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Evaluation of Noise Pollution Levels in Manufacturing Sectors in
Thika District-Kenya
James Mithanga
A Thesis Submitted in Partial Fulfillment for the Degree of Master
of Science in Occupational Safety and Health in the Jomo Kenyatta
University of Agriculture and Technology
2013
i
DECLARATION
This thesis is my original work and has not been presented for a degree in any other
university.
Sign……………………………
Date………………………
James Mithanga Njeri
This thesis has been submitted for examination with our approval as the University
Supervisors:
Signature ………………………..
Date………………………
Prof. Erastus Gatebe
JKUAT, Kenya
Signature ………………………..
Date………………………
Mrs. Margaret Gichuhi
JKUAT, Kenya
ii
DEDICATION
To my family for their support and encouraging words as I pursued my degree
iii
ACKNOWLEDGEMENT
I would like to express my earnest gratitude and appreciation to my supervisors Prof.
Gatebe and Mrs. Gichuhi. I thank them for their constructive comments and
corrections on the thesis. I also want to thank my family and friends who gave me
encouragement during the research. I particularly want to thank my wife Eunice
Wandia and my son Lincoln Njega. Thank you all for the support you gave me
through this period and God bless you. A project of this magnitude generally
required support of different forms from many other colleagues and experts who will
remain anonymous out of brevity rather than ingratitude.
iv
TABLE OF CONTENTS
DECLARATION ......................................................................................................... ii
DEDICATION ............................................................................................................ iii
ACKNOWLEDGEMENT .......................................................................................... iv
TABLE OF CONTENTS ............................................................................................. v
LIST OF TABLES ...................................................................................................... ix
LIST OF FIGURES ...................................................................................................... x
LIST OF PLATES ....................................................................................................... xi
LIST OF APPENDICES ............................................................................................ xii
LIST OF ABBREVIATIONS ................................................................................... xiii
OPERATIONAL DEFINITIONS ............................................................................. xiv
ABSTRACT .............................................................................................................. xvi
CHAPTER ONE .......................................................................................................... 1
INTRODUCTION ........................................................................................................ 1
1.1 Background Information .................................................................................... 1
1.2 Statement of the problem ................................................................................... 3
1.3 Justification ........................................................................................................ 4
1.4 Hypotheses ......................................................................................................... 6
1.5 Objectives ........................................................................................................... 6
1.5.1 General objective......................................................................................... 6
1.5.2 Specific objectives....................................................................................... 6
1.6 Scope of the study .............................................................................................. 7
1.7 Limitation of the study ....................................................................................... 7
CHAPTER TWO.......................................................................................................... 8
v
LITERATURE REVIEW ............................................................................................. 8
2.1 Sound and noise ................................................................................................. 8
2.2 Measurement of noise ........................................................................................ 9
2.2.1 Instrumentation for noise measurement .................................................... 12
2.3 Noise exposure ................................................................................................. 14
2.4 The anatomy and physiology of the ear ........................................................... 15
2.5 Effects of noise ................................................................................................. 18
2.5.1 Health effects............................................................................................. 18
2.5.2 Noise induced hearing loss ........................................................................ 19
2.5.3 Occupational hearing loss ......................................................................... 19
2.5.4 Non occupational hearing loss .................................................................. 20
2.6 Noise standards and protocols .......................................................................... 20
2.6.1 ISO and OSHA permissible exposure levels ............................................ 20
2.6.2 NIOSH Recommended exposure limit ...................................................... 20
2.7 Noise control in industrial premises ................................................................. 21
2.7.1 Introduction ............................................................................................... 21
2.7.2 Noise control at the source ........................................................................ 21
2.7.3 Noise control in a transmission path ......................................................... 22
2.7.4 Protecting the receiver ............................................................................... 22
2.8 Prevention of noise induced hearing loss ......................................................... 23
CHAPTER THREE .................................................................................................... 25
MATERIALS AND METHODS ............................................................................... 25
3.1 Research design ................................................................................................ 25
3.2 Target population ............................................................................................. 25
vi
3.3 Sampling frame ................................................................................................ 25
3.4 Sample size and sampling techniques .............................................................. 26
3.5 Data collection instruments .............................................................................. 27
3.6 Pilot survey....................................................................................................... 27
3.7 Data collection procedure................................................................................. 28
3.8 Data processing and analysis............................................................................ 30
CHAPTER FOUR ...................................................................................................... 31
RESULTS AND DISCUSSIONS .............................................................................. 31
4.1. Socio-economical characteristics of the participants ...................................... 31
4.1.1 Age categorization of employees .............................................................. 31
4.1.2 Gender categorization of employees ......................................................... 32
4.1.3 Educational level of the employees ........................................................... 34
4.2 Effects of occupational noise levels on communication and work among
employees in the manufacturing sectors sampled ............................................ 36
4.3 Noise compliance levels against set standard for the manufacturing sectors
sampled............................................................................................................. 43
4.3.1 Compliance to set standards ...................................................................... 43
4.3.2 Permissible Noise levels............................................................................ 44
4.3.3 Noise prevention program ......................................................................... 45
4.3.4 Noise measurements records ..................................................................... 46
4.3.5 Information and training of workers ......................................................... 47
4.3.6 Medical examinations and hearing tests.................................................... 49
4.4 Noise intensity in different departments of the selected manufacturing
industries .......................................................................................................... 51
vii
4.4.1 Noise levels in departments....................................................................... 51
4.4.2 Noise levels in the office department ........................................................ 52
4.4.3 Noise levels in the production departments .............................................. 53
4.4.4 Noise levels in the generator department .................................................. 54
4.5 Magnitude of occupational noise exposures of workers in different categories
of manufacturing industries .............................................................................. 56
CHAPTER FIVE ...................................................................................................... 59
CONCLUSIONS AND RECOMMENDATIONS ................................................. 59
5.1 Conclusions ...................................................................................................... 59
5.2 Recommendations ............................................................................................ 59
5.3 Suggestions for further research ....................................................................... 61
REFERENCES ......................................................................................................... 62
APPENDICES .......................................................................................................... 69
viii
LIST OF TABLES
Table 2. 1: Volume of different sounds encountered commonly, expressed in dB
(A) (MoL, 2010). ................................................................................... 12
Table 3. 1: Different categories of manufacturing industries that were sampled... 26
Table 4.1:
Chi-Square tests for number of years worked in the company ............ 31
Table 4.2:
Chi-Square tests on the gender of employees in the selected companies33
Table 4.3: Chi-Square on workers qualification of the selected companies .......... 35
Table 4.4:
Companies compliance to the set standards/rules on noise ................. 44
Table 4.5:
Analyzed data for compliance levels in different companies ............. 46
Table 4.6:
Analyzed noise level in the office department of the selected
companies ............................................................................................ 52
Table 4.7:
Analyzed noise levels in the production department of the selected
companies ............................................................................................ 54
Table 4.8:
Analyzed noise levels in the generator department of the selected
companies ............................................................................................ 55
Table 4.9:
Number of workers exposed to noise in 3 departments of the selected
companies ............................................................................................ 56
Table 4.10:
Noise exposure magnitude among employees in the selected
companies ........................................................................................... 57
ix
LIST OF FIGURES
Figure 4. 1:
Age categorization of employees ...................................................... 32
Figure 4. 2:
Gender percentage of the employees. ................................................ 33
Figure 4. 3:
Educational level of the resoponents in the eight companies ............ 35
Figure 4. 4:
Compliance to hearing PPE at work .................................................. 48
Figure 4. 5:
Compliance on training regarding noise ............................................ 49
Figure 4. 6:
Pre-employment hearing test ............................................................. 50
x
LIST OF PLATES
Plate 2. 1: Digital sound level meter, IEC 651, type 2, model: SL-4001. .............. 14
Plate 2. 2: Anatomical division of the Human ear ................................................. 17
xi
LIST OF APPENDICES
Appendix 1:
Questionnaire .................................................................................... 69
Appendix 2:
Industries compliance with the set rules and regulations on noise ... 73
Appendix 3: Questionnaire response ..................................................................... 74
xii
LIST OF ABBREVIATIONS
ACGIH
American conference of governmental industrial hygienist
ANSI
American national standard institute
dB(A)
Average weighted sound level in decibel unit
DOSHS
Directorate of Occupational safety and health services
HCP
Hearing conservative program
HPD
Hearing protective devices
ISO
International standards organization
KAM
Kenya association of Manufacturers
MOL
Ministry of labour
NIHL
Noise induced hearing loss
NIOSH
National institute of occupational safety and health
NIPTS
Noise induced permanent threshold shift
NITTS
Noise induced temporary threshold shift
OEL
Occupational Exposure Levels
OSHA
Occupational safety and health Act
PPE
Personal Protective Equipments
REL
Recommended exposure limit
SLM
Sound level meter
SPL
Sound pressure level
TWA
Time weighted average
WHO
World health organization
xiii
OPERATIONAL DEFINITIONS
Acoustics: the science of sound dealing with vibratory motion perceptible through
the organ of hearing.
Continuous noise: noise with negligibly small fluctuations of level within the period
of observation (ANSI S3.20-1995: stationary noise; steady noise)
Decibel (dB): unit measurement of sound pressure level (SPL) or intensity.
Exchange rate: An increment of decibels that requires the halving of exposure time
or a decrement of decibels that requires the doubling of exposure time.
Impulsive noise: a type of noise characterized by a sharp rise and rapid decay in
sound levels and is less than 1 second in duration. It also refers to impact noise
Intermittent noise: noise levels that are interrupted by intervals of relatively low
sound levels.
Permanent threshold shift (PTS) or permanent hearing loss: Permanent increase
in the threshold of audibility for an ear. Unit ‘dB’ (ANSI S3.20-1995)
Slow time weighting response: is a detector response on a sound level meter
recommended for occupational noise measurements (by NIOSH) as it is useful to get
the average values of vibration sound level.
Sociacusis: hearing impairment because of noise of recreational places like pop
music and car races.
Temporary threshold shift (TTS) or temporary hearing loss: Temporary increase
in the threshold of audibility for an ear caused by exposure to high intensity acoustic
stimuli. Such a shift may be caused by other means such as use of aspirin or other
drugs, Unit, dBs (ANSI S3.20-1995).
xiv
Tinnitus: often called ‘ringing or buzzing in the ears’. Onset may be due to noise
exposure and persist after a causative noise has ceased. It can also be induced by
several drugs like salicylates which induce vasoconstriction of the small vessels of
the cochlear microvasculature but the effects are reversible. Tinnitus is often a
precursor to NIHL and therefore an important warning signal.
xv
ABSTRACT
Noise is considered as any unwanted sound that may adversely affect the health and
wellbeing of individuals or populations exposed. This study assessed the magnitude
of occupational noise exposures to workers in different manufacturing sectors in
Thika District-Kenya. Systematic random sampling was used to select eight
manufacturing companies (one per sector) from Directorate of Occupational Safety
and Health Services and Kenya Association of Manufacturers registered workplaces
in Thika District. Thika district was selected because of its high concentration of
manufacturing companies. Data was collected through; environmental noise survey,
questionnaire survey, observation and secondary data for comparison. A sample size
of 400 (out of 2400 employee) participants from the eight selected manufacturing
industries were randomly recruited in this study as per the table of maximum return
of sample. In this study the males population was high (82%) as compared to females
(18%), hence gender had a significant association between the companies sampled.
This study also found that the generator department recorded the highest values of
between 88.7–96.4 dBs (χ2 = 2.40; p < 0.05, df = 1.00) while the office department
recorded the lowest values of between 38.1–50.1 dBs (p < 0.05) in all the selected
companies. The production department had the highest exposure magnitude in
relation to employees. The companies’ noise exposure levels had significant
association in terms of office departments (p = 0.04). The study concludes that
magnitude of noise exposure to the workers in generator and production units of
manufacturing industries in Thika District is high and recommends strict
enforcement of noise control regulations supported by necessary trainings, policies
and personal protective equipments.
xvi
CHAPTER ONE
1
INTRODUCTION
1.1
Background Information
Working environments and conditions for over three billion workers worldwide do
not meet the minimum standards and guidelines set by the World Health
Organization and the International Labour Organization for occupational health,
safety and social protection (WHO, 2007). The majority of the work forces around
the world do not have access to occupational health services. Only 5 to 10 percent of
work force in developing countries and 20 to 50 in the developed countries have
access to some kind of occupational health services. Due to this fact, presence of
hazards in the work place due to factors such as dust, heat stress, noise, toxic
chemicals, and dangerous machines which leads to huge burden of work-related
injuries, death and diseases is very common (Skanberg and Ohrstrom, 2002).
The occupational environment, as a subset of the general environment, is affected by
noise pollution in most of the undertakings around the world. This is mainly due to
the fact that man has been using different material aids, from industrial revolution to
date, such as machineries, equipments, devises, instruments among others, to make
the laborious working conditions simple, faster, economical and more productive
(Erdoğan and Yazgan, 2009). In this dynamic process of technological innovations,
however, men inevitably become victims of various hazards including noise. To this
effect, noise is one of the commonest occupational hazards of the modern world and
there is evidence to support the increasing prevalence of high level noise in the work
place. In many developing countries, including Kenya, occupational diseases in
particular and occupational safety and health issues in general have not, so far, been
1
given attention due probably, to lack of awareness. In many developed countries,
however, there are reported cases which show the effect of various industrial hazards
(physical, chemical, biological, ergonomical and psychosocial) on the work force
exposed to them and the consequence exhibited on the productivity and
socioeconomic dimensions (Özer and Irmak 2008). Occupational health is concerned
with health of workers in its relation to work and the working environment. It aims at
the promotion and maintenance, to the highest degree, of physical, mental, and social
well-being of workers in all occupations (MoL, 2010).
Noise, categorized as physical hazard, is known to cause workers hearing loss and
affect body parts other than the hearing organ. Some reports revealed that it causes
mental disturbances, masking of speech communications, and disturbance of work
performance, rest and sleep (Özer and Irmak 2008). Studies conducted in various
countries revealed that the effect of exposure to high noise levels with various
frequencies causes’ noise induced hearing losses of exposed workers (Bies and
Hansen, 2000; Yılmaz and Özer, 2005). Hearing loss is also caused by exposure to
non occupational noise, collectively known as sociacusis. It includes recreational and
environmental noises like loud music, guns and power tolls (NIOSH, 2010).
Combined exposures to noise and certain physical or chemical agents (vibration,
organic solvents such as Styrene Toluene, Zylene, N-hexane, Carbon di sulfide
carbon monoxide, ototoxic drugs, and certain metals) appear to have synergistic
effects on hearing loss (Starck, 2006). Some sensorineural hearing loss occurs
naturally because of aging; a condition termed as presbycusis. Conductive hearing
2
losses, as opposed to sensorineural hearing losses, are usually traceable to diseases of
the outer and middle ear (Zannin et al., 2003; Tang and Tong, 2004; Abo-Qudais and
Alhiary, 2004; Piccolo et al., 2005; Zannin et al., 2006; Pathak et al., 2008; Özer et
al., 2009).
Noise exposure is also associated with non auditory effects such as psychological
stress and disruption of job performance (Barboza et al., 1995) and possibly
hypertension. Noise may also be a contributing factor in industrial accidents.
Nevertheless, data are insufficient to endorse specific damage risk criteria for these
non auditory effects. It is also reported that many undertakings are affected by
unnecessary expenditures incurred as a result of noise exposure (NIOSH, 2000).
This study was carried out in manufacturing sector in Thika district. The study was
designed to investigate the noise levels of the working environment, hearing
conditions of the work force, level of awareness of the workers and finally to
evaluate the overall safety climate of the undertakings, as far as actions to prevent
noise as hazardous ambient factor is concerned. In relation to this, the study
developed some technical solutions to the existing noise problem in the working
premises which ultimately targeted to protect the vast work force under this
hazardous situation.
1.2 Statement of the problem
Works carried out in manufacturing sector require large number of employees and
heavy machines. An increase in mechanization also has resulted in an increase in
noise levels, leading manufacturing companies to generate enormous levels of noise.
Occupational noise in manufacturing sectors has reached unbearable levels due to the
3
reverberant nature of the narrower spaces. Therefore, it is hard to find a relatively
low-noise environment for workers. Although the equipment employed in
manufacturing are comparatively larger in size than the ones encountered in
production, they may be said to be less significant as the noise emitted from them
easily spreads hemi-spherically in the free sound field. In reality, the noise occurring
during production works that take place in manufacturing industries is noteworthy
when considering labour health and job performance as the highest disease and
illness rates in manufacturing continue to be worker’s permanent or temporary
hearing loss (Scott et al., 2004).
Additionally, it appears that noise can account for quickened pulse rates, increased
blood pressure and a narrowing of the blood vessels. Workers exposed to noise
sometimes complain of nervousness, sleeplessness and fatigue (U.S department of
labour). Therefore, it is of foremost importance to conduct research on this matter to
give suggestions to manufacturing management with respect to the health of workers
and maximizing the competence in productiveness. Noise-induced hearing loss
usually occurs initially at high frequencies (3k, 4k, or 6k Hz), and then spreads to the
low frequencies (0.5k, 1k, or 2k Hz) (Chen and Tsai, 2003).
1.3 Justification
Safety is a basic human need and right. Safety created the very foundation for our
wellbeing. Everyone should have the chance to live the whole life-cycle from
infancy to youth, from adulthood to old age, without suffering any preventable,
human induced accidents (Saari, 2006). However, in many developing countries,
including Kenya, occupational diseases in particular and occupational safety and
4
health issues in general have not, so far, been given attention due probably, to lack of
awareness. Hence, the majority of the working conditions are unsafe and highly
vulnerable to serious occupational injuries and death. In relation to this, the
economic costs of occupational injuries and accidents, reduction of productivity, loss
of production time are some of the impacts associated with it. Information on
occupational health and safety services is helpful in raising awareness at all levels
and making the problem of injuries more visible to the employees, employers, policy
makers and managers. In general the assessment made on occupational hazards like
excessive noise among workers is useful in the development of injury prevention
strategy for the worker. Here lies the significance of doing researches and surveys to
contribute to the safety of workers and improvement of productivity for the factories.
The progress of occupational noise induced hearing loss is insidious in that it creeps
up gradually over the months and years, largely unnoticed until it reaches
handicapping proportions. Despite it is a serious health threat, little attention is given
to hearing loss due to occupational exposures. The time to take preventive steps
should be before the hearing losses begin. Thika has many manufacturing sectors
compared to other towns and hence it is referred to as an industrial hub. Lots of
noises are emitted from machinery and hence causing noise pollution in the sector
and its environs. This research assessed this crucial problem of the vast productive
force to suggest possible solutions for it. Besides this it also served as base line
information to undertake further studies on similar settings in the future.
5
1.4 Hypotheses
1. The noise levels in the manufacturing sector in Thika District do not affect
communication and work among employees
2. The manufacturing industries in Thika District do not comply with the set
standard on noise levels
3. The noise intensity in different departments of the selected manufacturing
sectors in Thika District is not above the occupational exposure limits
4. The magnitude of occupational noise exposures of workers is not high in
different categories of manufacturing sectors in Thika District.
1.5 Objectives
1.5.1 General objective
The general objective of this study was to assess the magnitude of occupational noise
exposures of workers in different manufacturing sectors in Thika District.
1.5.2 Specific objectives
1. To determine the effects of occupational noise levels on communication and
work among employees in different manufacturing sectors in Thika District.
2. To assess the noise compliance levels against set standard within the
manufacturing sector in Thika District.
3. To establish the level of noise intensity in different departments of the
selected manufacturing sectors in Thika District.
6
4. To compare the magnitude of occupational noise exposures of workers in
different categories of manufacturing sectors in Thika District.
1.6 Scope of the study
The research was conducted to investigate the noise levels in different manufacturing
industries in Thika District. It covered eight manufacturing industries within the
District registered by both KAM and DOSH. The total sample size was 400
participants all distributed in three sections such as office, generator unit and
production departments. Noise levels were measured in all the three departments in
the eight selected manufacturing industries and compared accordingly.
1.7 Limitation of the study
Some of the limitations encountered in this study were; failure by the respondents to
return the filled questionnaires in time, management were hesitant in allowing
measurements of noise levels in some sections of the manufacturing sectors and
financial constraints on the side of the principal investigator since the was not
funded.
7
CHAPTER TWO
LITERATURE REVIEW
2.1 Sound and noise
Physically, sound is a mechanical disturbance propagated as a wave motion in air
and other elastic or mechanical media such as water or steel (Liu, 1999).
Physiologically, sound is an auditory sensation evoked by this physical phenomenon
(Özer and Irmak 2008). However, not all sound waves evoke an auditory sensation:
for example, ultrasound has a frequency too high to excite the sensation of hearing.
This means that all sound waves are not heard by human beings. The number of
vibrations of the sound waves per second (frequency) determines what we hear and
do not hear (Charante et al., 1990). The acoustic vibrations are divided into three
frequency regions, namely the infra(audible) sound vibrations with a frequency of up
to 20 Hz; sound (acoustic) vibrations in the frequency range from 20 to 20,000 Hz,
and ultrasonic vibrations of a frequency higher than 20,000 Hz. A young man, on the
average, percepts sound vibrations in the frequency range from 20 to 20,000 Hz. The
range of human conversation is from about 300 to 3,000 Hz. (Charante et al., 1990;
Cheremisinoff, 1996; Liu, 1999).
Noise is considered as any unwanted sound that may adversely affect the health and
wellbeing of individuals or populations by causing disturbance of human work, rest,
sleep and communication; or by damaging his hearing and evoke other
psychological, physiological, and possibly pathological reactions. It can also be
considered as a wrong sound, in the wrong place at the wrong time. Similarly, noise
8
pollution is defined as unwanted electromagnetic signal that produces a jarring or
displeasing effect and which interferes with human communication, comfort and
health (Bahita, 2001). Hence, from the acoustics point of view, sound and noise
constitute the same phenomenon of atmospheric pressure fluctuations about the
mean atmospheric pressure; the differentiation is greatly subjective. What is sound to
one person can very well be noise to somebody else (Nelson and Schwela, 1995).
2.2 Measurement of noise
Sound pressure level (SPL), expressed in decibels, is a measure of the amplitude of
the pressure change that produces sound. This amplitude is perceived by the listener
as loudness due to high noise intensity. In sound-measuring instruments, weighting
networks are used to modify the SPL. This is achieved by building a filter into the
instrument with a similar frequency response to that of the ear. This is called an Aweighting filter because it confirms with the internationally standardized Aweighting curves. Measurement done with this filter is usually written as dBs (A)
(Charante et al., 1990).
Disturbing sound is referred to as noise and it is also measured in A-weighting
frequencies. A-weighting is the most commonly used of a family of curves defined
in the International standard IEC 61672:2003 and various national standards relating
to the measurement of sound pressure level. A-weighting is applied to instrumentmeasured sound levels in effort to account for the relative loudness perceived by the
human ear, as the ear is less sensitive to low audio frequencies (Richard et al., 2004).
It is employed by arithmetically adding a table of values, listed by octave or third9
octave bands, to the measured sound pressure levels in dB. The resulting octave band
measurements are usually added (logarithmic method) to provide a single Aweighted value describing the sound; the units are written as dB (A). Other
weighting sets of values - B, C, D and now Z - are discussed below (Richard et al.,
2004).
A-frequency-weighting is mandated by the international standard IEC 61672 to be
fitted to all sound level meters. The old B- and D-frequency-weightings have fallen
into disuse, but many sound level meters provide for C frequency-weighting and its
fitting is mandated — at least for testing purposes — to precision (Class one) sound
level meters. D-frequency-weighting was specifically designed for use when
measuring high level aircraft noise in accordance with the IEC 537 measurement
standard. The large peak in the D-weighting curve is not a feature of the equalloudness contours, but reflects the fact that humans hear random noise differently
from pure tones, an effect that is particularly pronounced around 6 kHz. This is
because individual neurons from different regions of the cochlea in the inner ear
respond to narrow bands of frequencies, but the higher frequency neurons integrate a
wider band and hence signal a louder sound when presented with noise containing
many frequencies than for a single pure tone of the same pressure level (Richard et
al., 2004). Following changes to the ISO standard, D-frequency-weighting should
now only be used for non-bypass engines and as these are not fitted to commercial
aircraft — but only to military ones — A-frequency-weighting is now mandated for
all civilian aircraft measurements (Charante et al., 1990).
10
Z- or ZERO frequency-weighting was introduced in the International Standard IEC
61672 in 2003 and was intended to replace the "Flat" or "Linear" frequency
weighting often fitted by manufacturers. This change was needed as each sound level
meter manufacturer could choose their own low and high frequency cut-offs (–3dB)
points, resulting in different readings, especially when peak sound level was being
measured. As well, the C-frequency-weighting, with –3dB points at 31.5Hz and
8 kHz did not have a sufficient bandpass to allow the sensibly correct measurement
of true peak noise (Ronald 2010).
B- and D-frequency-weightings are no longer described in the body of the standard
IEC 61672 : 2003, but their frequency responses can be found in the older IEC
60651, although that has been formally withdrawn by the International Electrotechnical Commission in favour of IEC 61672 : 2003. The frequency weighting
tolerances in IEC 61672 have been tightened over those in the earlier standards IEC
179 and IEC 60651 and thus instruments complying with the earlier specifications
should no longer be used for legally required measurements (Charante et al., 1990;
Ronald 2010). Table 2.1 shows volumes of different sounds encountered daily.
11
Table 2.1: Volumes of different sounds encountered daily, dB (A)
Effect of human being
Highly injurious
Sound level in dB(A)
140
Sound source
Jet engine
Rivet hammer
Pain threshold
120
propeller plane
110
Rock drill, chain saw
100
Sheet metal workshop
90
Heavy truck
Risk
80
Heavily - trafficked street
Speech masking
70
Salon car
Irritating
60
loud conversation
50
Low conversation
40
Quite radio music
30
Whispering
20
quite urban apartment
10
Rustling leaves
Injurious
Hearing threshold
(Adapted from MoL, 2010)
Sound level meters have an A-weighting network for measuring A-weighted sound
level (NIOSH, 2010). Exposure limits are commonly measured in dB (A). When
used without a weighted network suffix, the expression should be dB SPL. Sound
intensity level and sound pressure level are expressed as logarithmic quantities, in
decibels (Poltev, 1985).
2.2.1 Instrumentation for noise measurement
According to NIOSH, (2010), noise measurement methods should conform to the
American National Standard Measurement of Occupational Noise Exposure, (ANSI
12
1996). The two most commonly used instruments for measuring noise exposures are
the sound level meter (SLM) and the noise dosimeter; is an instrument designed to
respond to sound in approximately the same way as the human ear and to give
objective, reproducible measurements of sound pressure level. Generally, all sound
measuring systems consist of a microphone, a processing section and a read-out unit.
Integrating-averaging sound level meters and noise dosimeters with Type 2
Classification or better are the preferred instruments for occupational surveys (Bruel
and Kjaer, 1984; Liu, 1999; ACGIH, 2006). Sound Pressure Level (SPL)
measurements are made with instruments which respond to all frequencies in the
audible range; but since the sensitivity of the ear varies with both frequency and
level, the SPL does not accurately represent the ear’s response. This condition is
corrected by weighting characteristics in sound level (NIOSH, 2010). The "A"
weighting network approximates the ears response to moderate-level sounds and is
commonly used in measuring noise to evaluate its effect on humans and has been
incorporated in many occupational noise standards (Bruel and Kjaer, 1984).
The response of a sound level meter’s is generally based on either a FAST or SLOW
exponential averaging. For typical occupational noise measurements, NIOSH
recommends that the meter response on a sound level meter be set at slow (NIOSH,
2010; Amedofu, 2002). Sound level meters (Plate 2.1) should be calibrated in order
to provide precise and accurate results. Noise exposure measurements on individuals
who move between many different noisy environments during the working day can
be obtained using Noise Dose Meters. The noise dosimeter may be thought of as a
sound level meter with an additional storage and computational function. It measures
13
and stores the sound levels during an exposure period and computes the readout as a
percent dose or Time Weighting Average (TWA) (NIOSH, 2010).
Plate 2.1: Digital sound level meter, IEC 651, type 2, model: SL-4001.
Source: (Nelson and Schwela, 1995).
2.3 Noise exposure
The sound from noise sources often fluctuates widely during a given period of time.
An average value can be measured, the equivalent sound pressure level (LAeqT).
The LAeqT is the equivalent continuous sound level which would deliver the same
sound energy as the actual A-weighted fluctuating sound measured in the same time
period (T).
Noise health effects are the health consequences of elevated sound levels. Elevated
workplace or other noise can cause hearing impairment, hypertension, ischemic heart
disease, annoyance, and sleep disturbance. Changes in the immune system and birth
14
defects have been attributed to noise exposure (Passchier-Vermeer and Passchier
2000). Although some presbycusis may occur naturally with age, (Rosenhall et al.,
2010) in many developed nations the cumulative impact of noise is sufficient to
impair the hearing of a large fraction of the population over the course of a lifetime
(Schmid 2007). Noise exposure also has been known to induce tinnitus,
hypertension, vasoconstriction, and other cardiovascular adverse effects (Rosenhall
et al., 2010). Beyond these effects, elevated noise levels can create stress, increase
workplace accident rates, and stimulate aggression and other anti-social behaviors
(Kryter and Karl 2000). The most significant causes are vehicle and aircraft noise,
prolonged exposure to loud music, and industrial noise. In Norway, road traffic has
been demonstrated to cause almost 80% of the noise annoyances reported (Schmid
2007). There may be psychological definitions of noise as well. Firecrackers may
upset domestic and wild animals or noise-traumatized individuals. The most
common noise-traumatized persons are those exposed to military conflicts, but often
loud groups of people can trigger complaints and other behaviors about noise. Infants
are easily startled by noise. Traffic noise alone is harming the health of almost every
third person in the WHO European Region. One in five Europeans is regularly
exposed to sound levels at night that could significantly damage health (PasschierVermeer and Passchier 2000).
2.4 The anatomy and physiology of the ear
In terms of sound pressure level, audible sounds range from the threshold of hearing
at 0 dB to the threshold of pain which can be 130 dBs and above. The subjective or
perceived loudness of a sound is determined by several complex factors. One such
15
factor is that the human ear is not equally sensitive at all frequencies. It is most
sensitive to sounds between 2 kHz and 5 kHz, and less sensitive at higher and lower
frequencies (Amedofu, 2002).
According to Liu (1999), sound reaches the ear usually through pressure waves in
air; a remarkable structure converts this energy to electrical signals which are
transmitted to the brain through the auditory nerves.
The human ear is capable of detecting vibratory motion as small as the molecular
motion of the air. The human ear consists of three main parts; the outer ear, middle
ear and inner ear. The outer ear, consisting of the pinna (auricle) and auditory canal,
collects the airborne sound waves which then vibrate the eardrum or tympanic
membrane, which is the interface with the middle ear. The middle ear has three small
bones, the ossicles (the malleus, the incus, and the stapes), that transfer the vibration
to the inner ear which consists of two separate systems, the semicircular canals for
controlling balance and the cochlea. The cochlea is a fluid-filled, snail shaped tube.
In response to an acoustic stimulus the fluid in the cochlea is disturbed and this
distorts the basilar membrane (corti) on whose upper surfaces are thousands of very
sensitive hair cells. The hair cells register this distortion and transform it into nerve
impulses which are then transmitted to the brain. Hence, the cochlea or cochlear
canal functions as a transducer; mechanical vibrations enter it; electrical impulses
leave it through the auditory nerve (Nelson and Schwela, 1995). The anatomical
division of different parts of the ear is presented in Plate 2.2. Prolonged exposure to
loud sounds causes damage to the hair cells with the result that hearing ability
16
becomes progressively impaired. At first, damage to a few hair cells is not
noticeable, but as more of the hair cells become damaged, the brain can no longer
compensate for the loss of information. Words run into each other, speech and
background noise cannot be distinguished and music becomes muffled. Considerable
and irreparable damage will have occurred by the time the listener becomes aware of
the loss. Loss of hearing caused by noise exposure is normally greatest at those
frequencies (around 4 kHz) where the ear is most sensitive (Guyton, 1987).
Plate 2.2: Anatomical division of the Human ear
Source: (Nelson and Schwela, 1995)
17
2.5 Effects of noise
2.5.1 Health effects
Negative effects of noise on human beings are generally of a physiological and
psychological nature. Hearing losses are the most common effects among the
physiological ones. It is possible to classify the effects of noise on ears in three
groups: acoustic trauma, temporary hearing losses and permanent hearing loss
(Boateng and Amedofu, 2004). Blood pressure increases, heart beat accelerations,
appearance of muscle reflexes, sleeping disorders may be considered among the
other physiological effects. The psychological effects of noise are more common
compared to the physiological ones and they can be seen in the forms of annoyance,
stress, anger and concentration disorders as well as difficulties in resting and
perception (Cheremisinoff, 1996; Atmaca et al., 2005; Guerra et al., 2005; Bedi,
2006).
The health effects of noise exposure can also be classified as non-auditory and
auditory. Non-auditory effects include stress, related physiological, behavioral
effects and safety concerns. Auditory effects include hearing impairment resulting
from excessive noise exposure. Noise-induced permanent hearing loss is the main
concern related to occupational noise exposure. The main auditory effects include
acoustic trauma that refers to sudden hearing damage caused by short burst of
extremely loud noise such as a gun-shot that rupture the tympanic membrane or
dislocate the ossicular chain and results in permanent hearing loss, tinnitus (ringing
or buzzing in the ear) and temporary hearing loss (Ladou, 1997; Liu, 1999;
Amedofu, 2002). Noise is not the only industrial hazard to hearing.
18
2.5.2 Noise induced hearing loss
Noise induced temporary threshold shift (NITTS) occurs immediately after exposure
to a high level of noise. There is gradual recovery when the affected person spends
time in a quiet place, however complete recovery may take several hours. Permanent
hearing loss, also known as noise induced permanent threshold shift (NIPTS),
progresses constantly as noise exposure continues month after month and year after
year. The hearing impairment is noticeable only when it is substantial enough to
interfere with routine activities. At this stage, a permanent and irreversible hearing
damage has occurred. Noise-induced hearing damage cannot be cured by medical
treatment and worsens as noise exposure continues. Generally, noise-induced hearing
loss (NIHL) is a cumulative process which comes as a result of both high levels of
noise and exposure times over a worker’s work history (Levy and Wegman, 1995).
2.5.3 Occupational hearing loss
In the workplace, hearing loss can be caused by blunt or penetrating head injuries,
explosions, and thermal injuries such as slag burns sustained when a piece of
welder’s slag penetrates the ear drum. All these conditions are treatable and
reversible. Sensori neural hearing loss results from deterioration of the cochlea,
usually due to loss of delicate hair cells from the organ of corti. Among the many
common causes of sensory hearing loss are continuous exposure to noise in excess of
85 dB, blunt head injury and exposure to ototoxic substances. Impulsive noises, such
as gunfire, appear to be particularly damaging (Passchier-Vermeer and Passchier
2000).
19
2.5.4 Non occupational hearing loss
Among the non occupational hearing disorders are presbycusis, hereditary hearing
impairment (HHI), metabolic disorder, sudden sensorineural hearing loss, infectious
origin, central nervous system disease and drug induced hearing loss are worth
mentioning. As a rule, hearing sensitivity diminishes with age, a condition known as
presbycusis (Levy and Wegman, 1995). Presbycusis (sometimes called senile
deafness) is a slow and progressive deterioration of hearing that is associated to
aging. Sociacusis refers to hearing impairment because of noise of recreational
places like pop music in bars and restaurants, snow mobile and car races (Neitzel,
2004).
2.6 Noise standards and protocols
2.6.1 ISO and OSHA permissible exposure levels
The International Standards Organization (ISO) (1999) sets energy criteria which
states that an increase in sound level from the permissible exposure 90 dB(A) to 93
dB(A) must be accompanied by a halving of the permissible exposure duration from
8 hours to 4 hours. In the United States, the OSHA defines another relationship
which permits that an increase in sound level from 90 dB(A) to 95 dB(A) is
accompanied by a halving of the allowable exposure duration from 8 to 4 hours
(NIOSH, 2010).
2.6.2 NIOSH Recommended exposure limit
The national institute for occupational safety and health (NIOSH) of the US
government communicates recommended standards to regulatory agencies (including
20
the Occupational Safety and Health Administration (OSHA) and to the Department
of Labour of the US government, health professionals in academic institutions,
industries, public interest groups and other government agencies in the occupational
safety and health community. In 2010, NIOSH published criteria for a recommended
standard: Occupational exposure to noise which provided the basis for a
recommended standard to reduce the risk of developing permanent hearing loss as a
result of occupational noise exposure.
2.7 Noise control in industrial premises
2.7.1 Introduction
In the industrial premises, it is important to remember that the objective of noise
control is not to reduce noise for its own sake, but for the sake of the receiver,
usually the human ear. Hence the straight forward approach recommended to be used
for noise control is the source-path-receiver concept (Liu, 1999).
2.7.2 Noise control at the source
As far as industrial setting is concerned, the most effective approach to noise control
is to redesign or replace noisy equipment. If this is not possible, significant
reductions in noise levels can be achieved by structural and mechanical
modifications or the use of mufflers, vibration isolators and noise protection
enclosures (Nelson and Schwela, 1995). The best way of controlling noise at its
source is to replace noisy machines with quieter machines or trying to reduce noise
by redesigning the machine after purchase. Substituting a quieter process, machine,
or tool is another method of controlling noise. For instance welding is a quieter
21
substitute for riveting, drilling for punching, pressing and rolling for forging. Besides
engineering controls noise reduction and isolation can be approached through
machine mounting or by architectural means. If machines are spaced adequately
apart noise levels can be within acceptable limits.
2.7.3 Noise control in a transmission path
Noise control in a transmission path can be achieved by absorbing the sound along
the path or by deflecting the sound in some other direction by placing a reflecting
barrier in its path. Using the absorptive capacity of the atmosphere is a simple and
economical method of reducing the noise level. If enough distance is available
between
machines,
the
amount
of
noise
produced
becomes
minimized
(Cheremisinoff, 1996). The distance from a point source is doubled; the sound
pressure level is lowered by 6 dB. If a soft, spongy material is placed on the walls,
floors and ceiling the reflected sound is diffused and soaked up (absorbed). Soundabsorbing materials such as acoustical tile, carpets, and drapes placed on ceiling,
floor, or wall surfaces can reduce the noise level (Nelson and Schwela, 1995;
Cheremisinoff, 1996). Placing physical barriers, screens, or deflectors in the noise
path is an effective way of reducing noise transmission. Sometimes enclosing a noisy
machine in a separate room or box is more practical and economical than quieting it
by altering its design, operation, or component parts.
2.7.4 Protecting the receiver
As an administrative approach of noise regulation for the workers, the amount of
continuous exposure to high noise levels must be limited. For hearing protection,
22
scheduling noisy operation for short intervals of time each day over several days is
preferable to a continuous eight-hour run for a day or two (Cheremisinoff, 1996). In
industrial or construction operations an intermittent work schedule benefits not only
the operator of the noisy equipment but also other workers in the vicinity. A personal
hearing protection devise is any devise designed to reduce the level of sound
reaching the ear drum. Ear muffs and ear plugs are the main types of hearing
protectors. Molded and pliable earplugs, cup-type protectors and helmets are
commercially available as hearing protectors. Such devices provide noise reductions
from 15 to 35 dB (Sound Research Laboratories, 1991).
2.8 Prevention of noise induced hearing loss
The OSHA has mandated that the presence of occupational noise at or above an 8hour time TWA exposure of 85 dB (A) is the threshold that triggers the need to
implement a hearing conservation program (HCP). The HCP is the recognized
method of preventing noise induced hearing loss in the occupational environment.
An effective HCP integrates noise monitoring, engineering controls, administrative
controls, worker education, selection and use of hearing protection devises (HPDs)
and periodic audiometric evaluations as important elements (Ladou,1997). Moreover
the presence of policy on the HCP and record keeping on all the above mentioned
elements is very important (Ismail and Elias, 2006). If workers noise exposure will
equal or exceed a TWA of 85 dB (A), then noise monitoring is required. This
collected information may be used by designers to conceptualize possible
engineering solutions which may involve the use of enclosures (to isolate sources or
receivers), barriers (to reduce acoustic energy along the path), or distance (to
23
increase the path and ultimately reduce the acoustic energy at the receiver) to reduce
worker noise exposure. Administrative controls include reducing the amount of time
a given worker might be exposed to a noise source in order to prevent the TWA
noise exposure from reaching 85 dB(A) and establishing purchasing guidelines to
prevent introduction of equipment that would increase worker noise dose. The
implementation of administrative controls requires management’s commitments and
constant supervision, particularly in the absence of engineering or personal
protection controls. Workers and management must understand the potentially
harmful effects of noise to ensure that the HCP is successful. Training is required to
be provided annually to all workers included in the HCP. Opportunities for
maintaining awareness occur during periodic safety meetings, as well as during
audiometric testing appointment when testing results are explained. Hearing
protection devises are used to attenuate high noise levels which expose workers and
are available in a variety of types from a number of manufacturers.
24
CHAPTER THREE
MATERIALS AND METHODS
3.1 Research design
This study employed a descriptive cross-sectional study designs. Key issues
evaluated were noise levels and compliance with set standards in the manufacturing
industries in 2012 and compared with the recorded data in 2011.
3.2 Target population
The study population was employees from different manufacturing sectors in Thika
Town. A total of eight industries were sampled and each industry employee who
participated in the study were sampled totaling to 400 employees shown in Table 3.1.
3.3 Sampling frame
The 8 selected manufacturing companies registered by both DOSHS and KAM were
sampled for this study. Simple random sampling was used to select the eight
manufacturing companies. To select participants in each company clustering was
done in which three clusters per company were sampled. The clusters were office
department, generator unit and the production department. To get the total sample
size, participants were selected using simple random sampling. Respondents meeting
accepting to participate in the study were assigned roman numbers and those who
picked even numbers were sampled for the study.
25
Table 3.1: Different categories of manufacturing industries that were sampled
Category
Code
Total number
of employees
Employees directly
affected by noise
Sampled
number
Chemical and allied (2)
MC1
78
56
27
Food and beverages
and tobacco (1)
MC2
167
142
68
Texture and apparels
(3)
MC3
1355
177
85
Plastics and rubbers
(1)
MC4
126
97
47
Paper and paperboard
(2)
MC5
136
130
63
Motor vehicle and
assembly and
accessories (1)
MC6
358
137
66
Metal and allied
industries (1)
MC7
150
80
39
Leather products and
footwear (1)
MC8
30
10
5
400
Total
*Key: Figures in bracket refers to the total number of industries per category
3.4 Sample size and sampling techniques
The sample size was determined using Fischer et al., (1998) equation which uses the
prevalence but in this study the prevalence is not known and therefore proportion
which uses 50% was used.
Equation 3.1: N = Z2Pq/d2
In equation (3.1) N is the sample size; Z is the value of standard variance of 1.96 at
95% confidence interval while P is the proportionate target population with the
26
particular characteristic, 50% is recommended by Fisher et al., (1998), d is the level
of statistical significance set and q is 1-p
Based on the equation a sample size of 384 employees was computed for this study.
A total of 400 questionnaires were administered for this study allowing 5% for
attrition and distributed according to the levels of exposure to noise and the size of
employees per company (Table 3.1) with a return rate of 100%. The sample sizes per
company were 27, 68, 85, 47, 63, 66, 39 and 5 participants for MC1, MC2, MC3,
MC4, MC5, MC6, MC7 and MC8, respectively.
3.5 Data collection instruments
The study captured both primary and secondary data. For primary data the study
employed the following instruments for data collections; - Noise level meter which
measures noise in dBs (A), structured questionnaires were also used- the
questionnaires were in 5 likert scale in which respondents had to tick one answer per
question out of the five provided alternative (strongly agree, agree, uncertain,
disagree and strongly disagree). Data retrieved from previous noise survey from
records formed the secondary data.
3.6 Pilot survey
The main purpose of the pilot survey was to pretest the questionnaire and other data
collection tools before the main study. After the pilot study, the questionnaires were
revised accordingly before the main study as described by Ahmed et al., (2004),
Atmaca et al., (2005), Guerra et al., (2005) and Bedi, (2006).
27
3.7 Data collection procedure
Data for this study was collected using the following instruments; - environmental
noise survey and questionnaires. Secondary data was also retrieved from record in all
the respective manufacturing companies.
Noise levels were measured in work stations corresponding to each sampled workers
position using a digital sound level meter, Bruel and Kjaer (2002) type-SL-4001,
with a range from 35- 130 db, whose frequency weighting networks were designed
to meet the IEC 651 type 2. This sound level meter has ‘A’ and ‘C’ frequency
weighting networks which are conformity to standards. It has also time weighting
(SLOW and FAST) which are dynamic characteristic modes. Moreover, the sound
level meter was calibrated at 94±0.2 dB before each measurement was conducted in
accordance to the procedure outlined in the standard manual of 9412-Sl-4001 for
precise and accurate results (Bruel and Kjaer 2002).
Since the characteristic A weighting was simulated as at the ‘Human Ear Listening’
response, it was recommended to be used for environmental noise level
measurements (Bruel and Kjaer, 1984). The SLOW time weighting range was used
as recommended by NIOSH (2010) and the standard procedure of the meter.
Measuring considerations like keeping the microphone dry, avoiding serious
vibrations during measurement, keeping conditions of temperature and humidity
were followed according to manufacturer instructions. Measurements were recorded
by holding the instrument at a height of 1.5 meters from the ground in the working
28
environments of the workers in order to properly determine the noise level to which
the workers are exposed, Atmaca et al., (2005).
Noise level measurements were made at each selected working site on three different
days and the averages of these were taken. For a working site, measurements were
done four times on the first day; two in the morning and two in the afternoon. These
measurements were averaged and taken as the noise level measurement of the first
day of that site. In a similar fashion, the averages of the second and third day
measurements were calculated. Finally, the averages of these three day
measurements represented the noise level of that specific working site. These
measurement procedures are similar to approaches employed in Atmaca et al. (2005)
and Bedi (2006). Noise surveys were carried out for each company for three major
departments: offices, production area and the compound area (major emphasizes on
the Generator room).
The main purpose of the questionnaire was to subjectively list out the presence of
factors that leads to hearing loss among workers, to identify the status of working
areas (noisy or not), to examine the provision and usage of hearing protection
devises among the workers in their respective working sites. For each respondent,
the purpose of the study was explained and a written consent was obtained on
voluntary bases from them before the questionnaire was administered. The
questionnaire captured administrative staffs (management) and general employees in
office, production and generator unit since they were all exposed to occupational
noise. A total of 400 questionnaires were administered. The researcher explained the
29
objective of the study to those participants who accepted to take part in the study
before signing of the consent form and there after giving the questionnaires to the
supervisors to be distributed to the employees in the various departments.
Secondary data from the noise measurements taken by the companies in the previous
year (2011) were considered for collaboration. This was mainly for the three major
departments: office, production and generator.
3.8 Data processing and analysis
Data was analyzed using SPSS version 16(TM) statistical package for comparison of
the occupational noise measurements against the standards of NIOSH, OSHA 2007
and Legal Notice number 25 of 2005. Five compliance items were identified from
the standards as: permissible noise levels, noise prevention program, noise
measurements records, information and training of workers, medical examinations
and hearing tests. The results of the statistical tests were analyzed at the 95%
confidence level to test the level of significance using Pearson chi square test.
Descriptive statistics was used to test research hypotheses. Data was interpreted for
frequencies, percentage distributions, trends and comparisons on different aspects
such as noise levels, the use of PPE, pre employment and post employment training
of
staff
on
noise
exposure
and
30
then
conclusions
were
drawn.
CHAPTER FOUR
RESULTS AND DISCUSSIONS
4.1. Socio-economical characteristics of the participants
The employee participant’s residence was categorized as Kiganjo 143 (35.5%),
Makongeni 135 (34.0%) and other areas of Thika 122 (30.5%). Majority of the workers
(69.55) resided in Makongeni and Kiganjo while a small percentage lived in other areas.
A total of 306 (76.5%) were married while the 94 (23.5%) were single. The worker's
qualification, gender and work experience showed that each was dependent of the type
of organization that the employee works in. All these parameters have significant
association between the organizations since the p - value is less than 0.05. This implies
that experienced workers are more informed on noise hazards (Table 4.1).
Table 4.1: Chi-Square tests for number of years worked in the company
Value
Df
Asymp. Sig. (2-sided)
Pearson Chi-Square
41.385a
28
.049
Likelihood Ratio
50.834
28
.005
Linear-by-Linear Association
.022
1
.881
N of Valid Cases
400
a. 15 cells (37.5%) have expected count less than 5. The minimum expected count is .26.
4.1.1 Age categorization of employees
The participants were distributed in different ages in which the youngest age group was
24 years while the oldest age category was 60 years (Figure 4.1). The employees were
31
categorized either as general employees 61.0% (244) or managerial staff 29.0% (156). A
total of 33.8% (135) employees reported to have worked for 1-5 years in their respective
companies, 145 had worked for 6-10 years, 54 had worked for 11- 15 years, 21 for 1620 years and 44 had worked for over 20 years. The workers age has a direct relation to
noise exposures resulting to hearing loss.
Figure 4. 1: Age categorization of employees
4.1.2 Gender categorization of employees
The majority of respondents were male employees 328(82 %) while the females were
minority 72(18%) as shown in Figure 4.2.
32
Figure 4. 2: Gender distribution of the employees.
Pearson Chi-square test was used to determine the association and the level of
significance at 95% confidence interval. The gender having statistical significant
association with the type of company in which an employee belongs was determined.
The p value calculated was 0.040 therefore the gender has a significant association
between the organizations since the p-value is less than 0.05 (Table 4.2).
Table 4.2: Chi-Square tests on the gender of employees in the selected companies
Value
Df
Asymp. Sig. (2-sided) p value
Pearson Chi-Square
14.719a
7
.040
Likelihood Ratio
14.668
7
.040
Linear-by-Linear
.788
1
.375
Association
N of Valid Cases
400
a. 3 cells (18.8%) have expected count less than 5. The minimum expected count is .90.
33
The work in the factories is mostly labour intensive which attracts most men hence noise
exposure in males is high. In a study done by Eurostat Company (2002), 43.0 % of the
workforces in the manufacturing sectors were female, with the percentage of women in
the workforce increasing. Men are exposed to noise more than twice as often as women
and men report that their health is at risk from their work in the form of hearing
disorders more than three times as often as women as reported by Eurostat Company
(2002). About 97.0 % of cases of noise-induced hearing loss reported were male. This is
no surprise as the sectors with exposure to the highest noise levels have a predominantly
male workforce. Majority of workers in the production department were males. In
studies, once noise exposure is controlled for, no gender difference is found in the
incidence of hearing disorders between men and women (Davis 1998). There is some
evidence that there may be gender differences in the experience of tinnitus (EstolaPartanen 2000). This is because industrial work attracts more males than females as seen
in this study.
4.1.3 Educational level of the employees
The results show that majority of the employees had certificates 212 (53.0%), diploma
holders were 163 (40.8%) while degree holders were the least 25 (6.2%) as presented in
Figure 4.3. The Pearson Chi-square for the workers qualifications and the type of
organization was determined and the values were 0.289. The p - value calculated is
greater than 0.05 therefore worker’s qualification have insignificant dependency on the
type of organizations (Table 4.3).
34
Figure 4.3: Educational level of the resoponents
Table 4.3: Chi-Square on workers qualification of the selected companies
Value
Df
Asymp. Sig. (2-sided)
Pearson Chi-Square
16.403a
14
.289
Likelihood Ratio
19.463
14
.148
Linear-by-Linear Association
.259
1
.611
N of Valid Cases
400
Exposure to noise is independent of workers’ qualifications and thus working in
factories does not require a lot of skills especial when doing manure work, which is why
majority of the workers highest education attained was certificates followed by diplomas
and the degree holders were the least. In this study manual workers, machine operators,
office staff and managerial staffs in all the departments participated in the study, Ahmed
35
et al., (2001) also did the same categorisation in his study on noise exposure levels in
the factories and found that similar results.
4.2
Effects of occupational noise levels on communication and work among
employees in the manufacturing sectors sampled
A total of 125 (31.2%) of the respondents had no communication problems in a noisy
environment while 225 (56.5%) agreed and 49 (12.2%) strongly agreed that
communication was hard in a noisy environment. A question was also asked to ascertain
the individuals who realize that it is noisy while communicating. The response was 45
(11.2%) strongly disagree and 179 (44.8%) disagree while 68 (17.0%) were not sure and
90 (22.5%) agree to this effect. On communications when machines were on 169
(42.2%) disagree that they do not communicate well while machines are on, 25 (6.2%)
were not sure, 189 (47.2%) agreed and 17 (4.2%) strongly disagreed. A total of 202
(50.5%) agreed that industry noise interferes with conversation and 89 (22.2%) strongly
agreed, 45 (11.2%) were not sure while 64 (16.0%) disagreed completely. On whether it
was easy or hard to follow conversation while machines were on 184 (46.0%) agreed, 40
(10.0%) were uncertain while 176 (44.0%) disagreed.
On whether loud noise in the industry makes one stops conversation 166 (29.0%)
agreed, 25 (6.2%) strongly agreed, 15 (3.8%) were not sure while 222 (55.5%) disagreed
and 22 (5.5%) strongly disagreed. On whether high levels of noise in the industry
makes it hard to concentrate in conversation 207 (51.8%) agreed, 64 (16.0%) strongly
36
agreed, 45 (11.5%) were uncertain while 62 (15.5%) disagreed. Workers who, while
communicating don’t realize its noisy is dependent on the type of organization. Pearson
Chi-square value=67.387a, df = 21, p = 0.0001 thus the variable have significant
dependency on the type of organizations since the p - value is less than p = 0.05. The
Pearson Chi-square on workers concentrating well while machines are on is independent
on the type of organization. Pearson Chi-square value = 22.281a, df = 21, p = 0.383 thus
those who do not communicate well while machines are on have insignificant
dependency on the type of organizations since the p-value is greater than p = 0.05. The
Pearson Chi-square on the workers industry noise interfering with conversation is
dependent on the type of organization. Pearson Chi-square value = 40.196a, df = 21, p =
0.007 thus the industry noise interferes with conversation have significant dependency
on the type of organizations since the p - value is less than p = 0.05.
In addition noise interferes with verbal communications leading to errors and failures to
respond to warning signs. In this study 225 (56.5%) respondents agreed to having
communication problems in noisy environment and 49 (12.2%) strongly agreed that
communication was hard in a noisy environment. This is a big percentage hence in case
of an accident; a big number of workers will be affected due to their inability to respond
to warning signs. There were several questions asked to the respondents regarding
communication in noisy environment, the response was overwhelming more than fifty
percent agreed to have problems in communicating in a noisy environment. Rule 11 of
the Kenya Subsidiary Legislation, 2005; Legal Notice No. 25 state that’s ‘The occupier
37
shall install where noise gives rise to difficulties in verbal or sound communication, a
visual warning system or any other means of communication’. In this study there were
no such signs in all the companies sampled except one company which was compliant.
On the effect of dangerous noise on the work environment 239 (59.8%) of the
respondents out of 400 (100.0%) agreed that they need a peaceful and quiet place to
perform their jobs. On the effect of high noise on the work environment 108 (27.0%)
agreed, 129 (32.2%) strongly agreed that they need a peaceful and quite place to
perform jobs that required a lot of concentration while the rest 129 (32.3%) disagreed.
On doing routine work in a noisy environment 112 (28.0%) had problems, 49 (12.2%)
were not sure while 218 (54.5%) were comfortable doing work in a noisy environment.
On the need to have a quite work environment while performing new tasks 192 (48.0%)
agreed, 38 (9.5%) strongly agreed, 69 (17.2%) were not sure while 101 (25.2%)
disagreed. On doing difficult work when heavy and noisy machine are running 196
(49.0%) agreed, 42 (10.5%) were not sure while the rest disagreed meaning it is hard for
them to work while heavy machines are running. On the sensitivity to industry noise 138
(34.5%) agreed, 35 (8.8%) strongly agreed, 25 (6.2%) were not sure while 180 (45.0%)
disagreed and 22 (5.5%) strongly disagreed that they were sensitive to industrial noise.
Half of the respondents’ agreed that they were accustomed to industry noise while half
of them disagreed with this issue.
38
The Pearson Chi-square the worker's need a quiet place to do difficult work is
independent on the type of organization. Pearson Chi-square value = 34.403a, df = 28, p
= 0. 188 therefore this variable has insignificant dependency on the type of the
organizations since the p-value is greater than 0.05. The Pearson Chi-square that
“Worker's have had no problem while doing routine work in noisy environment” is
independent on the type of organization one is working in. Pearson Chi-square value =
20.809a, df = 21, p = 0. 471 thus this variable has no significant dependency on the type
of organizations since the p-value is greater than 0.05. The Pearson Chi-square the
“Worker's Performance is worse in noisy places” is independent on the type of the
organization one is working in. Pearson Chi-square value = 20.979a, df = 21, p = 0. 460
therefore it has no significant dependency on the type of organizations since the p value is greater than 0.05.
Majority of the participants agreed to have problems working and concentrating when
heavy and noisy machines were running. Injuries have been shown to have a high
prevalence in noisy workplaces. Barreto, (1997) showed that the risks attributable to
noise and hearing loss together accounted for nearly half the injuries (Charante and
Mulder 1996) and a Brazilian study showed that intensity of noise was significantly
related with the risk of fatal injury in the steelworks (Barreto, 1997). Noise may not only
impede critical communication, but cause people to lose focus during dangerous tasks.
About 30.0% of the workers agreed that industrial noise had led to ear ache and ear
allergies (ringing of the ears due to high noise levels). Majority of the workers agreed
39
that the noise has lead to ear infection and trauma hence resulting to the use of
medications. The pattern of induced hearing problems and the need to use medication is
consistent with the finding of Boateng and Amedofu, (2004) in their study on noise
effects on hearing. Exposure to loud, destructive and hazardous noise is a common
experience in our day to day life. To allow such exposure to harm once hearing is a
personal choice. Studies have shown that for the 90th percentile exposed population, the
risk of presumed noise induced hearing loss (NIHL) increases exponentially for noise
levels beyond 85 dBs (A) and over a prolonged period (Gierke and Johnson 1978). The
NIHL manifest irreversible subtle change in the sensory cells and other structures in the
organs of corti in the cochlea. As a results the hair cells and supporting cells disintegrate
and the nerve fibres that innervate the hair cells disappear resulting in permanent
threshold shift and hence irreversible hearing loss at high frequencies (Lim and Dunn
2000; Bahadovi and Bohne 2005).
Family history on loss of hearing due to industrial noise 44(11.0%) were not sure while
the rest 356 (89.0%) disagreed. None agreed when asked whether industry noise had led
to head injuries before. When asked if industrial noise has resulted to ear allergies 15
(3.8%) agreed, 37 (9.2%) were uncertain while the rest 348 (87.0%) disagreed. On
whether industrial noise have led to ear infections and trauma 21 (5.2%) strongly
disagree, 15 (3.8%) were not sure while the rest either agreed or strongly agreed 364
(91.0%). On whether the industrial noise has lead one to be taking drugs, antibiotics or
any other medication regularly 50 (12.5%) agreed, 20 (5.0%) were not sure while 202
40
(50.5%) disagreed and 128 (32.0%) strongly disagreed (Appendix 4). Some medications
can result in damage to the auditory system with prolonged use and are referred to as
ototoxic.
Exposure to certain chemicals such as toluene and trichloroethylene can produce hearing
loss. More important, the interaction between noise and different chemicals may
produce more hearing loss than expected because they act synergistically (WHO, 2007;
Levy and Wegman, 1995; NIOSH, 2010). The Pearson Chi-square for Members in a my
family who had lost hearing before the age of 50 has a significant dependency on the
type of organization since p < 0.05 (Pearson Chi-square value = 26.664a, df = 14, p =
0.021). Those who have had head injuries before had a significant dependency on the
type of organizations since the p-value is less than 0.05 (The Pearson Chi-square. Value
= 26.968a, df = 14, p = 0 .019). The Pearson Chi-square for workers who have had ear
ache before is dependent on the type of organization (Pearson Chi-square value =
54.092a, df = 28, p = 0.002) since the p - value is less than 0.05. The Pearson Chi-square
for workers who have had ear allergies before is dependent on the type of organization
(Pearson Chi-square value = 67.264a, df = 21, p = 0.0001) since the p - value is less than
0.05. The Pearson Chi-square for workers who have had ear infections and trauma
before is dependent on the type of organization (Pearson Chi-square value = 46.019a, df
= 21, p = 0.001) since the p - value is less than 0.05.
41
The adverse effect of noise on hearing loss is categorized into; temporary threshold
shift, permanent threshold shift and a coustic trauma (Miller et al., 2006). Our sense of
hearing has evolved from the time where our survival depended of our hearing
perception of surrounding predators until today where noise’s amplitude has increased
much faster than our ear adaptability. Consequently, our cochlea, or “inner ear”, is not
designed to cope with highway traffic, loud music and industrial noise. This mismatch
between the auditory apparatus and the magnitude of noise stimuli constitutes a source
of stress for our ears, leading to what has become almost common knowledge: a
diminished hearing perception. Yet, there are health effects other than hearing damage
that are related to the fact that noise is a source of stress. Usually called “non auditory”
health effects, they have pervasive physiological consequences. Non auditory health
effects are considered one of the psychosocial stressors in the etiology of coronary heart
disease (Passchier-Vermeer and Passchier 2000).
It is hypothesized that noise leads to perturbation in hormonal balance and autonomic
nervous system which lead to chronic disease. For example, the inherent function of
hearing is to warn and produce normal stress reaction through the sympathetic and
endocrine systems. But when noise activates stress pathways continually, the response
may become pathogenic. Occupational epidemiology studies have shown strong
evidence for the effects of noise on the cardiovascular system through elevated rates of
blood pressure (Kempen 2002). The recognition of the effect of noise exposure on
physiological responses is not limited to pressure changes but also includes ischemic
42
heart disease (Babish 2005). None auditory health effects were not investigated in this
study although a high percentage of the respondents agreed that noise affects their social
life and has lead to stressful situations in one way or another. Noise also interferes with
activities and communications, therefore causing annoyance and cognitive performance
has been shown to be impaired in both adults and children (Stansfeld and Matheson
2003). There have been investigations of links between noise and reproductive
impairments, but these results have been inconclusive (Passchier-Vermeer and Passchier
2000).
4.3 Noise compliance levels against set standard for the manufacturing sectors
sampled
4.3.1 Compliance to set standards
The noise levels were measured against set standards of NIOSH, OSHA 2007 and Legal
Notice number 25 of 2005 on Noise. Five compliance items were identified from the
standards as: permissible noise levels, noise prevention program, noise measurements
records, information and training of workers, medical examinations and hearing tests.
43
Table 4.4: Companies compliance to the set standards/rules on noise
No.
Compliance items
Workplace complying with set
Percentage
standards
1.
Permissible Noise levels
5
62.5%
2.
Noise prevention
2
25%
programme
3.
Noise measurement records
8
100%
4.
Information and training of
1
12.5%
3
37.5%
workers
5.
Medical examinations and
hearing tests
4.3.2 Permissible Noise levels
On the compliance on permissible noise levels 5 companies (62.5%) complied while the
rest were not (Table 4.4). The p value for the permissible Noise levels was more than
0.05 (p = 0.087) hence there is no significant association between the companies
complying (Table 4.5) and those that were not complying (MC3 and MC 4). In
industrially advanced countries, attempts have been made through legislation or codes of
practice to protect the workers from noise pollution (NIOSH, 1999). In the United States
of America, the NIOSH recommended exposure limit (REL) is stated to be 85 dB(A),
A-weighted 85 dBA as an 8 hour Time Weighted Average (TWA) and the OSHA
threshold limit value (TLV) is 90 dB(A) for compliance issues such that no worker shall
be exposed to a noise level equal to or above 85 dB(A) for eight hours of working time
44
as it is considered as hazardous (Boer and Schroten, 2007). No worker is to be exposed
to noise levels in excess of 90dB (A) in eight hours within any 24 hours duration or
140dB (A) maximum instantaneous sound level at any given time. Noise transmitted
outside the workplace should not exceed 55dB (A) during the day and 45dB (A) at night
(Rule 4, Legal Notice 25 of 2005). Hence permissible exposure levels, according to ISO
and OSHA, are both based on 90dB (A) as an 8-hr TWA with 3dB and 5dB exchange
rates, respectively (Bruel and Kjaer, 1984).
4.3.3 Noise prevention program
Only two companies (25%) had a noise control program in place (Table 4.5). The p
value for the noise prevention program for all companies was more than 0.05 except
MC7, hence there is was no significant association between the companies complying
and those that were not complying (MC1,2,3,4,5,6,8). The employer is required to adopt
methods of work, which shall reduce noise exposure of workers to the recommended
noise levels and as far as practicable, walls and ceilings of workplaces shall be lined
with suitable sound absorbing material to prevent reflection of noise.
Where noise in a workplace exceeds the continuous equivalent of 85 dB (A) the
employer must develop and implement an effective noise control and hearing
conservation program. The program must be in writing and should address; - noise
measurement, education and training, engineering noise control, hearing protection, and
45
posting of notices in noisy areas, hearing tests and annual program review (Rule 5,
Legal Notice 25 of 2005).
Table 4.5: Analyzed data for compliance levels in different companies
Rule No.
Companies
Percentage
complying
P - value
4
MC1, 2,5,6 and 7
62.5
0.087
5
MC1 and 7
25
0.062
6
MC1 – 8
100
0.049
7
MC7
12.5
0.024
16
MC1, 2 and 7
37.5
0.055
4.3.4 Noise measurements records
The results showed that all the 8 companies (100%) carried out noise surveys as per the
requirements of the Legal Notice number 25 of 2005 on Noise. There was significant
association/relationship in all the companies studied regarding Rule No.6 as stated in
Table 4.5 with p-value of 0.049. Compliance with this Rule could be attributed to the
fact that most regulatory officers were keen on noise measurements record. The results
of the measurements carried out should be kept by the employer for a period of two
years and should be communicated to the workers (OSHA, 2007). It is the duty of
employers to carry out measurements of noise at least once in every period of twelve
months in order to determine the prevailing noise conditions. Noise exposure
measurement results is recorded and should specify: the date and time of the noise
measurement, the names and numbers of workers exposed, types of occupations
46
evaluated,
measuring
conditions,
measuring
method,
measuring
equipment,
recommended remedial measures taken and name of person taking the measurements.
4.3.5 Information and training of workers
On the compliance on personal protective equipments on noise 201 (50.2%) agreed, 92
(23.0%) were uncertain while the rest 107 (5.8%) disagreed. Those working in
production department and generator area agreed to be complying with noise PPE use
while those in the office departments were not required to use the PPE. Employers
should inform in writing all the workers in any process where noise level is above 90 dB
(A) on:- the results of any noise exposure measurements, the significance of those
results to the risk of hearing loss and at the request of the worker, the purpose of hearing
protection and testing. In addition the employer should also ensure that all workers
exposed to noise are fully trained on the hazards involved and instructed in the measures
available for the prevention, control and protection against noise exposure (Rule 7,
Legal Notice 25 of 2005). The results are shown in Figure 4.4.
47
Participant’s response on Industrial noise
Figure 4.4: Compliance to hearing PPE at work
On whether they have had any training regarding noise hazards at work 225 (56.2%)
agreed, 37 (9.2%) strongly agreed while 94 (23.5%) disagreed and 44 (11.0%) strongly
disagreed (Figure 4.5). Another aspect evaluated was on training regarding noise
hazards at work only one company (12.5%) had carried such a specialized training.
Early recognition and elimination of noise sources or the wearing of protective devices
such as those used in industrial settings may prevent hearing loss (Ladou, 1997).
48
Participant’s response on Industrial noise
Figure 4.5: Compliance on training regarding noise
There was no significance association in compliance with the rules between MC7 and
the other companies but within MC7 there was significant association in complying with
all the rules with Pearson chi-square value of 0.024 (Table 4.5). In this study only one
company MC7 was compliant with all of the requirements of the legal notice no. 25 of
2005 on Noise.
4.3.6 Medical examinations and hearing tests
A total of 66 (16.4%) agreed to have had this test, 20 (5.0%) were uncertain while the
rest 314 (78.6%) disagreed. Before employment in a noisy environment employees
49
should undertake pre employment hearing test. In every workplace where the level of
sound energy or vibration emitted can result in hearing impairment or be harmful to
health or otherwise dangerous, all practicable measures shall be taken by the employer
to ensure the elimination or control of such sound energy for purposes of protecting any
person who may be exposed (OSHA,2007) Rule 16. (1) The occupier shall provide
medical examinations and hearing tests for workers to noise above 85 dB(A) limit as
follows: an initial test upon employment; annual tests thereafter or at such an interval as
may be required by the directorate; Occupational hearing impairment shall be
compensated as an occupational disease. The result is shown in Figure 4.6.
Participant’s response on Industrial noise
Figure 4.6: Pre-employment hearing test
A total of 3 companies (37.5%) agreed to have done this test. The p value for the
medical examinations and hearing test was more than 0.05 (p = 0.055) hence there is no
50
significant association between the companies complying and those that were not
complying (Table 4.5). This study shows that the employees exposed to high noise
thresholds were not aware of the dangers such as accidents that they may be exposed to
if the management does not comply with the law. The need to raise the level of
awareness is critical. Experts in occupational Health and Safety firmly believe that
information and knowledge are powerful tools to support preventive initiatives. There is
need for the management to involve the employees exposed to high noise thresholds in
risk assessment, management and mitigations.
4.4 Noise intensity in different departments of the selected manufacturing
industries
4.4.1 Noise levels in departments
Three departments (offices, production area and the compound where the Generator is
located) were identified as common in all the companies and their Noise levels
measured to determine which department had the highest levels. The highest Noise level
in each of the department was recorded as the measured level for that department and
compared with the recorded values in 2011 in which the mean values were missing. The
occupational exposure limit for office departments, generator unit and production
department are 55dBs, 90dBs and 90dBs, respectively. Repetitive sounds are easier to
handle than continuous sounds. Employees in different departments were exposed to
different noise levels. Those working in the production departments were exposed to
51
noise above occupational exposure limits while those working in offices far away from
the machinery were exposed to low noise levels.
4.4.2 Noise levels in the office department
The noise level measured in 2012 in the offices was within the set standards except for
one company which was above the OEL. The noise levels in the office department in all
the selected companies were below the occupational exposure limit. The office
department in MC6 had noise levels above the OEL limits while the rest had noise levels
within the limits (Table 4.6).
Table 4.6: Analyzed noise level in the office department of the selected companies
Company
Office department
Pearson chi square
Measured values
2012 (mean values +/-1 )
2011
P – values
MC1
48.6
54.1
0.04
MC2
47.6
47.0
0.04
MC3
39.6
40.1
0.01
MC4
50.1
49.0
0.03
MC5
42.4
42.0
0.02
MC6
55.6
56.7
0.06
MC7
38.1
40.3
0.04
MC8
49.9
45.6
0.04
The MC6 had a p - value of 0.06 while the other companies’ p - values were below 0.05
thus being significant at 95% confidence level. The occupational exposure limits as per
the set standards for the office departments globally is 55dBs. The study measured and
52
compared the noise levels with this OEL. The measured values for the year 2011 were
extracted from the records in the manufacturing companies under investigation and
hence the means values were not available. Table 4.7 shows the p value and the degree
of freedom of all the selected companies. It was found that the noise levels in the offices
in all the companies were within the limit except MC6 which had noise levels slightly
above the OEL.
4.4.3 Noise levels in the production departments
Noise levels in the production area (2012) were measured, recorded and compared with
those of 2011 measurements. In most of the companies the noise levels were above the
OEL except MC1 2011 (84dBs) and MC7 2011 which was 88.2dBs. The production
department recorded noise levels above the OEL except MC7 whose noise levels were
within the expected limits. The production department recorded the highest noise levels
in all the selected companies. There was no significant difference in the noise levels in
all the companies in the production department except the MC7 whose p - value was
below 0.05. The p - value of the other companies was above 0.05 (Table 4.7).
53
Table 4.7: Analyzed noise levels in the production department of the selected
companies
Company
Production department
Pearson chi square
Measured values
2012 (mean values +/-1)
2011
f
P – values
MC1
91.6
84.0
2.00
0.0581
MC2
92.4
93.1
2.83
0.0981
MC3
95.3
95.3
2.83
0.0981
MC4
91.3
93.8
2.83
0.0981
MC5
94.7
94.5
2.83
0.0981
MC6
91.0
92.0
2.83
0.0981
MC7
90.0
88.2
2.03
0.0481
MC8
93.7
94.1
2.83
0.0981
4.4.4 Noise levels in the generator department
The noise levels in the generator department in all the 8 companies were above the set
standards except MC1 2011 at 89.4 dBs and MC7 which were recorded at 88.7 dBs and
89.0 dBs in 2012 and 2011, respectively. The generator department in all the selected
companies recorded the highest noise level which was above the occupational exposure
limit except MC7 which was within the limits of exposure. The generator area in the 7
companies is not compliant to the legal notice 25 of 2005 (Table 4.8).
54
Table 4.8: Analyzed noise levels in the generator department of the selected
companies
Company
Generator department
Measured value
2012 (mean values +/-1)
Pearson chi square
Statistical data analysis
2011
f
P – values
MC1
92.0
89.4
2.41
0.1268
MC2
93.7
91.2
2.41
0.1268
MC3
94.1
98.6
2.42
0.1268
MC4
95.2
97.1
2.45
0.1268
MC5
94.8
94.7
2.44
0.1268
MC6
97.0
98.2
2.49
0.1268
MC7
88.7
89.0
2.40
0.0268
MC8
96.4
94.9
2.41
0.1268
The p value for the companies with limits above OEL was above 0.05 while the p value
for MC7 was below 0.05. The noise levels over time in the different departments are not
statistically significant therefore the departments in the category of 90dBs and 55dBs,
respectively have no statistical difference except in one company per category. The
statistical analysis of data in this study has showed that noise levels in different
departments within the manufacturing industries are independent of each other while the
exposure level to different employees is dependent on the department one is working in.
Those employees working in the generator areas in this study are highly exposed to
noise levels above the OEL. This result are in agreement with the findings of Barreto et
al., (1997) who found out that employees operating heavy machines and those working
55
in generator departments were exposed to high levels of noise as compared to those
working in the office departments.
4.5 Magnitude of occupational noise exposures of workers in different categories of
manufacturing industries
Most of the workers were identified to be in the production area which had a high
number of employees in the companies studied (Table 4.12). Noise levels in the
production area were therefore used to assess the magnitude of occupational noise
exposure to the workers. The number of employees exposed were highest in MC3 (63)
while MC8 (3) had the least number of employees exposed to high noise levels as shown
in Table 4.9.
Table 4.9: Number of workers exposed to noise in 3 departments of the selected
companies
Company
Number of employees
Office
Production
Generator
Total employees
MC1
5
20
2
27
MC2
8
55
5
68
MC3
15
63
7
85
MC4
6
37
4
47
MC5
10
47
6
63
MC6
12
48
6
66
MC7
6
30
3
39
MC8
1
3
1
5
TOTAL
63
303
34
400
56
The MC8 exposure magnitude in terms of employees was low since only 3 (10.0%)
were in production, 1(0.3%) in the generator and 1 (0.3%) in the office. The MC3 had
the highest number of employees exposed to noise since 68(22.4%) worked in
production department, 7(2.3%) worked in the generator while 15(5.0%) worked in the
offices. Stansfeld and Matheson (2003) in their study on noise levels found out that the
bulk of workers in industries worked in the production department thus being exposed to
high noise levels. The results in this study confirm with their findings. The magnitude of
the exposure limit in the 8 selected companies showed that MC8 had the least number of
employee exposed to noise levels while MC3 had the highest number of employees
exposed to high noise levels. The p - value for the exposure magnitude is 0.49 for all the
companies therefore there is no association in terms of noise exposure from one
company to the other. The p - value for the number of employees exposed is 0.041
therefore the exposure level is dependent on the company one is working for while the
exposure magnitude depend on the department and the company one is working in (table
4.10).
Table 4.10: Noise exposure magnitude among employees in the selected companies
Asymp. Sig. (2-sided)
P – values
Pearson Chi-Square (7 comp) 41.385a 28
.049
0.049
Pearson for MC3
.041
0.041
Value
Likelihood Ratio
50.834
Linear-by-Linear Association .022
N of Valid Cases
Df
28
.005
1
.881
400
57
The exposure magnitude depends on the company one is working in. The companies
that employees more people exposes many peoples to noise levels above the OEL while
the companies that employs few people exposes less people to hazardous noise levels. If
the companies are compliant with the set standards then the magnitude of noise exposure
is low irrespective of the number of employees in a given time.
58
CHAPTER FIVE
CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
The results of this study showed that
1) Majority (68.5%) of the employees indicated that high occupational noise levels
in the manufacturing industries affect the work performance and communication
among them
2) Most (62.5%) of the manufacturing industries do not comply with set standards
on noise especially OSHA, 2007 and Legal Notice number 25 of 2005.
3) According to this study it is clear that employees working in the generator
department (88.7 – 97 dBs) were exposed to noise levels far beyond the
Occupational Exposure Limit while others in the office department (38.1 – 55.6
dBs) enjoy low levels of noise.
4) The majority (75.8%) of employees work in the production areas where the noise
levels in most of the companies was above the standards. This indicates that the
magnitude of occupational noise exposures of workers is high especially among
the males (82.0%) who are the majority in the industries as compared to their
female counterparts.
5.2 Recommendations
a) It is evident that majority of the employees in the selected industries not aware of
the risk associated with excessive noise in their work environment because they
fail to utilize the PPE provided and thus the organization should be conducting
59
regular education on noise hazards and the need to use noise PPEs such as
earplugs and muffs.
b) In conformity with ‘the factories and other places of work act’ (OSHA, 2007)
Kenya Subsidiary Legislation, 2005, Legal Notice No. 25. The ministry which
oversees the implementation of this rules and regulations should strictly enforce
the law in order to safe innocent employees who are being exposed to high levels
of noise yet they are not aware of the dangers of high noise levels.
c) It is recommended that sound absorbing and soundproof finishing of workroom
surfaces should be provided to place impermeable obstacles in the way of the
propagation of sound waves especially where sound limit are beyond the
exposure limits. Noise silencers and sound absorbers must be installed as
specified by the standard to suppress aerodynamic noises. Soundproofing include
the construction of barrier structures, such as walls or partitions, to safeguard the
workers from external noise.
d) To assess noise levels that spills over to the neighborhood from manufacturing
processes that are likely to produce much noise, more than 90 dBs.
e) Sound audits in the industries are important to prevent high level intensity of
noise, damaging the ear drums of the worker. In these connections all the
companies should measure the noises in different departments and ensure that
the levels are within the set standards.
60
5.3 Suggestions for further research
The study suggests further research to enhance knowledge on noise and in particular on:
a) Establishment of actual number of employees suffering from NIHL in the
manufacturing sectors.
b) Investigate the effectiveness of the regulatory bodies in the enforcement of the
Noise standards
c) Magnitude of noise exposure in other sectors of economy especially transports
agriculture and entertainment.
d) Establish none auditory health effects due to exposure of noise above the OEL in
the manufacturing industries.
e) A study on efficiency and effectiveness of the provided PPEs for Noise control.
61
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APPENDICES
Appendix 1: Questionnaire
Introduction and consent form
Hello, my name is JAMES MITHANGA a Masters student at Jomo Kenyatta University
of Agriculture and Technology, pursuing a Msc. Occupational safety and health. I would
like to understand how big the problem of occupational noise exposure is and how can it
be tackled ultimately to improve the occupational safety and health service in the
respective enterprises. In line with these clear objectives, I would like to ask you some
questions related to hearing associated with noise exposures at work. The information
that you tell me on this questionnaire will be kept strictly confidential. You don’t need
to write your name.
a)
Thank you in advance for your cooperation.
Questionnaire identification number...........
A. GENERAL INFORMATION
i.
Name of the organization........................................................................................
ii.
Place of work..........................................................................................................
iii.
Department.............................................................................................................
iv.
Area of residence....................................................................................................
v.
Marital status
vi.
Sex
69
vii.
Age...........................................................................................................................
.........
viii.
Worker’s
qualification………………………………………………………………........
ix.
Are you in management or a general
employee………………………………………….
x.
Number of years you have worked in the
industry………………………………………
Please mark only the box you feel best fits the statements below. There are no
wrong answers.
Strongl
y
disagre
e
1
2R
3
4
6
7
A. COMMUNICATION
I find it hard to communicate
while it is noisy
When am absorbed in a
conversation I do not notice if
it is noisy around me
In the industry I cannot
concentrate well on my
conversation when machines
are on
I
think
industry
noise
interferes with conversations
I find it very hard to follow a
conversation
when
the
machines are running
Loud sounds in the industry
makes
me
stop
my
conversation
High noise levels make it hard
for me to concentrate on my
conversation
70
disagre
e
Uncertai
n
Agre
e
Strongl
y agree
8
9R
10
11
12
13
14
R
15
16
17
R
18
R
19
20
21
22
23
24
B. WORK
I need peace and quiet place to
do difficult work
I have no problem to do
routine work in a noisy
environment
My performance is much
worse in noisy places
I need quiet surroundings to be
able to work on new tasks
When people around me are
noisy I don’t get on with my
work
If my work place was noisy I
would always try to find a way
for me to change this
I can do complicated work
even while heavy machines
are running
C. HABITAT
For a quiet place to live I
would
accept
other
disadvantages
I am very sensitive to industry
noise
When I am at work I become
accustomed to industry noise
It would not bother me to live
in a noisy surrounding
When children are noisy, I
prefer them not to play around
my surroundings
I don’t like noise activities in
my residential area
Noise from neighbours can be
extremely disturbing
D. LEISURE
I find it hard to relax in a noisy
environment
Listening to loud music helps
me relax after work
In the cinema I am annoyed by
other people whispering and
71
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
by rustling paper
When dancing I don’t mind
how loud the music is
At weekends I prefer quiet
surroundings
I avoid leisure activities which
are loud
E. SLEEP
I become very agitated if I can
hear someone talking while I
am trying to fall asleep
I can fall asleep even when it
is noisy
I need an absolutely quiet
environment to get a good
night’s sleep
Even the slightest noise can
prevent me from falling asleep
I do not feel well rested if
there has been a lot of noise
the night before
I wake up at the slightest noise
The sound of loud thunder
does not usually wake me up
F. INDUSTRY
NOISE/HEARING
Members in my family have
lost hearing before age of 50
I have had head injuries before
I have had an ear ache before
I have had ear allergies before
I have had ear infections and
trauma before
Do you take drugs, antibiotics
or medication regularly
Have you had pre-employment
hearing test
Do you usually wear hearing
protector at work
Have you ever been trained
regarding noise hazards at
work
72
Appendix 2: Industries compliance with the set rules and regulations on noise
RULE Compliance
MC1
MC2
MC3
MC4
MC5
MC6
MC7
MC8
√
√
X
X
√
√
√
X
√
X
X
X
X
X
√
X
√
√
√
√
√
√
√
√
Information and X
X
X
X
X
X
√
X
√
X
X
X
X
√
X
NO.
Items
4
Permissible
noise levels
5
Noise
prevention
programme
6
Noise
measurements
and records
7
training of
workers
16
Medical
√
examination
and hearing test
73
Appendix 3: Questionnaire response
Question
Communication
Work
Industry noise
Response
Agree
Strongly Disagree Strongly Uncertain
agree
disagree
Is Hard while in noisy place
226
0
125
49
0
Don't concentrate well while machines on
189
17
169
0
25
Industry noise interferes with conversation
202
89
64
0
45
Need peace and quiet place to do difficult work
108
129
83
46
34
Performance is worse in noisy places
137
0
84
36
143
Need quiet surrounding to be able to work on new tasks
192
38
0
101
69
Can do complicated work even when heavy machines
are running
196
21
84
57
42
Members in my family have lost hearing before age of
50
0
0
173
183
44
Have had ear ache due to industrial noise
0
21
190
42
24
Have had ear allergies before
15
0
258
90
37
Have had ear infections and trauma
0
21
212
152
15
Take drugs, antibiotics or medication regularly
20
0
202
128
20
Have had pre-employment hearing test
49
17
291
23
20
Usually wear hearing protector at work
156
45
84
23
92
Ever been trained regarding noise hazards at work
225
37
94
44
0
74
Total
400
400
400
400
400
400
400
400
400
400
400
400
400
400
400