PREVALENCE OF NOISE INDUCED HEARING LOSS AMONG SELECTED BOTTLING COMPANY WORKERS IN ILORIN, NIGERIA
A DISSERTATION SUBMITTED
BY
DR. TOYE GABRIEL OLAJIDE
TO
THE NATIONAL POSTGRADUATE MEDICAL COLLEGE OF NIGERIA IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF THE FELLOWSHIP OF THE MEDICAL COLLEGE IN OTORHINOLARYNGOLOGY (FMCORL)
SUPERVISORS:
(1) DR. F.E. OLOGE FWACS, FMCORL DEPT. OF OTORHINOLARYNGOLOGY, UNIVERSITY OF ILORIN TEACHING HOSPITAL, ILORIN. NIGERIA.
(2) PROF. C.C. NWAWOLO FWACS, FMCORL ENT UNIT, DEPT. OF SURGERY, LAGOS UNIVERSITY TEACHING HOSPITAL, LAGOS. NIGERIA.
CERTIFICATION
We, the undersigned, hereby certify that this research titled “PREVALENCE
OF NOISE INDUCED HEARING LOSS AMONG SELECTED BOTTLING COMPANY
WORKERS IN ILORIN, NIGERIA” was duly carried out within the guidelines of the
National Postgraduate Medical College of Nigeria, under our supervision.
Dr. F.E. Ologe, FWACS, FMCORL Senior Lecturer and Consultant Otorhinolaryngologist, Department of Otorhinolaryngology, University of Ilorin Teaching Hospital, Ilorin.
…………………………………
Prof. C.C. Nwawolo FWACS, FMCORL Assoc. Prof. and Consultant Otorhinolaryngologist, ENT Unit, Department of Surgery, Lagos University Teaching Hospital, Idi-Araba, Lagos.
……………………………….
2
THIS PAGE IS FOR ETHICAL CLEARANCE
3 DECLARATION
I, Dr. Toye Gabriel Olajide hereby declare that this work is original and was done by me under the supervision of Dr. F.E Ologe and Prof. C.C. Nwawolo.
The work has not been presented to any other College for a fellowship award nor has it been submitted elsewhere for publication.
Dr. T.G. Olajide, Department of Otorhinolaryngology, University of Ilorin Teaching Hospital Ilorin.
………………………………………………
DEDICATION
4 This work is dedicated to the Glory of Almighty God and to my parents, wife and children for their support, love and care.
5 ACKNOWLEDGEMENT
I am deeply indebted to the administration of the Nigerian Bottling Company
Ilorin and particularly the participants for their co-operation.
I also wish to acknowledge my supervisors Dr. F.E. Ologe and Prof. C.C.
Nwawolo for their guidance and support in carrying out this study.
I am very grateful to Mr. S.O Oladunmoye, a Clinical Audiologist who assisted with audiometric tests.
My sincare appreciation also goes to Professor B.A. Oyejola, Mr. Mathew
Onoja (Statistics Department, University of Ilorin) and Dr. Ojo, of Community Health
& Epidemiology Department, University of Ilorin Teaching Hospital, for the analysis of the data.
Finally I thank Prof. P .A. Okeowo, Drs. A.D. Dunmade, Segun
Busari, S. B. Alabi and O.G.B. Nwaorgu for their contributions and constructive criticisms during the course of this study.
6 TABLE OF CONTENT
Contents Page Title page i Certification ii Certificate of Ethical Clearance iii Declaration iv Dedication v Acknowledgment vi Table of Content vii Summary viii
CHAPTER I Introduction 1
CHAPTER II Aims & Objectives 6
CHAPTER III Literature Review 7
CHAPTER IV Materials & Method 15
CHAPTER V Results 20
CHAPTER VI Discussion 40
CHAPTER VII Conclusion & Recommendation 45 References 46 Appendix 54 Questionnaires 57
7 SUMMARY
BACKGROUND: Exposure to excessive noise is one of the most common causes of sensorineural hearing loss worldwide. The manufacturing sector, including bottling companies, are places where such exposure is being encountered.
AIM: This study was carried out to determine the prevalence of noise induced hearing loss and the use of hearing protective devices (HPD) among workers exposed to excessive industrial noise in a bottling company.
METHODS: A prospective study surveying workers of the production section
(noise exposed area) of Nigerian Bottling Company, Ilorin was carried out in
December, 2003 and December, 2005. Self administered questionnaire was used to extract information about worker’s demographic characteristics, drug, medical, and occupational history as well as information on use of hearing protective devices
(HPD). Noise mapping of the various departments of the factory was carried out.
Otological examination, tympanometry, audiometry was also carried out on selected subjects. Each worker, was interviewed, examined and assessed twice within the 2 year period.
RESULTS: Eighty four workers, made up of 76 (90.5%) males and 8(9.5%) females were studied. Their mean age was 33.0 ± 7.6 in 2003 and increased to 35.0
± 7.6 in 2005. The recorded noise levels in the production section ranged between
91.5-98.7 dBA. The prevalence of sensorineural hearing loss among workers was noted to be 64.9% and 86.9% for test one and test two respectively. The degree of hearing deterioration within the two years of this study was between 3.1-10.9% for the right ear and 4.8-10.7% for the left ear. More than half (53.6%) of the workers do
8 not have hearing protective devices (HPD). Of the 46.4% who have, only 38.5% claim to have used it regularly.
CONCLUSION: The findings showed that there was high prevalence of sensorineural hearing loss and significant hearing deterioration among workers from exposure to excessive noise over a two year period. There is no change in the use of hearing protective device (HPD) over the two years. There is need to enforce existing occupational health laws in our industries to prevent noise induced hearing loss (NIHL), since it is eminently preventable.
KEYWORDS: Prevalence, noise induced hearing loss, Bottling company workers
CHAPTER ONE
INTRODUCTION Noise can be described as a sound that lacks agreeable musical quality or as unpleasant sound 1, 2. Based on its temporal patterns, noise may be continuous, intermittent, impulsive, explosive or fluctuant. Intermittent noise is interrupted with periods of quiet, while continuous noise remains constant. Fluctuating noise rises and falls over time. Both impact and impulse noises are produced by a sudden intense sound wave but impact noise is caused by a collision while impulse noise is due to an explosion3.
Noise induced hearing loss (NIHL) is a clinical condition that occurs gradually over many years of exposure to intense noise levels. Exposure to excessive noise is one of the most common causes of hearing loss in the world4.
Being a major occupational hazard world wide, it constitutes an important public health priority because, as populations live longer and industrialization spreads,
NIHL will add substantially to the global burden of disability5, 6.
9 Although industrialization is a global index of development, it has been a mixed blessing to mankind. On one hand, it enhanced the quality of life and on the other hand, poses serious threats to the management of natural systems and public health7. In Nigeria, industrial development is pursued with vigour but without adequate care for the environment7,8.
A bottling company is a factory that manufactures, distributes, and markets alcoholic and non alcoholic beverages. Examples of such bottling companies are the
Nigeria Bottling Company, 7-UP Bottling Company, Limca Bottlers, Nigeria
Breweries Limited, Sona Breweries Limited, and Guinness Nigeria Limited.
The Nigeria Bottling Company has operated continuously in Nigeria since
1953 and it produces Coca-cola, Diet Coke, Sprite, Fanta, Schweppes, Eva water,
Gold Spot, Krest, Limca, Parle Club Soda, and Five Alive9. The Nigeria Bottling
Company is the largest bottler in Nigeria, a nation with an estimated 133.2 million inhabitants10. The company along with its bottling partners directly provides job opportunity for an approximately 9,500 people in Nigeria9.
In Can manufacturing as well as bottling plants, an average peak noise level of 100dBA is encountered11. Continual exposure to noise levels of this intensity damage and destroys hair cells within the inner ear thereby causing noise induced hearing loss (NIHL). The risk of injury and hearing loss to the ear increases with the intensity of noise level, duration, frequency of exposures, susceptibility of an individual and the type of noise 4,12,13 Individual susceptibility to NIHL varies greatly, but the reason for the difference in susceptibility is not well-understood14,15. Although
NIHL is an irreversible impairment, it is 100% preventable4,16, 17.
In the food and drink industries in India an estimated 29,000 workers (4.8% of the work force) suffered from ill health caused or made worse from exposure to
10 excessive noise at work in the year 2001/2002 18 . In Nigeria, it was observed that over 300,000 workers are exposed to noise exceeding 90dB (A) during an eight-hour working day8. In this regard, the textile industry has attracted more attention in
Nigeria, than other industries.
Many affected workers experience hearing loss considerably beyond 25 dB and this can have significant effects on their employment, as well as social and family interactions19. There is tinnitus, difficulty in detecting warning signals, comprehending speech, localizing and recognizing sound sources in the setting of background noise. Everyday activities such as watching television, using a phone or keeping up with a conversation in a group can become difficult. This may lead to feelings of isolation, depression and sometimes people withdraw from society rather than getting help for their hearing loss 19,20,21.
Many countries spend huge amount of money on claims through workers’ compensation board for workers who develop NIHL. For example in Alberta, Canada it is estimated to cost $5.4 million -- a considerable commitment for a disease that makes up only 0.3% of all claims22. The estimated costs of noise to developed countries, range from 0.2% to 2% of their GDP (gross domestic product) 6. There is no accurate information on the cost of NIHL in developing countries.
Developing countries, including Nigeria, often lack both effective legislation against noise and programme to prevent NIHL. Where these exist, they are often poorly enforced and implemented 6, 7. The Factories Act is the oldest and most comprehensive piece of legislation laying down minimum standards of occupational safety, occupational health, and welfare of workers in Nigeria workplaces. It has recently been updated but awaiting final approval by the country’s regulatory bodies8.
11 The Federal Government of Nigeria in 1988 established the Federal
Environmental Protection Agency (FEPA). The decree 58 of 1988 requires FEPA to establish environmental guidelines and standards for the abatement and control of all forms of pollution. Specifically, the decree authorizes it to, among other things, establish and prescribe natural guidelines, criteria and standards for water quality, air and atmospheric quality, effluent discharge. Others are noise control, hazardous substance discharge control and the removal of wastes23,24 . In addition, FEPA is given some enforcement powers including the right to inspect facilities and premises, search locations, seize items, and arrest people contravening any laws on environmental standards and prosecute them24.
A far-reaching programme aimed at prevention of noise hazards in Nigerian workplace was initiated with the assistance of the ILO-FINNIDA African safety and
Health Project in 1993 and 19948.
Coca-Cola Company requires each plant to adopt the Coca-Cola company’s
“eKO System”10. It is a system specific to the company, put in place to initiate her own environmental standards, performance indicator and internal reporting10. In
2001, the company began to implement a management system based on the ISO
14001 standards at all their plants and facilities with the aim to have all their group- wide certified by mid-200610. The crucial step which remains weak seems to be serious minded implementation of these guidelines.
JUSTIFICATION FOR THE STUDY
This study will enable us to assess the noise level in various departments of the company and give opportunity to assess the effect the noise exposure has on the
12 hearing thresholds of exposed workers. We will also be able to determine the knowledge, attitude towards and practice of hearing conservation.
This knowledge could provide baseline information on the magnitude of the problem, policy formulation towards conservation guidelines and helping those affected.
LIMITATIONS OF THE STUDY
(1) The issue of hearing loss and noise exposure in industrial setting is a
sensitive one, the management (employer) or individual (employee) tend to
hold back information. The employee may be afraid of losing his job and
management may not want to pay compensation.
(2) Otoacoustic emission measurement which can be used to detect early
effects of noise on hearing and also differentiate NIHL from other causes of
cochlear damage was not available for this study.
(3) Personal noise dosimeter which measures individual work noise dose
exposure over a period of time was not available for this study.
13 CHAPTER TWO
AIMS AND OBJECTIVES
GENERAL
1. To determine the prevalence of noise induced hearing loss among selected
workers exposed to excessive noise in the production area of Nigeria Bottling
Company Plc, Ilorin.
SPECIFIC
1. To determine any changes in the hearing thresholds of the selected factory
workers, using pure tone audiometry, after 2 years of further exposure to
excessive noise in the bottling company.
14 CHAPTER THREE
LITERATURE REVIEW
There is an abundance of literature on noise induced hearing loss (NIHL) in the developed countries, but in developing countries literature is scanty, particularly regarding the bottling factory.
HISTORICAL CONSIDERATIONS
As reported by Alberti, the risk of hearing loss from exposure to excessive noise was first noticed from the use of metals, with the problem been compounded in
1300 AD with the discovery of gunpowder 4. Ramazzini, in his “De Morbis Artificum”, reported that workers who hammered copper for a living had their ears so injured by the perpetual din that they became hard of hearing. If they lived to old age and continued to work they became completely deaf 25
Noise-induced hearing loss was accurately described in blacksmiths in 1831, and the expression “blacksmith’s deafness” was given26. By the 1880s Roosa and
Holt in America, Bezold in Germany and Barr in Great Britain had recognized the importance of excessive noise as a cause of hearing loss, citing military and civil causes. Holt in 1882 published a study of “boilermakers’ deafness” which showed that many workers who made steam boilers developed hearing loss27.
The site and nature of the lesion in the ear produced by excessive noise was first described by Haberman (1890), in a 75 year old blacksmith 28. A dip at 4KHz was observed; and the first audiometric data demonstrating the typical high frequency loss acquired by those exposed to excessive noise was published 29, 30.
15 PATHOPHYSIOLOGY OF NOISE INDUCED HEARING LOSS
Perception of sound depends on the conduction of mechanical sound energy through the ossicles of the middle ear to the hydraulic medium of the cochlea. The mechanical energy is transduced into neural afferent information by the hair cells of the organ of corti within the spiral structure of the cochlea. This function depends on the structural integrity of the hair cells and surrounding support cells, local vascular structures and the immediate micro-environment of the organ of corti which is bathed in a potassium rich fluid. With excessive noise exposure, cellular changes occur within the hair cells of the cochlea, including loss of cilia and disruption of the hair cells31. Partial disappearance of the organ of corti has been reported with destruction of the hair cells, the most extensive damage being in the lower basal coil 28. Outer hair cells are more susceptible to noise exposure than inner hair cells.
Also from pathological points of view, the main lesions noted are in the ciliated cells of the organ of corti where there is fragmentation and loss of hairs, breakage of cellular membrane, and leakage of the nucleus and proliferation of the cells of
Deiters 29. Sound exerts a shearing force on the stereo cilia of the hair cells lining the basilar membrane of the cochlear. When excessive, this force can lead to cellular metabolic overload, cell damage and cell death. Noise-induced hearing loss therefore represents excessive “wear and tear” on the delicate inner ear structures4.
Studies on occupational hearing loss have shown that a typical hearing loss pattern results regardless of the noise source, the country or region in which the exposure occurs. Noise induced hearing loss occurs predominantly at higher frequencies (3000-6000Hz), with the greatest effect at 4000Hz31-33.
16 Exposure to excessive noise damages the hair cells and the blood supply in the cochlea, beginning at a frequency around 4 KHz. The damage is initially temporary but with greater noise exposure becomes permanent4, 13. The immediate response to damaging noise is a transient blunting of hearing acuity which shifts the subjects’ threshold of barely audible sound up to a higher level of sound for a period of hours. These episodes of temporary threshold shift (TTS) indicate an exposure to a harmful level of noise. It is reversible usually within 16 hours. This can be regarded as auditory fatigue and most studies indicate that it is associated with no sensory cell damage or minimal, reversible cell changes. Repeated exposure to excessive noise enough to produce (TTS), will eventually lead to permanent threshold shift (PTS), which is an irreversible increase in hearing thresholds. At this point, there is irreversible hair cell damage4,14,33,34. In theory the damage reflects both the intensity of the noise and the length or duration of exposure in a fashion which is predictable
(“equal energy principle”), this is not linear with respect to exposure; rather, the worker may experience a disproportionate loss in the early years of the exposure34.
OCCUPATIONAL RISK FACTORS
The major factor for occupational hearing loss is exposure to noise on the job.
The effect of excessive noise on hearing depends on a number of factors. These include: the noise level, duration of the exposure, frequency of exposure, individual susceptibility and vulnerability due to environmental and biological factors.
Occupational safety regulation defines the maximum allowable noise exposure for a normal working period: 85 dB (A) or 90 dB (A) for an 8-hour day. Higher levels are permitted if a corresponding shorter exposure time occurs. After a considerable debate, Occupational Safety and Health Administration (OSHA) arrived at the level
17 of 90 dB (A) exposure over an eight (8) hour period as the highest allowable dose. At this level it was observed to produce acceptably low rates of noise induced hearing loss in excess of 25 dB in the 1000-2000-3000 Hz range12, 34. In Nigeria, FEPA recommends that a level of 90 dBA of noise exposure over an eight (8) hour period is the highest allowable dose for industrial workers35.
Based upon the equal energy principle noted above, higher levels of noise can be tolerated for proportionately shorter periods of time. OSHA has specified that a 5 dB “exchange rate” be used to calculate acceptable noise exposures
(permissible noise exposure levels). Thus, an exposure of four hours at 95dBA is equivalent to eight (8) hours of 90dBA, as is two hours of 100dBA. Regular exposure to levels in excess of these limits will substantially increase the risk of most workers to NIHL. However this does not rule out injury to some workers at levels less than those defined by OSHA 36, 37. The OSHA criteria are intended to protect the average worker from permanent threshold shift (PTS) for 40 years of exposure, for 50 weeks per year, for 8 hours per day. However these guidelines will not protect all workers from PTS and do not account for any non work noise exposure. An “action level” has been defined by OSHA thus; the first action level is 85dBA for an 8-hour working day, at which point an employer is obliged to monitor the hearing levels of his work force and to monitor noise levels at the work place. At the second action level of
90dBA, he is statutorily obliged to provide a hearing protection programme to include hearing protection, monitoring and efforts to reduce sound levels at source34,38.
DEGREE OF HEARING LOSS
The degree of hearing loss is usually based on the hearing thresholds recorded on pure tone audiometry. Other information that can be obtained from pure tone audiometry include type of hearing loss (conductive, sensorineural, mixed),
18 sidedness (unilateral or bilateral), and configuration. However, the principal characteristics of occupational NIHL as specified by the American College of
Occupational Medicine Noise and Hearing Conservation Committee include the following:
*It is always sensorineural.
*It is nearly always bilateral and symmetrical.
*It will only rarely produce a profound loss.
*It will not progress once noise exposure is stopped.
*The rate of hearing loss decreases as the threshold
increases.
*The 4 KHz frequency is the most severely affected and the
higher frequencies (3-6 KHz) are more affected than the
lower frequencies (500Hz-2 KHz).
*Maximum losses typically occur after 10-15 years of chronic
exposure.
*Continuous noise is more damaging than intermittent
noise33, 39.
In addition to audiometric test, many authorities now include otoacoustic emission (OAE) measurements because it provides an earlier indication of noise induced hearing damage than pure tone thresholds alone12, 40. Sliwinska –Kowalska et al41reported that it is difficult to distinguish between noise induced hearing loss and other diseases with cochlear hearing loss by the means of conventional audiometric tests. Otoacoustic emission measurement is useful in this respect. In cases of noise induced hearing loss, distortion product otoacoustic emission
(DPOAE) measurements demonstrate a very typical shape of DP-gram with the
19 decrease (notch) primarily at the frequencies of 3-4 KHz. Such a notch in DP-grams was not observed in the cochlear hearing loss caused by factors other than noise41.
AUDIOMETRIC NOTCH AS A SIGN OF NOISE - INDUCED HEARING LOSS. Although the characteristic pattern of NIHL was recognized early in the development of pure tone audiometry, the progression of this loss was first studied systematically in cross sectional studies of the Jute industry in Dundee 28 and in a cross section of general work place in England and Wales42. These studies confirmed that with exposure to broad band, steady noise or noise with an impulse component, the first sign was a dip or notch in the audiogram maximal at 4 KHz, with recovery at 6 and 8 KHz. They also showed that the notch broadens with increasing exposure, and may eventually become indistinguishable from the changes of aging
(presbyacusis) where the hearing shows a gradual deterioration at the high frequencies. It was noted that though 4 KHz is the classic frequency affected, the notch may be noted elsewhere because the frequency range of the noise also influences where the cochlear damage occurs43.
Sulkowski44 showed that, the hearing impairment induced by impulse noise was greater and is characterized by the maximum loss at 6 KHz frequency, 44 as opposed to the notch at 4 KHz typical of continuous noise45-47. Abel et al48 showed that the effect of continuous noise exposure was maximal in the region of 2-6 KHz.
The sensorineural hearing loss which were detected among 71 out of 130 industrial workers were bilateral, symmetrical and affected mainly frequencies 4- 6 KHz49,50.
20
HEARING PROTECTION IN INDUSTRY In industry, hearing protectors are formally called “personal hearing protective devices” (PHPDs). To address the increasing concern over occupational NIHL, many industries have adopted hearing conservation programs (HCPs) 2. An effective
HCP has five components:
* Assessment of noise levels
* Engineering controls
* Administrative controls
* Use of personal hearing protectors and
* Serial audiograms2.
Hazardous noise levels can be identified with sound level meters or individual dosimeters. Once dangerous noise levels have been identified, various control measures are taken to minimize exposure.
Engineering controls involve changes in the technology or equipment used in industry. Examples of this would include applying mufflers to pneumatic drills, or redesigning machinery to enclose noisy gear wheels.
Administrative controls include limiting time of exposure to noise, providing a less noisy work environment, and educating workers about the prevention of NIHL.
When engineering and administrative controls fail to reduce noise to an acceptable level, personal hearing protective devices (PHPD) are vital to prevent
NIHL 2, 17, 51. Earplugs, earmuffs and canal caps are the three main types of PHPDs.
Earmuffs with a tight seal are capable of reducing sound levels by about 45dB in the high frequencies while earplugs average about 30dB of attenuation. Worn together, they provide a maximum of approximately 50dB of sound reduction 2, 13,17,52,53.
21 However, it is important to note that no PHPD will be effective unless the worker consistently wears it. Therefore, the most important aspect of choosing a
PHPD is worker comfort and confidence in using the device2.
Finally HCP involves serial audiometry to allow early identification of individuals with worsening hearing and to assess the efficacy of the program.
OSHA regulations recommend hearing protection for time weighted average
(TWA) up to or greater than 85dBA and require it for TWA up to or greater than
90dBA. However, if a worker has experienced a significant shift even with only
85dBA TWA, hearing protection is required. Hearing protection is required in any area clearly designated as “hearing protection required “regardless of the exposure duration and in any area with unmeasured high noise levels 17, 36.
It is important to mention that no device can offer complete protection from the ubiquitous noise sources in our society. Whichever control measures are considered by employers, ideally it should be in consultation with an experienced industrial hygienist or noise control expert12, 54.
People who conduct hearing conservation programs need to be diplomatic, understanding, knowledgeable and vigilant in the training and motivation of workers.
The hearing protector may be uncomfortable; requiring a change to different size or type, or it may be damaged or worn, requiring replacement. Alternatively, the employee may wear them incorrectly. Hearing conservation programs administered to ill motivated employees are likely to be a waste of time and resources55.
22 CHAPTER FOUR MATERIALS AND METHOD
DESCRIPTION OF THE STUDY AREA
The Nigerian Bottling Company Plc is located along Coca-Cola Road, off Unity Road Ilorin. It is one of the biggest plants in Kwara State and it also serves parts of Osun, Oyo, Kogi and Niger States. Commissioned in April
1979, it has staff strength of about 420, including the depots staff. The company has a staff clinic, manned by a Resident Doctor, which provides medical services for the staff and their dependants. The University of Ilorin
Teaching Hospital is the closest tertiary health care facility to the company.
An introduction letter was collected from the Head of the Department of
Otorhinolaryngology (ENT), University of Ilorin Teaching Hospital to the General
Manager of Nigerian Bottling Company, Plc Ilorin requesting for permission to carry out the research in their factory. The purpose of the study and the benefit to be derived from there was explained to the Head of Units/Department and all workers in the production section in groups. While their consent to participate in the study was sought, they were assured of confidentiality, and that their individual responses would not be disclosed to their administrator.
STUDY POPULATION AND PARTICIPANTS SELECTION
The participants were workers of the production section of Nigerian Bottling
Company Plc, Ilorin, Nigeria who were exposed to excessive noise. All the one hundred and sixteen (116) workers in this section who gave their consent were interviewed. Two separate interviews and examinations were carried out on each participant at two year interval; December 2003 and December 2005.
23 ETHICAL CONSIDERATION
Ethical clearance for this study was obtained from the University of Ilorin
Teaching Hospital Ethics and Research Committee.
INSTRUMENTS / EQUIPMENTS
The following instruments / equipments were used during this study.
1. Otoscope (auriscope) – Dry cell battery operated
2. Diagnostic Audiometer Danplex AS 67
3. Impedance Tympanometer AT 235
4. Sound level meter Testo 815
5. Sound level meter calibrator Testo 0554.0009
DATA COLLECTION INSTRUMENT
A structured self-administered questionnaire was used to collect relevant information (see Appendix). It was divided into the following sections.
1 Bio and social demographic data
2 Past medical and drug history
3 Occupational history
4 Questions related to hearing protective device (HPDS)
5 Examination and hearing assessment of respondent
DATA COLLECTION
A sound level meter Testo 815, calibrated with a sound level meter calibrator
Testo 0554.0009 was used to determine the noise level in each section / department. Four readings were taken for each department per day over five days; and the average sound level for each department was recorded.
24 The questionnaire was administered to the study population between 1-4pm each day. This period covers their break and change over time which readily gave opportunity to interview and carry out test for workers coming for afternoon duty.
Workers on morning and night duty were interviewed and assessed the week they were on afternoon duty. The workers were all briefed about the procedure before the examination and audiometric test were carried out.
Otoscopy was carried out to assess the presence of wax, foreign body, ear discharge, or tympanic membrane perforation. Retraction, scarring and dullness of tympanic membrane were also assessed. Only patients with clear external auditory canals, intact and shiny tympanic membrane proceeded further in the study.
Impacted wax and foreign body were removed where it was possible.
Tympanometry was used to assess the middle ear function of each participant by using impedance Tympanometer AT235. It was carried out using a probe inserted into the external auditory canal making sure that the canal is air tight. The participant was instructed to sit down quietly and not to talk, cough, smile, laugh, sneeze, or swallow during the procedure. Those that had abnormal tympanograms were excluded from the study.
Pure Tone Audiometry (PTA) was carried out by a clinical audiologist using a standard, dully calibrated Diagnostic Audiometer Danplex AS 67, to determine their hearing threshold. This was done in a quiet room in the factory clinic (sound level about 43.3dB ), located at a remote distance to the production section and electricity generating house so that ambient noise will not mask the acoustic stimuli. (For logistic reasons, subjects could not be transferred to our hospital for audiometry in a sound proof booth. Although this is less than optimal, it is acceptable given the measured sound level, and a recent observation of significant agreement between
25 hearing thresholds measured in non soundproof working environments and soundproof booth)56. Each ear was tested separately and in each case it lasted for about 10 minutes for each subject. Air-conduction (A-C) and bone conduction (B-C) tests were performed. For air conduction frequencies 500Hz, 1000Hz, 2000Hz,
3000Hz, 4000Hz, and 8000Hz were tested via a well fitting earphone, TDH 39, mounted in cushion. And for bone conduction frequencies 500Hz, 2000Hz, 3000Hz,
4000Hz were tested via a bone vibrator applied to the mastoid bone. During the test, the subjects were visible to the tester. No visible or tactile clues were available to the subjects so as to prevent enhancing the auditory stimulus. Subjects were made to respond to pure tone by signaling (either raising a finger or pressing the response button) 57.
The pure tone average (PTA) was determined for an individual by calculating the mean decibel loss on air conduction at frequencies 0.5,1,2 and 4 kHz on the audiogram 58. The results were classified into normal, mild, moderate, moderately- severe, severe and profound hearing loss using American National Standards
Institute (ANSI) or International Standards Organization (ISO) references for signal intensity 3.
26 CLASSIFICATION OF DEGREE OF HEARING LOSS
HEARING THRESHOLD DEGREE OF HEARING LOSS
(dB)
- 10 -25 Within Normal limit
26 -40 Mild loss
41 -55 Moderate loss
56 -70 Moderate-severe loss
71 – 90` Severe loss
> 91 Profound loss
INCLUSION CRITERIA i. All consenting production area workers who were exposed to excessive noise
from factory machines. ii. Workers who were able to participate in the first and second tests.
EXCLUSION CRITERIA i. All non consenting factory workers. ii. Subjects with impacted wax which could not be removed at the study site. iii. Subjects with history of chronic suppurative otitis media, previous ear surgery,
head injury, measles, mumps and family history of hearing loss. iv. Participants with abnormal tympanograms.
DATA ANALYSIS
The data was analyzed using Epi Info version 6.04 and SPSS version 10.0 statistical soft ware. Relationships between variables were assessed using Chi Square and T- test. A P- value of equal to or less than 0.05 was taking as statistically significant.
27 CHAPTER FIVE
RESULTS
One hundred and sixteen participants in the production section were recruited into the study. However, 24 participants could not conclude the first test due to abnormal otological findings such as suppurative otitis media (10), impacted wax (2), and abnormal tympanograms (8). Four workers had incomplete data. Eight workers were not available for the second test two years later; and so were excluded from the analysis. Therefore a total of 84 participants were eligible for inclusion in the final analysis after the second survey.
They were 76 males (90.5%) and 8 females (9.5%). The male to female ratio was 9.5:1 (Table I).
Table I
DISTRIBUTION OF RESPONDENTS BY SEX Sex Test one Test two n (%) n (%) Male 76 (90.5) 76 (90.5)
Female 8 (9.5) 8 (9.5)
Total 84 (100) 84 (100)
M: F 9.5:1 M: F 9.5:1
28
The mean age was 33.0 years (SD7.6) for the first test, with majority being
20-29 years (44.0%) and 30-39 years (31.0%). The mean age of the workers at the second test was 35.0 years (SD±7.6), majority being 30-39 years
(41.6%) and 20-29 years (27.4%). The age difference was not statistically significant (Table II).
Table II DISTRIBUTION OF RESPONDENTS BY AGE
Age group Test one Test two (yrs) n (%) n (%) 20-29 37 (44.0) 23 (27.4)
30-39 26 (31.0) 35 (41.6) Chi square =5.481 40-49 19 (22.6) 22 (26.2) df = 3 P value = 0.1
50+ 2 (2.4) 4 (4.8)
Total 84 (100) 84 (100)
Mean = 33.0 Mean = 35.0 SD ± 7.6 SD ± 7.6
29
Majority of the workers (46.2%) had tertiary education (Table III).
Table III
DISTRIBUTION OF RESPONDENTS BY EDUCATIONAL LEVEL
Educational level Test one Test two
n (%) n (%)
Primary 13 (15.5) 13 (15.5)
Secondary 28 ( 33.3) 28 (33.3)
Tertiary 43 ( 46.2) 43 (46.2)
Total 84 ( 100) 84 (100)
30 The workers were exposed to noise levels above safety standards; 36(42.9%) in bottling department (98.7dB), 27(32.1%) in the maintenance department (96.6dB) and 21(25.0%) in the quality assurance department (91.5dB) during the first test.
They were also exposed to noise levels above safe levels, 36(42.9%) in bottling department (98.1dB), 27(32.1%) in the maintenance department (96.2dB) and
21(25.0%) in the quality assurance department (91.6dB) during the second test
(Table IV).
Table IV DISTRIBUTION OF RESPONDENTS BY DEPARTMENT AND NOISE LEVEL (DECIBEL)
Noise level (dBA) Department n (%) Test one Test two
Bottling 36 (42.9) 98.7 98.1
Maintenance 27 (32.1) 96.6 96.2
Quality Assurance 21 (25.0) 91.5 91.6
Total 84 (100)
31
The mean duration of employment of the workers in their current job was 9.0 years (SD6.2) and 9.9 years (SD±6.2) for tests one and two respectively. The majority (70.2%) being on the job for 10 years in test one, while (57.1%) had been on the job for ≤ 10years during the second test. (Table V).
Table V
DISTRIBUTION OF RESPONDENTS BY DURATION OF EMPLOYMENT
Duration of employment Test one Test two
(year) n (%) n (%)
1-10 59 (70.2) 48 (57.1)
11-20 19 (21.6) 27 (32.2) Chi Squ =3.122
df=2
21-30 6 (7.1) 9 (10.7) P value=0.2
Total 84 (100) 84 (100)
Mean =9.0 Mean =9.9 SD±6.2 SD±6.1
32 Only five (6.0%) of the workers had pre employment hearing test. The mean hearing thresholds at each frequency tested was elevated in both right and left ears.
The threshold is worsened with increasing frequency, but maximum was recorded at
4 KHz. The mean hearing thresholds were significantly worse in test two than in test one. The degree of deterioration of hearing loss between test one and two was noted to be in the range of (3.1-10.9%) for the right ear and (4.8-10.7%) for the left ear
(Table VI, Fig. 1 & 2).
TABLE VI MEAN HEARING THRESHOLD LEVELS OF RESPONDENTS
Rate of deterior MEAN HEARING THRESHOLD ation (%) FREQUENCY TEST ONE TEST TWO t df P. VALUE (KHz) (dB ±S.D) (dB ± S.D) R 0.5 25.95.8 29.1 7.1 10.9 -3.216 166 0.002 R 1.0 29.16.7 31.5 6.6 7.6 -2.319 166 0.002 R 2.0 30.26.2 32.6 6.2 7.4 -2.554 166 0.01 R 3.0 30.77.0 32.7 6.6 6.1 -1.988 166 0.05 R 4.0 33.38.1 34.7 7.6 4.0 -1.165 166 0.2 R 8.0 31.4 6.6 32.4 6.2 3.I -1.018 166 0.3
L 0.5 25.06.2 28.0 6.3 10.7 -3.093 166 0.002 L 1.0 27.36.7 30.4 7.3 10.2 -2.825 166 0.005 L 2.0 28.46.7 31.3 6.4 9.3 -2.811 166 0.006 L 3.0 27.85.8 31.2 6.3 10.9 -3.643 166 0.000 L 4.0 31.48.4 33.0 7.0 4.8 -1.363 166 0.2 L 8.0 29.1+6.7 31.06.9 6.1 -1.747 166 0.08
NB R = Right Ear L = Left Ear
33
Fig.1
34
Fig.2
35 Table VII showed mean hearing thresholds of subjects by department at each frequency for each ear for tests one and two. It follows the same patterns as above, but differences between departments were not consistent.
36 TABLE VII
37 The results of the audiometric test done showed mild SNHL in sixty-three
(75%) right ears, forty two (50%) left ears of the workers in test one as compared to test two with sixty eight (81%) right ears and sixty seven (79.8%) left ears. Moderate
SNHL was recorded in 2(2.4%) right ears and 2(2.4%) left ears in test one, compared to eight (9.5%) and three (3.6%) recorded in right and left ears respectively in test two. Normal hearing thresholds were recorded in 19 (22.6%) right ears and 40 (47.6%) left ears of workers in test one compared to test two where only 8(9.5%) of the right ears and 14(16.7%) of the left ears had normal hearing thresholds (Table VIII).
TABLE VIII Distribution of respondents showing degree of hearing loss
RIGHT EAR LEFT EAR DEGREE OF HEARING LOSS (dB) TEST ONE TEST TWO TEST ONE TEST TWO
N (%) N (%) N (%) N (%)
Within Normal limit < 26 19 (22.6) 8 ( 9.5) 40 (47.6) 14 (16.7)
Mild loss 26 – 40 63 (75.0) 68 (81.0) 42 (50.0) 67 (79.8)
Moderate loss 41-55 2 (2.4) 8 (9.5) 2 (2.4) 3 (3.6)
Total 84 (100) 84 (100) 84 (100) 84 (100)
38
Of the 59 workers in test one and 48 workers in test two, that had worked in the factory for 10years, 20.3% had normal hearing threshold in the right ear (22.9% in test two); 54.2% had normal hearing threshold in the left ear (62.5% in test two).
76.3% had mild hearing loss in the right ear (72.9% in test two); 42.4% had mild hearing loss in the left ear (37.5% in test two); 3.4% had moderate hearing loss in the right ear (4.2% in test two); and 3.4% had moderate hearing loss in the left ear
(none in test two). Of the19 workers in test one and 27 workers in test two, that had worked in the factory between 11-20 years, 31.6% had normal hearing threshold in the right ear (25.9% in test two); 31.6% had normal hearing threshold in the left ear
(25.9% in test two); 68.4% had mild hearing loss in the right ear (74.1% in test two);
68.4% had mild hearing loss in the left ear (66.7% in test two). Of the 6 workers in test one and 9 workers in test two, that had worked in the factory between 21-30 years, 16.7% had normal hearing threshold in the right ear (11.1% in test two);
33.3% had normal hearing threshold in the left ear (33.3% in test two); 83.3% had mild hearing loss in the right ear (88.9% in test two); 66.7% had mild hearing loss in the left ear (also 66.7% in test two). (Table IX).
39
TABLE IX
40 The prevalence of SNHL among the workers in the bottling department was
52.8% (81.9% in test two); maintenance department 81.5% (98.1% in test two); and quality assurance department 64.3% (80.9% in test two). The overall prevalence of hearing impairment among workers in test one was 64.9% in contrast to test two with a prevalence of 86.9 % (Table X).
41
TABLE X
42
More than half (53.6%) of the workers do not have hearing protective devices (HPD). Of the 39 who had HPD, 36 (92.3%) had ear muffs, and 3(7.7%) had ear plug. Also only 15(38.5%) claimed to use the device always and 2(5.1%) never use it. The situation remains the same in test two. (Table XI).
Table XI DISTRIBUTION OF SUBJECTS BY HEARING PROTECTIVE DEVICE (HPD) TEST ONE TEST TWO PARAMETER N (%) N (%)
I. Hearing protective device (HPD) Yes 39 46.4 39 46.4 No 45 53.6 45 53.6 Total 84 100.0 84 100.0 II. Type of HPD Ear muffs 36 92.3 36 92.3 Ear plug 3 7.7 3 7.7 Total 39 100.0 39 100.0 III. Use of HPD Never 2 5.1 2 5.1 Sometimes 22 56.4 22 56.4 Always 15 38.5 15 38.5 Total 39 100.0 39 100.0
43
Of the 45 workers that were exposed to excessive noise and do not have
HPD, 20.0% had normal hearing thresholds in the right ear (8.9% in test two); 33.3% normal hearing thresholds in left ear (15.6% in test two). Thirty five (77.8%) had mild hearing loss in the right ear (82.2% in test two); 62.2% had mild hearing loss in the left ear (80.0% in test two). 2.2% had moderate hearing loss in the right ear (8.9% in test two); 2.4% had moderate hearing loss in the left ear (2.4% in test two). Of the 15 workers that were exposed to excessive noise and claimed to have used HPD always 33.3% had normal hearing thresholds in the right ear (13.3% in test two);
60.0% had normal hearing thresholds in the left ear (6.7% in test two). 66.7% had mild hearing loss in the right ear (73.3% in test two); 40.0% had mild hearing loss in the left ear (86.7% in test two). None of them had moderate hearing loss in the right ear (13.3% in test two); none of them also had moderate hearing loss in the left ear
(6.7% in test two). Of the 22 workers that were exposed to excessive noise and uses the HPD sometimes, 18.2% had normal hearing thresholds in the right ear (9.1% in test two); 63.6% had normal hearing thresholds in the left ear (27.3% in test two);
77.3% had mild hearing loss in the right ear (81.8% in test two); 36.4% had mild hearing loss in the left ear (72.7%in test two). Of the two workers that had never use
HPD, one had normal hearing thresholds in the right ear (none in test two); both of them had normal hearing thresholds in the left ear (none in test two). One had mild hearing loss in the right ear (both in test two); none had hearing loss in the left ear
(both had mild hearing loss in the left ear in test two). (Table XII).
44 TABLE XII
45 Of the 37 workers in test one and 23 workers in test two within the age group 20-29 years, 18.9% had normal hearing thresholds in the right ear (21.7% in test two); 56.8% had normal hearing thresholds in the left ear(69.6% in test two).
75.7% had mild hearing thresholds in the right ear (78.3% in test two); 43.2% had mild hearing thresholds in the left ear (30.4% in test two). Only 5.4% had moderate hearing loss in the right ear (none in test two). Of the 26 workers in test one and 35 workers in test two within the age group 30-39years, 26.9% had normal hearing thresholds in the right ear (22.9% in test two); 42.3% had normal hearing thresholds in the left ear (42.9% in test two), 73.1% had mild hearing loss in the right ear (71.4% in test two); 53.8% had mild hearing loss in the left ear (54.3% in test two). None had moderate hearing loss in the right ear (5.7% in test two). 3.8% had moderate hearing loss in the left ear (2.9% in test two). Of the 19 workers in test one and 22 workers in test two within the age group 40-49 years, 21.1% had normal hearing thresholds in the right ear (22.7% in test two); 36.8% had normal hearing thresholds in the left ear
(31.8% in test two) .78.9% had mild hearing loss in the right ear (77.3% in test two);
63.2% had mild hearing loss in the left ear (68.2% in test two). Of the 2 workers in test one and 4 workers in test two who were aged above 50 years, 50% had normal hearing thresholds in the right ear(25.0% in test two); 50% had normal hearing thresholds in the left ear (50% in test two) . 50.0% had mild hearing loss in the right ear (75.0% in test two); none had mild hearing loss in the left ear (25.0% in test two).
50.0% had moderate hearing loss in the left ear (25% in test two). (Table XIII).
46 TABLE XIII
47 CHAPTER SIX DISCUSSION
The average noise exposure level recorded at the production area of the Nigerian
Bottling Company, Ilorin exceeds the 90.0dB (A) which is the maximum or highest allowable level of noise that a worker can be exposed to for a period of 8 hours per day as laid down by hearing conservation criteria34,59. In Nigeria a level of 90 dB (A) of noise exposure over an eight (8) hour period is the highest allowable dose recommended by FEPA35.
Only 5 (6.0%) of our study population, had pre employment hearing test done.
The proportion of those workers that had pre-employment hearing test done is very low when compared with the workers in the production section. It is not surprising since there is no enforcement on law stipulating pre-employment hearing test for factory workers in Nigeria. Where such a pre-employment test is required majority of workers tend to refuse the test, ignorantly supposing that negative findings may disqualify them from securing such jobs.
Result of pure tone audiometric test in this study also revealed significant increase in mean hearing threshold levels of workers both in test one and test two, worse at 4 KHz. It could be attributed to the excessive high level of noise they were exposed to in their various departments. Similar findings were observed in other studies44,50.
The prevalence rate of noise induced hearing loss among our study population was 64.5% and 86.9% for the first and second survey respectively. In the
47, 58, 60-62 literature prevalence rates of 3-82% have been reported . Importantly over a two year period the rate of deterioration was significantly high. It has been observed that the rate of deterioration in hearing threshold is more rapid in the first ten to
48 fifteen years of exposure to excessive noise33, 39. This study population falls within this category.
The implication of the above is that continued exposure of these workers to their current noise level will lead to worsening NIHL. Possibly by the time they reach retirement age they may have moderate to severe NIHL. This will significantly affect the quality of their post retirement life.
Life in retirement could be challenging because some people drop out of social circulation largely because their income cannot support their pre-retirement standard of living. There is also a tendency towards irrelevance in the society.
Significant hearing loss would worsen these and tip affected individuals into greater isolation. It also reduces the chances of post retirement employment and contribution to life. Ultimately the overall burden of the employment may become greater than its benefits.
In this study, the maximum mean hearing loss was recorded at 4 KHz in all the departments among the workers. These observations were also documented in previous studies 43, 46,47,58,63. Usually the 4 KHz is the greatest hearing threshold shift in typical NIHL. However, studies among workers at oil refinery in Taiwan recorded greatest hearing threshold shift in noise-exposed workers at 6 KHz63, 64.
The mean duration of employment for the workers in this study was 9.0 and 9.9 years. Majority (70.2%) of the workers in test one and 57.1% in test two had worked between 1-10 years. Permanent hearing threshold shift was noted in workers exposed to excessive noise for less than 10 years49. In some other studies the duration of employment was longer before they developed such permanent threshold shift65, 66. Thus the time duration of exposure before permanent hearing threshold shift varies; possibly depending on the noise intensity, type of noise and individual
49 susceptibility. It is therefore not wise to risk exposure to excessive noise, however brief.
In this study, more than half (53.6%) of our subjects did not have hearing protective devices (HPD). Some in the production section claimed they were never given at any time. It was observed during the process of data collection that some workers who had HPD did not wear them correctly. The workers seem to choose when they wore the devices. These we attribute to lack of counseling or education on the use of HPD. Also, there seems to be no law enforced regarding the use of
HPD.
There are various reports on the use of HPD among industrial workers exposed to excessive noise 26, 34, 47, 58, 66-69. Regular use of HPD in our study was
38.5% which is much lower than the over 60% reported among workers in Thailand and Korea65, 70. In one study although HPD was provided for 80.5% of the workers, only 5.1% wore them regularly; and the possibility of developing hearing loss due to excessive noise was only known by 35.5% of the noise exposed workers 71. In another study 80% of workers had “never” used such devices, 16.7% and 3.3% used cotton wool “occasionally” and “always” respectively to reduce exposure to excessive noise level in industry69. In our study, 6.5% of the workers used cotton wool as HPD; claiming that it is easier to insert and to remove.
Majority of our subjects who did not have HPD had mild sensorineural hearing loss affecting both ears in test one and worse in test two. Some progressed to moderate sensorineural hearing loss in test two. Also majority of those that claimed to have used HPD “always”, had hearing impairment worsening in test two.
This may be an indication of incorrect use or less than optimal compliance.
50 Correct and regular use of HPD is known to prevent noise induced hearing loss. Axlesson et al in their study revealed that those with normal hearing had used ear protector considerably and properly more than those with severe hearing loss52.
Reasons given for non regular and proper usage of HPDs among workers in this study, included inconveniences; being accustomed to the noise in the factory, device considered unnecessary and the non availability of genuine HPDs. Thai female workers gave similar reasons69. But in addition to the above reasons lack of proper counseling, health education, enforcement and monitoring seem to be major contributing factors.
There is no provision for regular measurement and monitoring of noise level in the production section. Thus excessive noise exposure, coupled with reluctant use of appropriate HPD leaves the majority of the exposed employees at high risk of developing NIHL. It is well to note that the regular use of HPD protects the hearing and that wearing hearing protection devices only “sometimes” is a practice, similar to non-use 58.
Although noise induced hearing loss should be bilateral and symmetrical49 a study done among industrial workers in two plants in Eastern Saudi Arabia58 and other studies recorded asymmetrical sensorineural hearing loss in some workers46,65,66. It was suggested that the asymmetry noted in one of such studies is a manifestation of lateral difference in susceptibility to noise damage66.
A mean age of 33.0 and 35.0 years was observed among the workers in the test one and two respectively. This is similar to other studies47, 58, 72. High male to female ratio of 9.5:1 was noted among the workers. This was expected as the labour intensive nature of the production section of most industries, relies on the need of
51 youthful, able bodied men at their prime age47. It is unfortunate that these men in their prime have to pay the heavy price of NIHL in search of their daily bread.
It is important to mention that in the general population current studies are in conclusive regarding specific patterns of gender differences in sensorineural hearing loss73-75. On the whole the male sex may be associated with increased incidence of hearing loss after adjusting for age. One of the major reasons adduced is related to more noise exposure, with the attending noise induced hearing loss in males. The preponderance of males in this study may add to the body of evidence in that respect.
Noise exposure outside work place as a cause of sensorineural hearing loss among our subjects may be difficult to determine. But there is overwhelming evidence that occupational noise exposure is a major factor in them.
52 CHAPTER SEVEN
CONCLUSION & RECOMMENDATION CONCLUSION
(1) The workers in the production area of Nigerian Bottling Company are
exposed to noise level in excess of permissible safe standards.
(2) The overall prevalence of sensorineural hearing loss among the study
population was 64.9% and 86.9% at test one and test two respectively.
(3) Maximal hearing threshold loss was noted at 4 KHz.
RECOMMENDATIONS
The following recommendations were made as a result of findings in this study.
(1) The noise level at various department of the factory should be monitored
regularly, may be monthly. Efforts, especially engineering and
administrative methods at keeping noise level within permissible safe
standards should be rigorously pursued.
(2) Pre employment hearing test should be included in the pre employment
medical test of all workers. This will serve as the individual worker’s
baseline measurements.
(3) Periodic audiometric measurements, at least once in every year, should be
carried out among workers. This will help to monitor the hearing threshold
of individual workers at risk. Workers with worsening hearing threshold
levels should be promptly re-assigned to non-noisy areas of the factory.
(4) Adequate counseling and health education regarding hearing conservation
should be carried out annually to all staff of the factory.
(5) Regular and correct use of HPD should be enforced and properly
monitored in the factory floor.
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61 APPENDIX
DEFINITION OF TERMS Noise – any undesired or unwanted sound, usually of high intensity.
High noise areas - where noise levels exceed approved safety standards usually
≥ 90dB.
Noise exposure limits – Defined as not exceeding 90dB for 8hrs a day in a 5-
day working week.
Decibel (dB) – a unit used to measure the intensity of sound i.e. its loudness.
Hertz (Hz) – a unit of measurement of frequency of sound and is numerically
equal to cycles per second.
Sound level meter – an instrument for the measurement of sound level.
Noise dosimeter - an instrument that integrates a function of sound pressure
over a period of time in such a manner that it directly indicates a noise dose.
Time - weighted average sound level – that sound level which if constant over
an 8-hour exposure, would result in the same noise dose as is measured.
Audiometry – a test carried out on an individual using a machine called an
audiometer, which determines the threshold of hearing at different frequencies.
Threshold hearing level - the minimum sound intensity detectable by the ear of
the subject.
Occupational hearing loss - a hearing impairment of one or both ears, partial or
complete, arising in or during the course of one’s employment.
ABBREVIATIONS
OSHA - Occupational Safety and Health Administration
EPA – Environmental Protection Agency.
NIOSH - National Institute for Occupational Safety and Health
62 NIHL – Noise Induced Hearing Loss
OAE – Otoacoustic emission
ANSI – American National Standard Institute
PHPD – Personal Hearing Protective Device
ISO – International Standard organization
FEPA – Federal Environmental Protection Agency.
63 CONSENT FORM
RESEARCH STUDY: PREVALENCE OF NOISE INDUCED
HEARING LOSS AMONG SELECTED BOTTLING COMPANY WORKERS
IN ILORIN, NIGERIA
I ………………………………………….of…………………………………….. hereby consent to participate in the above research study. Dr T.G. Olajide has explained the nature and benefits of the study to all the Head of Units /
Department and all Staff of production section.
Date…………………………………. Signed ………………………………….
I confirm that I have explained to you the purpose, nature and benefit of the study. All information obtained in this study is strictly confidential, and if any information is published there will not be any information, which will identify you as a participant.
Date………………………………… Signed …………………………………..
64 PREVALENCE OF NOISE INDUCED HEARING LOSS AMONG SELECTED BOTTLING COMPANY WORKERS IN ILORIN, NIGERIA
QUESTIONNAIRE Dear Respondent, this study is for research purpose and information provided will be treated as confidential. Thank you. BIO AND SOCIO DEMOGRAPHIC DATA 1. Name (Optional) ------2. Age ------Years 3. Sex Male ( ) Female ( ) 4. Educational level: None ( ) Primary ( ) Secondary ( ) post secondary ( ) 5. Department / Section------6. For how long have you been working in this factory? ------Years. 7. For how long have you been in the present department / section -years? 8. How many hours do you work here in a day? ------hours. 9. Did you carry out any hearing test before you started this job? .Yes ( ) No ( ) MEDICAL AND DRUG HISTORY 10 . Have you ever experienced any of the following, indicate when: Yes No Year i. Loss of consciousness ii. Fits / convulsion iii. Frequent cold/ catarrh iv. Head injury 11. Have you ever had any of the following illnesses, indicate when: Yes No Year i. Mumps ii. Measles iii. Meningitis iv. Chicken pox v. Sickle cell disease vi. Operation in the ear
65 12. Have you ever had any difficulty with hearing or noise in the ear following taking any of these drugs listed below? Yes No Year i. Aspirin ii. Quinine iii. Streptomycin iv. Gentamycin
13 . Did you have any of the following ear problems before you started this job? i. Ear discharge (e.g. pus or water) Yes ( ) No ( ) If Yes for how long------ii. Ear Ache (pain) Yes ( ) No ( ) iii. Noise in the Ear / head (Tinnitus) Yes ( ) No ( ) If Yes for how long ------Iv. Hearing Problem Yes ( ) No ( ) if Yes specify------v. Others (Specify) ------OCCUPATIONAL HISTORY 14 Are you exposed to noise in this section of the factory? Yes ( ) No ( ) Not sure ( ) 15 Do you know that continuous exposure to excessive noise can cause deafness? Yes ( ) No ( ) not sure ( )
16. Is it possible to protect factory workers from exposure to excessive noise and associated deafness? Yes ( ) No ( ) Not sure ( ) If Yes how can they be protected? (Choose from the following) i. Using hearing protective devices like ear plugs or muffs ii. By reducing the noise of machine using silencer or regular maintenance iii. By reducing the period of exposure to machine iv. Isolation of noisy machine v. Regular health education to the factory workers on hazard of noise vi. Change of department / section on regular basis vii. Other specify
66 17. Have you had any of the following Ear problems since you started working in this factory? i. Noise in the Ear / Head (Tinnitus) Yes ( ) No ( ) ii. Hearing loss Yes ( ) No ( ) iii. Inability to discriminate speech Yes ( ) No ( ) v. Other (specify)………………………………………. 18. Do you have any hearing protective device to reduce the noise you are exposed to? Yes ( ) No ( ) If yes what type of device? ------How often do you use this device? Never ( ) Sometimes ( ) Always ( ) If never, state reasons for not using hearing protective device. (Choose from the following) i. Device not available in the factory. ii. Considered not necessary. iii. Not convenient when used. iv. Noise level is low in the section / department. v. Other (specify)………………………………….. 19. Apart from hearing protective device do you adopt other method to protect yourself from the noise exposure? Yes ( ) No ( ) If yes state them------20. Have you assessed your hearing ability before in any hospital? Yes ( ) No ( ). If yes what prompted you to do the assessment? i. Routine Examination ii. Feeling of impaired hearing / blockage iii. Noisy sensation in the Ear / Head (Tinnitus) iv. Referral v. Other (specify)……………………………………………………….
67 HEARING ASSESSMENT I. OTOSCOPY (R) (L) Ear Canal ------Tympanic Membrane ------
B. TUNING FORK TEST (R) (L) ------Rinne ------Weber ------
C. PURE TONE AUDIOMETRY (500, 1000, 2000, 3000, 4000, 6000, 8000 Hz) (R) (L)
D. TYMPANOMETRY (R) (L) Middle Ear pressure ------Compliance ------Ear Canal volume ------Gradient ------
68