The effectiveness of hearing protective devices. An epidemiologic method for assessing the effectiveness of hearing conservation programs using audiometric data. Active noise reduction in aviation helmets during a military jet trainer test flight. A study of hearing changes among military conscripts in the Swedish Army. The impact of hearing conservation programs on incidence of noise-induced hearing loss in Canadian workers. The difference in protection efficiency between earplugs and earmuffs. An investigation performed at a workplace. An evaluation of hearing conservation program--a five-year longitudinal study. The effect of long term use of hearing protectors in industrial noise. Use of historical data and a novel metric in the evaluation of the effectiveness of hearing conservation program components. Hearing conservation programs (HCPs): the effectiveness of one company's HCP in a 12-hr work shift environment. Noise exposure and hearing conservation in U.S. coal mines--a surveillance report. Five-year follow-up study of hearing loss at several locations within a large automobile company. A controlled investigation of in-field attenuation performance of selected insert, earmuff, and canal cap hearing protectors. A multi-component intervention to promote hearing protector use among construction workers. Use of comparison populations for evaluating the effectiveness of hearing loss prevention programs. An evaluation of the effectiveness of two different insert types of ear protection in preventing TTS in an industrial environment. Efficacy of enforcement in an industrial hearing conservation program. Hearing conservation program for agricultural students: short-term outcomes from a cluster-randomized trial with planned long-term follow-up. An evaluation of the U.S. Air Force's detailed follow-up audiometric examination program. Effect of daily noise exposure monitoring on annual rates of hearing loss in industrial workers. Changes over time in audiometric thresholds in a group of automobile stamping and assembly workers with a hearing conservation program. Early indicators of hearing conservation program performance. Noise attenuation of communication hearing protectors against impulses from assault rifle.
The effectiveness of a hearing conservation program, and specifically the effectiveness of hearing protection devices (muffs in this case), was investigated over a five-year period, since the inception of the program at a major plant of the Ingersoll-Rand Company. The study concentrated on three groups (Class I, II, and III) of 213 employees whose noise level exposure did not change during the five-year study period. A hearing conservation criterion of 90dBA was utilized. One group consisted of office workers in which the level was well below this, a second group from a machine shop in which the level was slightly below the criterion, and a third group from foundry areas in which the levels were considerably above the 90dBA level. Personal ear protection was worn during the study period only by the last group. The mean differences in hearing levels were insignificant and were essentially the same in the three groups, at each frequency, and regardless of the baseline hearing thresholds. It is apparent that there were no significant changes in hearing threshodls during the study period among a non-noise exposed group; a mild to moderate noise-exposed group; and a group exposed to high levels of steady state noise, but wearing ear protectors. These results indicate that a hearing conservation program which includes audiometric testing and personal ear protection, utilizing a hearing conservation criterion of approximately 90dBA, does adequately protect the hearing of noise-exposed workers. A hearing conservation program (HCP) must include audiometric monitoring. In keeping with this requirement, enormous bodies of audiometric data have been accumulated. However, only a limited number of methods are available for using audiometric data to assess HCP effectiveness. This study illustrates an epidemiologic method. The risk of developing hearing loss (measured by the standard threshold shift) was compared between study and reference populations using the risk ratio. The study population had an increased risk of nearly 3-fold. Epidemiologic risk comparison methods, using reference populations, offer an alternative to current methods for HCP evaluation using audiometric data. Cockpit noise measurements were carried out in a two-seat jet trainer. For the continuous time and frequency analyses a two-channel tape-recording system was constructed of two miniature microphones connected through an amplifier to a digital tape-recorder. The analysed and averaged noise exposure including radio communication was 80-81 dB when the ANC system was on and 84-89 dB when the ANC system was off. For the conventional flight helmet the same noise exposure was 86 dB, and the noise exposure in the cockpit was 104-106 dB. The effect of the ANC system on the averaged noise exposure (L(Aeq8min)) was an improvement of 4-8 dB over the noise attenuation of the same helmets when the ANC system was off. Both ANC systems worked properly during the test flights. No severe ringing or voice circulation was found except during extreme vibration. The aim of the study was to investigate the incidence and the relative risk of significant threshold shift (STS, >or=15 dB deterioration at any ear and audiometric frequency) during primary military service (7-9 months), and to investigate whether subjects with an initial slight hearing loss (thresholds>or=25 dB HL at any audiometric frequency and ear) were under increased risk. The investigation was made as a prospective audiometric study and included 747 men. An age-matched group of 138 individuals served as an unexposed control group, whose incidence of STS was 2.9%. In the exposed group the incidence was 7.9% and the relative risk 2.7 risk ratio (RR). In the subgroup of 95 persons, who already at reporting-for-training had a mild hearing loss, the incidence was 17%. The relative risk for STS in this group compared to the control group was 6.8 (RR), and compared to those with normal hearing at reporting was 3.1 (RR). In spite of hearing conservation efforts, hearing deterioration still occurs, above all in the artillery. Those who already at reporting-for-training had a mild hearing loss were at higher risk for STS compared to those with initially normal hearing. Noise exposure remains one of the most ubiquitous of occupational hazards. Hearing conservation program legislation and the programs themselves were designed to lower risk of resulting occupational noise-induced hearing loss, but there has been no broad-based effort to assess the effectiveness of this policy.
                The incidence of a 10-dB standard threshold shift was examined in a group of Canadian lumber mill workers, using annual audiogram series obtained from the Workers' Compensation Board of British Columbia for the period 1979-1996 and using Cox proportional hazard models.
                Mean cumulative noise exposure was 98.1 dB-years. The audiograms from 22,376 individuals, among whom there were 2,839 threshold shifts of 10 dB or greater (i.e., a "standard threshold shift"), were retained in multivariable analyses. After adjusting for potential confounders, continuous use of hearing protection, and initial hearing tests later in the study period, the risk for standard threshold shift was reduced by 30%. Risk increased sixfold, however, in those with the highest noise exposure.
                Hearing conservation programs may be effective in reducing overall incidence of hearing loss. In the absence of noise control at source, however, highly exposed workers remain at unnecessary risk.
                Copyright 2008 Wiley-Liss, Inc. The hearing thresholds of shipyard workers have been measured with a Békésy sweep audiometer. The number of employees at different workplaces is so large that it is possible to select groups of workers of specified ages who have been employed by the shipyard for many years. These workers have used either earplugs of earmuffs for 5--10 years and have also been working all the time in almost the same noise environment. Three ways of investigation have been used to observe differences in the hearing levels between 'plug-men' and 'muff-men'. All three show a greater hearing impairment for 'muff-men' than for 'plug-men'. Under certain conditions earplugs provide the most effective protection although the attenuation is higher for earmuffs than for earplugs. nan nan To evaluate the effectiveness of hearing conservation programs (HCP) and their specific components in reducing noise-induced hearing loss (NIHL).
                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.
                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.
                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. An existing hearing conservation program (HCP), originally designed when an 8-hr work shift schedule was in effect, was evaluated at a plant site where a 12-hr work shift schedule is now utilized. The study included the following phases: a noise analysis of the work environment, HCP evaluation through the use of audiometric data base analysis (ADBA), applying ADBA procedures and a comparison of the shift in hearing threshold levels (HTLs) for the 8-hr and 12-hr work shifts, and an evaluation of the hearing protection devices (HPDs) being used at the facility over the 12-hr work shift by measuring temporary threshold shift (TTS). The mean measured employee time-weighted average (TWA) in the process area where the TTS study was conducted was 92 dBA. It was found that the existing HCP is at best marginal. The most likely causes of this less-than-desirable rating are inadequate audiometric testing procedures and inadequate HPD utilization. Furthermore, it was concluded that, at this time, the introduction of the 12-hr work shift has had no impact on the level of effectiveness of the HCP. In evaluating the three HPDs in use at the facility (3-M foam earplug, E-A-R foam earplug, and Bilsom Soft earplug), it was found that they all offered effective protection from noise at all audiometric test frequencies (0.5 to 6 kHz) except 0.5 kHz. All three HPDs exhibited TTS at 0.5 kHz with the TTS measured significant at the p less than 0.05 level for the E-A-R and 3-M wearer groups. This study examines the patterns and trends in noise exposure documented in data collected by Mine Safety and Health Administration inspectors at U.S. coal mines from 1987 through 2004. During this period, MSHA issued a new regulation on occupational noise exposure that changed the regulatory requirements and enforcement policies. The data were examined to identify potential impacts from these changes. The overall annual median noise dose declined 67% for surface coal mining and 24% for underground coal mining, and the reduction in each group accelerated after promulgation of the new noise rule. However, not all mining occupations experienced a decrease. The exposure reduction was accompanied by an increase of shift length as represented by dosimeter sample duration. For coal miners exposed above the permissible exposure level, use of hearing protection devices increased from 61% to 89% during this period. Participation of miners exposed at or above the action level in hearing conservation programs rapidly reached 86% following the effective date of the noise rule. Based on inspection data, the occupational noise regulation appears to be having a strong positive impact on hearing conservation by reducing exposures and increasing the use of hearing protection devices and medical surveillance. However, the increase in shift duration and resulting reduction in recovery time may mitigate the gains somewhat. This longitudinal epidemiologic study was designed to investigate hearing loss over a 5-year period among noise-exposed employees of a large automobile company and to assess effectiveness of hearing conservation programs at locations representing the spectrum of operations (assembly, light manufacturing, heavy manufacturing and machining, metal fabrication, and founding). Based on computerized audiometric test data, the study summarizes methodology developed for measuring occupational hearing loss and its application in evaluating programs at these locations, which had maximal 8-hr time-weighted average (TWA) noise exposures ranging from 104 to 110 dB(A). Methods presented here provide for consideration of age and hearing level of study subjects at baseline audiogram and clearly demonstrate the extent of hearing loss during the study period. Among five study locations, the average hearing loss at 2,000-4,000 Hz in the worst-loss ear ranged from 3.4 to 6.2 dB over the follow-up period; after adjustment for presbycusis, the loss was less than 2 dB at all but one location, which showed a loss of nearly 4 dB. In comparison to a control group of nonnoise-exposed employees, hearing conservation programs at four of the five locations were judged to be effective. One location, a metal fabrication plant with a large percentage of employees having an 8-hr TWA noise exposure over 90 dB(A), was particularly noted for the effectiveness of its program. A field study assessed the actual spectral noise attenuation achieved by 40 industrial workers wearing four different hearing protection devices (HPDs) while on the job. The effect of two different HPD fitting procedures (subject fit vs. trained fit) on attenuation performance over two three-week periods of protector use was determined. Subjects were retrieved from their workplaces without prior knowledge of when they were to be tested and were not permitted to readjust the fit of their HPDs. Attenuation data were then collected using psychophysical procedures testing real ear attenuation at threshold. Statistical analyses indicated that the earplugs' attenuation significantly improved when training for proper fitting was used, whereas the earmuff and the ear canal cap were relatively insensitive to the training effect. The training was most effective for a slow-recovery foam plug over the three-week period. Results confirmed that laboratory protocols designed to simulate workplace influences on attenuation may not be relied on to yield reasonable estimates of field protection performance of HPDs, particularly for earplugs; however, the laboratory results were much better predictors of field protection for the earmuff. This study also demonstrated that the labeled manufacturers' noise reduction ratings (NRRs) substantially overestimated the actual field attenuation performance. 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. One approach for evaluating the effectiveness of Hearing loss prevention programs (HLPPs) is to compare the rate of hearing loss in a study population with that in a reference population. This approach was used to evaluate the HLPP of a population of 14,900 employees of an industrial company with branches across the United States. Three reference populations were selected from a database of 22 industrial companies compiled under the sponsorship of the National Institute for Occupational Safety and Health. The risk of hearing loss in the study population was estimated relative to each of the three reference populations using the Cox proportional hazards model after adjustment for race, age at baseline, and hearing threshold at time of enrollment in the HLPP. In comparison with the three reference populations, hearing loss was 2.1 to 3.9 times more likely to occur in study population males and 1.8 to 5.1 times more likely in study population females. The 95% confidence interval around each risk estimate precluded unity, indicating that each risk estimate was statistically significant. These results indicate that the performance of the subject HLPP needs improvement. This study demonstrated the use of comparison populations for evaluating the effectiveness of HLPPs. The effectiveness of a V-51R insert hearing protector in preventing daily temporary threshold shifts in one industrial environment where the employees were exposed to an A-weighted energy average noise level of 95.6 dB was investigated. For comparison purposes the E-A-R Plug Insert hearing protector was also evaluated. The results indicated that the employees who wore the V-51R design incurred significant daily shifts in their hearing levels as compared to their initial hearing exam and significantly greater shifts than the employees who wore the E-A-R Plugs. The greater than expected measured shifts in hearing levels over the past six years in the two departments investigated is attributed at least partially to the use of the V-51R design. Relative efficacy of various levels of enforcement in the use of personal hearing protective devices was investigated among employees of a large industrial plant. The main variable was that each of four groups of employees worked during a different period of enforcement policy on the use of personal hearing protection. Analysis of variance of mean hearing levels using three different audiometric grading schemes with different levels of sensitivity, namely, the 0.5, 1, 2 kHz Hearing Level Index, the 1, 2, 3 kHz Hearing Level Index, and the 4000 Hz single puretone test indicate that the enforcement policy did have a dramatic effect on the efficacy of the hearing conservation program and should give similar results in other industrial settings. When and where the use of personal hearing protection was left to the employee it was found that hearing loss among the noise-exposed was very much in excess of that among a non-noise-exposed group. Mandatory use of personal protective devices was found to be much more effective in conserving hearing that the voluntary approach. Mandatory use of earmuffs exclusively proved to be less effective than mandatory use of personal hearing protection when the employee was given a choice of earmuffs or earplugs. Enactment of the Occupational Safety and Health Act did not result in greater hearing conservation over the existing company mandatory hearing conservation program which is quite effective. (1) To conduct a contemporary analysis of historical data on short-term efficacy of a 3-year hearing conservation program conducted from 1992 to 1996 in Wisconsin, USA, with 753 high school students actively involved in farm work; (2) to establish procedures for assessment of hearing loss for use in a recently funded follow-up of this same hearing conservation program cohort.
                We analyzed a pragmatic cluster-randomized controlled trial, with schools as the unit of randomization. Thirty-four rural schools were recruited and randomized to intervention or control. The intervention included classroom instruction, distribution of hearing protection devices, direct mailings, noise level assessments, and yearly audiometric testing. The control group received the audiometric testing.
                Students exposed to the hearing conservation program reported more frequent use of hearing protection devices, but there was no evidence of reduced levels of noise-induced hearing loss (NIHL).
                Our analysis suggests that, since NIHL is cumulative, a 3-year study was likely not long enough to evaluate the efficacy of this intervention. While improvements in reported use of hearing protection devices were noted, the lasting impact of these behaviors is unknown and the finding merits corroboration by longer term objective hearing tests. A follow-up study of the cohort has recently been started. The authors used information on individuals demonstrating permanent threshold shifts contained in the United States Air Force Hearing Conservation Data Registry to evaluate the effectiveness of detailed follow-up audiometric examinations as part of the USAF Hearing Conservation Program. Analysis yielded a relative risk of 1.00 with a 95% confidence interval of 0.97-1.03, which indicates a high probability that the true effect of these audiograms on the results of the next annual exam is minuscule, if not zero. 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.
                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.
                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).
                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. Noise induced hearing loss (NIHL) is among the 10 leading occupational diseases, afflicting between 7.4 and 10.2 million people who work in noise above 85 dBA. Although mandatory hearing conservation programs (HCPs) have been in effect since 1972, this problem persists, as hearing protectors are not consistently used by workers, or may not attenuate to manufacturer's estimates in real world conditions. In this study, information from noise and hearing protection use measurements taken at an automobile assembly plant were used to construct average lifetime noise exposure and hearing protection compliance estimates for use in modeling to predict both total hearing loss and onset of two accepted definitions of hearing loss. There were 301 males and females in this cohort; their mean age was 42.6 (7.2) years, and mean tenure was 14.3 (3.5) years. Average length of follow-up was 14.0 years. There were 16 members of this cohort who had hearing loss at the speech frequencies (defined as an average hearing level > or = 25 dB at 500, 1000, and 2000 Hz). In cross-sectional multivariate analyses, years of employment, male gender, and proportion of time wearing hearing protection were the factors most associated with hearing loss at the average of 2000, 3000, and 4000 Hz (p < 0.0001) controlling for age, transfer status (as a surrogate for previous noise exposure), race, and lifetime average noise exposure. The most consistent predictor of hearing loss in both univariate and multivariate analyses was percentage of time having used hearing protection during the workers' tenure. Retrospective analysis of initial audiograms from 21 hearing conservation programs (HCPs) revealed several statistical protocols capable of identifying HCPs of known performance. American National Standards Institute (ANSI) and Occupational Safety and Health Administration (OSHA) protocols clearly identified 3 HCPs known to have demonstrated excellent overall programs. ANSI and OSHA outcomes appeared equivalent in ability to provide early warnings of potentially unacceptable HCP practices. The noise attenuation values of commercial and military versions of earmuffs were measured using a Finnish assault rifle (RK762) as the sound source. The C-weighted peak level at the entrance of the left ear of the shooter was 156 dB (SD 1.0 dB; n = 25 shots). The noise was analyzed both outside and inside ear muffs on military volunteers on an open shooting range. All the earmuffs attenuated the C-weighted peak level to a value of less than 135 dB, which is less than the proposed values recommended by hearing damage criteria. Communication hearing protectors seem to function and attenuate sufficiently against the peak levels of the impulse noises used in this study.
There is low quality evidence that implementation of stricter legislation can reduce noise levels in workplaces. Even though case studies show that substantial reductions in noise levels in the workplace can be achieved, there are no controlled studies of the effectiveness of such measures. The effectiveness of hearing protection devices depends on training and their proper use. There is very low quality evidence that the better use of hearing protection devices as part of HLPPs reduces the risk of hearing loss, whereas for other programme components of HLPPs we did not find such an effect. Better implementation and reinforcement of HLPPs is needed. Better evaluations of technical interventions and long-term effects are needed.