Industrial Noise Exposure Research Articles

Medicolegal significance of asymmetrical hearing loss in cases of industrial noise exposure

In Australia, the current guidelines for evaluation of noise-induced hearing loss suggest that, in cases of asymmetrical loss, 'the worse ear be equated to the better ear' for purposes of compensation. This study aimed to establish that such a method was prejudicial to the worker (i.e. the plaintiff). In consideration of the legal duty 'to co-construct the ideas of truth and the ideas of justice in the context of legal proceedings', our study objectives were (1) to document the incidence of asymmetrical hearing loss in compensation cases seen in our practice, and (2) to provide a reasoned argument for inclusion of the same for compensation considerations. Open, retrospective, clinical study. Australian plaintiffs with asymmetrical hearing loss (who comprise a significant percentage of industrial hearing loss legal cases) may be excluded from full consideration of their hearing loss as a result of the current guidelines. In contrast to the process of medical diagnosis and treatment, it appeared that the application of accepted probability standards within the legal process may permit inclusion of such clients' hearing loss in compensation considerations. This study included 208 consecutive clients referred by legal practitioners for assessment of hearing loss for compensation purposes. A total of 22.6 per cent of clients (47 of 208) had asymmetrical hearing loss, with the left side having the greater loss in 60 per cent of cases. We believe that asymmetrical hearing loss should be included in compensation considerations, both on medical and legal grounds.

An Overview of Industrial Employees' Exposure to Noise in Sundry Processing and Manufacturing Industries in Ilorin Metropolis, Nigeria

In this work, an overview of industrial employees' noise exposure level in five selected processing and manufacturing industries in Ilorin are evaluated and compared. Emphasis is given to noise emitted by individual industrial machinery from the selected industries. Event L(Aeq) and LN cycle were studied to identify the noisy machines and to generate baseline data. Findings show that, hammer mill machine from mineral crushing mills produced the highest average noise (98.4 dB(A), electric generator1 (95.6 dB(A) from soft drink bottling industry, electric generator (97.7 dB(A)) from beer brewing and bottling industry, vacuum pump (93.1 dB(A)) from tobacco making industry and electric generator 2 (94.1 dB(A) from mattress making industry. The highest and lowest average noise exposure levels are recorded in mineral crushing mills (93.16 dB(A)) and mattress making industry (84.69 dB(A)) respectively. The study shows that at 95% confidence level, there is significant difference (p<0.05) in noise levels in the industries surveyed. The percentages of machines emit noise above FEPA and OSHA recommendation (90 dB(A)) are: soft drink bottling industry (83.3%), beer brewing and bottling industry (42.9%), tobacco making industry (71.4%), mattress making industry (11.1%) and minerals crushing mills (87.5%). In the past 20 years, the noise levels in soft drink bottling industry reduced by 0.58 dB(A) and that of beer brewing and bottling industry reduced by 9.66 dB(A). But that of mattress making industry increased by 2.69 dB(A). On the average, the noise level in these industries has reduced by 2.52 dB(A). The results of this study show that the noise control measures put in place have significant impact on the noise exposure level in the industries surveyed.

Laboratory synthesis of industrial noise environments with predetermined statistical properties

High‐level nonGaussion noise is commonly found in a variety of industrial environments. Recent experiments have shown that for a given energy level, the statistical properties of a noise can have a strong effect on the extent of hearing loss produced in exposed individuals. In order to study, in an animal model, the effects on hearing of such noise environments, the statistical properties of the noise as embodied in the kurtosis metric must be under experimental control. For a fixed value of kurtosis and energy level the following four variables will have a strong effect on hearing loss: (1) peak histogram; (2) interval histogram; (3) duration of noise transients; and (4) level of any background Gaussian noise. Simulations have shown that the relations among kurtosis and these variables are nonlinear. However, under certain restricted conditions, these relations may be linear. Accordingly, two strategies for designing controlled industrial noise exposures are presented: (1) the interval‐priority model and (2) the duration‐priority model. Computer simulations and measurements of actual acoustic environments showed that these two models could be effectively used to simulate a wide variety of realistic industrial noises.

Combined Effects of Noise and Shift Work on Fatigue as a Function of Age

The study was conducted to analyse possible interactions between noise and shift work on fatigue as a function of age. In a large questionnaire survey, we assessed personal and environmental risk factors related to fatigue. Noise exposure at work (LAeq, 8hr) was measured with personal noise dosimetry. The sample included 254 day and shift workers, and was divided into 2 age groups (<40- and >40-year-olds). Noise exposure had a main effect on fatigue. The highest noise exposure resulted in an increase in the fatigue level of older shift workers. The quantity of sleep mainly depended on the type of shift and age. Our data suggest that the most important factor generating fatigue could be related to industrial noise exposure, a factor which seems to aggravate work-related fatigue generated in a synergic manner by shift work and ageing. Senior workers should be prevented from cumulating those occupational stressors.

Temporary threshold shift due to recreational firearm use

To assess whether a temporary threshold shift occurred after recreational firearm use. An observational study of 25 subjects using ear protection in an indoor rifle range. Hearing was evaluated before and after shooting five rounds with a 0.22 calibre rifle over 10 minutes. A threshold shift of 5 dB was found to be statistically significant, while a shift of 10 dB was clinically significant. Twenty-four candidates had a statistically significant threshold shift, while 12 had a clinically significant threshold shift. Two subjects with previous industrial noise exposure had threshold shifts at more frequencies than other subjects. There was no significant preference for either ear. One subject showed no changes. This small study sheds some light on impulse noise behaviour in an indoor shooting range, but no definite conclusions can be drawn. The side of shooting did not influence threshold changes in either ear.

Individual Perception of Noise Exposure and Hearing Protection in Industry

Existing approaches that explain the behavior of workers in noisy environments rarely include quantitative variables related to central factors such as noise exposure levels and workers' hearing status. The aim of this study is to analyze the relationship among individual, contextual, and perceptual-cognitive factors and the use of hearing protection devices (HPDs). We studied 516 industrial workers exposed to noise levels greater than the Portuguese action level and developed a conceptual model for HPD use. The multivariate data analysis of the several variables considered revealed that individual risk perception and the outcome value for hearing preservation were the main direct predictors of the use of HPDs. Workers' opinions about the company's safety climate and their perception of noise exposure effects also play important roles as predictors. However, much of the effects of these factors are indirect (i.e., mediated by other variables). Furthermore, these results suggest that risk perception should be considered an essential issue in the design and implementation of any hearing conservation program, particularly in the development of training programs. Actual or potential applications of this research include the definition of more accurate strategies for promoting and motivating the use of HPDs.

Sound Pressure Levels Experienced by the High School Band Director

Portable noise dosimeters were used to determine the levels of noise exposure experienced by high school band directors. In addition, sound reverberation times were measured to determine the appropriateness of existing acoustic conditions for the band rehearsal environment. A total of 63 sound pressure measurements were taken during the rehearsals of 10 high school bands located in cities along the Front Range of Colorado. Single sample t-tests and effect size calculations were employed to compare the sound pressure levels of all band rehearsals with the industrial noise standards of the Occupational Health and Safety Administration (OSHA), the American Conference of Governmental and Industrial Hygienists (ACGIH), and the National Institute of Occupational Safety and Health (NIOSH). Multiple regression analysis was used to determine the effect of room environmental factors on the sound pressure levels. While conducting high school ensembles, 60% of participating band directors experienced sound pressure levels at or exceeding 90 dBA. These levels and the mean noise doses and 8-hour projected noise doses observed were within the OSHA standards for industrial noise exposure, but exceeded the industrial noise exposure standards set by ACGIH and NIOSH. Multiple regression analysis performed on the room volume (cubic feet), the level of acoustic treatment, and the mean reverberation time were found to predict 77.8% of the variance in sound pressure levels in this study.

Monitoring audiometry for occupational hearing loss: A case for eliminating 500 Hz

Audiometric monitoring is an important element in hearing conservation programs. Nearly every existing hearing conservation standard dictate that hearing thresholds should be measured at specific frequencies, and that 500 Hz be among those frequencies tested. Actual and estimated noise-induced permanent threshold shifts were evaluated as a function of exposure duration and exposure level. The results demonstrate 500 Hz to be of little value in assessing noise-induced hearing loss for typical industrial noise exposures of up to 40 years, at least for time-weighted average exposures of up to 100 dB&amp;lt;th&amp;gt;A. Furthermore, few hearing conservation programs currently require audiometric monitoring to be performed in an environment that meets ANSI standards for maximum permissible background noise levels. This is particularly likely to compromise hearing testing at 500 Hz. As a result, this paper argues against the need for testing at 500 Hz, and recommends it be eliminated as a required test frequency in audiometric monitoring for noise-induced occupational hearing loss.

Analysis of impact/impulse noise for predicting noise induced hearing loss

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

An investigation of noise levels in Alberta sawmills.

Noise exposure in the sawmill industry is an area of concern. This study documents the level of noise exposure in nine sawmills in the province of Alberta, Canada. Personal noise monitoring data were collected in nine Alberta sawmills, in winter and in summer (n = 213). Exposures were considered in light of an estimated "real world" noise reduction rating (NRR) calculation assuming use of conventional hearing protection. Limited comparisons were made with spot area monitoring data. Only 10% of the personal monitoring measurements were below the Alberta 8-hr exposure limit of 85 dBA. Twenty-seven percent of the personal monitoring measurements were 95 dBA or higher. Worker enclosures played a large role in reducing noise exposure. There were no significant differences between seasons in noise category distributions (P = 0.61). The planermen and planer infeed operators had the highest percentage of personal monitoring measurements 95 dBA or higher (62% and 82%, respectively). Based on a conservative formula, a risk of excess noise exposure could exist even when wearing required hearing protection due to very high noise levels found in planing operations in sawmills.

Progressive noise induced hearing loss caused by hearing AIDS, a dilemma for the worker and the expert alike

Investigating cases of noise induced hearing loss the expert is often confronted with the situation that the hearing loss is progressive although the noise exposure has been reduced to almost non-damaging levels. Other causes such as age, hereditary deafness, head injuries, blasts, internal diseases can be excluded. Hearing aids as sources of damaging noise? By consulting the protocol of the hearing-aid acoustician and by own examinations the expert should obtain the following data: loudness level that yields best discrimination score of speech; level of discomfort for tones and speech, discrimination score that is achieved under free field condition with a speech level of 65 dB, using the hearing aids. Furthermore he should explore the circumstances under which the hearing aids are used: how many hours per day, at what occasions etc.? It is likely that in using the hearing aids they are adjusted to emit an intensity level identical to the one yielding the optimal discrimination score. If this e. g. is 100 dB and the hearing aids are used for 2 hours per day this would be equivalent to an exposure to industrial noise of 94 dB (A) for 8 hours daily without ear protection. Among all individuals working under industrial noise exposure today only about 1 - 2 % having unusually vulnerable inner ears will suffer a noise induced hearing loss. On the other hand workers in industrial noise are accustomed to loud noise levels, usually have a raised threshold of discomfort and therefore are likely to adjust their hearing aids to such high intensities. The expert will have to decide whether in an individual case the industrial noise exposure or the use of the hearing aids is the dominant risk for further damage. The consequences in respect to the regulations of the workers' health insurance are discussed.

Effects of industrial noise exposure on distortion product otoacoustic emissions (DPOAEs) and hair cell loss of the cochlea – long term experiments in awake guinea pigs

Distortion product otoacoustic emissions (DPOAEs), a sensitive detector of outer hair cell (OHC) function, cochlear microphonics (CM), and hair cell loss have been monitored in 12 awake guinea pigs before and after 2 h exposure to specific, played-back industrial noise (105 dB SPL maximal intensity). All animals had stable DPOAE levels before noise exposure. In the first hours after noise exposure DPOAE levels were reduced significantly. In about 70% a partial recovery of the DPOAEs was found within 4 months after noise exposure. In 16% of the investigated ears no recovery of DPOAEs was observed. However, in a few ears increased DPOAEs were observed after noise exposure. Exposure to industrial noise caused both morphological changes in the middle turns of the cochlea and electrophysiological changes in the middle frequency range. A close correlation existed between reduced DPOAE levels, loss in CM potentials, and area of damaged or lost OHCs, but not with the numbers of damaged or lost OHCs in the cochlea. It can be concluded that continuous industrial noise causes a damage to OHCs which differs form the damage caused by impulse noise.

Noise exposure, hearing loss, and hearing conservation in the construction industry

Workers in certain sectors of the construction industry incur more noise-induced hearing loss than in most other trades. This paper reviews data on noise exposure and hearing loss in the construction industry, gathered mainly in Washington State, British Columbia, Canada, and Sweden. The problem of worker mobility, where temporary employment is typical even for unionized workers, has hampered the implementation of effective hearing conservation programs in the construction industry. Solutions to this problem include a central repository for audiometric test results and information on training and noise control programs. Multiemployer benefit programs concerning health insurance and pensions provide models in the United States. A hearing conservation program specific to construction noise has been successfully implemented in British Columbia, with a resulting decrease in the incidence of noise-induced hearing loss.

Occupational noise and solvent exposure in the printing industry

The study examined the effects on hearing from occupational noise and solvent exposure in the printing industry and was conducted by measuring a selection of workers’ daily noise dose, sampling personal solvent exposures and audiometric testing before and after shifts for the detection of a hearing threshold shift. Audiometric test results were inconclusive due to the inadequate testing areas provided at each workplace. Personal monitoring confirmed that where solvent exposure occurs, high noise levels are usually also present. Fifty-three percent of the noise dose level measurements exceeded the statutory limit LAeq,8h of 85 dB and a further 9% exceeded the limit of 140 dB (Lin). Twenty-two percent of the analyzed solvent exposure samples revealed benzene, with 5% exceeding the worksafe exposure standard of 16 mg/m3. The lack of essential information contained in Material Safety Data Sheets (MSDSs) for substances used in the printing industry was highlighted. Accurate MSDSs are required to assist employers in discharging their obligation to provide correct information about hazardous substances to employees under the Workplace Health and Safety Act of 1995, as well as the hazards associated with those substances. Better information is required in an MSDS, from manufacturers and suppliers, as to the specific properties and health hazards of a hazardous substance.

Types and frequencies of abnormal sound levels when using noise dosimeters to establish worker TWAs

The potential contamination of noise dosimetry noise exposure findings as impacted by the following types of artifacts was investigated: thumping of the microphone, moving the microphone around during the sample, hollering directly into the microphone, effects of body reflections, and blowing directly at the microphone. The findings from this investigation support the assumption that contamination of noise dosimetry daily noise exposure results is not of significant concern, at least when using a 5-dB exchange rate (OSHA). In addition, the detailed histogram records obtained from conducting noise dosimetry noise exposure surveys at five large industrial facilities were reviewed. Of the over 28 000 histogram samples reviewed, less than 14 samples indicated potential contamination from unusual noise sources. In summary, the results of this study confirm what the authors have observed over many years of conducting industrial noise exposure studies using noise dosimetry: contamination of noise dosimetry findings is not a significant issue (at least when a 5-dB exchange rate is utilized).

The effects of chronic industrial noise exposure on urinary cortisol, fatigue and irritability: a controlled field experiment.

This quasiexperimental field study explored the effect of noise attenuation on urinary cortisol excretion (sampled three times, at 6:30 and 10:30 AM and 1:30 PM) and reported fatigue and postwork irritability among 35 healthy industrial workers chronically exposed to high ambient noise levels (> 85 dB [A]) without using ear protectors. The results indicated that under conditions of chronic noise exposure the cortisol level at the end of the workshift was high and almost reached the morning level. This elevation in cortisol excretion was accompanied by high levels of accumulated fatigue and postwork irritability. Attenuating the noise reaching the eardrum by 30 to 33 dB, by fitting the same workers with earmuffs for a period of 7 working days, resulted in a significant improvement in both psychological and physiological stress reactions. Besides decreasing noise intensity, no other changes were made, either to ongoing work activities or to the other characteristics of the ambient noise. The cortisol level declined steadily during the workshift and exhibited the normal cortisol diurnal rhythm. At the end of the workshift, this level was significantly lower (P < .05) than that observed under the chronic noise-exposure condition. There was also a concomitant reduction in reported fatigue (P < .05) and postwork irritability (P < .01). These findings demonstrate the "net" contribution of ambient noise to elevating stress reactions to regular work demands.

Temporary Threshold Shift and Otoacoustic Emissions after Industrial Noise Exposure

The objective of the present study was to investigate whether employees in a noise-exposed environment developed changes in cochlear function as manifested by elevation of pure-tone threshold and/or reduction in transient evoked otoacoustic emission (TEOAE) amplitude. Pure-tone air-conduction audiometry, otoacoustic emissions (OAEs) and tympanometry were recorded in 13 healthy employees on three consecutive days both before and after 7 h of noise exposure. Employees exposed to an industrial noise level of 85-90 dBA developed significant pure-tone air-conduction threshold elevation at 4 and 6 kHz. A significant reduction of the TEOAE amplitude was found. There was no correlation between temporary threshold shift (TTS) and TEOAE reduction.

Industrial Noise Exposure and Ambulatory Blood Pressure and Heart Rate

Studies on the effects of long-term exposure to industrial noise on resting blood pressure have yielded inconsistent results. Ambulatory blood pressure and heart rate were monitored simultaneously with noise exposure in normotensive male industrial workers in Israel (85 aged 25 to 44 and 77 aged 45 to 65 years). In the younger group, average ambulatory systolic blood pressure was 3.2 mm Hg higher and diastolic blood pressure 2.3 mm Hg higher in subjects exposed to more than 85 dBa (P less than .001), after adjusting for potential confounding variables. In those aged 45 to 65, ambulatory systolic blood pressure was 3.3 mm Hg lower and diastolic blood pressure unchanged in noise-exposed subjects. Ambulatory heart rate was 2.7 and 2.6 beats per minute higher at the higher noise level (P = .002) in the respective age groups. These findings suggest that industrial noise exposure is associated with higher ambulatory blood pressure and heart rates in men under 45 years old, but the effect on blood pressure appears to diminish considerably with age.

Field studies: Industrial exposures

The databases and models for the prediction of noise-induced permanent threshold shift (NIPTS) from industrial noise exposures are reviewed. Models available in 1973, compared with later models and data, are shown still to be reasonable. The effect of hearing conservation procedures on the acquisition of new data is discussed. Because of the impact of hearing conservation, new research focus is recommended in three areas: sex differences, newly hired individuals exposed for the first time in occupational noise, and the contribution of nonoccupational noise through the use of questionnaires and dosimetry.

Hearing Compensation Evaluation

Compensation claims for hearing loss are increasing. Physicians and audiologists supply necessary information regarding probable cause and amount of loss for evaluating these claims. Compensable hearing loss can arise from several sources. The principal activity has been claims based on industrial noise exposure. Compensation evaluation is considered as a consequence of noise-induced hearing loss, but the evaluation procedure is applicable regardless of the cause of hearing loss.