Measurement and monitoring controls of occupational hazard for Respirable Crystalline Silica

Measurement and monitoring controls of occupational hazard for Respirable Crystalline Silica

Summary

Silica is a mineral compound made up of one silicon atom and two oxygen atoms (SiO2). It has a melting point of 1,600°C and is a colorless, odorless, and noncombustible solid [American Conference of Governmental Industrial Hygienists (ACGIH) 2001]. Crystalline silica is formed when silica molecules are lined up in order and in crystal form. It is an abundant mineral in rock, sand, and soil. Quartz is a term often used to refer to crystalline silica dust.

Introduction

Crystalline silica has been used in many industries such as blast furnaces, cement manufacturing, glass and concrete mixing product manufacture, ceramics, clay, glass and china pottery, electronic, foundry, sand-blasting and manufacturing abrasives, and many construction activities (Altindag et al. 2003; Flanagan et al. 2003; Irwin 2003; Rappaport et al. 2003). It is used as an abrasive agent in many industrial applications. Occupations having a high potential for exposure to crystalline silica dust (respirable quartz) are metal, coal, and nonmetal (except fuels) mining; foundry, stone clay, and glass production work; and agricultural, chemical production, highway repair, and tuck-pointing work [Akbar-Khanzadeh and Brillhart 2002; Occupational Safety and Health Administration (OSHA) 2004; Rappaport et al. 2003].

Description of the Hazard

Silica dust is an inhalation hazard. Workers may be at risk of silicosis from exposure to silica dust when high-velocity impact shatters the sand into smaller, respirable (< 0.5 to 5.0 µm in diameter) dust particles. Silicosis is a disease where scar tissue forms in the lungs and reduces the ability to extract oxygen from the air. Symptoms of silicosis can be acute, accelerated, or chronic. Acute silicosis may develop within weeks and up to 5 years after breathing large amounts of crystalline silica. Accelerated silicosis may develop shortly after exposure to high concentrations of respirable crystalline silica, whereas chronic silicosis occurs after =10 years of exposure to relatively low concentrations of crystalline silica [American Thoracic Society 1997; National Institute for Occupational Safety and Health (NIOSH) 2002]. Many workers in a wider range of industries are exposed to silica, usually in the form of respirable quartz (OSHA 2001, 2003).

Applicable Legislation and Standards

OSHA has estimated that more than 2 million workers are exposed to crystalline silica dust in the general, maritime, and construction industries (OSHA 2003). More than 100,000 workers have high-risk exposure to airborne silica dust through construction and mining operations (Akbar-Khanzadeh and Brillhart 2002; NIOSH 1991). There were an estimated 3,600-7,300 newly recognized silicosis cases per year in the United States from 1987 to 1996 (Rosenman et al. 2003). Between 1990 and 1996, 200-300 deaths per year are known to have occurred where silicosis was identified as a contributing cause on death certificates (Akbar-Khanzadeh and Brillhart 2002; OSHA 2003).

The International Agency for Research on Cancer (IARC 1987, 1997) classified crystalline silica as a known human carcinogen. Exposure to crystalline silica has been associated with an increased risk of developing lung cancer (Engholm and Englund 1995; Knutsson et ...