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Rooting Out Respirable Crystalline Silica


An advanced method helps metalcasters determine the causes of exposure. ERIC PYLKAS, STANTEC CONSULTING, MEQUON, WISCONSIN AND ROBERT SCHOLZ, TRC ENVIRONMENTAL CORP., BROOKFIELD, WISCONSIN


Health Administration (OSHA) since the introduction of the OSHA Act of 1970. Since that time, met- alcasting facilities have worked to lower silica exposure levels to meet the OSHA permissible exposure limit (PEL), but improvements in engineering and work practice controls have not been successful in all cases. In particular, manual operations where dust is dispersed with substantial energy produced by the process itself, such as chipping and grinding castings with portable tools, have produced substantial challenges to providing exposure protection using engineering means. OSHA recently issued a proposed rule to lower the silica PEL, which would increase the challenge. The principal measure to assess silica exposure levels and


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xposures to respirable crystalline silica have been regulated by the Occupational Safety and


provide a basis for reduction actions has been shift-long time-weighted average (TWA) exposure sampling. This


method averages air contaminant concentration in the breathing zone over the work shift. Measur- ing an average exposure is useful in establishing compliance status but not in defining and prioritiz- ing root causes that contributed to that exposure average, which is an essential step in an effective exposure reduction program. A method employing real-time


exposure sampling enables met- alcasters to quantify and prioritize root causes of silica exposure. It can be used to provide a basis for establishing engineering param- eters for effective ventilation control of silica sources and for optimizing work practices.


Modes of Silica Exposure in Sand Casting


In a sand casting facility, silica


Fig. 1. The definition of source and fugitive emissions is illustrated.


dust sources may be distributed throughout operations, creating a situation where it is ubiquitous in


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