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Noise-induced hearing loss: Prevalence, degree of hearing loss and impairment criteria in South African gold miners
Introduction and study rational
Noise-induced hearing loss is no new phenomenon but the last two centuries has seen a significant increase in its occurrence. This can be attributed to the industrial revolution which saw the increase of mechanical equipment capable of producing hazardously loud noise and the widespread availability of gunpowder. It was noiseinduced hearing loss (NIHL) which “gave birth” to the profession of Audiology in the 1940s when soldiers returned from World War II with acquired hearing loss caused by gunfire and explosions (Clark, 2000). Today it is estimated that over one-third of the 28 million Americans who have some degree of hearing loss, were affected, at least partly, by noise (American Speech-Language-Hearing Association (ASHA, 2007). Excessive noise exposure is also prevalent in developing countries, such as Africa, in the formal (e.g. mining and construction) and informal occupational sector (e.g. vehicle repair) as well as the non-occupational sector (urban, environmental and leisure) (World Health Organization (WHO), 1997). The WHO estimates that 18% of adult-onset hearing losses in the 20 southern most countries in Africa (AFRE
region), including South Africa, might be due to NIHL in the workplace (Nelson et al., 2005b).
Noise can be defined as unwanted sounds that have the potential to interfere with communication or damage people’s hearing (Franz & Phillips, 2001). Noise exposure levels related to an 8-hour working day (LEx,8h), exceeding the occupational exposure limit (OEL) of 85 dB A1, are considered to be dangerous to the auditory system (Plontke, Zenner & Tübingen, 2004; Franz & Phillips, 2001). Excessive noise, at this limit or exceeding it, can irreversibly damage sensory hair cells of the cochlea. This results in a progressive, sensorineural, hearing loss that is predominantly noted in the high frequency region with a typical notch at 4 kHz (Śliwinska-Kowalska, Dudarerewicz, Kotył0, Zamysłowska-Szmytke, Wlaczyk- 1 Sounds at some frequencies are more hazardous than at other frequencies. The use of A-weighted sound levels cancels these effects, so that two sounds with the same dB A level have approximately the same hazard (Dobie, 2001).
Łuszczyńska, Gadja-Szadkowska, 2006; McBride & Williams, 2001; Rabinowitz, Galusha, Slade, Dixon-Ernst, Sircar, & Dobie, 2006 & May, 2000). Significant individual variability in susceptibility to NIHL is evident and may be due to many factors including a history of exposure to noise, previous treatment with ototoxic drugs, exposure to organic solvents, long-term smoking, gender, pigmentation, age and genetic make-up (Perez, Freeman & Sohmer, 2004; Agrawal, Niparko, Dobie, 2010). Despite the variability in susceptibility to NIHL, no one is immune to the devastating effect of loud noise over a prolonged period of time. The result is a disabling condition which negatively affects a person’s ability to communicate and interact socially with detrimental effects on work performance (Passchier-Vermeer & Passchier, 2000).
In the 1940s the treatment of NIHL was accentuated, but since then the emphasis has shifted from treatment to prevention. NIHL is now recognised as a preventable health effect of excessive noise in the workplace (Nelson, Nelson, Concha- Barrientos, & Fingerhut, 2005a). In the interest of prevention noise exposure in the workplace should be investigated. Review of the literature reveals that information on the level of noise exposure in the workplace is not readily available internationally. In this regard a WHO review to determine the global burden of occupationally induced NIHL stated that summary statistics on noise exposure are not available for most industrialising and non-industrialised countries (Nelson, et al., 2005a). In search for information on occupational noise exposure levels the researchers reviewed 17 studies conducted in 12 countries in South America, Africa, and Asia. The review reported on high occupational noise exposure levels (85 dB A or more) and associated hearing loss which occurred in a wide range of workplaces, including manufacturers of foods, fabrics, printed materials, metal products, drugs, watches, and in mining. Based on United States of America (USA) data the researchers estimated the proportion of workers in each occupational category with exposure to noise at or above 85 dB A in nine economic sectors. The industry with the highest estimated value was mining with an estimated 0,85 of all the production workers and labourers exposed to noise levels at or above 85 dB A (Nelson, et al., 2005a).
In South Africa mining is the country’s largest industry employing 5,1% of all workers in the non-agricultural, formal sectors of the economy, a reported total of 458 600 employees in 2006 (Mwape, Roberts, & Mokwena, 2007). The processes associated with mining generate tremendous noise as a result of activities including percussion drilling, blasting and crushing of ore which is often exacerbated by confined and reflective spaces (MHSC2, 2005). The results of a recent study investigating the profiles of noise exposure in South African mines indicate that the mean noise exposure levels in the South African mining industry range from 63.9 dB A to 113.5 dB A and that approximately 73.2 per cent of miners in the industry are exposed to noise levels of above the legislated OEL of 85 dB A (Edwards, Dekker, & Franz, 2011). In a recent study by (Phillips, Heyns, & Nelson, 2007), commissioned by the MHSC) the noise and vibration levels recorded during the operation of three types of rock drills currently used in the mining industry were compared. The researchers concluded that typical noise levels on conventional equipment are still exceeding the
occupational exposure limit.
CHAPTER ONE INTRODUCTION AND RATIONAL .
1.1. Introduction and study rational .
CHAPTER TWO LITERATURE REVIEW
2.1. Historical overview of noise-induced hearing loss (NIHL)
2.2. Worldwide prevalence of NIHL
2.3. Prevalence of NIHL in South African mining .
2.4. NIHL Mechanism of damage
2.5. NIHL and the audiogram
2.5.1. The notched audiogram .
2.6. Individual susceptibility and confounding factors in NIH
CHAPTER THREE LITERATURE REVIEW
3.1. Defining noise hazard
3.1.1. Historical overview of noise definitions and measurements
3.1.2. Noise measurement scales
3.2. Damage risk criteria: Levels and duration of noise exposure
3.2.1. Level of noise exposure – where does the risk to human hearing begin?
3.2.2. Duration of noise exposure – the time-intensity relationship
3.3. Exposure limit .
3.4. Compensation for hearing impairment
3.4.1. Formulae and calculation of hearing impairment
3.4.2. Contribution of age when calculating hearing impairment
3.5. Summary and conclusion
CHAPTER FOUR METHODOLOGY
4.1. Introduction
4.2. Problem statement
4.3. Aims
4.4. Hypotheses
4.5. Research Design
4.6. Ethical considerations.
4.7. Sample
4.7.1. Population
4.7.2. Criteria for selection of participants
4.7.2.1. Noise exposure
4.7.2.2. Age, race and gender
4.7.3. Description of research participants
4.8. Data Collection
4.8.1. Collection protocols and procedures
4.8.2. Personnel requirements for data collectio
4.8.3. Requirements of the equipment and test procedures for data collection
4.9. Data analysis procedure
4.10. Validity and reliability
4.11. Chapter summary
CHAPTER FIVE RESULTS
CHAPTER SIX DISCUSSION
CHAPTER SEVEN CONCLUSION .
CHAPTER EIGHT REFERENCES
APPENDIXES
