|Year : 2015 | Volume
| Issue : 3 | Page : 151-155
Silica exposure in the glass industry and human health risk assessment
Beheshteh Jebelli1, Iran Ghazi2, Amir Mahamoodzadeh2, Elham Ghazanchaei2
1 Chronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran
2 Research Institute of ShakhesPajouh, Isfahan, Iran
|Date of Web Publication||20-May-2015|
Research Institute of Shakhespajouh, Isfahan
Source of Support: None, Conflict of Interest: None
Introduction: Among adverse effects in mines and industries, silica dust often been the subject of many controversies. Its severe and incurable side effects call for special attention to as well as assessment and control in workplaces. This study aims to determine the rate of silica concentration in the breathing zones of the glass industry in a comparison to standard limits in order to improve the safety of workers exposed to these particles. Materials and Methods: Being conducted in a glass factory in Tehran, this research employed a sampling method to measure the silica dust diffusion in six consecutive years from 2005 to 2010. The most effective method of dust level measurement in a workplace is to take samples in the breathing zone of workers exposed to it. In the subject factory, the sampling was performed in four sectors with the highest level of occupational exposure to the respirable dust. (1) Material charging unit, Excavator Operator. (2) Miscellaneous material weighing Operator (mixer). (3) Material charging, loading unit Operator. (4) Discharge (unloading) zone. The silica compound sampling and measur was conducted via the method by National Institute of US Occupational Health and Safety (NIOSH). By this method, the silica particles in the air were collected on the sorbent tube containing activated carbon (coconut shell) SKC-USA No. 226-01 and the sampling pump Model 222 ml/count, SKC with a flow rate of two liters per minute in the active method for 30 minutes. Then, observing necessary conditions and the chain of cold (Stored at 4C), the samples were transferred to the laboratory. The breathing zone samples were also collected from the four mentioned sectors by the sampling pump. Samples were analyzed with the Flame Ionization Detector, when they were transferred to the laboratory by Gas Chromatography Apparatus with the Flame. Results: Time-weighted a Average (TWA) exposure was at its highest level in 2009 and at its lowest level in 2008. Findings of the study also revealed that the amount of environmental silica dust threshold limit value in the material charging Unit of loading and Excavator Operators in the discharge zone was higher than the threshold limit value. After determining the dispersion density of suspended silica particles, TLV, TWA, and the non-cancer risk ratio of the particles in the mentioned sectors, control strategies and corrective suggestions were proposed. Conclusions: Results showed that, the silica concentration in the breathing zone of the glass industry was higher than the threshold limit value. Silica is a carcinogenic material causes chronic respiratory diseases and silicosis, therefore it is recommended to observe the safety principles and use wet silica in stead. The concentration of silica is at its highest level in the loading and unloading units, thus the engineering and managing controls should be utilized to avoid the direct exposure to these suspended particles. Moreover, the workers in these sectors should be well-trained regarding the exposure to silica and use of individual protective equipment.
Keywords: Glass industry, non-cancer risk, silica, suspended particles, silicosis
|How to cite this article:|
Jebelli B, Ghazi I, Mahamoodzadeh A, Ghazanchaei E. Silica exposure in the glass industry and human health risk assessment. Int J Health Syst Disaster Manage 2015;3:151-5
|How to cite this URL:|
Jebelli B, Ghazi I, Mahamoodzadeh A, Ghazanchaei E. Silica exposure in the glass industry and human health risk assessment. Int J Health Syst Disaster Manage [serial online] 2015 [cited 2019 Jan 18];3:151-5. Available from: http://www.ijhsdm.org/text.asp?2015/3/3/151/157385
| Introduction|| |
It is very important to investigate and research on pollutions and harmful factors in workplace in the industrial age, when the health comprises a large share in the society. For we live in an era that normalizing humans physically and emotionally is definitely considered as the base of social and economic growth of the society. 
The glass industries are old in Iran. Although silica is one of the most necessary materials to make glass, it has serious complications on our body systems particularly on respiratory system and causes silicosis and respiratory cancer, thus, this study is so important. This study aims to determine the concentration of silica in the worker's breathing air of the glass industry in comparison with the standard amounts to improve the safety of workers exposing to these particles.
Unfortunately, workplace contamination is resulted by human efforts in providing a better life.  In Today's age of technology, pathogens are not only microbial and biological factors anymore, but various environmental factors also play a major role in the spread of diseases.  Nowadays in Iran, more than 2 million people work in industrial plants. Every worker typically works 8 hours a day and often six days a week; spending the whole 48 hours in a workplace and being exposure to environment factors and conditions. 
On the other hand, different factors such as contact with toxic materials and harmful chemicals or harmful Physical factors put the workers health at risk in most industrial centers.  For example in the glass industry from preparing materials to glass melting process and preparation of the final products, workers are expose to inhaling free silica dust, irritating alkalis gas or vapor due to combustion and melting materials, working in a hot weather, contact to infrared radiation and eventually the dangerous of touching the cutting pieces and glasses, etc. 
The glass is in fact a substance that is obtained from special melting materials, so that it was not crystallized by cooling down and it remains in the amorphous (non crystalline) state. The specific gravity of Glass is 2.5 cubic centimeters and it is very brittle and fragile. Glass is resistant against all chemicals even strong acids and alkalis and it is not influenced by corrosion. It is only influenced by acid Fluoric that caused the glass to dissolve.  In glass industry, it is used the materials such as feldspar, dolomite, salt cake, soda and silica and in fact 96% of glass is made of silica. , There are five basic steps to produce glass in glass industry: (1) Mixing, (2) Melting, (3) Forming, (4) Gradually cooling down, (5) The final operation.
The maximum allowable concentration of any toxic substance consist of the amount of harmful material that a person or an ordinary worker expose to it constantly 8 hours a day for a week and there is no complication and effects of intoxication during the long time. The allowable thresholds of silica powder is 10 mg/m3 and for amorphous silica is 0.05 mg/m3 (2).
Silicosis is a debilitating lung disease that leads to loss of lung function and constraints of individual activity in the advanced forms and it causes disability. ,
The effect of these factors and harmful conditions results the emergence of numerous diseases and complications such as silicosis, and other lung disease such as emphysema, eye problems such as cataract, heat stroke and different injuries. 
Therefore it is necessary to collect data through surveys on health in the workplace and provide effective recommendations to improve the environmental conditions of the industries and supply the health of this large group of the population who our country's progress and survival is depended on their mighty arm strength.
| Materials and Methods|| |
The study was conducted in a large glass factory in the west of Tehran. Since this plant is one of the largest and the most important glass factory, and manufactures a variety of glass, glass bottles and etc. Therefore, the researchers selected this factory as the study site. The factory was founded in 1347 in Tehran and it has several distinct subsets areas about 5000 square meters and a workforce of around 2,000 people.
For sampling and measuring the silica concentration in the breathing zone of diffuse silica dust in the studied plant, the individual sampling method was used taking 30 minutes, with 2 liters per minute discharge and 120 liters of air volume. In this method, the criteria provided by National Institute for Occupational Safety and Health (NIOSH) was used for sampling the whole dust to determine the total weight of aerosol and respirable dust and respirable weight fraction.
The instruments used in this method include the collector of silica dusts containing 10 mm silicon nylon, membrane filter made of PVC with a diameter of 37 mm and a pore size of 5 microns and a closed-head filter holder with a diameter of 37 mm, and personal sampling pump model SKC, Rotameter and Desiccator. Ahead of the sampling, we dried filter, weight it, calibrated individual sampling pump, and used a control filter along with each prototype samples. The samples were taken from different part of glass factory. According to NIOSH, we used the method of X-ray diffraction to analyze the diffuse silica dust samples for qualitative and quantitative determination of free silica samples.
Dust concentration of workplace air in milligrams per cubic meter
W1 = Weight of filter before sampling in mg
W2 = Weight of filter after sampling by mg
∆t = Sampling time (h)
Q = Sampling pump flow rate in liters per minute (with the correction of air sampled volume to volume at standard conditions).
Finally we entered the results in the software RAIS and it showed the amount HQ and the risk of the region based on carcinogenic.
| Results|| |
According to [Table 1], the results showed that the amount of HQ (Hazard Quotient) was more than the threshold limit value in the loading and unloading units.
A hazard Quotient is the ratio of the potential exposure to a substance and the level at transpired, which no adverse effects are expected. If the Hazard Quotient is calculated to be less than 1, then no adverse health effects are expected as a result of exposure. If the Hazard Quotient is greater than 1, then adverse health effects are possible. The Hazard Quotient cannot be translated to a probability that's adverse health effects will occur, and is unlikely to be proportional to risk. It is especially important to note that a Hazard Quotient exceeding 1 does not necessarily mean that adverse effects will occur.
The results in [Table 2] show that the hazard ratio in loading and unloading place is still greater than the threshold limit value.
According to [Table 3], the results show the risk ratio is higher than the threshold limit value in discharge unit in 2007.
According to [Table 4], the results show the risk ratio is still higher than allowable standard limit in discharge unit of factory in 2008.
According to [Table 5], the results show that the amount of silica particles in both charge and discharging places is higher than the threshold limit value.
According to [Table 6], the results show the concentration of silica in charge and discharge places is still higher than the threshold limit value in 2010.
According to [Figure 1], the results show that TWA had a downward trend from 2005 to 2008 and the amount of pollutant silica exposure have been declining, but in 2009 it had an upward trend and in 2010 it was inconsiderably declining due to the use of the wet silica in this factory.
|Figure 1: Comparison of averaging weight of Contact with silica suspended particles in the glass factory in 2005-2010|
Click here to view
Regarding to environmental dust measurements in different parts of the glass factory and a comparison with the allowable rate of 8 hours group working or 40 hour weekly work, the amount of environmental silica powder dust in loading and unloading units were more than allowable rate and it was measured the diffusion average of total dust in the breathing zone air in different parts of the plant, ranging between 7.8 micrograms per cubic meter to 25.1 micro grams per cubic meter.
| Discussion and Conclusion|| |
A study titled as "the assessment of workers 'exposure to silica dust in Mazandaran workshops" was conducted by Mohammadian et al., in 1393. The results showed that the average exposure to respirable silica particles in the workers' breathing zone air of four industry groups -casting, producing glass, producing asphalt, brick-burning and producing sand- is more than the threshold limit value. It is consistent with our results. 
The researches done by Dehqan et al., in the glass factory and by Naghizadeh et al., in the iron mine conducted using X-ray diffraction. The results showed that the concentration of free silica in the air is higher than the threshold limit value which is consistent with our results. 
Also a study conducted in the United States on workers exposed to silica in the sand workshops. The results showed that the average exposure of workers is higher than the threshold limit value which is also consistent with our results. 
The accepted limit for exposure to crystalline free silica particles of Christobalite is considered 0.5 mg/m3 (respirable particles) for 8 hours working per day.  Therefore, the amount of silica dust in the listed parts is higher than the threshold limit value.
Given that the average of workers' exposure to silica is higher than the amount recommended by NIOSH and the exposure to silica has harmful effects on workers' health, it is needed to control workers' exposure to silica in the units that silica density are higher than the threshold limit value in occupational exposure and it should be given a priority to corrective action. Therefore, it is suggested:
- Using wet silica in such a way that all dust produced from different operations will mix completely with water with no entrance into the air
- Diagnosing the time generated silica dust and planning to eliminate or control the dust at the source and use of engineering controls such as local ventilation (dust collector) and the use of making wet methods to prevent releasing dust and routine maintenance of dust control systems to optimize their function
- Cleaning materials or equipment in a manner that does not cause to release particles into the air and they should be cleaned by the wet cleaners or water hose. Never use compressed air and avoid dry sweeping rather than wet sweeping method
- Minimizing the exposure to through appropriate working practices for workers including markup and highlight some areas of generating dust and wearing Protective disposable or washable clothes in workplace and if possible, showering and wearing clean suits before leaving the work area to prevent contaminating clean cars and other places
- Provide annual medical examinations for workers who may have had contact with inhaling crystalline silica
- Providing appropriate landscaping plants in old parts of factory in order to prevent the release of substances while vehicles traffic and prevent from falling material in transition systems and conveyor belts
- Using suitable respiratory protective equipment (the respirators should be used only when engineering control methods cannot keep the contact with the silicon below the NIOSH recommended exposure limit)
- Providing workers by exercises that includes of getting information about the health effects, practicing the correct way of working and using personal protective equipment (PPE).
| References|| |
The Royal Society and The Royal Academy of Engineering. Possible adverse health, environmental and safety impacts. Nanoscience and Nanotechnologies: Opportunities and Uncertainties. Ch. 5. 2004. Clyvedon Press, Cardiff UK, Latimer Trend Ltd. Plymouth UK.
Napierska D, Thomassen L, Lison D, Martens J, Hoet T. The nanosilica hazard: Another variable entity particle and fibre toxicology. Int J Equity Health 2010;39:2-7.
Fen W, Feng G, Minbol L, Huihui Y, Yongping H, Jianwen L. Oxidative stress contributes to silica nanoparticle induced cytotoxicity in human. Embryonic Kidney Cells Toxicol In Vitro
Myers JE, Garisch D, Myers HS, Cornell JE. A Respiratory epidemiological survey of workers in a small South African foundry. Am J Ind Med 1987;12:1-9.
Davis GS, Hendric JE. Occupational disorders of the lung. Curr Opin Pulm Med J 2002:106-23.
Clarke NE Sr. Silicosis and diseases of retired iron foundry workers. IMS Ind Med Surg 1972;41:22-5.
EPA office of compliance sector notebook project profile of the stone, Glass and concrete products Industry-September; 1995.
Allen GC, Samimi B, Ziskind M, Weill H. X Ray diffraction determination of alpha-quartz in reparable and total dust sample from sand-blasting operation. Am Ind Hyg Assoc J 1974;35:711-7.
WHO, Recommended health-based limits in occupational exposure to selected mineral dusts (silic-coal). Geneva: World Health Organization; 1984, No, 734.
Lomax JD, Johanning E. Occupational medicine. Philadelphia: Lippincott Williams and Wilkins; 2001. p. 141-3.
Banks DE, Parker JE. Occupational lung disease: An international perspective. 1 st
ed. London: Chapman and Hall; 1998. p. 21-44.
ACGIH American Conference of Governmental Industrial Hygienists, Threshold limit values for chemical substances and physical agents and biological indices. Cincinnati: ACGIH, 2009.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]