracy at lower decibels. However, limitations such as reduced accuracy at higher decibels and lack of A-weighting for regulatory compliance hinder their use in professional settings. Further development and real-world testing are needed.

Application of the occupational health risk assessment model in predicting the risk of noise-induced hearing loss in noise-polluted manufacturers in southern China

Objective. This study aimed to evaluate the correlation between occupational noise-induced hearing loss (ONIHL) and noise exposure in different positions within manufacturing facilities that primarily produce electronic devices, wooden furniture and hardware machinery in southern China and to investigate the practical application of the risk assessment model. Methods. Noise exposure data were collected from 115 workers in 10 manufacturing industries in southern China through on-site investigation. Subsequently, sample testing was conducted in accordance with Chinese standards. The 31 job positions investigated were classified into two similar exposure groups (SEGs). The occupational health risk assessment (OHRA) model was used to evaluate the risks of ONIHL in various job positions. Results. More than half of the positions in both groups had noise levels exceeding 85 dB. In both SEGs, male workers exhibited similar risk patterns of acquiring hearing impairment, with a more pronounced and earlier risk of hearing loss compared to female workers. Age was also found to be a risk factor for hearing impairments. Conclusion. The ORHA model demonstrated a positive correlation between noise exposure levels and NIHL. This model can help employers assess job management with noise exposure and take measures to implement an effective risk management system.

Self-reported occupational noise exposure and hearing protection device use among NHANES participants and the risk of hearing loss

Occupational noise exposure continues to be a prevalent hazard in many industries. While the proliferation of noise dosimeters and wearable devices has made it easier to assess a worker's exposure to noise, many employees exposed to hazardous (i.e., >85 dBA) levels of noise may go their entire career without ever having their personal noise levels measured. In contrast to other occupational exposures, noise is easily perceived by the individual exposed, allowing them to develop subjective judgments regarding its characteristics. To determine whether such self-reported exposures to occupational noise are associated with hearing loss, this analysis used audiometric data and self-reported occupational exposure to loud noise from the National Health and Nutrition Examination Survey (NHANES), which has collected such data from 1999 to May 2020. Linear and logistic regressions models found a statistically significant association between self-reported noise exposure and worsened hearing at the 3, 4, 6, and 8 kHz hearing frequency as well as an elevated odds ratio for the development of hearing loss greater than 25 dB at the 2, 3, and 4 kHz audiometric frequencies. The results of this analysis suggest that in the absence of exposure measurements, workers are likely able to detect exposure to hazardous levels of noise. In these instances, additional measurements should be collected to determine if the workers should be enrolled in a hearing conservation program.

Time Trend of Occupational Noise-induced Hearing Loss in a Metallurgical Plant With a Hearing Conservation Program

Background

This study aimed to analyze the trend of occupational noise-induced hearing loss (ONIHL) in Brazilian workers at a metallurgical plant with a hearing conservation program (HCP), which has been addressed in a previous study.

Methods

All 152 workers in this time series (20032018) participated in the HCP and used personal protective equipment. All annual audiometry records in the company's software were collected from the electronic database. The trend of ONIHL was analyzed with the joinpoint regression model. The hearing thresholds of ONIHL cases at the end of the series were compared with those found in a national reference study.

Results

The binaural mean hearing thresholds at 3, 4, and 6 kHz at the end of the series were higher for ages ≥50 years, exposures ≥85 dB (A), time since admission >20 years, and maintenance workers. Significance was found only in the group divided by age. There was an increasing time trend of ONIHL, though with a low percentage variation for the period (AAPC = 3.5%; p = 0.01). Hearing thresholds in this study differed from the reference one.

Conclusion

Despite the unmet expectation of a stationary trend in the study period, the time pace of ONIHL evolution did not follow what was expected for a population exposed to noise. These findings signal to the scientific community and public authorities that good ONIHL control is possible when HCP is well implemented.

Utilizing Artificial Neural Networks for Establishing Hearing-Loss Predicting Models Based on a Longitudinal Dataset and Their Implications for Managing the Hearing Conservation Program

Background

Though the artificial neural network (ANN) technique has been used to predict noise-induced hearing loss (NIHL), the established prediction models have primarily relied on cross-sectional datasets, and hence, they may not comprehensively capture the chronic nature of NIHL as a disease linked to long-term noise exposure among workers.

Methods

A comprehensive dataset was utilized, encompassing eight-year longitudinal personal hearing threshold levels (HTLs) as well as information on seven personal variables and two environmental variables to establish NIHL predicting models through the ANN technique. Three subdatasets were extracted from the afirementioned comprehensive dataset to assess the advantages of the present study in NIHL predictions.

Results

The dataset was gathered from 170 workers employed in a steel-making industry, with a median cumulative noise exposure and HTL of 88.40 dBA-year and 19.58 dB, respectively. Utilizing the longitudinal dataset demonstrated superior prediction capabilities compared to cross-sectional datasets. Incorporating the more comprehensive dataset led to improved NIHL predictions, particularly when considering variables such as noise pattern and use of personal protective equipment. Despite fluctuations observed in the measured HTLs, the ANN predicting models consistently revealed a discernible trend.

Conclusions

A consistent correlation was observed between the measured HTLs and the results obtained from the predicting models. However, it is essential to exercise caution when utilizing the model-predicted NIHLs for individual workers due to inherent personal fluctuations in HTLs. Nonetheless, these ANN models can serve as a valuable reference for the industry in effectively managing its hearing conservation program.

Quantitative levels of noise exposure and 20-year hearing decline: findings from a prospective cohort study (the HUNT Study)

OBJECTIVE

We aimed to assess the association between occupational noise exposure and long-term hearing decline.

DESIGN

This prospective cohort study used linear regression to investigate the association between occupational noise exposure and 20-year hearing decline, adjusted for important confounders.

STUDY SAMPLE

The Norwegian cohort (N = 4,448) participated in two population-based health studies with pure-tone audiometry; HUNT2 1996-1998 and HUNT4 2017-2019. Exposure assessments included a quantitative job exposure matrix (JEM) and questionnaires.

RESULTS

The participants (40.2% men, 20-39 years at baseline) had a mean 20-year decline (3-6 kHz) of 11.3 ± 9.8 decibels (dB). There was a positive association between 20-year logarithmic average noise level (JEM-based, LEX,20y) and 20-year hearing decline among men. Compared with no exposure ≥80 dB during follow-up, minimum 5 years of exposure ≥85 dB (JEM-based) predicted 2.6 dB (95% CI: 0.2-5.0) larger 20-year decline for workers aged 30-39 years at baseline, and -0.2 dB (95% CI: -2.2 to 1.7) for workers aged 20-29 years. Combining JEM information with self-reported noise exposure data resulted in stronger associations.

CONCLUSION

This large longitudinal study shows an association between JEM-based noise exposure level and increased 20-year hearing decline among men. Contrary to expectations, the associations were weaker among younger workers, which might reflect a latency period.

A Systematic Literature Review of the Factors Influencing Hearing Protection Device Usage among Industrial Workers

This systematic literature review (SLR) aims to determine the factors influencing the use of hearing protection devices (HPDs) among industrial workers. This study was guided by the PRISMA Statement (Preferred Reporting Items for Systematic reviews and Meta-Analyses) review method, and four databases comprising Scopus, Science Direct, PubMed, Wiley Online Library, and Google Scholar were employed. A total of 196 articles were identified, and 28 studies on the factors associated with HPD use among industrial workers from 2006 to 2021 met the inclusion criteria. Resultantly, five main themes emerged from this review: sociodemographic (29%), interpersonal influences (18%), situational influences (18%), cognitive-perceptual (29%), and health-promoting behavior (6%) associated with HPD use among industrial workers. A total of 17 sub-themes were identified, including age, gender, educational level, noise level, working experience, social models, interpersonal support, social norms, safety climate, training, organizational support, perceived barrier, perceived susceptibility, perceived severity, perceived benefit, self-efficacy, and cues to action. The significant factors influencing workers to use HPDs are sociodemographic, interpersonal influences, situational influences, and health-promoting behavior. Future studies should focus on the cues to action toward human behavior influencing the use of HPDs, workers' health status, and comorbidities of hearing loss. Therefore, this systematic study gives valuable reference resources for up-and-coming researchers as well as new knowledge to expert professionals and academics in various industries.

The prevalence of occupational exposure to noise: A systematic review and meta-analysis from the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury

BACKGROUND

The World Health Organization (WHO) and the International Labour Organization (ILO) are developing joint estimates of the work-related burden of disease and injury (WHO/ILO Joint Estimates), with contributions from a large network of individual experts. Evidence from mechanistic and human data suggests that occupational exposure to noise may cause cardiovascular disease. In this paper, we present a systematic review and meta-analysis of the prevalence of occupational exposure to noise for estimating (if feasible) the number of deaths and disability-adjusted life years from cardiovascular disease that are attributable to exposure to this risk factor, for the development of the WHO/ILO Joint Estimates.

OBJECTIVES

We aimed to systematically review and meta-analyse estimates of the prevalence of occupational exposure to noise.

DATA SOURCES

We searched electronic academic databases for potentially relevant records from published and unpublished studies, including Ovid Medline, PubMed, EMBASE, and CISDOC. We also searched electronic grey literature databases, Internet search engines, and organizational websites; hand-searched reference list of previous systematic reviews and included study records; and consulted additional experts.

STUDY ELIGIBILITY AND CRITERIA

We included working-age (≥15 years) workers in the formal and informal economies in any WHO Member and/or ILO member State, but excluded children (<15 years) and unpaid domestic workers. We included all study types with an estimate of the prevalence of occupational exposure to noise, categorized into two levels: no (low) occupational exposure to noise (<85dBA) and any (high) occupational exposure to noise (≥85dBA).

STUDY APPRAISAL AND SYNTHESIS METHODS

At least two review authors independently screened titles and abstracts against the eligibility criteria at a first stage and full texts of potentially eligible records at a second stage, followed by extraction of data from qualifying studies. We combined prevalence estimates using random-effect meta-analysis. Two or more review authors assessed the risk of bias and the quality of evidence, using the RoB-SPEO tool and QoE-SPEO approach developed specifically for the WHO/ILO Joint Estimates.

RESULTS

Sixty-five studies (56 cross-sectional studies and nine cohort studies) met the inclusion criteria, comprising 157,370 participants (15,369 females) across 28 countries and all six WHO regions (Africa, Americas, Eastern Mediterranean, Europe, South-East Asia, and Western Pacific). For the main analyses, we prioritized the four included studies that surveyed national probability samples of general populations of workers over the 58 studies of workers in industrial sectors and/or occupations with relatively high occupational exposure to noise. The exposure was generally assessed with dosimetry, sound level meter, or official or company records; in the population-based studies, it was assessed with validated questions. Estimates of the prevalence of occupational exposure to noise are presented for all 65 included studies, by country, sex, 5-year age group, industrial sector, and occupation where feasible. The pooled prevalence of any (high) occupational exposure to noise (≥85dBA) among the general population of workers was 0.17 (95% confidence interval 0.16 to 0.19, 4 studies, 108,256 participants, 38 countries, two WHO regions, I2 98%, low quality of evidence). Subgroup analyses showed that pooled prevalence differed substantially by WHO region, sex, industrial sector, and occupation.

CONCLUSIONS

Our systematic review and meta-analysis found that occupational exposure to noise is prevalent among general populations of workers. The current body of evidence is, however, of low quality, due to serious concerns for risk of bias and indirectness. Producing estimates of occupational exposure to noise nevertheless appears evidence-based, and the pooled effect estimates presented in this systematic review are suitable as input data for the WHO/ILO Joint Estimates (if feasible). Protocol identifier: 10.1016/j.envint.2018.09.040 PROSPERO registration number: CRD42018092272.

Temporary Threshold Shifts among Iron and Steel Factory Workers in Tanzania: A Pre-Interventional Study

Background

Workers in iron and steel factories in Tanzania are exposed to noise levels above recommended limit values, without using hearing protection devices. Exposure to noise levels above 85 dB(A) is associated with temporary threshold shifts (TTS) of human hearing. Nevertheless, there are few studies of noise and hearing from African countries.

Objective

To determine whether the normal hearing workers in Tanzania experiences TTS after full-shift occupational noise exposure of 85 dB(A) and above.

Methods

A total of 55 workers were included. Full-shift personal noise measurements were conducted. Pre- and post-shifts pure-tone audiometry were conducted for each worker. TTS was defined as a 10 dB or greater change at 1000, 2000, 3000 or 4000 Hz in either ear.

Results

We found that 85.5% of the workers developed TTS across the work shift. There was significant increase in mean hearing thresholds across shift at 1000, 2000, 3000 and 4000 Hz among the workers exposed to an average personal noise exposure (LAeq,8h) of 90.4 dB(A) (SD = 2.7). The difference in mean hearing thresholds was higher at 4000 Hz [Arithmetic Mean (AM) = 10 dB SD = 4 dB] compared to that of 1000 Hz (AM = 4 dB SD = 3 dB), 2000 Hz (AM = 4 dB SD = 4 dB), and 3000 Hz (AM = 9 dB SD = 6 dB), respectively.

Conclusions

Interventions to reduce occupational personal noise exposure are warranted to reduce the high risk of developing a permanent threshold shift with persistent high noise exposure. An intervention study is planned for this group of workers.

Occupational Noise Exposure and Longitudinal Hearing Changes in Post-9/11 US Military Personnel During an Initial Period of Military Service

OBJECTIVES

Auditory impairments, particularly those resulting from hazardous occupational noise exposures, are pressing concerns for the US Departments of Defense (DoD) and Veterans Affairs (VA). However, to date, no studies have estimated the rate of hearing threshold change that occurs during service or how changes may vary by military occupation. Hearing threshold changes during military service have historically been reported as the proportion of Service members demonstrating a significant threshold shift. This approach does not capture the rate of the hearing threshold change or the specific audiometric frequencies impacted. Determining the rate of hearing threshold change, and factors that affect the rate of change, is important to elucidate the impact of military service on hearing and to guide prevention strategies and subsequent hearing health care. Our primary objective was to estimate the annual rate of hearing threshold change during military service as a consequence of military occupational noise exposure ranking.

DESIGN

We linked audiometric data, collected from military personnel as part of a DoD hearing conservation program, to data describing demographic and military-service characteristics obtained from individuals enrolled in the Noise Outcomes In Service members Epidemiology Study. The analytic cohort included Veterans who enlisted in military service after September 2001 (n = 246). We examined the longitudinal association between military occupations categorized as having a low, moderate, or high noise exposure ranking and pure-tone hearing thresholds (500 to 6000 Hz) using a hierarchical linear model. The average annual rate of hearing threshold change and their 95% confidence intervals were estimated by service branch, military occupational noise exposure ranking, and audiometric test frequency.

RESULTS

On average, hearing threshold change ranged between -0.5 and 1.1 dB/year and changes over time varied by service branch, audiometric test frequency, and military occupation noise ranking. Generally, higher test frequencies (3000 to 6000 Hz) and military occupations with moderate or high noise exposure rankings had the greatest average annual rates of hearing threshold change; however, no dose-response relationship was observed. Among Marine Corps personnel, those exposed to occupations with high noise rankings demonstrated the greatest average annual rate of change (1.1 dB/year at 6000 Hz). Army personnel exposed to occupations with moderate noise rankings demonstrated the greatest average annual rate of change (0.6 dB/year at 6000 Hz).

CONCLUSIONS

This study (1) demonstrates the unique use of DoD hearing conservation program data, (2) is the first analysis of hearing threshold changes over time using such data, and (3) adds to the limited literature on longitudinal changes in hearing. The difference in hearing threshold changes across military branches is likely indicative of their varying noise exposures, hearing protection device use and enforcement, and surveillance practices. Results suggest Marine Corps and Army personnel are at risk for hearing threshold changes and that, among Army personnel, this is most pronounced among those exposed to moderate levels of occupational noise exposure. Estimates of the rate of hearing threshold change by frequency and factors that impact hearing are useful to inform the DoD's efforts to protect the hearing of their Service members and to the Veterans Affairs's efforts to identify and rehabilitate those most likely to experience hearing threshold change.

The Accuracy of iPhone Applications to Monitor Environmental Noise Levels

OBJECTIVE

The Control of Noise at Work Regulations came into force in Great Britain in 2005, requiring all work environments to be monitored for potentially harmful noise exposure levels. This study evaluated the effectiveness of a number of iPhone phone applications (apps) (Apple, Cupertino, CA) to accurately measure noise exposure, which may prove effective when a specialist-calibrated sound level meter is not readily available.

METHODS

Suitable apps were identified using the search terms noise and decibel through the App Store (Apple). Apps that were free to download and had at least one rating were included. Apps were evaluated using a calibrated pure tone sound field and a soundproof testing booth. A 3-frequency audiogram (1000 Hz, 2000 Hz, and 4000 Hz) was used at 25 dB, 40 dB, 55 dB, 70 dB, and 85 dB. Linear regression was carried out to assess accuracy.

RESULTS

Nine apps were tested in total, with four out of nine providing a goodness-of-fit coefficient (R² value) over 0.9. The most effective app was found to be the NIOSH (National Institute for Occupational Safety and Health) Sound Level Meter (EA LAB, Slovenia) with an R² of 0.97. The least effective app was the Decibel Meter With Recorder (Jianhua Ming, China) with an R² of 0.62.

CONCLUSION

This study has shown significant variation in the ability of iPhone apps (Apple) to accurately predict environmental dB levels. However, if the correct app is used, an iPhone represents a relatively reliable means of measuring noise exposure levels when a specialist calibrated sound level meter is not readily available.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:E59-E62, 2021.

Early hearing slope as a predictor of subsequent hearing trajectory in a noise-exposed occupational cohort

Variations in individual susceptibility to noise-induced hearing loss have been observed among workers exposed to similar ambient noise levels but the reasons for this observation are poorly understood. Many workers are exposed to hazardous levels of occupational noise throughout their entire careers. Therefore, a mechanism to identify workers at risk for accelerated hearing loss early in their career may offer a time-sensitive window for targeted intervention. Using available longitudinal data for an occupationally noise-exposed cohort of manufacturing workers, this study aims to examine whether change in an individual's high frequency hearing level during the initial years of occupational noise exposure can predict subsequent high frequency hearing loss. General linear mixed modeling was used to model later hearing slope in the worse ear for the combined frequencies of 3, 4, and 6 kHz as a function of early hearing slope in the worse ear, age at baseline, sex, race/ethnicity, mean ambient workplace noise exposure, and self-reported non-occupational noise exposure. Those with accelerated early hearing loss were more likely to experience a greater rate of subsequent hearing loss, thus offering a potentially important opportunity for meaningful intervention among those at greatest risk of future hearing loss.

Risk of noise-induced hearing loss due to recreational sound: Review and recommendations

This review was conducted to address three questions related to recreational sound exposure: (1) what criteria are used to determine noise exposure limits, (2) are there differences in the risk of hearing loss from occupational noise versus recreational sound, and (3) what is an appropriate exposure limit for recreational sound? For the first question, most standards specify an 8-h occupational noise exposure limit (L_EX) of 85 dBA. This limit assumes that some workers exposed at the limit will develop hearing loss. To eliminate the risk of hearing loss, a 24-h equivalent continuous level (L_EQ24h) limit of 70 dBA is appropriate. For the second question, there is some evidence that the effects of occupational noise on hearing may be worse than energetically equivalent recreational sound. Limits developed for noise are nevertheless applicable to recreational sound, and use of existing statistical models to predict hearing loss from recreational sound is appropriate, with the caveat that these models are limited to durations ≤40 years. For the third question, a recreational sound limit of 80 dBA L_EX, equivalent to a 75 dBA L_EQ24h, will virtually eliminate the risk of recreationally induced hearing loss in adults. Lower limits may be warranted for vulnerable or susceptible individuals.

Prevalence and determinants of noise-induced hearing loss among workers in the automotive industry in China: A pilot study

Objective

Data on noise‐induced hearing loss (NIHL) in the automotive industry are rare. This pilot study aimed to investigate the prevalence and determinants of NIHL among workers in the automotive industry in China.

Methods

A cross‐sectional survey was conducted with 6557 participants from the automotive industry. The questionnaire survey was administered, and individual noise exposure level (L_Aeq.8h) and hearing loss level were measured.

Results

Of participants, 96.43% were male; the median age was 27.0 years and 28.82% had NIHL defined as adjusted high‐frequency noise‐induced hearing loss (AHFNIHL). Concerning individual noise levels (L_Aeq.8h), 62.53% exceeded 85 dB(A), which were mainly concentrated in various jobs, including metal cutting, surface treatment, stamping, welding, grinding, assembly, plastic molding, and forging. Each typical noise source generated its own unique temporal waveform shape with the type of non‐Gaussian noise. Of workers, 53.15% regularly used hearing protector devices (HPD), and the proportion of regular HPD use increased with L_Aeq.8h. The trend test showed that the prevalence of AHFNIHL in male workers significantly increased with an increase in L_Aeq.8h at <94 dB(A) and cumulative noise exposure (CNE) in each age group (P < 0.05 or P < 0.01). A logistic regression analysis showed that CNE and HPD usage frequency were important factors contributing to AHFNIHL.

Conclusions

CNE and HPD usage frequency were the determinants for NIHL. Much more human surveys are needed to understand the prevalence and determinants of NIHL in the automotive industry in China.

Evaluating hearing loss risks in the mining industry through MSHA citations

A new noise regulation for the mining industry became effective in 2000, providing a consistent regulatory requirement for both coal and non-coal mining divisions. The new rule required mines to implement hearing conservation programs, including a system of continuous noise monitoring, provision of hearing protection devices, audiometric testing, hearing loss training, and record keeping. The goal of this study was to assess hearing conservation program compliance, and excessive noise exposure and hearing loss risks for both coal and non-coal mining divisions through evaluating MSHA citations. We analyzed 13,446 MSHA citations from 2000-2014 pertinent to 30 CFR Part 62. Descriptive statistics were generated and comparisons were made among mines of different commodities. In addition, one-way ANOVA on ranks was conducted to estimate the correlation between excess risks and establishment size. Results showed that 25.6% of coal mines and 14.7% of non-coal mines were cited at least once during this period of time. Larger numbers of noncompliance were seen in stone, sand, and gravel mines (SSG). Results also suggested inadequate efforts in both audiometric testing and minimizing risk after excessive noise exposure. Finally, establishment size of mine was correlated with the increasing risk of noncompliance. We anticipate that this study can guide resource allocation for preventing noise-induced hearing loss, and help improve risk management in mining.

Noise-Induced Hearing Loss - A Preventable Disease? Results of a 10-Year Longitudinal Study of Workers Exposed to Occupational Noise

Aims:

To survey current, Danish industrial noise levels and the use of hearing protection devices (HPD) over a 10-year period and to characterise the association between occupational noise and hearing threshold shift in the same period. Furthermore, the risk of hearing loss among the baseline and the follow-up populations according to first year of occupational noise exposure is evaluated.

Materials and Methods:

In 2001–2003, we conducted a baseline survey of noise- and hearing-related disorders in 11 industries with suspected high noise levels. In 2009–2010, we were able to follow up on 271 out of the 554 baseline workers (49%). Mean noise levels per industry and self-reported HPD use are described at baseline and follow-up. The association between cumulative occupational noise exposure and hearing threshold shift over the 10-year period was assessed using linear regression, and the risk of hearing loss according to year of first occupational noise exposure was evaluated with logistic regression.

Results:

Over the 10-year period, mean noise levels declined from 83.9 dB(A) to 82.8 dB(A), and for workers exposed >85 dB(A), the use of HPD increased from 70.1 to 76.1%. We found a weak, statistically insignificant, inverse association between higher ambient cumulative noise exposure and poorer hearing (−0.10 dB hearing threshold shift per dB-year (95% confidence interval (CI): −0.36; 0.16)). The risk of hearing loss seemed to increase with earlier first year of noise exposure, but odds ratios were only statistically significant among baseline participants with first exposure before the 1980s (odds ratio: 1.90, 95% CI: 1.11; 3.22).

Conclusions:

We observed declining industrial noise levels, increased use of HPD and no significant impact on hearing thresholds from current ambient industrial noise levels, which indicated a successful implementation of Danish hearing conservation programs.

Assessing Hearing Conservation Program Effectiveness: Results of a Multisite Assessment

OBJECTIVES

Noise-induced hearing loss (NIHL) remains one of the most prevalent occupational diseases. Occupational hearing conservation programs (HCPs) can reduce the risk of NIHL, but there remains no consensus on assessing HCP effectiveness. We conducted a multisite, mixed-method assessment of HCP programs.

METHODS

At 13 manufacturing plants, we performed assessments, including interviews with program staff and worker focus groups and surveys. We analyzed the association between these assessments and age-corrected NIHL rates.

RESULTS

Only a few items from the HCP staff interviews correlated with NIHL rates. For the employee survey, management commitment to NIHL prevention and being counseled about NIHL were strongly associated with NIHL rates.

CONCLUSION

Management commitment and counseling of workers about NIHL may be key factors in program effectiveness. A combination of qualitative and quantitative methods appears to be useful for assessing HCPs.

Occupational noise exposure and risk of hypertension in an industrial workforce

BACKGROUND

Community noise exposure has been shown to increase the risk of hypertension; however, the relationship between occupational noise exposure and hypertension is less clear.

METHODS

Using an inception cohort of workers in a specialty metals manufacturing company, we retrospectively assessed occupational noise exposure, hearing acuity, and incident hypertension diagnoses using administrative datasets. Time-weighted average noise exposure levels were assigned to employees based on their job histories. Cox proportional hazards models were performed to determine the association of noise exposure with risk of incident hypertension.

RESULTS

The adjusted hazard ratio (HR) of incident hypertension did not significantly differ between groups by cumulative continuous or categorized noise exposure metric.

CONCLUSION

We found no increased risk of incident hypertension with exposure to occupational noise among workers. Further assessment examining workers' use of hearing protection devices is warranted.

Empirical estimation of the grades of hearing impairment among industrial workers based on new artificial neural networks and classical regression methods

Background:

Prediction models are used in a variety of medical domains, and they are frequently built from experience which constitutes data acquired from actual cases. This study aimed to analyze the potential of artificial neural networks and logistic regression techniques for estimation of hearing impairment among industrial workers.

Materials and Methods:

A total of 210 workers employed in a steel factory (in West of Iran) were selected, and their occupational exposure histories were analyzed. The hearing loss thresholds of the studied workers were determined using a calibrated audiometer. The personal noise exposures were also measured using a noise dosimeter in the workstations. Data obtained from five variables, which can influence the hearing loss, were used as input features, and the hearing loss thresholds were considered as target feature of the prediction methods. Multilayer feedforward neural networks and logistic regression were developed using MATLAB R2011a software.

Results:

Based on the World Health Organization classification for the grades of hearing loss, 74.2% of the studied workers have normal hearing thresholds, 23.4% have slight hearing loss, and 2.4% have moderate hearing loss. The accuracy and kappa coefficient of the best developed neural networks for prediction of the grades of hearing loss were 88.6 and 66.30, respectively. The accuracy and kappa coefficient of the logistic regression were also 84.28 and 51.30, respectively.

Conclusion:

Neural networks could provide more accurate predictions of the hearing loss than logistic regression. The prediction method can provide reliable and comprehensible information for occupational health and medicine experts.

Occupational noise exposure and hearing: a systematic review

Purpose

To give a systematic review of the development of noise-induced hearing loss (NIHL) in working life.

Methods

A literature search in MEDLINE, Embase, Web of Science, Scopus, and Health and Safety Abstracts, with appropriate keywords on noise in the workplace and health, revealed 22,413 articles which were screened by six researchers. A total of 698 articles were reviewed in full text and scored with a checklist, and 187 articles were found to be relevant and of sufficient quality for further analysis.

Results

Occupational noise exposure causes between 7 and 21 % of the hearing loss among workers, lowest in the industrialized countries, where the incidence is going down, and highest in the developing countries. It is difficult to distinguish between NIHL and age-related hearing loss at an individual level. Most of the hearing loss is age related. Men lose hearing more than women do. Heredity also plays a part. Socioeconomic position, ethnicity and other factors, such as smoking, high blood pressure, diabetes, vibration and chemical substances, may also affect hearing. The use of firearms may be harmful to hearing, whereas most other sources of leisure-time noise seem to be less important. Impulse noise seems to be more deleterious to hearing than continuous noise. Occupational groups at high risk of NIHL are the military, construction workers, agriculture and others with high noise exposure.

Conclusion

The prevalence of NIHL is declining in most industrialized countries, probably due to preventive measures. Hearing loss is mainly related to increasing age.

Electronic supplementary material

The online version of this article (doi:10.1007/s00420-015-1083-5) contains supplementary material, which is available to authorized users.

Prediction of hearing loss among the noise-exposed workers in a steel factory using artificial intelligence approach

PURPOSE

Prediction of hearing loss in noisy workplaces is considered to be an important aspect of hearing conservation program. Artificial intelligence, as a new approach, can be used to predict the complex phenomenon such as hearing loss. Using artificial neural networks, this study aims to present an empirical model for the prediction of the hearing loss threshold among noise-exposed workers.

METHODS

Two hundred and ten workers employed in a steel factory were chosen, and their occupational exposure histories were collected. To determine the hearing loss threshold, the audiometric test was carried out using a calibrated audiometer. The personal noise exposure was also measured using a noise dosimeter in the workstations of workers. Finally, data obtained five variables, which can influence the hearing loss, were used for the development of the prediction model. Multilayer feed-forward neural networks with different structures were developed using MATLAB software. Neural network structures had one hidden layer with the number of neurons being approximately between 5 and 15 neurons.

RESULTS

The best developed neural networks with one hidden layer and ten neurons could accurately predict the hearing loss threshold with RMSE = 2.6 dB and R(2) = 0.89. The results also confirmed that neural networks could provide more accurate predictions than multiple regressions.

CONCLUSIONS

Since occupational hearing loss is frequently non-curable, results of accurate prediction can be used by occupational health experts to modify and improve noise exposure conditions.

Acoustic neuroma: potential risk factors and audiometric surveillance in the aluminium industry

OBJECTIVES

To look for an association between acoustic neuroma (AN) and participation in a hearing conservation programme (HCP) and also for an association between AN and possible occupational risk factors in the aluminium industry.

METHODS

We conducted a case-control analysis of a population of US aluminium production workers in 8 smelters and 43 other plants. Using insurance claims data, 97 cases of AN were identified between 1996 and 2009. Each was matched with four controls. Covariates included participation in a HCP, working in an aluminium smelter, working in an electrical job and hearing loss.

RESULTS

In the bivariate analyses, covariates associated with AN were participation in the HCP (OR=1.72; 95% CI 1.09 to 2.69) and smelter work (OR=1.88; 95% CI 1.06 to 3.36). Electrical work was not significant (OR=1.60; 95% CI 0.65 to 3.94). Owing to high participation in the HCP in smelters, multivariate subanalyses were required. In the multivariate analyses, participation in the HCP was the only statistically significant risk factor for AN. In the multivariate analysis restricted to employees not working in a smelter, the OR was 1.81 (95% CI 1.04 to 3.17). Hearing loss, an indirect measure of in-ear noise dose, was not predictive of AN.

CONCLUSIONS

Our results suggest the incidental detection of previously undiagnosed tumours in workers who participated in the company-sponsored HCP. The increased medical surveillance among this population of workers most likely introduced detection bias, leading to the identification of AN cases that would have otherwise remained undetected.

Hearing profile of brazilian forestry workers' noise exposure

Introduction Researchers studying the hearing health of forestry workers have revealed the presence of a noise-induced hearing loss (NIHL) in this population and have concluded that the vibration of the equipment, the carbon monoxide released by motors, and pesticides might also contribute to NIHL.

Objective To analyze the noise exposure in the Brazilian forestry industry workers and the effects on hearing.

Methods The study sample comprised 109 employees of a company that specialized in reforestation. Their participants' mean age was 35.5 years (21 to 54 years), mean tenure at the company was 3.9 years (1 to 13 years), and mean total duration of noise exposure was 12.3 years (1 to 30 years). The existing documentation reporting on the jobs risk analysis was examined, noise level was measured, and pure tone audiometry was performed in all participants. Participants were divided into three groups according to their noise exposure levels in their current job.

Results Of the participants who were exposed to noise levels less than 85 dBA (decibels with A-weighting filter), 23.8% had hearing loss, and 5.5% of the participants who were exposed to noise ranging from 85 to 89.9 dBA and 11% of the participants who were exposed to noise greater than 90 dBA had audiogram results suggestive of NIHL.

Conclusion The implementation of a hearing loss prevention program tailored to forestry workers is needed.

Longitudinal changes in hearing threshold levels of noise-exposed construction workers

PURPOSE

Longitudinal analysis of audiometric data of a large population of noise-exposed workers provides insight into the development of noise-induced hearing loss (NIHL) as a function of noise exposure and age, particularly during the first decade of noise exposure.

METHODS

Data of pure-tone audiometry of 17,930 construction workers who underwent periodic occupational hearing screening at least twice during a 4-year period were available for analysis. These concerned all follow-up measurements of the baseline cohort described by Leensen et al. (Int Arch Occup Environ Health 84:577-590, 2011). Linear mixed models explored the relationship between the annual rate of change in hearing and noise exposure level, exposure duration, and age. Data of 3,111 workers who were tested on three occasions were used to investigate the pattern of hearing loss development.

RESULTS

The mean annual deterioration in hearing in this study population was 0.54 dB/yr, and this became larger with increasing noise exposure level and increasing age. Remarkably, during the first decade of noise exposure, an improvement in hearing threshold levels (HTLs) was observed. The change in hearing over three measurements showed a concave development of hearing loss as a function of time, which corresponds to NIHL development.

CONCLUSIONS

Overall, hearing deteriorated over the measurement period. Because HTLs at follow-up were better than those obtained at baseline, no statement can be made about the NIHL development during the first decade of noise exposure. This improvement in HTLs rather resembles the result of measurement variation in occupational screening audiometry than an actual improvement in hearing ability.

Methods for evaluating temporal trends in noise exposure

OBJECTIVE

Hearing conservation programs have been mandatory in many US industries since 1983. Since then, three program elements (audiometric testing, hearing protection, and training) have been the focus of much research. By comparison, little has been done on noise exposure evaluation.

DESIGN

Temporal trends in time weighted average (TWA) exposures and the fraction of measurements exceeding 85 dBA were evaluated by facility, by exposure group within facility, and by individual worker within facility.

STUDY SAMPLE

A large dataset (> 10 000 measurements over 20 years) from eight facilities operated by a multinational aluminum manufacturing company was studied.

RESULTS

Overall, exposures declined across locations over the study period. Several facilities demonstrated substantial reductions in exposure, and the results of mean noise levels and exceedance fractions generally showed good agreement. The results of analyses at the individual level diverged with analyses by facility and exposure group within facility, suggesting that individual-level analyses, while challenging, may provide important information not available from coarser levels of analysis.

CONCLUSIONS

Validated metrics are needed to allow for assessment of temporal trends in noise exposure. Such metrics will improve our ability to characterize, in a standardized manner, efforts to reduce noise-induced hearing loss.

Development of the hearing protection assessment (HPA-2) questionnaire

BACKGROUND

Noise-induced hearing loss (NIHL) remains an important occupational health issue as the second most commonly self-reported occupational injury or illness. The incorrect and inconsistent use of hearing protection devices (HPDs) compromises their effectiveness in preventing NIHL.

AIMS

To describe the development of an easily administered yet robust questionnaire to investigate factors that influence HPD use.

METHODS

A hearing protection assessment (HPA-2) questionnaire was developed using items based on themes identified in our previous research. These fell into two classes: supports and barriers to wearing HPD, which formed two scales within the questionnaire. The questionnaire, which also included demographic items, was administered to workers from 34 manufacturing companies. The internal consistency of the scales was tested, and factor analysis was conducted to investigate the underlying structure of the scales.

RESULTS

Of the 1053 questionnaires distributed, 555 completed questionnaires were received giving a response rate of 53%. The Cronbach's alpha for the barriers scale (α = 0.740) and supports scale (α = 0.771) indicated strong internal reliability of the questionnaire. The supports and barriers were further described as five key factors (risk justification, HPD constraints, hazard recognition, behaviour motivation and safety culture) that influence hearing protection behaviour. Workers who reported always using HPDs had more supports across these factors, while those who did not always wear HPDs reported more barriers.

CONCLUSIONS

The HPA-2 questionnaire may be useful in both research and interventions to understand and motivate hearing protection behaviour by identifying and targeting supports and barriers to HPD use at different levels of the ecological model.

Effect of workplace noise on hearing ability in tile and ceramic industry workers in Iran: a 2-year follow-up study

INTRODUCTION

Noise as a common physical hazard may lead to noise-induced hearing loss, an irreversible but preventable disorder. Annual audiometric evaluations help detect changes in hearing status before clinically significant hearing loss develops. This study was designed to track hearing threshold changes during 2-year follow-up among tile and ceramic workers.

METHODS

This follow-up study was conducted on 555 workers (totally 1110 ears). Subjects were divided into four groups according to the level of noise exposure. Hearing threshold in conventional audiometric frequencies was measured and standard threshold shift was calculated for each ear.

RESULTS

Hearing threshold was increased during 2 years of follow-up. Increased hearing threshold was most frequently observed at 4000, 6000, and 3000 Hz. Standard threshold shift was observed in 13 (2.34%), 49 (8.83%), 22 (3.96%), and 63 (11.35%) subjects in the first and second years of follow-up in the right and left ears, respectively.

CONCLUSIONS

This study has documented a high incidence of noise-induced hearing loss in tile and ceramic workers that would put stress on the importance of using hearing protection devices.

Impact of daily noise exposure monitoring on occupational noise exposures in manufacturing workers

OBJECTIVE

Despite the use of hearing protection devices (HPDs), noise induced hearing loss (NIHL) remains one of the most prevalent occupational conditions. A new technology allows for daily monitoring of noise exposures under HPDs. We report on an intervention employing the voluntary use of this technology in a worksite setting.

DESIGN

Volunteers were fitted with a device allowing them to monitor noise exposure under their hearing protection on a daily basis. The trends in noise exposures for individuals who completed at least six months of the intervention were analysed.

STUDY SAMPLE

Recruitment occurred at three manufacturing facilities, with 127 workers enrolling and 66 workers actively using the device during their work shifts.

RESULTS

Among volunteers downloading regularly, the percentage of daily exposures in excess of the OSHA action level (85 dBA) decreased from 14% to 8%, while the percentage of daily exposures in excess of 90 dBA decreased from 4% to less than 2%.

CONCLUSION

Initial results from this longitudinal study indicate that volunteers find daily noise exposure monitoring to be feasible, and that workers who monitor daily are able to reduce exposures. The results of subject adherence shed light on the challenges and possibilities of worksite interventions for health and safety.

Noise exposure reconstruction and evaluation of exposure trends in two large automotive plants

This study used a task-based approach to reconstruct employee noise exposures at two large automotive manufacturing plants for the period 1970-1989, utilizing historic noise measurement data, work history records, documented changes in plant operations, focus group discussions, structured interviews with long-tenure employees, and task-based job profiles. Task-based job noise exposure profiles were developed in the 1990s when the plants conducted task-based noise monitoring. Under the assumption that tasks and time-at-task profile within jobs did not change over time, these profiles were applied to historic jobs. By linking historic noise exposure measurements to job tasks, this approach allowed task-based reconstructed noise exposure profiles to capture variability of daily noise exposures. Reconstructed noise exposures, along with task-based noise exposure measurements collected at each plant during the 1990s, were analyzed to examine time trends in workplace noise levels and worker noise exposure. Our analysis of noise exposure trends revealed that noise levels for many jobs declined by ≥3 dBA from 1970 to 1998 as operational and equipment changes occurred in the plants and some noise control measures were implemented, but for some jobs, noise levels increased in the mid- to late 1990s, most likely because of an increase in production at that time. Overall, the percentage of workers exposed to noise levels >90 dBA decreased from 95% in 1970 to 54% in 1998 at one of the plants and decreased from 36% in 1970 to ~5% in 1999 at the other plant. These reductions indicate a degree of success for the hearing conservation program. However, the actual number of employees with noise exposure >90 dBA increased because of a substantial increase in the number of production employees, particularly in jobs with high noise levels, which shows a hearing conservation program challenge that companies face during periods of increased production. Future analysis of hearing levels in these plant populations will help determine whether noise level reduction translates into decreased hearing loss at these plants.

Measurement and analysis of 8-hour time-weighted average sound pressure levels in a vivarium decontamination facility

Occupational noise exposure is a recognized hazard for employees working near equipment and processes that generate high levels of sound pressure. High sound pressure levels have the potential to result in temporary or permanent alteration in hearing perception. The cleaning of cages used to house laboratory research animals is a process that uses equipment capable of generating high sound pressure levels. The purpose of this research study was to assess occupational exposure to sound pressure levels for employees operating cage decontamination equipment. This study reveals the potential for overexposure to hazardous noise as defined by the Occupational Safety and Health Administration (OSHA) permissible exposure limit and consistent surpassing of the OSHA action level. These results emphasize the importance of evaluating equipment and room design when acquiring new cage decontamination equipment in order to minimize employee exposure to potentially hazardous noise pressure levels.

Usability of a daily noise exposure monitoring device for industrial workers

OBJECTIVES

Usability is an important but often overlooked aspect of personal protective equipment technology. As part of a worksite intervention trial of a new technology for prevention of noise-induced hearing loss that allows workers to monitor their noise exposure inside of hearing protection on a daily basis, we studied the usability of the daily noise exposure monitoring device.

METHODS

We conducted surveys and focus groups for workers enrolled in an intervention trial of daily use of a noise dosimeter with a microphone fitted inside of an individual's hearing protector (QuietDose). Volunteers completed a baseline and annual survey that included questions about perceived usability of the QuietDose device. Responses to usability questions on the annual survey were abstracted and compared to whether the individual was still using the device. Finally, 16 in-depth focus groups were conducted with subjects to qualitatively explore common themes regarding the usability of the technology.

RESULTS

Reported problems downloading data or starting and stopping the monitoring device and/or ear discomfort were associated with whether individuals chose to continue monitoring and downloading their noise exposure data. Perceived benefits of the technology included the perception that it could help preserve hearing.

CONCLUSIONS

A novel technology that allows workers to record noise exposures inside of hearing protectors on a daily basis has been developed. Current users of the device report positive perception about how the device is helping them prevent noise-induced hearing loss. However, in its current version, users reported a number of usability barriers that are associated with stopping use of the device. These barriers to use should be addressed as the technology progresses.

Hearing effects from intermittent and continuous noise exposure in a study of Korean factory workers and firefighters

Background

South Korea and surrounding countries in East Asia are believed to have the highest proportion in the world of high frequency hearing loss due to occupational noise exposure, yet there has been limited information published in international journals, and limited information for control of noise in local workplaces beyond strategies from western countries. We exploit medical surveillance information from two worker groups to enhance local knowledge about noise-induced hearing loss and explore the possible importance of shift work to risk.

Methods

Four-years of hearing data were evaluated for 81 male farm machine factory workers and 371 male firefighters who had successfully completed a health examination and questionnaires for the duration of the study period. The averages of hearing thresholds at 2, 3, and 4 kHz were used as the primary end-point for comparison. Repeat measure analysis adjusted for age, exposure duration and smoking status was used to measure the difference in hearing threshold between the two groups.

Results

Noise levels were measured in the factory at a mean of 82 dBA, with a range of 66-97. No concurrent measurements were taken for the firefighters, but historic comparison values showed a wider range but a similar mean of 76-79 dBA. Although losses during follow-up were negligible, the factory workers had significantly (P < 0.0001) more hearing loss at the baseline of the study than the firefighters in both ears at 2, 3, and 4 kHz, adjusted for age, duration of employment and smoking status. Among those with 10 years of employment, mean losses at these frequencies among the factory workers fell into the impairment range (> 25 dB loss). Firefighters also showed increased losses associated with longer exposure duration, but these were significantly less marked. Losses at lower frequencies (< or = 1 kHz) were negligible in both groups.

Conclusions

Korean work environments with continuous noise exposure in the measured range should consider implementation of a hearing conservation program. Further evaluation of hearing loss in workers exposed to irregular or intermittent high noise levels, such as firefighters, is also warranted.

Use of historical data and a novel metric in the evaluation of the effectiveness of hearing conservation program components

OBJECTIVES

To evaluate the effectiveness of hearing conservation programs (HCP) and their specific components in reducing noise-induced hearing loss (NIHL).

METHODS

This retrospective cohort study was conducted at one food-processing plant and two automotive plants. Audiometric and work-history databases were combined with historical noise monitoring data to develop a time-dependent exposure matrix for each plant. Historical changes in production and HCP implementation were collected from company records, employee interviews and focus groups. These data were used to develop time-dependent quality assessments for various HCP components. 5478 male (30,427 observations) and 1005 female (5816 observations) subjects were included in the analysis.

RESULTS

Analyses were conducted separately for males and females. Females tended to have less NIHL at given exposure levels than males. Duration of noise exposure stratified by intensity (dBA) was a better predictor of NIHL than the standard equivalent continuous noise level (L(eq)) based upon a 3-dBA exchange. Within this cohort, efficient dBA strata for males were <95 versus ≥ 95, and for females <90 versus ≥ 90. The reported enforced use of hearing protection devices (HPDs) significantly reduced NIHL. The data did not have sufficient within-plant variation to determine the effectiveness of noise monitoring or worker training. An association between increased audiometric testing and NIHL was believed to be an artifact of increased participation in screening.

CONCLUSIONS

Historical audiometric data combined with noise monitoring data can be used to better understand the effectiveness of HCPs. Regular collection and maintenance of quality data should be encouraged and used to monitor the effectiveness of these interventions.

Effect of daily noise exposure monitoring on annual rates of hearing loss in industrial workers

OBJECTIVES

Occupational noise-induced hearing loss (NIHL) is prevalent, yet evidence on the effectiveness of preventive interventions is lacking. The effectiveness of a new technology allowing workers to monitor daily at-ear noise exposure was analysed.

METHODS

Workers in the hearing conservation program of an aluminium smelter were recruited because of accelerated rates of hearing loss. The intervention consisted of daily monitoring of at-ear noise exposure and regular feedback on exposures from supervisors. The annual rate of change in high frequency hearing average at 2, 3 and 4 KHz before intervention (2000-2004) and 4 years after intervention (2006-2009) was determined. Annual rates of loss were compared between 78 intervention subjects and 234 controls in other company smelters matched for age, gender and high frequency hearing threshold level in 2005.

RESULTS

Individuals monitoring daily noise exposure experienced on average no further worsening of high frequency hearing (average rate of hearing change at 2, 3 and 4 KHz = -0.5 dB/year). Matched controls also showed decelerating hearing loss, the difference in rates between the two groups being significant (p < 0.0001). Analysis of a subset of intervention subjects matched to controls for initial rate of hearing loss showed a similar trend but the difference was not statistically significant (p = 0.06).

CONCLUSION

Monitoring daily occupational noise exposure inside hearing protection with ongoing administrative feedback apparently reduces the risk of occupational NIHL in industrial workers. Longer follow-up of these workers will help determine the significance of the intervention effect. Intervention studies for the prevention of NIHL need to include appropriate control groups.

A retrospective analysis of noise-induced hearing loss in the Dutch construction industry

Purpose

Noise exposure is an important and highly prevalent occupational hazard in the construction industry. This study examines hearing threshold levels of a large population of Dutch construction workers and compares their hearing thresholds to those predicted by ISO-1999.

Methods

In this retrospective study, medical records of periodic occupational health examinations of 29,644 construction workers are analysed. Pure-tone audiometric thresholds of noise-exposed workers are compared to a non-exposed control group and to ISO-1999 predictions. Regression analyses are conducted to explore the relationship between hearing loss and noise intensity, noise exposure time and the use of hearing protection.

Results

Noise-exposed workers had greater hearing losses compared to their non-noise-exposed colleagues and to the reference population reported in ISO-1999. Noise exposure explained only a small proportion of hearing loss. When the daily noise exposure level rose from 80 dB(A) towards 96 dB(A), only a minor increase in hearing loss is shown. The relation of exposure time and hearing loss found was similar to ISO-1999 predictions when looking at durations of 10 years or more. For the first decade, the population medians show poorer hearing than predicted by ISO-1999.

Discussion

Duration of noise exposure was a better predictor than noise exposure levels, probably because of the limitations in noise exposure estimations. In this population, noise-induced hearing loss was already present at the beginning of employment and increased at the same rate as is predicted for longer exposure durations.

A multi-component intervention to promote hearing protector use among construction workers

Hearing protection devices (HPD) remain a primary method of prevention of noise-induced hearing loss despite their well-known limitations. A three-pronged intervention to increase HPD use was conducted among construction workers and included a baseline hearing loss prevention training, follow-up 'toolbox' (TB) reinforcement trainings, and use of a personal noise level indicator (NLI). A total of 176 subjects on eight sites completed three assessments. Prior to intervention, HPDs were used an average of 34.5% of the time and increased significantly, up about 12.1% after intervention and 7.5% two months after interventions were completed. The increase in HPD use was greatest among the group receiving both TB and NLI interventions; up about 25% from baseline, and this group was about two times more likely to use HPDs than the BL (baseline) training only group. This study demonstrates the mild impact of a well-constructed HPD use training and provides support for the additional use of a personal NLI to increase use of HPDs among construction workers. The most effective procedures for using such instruments require further exploration.

Effects of externally rated job demand and control on depression diagnosis claims in an industrial cohort

This study examined whether externally rated job demand and control were associated with depression diagnosis claims in a heavy industrial cohort. The retrospective cohort sample consisted of 7,566 hourly workers aged 18-64 years who were actively employed at 11 US plants between January 1, 1996, and December 31, 2003, and free of depression diagnosis claims during an initial 2-year run-in period. Logistic regression analysis was used to model the effect of tertiles of demand and control exposure on depression diagnosis claims. Demand had a significant positive association with depression diagnosis claims in bivariate models and models adjusted for demographic (age, gender, race, education, job grade, tenure) and lifestyle (smoking status, body mass index, cholesterol level) variables (high demand odds ratio = 1.39, 95% confidence interval: 1.04, 1.86). Control was associated with greater risk of depression diagnosis at moderate levels in unadjusted models only (odds ratio = 1.47, 95% confidence interval: 1.12, 1.93), while low control, contrary to expectation, was not associated with depression. The effects of the externally rated demand exposure were lost with adjustment for location. This may reflect differences in measurement or classification of exposure, differences in depression diagnosis by location, or other location-specific factors.

Exposure to hazardous workplace noise and use of hearing protection devices among US workers--NHANES, 1999-2004

BACKGROUND

To estimate the prevalence of workplace noise exposure and use of hearing protection devices (HPDs) at noisy work, NIOSH analyzed 1999-2004 data from the National Health and Nutrition Examination Survey (NHANES).

METHODS

A total of 9,275 currently employed workers aged > or =16 years were included in the weighted analysis. Hazardous workplace noise exposure was defined as self-reported exposure to noise at their current job that was so loud that the respondent had to speak in a raised voice to be heard. Industry and occupation were determined based on the respondent's current place and type of work.

RESULTS

Twenty-two million US workers (17%) reported exposure to hazardous workplace noise. The weighted prevalence of workplace noise exposure was highest for mining (76%, SE = 7.0) followed by lumber/wood product manufacturing (55%, SE = 2.5). High-risk occupations included repair and maintenance, motor vehicle operators, and construction trades. Overall, 34% of the estimated 22 million US workers reporting hazardous workplace exposure reported non-use of HPDs. The proportion of noise-exposed workers who reported non-use of HPDs was highest for healthcare and social services (73.7%, SE = 8.1), followed by educational services (55.5%).

DISCUSSION

Hearing loss prevention and intervention programs should be targeted at those industries and occupations identified to have a high prevalence of workplace noise exposure and those industries with the highest proportion of noise-exposed workers who reported non-use of HPDs.

Verifying the attenuation of earplugs in situ: method validation on human subjects including individualized numerical simulations

The microphone in real ear (MIRE) protocol allows the assessment of hearing protector's (HPD) attenuation in situ by measuring the difference between the sound pressure outside and inside the ear canal behind the HPD. Custom-made earplugs have been designed with an inner bore to insert the MIRE probe containing two microphones, the reference microphone measuring the sound pressure outside and the measurement microphone registering the sound pressure behind the HPD. Previous research on a head and torso simulator reveals a distinct difference, henceforth called transfer function, between the sound pressure at the MIRE measurement microphone and the sound pressure of interest at the eardrum. In the current study, similar measurements are carried out on humans with an extra microphone to measure the sound pressure at the eardrum. The resulting transfer functions confirm the global frequency dependency found earlier, but also show substantial variability between the ears with respect to the exact frequency and amplitude of the transfer functions' extrema. In addition, finite-difference time-domain numerical models of an ear canal with earplug are developed for each individual ear by including its specific geometrical parameters. This approach leads to a good resemblance between the simulations and their corresponding measurements.

Audiometric "early flags" for occupational hearing loss

OBJECTIVE

OSHA criteria for recording occupational noise-induced hearing loss (NIHL) do not ensure early detection, yet scientific consensus is lacking regarding optimal "early flags" for NIHL. This study compares early flag metrics to the subsequent development of recordable hearing loss.

METHODS

In a longitudinal analysis of industrial audiograms, we calculated time from flag event to recordable hearing loss as well as 10 year risk of recordable hearing loss following flag occurrence.

RESULTS

The 10 dB non-age-corrected STS and the 8 dB age-corrected shift at 2, 3, and 4 kHz optimally combined positive predictive value and length of time to recordable hearing loss.

CONCLUSIONS

Professionals supervising audiometric surveillance must balance predictive value of early flags with timeliness of detection. This study provides a framework for validation and selection of audiometric early flags in hearing conservation settings.