DEVELOPMENT OF PREDICTIVE MODELS FOR SYNERGISTIC IMPACT OF AGE, PERIOD OF EXPOSURE AND NOISE LEVEL IN QUARRIES ON HEARING THRESHOLD OF WORKERS

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.