Control Of Exposure To Silica Dust

In practical language, Crystalline Silica addresses what crystalline silica is, where it is found and used, and how it is identified. In addition, the book discusses the regulatory decisions yielding new interest in this ubiquitous substance and presents an overview of the techniques used to determine its presence and abundance. A list of selected readings and supplemental resources and a glossary of terms beyond the scope of this publication round out the text.

Respirable silica dust exposure has long been known to be a serious health threat to workers in many industries. Overexposure to respirable silica dust can lead to the development of silicosis— a lung disease that can be disabling and fatal in its most severe form. Once contracted, there is no cure for silicosis so the goal must be to prevent development by limiting a worker's exposure to respirable silica dust. In addition, the International Agency for Research on Cancer (IARC) has concluded that there is sufficient evidence to classify silica as a human carcinogen. For workers in the metal/nonmetal mining industry, the Mine Safety and Health Administration (MSHA) regulates and monitors exposure to respirable silica dust through personal dust sampling. Recent MSHA personal sampling results indicate that overexposures to respirable silica dust continue to occur for miners in metal/nonmetal mining operations. From 2004 to 2008, the percentages of samples that exceeded the applicable respirable dust standard for the different mining commodities were: • 12% for sand and gravel • 13% for stone • 18% for nonmetal • 21% for metal Of the 2,407 deaths attributed to silicosis in the United States from 1990–1999, employment information was available for 881 deaths. Metal/nonmetal mining was the industry recorded for over 15% of these 881 deaths, with mining machine operator the most frequently recorded occupation. In light of ongoing silica overexposures and reported silicosis deaths in metal/nonmetal miners, an ongoing threat to miners' health is evident. This handbook was developed to identify available engineering controls that can assist the industry in reducing worker exposure to respirable silica dust. The controls discussed in this handbook range from long-used controls which have developed into industry standards, to newer controls, which are still being optimized. The intent is to identify the “best practices” that are available for controlling respirable dust levels in underground and surface metal/nonmetal mining operations. This handbook provides general information on the control technologies along with extensive references. In some cases, the full reference(s) will need to be accessed to gain in-depth information on the testing or implementation of the control of interest.

This guidance document addresses the control of employee exposures to respirable dust containing crystalline silica, which is known to cause silicosis, a serious lung disease, as well as increase the risk of lung cancer and other systemic diseases. This document provides information on the effectiveness of various engineering control approaches for several kinds of construction operations and equipment, and contains recommendations for work practices and respiratory protection, as appropriate. Quartz is the most common form of crystalline silica. In fact, it is the second most common surface material accounting for almost 12% by volume of the earth's crust. Quartz is present in many materials in the construction industry, such as brick and mortar, concrete, slate, dimensional stone (granite, sandstone), stone aggregate, tile, and sand used for blasting. Other construction materials that contain crystalline silica are asphalt filler, roofing granules, plastic composites, soils, and to a lesser extent, some wallboard joint compounds, paint, plaster, caulking and putty. Cristobalite, a less common form of crystalline silica, is formed at high temperatures (>1,470 C) in nature and by industrial processes. The ceramic and brick lining of boilers and vessels, some ceramic tiles, and volcanic ash contain cristobalite. The recommendations presented in this document are based on a review of information in the published literature, NIOSH In-Depth Survey Reports and OSHA inspection data. Engineering control evaluations reported in the published literature were generally performed in controlled work environments and may not reflect actual workplace exposures experienced at construction worksites. Moreover, potential silica exposure levels will depend on the concentration of silica in materials at construction sites, as well as factors in the work environment (such as enclosed, semi-enclosed, or open spaces and/or multiple operations generating silica dust) as well as environmental conditions (such as wind direction and speed). Therefore, OSHA encourages employers to conduct periodic exposure monitoring to confirm that engineering and work practice controls are effective and that appropriate respiratory protection is being used where necessary. Controls continue to evolve and OSHA encourages equipment suppliers and contractors to work with industrial hygienists to evaluate new designs and products to obtain objective information that can be used to evaluate performance and support informed decisions on use."

Throughout the mining and processing of minerals, the mined ore undergoes a number of crushing, grinding, cleaning, drying, and product sizing operations as it is processed into a marketable commodity. These operations are highly mechanized, and both individually and collectively these processes can generate large amounts of dust. If control technologies are inadequate, hazardous levels of respirable dust may be liberated into the work environment, potentially exposing workers. Accordingly, federal regulations are in place to limit the respirable dust exposure of mine workers. Engineering controls are implemented in mining operations in an effort to reduce dust generation and limit worker exposure.

The Construction Chart Book presents the most complete data available on all facets of the U.S. construction industry: economic, demographic, employment/income, education/training, and safety and health issues. The book presents this information in a series of 50 topics, each with a description of the subject matter and corresponding charts and graphs. The contents of The Construction Chart Book are relevant to owners, contractors, unions, workers, and other organizations affiliated with the construction industry, such as health providers and workers compensation insurance companies, as well as researchers, economists, trainers, safety and health professionals, and industry observers.