Distribution of risk factors for hearing loss: implications for evaluating risk of occupational noise-induced hearing loss

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

Noise exposure and hearing conservation for farmers of rural Japanese communities

Agricultural mechanization in Japan has progressed dramatically since 1955 with the introduction of tractors, harvesters, and processing machines. These technological developments have resulted in an increase in exposure to sources of noise that are not only annoying, but damaging to hearing. The present study was undertaken to determine, whether Japanese farmers are at risk for noise-induced hearing loss in comparison with office workers, and by evaluating the present conditions regarding occupational noise levels among agricultural workers.The results suggest that farmers, especially male farmers, have a high prevalence of hearing loss in the higher frequency ranges. Daily noise exposure levels in L_Aeq ranged from 81.5 to 99.1 dBA for tea harvesting and processing, and from 83.2 to 97.6 for sugar cane harvesting. Taking into account their rather long working hours and excessive noise from farm machinery, it is concluded that farmers are at risk for noise-induced hearing loss. These findings clearly indicate a strong need for implementation of hearing conservation programs among agricultural workers exposed to machinery noise.     

Road traffic noise exposure in residential complexes built at different times between 1950 and 2000 in Hong Kong

This paper attempts to determine the exposure of the urban population to road traffic noise living in residential complexes built at different times between 1950 and 2000 in Hong Kong. Noise exposure was estimated at the residents’ dwelling, neighborhood and community by noise mapping. The purpose of the study is to find out if the noise exposure levels of these residential complexes have improved as a result of stepped up noise control and reduction efforts. A total of 212 residential complexes built at different times, by the government and private sector in different districts, were selected for noise assessment. The results show that, compared to private housing, public housing estates are generally exposed to less road traffic noise. The study has also found that, over the 50-year period, the dwelling noise exposure levels of the recently built residential complexes are lower than the older ones, showing some improvement over time. This is particularly more noticeable at the high exposure end. There is however only some small differences in noise level between recent and old developments at the community scale both for public and private housing estates.     

Noise exposure from leisure activities: a review

Over the past two decades there has been increasing concern about the role of nonoccupational, or leisure noise on hearing. This paper reviews published studies that detail the noise levels and potential effects of some noisy leisure activities. Considered are the most common sources of leisure noise: exposure to live or amplified rock, classical, or jazz music; exposures from personal listening devices ("walkman" type); noise around the home, and hunting and target shooting. Although all activities listed above have the potential for dangerous levels of noise exposure, the most serious threat to hearing comes from recreational hunting or target shooting.     

Industrial noise levels and annoyance in Egypt

Annoyance and increase of accident risk of workers from industrial noise levels in Egypt were studied. 683 workers from 15 Egyptian sites of industry, ranging from food to metal industry were evaluated. The goals of this study are to carry out measurements to evaluate industrial noise levels, are these levels exceeded the permissible levels set by Egyptian noise standard and policy to protect public health of workers?, to examine worker’s attitudes towards industrial noise, to know the relationship between industrial noise levels and degree of annoyance. Results showed that equivalent continuous noise levels ranged from 70 to 100 dB (A). Annoyance of respondents showed that 47.1% were highly annoyed, 5.8% their hearing were harmed. There was a strong relationship between industrial noise levels and percentage of highly annoyed respondents. By increasing industrial noise level possibility of workers to make accident was also increased. Respondents suggest less maximum daily exposure duration than those set by Egyptian law.     

Hearing loss from gun and railroad noise--relations with ISO standard 1999.

Pure-tone hearing thresholds and anamnestic data pertaining to nosocusis and exposure to gun noise were analyzed for 9778 male railroad train-crew workers. A major portion of losses in hearing sensitivity due to railroad noise are obscured in comparisons of hearing levels of trainmen with the hearing levels of the unscreened samples of United States males given in Annex B, ISO 1999 [ISO 1999 (1990), "Acoustics--Determination of occupational noise exposure and estimation of noise-induced hearing impairment" (International Organization for Standardization, Geneva)]. Comparisons of the hearing levels, adjusted for nosocusis, of trainmen who had used no guns, with the hearing levels of otologically and noise screened males (Annex A, ISO 1999) reveal significant losses due to railroad noise. Additional losses were found at high frequencies in trainmen who had used guns. It appears that the effective Leq8h exposure level of trainmen to railroad noise is about 92 dBA, and 87-89 dBA to gun noise. These results are in general agreement with those of study of railway workers by Prosser et al. [Br. J. Audiol. 22, 85-91 (1988)]. Asymmetries in losses between the two ears, effects of ear protection, losses from nosocusis, and losses from sport, as compared to military, gun noise exposures, are examined.     

Influence of source directivity on noise levels in industrial halls: Simulation and experiments

Noise exposure of workers in industrial halls is mainly induced by noisy machines whose acoustical features are often globally known by Sound Pressure Level. The evaluation of the directivity of these noise sources can help to anticipate specific solutions for noise reduction.This study shows how the directivities of three wood-working machines have been characterized. Some characterisations have been achieved with a simple and fast acoustical intensity mapping which meets the constraints of industrial areas.When source directivity is evaluated, its influence on the noise field in industrial halls can be assessed. Some simulations and some experiments allowed the estimation of the noise field induced in workshops by both directional and omnidirectional sources. Comparison of the fields prove that the noise distribution is influenced by the source directivity if the halls are empty. As soon as the halls contain scattering objects, the directivity effect is reduced a lot and the noise field remains nearly the same far from the source whatever source used. Nevertheless, workers close to a machine are exposed to noise according to their position with respect to the machine. Exposure at the workplace can vary from 4 to 8 dB(A) according to the directivity of machines such as those measured in the trials.     

Statistical evaluation of occupational noise exposure

Assessment of the risk involved in occupational noise exposure (L_EP,d) is significantly affected by assumptions and uncertainties in setting true exposure conditions meaning that the calculation according to the European legislation might not be fully representative.The paper describes a probabilistic model to evaluate occupational noise exposure and calculate the confidence interval for L_EP,d. This confidence interval is defined in function of the number of samples of both exposure time and equivalent noise level that must be taken in different areas of the work environment or for different operator tasks. The model determines the minimum number and the type of samples to obtain a confidence interval for L_EP,d which falls with the given level of precision entirely into the classes defined by 86/188/CEE Directive (and following 2003/10/CE Directive).Finally, the model has been applied (by means of a software tool implementing the model and developed by the authors) to a newspaper rotary press plant, where production is supervised by a team of workers that access the various parts of the plant (3 vertical levels) for regulation and/or maintenance.     

Design and preliminary results of an interdisciplinary field study on urban noise

Herein is described a field study on noise situations and their effects in Hamburg, West Germany. The three main subjects of study have been to identify common sources of urban noise and acoustically describe the exposure, to investigate the effects on humans of noise exposure and to make an evaluation of noise effects and compare different kinds of noise in regard to annoyance. As the study has not yet been completed, only preliminary results are set forth.     

The response to railway noise in residential areas in Great Britain

The effects of railway noise on residents have been measured with a combined social survey (1453 respondents) and noise measurement survey (over 2000 noise measurements) at 403 locations in 75 study areas in Great Britain. In the analysis of the data methods have been used which take into account many typical noise survey problems including noise measurement errors, unique locality effects and the weakness of the noise annoyance relationship. Railway noise bothers 2% of the nation's population. Approximately 170 000 people live where railway noise levels are above 65 dB(A) 24 hour L_eq. Annoyance increases steadily with noise level; thus there is no particular “acceptable” noise level. Railway noise is less annoying than aircraft or road traffic noise of equivalent noise level, at least above 50 to 65L_eq. Noise is rated as the most serious environmental nuisance caused by railways. Maintenance noise is rated as a bigger problem than passing train noise. Vibration is the most important non-noise problem. Reactions to vibrations are related to distance from route, train speed and number of trains. The railway survey's highly stratified, probability sample design with many study areas makes it possible to evaluate the effects of area characteristics on reactions. The 24 h L_eq dB(A) noise index is more closely related to annoyance than are other accepted noise indices examined. There is no support for ambient noise level or night-time corrections. Thirteen railway operation characteristics were examined. One, the type of traction, has a strong effect on reactions after controlling for L_eq (overhead electrified routes are the equivalent of about 10 dB less annoying at high noise levels). Three indicators of railway ancillary noises and non-noise environmental nuisances affect annoyance but most operational characteristics have no effect. The effects of over 35 demographic, attitudinal and neighbourhood characteristics on annoyance are examined. Though most objective characteristics of neighbourhoods and respondents are not correlated with annoyance, three do decrease annoyance (older dwellings, older respondents, and life-time residence). The attitudes which affect annoyance with railway noise are not general ones about railways as transportation sources, but rather ones which are specific to the neighbourhood setting or to railways as environmental intrusions in the neighbourhood. Such attitudes often have less effect on annoyance at low noise levels. In such cases it is the reactions of the more annoyed types of people which are most closely related to noise level.     

The effect of traffic noise on sleep of young adults in their homes

The disturbance of sleep by traffic noise is a major problem area in noise pollution. Extensive laboratory tests using multichannel electroencephalograms (EEG) have been carried out by many workers to determine the general response of people when exposed to noise during sleep. An experimental technique for obtaining results in people's homes has been developed using a simplified one-channel EEG. The responses of six people in the age range 19-24 were measured. A significant correlation was found between sleep disturbance and traffic noise when the noise is expressed in EPNdB. In the home experiments the subjects appeared to be approximately 10 dB less sensitive to noises than laboratory subjects for similar noise exposure. There also appeared to be some adaptation to the noise exposure; however, only one subject was tested for a period of 20 days and was insufficient to give definite results on adaptation.     

Relationship between exposure to multiple noise sources and noise annoyance

Relationships between exposure to noise [metric: day-night level (DNL) or day-evening-night level (DENL)] from a single source (aircraft, road traffic, or railways) and annoyance based on a large international dataset have been published earlier. Also for stationary sources relationships have been assessed. Here the annoyance equivalents model concerning noise annoyance from combined sources and the underlying assumptions are presented. The model first translates the noise from the individual sources into the equally annoying sound levels of a reference source, road traffic, and then sums these levels giving total level L. The annoyance from the combined sources is found by substituting exposure L in the road traffic exposure-annoyance relationship. The most important assumption, independence of the contributions of the sources, is discussed. It appears that independence will be violated substantially only due to the effect of the presence or absence of a quiet side of building which is not incorporated in the model. For use in practice the application of the model is broken down in five steps. The step by step procedure can be used for the assessment of the total noise level and the associated total annoyance on the basis of the DNL or DENL values of the individual sources.     

A snapshot of young adults’ noise exposure reveals evidence of ‘Binge Listening’

There have been several previous studies into daily noise exposure levels in modern urban communities, which typically report mean noise exposure levels (L_Aeq) for adults between 73 and 79 dB. In this study, rather than focus on group mean exposures across a wide age range, individual patterns of noise exposure over 4- and 5-day periods were examined in a group of 45 young adults aged 18–35 years. The main objective of the study was to determine the extent to which young adults exhibit a ‘binge listening’ pattern of noise exposure, i.e., high weekend leisure noise vs. low weekday work noise exposure. A secondary objective was to identify the types of activities that generate the highest noise exposures. The results showed that although most participants (60%) were exposed to low daily noise levels, 33% of participants exhibited a ‘binge listening’ exposure pattern characterized by one or two high-noise days, usually a Friday, Saturday or Sunday, preceded or followed by much quieter days. The most notable high-noise activities were playing an instrument solo or in a band; attending a nightclub; and attending a pop concert, each of which recorded average noise levels greater than 100 dB. Future research is needed to determine whether ‘binge listening’ is more or less harmful than the chronic exposure presupposed in traditional risk models, however, under the equal-energy principle, repeated ‘binge’ noise exposures from weekend visits to nightclubs, live music events and other high-noise events represent a significant risk to long-term hearing health.     

Selection of hearing protectors

A method for selection of hearing protectors based on attenuation and comfort is presented. For the attenuation, the data provided by the manufacturer are used after being derated. A protector is selected when its attenuation is higher than the measured (or calculated) noise exposure minus the criterion level set by regulations or legislation. When large numbers of workers are involved, group noise exposure and associated standard deviation are to be used.Comfort is assessed by using a specially developed questionnaire. Protectors are distributed to ten workers who have to wear them during an entire shift. The questionnaire is completed prior to and after wearing the protectors.     

Risk factors for hearing loss at different frequencies in a population of 47,388 noise-exposed workers.

Weighted regression analysis was applied to determine the dependence of the hearing thresholds of 47,388 noise-exposed workers on age, sex, noise immission level, ear disease, head injury, tinnitus, hearing protector usage, and audiometric frequency in the range from 0.5 to 6 kHz. It could be shown that the hearing thresholds at any frequency are dominated by the age of the worker and that women, after equivalent exposure conditions, hear better than men. The relative effects of sex, noise immission level, ear diseases, tinnitus, and hearing protector usage are related to the audiometric frequency. Users of hearing protectors at the last audiometric investigation hear worse than nonusers. Hearing protector usage is strongly related with the hearing threshold in the low-frequency range. The noise immission level does not noticeably affect the hearing threshold below 3 kHz. The most important frequency of the noise immission level is as expected 4 kHz. For 4 kHz, it was shown that the variables age, noise immission level, tinnitus, head injuries, and ear diseases act in a good approximation additively on the pure-tone hearing threshold.     

Nonoccupational noise: exposures associated with routine activities

Efforts to characterize nonoccupational noise exposures have focused primarily on infrequent, episodic events. Few studies have assessed noise levels resulting from routine daily activities. In the current study, 112 construction workers wore datalogging noise dosimeters and simultaneously completed activity logs during two phases of data collection. The 81 subjects monitored in phase 1 received logs listing numerous preselected occupational and nonoccupational activities, while the 31 subjects monitored in phase 2 used free-field logs and reported nonoccupational activities in greater detail. Nearly all of the 221,439 1-min intervals of nonoccupational L(eq) level and activity reporting were below 70 dBA; only a small percentage exceeded 80 dBA. The primary contributor to nonoccupational noise exposure was traveling in a car or bus, while time at home contributed the least. One hundred seventy 24-h L(eq) levels were computed from the 1-min noise level data. The percentage of phase 2 workday L(eq(24)) levels which exceeded 80 dBA was higher than that of the nonworkday levels. The mean L(eq(24)) level of phase 2 workdays was higher than that of nonworkdays, and the difference was statistically significant. Routine nonoccupational noise exposures contributed much less to total noise dose than occupational exposures in the subjects evaluated.     

Citizens’ perception of the efficacy of airport noise insulation programmes in Spain

Airport noise insulation programmes (NIPs) implement active measures for reducing the amount of noise to which people are exposed without impacting the operating capacity of an airport. This is the reason why they are one of the most extended actions adopted internationally by airport authorities to fight noise in airport surroundings.Beyond the assumption that a correct implementation of the NIP will significantly reduce sound exposure, this research aims to determine the efficacy of the NIP as a result of the beneficiaries’ subjective perception in terms of satisfaction, and the reduction of the reported annoyance.A telephone survey was carried out in more than 650 dwellings in the surroundings of several Spanish Airports (Alicante, Bilbao, Grand Canary, Malaga, Palma de Mallorca). The results have shown that: (a) the beneficiaries have a generally positive perception regarding the actions implemented, (b) they are quite satisfied regarding the insulation of the façades after NIP implementation, (c) they report a reduction of the annoyance, but (d) they still perceive aircraft noise as a source of disturbance.The statistical analysis of the results has also shown that there are some non-acoustic factors influencing citizens’ perception of NIPs. Factors such as the aesthetic of windows, or the reliability and professionalism of the workers and technicians involved in the NIP, have been shown to modify people’s reaction. But, the dissatisfaction with legal aspects of Spanish regulations concerning a lower protection of some practical spaces (like, bathrooms and kitchens that have been left out in many cases) has been found to be the factor most affecting people’s response.     

Recent studies of temporary threshold shift (TTS) and permanent threshold shift (PTS) in animals

It is well known that excessive exposure to noise results in temporary and/or permanent changes in hearing sensitivity in both human and animal subjects. The purpose of this review is to describe the major findings from laboratory studies of experimentally induced hearing losses, both temporary and permanent, resulting from exposure to noise in animal subjects which have been published since the report of Kryter et al. (1966). The data reviewed support the following general statements: (1) The chinchilla is the most widely used and most appropriate animal model for studies of noise-induced hearing loss; (2) with continuous exposures to moderate-level noise, thresholds reach asymptotic levels (ATS) within 18-24 h; (3) permanent threshold shifts, however, depend upon the level, frequency, and the duration of exposure; (4) below a "critical level" of about 115 dB, permanent threshold shift (PTS) and cell loss are generally related to the total energy in continuous exposures; (5) periodic rest periods inserted in an exposure schedule are protective and result in less hearing loss and cochlear damage than equal energy continuous exposures; and (6) under some schedules of periodic exposure, threshold shifts increase over the first few days of exposure, then recover as much as 30 dB as the exposure continues.     

Hearing and personality: A review

The personality of individuals has been shown to interact with their auditory system in a variety of ways. Subjects with different personalities may differ in their physiological responses to sounds, in their perception of sounds and in the way in which noise influences their performance of a variety of tasks. Severe deafness appears to influence the personality of patients, and fairly characteristic changes are found in specific auditory disorders. The annoyance caused by a variety of noises is influenced by the person's personality and in the past a noise annoyance scale has been used as a measure of neuroticism.