π· = οΏ½π‘1 + π‘2 + π‘3 + β― + π‘π οΏ½ π₯100 = οΏ½β π‘π οΏ½ π₯100 β¦ (2)
background noise levels during all tests satisfied
International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 2221
ISSN 2229-5518
Chagok, N.M.D.1, Fom, T.P.2, Domtau, D.L.3 and Mado, S.D.4
1, 2, 3, 4Department of Physics, University of Jos, Nigeria
*E-mail of the corresponding author: nchagok@yahoo.com
In this paper, the dose range of 20% to 30000000% was considered corresponding to a time-weighted average range of 63dBA to 124.8dBA. This range represents a typical exposure dosage range in most industries/companies in Jos (Chagok, 2010) and possibly Nigeria and other developing countries. The doses and their corresponding time-weighted averages confirm the 3dBA doubling rate and also support the Equal Energy Hypothesis (EEH).
Noise is a common environmental pollutant and is almost an inescapable by-product of industrial mechanization. Unlike other forms of environmental pollutants, noise does not physically accumulate in the atmosphere but its effects are numerous (Priest, 1973). The effects of noise on human emotions range from negligible, through annoyance and anger to psychologically disruptive. Physiologically, noise can range from harmless to painful and to physically damaging (Kinsler et al., 1982). Generally, todayβs environment exposes each of us to noise levels that may damage our hearing, interfere with activities in our daily lives and may degrade the quality of our life-style. Therefore, noise effects are no longer
studied simply as constituting an occupational
health problem, in which a workmanβs hearing, is damaged due to long-term exposure on the job, instead it encompasses all effects of noise including both in-door and outdoor environments inhabited by beings (Chagok et al., 2013b). It has been demonstrated in so many studies that prolonged exposure to noise can result in a persistent shift in the threshold of hearing (Coles et al., 1968; Passchier-Vermeer, 1974; Ward, 1975; Berger et al.,
1978; Stevin, 1982; Alberti, 1998; Nash, 2000; Chagok and Gyang, 2012; Chagok et al., 2013a). The greater the intensity of the noise the greater the probable threshold shift is intuitively reasonable and factually demonstrable from the results of investigations where different noise- exposed groups were studied under common
IJSER Β© 2013 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 2222
ISSN 2229-5518
audiometric and test protocol (Chagok and Gyang,
2012; 2013).
An important part of any noise control program is the establishment of appropriate criteria for the determination of an acceptable solution to the noise problem. Thus, where the total elimination of noise is impossible, appropriate criteria provide a guide for determining how much noise would be acceptable. At the same time, criteria provide the means for estimating how much reduction will be required. The required reduction in turn provides
the means for determining the feasibility of
specified noise level, including allowance for age.
Chagok and Gyang (2013) recommended for promulgation by regulatory agencies for occupational noise exposure 70dBA as an 8-hour time weighted average. This was not, however, put in the form of noise dose. The daily noise exposures in the mills consist of exposures to different noise levels for different durations. To quantify the noise exposure, the daily noise dose (D) was used. This permits a reliable estimation of the employeesβ daily equivalent exposure. The
equivalent continuous noise level of a time-varying
alternative proposals for control, and finally the
noise
Leq is given by Cunniff (1977) as
means for estimating the cost of meeting the
relevant criteria (Smith et al., 1996). From the
πΏππ =
πΏ1
πΏ2
πΏπ
systematic studies of Chagok and Gyang (2013), it has been possible to establish a definite
10πππ10 οΏ½π‘1 π₯1010 + π‘2 π₯1010 + β― + π‘π π₯1010 οΏ½οΏ½π
(1)
...
relationship between threshold shift and duration of exposure, the level and pattern of noise being invariant (on a cyclic daily basis) throughout the duration for a wide range of exposure. The relations so established permit the calculations of statistical distributions of noise-induced pure-tone threshold shift at various audiometric frequencies
for a population exposed for a specified time to a
T is the total time, i.e. βti and t i is the time in hours the workers work in a section whose sound
level reading is Li .
When the daily noise exposure consists of periods of different noise levels, the daily dose (D) shall not equal or exceed 100, as calculated according to
IJSER Β© 2013 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 2223
ISSN 2229-5518
π· = οΏ½π‘1 + π‘2 + π‘3 + β― + π‘π οΏ½ π₯100 = οΏ½β π‘π οΏ½ π₯100 β¦ (2)
background noise levels during all tests satisfied
π1
π2
π3
ππ
ππ
π‘π is the total time of exposure at a specified noise level and ππ is the exposure duration for which
noise at this level becomes hazardous.
The daily dose can be converted into an 8-hr time weighted average (TWA) according to the expression
πππ΄ = 10πππ οΏ½ π· οΏ½ + 70β¦β¦β¦β¦β¦β¦β¦β¦β¦... (3)
100
The 70 in equation (2) comes from the
recommended occupational noise exposure of
70dBA as an 8-hr time-weighted average.
Pure tone audiometry was used to establish hearing thresholds at 250Hz, 500Hz,
1000Hz, 2000Hz, 4000Hz and 8000Hz for noise
exposures. Chagok and Gyang (2012; 2013) reported the measurement of A-weighted Sound Pressure Levels and Sound Spectrum Levels, at machine-operator positions in
companies/industries using π΅ππ’ππ & πΎππππ Impulse
Precision Sound Level Meter Type 2209 in
conjunction with β
-Octave Filter set, Type 1616 and the audiometric tests of selected workers carried out using Beltone 112 Audiometer. The
the octave band level requirements of ANSI S3.1-
1977. From the empirical study of Chagok and
Gyang (2012; 2013), a damage risk criteria of
70dBA was proposed for exposure to steady-state broad-band noise by regulatory agencies and was used to compute the monaural impairment and handicap for exposure to noise (Chagok et al.,
2013c). Results of the empirical work were used for
the computation of the daily dose (D) and the time- weighted average (TWA).
IJSER Β© 2013 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 2224
ISSN 2229-5518
Dose range of 20% to 30000000% was considered and corresponding time-weighted average range of
63.0dBA to 124.8dBA computed are as shown in
table 1. This range corresponds to the typical exposure dosage range in most industries/companies in Jos (Chagok, 2010). From the table, it may be noted that a dose of 100% corresponds to a time-weighted average of 70dBA, an 8-hr time-weighted average at and or below which there will be no noise-induced hearing loss. Interestingly, a dose of 200% corresponds to a time-weighted average of 73dBA, confirming the
3dBA doubling rate. This is also true for all the
computed values. Noise-induced hearing loss begins to occur at any dose higher than 100%, i.e. at any time-weighted average higher than 70dBA.
Table 1: Dose (D) and Time-Weighted Average
(TWA) for Noise Exposure
Dose (%) | TWA (dBA) | Dose (%) | TWA (dBA) | Dose (%) | TWA (dBA) |
20 | 63.0 | 2500 | 84.0 | 400000 | 106.0 |
30 | 64.8 | 3000 | 84.8 | 450000 | 106.5 |
IJSER Β© 2013 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 2225
ISSN 2229-5518
The noise dosage in most work environments in companies/industries is not known and workers may be exposed to noise levels that may be damaging to their hearing mechanism resulting to
noise-induced hearing loss. Equation (2) or table 1
could be used to estimate the values for the dose
(d) and the corresponding time-weighted average (TWA). For hearing conservation, the dosage of industries/companies in which workers work must always be less than 100%. However, if the dosage is more than 100%, hearing protection must be provided by the employers and the employees are encouraged to use them. The authors suggest that
(i) Noise assessment of workplaces be
carried out regularly
(ii) Employers should provide hearing protection and employees should develop the habit of using the hearing protection provided if the dosage assessed is 100% and above.
(iii) Regulatory agencies must also be alive to their responsibilities of ascertaining that companies/industries comply with the standards.
REFRENCES
[1] Alberti, P.W. (1998). Hearing Conservation In: Peter W. Alberti and Robert J. Ruben (eds), Otologic Medicine and Surgery, Churchill Livingstone Inc.
pp. 253-271
[2] Berger, E.H., Royster, L.H. and Thomas, W.G. (1978).
Presumed Noise-Induced Permanent Threshold Shift
Resulting from Exposure to an A-Weighted Leq of
IJSER Β© 2013 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 2226
ISSN 2229-5518
89dB. Journal of the Acoustical Society of America
64(1): 192-197.
[3] Chagok, N.M.D. (2010). Studies of Occupational Noise Hazards in Jos. PhD Thesis Unpublished. University of Jos, Jos-Nigeria. 172p
[4] Chagok, N.M.D and Gyang, B.N. (2012). An
Exploratory Study on Hearing Loss due to Exposure to Steady-State Broadband Noise. Biological and Environmental Sciences Journal for the Tropics 9(3):
34-41
[5] Chagok, N.M.D, Gyang, B.N. (2013). ProposedDamage (Deafness) Risk Criteria for Exposure to Steady State Broadband Noise: An Empirical Study. International Journal of Scientific & Engineering Research 4(1) issue
2:1-6
[6] Chagok, N.M.D., Gyang, B.N., Adoga, A.S. (2013a).Trade-off between Steady-State Broadband Noise Levels and Time of Exposure for Zero Noise- Induced Hearing Loss. Journal of Biology, Agriculture And Healthcare 3(2): 106-111
[7] Chagok,N.M.D., Gyang, B.N., Domtau, D.L. and Mado,
S.D. (2013b). Workerβs Response (Attitudes) Towards Exposure to Steady-State Broad-Band Industrial Noise in Jos. Journal of Natural Sciences Research 3(5):
171-181
[8] Chagok, N.M.D., Fom, T.P., Izam, M.M., Domtau, D.L.and Jwanbot D.I. (2013c). Predicted Impairment And Handicap from Exposure to Steady-State Broad- Band Industrial Noise. Advances in Physics Theories
and Applications. Accepted for publication Coles,
R.R.A.,
[9] Garinther, G.R., Hodge, D.C, and Rice, C.G. (1968).
Hazardous Exposure to Impulse Noise. Journal of the
Acoustical Society of America 43: 336-343.
[10] Cunniff, P.F. (1977). Environmental Noise Pollution
New York: John Wiley and Sons, 210p.
[11] Kinsler, L.E. Frey, A.R., Coppers, A.B. and Sanders, J.V. (1982). Fundamentals of Acoustics 3 edn. New York: John Wiley and Sons, 480p.
[12] Nash, J.L. (2000). What is wrong with Hearing
Conservation? Occupational Hazards 62(1): 41-44.
[13] Passchier β Vermeer, W. (1974). Hearing Loss due to Steady-State Broad Band Noise. Journal of the Acoustical Society of America 56(5): 1585-1593.
[14] Priest, J. (1973). Problems of our Physical Environment, Energy Transportation Pollution. London:Addison-Wesley Publishing Company. Pp 266-274.
[15] Smith, B.J., Peter, R.J. and Owen, S. (1996). Acoustics and Noise Control 2nd edition. Addison Wesley Longman Ltd 330p.
[16] Stevin, G.O. (1982). Spectral Analysis of Impulse
Noise for Hearing Conservation purposes. Journal of
The Acoustical Society of America 72(6): 1845-1854 [17] Ward, W.D. (1975). Acoustic Trauma and Noise-
Induced Hearing Loss. In: D.B. Tower Raven(ed), Human Communication and its Disorders. New York: John Wiley and Sons. pp 221-229.
IJSER Β© 2013 http://www.ijser.org