Exposure to Noise Induced at Work and Prevention Practice Among Workers of Stone Mining Company, An Giang, 2018

Noise is one of the most common occupational hazards in Vietnam, causing occupational hearing impairement. Stone mining is among the high-risk working environment. This study aims to describe noise exposure and prevention practice among workers of stone mining in An Giang province. A cross-sectional study using a quantitative method was conducted in 2018. 176 noise samples were collected, and 215 workers were interviewed using a structured questionnaire. Results show that workers at grinding section exposed with the high level of noise (compared to national standards) and they did not practice adequately to protect themselves from the hazard. Workers aged above 39 years old and had more than 10-year working experience had better prevention practice than the other groups. The differences were statistically significant. It is concluded that workers were exposed to the high level of noise at work, their practice regarding hearing impairement prevention was not adequate, and age, years of working were associated factors with prevention practice among workers.


Introduction
Noise exposure at work is one of the most common occupational hazards. Occupational hearing impairment is also among the leading occupational diseases in all countries (Lie, A et al, 2016). Early detection and prevention of noise exposure can protect workers from permanent hearing loss.
According to the report of the Administration of Environmental Health Management, hearing loss occupied 64.4% of all occupational diseases. Noise exposure was the second-ranking hazard which occupied 14.7% of all workplace samples that did not meet national standards (Anh Luong Mai, 2017).
Mining and stone mining has been developed rapidly in recent years in Vietnam (Linh Bui Hong, 2013) Stone mining companies provide occupations for hundred thousand workers and contribute significantly to the economic development of different provinces. However, reports also showed that there were occupational health and safety issues among stone mining sector. Problems were perceptions of employers, employees on occupational health and safety, the high level of noise and dust, and limited control measures (Linh Bui Hong, 2013).
The An Giang stone mining company is located in An Giang province. The company has experienced more than ten years working in the area. The company provide stone for different construction sites in surrounded provinces. Even though labour protection council was established at the company, annual health checks were conducted regularly, occupational hazards like noise still exist and threaten the health of workers. This paper aims to discuss the situation of noise exposure and prevention practice among workers of the company.

Methodology
A cross-sectional study was designed using a quantitative method to collect data for both noise measurement and workers' practice. Noise data were collected following the Ministry of Health's guidance while workers' practice data were collected using a structured questionnaire.

Study sites and study period:
This study was conducted from January to August 2018 at An Giang stone mining in An Giang province, a province in the South of Vietnam. The company was founded in 1975 and upgraded since 2007. The company is one of the companies which has biggest productivities in An Giang province and in the Western Southern region of Vietnam. The productivity of the company ranges from 1.6 -2.0 million m3 per year. The company has 4 mining areas and 17 grinding sections (See Fig  1). The company comply with national legislation on occupational health and safety; working environmental data were recorded annually. Some occupational hazards were noise, chemical, silica dust and safety hazards.
Study subjects and sample size: 176 samples were taken for noise measurement. The number of samples for each working section was: -Mechanics section: 08 samples -Mining section: 32 samples -Grinding section: 136 samples The whole sampling was applied to collect data for the practice of workers. Totally 215 workers were interviewed. Four other workers were excluded from the study as they did Submission date: 06-03-2020 | Review date: 22-09-2020 not match research criteria (contracted for at least 6 months and available at the time of the data collection).

Sampling method Environment sampling:
Noise samples were collected at 3 sections of the company. Samples were collected at the middle of morning shifts and afternoon shifts (2 samples for each position).
Mechanics sections: samples were collected at the centre of each section. There are two mechanics sections; totally 8 samples were collected.
Mining sections: there are 4 mining sections, two working positions were selected for each section, totally 32 samples were collected.
Grinding sections: there are 17 grinding chains, so totally 136 samples were collected for all 34 working positions.

Worker Sampling
The whole sample was applied, and workers were selected based on criteria: -Contracted for at least 6 months -Working directly at the sections (not include administration staff) -Available at the time of data collection Workers were interviewed during their break. Only workers voluntarily agreed to participate were chosen to be interviewed by public health professionals from An Giang Center for Disease Control and Prevention.
The questionnaire was piloted in 10 workers before the main study implemented.
After data collection, all quantitative data were cleaned, coded before processing. + Not meet the standard: Noise level > 85dBA and above frequency range.

Prevention practice
The questionnaire includes 28 questions: 6 questions on personal details, 5 questions on knowledge, 5 questions on attitude and 12 questions on worker's practice.
The adequate practice was considered when workers reported correctly for > 8 over

Data analysis
Data were processed using Epidata and SPSS 18.0 software. Descriptive and regression analysis were applied.
Main variables are: -Noise level; -Prevention practice of workers: using protection devices, maintain earplugs, time exposed to noise per day, and break time; -Independent variables: gender, age, years of work, ethics, education, working section.

Ethical clearance
This study was approved by Ethical Committee of Hanoi University of Public Health (Decision 121/2018/YTCC-HĐ3). This study was allowed by the company. Workers had the right to refuse to participate and can stop at any time of the study. All information was provided to workers and the company in an information sheet. The worker had no or low risk when participating in this study.

Noise exposure at different sections of the company:
The study was conducted at three types of the section of the company (mechanics, mining and grinding section. 176 samples were taken for noise measurement. Table 1 regulation (72,16%). The workers working at mining sections were exposed to the high level of noise (32/32 samples were higher than the standard limit), the highest noise level even reached a level of 100,5 dBA. Following was grinding section with 69,85% of samples higher than the standard limit. Results of noise level at mechanics sections show that all of 8 samples met the national standard. According to the Occupational Safety and Hygiene Law, the noise level at work should not exceed 85.0 dBA while working for 8 hours per day. If the noise level increase for 3 dBA, working hour per day should be cut off by half. It means that with the noise level at mining sections, workers should not expose for more than 30 minutes (with a noise level below 97 dBA).
Noise levels were also measured at different audible frequency range (from 63 Hz to 8000 Hz). According to Table 2, almost all of the unmet standard samples were samples collected at mining and grinding sections at frequency range 250 -8000Hz. Noise level differences were highest at the frequency range of 4000Hz with a national standard limit of 76 dBA while the highest level was 94.8 dBA (the difference reached 18.8dBA). At frequency range of 1000Hz, the national standard limit is 80 dBA while the highest noise level at mining section was 97.6 dBA (the difference reached 17.6dBA) At frequency range of 2000 Hz and 500 Hz, the study also found that mining sections and grinding sections also had noise level above national standards, while at the frequency range of 250 Hz and 8000 Hz, Only mining sections were found to have noise level above national standards of 86 dBA and 74 dBA. Table 3 shows the proportion of noise level above the national limit at a different octave band. It was found that the noise level above the national limit was mainly at high octave band. They were at octave band of 1000Hz (76.14%). 2000Hz (65.91%) and 4000Hz (53.98%) and following by samples measured at octave band of 500 Hz (52.84%), 8000 Hz (23.3%) and 250 Hz (17.61%). The low-frequency range at a frequency of 63Hz. 125Hz had the highest percentage of samples (100%) that met national standards. All standards were regulated in Circular 24/2016/TT-BYT in 2016. The circular regulated limits of noise at different workplaces and exposure recommendations.

Prevention practice of workers
Workers working at the workplace which has noise level exceeds limit are requested to use hearing protection devices.
All devices need to meet national standards of hearing protection device. Table 4 shows the proportion of workers used hearing protection devices according to their self-reports, workers were also asked to report about the frequency of use and how they maintained their hearing protection devices. Results show that the proportion of workers had correct practice of using hearing protection devices was only 21.40%. Among 46 workers, those used hearing protection devices during the work shift, no one used them frequently.
100% of workers reported that they were equipped with simple hearing protection devices (earplugs). 100% of them also reported that the equipment was effective in reducing noise exposure. Among 46 workers who used earplugs, only 47.83% maintained and cleaned their earplugs correctly. Workers who exposed to noise-induced at work are requested to be monitored by their colleagues and team leaders about their practice on using personal protective equipment. As showed in Table 4, only 21.4% of workers used earplugs, and non of them used the equipment adequately. Table 5 shows results on how workers remind each other to use earplugs. There were still 38.60% of workers did not remind their colleagues to wear earplugs.
According to the guidance from the Ministry of Health, workers should also be moved to other sections with lower level of noise. Reports from workers of the company show that 100% of workers were not moved to other sections with a lower level of noise during the last 12 months to the study period According to Table 6. 100% of workers worked for less than 8 hours per day and took at least 30 minutes break. Study results also show that 100% of workers took regular annual health check. Even though workers following regular guidance about working hour while exposing to the noise level above 85 dBA, none of them follows the guidance on reducing working hour by half if noise level increased for 3 dBA (Circular 24/2016/TT-BYT).
Results on the practice of workers were calculated based on elements on wearing hearing protection devices, frequency of use, maintenance, remind others to use and taking working hour adequately. Results on Table 7 show that only 21.4% of workers had a good practice on the prevention of occupational hearing impairment.
There are several factors such as personal characteristics, working experience, working positions, knowledge on prevention of occupational hearing impairment and attitude on Tab. 6. Work schedule Tab. 7. Proportion of workers had good prevention practice Tab. 6. Plan pracy Tab. 7. Odsetek pracowników stosował dobre praktyki prewencyjne the risk of having an occupational hearing impairment. Results are shown in Table 8.
According to Table 8, workers older than 39 years old were 4.6 times more likely had better practice than workers under 39 years old. Workers had more than 10 years working were 7.1 times more likely had better practice than the others. The differences were statistically significant with p < 0.0001.
Tables 3.8 also shows that workers with a higher level of education had better practice; workers who were Kinh ethnic had a better practice than other ethnics. However, the differences were not statistically significant. There was also no statistical evidence of an association between knowledge and attitude of workers and prevention practice.

Discussion
Results in this study showed 72.16% of samples did not meet national technical regulation. This proportion was higher than that of the study of Kien Nguyen The et al. (2013) with 48.0% of samples. Another cross-sectional study at different stone mining áreas showed a level of noise ranged from 85.5 dBA to 102.7 dBA.
The noise level that higher than national limit was mostly at the high frequency of range, highest at 1000Hz (76,14%), 2000 Hz (65,91%), following by 4000Hz (53,98%) and 8000Hz was 23,30%. Similar results were also found in the study of Khanh Nguyen Quang et al. (2002) showing the high noise level at a frequency of range from 1000 -8000Hz, and this was the main cause of permanent hearing loss in workers.
This study shows that 21.40% of workers had good prevention practice. This proportion was lower than that of study of Khoa Vo Tan (Khoa Vo Tan, 2016) was 25% and Sung Tran Van (Sung Tran Van et al. 2017) 26,5% but slightly higher than that of study of Rus RM, Daud A, Musa KI, Naing L.(2008) was 19,36%.
The proportion of workers used hearing protection devices was 21,4%. This result was lower than in the study of Chan Nguyen Dang Quoc (2006) (37,4%). All of the workers were equipped with earplugs. However, workers did not use them frequently. Percentage of workers used earplugs frequently in this study was lower than that of study of Sung Tran Van 37,1% (Sung Tran Van et al. 2017), Vo Tan Khoa 15,79%(Khoa Vo Tan, 2016), Gabrielle H. Saunders (2014) + Maintain earplugs and take annual health check: In this study, the proportion of workers maintain earplugs adequately was 47,83% These results show that workers did not recognize the risk of using uncleaned earplugs. 100% of workers had an annual health check, this was much higher than in the study of Khoa Vo Tan 97,76% ( Khoa Vo Tan, 2016) and Thuy Hoang Minh (97,6%)( Thuy Hoang Minh, 2011). + Switching of work tasks: 100% of workers did not change their section or positions, even though the company identified some cases of hearing impairment. + Provide hearing protection devices and monitoring of use: The company provided earplugs for 100% of workers, this similar to results of the study of Khoa Vo Tan (100%) (Khoa Vo Tan, 2016). However, the company did not monitor the use of earplugs; only 61,4% reported that the company supervised that use of earplugs, no punishment was announced. + Work schedule and break: The company organized working time adequately with a working hour less than 8 hours and at least 30 minutes break.
Age and years of working at the company were factors associated with prevention practice in this study. It was found that the older age, the better practice. This result is different from that of Vo Tan Khoa (Khoa Vo Tan, 2016), and Sung Tran Van (2017).
No statistical differences between ethnic groups, education groups. No association between knowledge and attitude of workers with prevention practice. These results were different from that of Sung Tran Van study. In Tran Sung Van study, workers with better knowledge had better practice on hearing lost prevention (Sung Tran Van et al. 2017).

Conclusions and recommendations
This study shows results on the noise level at the stone mining company. Mining and grinding sections were sections Tab. 8. Factors associated with prevention practice of workers Tab. 8. Czynniki związane z praktyką prewencyjną pracowników where workers exposed with high noise level with noise level ranged from 97.43 -99.49 dBA for grinding sections and 85.18 -88.28 dBA for mining sections.
The proportion of workers who had good prevention practice was relatively low (21.40%).
Factors associated with the good practice were the age of workers and years of working at the company It is recommended that the company should take actions to reduce the noise level at mining and grinding sections and to educate workers and to monitor the compliance of workers especially those who are younger than 39 years old and have less than 10 years of working experiences