Abstract:
Despite the importance of quarry operations to the construction industry in developing
countries, the excessive occupational noise involved in quarry operations is a threat to the
health of workers. Studies have shown that the age and years of work exposure (YE) are
two of the major factors that contribute to auditory health problems among the quarry
workers. Information on the effect of noise and related susceptibility factors on hearing
damage among Nigerian quarry workers are sparse. This study was conducted to develop
suitable models in order to investigate the synergistic influence of age, YE and Noise
Level (NL) in quarries on the Hearing Threshold (HT) of workers.
Questionnaires were administered to 204 quarry workers, who were randomly selected in
the year 2018 from four different quarry sites in southwestern Nigeria, to obtain the age
and YE. A follow up study was conducted on 185 of them in 2019. The NL at the quarry
sites during the working hours were measured using a digital sound level meter, while an
audiogram measured the HT at eight different frequencies (0.25, 0.50, 1.00, 2.00, 3.00,
4.00, 6.00 and 8.00kHz). Using ANOVA, eight regression models were developed and
validated to predict both the effects of age, YE and NL on HT, and the safe HT. These
were used to test for both the similarity of the NL conditions in the sites and the predictive
significance of the regression model terms. The predictive accuracies of the developed
models were evaluated using the predicted R2, while paired sample t-test and correlation
statistics were used to ascertain the impact of the workers’ continual exposure to noise
within the study period. Analyses were done using t-test at α0.05.
The percentage distribution of their age range in years were 9.7% (15-30), 50.8% (31-45),
38.4% (46-60), and 1.1% (60+). The mean age and YE were 42±9.01 and 18±7.03 years,
respectively. The NL were in the range of 87.30-116.98dB as against the permissible
exposure level of 85.00dB. The NL conditions on the sites were not significantly different
(101.61±0.38, 99.28±0.51, 100.51±1.01, 99.28±0.10). The Mean HT of the workers was
45.60±1.24dB and 75.0% of them had HT higher than the safe HT of ≤30.00dB. The age
predicted the workers’ HT at all frequencies considered. The YE significantly predicted
the HT at 1.00, 2.00, and 4.00 kHz, while NL significantly predicted the HT at 0.25 and
0.50 kHz. The models’ predicted R2 range was 0.71 – 0.82. The safe HT was predicted
with age ≤52 years and YE ≤32 years. The validation results were in agreement with the
data obtained during the experiment. The correlation and paired sample ranges were 0.17-
0.79 and 6.50-26.7, respectively, which showed that the workers' HT continuously
depreciated within the study period.
The developed models established that the synergistic factors of age, years of exposure
and noise level influenced the hearing threshold of quarry workers. Thus, the models can
be used for making decision in achieving workers’ safe operations in quarry industry.
