OSHA Update Regarding Crystalline Silica
Joe Kretchik
Chemical Health & Safety, Volume 10, Number 4
July/August 2003
OSHA is moving forward with plans to develop a comprehensive standard on crystalline silica that will cover workers in all three industrial sectors (General Industry, Construction, and Maritime). In addition to a lower PEL, it will also include provisions for health screening.
Silica has long been recognized as a cause of occupational lung disease but it continues to impact the health of workers in many industries. Each year there are still 200-300 reported deaths from silicosis in the United States and there is evidence to suggest that silicosis deaths may be under reported. The construction industries, foundries, and abrasive blasting are all well known sources of silica exposure but potential exposure to crystalline silica is also found in the Paint, Rubber and Plastics, Roofing, Soaps and Cosmetics, Agricultural Chemicals, Jewelry, and Ceramics Industries among others.
Crystalline silica is a significant component of the earth's crust. Silica refers to the chemical compound silicon dioxide (SiO2), which occurs in a crystalline or noncrystalline (amorphous) form. Crystalline silica may be found in more than one form (polymorphism). The polymorphic forms of crystalline silica are alpha quartz, beta quartz, tridymite, cristobalite, keatite, coesite, stishovite, and moganite.
Workers are usually exposed to crystalline silica in the form of respirable quartz or, less frequently, cristobalite. Chronic silicosis is usually a nodular pulmonary fibrosis, resulting from the exposure of employees over long periods of time (usually 10 years or more). Exposure to high levels of respirable crystalline silica causes acute or accelerated forms of silicosis that may occur sooner and are ultimately fatal. The current OSHA permissible exposure limit (PEL) for general industry is based on a formula recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) in 1971 [PEL=10mg/cubic meter/(%silica + 2), as respirable dust]. The current PEL for construction and maritime (derived from ACGIH's 1962 Threshold Limit Value) is based on particle counting technology, which is considered obsolete. NIOSH and ACGIH recommend a 50ug/m3 exposure limit for respirable crystalline silica.
A NIOSH Hazard Review, "Health Effects of Occupational Exposure to Respirable Crystalline Silica" was published in April 2002 (NIOSH Publication No. 2002-129). It concluded that over a working lifetime, workers have a significant chance of developing silicosis when exposed to respirable crystalline silica at the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL), the Mine Safety and Health Administration (MSHA) PEL, or the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL).
In addition to the potential for silicosis the International Agency for Research on Cancer (IARC) has designated crystalline silica as a known human carcinogen. Exposure to crystalline silica has also been associated with an increased risk of developing tuberculosis and other nonmalignant respiratory diseases. Exposure studies and OSHA enforcement data indicate that some workers continue to be exposed to levels of crystalline silica far in excess of the current exposure limits.
Over the past several years, OSHA has attempted to address these issues through a variety of non-regulatory approaches, including a Special Emphasis Program on silica in October 1997, sponsorship with NIOSH and MSHA of the National Conference to Eliminate Silicosis, and dissemination of guidance information on its Web site. OSHA has now determined that rulemaking is a necessary step to ensure that workers are protected from the hazards of crystalline silica. There is also a specific need for the OSHA to modernize its exposure limits for construction and maritime industries.
The target for beginning the process involves initiating the Small Business Regulatory Enforcement Fairness Act (SBREFA) consultations with small business in June of 2003 with a Notice of Proposed Rule Making (NPRM) in November of 2003. Additional information may be found on OSHA's website www.osha.gov.
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Chemical Health & Safety is the official publication of the American Chemical Society Division of Chemical Health and Safety and is published by Elsevier Science.
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