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The status of silica.

The Status of Silica This report, revised since publication elsewhere, was prepared by the Casting Industry Suppliers Association to bring the users of silica sand up to date on use of the material and potential health hazards it may pose.

The term silica refers to a naturally occurring mineral consisting of silicon dioxide (Si[O.sub.2]). Silica is present in a substantial portion of the Earth's crust. It is present in beach sand, garden soil clay, bricks, tiles, toothpaste, etc. Silica is used extensively in household scouring powders, paint and many industrial products. In the metalcasting industry, it is found in numerous items, including refractory materials, molding sands and core and mold washes.

The overwhelming majority of silica exists as quartz, a crystalline form of Si[O.sub.2]. Crystalline silica (Quartz, CAS #14808-60-7) has been characterized as a health hazard because of the following: * Excessive exposure to quartz dusts having particle diameters [is less than or equal to] 10 [Mu]m can cause permanent changes in the lung parenchyma, including the related vascular and lymph system. These changes include: fibrosis, nodular fibrosis, lymph node fibrosis and changes in the pulmonary blood vessels. This disease is called silicosis. * The International Agency for Research on Cancer (IARC) has concluded that there is sufficient evidence for the carcinogenicity of crystalline silica to experimental animals and limited evidence for the carcinogenicity of crystalline silica to humans. IARCs definitions of "sufficient and limited" evidence are shown in the addendum to this article.

The OSHA permissible exposure limit (PEL) for respirable quartz given in 29 CFR 1900. 1000 Table Z-3 is 0.100 mg/[m.sup.3]. The American Conference of Governmental Industrial Hygienists has proposed a permissible exposure limit for quartz dust of 0.1 mg/[m.sup.3] (respirable) and 0.3 mg/[m.sup.3] (total). The 1974 NIOSH criteria document relating to occupational exposure to crystalline silica estimates 1.2 million workers in the United States are exposed to quartz in the mining, manufacturing, construction and agricultural industries.

NIOSH suggested health and safety procedures to minimize exposure to quartz. They include the following: * Employers should institute a medical surveillance program for all employees who work in areas where the TWA concentration of respiratory quartz dust may exceed the PEL. * In areas where quartz concentrations in the atmosphere are likely to exceed the standard, appropriate warning signs, barricades or work practices should be employed to restrict access to unauthorized persons. * Affix suitable warning labels to containers used for shipping material having a quartz content and containing respirable dust or that will be used in an application that will generate respirable dust. * Inform each worker exposed or potentially exposed to respirable dusts of the hazards and proper methods for safe use and precautions to minimize exposure. * Where feasible, engineering design of equipment shall include provisions to reduce exposure of workers to quartz dust to the permissible exposure limit or below.

The OSHA communication standard requires manufacturers of silica-containing products to include a cancer warning on the MSDS and label whenever the silica content exceeds 0.1%. The mere presence of silica in a product does not necessarily produce harm. The degree of hazard depends on the amount of material, how it is handled and what controls are available. Read and follow the safe handling precautions provided on the MSDS.

Remember, notification of the presence of silica in a product does not automatically mean you will be harmed if you use the product. Notification is to inform you that you should become familiar with the potential danger and take the suggested precautions.
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Title Annotation:also includes a related article on the health aspects of silica
Publication:Modern Casting
Date:Jul 1, 1989
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