Use Of Earmuffs Research Articles

Effects of noise intensity on concentration levels of chainsaw operators and harvesting workers in industrial forest plantation, North Sumatera, Indonesia

Background Noise has the potential to affect the comfort and health of workers. The objective of this research was to determines the effects of noise on the concentration levels of both chainsaw operators and harvesting workers in industrial forest plantation, North Sumatra, Indonesia. Methods This experimental study included 20 respondents which consisted of 10 chainsaw operators/helpers and 10 harvesting workers. All respondents were exposed to the sound of a chainsaw in three different conditions (idle, half gas and racing conditions) with and without personal protective equipment (PPEs: earmuffs, ear plugs and without PPE). The sound intensity produced by the chainsaw and the noise received by the respondents were measured using a sound level meter. Respondents’ perception toward noise was recorded using a Likert scale. Respondents’ concentration level was assessed by giving 25 math-questions to be answered within 10 minutes. Wilcoxon sign rank test was used to analysed paired data. Results The average sound intensity received by respondents’ left and right ears were lower than the average sound intensity produced by the chainsaw. The use of earmuffs leads to better perception towards noise when compared with the use of earplugs and the absence of any PPE. Based on Wilcoxon test, the noise did not have significant impact on the concentration level of chainsaw operators, whilst the contrary result is true for harvesting workers. Conclusions The research indicated that although the noise produced by the chainsaw was considered noisy for both chainsaw operators and harvesting workers, it did not have a significant effect on the concentration level of chainsaw operators and only affected the harvesting workers. Therefore, given that the harvesting workers were still affected by the noise, noise control measures are still needed to ensure occupational safety and health for the workers.

Effects of noise intensity on concentration levels of chainsaw operators and harvesting workers in industrial forest plantation, North Sumatera, Indonesia.

Noise has the potential to affect the comfort and health of workers. The objective of this research was to determines the effects of noise on the concentration levels of both chainsaw operators and harvesting workers in industrial forest plantation, North Sumatra, Indonesia. This experimental study included 20 respondents which consisted of 10 chainsaw operators/helpers and 10 harvesting workers. All respondents were exposed to the sound of a chainsaw in three different conditions (idle, half gas and racing conditions) with and without personal protective equipment (PPEs: earmuffs, ear plugs and without PPE). The sound intensity produced by the chainsaw and the noise received by the respondents were measured using a sound level meter. Respondents' perception toward noise was recorded using a Likert scale. Respondents' concentration level was assessed by giving 25 math-questions to be answered within 10 minutes. Wilcoxon sign rank test was used to analysed paired data. The average sound intensity received by respondents' left and right ears were lower than the average sound intensity produced by the chainsaw. The use of earmuffs leads to better perception towards noise when compared with the use of earplugs and the absence of any PPE. Based on Wilcoxon test, the noise did not have significant impact on the concentration level of chainsaw operators, whilst the contrary result is true for harvesting workers. The research indicated that although the noise produced by the chainsaw was considered noisy for both chainsaw operators and harvesting workers, it did not have a significant effect on the concentration level of chainsaw operators and only affected the harvesting workers. Therefore, given that the harvesting workers were still affected by the noise, noise control measures are still needed to ensure occupational safety and health for the workers.

Noise Isolation System for Indoor Industrial Ventilation

The prevalence of hearing loss among workers in Ecuador is concerning, with up to 40% affected. One of the root causes is the lack of insulation in sources of noise generation. This study presents a practical solution to reduce noise contamination in indoor industrial facilities and to extend the usability of functional old equipment by enabling the addition of accessories, specifically in the sanding and classification areas of an agglomerate manufacturing industry. An isolation camera was designed and implemented using a combination of insulating materials to reduce the noise of a main ventilator and to ensure compliance with local noise regulations. The design and simulation were carried out using CAD tools and the finite element method (FEM) to ensure a simple assembly design, and the camera was manufactured using rapid prototyping tools with lightweight and cost-effective materials, such as wood, foam, and metal. The camera was tested in situ, and its effectiveness was evaluated through functional tests and noise level measurements. The implementation of the camera resulted in a 16% reduction in pressure noise and a 95% reduction in noise frequency. With the additional use of earmuffs, the pressure reduction improved to 44%. These values ensured that noise levels remained 27% below the limit set by Decree 2393, significantly reducing the impact of noise on workers.

Effects of Earmuffs and Eye Masks on Propofol Sedation during Spinal Anesthesia for Orthopedic Surgery: A Randomized Controlled Trial.

Intravenous sedative drugs are commonly administered during regional anesthesia. However, reducing the excessive use of sedatives while providing adequate sedation is important from the clinical perspective, since the use of sedatives can cause considerable complications. We hypothesized that the application of earmuffs and eye masks would help reduce the sedative dose required to maintain proper sedation by blocking external stimuli. Patients who underwent orthopedic surgery under spinal anesthesia were randomly allocated to the control (no intervention) or intervention group (wearing earmuffs and eye masks). Intravenous sedation was administered using target-controlled infusion of propofol. The target concentration was controlled to maintain a Modified Observer's Assessment of Alertness and Sedation score of 3 or 4. The primary outcome was the intraoperative propofol requirement. We also investigated the incidence of apnea, and patient satisfaction. Propofol requirement was significantly lower in the intervention group than that in the control group (2.3 (2.0-2.7) vs. 3.1 (2.7-3.4) mg·kg-1·h-1; p < 0.001). Intraoperative apnea occurred less frequently (p = 0.038) and patient satisfaction was higher (p = 0.002) in the intervention group compared to the control group. This study demonstrated that the use of earmuffs and eye masks during sedation was associated with lower propofol requirement and improved sedation quality.

Noise intensity and its impact on the perception and concentration level among forest harvesting workers in industrial forest plantation, North Sumatera, Indonesia

Background: Noise has the potential to affect the comfort and health of workers. The objective of this research was to find out the effect of noise caused by the timber harvesting process using chainsaws on the concentration of workers in an industrial forest plantation. Methods: This experimental study included 20 respondents which consisted of 10 chainsaw operators/helpers and 10 non-chainsaw operators. All respondents were exposed to the sound of a chainsaw in three different conditions (idle, half gas and racing conditions) with and without personal protective equipment (PPE). The sound intensity produced by the chainsaw and the noise received by the respondents were measured using a sound level meter. Respondents’ perception toward noise was recorded using a Likert scale. Respondents’ concentration level was assessed by giving 25 math-questions to be answered within 10 minutes. Wilcoxon sign rank test was used to analysed paired data. Results: The average sound intensity received by respondents’ left and right ears were lower than the average sound intensity produced by the chainsaw. The use of earmuffs leads to better perception towards noise when compared with the use of earplugs and the absence of any PPE. The Wilcoxon test result showed that noise did not have significant impact on the concentration level of chainsaw operators, whilst the contrary result is true for non-chainsaw operators. Conclusions: The research indicated that although the noise produced by the chainsaw machine was considered noisy for both chainsaw operators and non-chainsaw operator, it did not have a significant effect on the concentration level of chainsaw operators and only affected the non-chainsaw operators. Therefore, given that the non-chainsaw operators were still affected by the noise, noise control measures are still needed to ensure occupational safety and health for the workers.

Selection of Earmuffs and Other Personal Protective Equipment Used in Combination.

In a work environment, in addition to noise, people may be exposed to other harmful factors. Therefore, they wear both hearing protectors and other personal protective equipment (OPPE). Incorrect use of such a combination may increase the risk of hearing loss. The aim of this study was to determine whether the simultaneous use of earmuffs and other personal protective equipment could affect the effectiveness of hearing protection. The study was carried out under laboratory conditions using an acoustic test fixture. This fixture replicated the anatomical shapes of the head and the pinnae, and was also equipped with ear simulators. The study was carried out for five models of earmuffs and eight models of other personal protection equipment. We found that a change in the sound pressure level (SPL) under the earmuffs when using a full face respirator could reach up to 40 dB. On the other hand, the use of a half respirator had practically no adverse impact on the efficiency of hearing protection. In the selection process, it is recommended to consider safety spectacles equipped with thin temples, and half respirators equipped with band adjustment elements positioned on the facial part, rather than the back, of the user’s head.

A study of the real-world noise attenuation of the current hearing protection devices in typical workplaces using Field Microphone in Real Ear method.

Actual noise reduction of the earmuffs is considered as one of the main challenges for the evaluation of the effectiveness of a hearing conservation program. The current study aimed to determine the real world noise attenuation of current hearing protection devices in typical workplaces using a field microphone in real ear (FMIRE) method. In this cross-sectional study, five common earmuffs were investigated among 50 workers in two industrial factories with different noise characteristics. Noise reduction data was measured with the use of earmuffs based on the ISO 11904 standard, field microphone in real ear method, using noise dosimeter (SVANTEK, model SV 102) equipped with a microphone SV 25 model. The actual insertion losses (IL) of the tested earmuffs in octave band were lower than the labeled insertion loss data (p < 0.05). The frequency nature of noise to which workers are exposed has noticeable effects on the actual noise reduction of earmuffs (p < 0.05). The results suggest that the proportion of time using earmuffs has a considerable impact on the effective noise reduction during the workday. Data about the ambient noise characteristics is a key criterion when evaluating the acoustic performance of hearing protectors in any workplaces. Comfort aspects should be considered as one of the most important criteria for long-term use and effective wearing of hearing protection devices. FMIRE could facilitate rapid and simple measurement of the actual performance of the current earmuffs employed by workers during different work activities.

Attenuation of earmuffs used simultaneously with safety spectacles in exposure to impulse noise

Impulse noise is particularly hazardous to the hearing of exposed individuals. In many real-life scenarios, the only protective measure used to reduce the level of impulse noise is hearing protectors. These scenarios include firing ranges. Aside from hearing protectors, shooters use personal safety spectacles. The purpose of this paper was to determine the effect of the simultaneous use of earmuffs and safety spectacles on the sound attenuation of earmuffs during exposure to impact noise. The research was completed with the MIRE method and included the determination of sound attenuation changes in five different models of earmuffs, used simultaneously with three different models of safety spectacles and prescription glasses. The impulse noise source used was a starting pistol, which generated C-weighted peak sound pressure level at a mean of 136.7 dB. The tests demonstrated that the simultaneous use of safety spectacles and earmuffs reduces the impulse noise attenuation of the earmuffs by up to 9 dB. Such sound attenuation changes occurred during simultaneous use of earmuffs with safety spectacles, which feature temples with a rectangular cross-section. The tests also demonstrated that the effect of prescription glasses on sound attenuation was unusually high; prescription glasses reduced the impulse sound attenuation of earmuffs by as much as 18 dB. Keywords: acoustics, noise protection, impulse noise, hearing protectors, earmuffs, noise attenuation

Evaluating the effect of training along with fit testing on earmuff users in a Chinese textile factory

ABSTRACTA hearing protection fit testing was conducted on workers (n = 189) in a textile factory in southern China. The 3M E-A-Rfit Dual-Ear Validation System was used to measure the personal attenuation rating (PAR) on an over-the-head style earmuff at the work site. In addition, PARs were obtained several times throughout the same work shift to capture different fits on 39 workers. Follow-up visits were conducted in approximate 6-month or 12-month intervals to repeat the fit testing. Both the immediate and residual effects of training on the field attenuation of hearing protection devices obtained by workers, and the effects of training toward improving the attenuation and protection of earmuffs after a period of daily use, were observed. A questionnaire survey was used to assess the awareness of hearing health and motivation toward the use of earmuffs in a high temperature environment. The results showed that there were wide variations in PARs among the workers tested. The one-on-one training together with fit testing improved PAR and helped to reduce the negative impact caused by use of protective hair covers. Since earmuffs are often used for long periods of time (>1 year), repeating fit tests could be helpful in order to verify the attenuation received throughout their useful life.

The effectiveness of earmuffs on the physiologic and behavioral stability in preterm infants

BackgroundThe use of earmuffs can protect preterm infants against negative effects of high noise levels in the neonatal intensive care unit. This study was aimed at assessing the effectiveness of the earmuffs on the physiologic and behavioral responses in preterm infants. MethodsA crossed over controlled trial was conducted at Aliasghar Hospital (Tehran, Iran) in 2014. Thirty-six preterm infants cared in closed incubators, 18 cases wore a pair of silicon earmuffs in the first day and the others were worn it at the second day. During 2 consecutive days, all subjects were observed as their own controls (without earmuffs). Physiologic (body temperature, heart rate, respiratory rate, systolic, diastolic pressures, arterial Oxygen Saturation) and behavioral responses (according to the Anderson behavioral state scoring system) were assessed every 2 h for 8 h long during daytime for two consecutive days. ResultsThe application of earmuffs could decrease the rate of the heart and respiratory while could increase the amount of oxygen saturation (p < 0.05). The results also showed that the preterm infants with earmuffs had lower ABSS score and a better light sleep compared to those without earmuffs (2.38 ± 0.47 versus 4.8 ± 0.97, p < 0.05). ConclusionThe results indicated that using the earmuffs reduces the level of noise in NICUs following by improving the preterm neonates' physiological stability and behavioral states of ABSS.

Attenuation of earmuffs used simultaneously with respiratory protective devices

In the work environment, apart from the noise, employees may be exposed to other harmful factors. Therefore, they wear hearing protectors and other personal protective equipment. The aim of the study was to determine whether simultaneous use of earmuffs and respiratory protective devices affects the attenuation of earmuffs. The study was conducted in laboratory conditions using the subjective REAT (Real Ear Attenuation at Threshold) and objective MIRE (Microphone in Real Ear) methods. The REAT method was used to measure sound attenuation of earmuffs, while MIRE was used to determine changes in attenuation of earmuffs due to the use of other personal protective equipment. The study showed reduction in attenuation of earmuffs due to the use of a full face mask up to 20 dB. Using a full face mask causes that attenuation of earmuffs in the low frequency range is close to zero. Reduction in attenuation due to the use of half masks for complete with particle filters (half masks) is 3-15 dB. Simultaneous use of earmuffs and filtering half masks makes small changes in attenuation not exceeding 3 dB. The study showed that full face masks give the greatest reduction in attenuation of earmuffs. On the other hand, the least reduction is observed in the case of filtering half masks. There is a significant difference between the reduction in attenuation of earmuffs worn with half masks for complete with particle filters because they may be equipped with different kind of the head strap. Med Pr 2017;68(3):349-361.

Directivity of hearing of auditory danger signal emitted by overhead crane.

The objective of the research has been to provide an answer to the question of what the possibilities of determining the direction of approach of the auditory danger signal emitted by an overhead crane appropriately are. Cases of use and no use of earmuffs (in the passive mode and level-dependent ones) were all taken into consideration. The auditory danger signal and ambient noise were recorded in an industrial hall. Signals were reproduced at an experimental set-up, using a large number of speakers. Eight speakers for reproduction of the auditory danger signal were placed above a subject's head. The study participants would indicate the direction from which, according to them, the auditory danger signal was being emitted. The average percentage rate of the correct localization amounted to 75.8% when the overhead crane's signal wasn't masked. The presence of ambient noise caused a reduction of the number of correctly identified localization to 66.6%. The use of earmuffs in the passive mode resulted in the worst results (44.5%). There is some improvement when level-dependent earmuffs are used (57.3%). In situations where it is important to identify the direction from which the auditory danger signal generated by the crane's signaling device is approaching, it is beneficial to use level-dependent earmuffs rather than earmuffs in the passive mode. Correct identification of whether the auditory danger signal generated by the crane's signaling device is approaching from the left or right side is almost perfect, however correct identification of whether the signal is approaching from the front or back of a person is not always possible. Med Pr 2016;67(5):589-597.

The effects of noise reduction by earmuffs on the physiologic and behavioral responses in very low birth weight preterm infants

ObjectivePreterm infants are exposed to loud noises during their stay in the neonatal intensive care unit which can lead to physiologic and behavioral alterations and even hearing loss. The use of earmuffs can reduce sound level and these changes. The objective of the present study is to evaluate the effectiveness of the earmuffs in preterm infants solely cared for in closed incubators. MethodsA comparative prospective study comprising 20 clinically stable preterm infants weighing less than 1500g cared in closed incubator was conducted. Preterm infants acted as their own controls whereby they were observed without earmuffs (Group 1) for 2 days and with earmuffs (Group 2) on consecutive 2 days. The preterm infants’ physiologic responses and Anderson Behavioral State Scoring System (ABSS) scores were assessed over 30s every 2h for 8h during daytime for 4 days. ResultsOut of 20 preterm infants, 6 were male and 14 female with a mean birth weight of 1220±209g, gestational age of 29.9±2.1 weeks. The total number of measurements was 320. The mean ABSS scores of Group 1 and 2 were 3.07±1.1 and 1.34±0.3, respectively. Statistically significant difference was noted between the means of ABSS scores (p<0.001). Preterm infants with earmuffs (87.5%) were more frequently observed in a quiet sleep state of ABSS compared with those without earmuffs (29.4%). ConclusionsNoise level reduction was associated with significant improvement in behavioral states of ABSS. We suggest that noise reduction in preterm infants with earmuffs is helpful by improving sleep efficiency and increasing time of quiet sleep.

Comparison of User Volume Control Settings for Portable Music Players with Three Earphone Configurations in Quiet and Noisy Environments

Listening to music is one of the most common forms of recreational noise exposure. Previous investigators have demonstrated that maximum output levels from headphones can exceed safe levels. Although preferred listening levels (PLL) in quiet environments may be at acceptable levels, the addition of background noise will add to the overall noise exposure of a listener. Use of listening devices that block out some of the background noise would potentially allow listeners to select lower PLLs for their music. Although one solution is in-the-ear earphones, an alternative solution is the use of earmuffs in conjunction with earbuds. There were two objectives to this experiment. The first was to determine if an alternative to in-the-ear earphones for noise attenuation (the addition of earmuffs to earbuds) would allow for lower PLLs through a portable media player (PMP) than earbuds. The second was to determine if a surrounding background noise would yield different PLLs than a directional noise source. This was an experimental study. Twenty-four adults with normal hearing. PLLs were measured for three earphone configurations in three listening conditions. The earphone configurations included earbuds, canal earphones, and earbuds in combination with hearing protection devices (HPDs). The listening conditions included quiet, noise from one loudspeaker, and noise from four surrounding loudspeakers. Participants listened in each noise and earphone combination for as long as they needed to determine their PLL for that condition. Once the participant determined their PLL, investigators made a 5 sec recording of the music through a probe tube microphone. The average PLLs in each noise and earphone combination were used as the dependent variable. Ear canal level PLLs were converted to free-field equivalents to compare to noise exposure standards and previously published data. The average PLL as measured in the ear canal was 74 dBA in the quiet conditions and 84 dBA in the noise conditions. Paired comparisons of the PLL in the presence of background noise for each pair of earphone configurations indicated significant differences for each comparison. An inverse relationship was observed between attenuation and PLL whereby the greater the attenuation, the lower the PLL. A comparison of the single noise source condition versus the surrounding noise condition did not result in a significant effect. The present work suggests that earphones that take advantage of noise attenuation can reduce the level at which listeners set music in the presence of background noise. An alternative to in-the-ear earphones for noise attenuation is the addition of earmuffs to earbuds.

Hearing threshold shift measured by otoacoustic emissions after shooting noise exposure in soldiers using hearing protectors

The aim of the study was to assess the influence of short-term impulse noise to temporary threshold shift in soldiers using hearing protectors. The study included 80 subjects with correct tympanic membrane and thresholds measured by pure-tone audiometry less than 20 dB. There were two groups: 40 soldiers protected during shooting and 40 young males who didn't shoot. TEOAE were performed by ILO 292 Echoport Otodynamics device 3 to 5 minutes before shooting and 2 minutes and 1, 2, and 3 hours after shooting. Short-term exposure to impulse noise generated by five gunshots from the rifle kbk AKMS hasn't induced temporary threshold shift of hearing for chosen frequencies in soldiers using hearing protectors. Spectral analysis for chosen frequencies revealed that measurement reproducibility, stimuli level, and probe stability appeared to be comparable and repeatable. Our results show that the use of hearing protectors safeguarded against impulse noise. The use of earmuffs is strongly recommended because they seem to sufficiently attenuate shooting noise.

Impulse noise and acute acoustic trauma in Finnish conscripts. Number of shots fired and safe distances.

This prospective study of acute acoustic trauma (AAT) from exposure to impulse noise during compulsory military service focused on three issues the number of shot or explosion impulses that the conscript was exposed to at the time of AAT, distance of injured ear from causal firearm, and the circumstances under which AAT occurred protected ears. The series includes 449 consecutive, verified cases of AAT seen at the Central Military Hospital in Helsinki, Finland, in the period 1989-1993. AAT usually occurred during combat training (87%) as a result of exposure to impulses from small arms (83%). In 41%. AAT was caused by a single shot or detonation impulse. As many as 92% of all AATs occurred within 2 m of the causal firearm. Fourteen percent were wearing hearing protectors when the accident took place, but every third had badly fitting protectors or had neglected safety regulations and used insufficient protection. Of all AATs caused by one noise impulse in protected ears. 83% were attributable to heavy arms and only 14% to small arms. The results of the study suggest that combined use of earmuffs and earplugs in association with a safe distance of over 5 m from the noise source gives adequate protection against AAT. However, for conscripts using certain heavy arms e.g. hazooka. more effective hearing protection should be developed.

Physical Characteristics of Gunfire Impulse Noise and its Attenuation by Hearing Protectors

The peak sound pressure level (SPL), spreading of pressure wave and other physical characteristics of the impulse noise from weapons were studied in actual shooting conditions for assessment of gunfire noise exposure. Additionally, the attenuation of SPL by hearing protectors was measured with miniature microphones to evaluate protection efficiency in real shooting conditions. The peak SPLs at the shooter's ear ranged from 132 dB (miniature rifle) to 183 dB (howitzer). The spectral content of the main part of the acoustic energy was less than 400 Hz (peak 16-100 Hz) for large-caliber weapons and 150-2,500 Hz (peak 900-1,500 Hz) for small-caliber weapons (rifles). The safe distances from the noise source (less than 140 dB peak SPL) were 50-200 m for large-caliber weapons. Rifle impulses (assault rifle, caliber 7.62) had a peak SPL of 154 dB at a distance of 4 m from the muzzle. The peak SPLs of different explosives ranged from 125 to 185 dB at distances of 10 to 300 m. In rifle shooting, the attenuation efficiency of earplugs (16dB) or small-volume (thin) earmuffs (17 dB) was not sufficient and their use as sole protectors cannot be recommended. Instead, large-volume earmuffs should be used. Impulses from pistol and shotgun were fairly effectively attenuated both by small-volume and large-volume earmuffs. All kinds of earmuffs appeared to be ineffective (attenuation less than 15 dB) against impulses from large-caliber weapons with energy content at very low frequencies. Therefore, the combined use of earmuffs and earplugs is recommended for the most noisy operations. On the basis of the present data, wider safety zones were adopted in the Finish Defence Forces at shooting with different weapons.

Hearing protection against high-level shooting impulses in relation to hearing damage risk criteria

The earmuff attenuation of acoustic impulses produced by large-caliber weapons was measured with a high-speed microcomputer controlled unit. The estimated accuracy was +/- 1 dB in peak sound-pressure level measurements. The peak levels outside earmuffs were 184 dB for the heavy bazooka and 172 dB for the hand-held bazooka (re: 20 microPa). Heavy bazooka impulse peak levels were attenuated from 7 to 19 dB by the earmuffs depending on the mass and volume of the measured three types of earmuffs. Hand-held bazooka impulse peak levels were attenuated by the earmuffs from 9 to 15 dB. The risk limits for hearing loss from a single impulse were exceeded in spite of the use of earmuffs when the criteria of CHABA (USA) or Pfander (Germany) were applied. The unexpectedly low attenuation was due to the low-frequency waveform of the high-level impulses. The earmuffs were found to prolong the impulse duration, which may reduce the benefit otherwise achieved by attenuation of the peak levels.

Sensory-neural hearing loss during combined noise and vibration exposure. An analysis of risk factors.

A detailed analysis of risk factors for the development of sensory-neural hearing loss (SNHL) was carried out on 122 forest workers. These forest workers were selected from a larger group (n = 217) by restricting the age range to 30-55 years. The hearing threshold of the left ear at 4000 Hz was measured and the effect of age, exposure, systolic and diastolic blood pressure (DBP), presence of vibration-induced white finger (VWF), tobacco smoking and use of earmuffs were evaluated in multiple linear regression analysis. Robinson's nonlinear model was used to evaluate the rate of hearing loss. Aging was the major risk factor and it explained 15.4% of the variance of the SNHL. The presence of VWF was the second most important single risk factor and explained a further 5.2% of the SNHL. Elevation of DBP correlated significantly with SNHL and explained an additional 4.1% of the SNHL. These main factors were able to explain about 26% of the spread of SNHL. Additional factors in the analysis, e.g. smoking, systolic blood pressure, did not significantly contribute to the genesis of SNHL. When Robinson's model was applied to the SNHL data, on a group basis, we did not observe any exaggerated risk of hearing loss due to combination of noise and vibration. In combined exposure subjects with VWF as well as subjects with enhanced DBP will run a higher risk for SNHL.

Efficacy of enforcement in an industrial hearing conservation program.

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.