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Year : 2012  |  Volume : 14  |  Issue : 57  |  Page : 68-71
Early occupational hearing loss of workers in a stone crushing industry: Our experience in a developing country

Department of Surgery, E.N.T. Unit, University of Ghana Medical School, Accra, Ghana

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Date of Web Publication18-Apr-2012
 
  Abstract 

Noise-induced hearing loss (NIHL) is an irreversible sensorineural hearing loss associated with exposure to high levels of excessive noise. This paper aims to assess the prevalence of early NIHL and the awareness of the effects of noise on health among stone crushing industry workers. This was a comparative cross-sectional study in Ghana of 140 workers from the stone crushing industry compared with a control group of 150 health workers. The stone workers and controls were evaluated using a structured questionnaire, which assessed symptoms of hearing loss, tinnitus, knowledge on the health hazards associated with work in noisy environment and the use of hearing protective device. Pure tone audiometric assessment was carried out for stone workers and controls. Noise levels at the work stations of the stone workers and of the controls were measured. Statistical Analysis of data was carried out using SPSS package version 16. The mean age of stone workers and controls was 42.58±7.85 and 42.19±12 years, respectively. Subjective hearing loss occurred in 21.5% of the workers and in 2.8% of the controls. Tinnitus occurred in 26.9% of stone workers and 21.5% of controls, while 87.5% stone workers had sound knowledge on the health hazards of a noisy environment. Early NIHL in the left ear occurred in 19.3% of the stone workers compared with 0.7% in controls and in the right ear, it occurred in 14.3% of the stone workers and in 1.3% of the controls; P<0.005. In conclusion, the prevalence rate of early NIHL among stone crushing workers is about 19.3% for the left ear and 14.3% for the right ear.

Keywords: Early noise-induced hearing loss, stone crushing noise, developing country workers

How to cite this article:
Kitcher ED, Ocansey G, Tumpi DA. Early occupational hearing loss of workers in a stone crushing industry: Our experience in a developing country. Noise Health 2012;14:68-71

How to cite this URL:
Kitcher ED, Ocansey G, Tumpi DA. Early occupational hearing loss of workers in a stone crushing industry: Our experience in a developing country. Noise Health [serial online] 2012 [cited 2019 Sep 20];14:68-71. Available from: http://www.noiseandhealth.org/text.asp?2012/14/57/68/95134

  Introduction Top


Noise-induced hearing loss (NIHL) is an irreversible sensorineural hearing loss associated with excessive noise exposure. The global estimates of disabling hearing loss from occupational hearing loss range from 7% to 21%. [1] Noise in excess of 85 dB (A) in a work environment of an 8-h daily work regime predisposes workers to NIHL. [2]

NIHL is usually bilateral and symmetrical, affecting higher frequencies (3 k, 4 k or 6 k Hz) and subsequently lower frequencies (0.5 k, 1 k or 2 k Hz). [3] Boateng and Amedofu [4] confirmed the presence of noise-induced loss among local saw mills, printing press and corn mill workers. Other local studies by the same authors and others [5] documented the problem of occupational hearing loss among surface gold mining workers. There is currently no local data on noise-induced hearing impairment among stone crushers and allied concrete product manufacturing industry and, hence, the study.

The debate on the most sensitive tool for early detection of NIHL still continues; however, studies by Riga et al. [6] recommended extended high-frequency audiometry (EHFA) as a protocol for detection of early NIHL. This recommendation has also been supported by the studies of Somma et al., [7] who indicated that EHFA is more sensitive than conventional audiometry in detecting NIHL. However, hearing loss in the EHF range seems an age-dependent phenomenon, with progression into the lower speech range frequencies with increasing age. Seixas et al. [8] however recommended Distortion product of OAE (DPOAE)s for hearing surveillance in an industrial setting, and indicated the fact that it is somewhat more sensitive to these early changes than is evident with a standard pure tone audiometer.

Aim

To assess the prevalence of early NIHL and to determine the awareness of the effects of noise on health.


  Methods Top


This study was conducted on workers of a privately owned large-scale stone crushing and concrete products manufacturing industry situated in the suburb of the city of Accra. The main activities of this industry include crushing large stone into smaller pieces for road and building construction and also the production of concrete drains and blocks.

It uses electric-powered heavy duty engines in the production of these products. Associated with this manufacturing process is work environmental noise. Even though the workers are provided with ear muffs, compliance is a problem. Our study provided the first opportunity for hearing conservation programme and assessment of stone workers compliance to preventive measures. Informed consent was obtained from all workers after explaining the purpose and procedure of the study.

One hundred and forty workers of a stone crushing industry were recruited for this study. Each worker was assisted when necessary by the authors to complete a structured questionnaire that assessed subjective symptoms of hearing loss, tinnitus, knowledge on the health hazards associated with work in noisy environment, the use of hearing protective device, duration of service at this industry and nature of work [Figure 1]. Noise measurement was carried out at each work station of the industry when the machines were in full operation to ascertain whether the level of noise in the work station will potentially lead to occupational hearing loss and whether protection is needed. The sound level meter (S.L.M.) used was a digital RS-232 Sound Level Meter 72-860A (manufactured in Taiwan, Republic of Korea by Tenma test Equipment Springboro, Ohio.) set for A weighting. The desired response of the S.L.M. was set at slow position and the microphone was placed in such a way that it was not in acoustic shadow of any obstacle or in any appreciable field of reflected waves. The measurement of maximum and minimum noise levels for each station was carried out by the Senior Audiologist. The desirable threshold limit of sound permissible for noise exposure for these workers should be 85 dB (A) or less. The pure tone audiometric assessment of the stone workers was carried out in batches of 20 workers per day and at least 14 h after the last exposure to noise. The audiometric evaluation of these workers was carried out at the audiology center in a teaching hospital in the city of Accra, which was well equipped with a noise-proof audiology booth and with an ambient noise level of 34-40 dB(A). Before the audiometry, each worker had otoscopy by the senior author to rule out any outer or middle ear diseases. A qualified audiologist (second author) carried out, on each worker, a conventional eight-frequency pure tone audiometric assessment (PTA) in 5 dBHL steps at frequencies of 250, 500, 1000, 2000, 3000, 4000, 6000 and 8000 Hz in both ears using the GSI 16 Clinical Audiometer (manufactured by Grason-Stradler in Littleton Massachusetts). One hundred and fifty health workers (nurses, doctors and paramedical staff) who had no history of excessive noise exposure from the same teaching hospital within the city of Accra were similarly recruited as controls and were evaluated. The data was entered into a computer and analyzed using SPSS version 16 programme and a comparative outcome in respect of high-frequency notch (early NIHL) and other outcomes of the study was obtained.
Figure 1: Questionnaire for controls and subjects

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  Results Top


Three (2.1%) females and 137 (97.9%) males participated as stone workers and 125 (83.3%) females and 25 (16.7%) males participated as controls. The stone workers occupational job groups were Machine operators, Mechanics, Artisans (embracing painters, carpenters, masons, plumbers and electricians), Welders, Administrative staff (including accountants, cooks, stewards and security officers), Laboratory staff, Drivers and Storekeepers [Table 1].
Table 1: Occupational job groups of workers in the stone crushing industry

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The mean age of the stone workers was 42.58±7.85 years and their median age was 43 years. The mean age of the health workers (control) was 42.19±12 years and their median age was 45.5 years.

The ages of the stone workers ranged between 20 and 63 years while that of the controls ranged between 26 and 61 years. Majority of the workers, 81 (59.6%), had worked for 10 years or less and 47 (34.6%) had worked between 11 and 20 years, and a minority, 8 (5.9%), had been engaged between 21 and 30 years [Table 2]. The subjective symptoms of hearing loss occurred in 21.5% and 2.8% of the workers and controls, respectively, while the symptoms of subjective tinnitus occurred in 26.9% and 21.5% of the stone workers and control groups, respectively. We noted that 87.5% of the stone workers had sound knowledge on the health hazards of working in a noisy environment, but only 5.5% of these workers actually used hearing protective devices. The noise levels of the work stations of the stone crushing industry, excluding the administrative offices, ranged between 61.2 dB (A) and 99.6 dB (A) [Table 3]. The details of work specification and activities at the work stations, excluding the administrative offices, is summarised as follows: 1. Work station has a stone crushing plant that breaks large stones into smaller pieces; 2. Work station is a mechanic shop where repair works of heavy duty machines are carried out; 3. and 4. Work stations have machines for manufacturing concrete blocks and large concrete pipes, respectively; 5. Work station is a metal work and welding shop where welding and various types of metal works are undertaken to support this industry; number 6. Work station had a machine for the manufacture of concrete gutter drains; and number 7. Work station is a quality assurance laboratory that is equipped with a noisy machine for the laboratory work. The administrative offices included the accounts, stores, security and administrative managers' offices. The minimum noise level in the administrative offices was 58 dB (A), while the maximum noise level was 78 dB (A). The noise level of the work environment of the controls ranged between 54.2 dB (A) and 69 dB (A).
Table 2: Duration of period of work by workers in the stone crushing industry

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Table 3: Noise levels at work stations in the stone crushing industry

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The typical audiometric configuration of early NIHL (high-frequency notch) occurred in the left ears of 27 (19.3%) stone workers, while only one (0.7%) health worker had high-frequency notch; P<0.005. This typical audiometric configuration was also seen in the right ear of 20 (14.3%) stone workers. while only two (1.3%) health workers had the characteristic high-frequency notch of NIHL; P<0.005 [Table 4] and [Table 5]. The artisans and the machine operators were the most vulnerable group as far as the occurrence of early noise-induced hearing impairment is concerned. The prevalence of early NIHL increased with increased duration of work at the industry.
Table 4: Early noise-induced hearing loss in the left ear

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Table 5: Early noise-induced hearing loss in the right ear

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  Conclusion Top


The prevalence of early NIHL among the stone workers, considering the total number of ears, was 33.6% compared with 2% in the controls. Majority of the stone workers had sound knowledge of health hazards of working in a noisy environment.


  Discussion Top


This study confirmed the fact that workers in the stone crushing industry are exposed to hazardous noise, which is contributory to the high prevalence of early noise-induced sensorineural hearing loss, compared with the controls. Our observation is in agreement with the findings of Gonçalves et al. [9] that noise is a higher risk factor than age when considering sensorineural hearing loss. The prevalence of early NIHL of 33.6% in this study is lower than 50% noted by Harger et al. [10] in their evaluation of occupational noise exposure among marble workers in Brazil and also a prevalence of 64.9% by Ologe et al. [11] in a study of NIHL among bottling workers, reflecting differences in demographic factors and sources of noise and duration of work among these subjects. Our lower prevalence rate may be due to the fact that our study focused only on early NIHL among our study group. Hearing protection is crucial in our quest to prevent irreversible sensorineural hearing loss. However, compliance is poor, as shown by only 5.5% in our study population. This is not dissimilar to an earlier study by Omokhodin et al.,[12] who found that the compliance rate among mill workers was 0%. The common reasons for lack of use of hearing protective devices is discomfort [13] associated with wearing ear plugs, ear caps and ear muffs and, sometimes, tinnitus as noted by Mendes et al. [14] in their study on acceptance of hearing protection aids among members of instrumental and voice musician bands. The availability of hearing protective devices at work place in our study did not automatically lead to usage of this device. The workers will need both knowledge on the harmful effects of noise on hearing and motivation coupled with strict enforcement on the use of hearing protective devices if occupational NIHL is to be prevented. The finding of a high-frequency notch may not necessarily be due to noise exposure. A recent study by other workers [15] has noted that the high-frequency notch without excessive noise exposure or any other known factor is common and is not diagnostic of NIHL unless there is a convincing history of hazardous noise exposure. The stone crushers in this study no doubt had exposure to hazardous levels of noise and we are convinced that the classical audiometric pattern of high-frequency notch obtained can largely be attributed to occupational noise exposure. This pattern is very significant statistically when we compare the prevalence of NIHL between stone workers and controls. It was not possible to perfectly age match the two populations studied; in addition, we were unable to obtain pre-employment audiograms of the stone workers as this was their first time of having a voluntary hearing assessment. As a result of these weaknesses, we decided to focus our hearing assessment outcomes on early NIHL outcomes as we can confidently attribute this finding to noise exposure in our comparative analysis. Some of our subjects who were in the minority did not answer the questionnaire completely, contributing to a shortfall in the measurement of some of our outcomes, reflecting a minor weakness in our supervision of the structured questionnaire.

 
  References Top

1.Nelson DL, Nelson RY, Concha-Barrientos M, Fingeruhut M. The global burden of occupational noise-induced hearing loss. Am J Ind Med 2005;48:446-58.  Back to cited text no. 1
    
2.National Institute of health. Consensus conference. Noise and hearing loss. JAMA 1990;263:3185-90.  Back to cited text no. 2
    
3.Rabinowitz P, Rees T. Occupational hearing loss. In: Rosenstock, Cullen M, Bodkin C, Relic C, editors. Textbook of occupational and environmental medicine. 2 nd ed. Philadelphia, USA: Elsevier Saunders; 2005. p. 426-36.  Back to cited text no. 3
    
4.Boating CA, Amedofu GK. Industrial noise pollution and its effect on the hearing capabilities of workers: A study from saw mills, printing presses and corn mills. Afr J Health Sci 2004;11:55-60.  Back to cited text no. 4
    
5.Amedofu GK. Hearing-impairment among workers in a surface gold mining company in Ghana. Afr J Health Sci 2002;9:91-7.  Back to cited text no. 5
    
6.Riga M, Korres G, Balatsouras D, Koress S. Screening protocols for the prevention of occupational noise-induced hearing loss: The role of conventional and extended high frequency audiometry may vary according to the years of employment. Med Sci Monit 2010;16:CR352-6.  Back to cited text no. 6
    
7.Somma G, Copetta L, Magrini A, Parrella M, Cappelleti MC, Gardi S, et al. Extended high frequency audiometry in the prevention of noise-induced hearing loss. G Ital Med Lav Ergon 2007;29(3 Suppl):258-60.  Back to cited text no. 7
    
8.Seixas NS, Goldman B, Sheppard L, Neitzel R, Norton S, Kujawa SG. Prospective noise induced changes to hearing among construction industry apprentices. Occup Environ Med 2005;62:309-17.  Back to cited text no. 8
    
9.Gonçalves CG, Mota PH, Marques JM. Noise and age: Influence on the hearing of individuals with ages between 50-70 years. Pro Fono 2009;21:57-62.  Back to cited text no. 9
    
10.Harger MR, Barbosa-Branco A. Effects of hearing due to occupational noise exposure of marble industry workers in the Federal District, Brazil. Rev Assoc Med Bras 2004;50:396-9.  Back to cited text no. 10
    
11.Ologe FE, Akande TM, Olajide TG. Occupational noise exposure and sensorineural hearing loss among workers of a steel rolling mill. Eur Arch Otorhinolaryngol 2006;263:618-21.  Back to cited text no. 11
    
12.Omokhodion FO, Adeosun AA, Fajola AA. Hearing impairment among mill workers in small scale enterprises in southwest Nigeria. Noise Health 2007;9:75-7.  Back to cited text no. 12
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13.Rashaad Hanisia M, Dickinson D. Hearing protection device usage at a South African gold mine. Occup Med (Lond) 2010;60:72-4.  Back to cited text no. 13
    
14.Mendes MH, Morata TC, Marques JM. Acceptance of hearing protection aids in members of an instrumental and voice music band. Braz J Otorhinolaryngol 2007;73:785-92.  Back to cited text no. 14
    
15.Osei-Lah V, Yeoh LH. High frequency audiometric notch: An outpatient clinic survey. Int J Audiol 2010;49:95-8.  Back to cited text no. 15
    

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Correspondence Address:
Emmanuel D Kitcher
E.N.T.Unit, Department of Surgery, University of Ghana Medical School, P.O. Box 4236, Accra
Ghana
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1463-1741.95134

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