CC BY
27Electronic Journal «Technical Acoustics» http://www .ejta.org
2009, 10
U. E. Asuquo1*, M. U. Onuu1, A. U. Asuquo2
1 Department of Physics, University of Calabar, P.M.B. 1115, Calabar, Cross River State, Nigeria 2Department of Anaesthesiology, University of Calabar, Teaching Hospital, Calabar, Cross River State, Nigeria
Effects of exposure to loud noise on the hearing of the residents of Calabar, Cross River State, Nigeria
Received 25.06.2009, published 16.09.2009
The effects of noise on hearing have been assessed among residents of Calabar, Cross River State, Nigeria, using subjective and objective measures. A 39-item questionnaire was used for the subjective measure. A sample size of 1000 persons in the high noise Zones (noise level>80 dB(A)) was randomly selected and used as a study group while 1000 persons in the low noise Zones (noise level<50 dB(A)) were also randomly selected and used as the control group. Results on Pure Tone Audiometry (PTA) was used to assess the hearing acuity of the respondents and to determine if there was any effect of exposure to loud noise on the hearing of those in the high noise zones. Using a statistical analysis software (SAS), a probability value of 0.0001 (<0.05) and a calculated chi-square (x2) value of 82.2509 (tabulated X2=5.22) were obtained. Thus implying that exposure to loud noise does affect hearing of residents in the high noise Zones.
Keywords: noise, hearing acuity, pure tone audiometer.
INTRODUCTION
As the society develops technologically, more and more people are exposed in one way or the other to noise exceeding 65 dB(A). In some countries, more than half of the population is exposed, in others less than 10%. When one realizes that at 65 dB(A) sleeping becomes seriously disturbed and most people become annoyed, it is clear that noise is a genuine environmental health problem. The acoustic world around us continuously stimulates the auditory system. The brain selects relevant signals from the acoustic input, but the ear and the lower auditory system are continuously receiving stimulation. This is a normal process and does not necessarily imply disturbing and harmful effects. The auditory nerves provide activating impulses to the brain, which enable us to regulate our vigilance and wakefulness necessary for optimum performance.
Problems associated with noise - induced hearing loss are not new. In the middle ages, workers in certain profession such as blacksmithing, mining, and church bell ringing were known to become deaf, or partially deaf, after years of work [1]. However, with technological development, the number of workers exposed to excessive noise increased significantly as has the number of people exposed to other sources of noise, such as transportation noise and loud music [2].
The risk of much increased rates of occupationally acquired hearing loss must be met by strong preventive measures in engineering and medicine in both developed and developing
countries. Furthermore, in most countries, hearing impairment due to community noise exposure (sociacusis) has become a problem of concern [1]. It has also been reported that community generated noise may have a number of direct/indirect adverse effects on communication, performance, and behaviour; non auditory physiological effects; noise-induced disturbance of sleep; and community annoyance [2-7].
The indirect or secondary effects of noise are often difficult to quantify and satisfactory assessment models are lacking. Often, large-scale epidemiological or social surveys would be required for assessment. There may be a greater percentage of our population at risk from adverse effects of noise.
HYPOTHESES OF STUDY
The following null hypotheses were used for the research;
i. There is no relationship between objective measure of noise using sound level meter and the subjective measure of noise using questionnaires.
ii. There is no relationship between exposure to loud noise and noise - induced hearing loss.
MATERIALS AND METHOD
The materials used for this study are the sound level meter for measuring the sound level of the zones, an audiometer for testing hearing acuity and a 39-item questionnaire for subjective assessment of the respondents.
Site description
Guided by our preliminary measurements, the following sites were selected.
High noise zone
i. Federal Government Girl's College, Calabar
ii. Federal Airport Authority of Nigeria, Calabar
iii. Ayo's Wood Industrial Company, Export Processing Zone, Calabar
iv. Kelvin Wood Industry, Export Processing Zone, Calabar
v. Boa Yoa Huan Iron/Steel Company, Export Processing Zone, Calabar
vi. Timber Market, Marian Road, Calabar
vii. Niger Mill Company, Calabar
viii. System Metals Company, Calabar
Low noise zone
i. Government Secondary School, Anantigha, Calabar
ii. Aqua Vista, Anantigha, Calabar
iii. Unical Staff Quarters, Calabar
iv. Crutech, Staff Quarters, Calabar
v. Unical Satellite town, Calabar
vi. Akim Akim Model Secondary School, Calabar
vii. Federal Housing Estate, Calabar
viii. Essien Town, Calabar
In these high noise Zones, Zone 1 is the federal Government Girl's College, Calabar. This zone is largely a secondary school, which is supposed to be noise free. However, its closeness to Margaret Ekpo International Airport, Calabar made it a very noisy zone.
Zone 2 is the Airport zone. The high noise recorded in this zone is mainly due to air traffic in the Margaret Ekpo International Airport, Calabar. There are several residential houses and two Secondary Schools within this zone.
Zone 3, 4 and 5 are companies located within the Export Processing Zone, Calabar. The major machines in Ayos Wood International Company and Kevin Wood Industry are sawing and spraying machines. There are also some machines to smoothen wood. The major machines in Boa Yoa Huan Jian Iron/Steel Company are welding, shaping and cutting machines.
The major machines in zone 6 which is Timber Market, Akim, Calabar are sawing and spraying machines.
Niger Mills Company Plc located in the heart of Calabar Municipality has Rolling Mills (Buhler) as the major machine.
In System Metal Company, Calabar, the major machines are pressing and cutting machines.
All the zones in the low noise zones are basically made up of residential areas with no major noise sources, apart from noise caused by traffic. The areas chosen however had small volume of traffic flow.
Generally, all the zones in the high noise zones had noise levels of 80 dB(A) or above while the low noise zones had noise levels 50 dB(A) or below.
Measurements of noise levels
Noise levels at schools and their surroundings were measured objectively using a precision sound level meter (Bruel and Kjaer) type 2203 with octave band filter (B&K) type 1613. After identifying the sties, measurements were then made at various points by an accredited Acoustician from the Department of Physics, University of Calabar, Nigeria.
During the noise level measurements the sound level meter was held in such a way that the microphone was at least one meter from any reflecting surface and 1.2 m from the ground, corresponding to the ear level of an average person [8, 9].
Measurements were taken in sixteen zones - eight high noise zones and eight low noise zones. The high noise zones had average noise levels of 80 dB(A) or above, a level which may be hazardous to the hearing of most people [1]. The low noise zones had average noise levels of 50 dB(A) or below, a level above which most person complain [10, 11].
Measurements were taken between 7 am and 9 am, and 2 pm and 4 pm on working days (Monday to Fridays). About fifty random readings were taken at different locations within each zone and the sound level of each zone was calculated.
Hearing assessment
Hearing assessment of the respondents was done by a trained Technician using a pure tone audiometer in the Department of Otolaryngology, University of Calabar Teaching Hospital, Calabar using the audiometer. The frequency of the audiometer was varied from 64 Hz to over 8000 Hz. Amplitude was varied by 5 dB increments. The oscillator was used to change pitch so that a range of sounds can be tested. Hearing threshold measurements were carried out separately for both the right and left ears of the 2000 subjects using the Hughson-Westlake (ascending/descending) procedure. Each audiometric test was preceded by an auriscopic examination in order that any coexistence significant aural pathological conditions such as wax impaction, tympanic membrane perforation, etc., could be detected.
The test produced a graph showing the lowest decibel level at which each frequency was heard and traced a profile of the person's threshold of hearing, which was compared to a line on the graph representing normal hearing levels. Hearing threshold levels is as follows [12]. < 25dB - normal hearing
26 40dB - mild hearing loss
41 60dB - moderate hearing loss
61 80dB - severe hearing loss
> 80dB - profound hearing loss
Social survey: questionnaire and description
The respondents were served with questionnaires which contained standard questions tailored towards getting their reactions about the effects of noise on them. The questionnaires, was structured to, among others, elicit information on general sociodemographic characteristics viz: age, sex, educational level, medical and occupational history of diseases and conditions that could cause hearing impairment.
Section A was the introductory section with question that were to help the interviewer to identify the area of interview, the date of interview, the time of interview and also some personal information about the respondents like their heights, weights and pulses.
Section B was designed to collect information on the respondent and their noise response, including respondents' attitude toward their neighborhood and their rating of specific and overall noise levels. Personal information on the respondents such as age, marital status, sex, educational level attained, and duration of stay in area were also collected in their section. Only questionnaires of those who had stayed or schooled/worked in their location for a minimum of three years were used for analysis, since it is believed that respondents might have been adequately adjusted to the noise environment in their area within three years.
Section C (questions 14 - 18), sought to identify the noise sources complained of by the respondents in their area, the intensity of the noise compared to normal conversation, the frequency of occurrence, the period of the day it is loudest and how he/she is affected by the noise.
The last section D: (question 19 - 39) sought to find out the actual effects of noise on the health of the respondents. Respondents were asked questions on the frequency of their visit to hospital, the nature of sickness they were treated for and the type of drugs administered to them. Information was also obtained here on the family history of heart related sicknesses like hypertension.
Subjective measurement
Subjective measurement was done using questionnaires. A total of 1300 questionnaires were distributed in the high noise zones while 1200 were distributed in the low noise zones. 1100 (85.6%) were collected back from the high noise zones while 1050 (87.5%) were collected back from the low noise zones. However, 1000 questionnaires were accepted for analysis from both the low and the high noise zones.
This is because 100 and 50 questionnaires were rejected from the high noise zones and the low noise zones, respectively because the respondents did not stayed or worked/schooled in the area for up to three years.
RESULTS
The effects of exposure to loud noise on hearing of people in Calabar were assessed by comparing the hearing acuity and subjective responses of respondents in the high noise zones with that of respondents in the low noise zones. The respondents taken were those that have resided or done business in these areas for at least three years, a period believed to be enough for the respondents to be adapted to the noise environment of the zone. Results of physical measurements are presented in Tables 1, 2, 3 and 4.
Table 1. Noise levels in the high noise zones
Background A-Weighted Lmax
S/N Location Code Noise SPL ± 0.5
± 0.5 dB(A) ± 0.5 dB(A) dB(A)
1 Federal Govt. Girls College Calabar HNZ 1 56.0 118.0 121.5
2 Federal Airport Authority Schools, Calabar HNZ 2 51.0 116.5 120.0
3 Ayo's Wood, EPZ, Calabar HNZ 3 54.0 109.5 112.0
4 Kelvin Wood, EPZ, Calabar HNZ 4 57.0 102.0 108.0
5 BaoYoa Huan Jian Iron/Steel Coy, Calabar HNZ 5 54.5 110.0 115.0
6 Timber Market, Marian, Calabar HNZ 6 50.5 116.0 119.0
7 Niger Mills Company, Calabar HNZ 7 60.5 129.0 131.0
8 System Metal Company, Calabar HNZ 8 60.0 112.0 118.0
Table 2. Noise levels in the low noise zones
S/N Location Code Background Noise Level ± 0.5 dB(A)
1 Govt. Sec. Sch, Anatigha, Calabar LNZ 1 47.5
2 Aqua Vista, Calabar LNZ 2 40.0
3 Uncial Staff Quarters LNZ 3 44.5
4 Cross River State University Staff Quarters LNZ 4 40.0
5 Uncial Satellite Town, Calabar LNZ 5 43.5
6 Akim Akim Sec. Sch, Calabar LNZ 6 38.0
7 Federal Housing Calabar LNZ 7 47.0
8 Essien Town, Calabar LNZ 8 44.5
Table 3. Hearing assessment in the high noise zones
„, , ,,, , Number of Respondents
Threshold levels (dB)-=-r-;-c--—--
_ _Right ear_Left ear
<_ 25 540 367
26 - 40 392 560
41 - 60 60 40
61 - 80 5 25
> 80 3 8
Table 4. Hearing assessment of respondents in the low noise zones
Threshold Levels _Number of Respondents
(dB)_Right ear_Left ear
< 25 620 720
26-40 375 251
41-60 3 20
61-80 2 7
> 80 1 2
Results of survey with questionnaire
A total of 3000 questionnaires were distributed in the different zones in Calabar. Only 1000 questionnaires were accepted for use in each zone for this study, giving a total of 2000. Others were rejected for various reasons which include incomplete response and duration of stay in the zone. The results of the surveys with questionnaire are summarized in tables 5 to 16.
Distribution by age and sex
Tables 5 and 6 show the age distribution of respondents in the high noise zones and the low noise zones respectively.
Tables A1 and A2 show the distribution by sex of the respondents in the high and low noises zones respectively (Appendix I).
Table 5. Age distribution of respondents in the high noise zones
Age distribution (years)
Zone < 20 20-29 30-39 40-49 > 50 Total
HNZ 1 17 59 34 12 10 132
HNZ 2 33 117 37 19 2 208
HNZ 3 62 19 6 4 1 92
HNZ 4 65 22 9 7 4 107
HNZ 5 33 92 32 19 2 178
HNZ 6 12 54 34 11 10 121
HNZ 7 40 17 13 3 1 74
HNZ 8 37 27 13 11 0 88
Total 299 407 178 86 30 1000
% 29.9 40.7 17.8 8.6 3.0 100
Table 6. Age distribution of respondents in the low noise zones
Age distribution (years)
Zone <20 20-29 30-39 40-49 >50 Total
LNZ 1 54 30 20 15 0 119
LNZ 2 7 21 5 2 2 37
LNZ 3 47 83 27 13 0 170
LNZ 4 6 22 7 4 1 40
LNZ 5 67 105 40 35 20 267
LNZ 6 210 25 30 20 4 289
LNZ 7 20 11 7 7 0 45
LNZ 8 6 21 4 2 0 33
Total 417 318 140 98 27 1000
% 41.7 31.8 14.0 9.8 2.7 100
Figures A1 and A2 are bar charts showing the percentage age distribution in the high and low noise zones respectively (Appendix II).
Distribution by marital status
Tables A3 and A4 show the distribution by marital status of the respondents in the high noise zones and the low noise zones respectively (Appendix I).
Distribution by educational level
Tables A5 and A6 show the distribution by educational level of respondents in the high noise zones and the low noise zones respectively (Appendix I).
Distribution by duration of exposure
Tables A7 and A8 show the duration of exposure per day for the respondents in the high and low noise zones respectively (Appendix I).
Duration of exposure to noise is very important when considering the effects of noise on health. It can be seen in Figure A3 (Appendix II) that a greater percentage (79% and 59% respectively) of the respondents are exposed to noise between 5 and 8 hours daily.
Tables A9 and A10 show the distribution of duration of exposure for the respondent in years in the high and the low noise zones respectively (Appendix I).
Questionnaires of respondents who had not stayed up to three years in their vicinity were discarded. 16.4% of respondents are exposed to noise above 8 years in high noise zones while 9.4% of respondents are exposed to noise above 8 years in the low noise zones.
Tables 7 and 8 show the noise assessments by respondents in high noise and low noise zones respectively.
Table 7. Noise assessment by respondents in high noise zones
Noise rating
Zones Very noisy Noisy Moderately noisy Quiet Very quiet Total
HNZ 1 70 28 20 8 6 132
HNZ 2 84 105 12 6 1 208
HNZ 3 35 30 6 11 10 92
HNZ 4 42 40 14 6 5 107
HNZ 5 69 60 40 6 3 178
HNZ 6 47 55 17 0 2 121
HNZ 7 50 10 9 5 0 74
HNZ 8 46 30 8 2 2 88
TOTAL 443 358 126 44 29 1000
% 44.3 35.8 12.6 4.4 2.9 100
Table 8. Noise assessment by respondents in low noise zones
Noise rating
Zones Very noisy Noisy Moderately noisy Quiet Very quiet Total
LNZ 1 16 50 40 10 3 119
LNZ 2 5 8 17 6 1 37
LNZ 3 36 84 40 5 5 170
LNZ 4 3 19 12 4 2 40
LNZ 5 68 75 97 22 5 267
LNZ 6 60 85 100 24 20 289
LNZ 7 7 19 14 4 1 45
LNZ 8 3 19 7 3 1 33
TOTAL 198 359 327 78 38 1000
% 19.8 35.9 32.7 7.8 3.8 100
ANALYSIS OF RESULTS
Correlation between the subjective and objective responses
To determine how related the subjective responses, assessed by the use of questionnaires as the study instrument were to the objective responses measured with the sound level meter, the coefficients of correlation[13, 14] were calculated for the noise measurements.
First comparison was accomplished by introducing scale values in the form of numbers to represent the respondents' noise rating. The numbers 5, 4, 3, 2 and 1 are introduced to represent "very noisy", "noisy", "moderately noisy", "quiet" and "very quiet" options respectively.
Multiplying these numbers by their corresponding frequency of responses to obtain the corresponding weighted ratings and dividing the weighted ratings by their respective total respondents per zone, the overall average scale values for each zone was calculated [15].
The overall average scale values for the zones represented the overall environmental noise rating for that particular zone. The above steps are summarized in Tables 9 and 10 for the high noise zones and the low noise zones respectively.
The objective responses measured with the sound level meter represent x-variates and the subjection responses represented by corresponding average value per zone (nx/n), as y-variates. Substituting these data into equation 1 (Appendix IV), we have the correlation coefficient to be 0.66 and 0.56 for the high noise zones and the low noise zones respectively. The results show that there are good correlations between the two measurements in both zones.
Table 9. Community noise rating in high noise zones
Zones Very noisy Noisy Moderately noisy Quiet Very quiet Response pei zone (n) Weighting rating per zone (nx) Average value per zone (nx/n)
5 4 3 2 1
HNZ 1 70 28 20 8 6 132 544 4.12
HNZ 2 84 105 12 6 1 208 889 4.27
HNZ 3 35 30 6 11 10 92 345 3.75
HNZ 4 42 40 14 6 5 107 429 4.01
HNZ 5 69 60 40 6 3 178 726 4.08
HNZ 6 47 55 17 0 2 121 508 4.20
HNZ 7 50 10 9 5 0 74 327 4.42
HNZ 8 46 30 8 2 2 88 In = 1000 382 I(nx) = 4150 4.34 I(nx/n) = 33.19
Table 10. Community noise rating in low noise zones
Zones Very noisy Noisy Moderately noisy Quiet Very quiet Response pei zone (n) Weighting rating per zone (nx) Average value per zone (nx/n)
5 4 3 2 1
LNZ 1 16 50 40 10 3 119 423 3.55
LNZ 2 5 8 17 6 1 37 121 3.27
LNZ 3 36 84 40 5 5 170 651 3.83
LNZ 4 3 19 12 4 2 40 137 3.43
LNZ 5 68 75 97 22 5 267 980 3.67
LNZ 6 60 85 100 24 20 289 1008 3.49
LNZ 7 7 19 14 4 1 45 162 3.60
LNZ 8 3 19 7 3 1 33 In = 1000 119 I(nx)= 3601 3.61 I(nx/n) = 28.45
Correlation between distribution of respondents' ages in high noise zones and low noise zones
Correlation between distribution of respondents' ages in high noise zones and low noise zones was analysed using the correlation equation (Appendix IV). The total of the age ranges in Table 5 represents x-variates and the total of the age ranges in Table 6 represents y-variates. Substituting these data into equation 1, the correlation coefficient was found to be 0.88, a high correlation, showing that the effect due to differences in ages of respondents in the two zones can be neglected.
Correlation between distribution of respondents' sexes in high noise zones and low noise zones
Correlation between distribution of respondents' sexes in high noise zones and low noise zones was also analysed using the correlation equation (Appendix IV). The total in Table A1 represent x-variates and the total in Table A2 represent y-variates. Substituting these data into equation 1, the correlation coefficient was found to be 1.0, giving a very high correlation, showing that there will be no effect due to differences in sexes of respondents in the two zones.
Effects of noise on hearings
The hearing assessment of respondents in the high and low noise zones were shown in Tables 3 and 4 respectively. Analyses of these tables using the Statistical Analysis Software (SAS) [13] give the results as shown in Table A11 (Appendix III).
The results in Tables 3 and 4 show that majority of respondents had hearing loss. In the high noise zone, 1.45% had hearing loss in different degrees in the right ear while 15.82% had hearing loss in the left ear. In the low noise zones, 9.43% had hearing loss in the right ear while 6.98% had hearing loss in the left ear.
The probability value is 0.0001. This is statistically significant and so we reject the null hypothesis that there is no relationship between exposure to loud noise and noise-induced hearing loss.
To further confirm our decision, we consider the chi-squares value. Here, the chi-square (X2) value is 82.2509. The tabulated (x2) value is 5.22. Therefore, since the calculated (x2) is greater than the tabulated (x2), this confirms the null hypothesis should be rejected.
Therefore, we can conclude from the analysis that exposure to loud noise do cause noise-induced hearing loss, as seen in this study.
DISCUSSIONS AND CONCLUSION
Noise is a disturbance to the human environment that is escalating at such a high rate that it will become a major threat to the quality of human lives if nothing is done to reduce it. Noise is not a new hazard. It has been a constant threat since the industrial revolution. Too much noise exposure may cause a temporary change in hearing (your ears may feel stuffed up) or a temporary ringing in your ears (tinnitus). These short-term problems usually go away within a few minutes or hours after leaving the noise. However, repeated exposures to loud noise can lead to permanent, incurable hearing loss or tinnitus.
To assess the effects of noise on the hearing of residents of Calabar, a 39 - item questionnaire was used for the subjective measures while a factory calibrated sound level meter was used for the objective measure.
The correlation coefficient between both measures was calculated for the high noise zones and the low noise zones using the rating given by Molino [15]. The correlation coefficients were found to be 0.66 and 0.55 for the high noise zones and the low noise zones respectively. This is in agreement with previous studies [16, 17]. The results show that there is a better correlation between the two measures in the high noise zones. This is probably because there is increased awareness to noise due to the higher noise levels in these zones.
The correlation coefficients for both zones were positive. This means that we can base our decisions on the effects of noise on respondents on the social survey.
Everyone of us has experienced changes in our hearing as a result of loud noise, but what most people may not realize is that irreversible damage might be done to their hearing as a result of such exposures. According to the US public health service [18], some 10 million of the estimated 21 million Americans with hearing impairments owe their losses to noise exposure [19]. Bethesda [20] reported that an individual could develop a noise-induced hearing loss if he/she was exposed to sound that were too loud, say from 80 dB(A).
Further researches confirmed that it did not matter whether the sound was pleasant or unpleasant but that if one is exposed to loud noise for a sufficiently long time, hearing would be permanently damaged [21].
Noise-induced hearing loss is as a result of the damage to the structural organs of the inner ear, especially the hair cells due to the long exposure to harmful noise. In fact, noise-induced hearing loss is one of the most common causes of nerve deafness. It is sometimes accompanied by Tinnitus - a roaring, ringing or hissing noise [22].
This study was carried out among respondents in the high noise zones of Calabar town to assess, among other effects, the effect of noise on their hearing. 1000 respondents in the low noise zones were used as a control group. From the results obtained, the following observations were made: About 30% of the respondents in the high noise zones had hearing losses of varying degrees on either the left or right ear or both. 16.13% had hearing loss of various degrees in either the left ear or the right ear or both among respondents in the low noise zones.
Further analysis revealed that the null hypothesis that there is no effect of noise on hearing should be rejected. Hence, we conclude that exposure to loud noise do affect our hearing. This conclusion agrees with many earlier findings [23-28].
There are statistical significant differences in mean threshold levels ((p = 0.0001(<0.05)) and X = 82.2509 when the tabulated X = 5.22) between residents in the high noise zones and those in the low noise zones. We believe that this difference would have been higher but for the fact that even those considered under the low noise zones do move to the high noise zones from time to time.
Sources of noise have been increasing rapidly in Calabar, especially with its new status as a tourist State capital, which attracts influx of human, cars, machineries and industries. Exposure to damaging noise however, does not come only form the workplace. One can be exposed to a potentially damaging noise through stereo headsets, operating power tools for yard work, having a long daily commute in heavy traffic, or using a number of household appliances. Recreational activities such as hunting, target shooting, motor boating, waterskiing, jet skiing, snowmobiling, motorcycle riding, woodworking, rock music, or stereo headsets are sources of hazardous noise. So are some movie theaters, home entertainment centers, car stereo systems, health clubs, dance clubs, bars, and amusement centers. One can project that the noise situation in Calabar will only grow from bad to worse in the next few years.
The truth is that no one is totally free from the health effects of noise, be it industrial, traffic or environmental noise. Noise has been clearly identified as an important cause of physical and physiological stress in this study and in a dozen of other studies since stress has been directly linked with many of our most common health and physiological problems.
The rate of hearing loss among residents in Calabar, Nigeria can be reduced by reducing noise levels and duration of exposure. The Federal Government of Nigeria and Cross River State Government can achieve this by enacting and enforcing laws on noise. Maximum permissible exposure levels and duration of exposure recommended by the international Institute of Noise Control Engineering (I-INCE), USA [29] can be adopted with the view to protecting the health and safety of the residents of Calabar against high noise levels. Others like ISO [30] recommended a limit of 85-90 dB(A) Leq; United Kingdom [31] and China [32] recommended a limit of 90 dB(A) Leq.
ACKNOWLEDGEMENT
We wish to acknowledge A. I. Menkiti, a Professor in the Department of Physics, University of Calabar, Nigeria, for his immense contributions in the field of Acoustics.
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