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Guidelines and limits for occupational exposure to crystalline silica.
Silica and silica-induced lung diseases. Castranova V, Vallyathan V, Wallace WE, eds. Boca Raton, FL: CRC Press, 1995 Dec; :15-22
The evolution of dust sampling techniques and work place exposure limits were described for dust containing crystalline silica. The Greenburg/Smith impinger developed in 1925 was used for 30 years as the dust sampling method of choice in US mines and factories. Dust particles collected in the impinger solution were counted with a technique adapted from counting plankton in water. In 1962, a threshold limit value (TLV) for silica dust was adopted by the American Conference of Governmental Industrial Hygienists (ACGIH). The TLV was intended as a guideline, not a legal standard. In 1986, the ACGIH revised the silica TLV, requiring direct measure of respirable silica with a TLV of 0.1mg/m3 for alpha quartz (14808607) and 0.05mg/m3 for cristobalite (14464461) and tridymite (15468323). In 1976, NIOSH proposed a recommended exposure limit (REL) that limited crystalline silica to 0.05mg/m3 as a time weighted average during a 40 hour week. This REL was intended to prevent silicosis. Respirable dust was defined as the dust collected by a 10 millimeter nylon cyclone at 1.7 liter/minute. Standards that regulated exposure to crystalline silica in the US depended on laws passed for certain industrial classifications, such as construction, agriculture, maritime industries, and mining, and evolved from recommended ACGIH TLV values. The Walsh/Healy Public Contract Act required employers with government contracts exceeding 10,000 dollars to comply with the permissible exposure limit of 0.1mg/m3 for alpha quartz and 0.05mg/m3 for cristobalite and tridymite measured directly as respirable dust. Progress in measurement methods and dose/response relationships led to an evolving set of exposure limits over 75 years. The author concludes that current recommendations from NIOSH are to control exposure to all forms of crystalline silica below 0.05mg/m3, while reviewing data on carcinogenicity.
Dust-exposure; Dust-inhalation; Respirable-dust; Silicates; Dust-analysis; Humans; Respiratory-system-disorders; Occupational-hazards; Occupational-respiratory-disease
14808-60-7; 14464-46-1; 15468-32-3
Castranova-V; Vallyathan-V; Wallace-WE
Silica and silica-induced lung diseases
Page last reviewed: May 5, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division