Introduction:
Occupational exposure to silica crystals has long been identified and recognized in most of the industries. There are various industries that involved the silica dusts, where some are highly exposed beyond the threshold limits for the substances. The problem with the occupational exposure of workers to silica crystals are often not taken seriously be employer and employee alike. Exposure to silica in the occupational environment results to health effects such as silicosis and other related diseases. People who are working with these crystals are prone to respiratory effects as well. There is a problem in the safety and health regulations regarding occupational exposure to silica dusts as most agencies resist to shift to more stringent standards that would greatly prevent the adverse health effects of silica exposure such as cancers, kidney and lung illnesses, and even fatal conditions. Potential costs and controls are challenges in industries as they cope on how to implement them (Hazards, 2014).
Silica crystals are basic components of granite, sand, soil, and other minerals. They are important materials for most industries. The most common form of this substance is quartz, where it is mostly found in sands, bricks, mortars, stones, rocks, and blocks (OSHA, 2002). The silica crystals can get into the body through inhalations and can penetrate into the lungs of the human due to its very small size of about 10micrometer. These small crystalline silica is considered as health hazard and belongs to the occupational health concerns (Glenn, 2008).There are many adverse health problems caused by exposure to silica crystals. Silicosis is a diseases that is prevalent since the early 1870s. This disease is characterized by respiratory tissues inflammation that would lead to fibrosis where the efficiency of breathing of the body is reduced. Silicosis is also associated with acute silicosis and other chronic exposures. There are also other related diseases that are caused by exposure to silica such as pulmonary tuberculosis, emphysema, asthma, bronchitis, and lung cancer. There are also other non-respiratory diseases related to the substance that causes autoimmune diseases, chronic renal diseases, and scleroderma (Glenn, 2008). This paper presents the occupational exposure of silica, how it affects the human health, legal codes, and implementations of the prevention of the adverse effects.
Review of Related Literature:
Silica
Silica is a substance containing the compounds silicon dioxide (SiO2). The two elements found in silica are oxygen and silicon that are highly abundant in the Earth’s crust. Silica appears to have crystalline structure with several polymorphs formations. The most common forms are quartz, tridymate, and cristobalite. Quartz is the silica polymorph that thermodynamically stable under ambient conditions. Other forms of silica are melanophlogite and moganite that are existent under high pressure and high temperatures. Quartz is very abundant in the lithosphere comprising around 12% of the earth’s composition. These kind of silicon is found in all kinds of rocks: the metamorphic, sedimentary, igneous, and even soil. They are most common in sandstone, loose rocks, sand and gravel, and solid rocks. Due to the stability of quartz, they have high chemical resistance, high hardness, and high melting point (Maciejewska, 2008). The current standard for the silica dusts as established by OSHA is only 10 milligram silica per cubic meter, with only 8 hour exposure in a work shift. NIOSH recommended the exposure limits to be changed to 50 micrograms of silica per cubic meter of air, for 40 hours a week exposure. The occupational exposure of silica such as the abrasive blasting presents severe health hazards and various related adverse health effects (NIOSH, 1978).
Industries of Silica
There are various activities in the industry that could result to silica exposure to the workers such as the rock drilling, roof bolting, sandblasting, stonecutting, quarrying, lead based paint applications, tunneling, granite operations, and foundry works. Specific application includes the use of calcined diatomaceous earth used as filtering media. These substances are mostly used in food and beverage industries. Asphalt paving manufacturing is also a work environment that pose threats to workers towards silica dust. There are silica dusts and sands that appear as fine dusts that expose workers via rotary dryers. Rotary kilns in paper and pulp mills, cupola furnaces, and other manufacturing locations are potential sources of exposures to silica to workers. In the food industry, silica exposure happens in the sorting, washing, and grading areas of produces of potatoes and beans (MNOSHA, 2012). Other industries that have working environment with high potential of silica exposure includes construction, pottery and clay, foundries, glass, ready-mix concrete, refractories, abrasive blasting, jewelry production, dental laboratories, paintings, and hydraulic fracturing of oils and gas. Occupational safety occurs in the working environment when there is large quantities of the silica materials used in the industries. OSHA has estimated that there are more than 2.3 millions workers in the US that are exposed to silica, and that the major part of about 90% is in the industry of construction (OSHA, 2012).
Health Risks of Silica
The exposure to dusts is linked to the risks of death in various studies about occupational and environmental studies. The estimated death result of WHO reaches up to 1.4% of death instances associated with dust particles exposure. In the study done by Chen et al (2012), it is stated that there are adverse health effects to silica exposure. There are also cases where the mortality rate of silica dust exposure is estimated to about 15.2%. The data in this study suggests that the silica dust exposure raises the risks of respiratory diseases and death to the workers. In the traditional studies, the primary cause of death of these dust exposed workers are due to non-malignant respiratory diseases. However, in this paper, it is noted that the number of deaths due to respiratory related diseases had decreased, and the circulatory system related diseases had increased. Pulmonary heart disease is primarily due to exposure to high dust concentrations. Although several reports associated the cardiovascular mortality with particulate matter from combustion source, silicon cannot be counted as the direct reason to its high incidence since silica did not came from combustion sources. Silica is made up the silicon oxygen tetrahedral crystals continuous framework which are important constituents of felsitic and igneous rocks. Still, there are high cases of ischemic heart disease prevalence in the dust exposures in various industries such as in the gold miners in South Africa. This placed the mechanisms of non-combustion source silica particulates as cause for CVD as unknown. Possible explanations cross the possibility of the particulates passing into the pulmonary epithelium in the lung receptors and cardiovascular system causing indirect effects of inflammatory responses and pulmonary oxidative stress.
There are several health adverse effects to the exposure to silica dust in the working environment. There are multiple diseases associated with the exposure primarily on the respiratory associated illnesses. The occupational silica exposure ranked as one of the most vital health concern in most countries. Reports stated that there are around 23 million workers are exposed to occupation silica particulates in China, 1.7 million in the US, 10 million in India, and 3 million in the Europe countries (Chen et al, 2012). The silica dust exposure as associated to the lung cancer risk posed to be a controversial issue for several years. According to study, the risk ratios averaged from 1.45 to 1.53 in terms of silica dust exposure and lung cancer relationship.
In Europe, the 2 million people exposed to silica dust as gathered by the national databases of MEGA in Germany and COCCHIC in France, provide data that silica dust crystals is indeed prevalent in most work environments. According to the Central Statistical Office GUS of Poland, there are about 50 thousand people that are exposed to dusts, with exposures exceeding the occupational exposure limits posing health risks and development of lung fibrosis. The industries that are receiving the highest concentrations of exposure to crystalline silica dust includes workers that are involved in bore tunnels, abrasive cleaning, crushing, grinding, building and drilling of rocks, casting cleanings, furnace repairs, ceramic wares, refractories, and abrasive industries. Manufacturing plants of fertilizers and pesticides are also involved in exposure to silica especially when they use silica as fillers (Maciejewska, 2008).
Exposure to Silica Dust Prevention
Substance Exposure Assessment
The assessment of the occupational exposure of workers to silica dust involves multi-phase process. At the first stage, the collection and gathering of information about the technological processes as well organization framework is necessary in the identification of the sources of exposure. Then, there is the comprehensive field measurement to the concentrations of the agent substance including the evaluation of the workplace hygienic conditions. After the assessment, there is the testing procedures, where the limit values of the substances are implemented.
Setting Limits
The legal aspects and risk management for silica dust exposure are significant. The professionals in the SH&E are setting the exposure limits to these substances. ACGIH has updated the threshold limit values (TLVs) of the silica dust exposure in the year 2006, with only 8-hour average time for exposure too crystalline silica. Changes in the exposure limit doubled up to 0.05 mg/m3 to avoid the cases of lung cancers. IN the year 2006, the objection of the TLV by several groups and industries as lead by Elaine Chao of the American Chemistry Council in 2006 required the presence of MSDS for the substance. OSHA and MSHA both presented exposure limits to this substance, where they are basing their data on the ACGIH TLV results in 1960 and 1970. The current level of exposure of this product released was recommended by the ACIGH and NIOSH. OSHA set the permissible level, where it is compared with the respirable dusts through TLV (Glenn, 2008). In most countries, there is one standard value for the silica. However, several countries also consider different standards for different polymorphs of silica. Quartz , trdymite, and cristobalite are actually considered one by in the setting up of standards(Maciejewska, 2008).
Engineering Controls
Since the 1920s, there had been engineering controls that were in place in some industries to address the exposures of workers to the silica. In the automotive industry where there is abrasive blasting, controls placed include the presence of enclosed units, ventilation controls, wetting methods, positive pressure, and good housekeeping. In the later years during the 1950s and 60s, various groups and associations published recommendations that addressed the respiratory exposure of workers during abrasive blasting works. There are also several countries in Europe that banned the use of silica in abrasive blasting. In the 1970s, the BIOSH has investigated the practices in the abrasive blasting ad the results of the investigation highlighted the silica exposures requiring respiratory measures. Some of the suggested solutions included the utilization of separate air supply (Cyrs et al, 2014).
Administrative Controls
Controls for the administration is necessary in the prevention of the risks of silica dusts to workers. As a general rule, workers are expected to follow the implement routine practices set by the company. Some of the practices may involve washing of hands and gloves disposal safely after work. There are also protocols to follow in terms of contact, airborne, and droplet precautions. Employees are expected to follow certain work etiquette (WorkSafeBC, 2009). Good housekeeping practices is also one of the best way to prevent adverse effects of silica dusts in the workplace.
How to protect against Silica Exposure
It is important for the workers to be protected from the exposure from the occupational silica exposure to reduce the health threats to the workers. Several steps can be done in order to mitigate the consequences of the silica exposure in industries (OSHA, 2002):
The silica substances can be replaced with safer substitutes if feasible.
There must be the provision of the administrative and engineering controls. Implementations of control is seen through the use of blasting cabinets, and Local Exhaust Ventilation (LEV) system.
Reduce the exposures to values below PEL, otherwise, require the use of PPE for protective measures.
Utilization of the available work spaces for dust exposure control.
Use of water sprays in the workplace to avoid dusts in roaming around the vicinity.
Wearing of certified respirator and specific respirators for use during abrasive blasting.
Wearing of washable work clothes. Dust must be vacuumed from the clothes. Employees must change to new and clean clothing after work.
There should be trainings, health screenings, exposure monitoring, and surveillance programs to assess and evaluate the adverse effects of the silica exposures.
The operational procedures and job tasks for the people involved in the workplace should include processes on how to protect oneself in the workplace.
Employees should be made aware of the health hazards caused by the exposure to silica.
Washing of hands and face outside the dusty premises.
Workers should be made aware that these substances are not just dust, they are silica.
Recommendation:
The adverse effects of the silica exposure in the workplaces are not all treatable. The best approach is not finding the cure for these things, but on how to prevent them such as control of the occupational respirable silica. Currently, the public has little knowledge about this substance and their adverse effects to the human health. Thus, there is a need for improving the preventive measures and increase in the educational measures in the workplaces. Prevention measures include the anticipation for any occurrence of the hazardous exposure at any time, the evaluation of the sources of exposures, and the implementation of the controls. Engineering controls can be done through process isolation, dust suppression, and ventilations. There are also administrative controls like shifting to alternative abrasives use, and personal protection equipment. Education of the employees and the employer plays a critical role in the organization as the selection and establishment of controls can be identified, and the potential sources of problems be addressed immediately. For the educational program, vocational courses can be utilized for highly risky occupational operations to train those personnel on how to reduce risks and prevent them as well (American Thoracic Society, 1997).
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