Background Types Of Silica Crystalline Silica example essay topic

BACKGROUND Types of Silica Crystalline silica may be of several distinct types. Quartz, a form of silica and the most common mineral in the earth's crust, is associated with many types of rock. Other types of silica include cristobalite and. Potential for Exposure During Construction Concrete and masonry products contain silica sand and rock containing silica.

Since these products are primary materials for construction, construction workers may be easily exposed to respirable crystalline silica during activities such as the following: . Chipping, hammering, and drilling of rock. Crushing, loading, hauling, and dumping of rock. Abrasive blasting using silica sand as the abrasive.

Abrasive blasting of concrete (regardless of abrasive used). Sawing, hammering, drilling, grinding, and chipping of concrete or masonry. Demolition of concrete and masonry structures. Dry sweeping or pressurized air blowing of concrete, rock, or sand dust Even materials containing small amounts of crystalline silica may be hazardous if they are used in ways that produce high dust concentrations.

HEALTH EFFECTS OF CRYSTALLINE SILICA EXPOSURE Description of Silicosis When workers inhale crystalline silica, the lung tissue reacts by developing fibrotic nodules and scarring around the trapped silica particles [Silicosis and Silicate Disease Committee 1988]. This fibrotic condition of the lung is called silicosis. If the nodules grow too large, breathing becomes difficult and death may result. Silicosis victims are also at high risk of developing active tuberculosis [Myers et al.

1973; Sher son and Lander 1990; Bailey et al. 1974]. A worker's lungs may react more severely to silica sand that has been freshly fractured (sawed, hammered, or treated in a way that produces airborne dust) [Vallyathan et al. 1988]. This factor may contribute to the development of acute and accelerated forms of silicosis. Types of Silicosis A worker may develop any of three types of silicosis, depending on the airborne concentration of crystalline silica: Chronic silicosis, which usually occurs after 10 or more years of exposure to crystalline silica at relatively low concentrations Accelerated silicosis, which results from exposure to high concentrations of crystalline silica and develops 5 to 10 years after the initial exposure Acute silicosis, which occurs where exposure concentrations are the highest and can cause symptoms to develop within a few weeks to 4 or 5 years after the initial exposure [Peters 1986; Ziskind et al.

1976] Complications Initially, workers with silicosis may have no symptoms. As silicosis progresses, there may be difficulty in breathing and other chest symptoms such as cough. Infectious complications may cause fever, weight loss, and night sweats. Severe mycobacteria l or fungal infections can complicate silicosis and may be fatal [Ziskind et al. 1976; Owens et al. 1988; Bailey et al.

1974]. Fungal or mycobacteria l infections are believed to result when the lung cells (macrophages) that fight these infections are overwhelmed with silica dust and are unable to kill mycobacteria and other organisms [Allison and Hart 1968; Ng and Chan 1991]. About half of the mycobacteria l infections are caused by Mycobacterium tuberculosis (TB), with the other half caused by M. kansas ii and M. avi um-intracellular e [Owens et al. 1988]. Nocardia and Cryptococcus may also cause infections in silicosis victims [Ziskind et al.

1976]. Medical evaluations of silicosis victims usually show the lungs to be filled with silica crystals and a protein material [Owens et al. 1988; Buchner and Ansari 1969]. Pulmonary fibrosis (fibrous tissue in the lung) may or may not develop in acute cases of silicosis, depending on the time between exposure and onset of symptoms. Furthermore, evidence indicates that crystalline silica is a potential occupational carcinogen [NIOSH 1988; IARC 1987; DHHS 1991], and NIOSH is reviewing the data on carcinogenicity.