Annals of Tropical Medicine and Public Health

: 2017  |  Volume : 10  |  Issue : 6  |  Page : 1740--1745

Evaluation of noise effects on standard threshold shift employees of technical and professional organization according to the audiogram and sound overall level measurement in Ilam: A cross-sectional study

Farnaz Safarpor1, Mohsen Jalilian2, Meghdad Kazemi1, Maryam Jamshidzad1, Maedeh Kamalvandi1, Nematullah Kurd1,  
1 Department of Occupational Health Engineering, Faculty of Health, Ilam University of Medical Sciences, Ilam, Iran
2 Department of Public Health, Ilam University of Medical Science, Ilam, Iran

Correspondence Address:
Nematullah Kurd
Department of Occupational Health Engineering, Faculty of Health, Ilam University of Medical Sciences, Ilam, Iran


Background: Noise is one of the most prevalent physically harmful factors in working environment which can cause many problems that one of them is hearing loss. Therefore, the aim of this study was to assess occupational exposure with sound (noise) in training workshops of Technical and Vocational Organization of Ilam and to determine the rate of change in hearing threshold of people working in these workshops. Materials and Methods: A cross-sectional study was carried out on 60 people which working in 8 workshops of Technical and Vocational Organization of Ilam which are selected by census report. Demographic data of studied people are collected using a researcher-made checklist and measuring the overall balance of sound level meter set model 450 is used. Changes in hearing threshold of people are assessed using audiometer. Finally, data are analyzed using SPSS 20 by conduct Spearman correlation and Pearson's correlation statistical tests in asignificant level of 0.05. Results: The results show that there have been 8.62 dB change in hearing threshold of the left ear, 8.73 dB in right ear, and 6.74 dB in both ears of studied people averagely. The highest level of sound pressure balance is related to cutting-wood workshop, and the Equivalent exposure level (Leq) is more than national standard level (85 dB) in mosaic, lapidary, and welding workshops. Spearman correlation test shows a significant relationship between the highest level of sound balance in welding workshop (112 dB) and the average total loss (8.15 dB) for both ears (P < 0.05). Conclusion: According to the findings of this study, there is an urgent need for monitoring, assessing and control of other workshops of Ilam Technical and Vocational Organization to investigate the overall balance of sound and change in hearing threshold of people working in the workshops.

How to cite this article:
Safarpor F, Jalilian M, Kazemi M, Jamshidzad M, Kamalvandi M, Kurd N. Evaluation of noise effects on standard threshold shift employees of technical and professional organization according to the audiogram and sound overall level measurement in Ilam: A cross-sectional study.Ann Trop Med Public Health 2017;10:1740-1745

How to cite this URL:
Safarpor F, Jalilian M, Kazemi M, Jamshidzad M, Kamalvandi M, Kurd N. Evaluation of noise effects on standard threshold shift employees of technical and professional organization according to the audiogram and sound overall level measurement in Ilam: A cross-sectional study. Ann Trop Med Public Health [serial online] 2017 [cited 2020 Jul 14 ];10:1740-1745
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Noise is one of the important harmful factors in the working environment which is produced by various machineries and processes. Employees' exposure to noise is considered to be one of the prevalent problems in working environments around the world that can lead to several problems, among which hearing loss is the most prevalent.[1],[2],[3],[4] According to the estimation of the National Institution of Occupational Safety and Health of America, about 30 million American employees are exposed to harmful noise (85 dB). The number is about 35 million in European Union in such a way that occupational hearing loss is known as one of major European occupational disease.[5] An estimation of current data indicates that about 2 million of employees in Iran are exposed to harmful noises. Hence, it can be imagined that aspects of this problem are significant in Iran.[6],[7] Sound can have harmful effects on man's health, especially on hearing organs through electromagnetic waves. The impact on balance system, optic, neural, mind impacts, and also social and psychological effects are considered as undesirable impacts of sound on human beings. In the case of repeated exposures to noise and becomes permanent, it may lead to permanent hearing loss without subsequent recovery (due to the destruction of cilium cells of Cretan in the inner ear).[8] Having exposure to high volume of sounds within short periods (from a few seconds to several hours) leads to temporarily hearing loss, which in fact is temporary threshold shift that reverses after 24 h. In the case of repeated exposure to sounds that first lead to just shifting hearing threshold, permanent threshold shift would be seen, which is observed prevalently among employees exposed to high volumes of sound at work.[9] Hearing loss caused by exposure to sounds from work environment is one of the significant diseases that can influence individual efficiency and safety, but its importance is mostly ignored which can interrupt communications with others and it also causes not hearing warning sounds, and it may be accompanied by communication problems, increased stress and reduced efficiency.[2] Fortunately, the occupational hearing loss can be prevented. Preventing hearing loss resulted from sounds is just as beneficial for workers as it may also be for employers because employers can take benefits from reducing medical and compensation costs for workers. Therefore, an effective plan for hearing protection seems necessary.[10] Small industrial workshops are not an exception, and there is a problem of exposure to noise for workers of these industries, which has been less considered as due to various reasons.[11] Regarding abundance of small workshops and presence of machineries producing noises in workshops of Technical and Vocational Organization and also by referring to the importance of employees' well-being, this study is carried out with the purpose of assessing the level of sound and its effects on employees' hearing loss in Ilam workshops of Technical and Vocational Organization.

 Materials and Methods

This study was a cross-sectional research which conducted on 60 people of 8 workshops including welding, wood industry, etching, lapidary, auto repair, agricultural machinery, sewing, and mosaic in Technical and Vocational Organization in Ilam city, west of Iran in 2016. A researcher made checklist is prepared to collect general information and demographic characteristics of studied people such as age, car experience, sicknesses, environmental characteristics, and features of each workshop, and other characteristics related to sound. Interrupted factors such as using special drug (streptomycin and gentamicin), ear sicknesses background and others which can have impacts on hearing are assessed in studied people, and people having these characteristics are eliminated from the study. Data collecting tools consisted of devices sound level meter model CEL450 and portable audiometer equipped with an acoustic room with calibration certificate. Calibration of audiometer devices was determined according to standard methods and attached calibrator at the workplace at a frequency of 1000 Hz. The first step of measuring and assessing sounds was to collect required data about working environment and the way of workers' exposure and to do this first a simple map of workplace was prepared with the scale and place of equipment installation, especially” sound generators” and then related data for the places of workers' passing and traffic, their exposure times to the sound, shifts changes, and managerial information such as overtimes, workflows, and leaves were registered. An assessment of workers' exposure was done through measuring sound pressure level (SPL) at scale A and frequency analysis was performed for stations with sound pressure level >85 dB. Determining the measuring environmental sound plan networks are divided into 5 × 5 dimensions after preparing primary map of each workshop and determining the sources of sound regarding the workshops' areas (500–1000 M2). Sound pressure level was measured in each station in network A and with the slow speed with one octave band frequency. During this study, first a source of sound generation at workshops was identified. Then, in scale A at the center of all areas, sound pressure level was measured, and results were recorded.

Measuring hearing condition by audiometer was done using total World Health Organization audiogram test and total audiology way test.[12] Before entering to workplace and starting working shift, individuals were examined in the acoustic room. Pure sounds at various intensities and frequencies 250,500, 1000, 2000, 4000, and 8000 Hz was transferred to both ears through headphone and hearing threshold was measured, which is known as air conduction threshold. Results of hearing threshold were recorded on certain diagram or table called audiogram.

To determine permanent hearing loss caused by noise, the hearing threshold was calculated at each four important frequencies 500, 1000, 2000, and 4000 Hz was introduced in the following formula after deducting age and the level of permanent hearing loss with indicator NIHL (noise-induced hearing loss) was obtained.

NIHL = TL 500 + TL 100 + TL 12000 + TL 14000/4

TL: hearing threshold at considered frequency for both earsNIHL: noise-induced hearing loss.

Through the following equation, total hearing loss induced by noise for both ears would be calculated.[13]

NIHLt = (NIHLb × 5) + (NIHLp)/6

NIHLt: Total permanent loss for both earsNIHLb: Permanent loss for better earNIHLp: Permanent loss for weak ear.

By having permanent loss based on the following way can would be determined the level or monaural impairment for each ear:

MI (%) = (NIHL – 25) ×1.5

MI: Monaural impairment for each ear.

Monaural impairment for both ears is obtained through the following equation:

MIt= (MIb × 5) + (MIp × 1)/6

MIt: Total monaural impairment for both earsMIb: Monaural impairment for better earMIp: Monaural impairment for weak ear.

World Health Organization considers average hearing threshold at 500, 100, 2000, and 4000 frequencies to determine hearing loss degree. According to division prepared by this organization average loss of <25dβ is considered natural, 26–40 little hearing loss, 41–60 average hearing loss, 61–80 sever, and >81 deep hearing loss or being deaf. After collecting data and outputs from devices, they were introduced into a predesigned table, and by related formulas, the average sound pressure for each workshop and the level of workers' hearing loss for each workshop was obtained.


All of the individuals participating in the present research were 60 selected among 8 workshops. Their average age was 30.9 ± 7.9 and their mean work experience was 6 years. Of the total population, 93.3% was men and 7.7% was women. Demographic information, hearing disability degree (in the right, left and both ears), and the amount of exposure of studied subjects are presented in [Table 1]. The mean of change in hearing threshold of individuals were 8.62, 8.73, and 6.74 for left, right, and both ears. A total of 22 individuals of studied people were exposed to sound pressure level <85 dB, 26–85 to 90 dB and 12 to >90 dB. Mean of sound pressure level at workshops is shown in [Figure 1]. As presented, the highest level of sound pressure is related to welding workshop (112 dB) and the lowest level is related to sewing workshop (70 dB) [Table 2]. Etching workshop had the highest percentage for having a number of stations >85 dB. Nearly 43.33% of participants during this study were exposed to sounds higher than 85 dB. The highest level of hearing loss at frequency 4000 and then at 3000, 6000, and 8000 Hz was obtained. The mean of permanent hearing loss for both ears (the average of hearing loss at frequency 500, 2000, 1000, and 4000 for both ears) in 44% of participants was trivial, and it was severe hearing loss for 10% [Figure 2]. The relationship between right ear disability, left ear disability and overall disability of ear and demographic variables are studied using Pearson's correlation coefficient test and it is observed that there is not any meaningful relationship between age variable and left ear disability, but there is a meaningful relationship between age and right ear disability (P = 0.007). It is also observed that Pearson's correlation coefficient is meaningful for the relationship between working experience and left ear hearing loss, right ear and both ears. [Table 3] shows mean Leq and average of total hearing loss at each workshop, in which the most sound pressure level is related to welding workshop with 112 dB and total mean loss of 8.15 dB for both ears. The least sound pressure level is related to sewing workshop with 71.14 dB and hearing loss of both ears was 6 dB. [Figure 3] shows mean of ear disability percentage in employees of different workshops and as it is observed wood industries have got the most disability percentage (34.68% disability for both ears).{Table 1}{Figure 1}{Table 2}{Figure 2}{Table 3}{Figure 3}


Environmental studied shows that sound pressure level mean is higher than national permission level (according to technical committee of vocational hygiene, the approve level is 85 dB) in wood industry (97.3 dBA), etched (94 dBA), welding (86 dBA), lapidary (88.7 dBA), and mosaic workshops (87 dBA) among all studied workshops. Level of equivalent exposures is 98 dB in welding workshop, 95 dB in wood industry workshop, 89 dB in the lapidary workshop, and 98 dB in mosaic workshop that all of them are higher than permissible amount. Nekohi et al.[14] has done a study on small workshops in Bejnourd and welding workshop has a sound level of 91.13 dB, wood industry 86.7 dB and cutting 86.4 that all of them have sound pressure level higher than the permissible amount which is similar to the present study. These results are also similar to those of Ketabi et al.[12] on assessing screening sound method performance to estimate sound risk on small workshops in Hamadan city.[15] Analyzing workers' hearing loss showed that 8.73% in right ear, 8.62% in left ear and 6.74% in both ears have hearing loss >25 dB and these are much lower than the results of Aghilinezhad et al.[16] study on effects of work environment noise on hearing of people working in small workshops in Tehran in which workers' hearing loss were 49.5, 46.8, and 46.8 for the right, left and both ears, respectively. The highest level of hearing the loss in studied workshops and individuals is obtained in 4000 Hz frequency which is an important factor in monitoring and controlling sound. In other studies like that of Pourabdiyan [4] and Ghotbi [17] similar results are found. Of course, the highest level of hearing loss was observed for workers of wood industry workshop with the level of 24.68 dB. The next highest levels were obtained respectively in mosaic, welding, sewing, auto repair, agriculture machineries, lapidary, and etching workshops. Although the level of total ear loss does not indicate a big figure compared to equivalent level, the main reason was low work experience (6 years) for this group of participants, and it can be predicted that the longer exposure would lead to the higher loss level. In a study by Tajic et al.[18] on a hearing system of workers in one of Arak metal industries, hearing loss was obtained 7.3% for welding workers which is similar to mean of hearing loss for both ears in this study. Pearson correlation coefficient is 0.05 between age, working experience and hearing loss in both ears which shows a meaningful relationship between overall hearing loss and studied variables of age and work experience. In a study by Naeeini  et al. entitled “the analysis of hearing condition of noisy workshops workers,” it is identified that the possibility of hearing damage increases with aging in such a way that workers aging between 25–34 has 60% natural hearing, 35–44 has 5.76% and 55–64 has 9.42%.[19] In a study by Ahmadi et al. entitled “An Evaluation of hearing loss due to noise exposure in industry workers of auto body repair” it was concluded that exposure level to noise was 98.2 ± 4.2 dB and hearing loss of both ears was 22.1 ± 9.16 dB. The highest level of hearing loss was observed in left ear at frequency of 4000 Hz equaled to 4.42 dB and in the right ear at frequency 8000 equaled to 1.37 dB and there was a direct relationship between damage limit and work experience and individuals' age.[19] In a study by Aghilinezhad et al.[16] entitled “examining the impact of the noise of workplace on hearing of individuals working in Tehran small workshops” it was shown that mean equivalent level of workers' exposure was 94.2 ± 6.72 dB and it was 78.84 ± 3.97 dB for the examined group. It was found that exposure equivalent level was considered as first factor and age factor and work experience was considered to be next predictive factor for hearing loss.[13] Other studies confirmed the meaningful relationship between age and work experience with increasing hearing loss such as studies by Ferrite,[20] Tabuchi,[21] Barba,[22] Tajic,[18] Zamanian,[23] Fazli,[24] and Pourabdian [4] that all of their results are similar to the results of present study.


Results of this study show that sound pressure level is higher than national standard permission level in most of the studied workshops. Therefore controlling sound at resources, using sound absorbing panels to avoid sound emission, using suitable individual protection equipment and doing periodical experiments during and before employment to identify sensitive individuals can be effective in controlling the dangers of environmental damaging sounds and preventing hearing damage of workers. There is also need for monitoring and assessing other workshops of Technical and Professional Organization to analyze sound pressure level and change in hearing threshold of people working in these workshops.


The authors would like to thank and appreciate the technical and professional organization staff in Ilam who provided the arrangements for of the study.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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